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  • 1. Alm, L.
    et al.
    Farrugia, C. J.
    Paulson, K. W.
    Argall, M. R.
    Torbert, R. B.
    Burch, J. L.
    Ergun, R. E.
    Russell, C. T.
    Strangeway, R. J.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Giles, B. L.
    Differing Properties of Two Ion-Scale Magnetopause Flux Ropes2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 114-131Article in journal (Refereed)
    Abstract [en]

    In this paper, we present results from the Magnetospheric Multiscale constellation encountering two ion-scale, magnetopause flux ropes. The two flux ropes exhibit very different properties and internal structure. In the first flux rope, there are large differences in the currents observed by different satellites, indicating variations occurring over sub-d(i) spatial scales, and time scales on the order of the ion gyroperiod. In addition, there is intense wave activity and particle energization. The interface between the two flux ropes exhibits oblique whistler wave activity. In contrast, the second flux rope is mostly quiescent, exhibiting little activity throughout the encounter. Changes in the magnetic topology and field line connectivity suggest that we are observing flux rope coalescence.

  • 2.
    Andriopoulou, Maria
    et al.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Nakamura, Rumi
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Wellenzohn, Simon
    Karl Franzens Univ Graz, Inst Geophys Astrophys & Meteorol, Graz, Austria..
    Torkar, Klaus
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Baumjohann, Wolfgang
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Khotyaintsev, Yuri V.
    Swedish Inst Space Phys IRF, Uppsala, Sweden..
    Dorelli, John
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Plasma Density Estimates From Spacecraft Potential Using MMS Observations in the Dayside Magnetosphere2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 4, p. 2620-2629Article in journal (Refereed)
    Abstract [en]

    Using spacecraft potential observations with and without active spacecraft potential control (on/off) from the Magnetospheric Multiscale (MMS) mission, we estimate the average photoelectron emission as well as derive the plasma density information from spacecraft potential variations and active spacecraft potential control ion current. Such estimates are of particular importance especially during periods when the plasma instruments are not in operation and also when electron density observations with higher time resolution than the ones available from particle detectors are necessary. We compare the average photoelectron emission of different spacecraft and discuss their differences. We examine several time intervals when we performed our density estimations in order to understand the strengths and weaknesses of our data set. We finally compare our derived density estimates with the plasma density observations provided by plasma detectors onboard MMS, whenever available, and discuss the overall results. The estimated electron densities should only be used as a proxy of the electron density, complimentary to the plasma moments derived by plasma detectors, especially when the latter are turned off or when higher time resolution observations are required. While the derived data set can often provide valuable information about the plasma environment, the actual values may often be very far from the actual plasma density values and should therefore be used with caution.

  • 3. Argall, M. R.
    et al.
    Paulson, K.
    Alm, L.
    Rager, A.
    Dorelli, J.
    Shuster, J.
    Wang, S.
    Torbert, R. B.
    Vaith, H.
    Dors, I.
    Chutter, M.
    Farrugia, C.
    Burch, J.
    Pollock, C.
    Giles, B.
    Gershman, D.
    Lavraud, B.
    Russell, C. T.
    Strangeway, R.
    Magnes, W.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Khotyaintsev, Yu. V.
    Ergun, R. E.
    Ahmadi, N.
    Electron Dynamics Within the Electron Diffusion Region of Asymmetric Reconnection2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 146-162Article in journal (Refereed)
    Abstract [en]

    We investigate the agyrotropic nature of electron distribution functions and their substructure to illuminate electron dynamics in a previously reported electron diffusion region (EDR) event. In particular, agyrotropy is examined as a function of energy to reveal detailed finite Larmor radius effects for the first time. It is shown that the previously reported approximate to 66eV agyrotropic "crescent" population that has been accelerated as a result of reconnection is evanescent in nature because it mixes with a denser, gyrotopic background. Meanwhile, accelerated agyrotropic populations at 250 and 500eV are more prominent because the background plasma at those energies is more tenuous. Agyrotropy at 250 and 500eV is also more persistent than at 66eV because of finite Larmor radius effects; agyrotropy is observed 2.5 ion inertial lengths from the EDR at 500eV, but only in close proximity to the EDR at 66eV. We also observe linearly polarized electrostatic waves leading up to and within the EDR. They have wave normal angles near 90 degrees, and their occurrence and intensity correlate with agyrotropy. Within the EDR, they modulate the flux of 500eV electrons travelling along the current layer. The net electric field intensifies the reconnection current, resulting in a flow of energy from the fields into the plasma. Plain Language Summary The process of reconnection involves an explosive transfer of magnetic energy into particle energy. When energetic particles contact modern technology such as satellites, cell phones, or other electronic devices, they can cause random errors and failures. Exactly how particles are energized via reconnection, however, is still unknown. Fortunately, the Magnetospheric Multiscale mission is finally able to detect and analyze reconnection processes. One recent finding is that energized particles take on a crescent-shaped configuration in the vicinity of reconnection and that this crescent shape is related to the energy conversion process. In our paper, we explain why the crescent shape has not been observed until now and inspect particle motions to determine what impact it has on energy conversion. When reconnection heats the plasma, the crescent shape forms from the cool, tenuous particles. As plasmas from different regions mix, dense, nonheated plasma obscures the crescent shape in our observations. The highest-energy particle population created by reconnection, though, also contains features of the crescent shape that are more persistent but appear less dramatically in the data.

  • 4. Breuillard, H.
    et al.
    Le Contel, O.
    Chust, T.
    Berthomier, M.
    Retino, A.
    Turner, D. L.
    Nakamura, R.
    Baumjohann, W.
    Cozzani, G.
    Catapano, F.
    Alexandrova, A.
    Mirioni, L.
    Graham, D. B.
    Argall, M. R.
    Fischer, D.
    Wilder, F. D.
    Gershman, D. J.
    Varsani, A.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Khotyaintsev, Yu. V.
    Marklund, G.
    Ergun, R. E.
    Goodrich, K. A.
    Ahmadi, N.
    Burch, J. L.
    Torbert, R. B.
    Needell, G.
    Chutter, M.
    Rau, D.
    Dors, I.
    Russell, C. T.
    Magnes, W.
    Strangeway, R. J.
    Bromund, K. R.
    Wei, H.
    Plaschke, F.
    Anderson, B. J.
    Le, G.
    Moore, T. E.
    Giles, B. L.
    Paterson, W. R.
    Pollock, C. J.
    Dorelli, J. C.
    Avanov, L. A.
    Saito, Y.
    Lavraud, B.
    Fuselier, S. A.
    Mauk, B. H.
    Cohen, I. J.
    Fennell, J. F.
    The Properties of Lion Roars and Electron Dynamics in Mirror Mode Waves Observed by the Magnetospheric MultiScale Mission2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 93-103Article in journal (Refereed)
    Abstract [en]

    Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi-perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency similar to 100Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi-perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05-0.2f(ce) by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first-time 3-D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi-linear pitch angle diffusion and possible signatures of nonlinear interaction with high-amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes.

  • 5.
    Breuillard, H.
    et al.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France..
    Matteini, L.
    UPMC Univ Paris 06, Univ Paris Diderot, PSL Res Univ, LESIA Observ Paris,CNRS, Meudon, France..
    Argall, M. R.
    Univ New Hampshire, Durham, NH 03824 USA..
    Sahraoui, F.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France..
    Andriopoulou, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Le Contel, O.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France..
    Retino, A.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France..
    Mirioni, L.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France..
    Huang, S. Y.
    Wuhan Univ, Sch Elect & Informat, Beijing, Peoples R China..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Wilder, F. D.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Goodrich, K. A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Ahmadi, N.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Yordanova, E.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Vaivads, A.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Turner, D. L.
    Aerosp Corp, Space Sci Dept, El Segundo, CA 90245 USA..
    Khotyaintsev, Yu. V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Chasapis, A.
    Univ Delaware, Newark, DE USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Durham, NH 03824 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Strangeway, R. J.
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Moore, T. E.
    Giles, B. L.
    Paterson, W. R.
    Pollock, C. J.
    Lavraud, B.
    Univ Paul Sabatier, CNRS UMR5277, IRAP, Toulouse, France..
    Fuselier, S. A.
    Southwest Res Inst, San Antonio, TX USA..
    Cohen, I. J.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 859, no 2, article id 127Article in journal (Refereed)
    Abstract [en]

    The Earth's magnetosheath, which is characterized by highly turbulent fluctuations, is usually divided into two regions of different properties as a function of the angle between the interplanetary magnetic field and the shock normal. In this study, we make use of high-time resolution instruments on board the Magnetospheric MultiScale spacecraft to determine and compare the properties of subsolar magnetosheath turbulence in both regions, i. e., downstream of the quasi-parallel and quasi-perpendicular bow shocks. In particular, we take advantage of the unprecedented temporal resolution of the Fast Plasma Investigation instrument to show the density fluctuations down to sub-ion scales for the first time. We show that the nature of turbulence is highly compressible down to electron scales, particularly in the quasi-parallel magnetosheath. In this region, the magnetic turbulence also shows an inertial (Kolmogorov-like) range, indicating that the fluctuations are not formed locally, in contrast with the quasi-perpendicular magnetosheath. We also show that the electromagnetic turbulence is dominated by electric fluctuations at sub-ion scales (f > 1Hz) and that magnetic and electric spectra steepen at the largest-electron scale. The latter indicates a change in the nature of turbulence at electron scales. Finally, we show that the electric fluctuations around the electron gyrofrequency are mostly parallel in the quasi-perpendicular magnetosheath, where intense whistlers are observed. This result suggests that energy dissipation, plasma heating, and acceleration might be driven by intense electrostatic parallel structures/waves, which can be linked to whistler waves.

  • 6.
    Burch, J. L.
    et al.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Cassak, P. A.
    Univ Virginia, Dept Phys & Astron, Morgantown, WV USA..
    Webster, J. M.
    Rice Univ, Dept Phys & Astron, Houston, TX USA..
    Torbert, R. B.
    Southwest Res Inst, San Antonio, TX 78238 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Rager, A. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA..
    Hwang, K. -J
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Genestreti, K. J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Allen, R. C.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Chen, L. -J
    Wang, S.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Gershman, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le Contel, O.
    Univ Paris Sud, Observ Paris, Lab Phys Plasmas, CNRS,Ecole Polytech,UPMC Univ Paris 06, Paris, France..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Planetary Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth & Planetary Sci, Los Angeles, CA USA..
    Wilder, F. D.
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Hesse, M.
    Univ Bergen, Dept Phys & Technol, Bergen, Norway..
    Drake, J. F.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Swisdak, M.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Price, L. M.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Shay, M. A.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Pollock, C. J.
    Denali Sci, Healy, AK USA..
    Denton, R. E.
    Dartmouth Coll, Dept Phys & Astron, Hanover, NH 03755 USA..
    Newman, D. L.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Localized Oscillatory Energy Conversion in Magnetopause Reconnection2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 3, p. 1237-1245Article in journal (Refereed)
    Abstract [en]

    Data from the NASA Magnetospheric Multiscale mission are used to investigate asymmetric magnetic reconnection at the dayside boundary between the Earth's magnetosphere and the solar wind. High-resolution measurements of plasmas and fields are used to identify highly localized (similar to 15 electron Debye lengths) standing wave structures with large electric field amplitudes (up to 100 mV/m). These wave structures are associated with spatially oscillatory energy conversion, which appears as alternatingly positive and negative values of J . E. For small guide magnetic fields the wave structures occur in the electron stagnation region at the magnetosphere edge of the electron diffusion region. For larger guide fields the structures also occur near the reconnection X-line. This difference is explained in terms of channels for the out-of-plane current (agyrotropic electrons at the stagnation point and guide field-aligned electrons at the X-line).

  • 7.
    Burch, J. L.
    et al.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Webster, J. M.
    Rice Univ, Dept Phys & Astron, Houston, TX USA..
    Genestreti, K. J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Torbert, R. B.
    Southwest Res Inst, San Antonio, TX 78238 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Fuselier, S. A.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Rager, A. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Allen, R. C.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Chen, L. -J
    Wang, S.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Le Contel, O.
    Univ Paris Sud, UPMC Univ Paris 06, Lab Phys Plasmas, CNRS,Ecole Polytech,Observ Paris, Paris, France..
    Russell, C. T.
    Univ Calif Los Angeles, Earth & Planetary Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Earth & Planetary Sci, Los Angeles, CA USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Jaynes, A. N.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Wilder, F. D.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Hwang, K. -J
    Goldstein, J.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Wave Phenomena and Beam-Plasma Interactions at the Magnetopause Reconnection Region2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 2, p. 1118-1133Article in journal (Refereed)
    Abstract [en]

    This paper reports on Magnetospheric Multiscale observations of whistler mode chorus and higher-frequency electrostatic waves near and within a reconnection diffusion region on 23 November 2016. The diffusion region is bounded by crescent-shaped electron distributions and associated dissipation just upstream of the X-line and by magnetic field-aligned currents and electric fields leading to dissipation near the electron stagnation point. Measurements were made southward of the X-line as determined by southward directed ion and electron jets. We show that electrostatic wave generation is due to magnetosheath electron beams formed by the electron jets as they interact with a cold background plasma and more energetic population of magnetospheric electrons. On the magnetosphere side of the X-line the electron beams are accompanied by a strong perpendicular electron temperature anisotropy, which is shown to be the source of an observed rising-tone whistler mode chorus event. We show that the apex of the chorus event and the onset of electrostatic waves coincide with the opening of magnetic field lines at the electron stagnation point.

  • 8.
    Butler, Alexandre
    et al.
    Univ Paris Saclay, LPGP, UMR CNRS 8578, Univ Paris Sud, F-91405 Orsay, France..
    Brenning, Nils
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Univ Paris Saclay, LPGP, UMR CNRS 8578, Univ Paris Sud, F-91405 Orsay, France.; Linkoping Univ, Plasma & Coatings Phys Div, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Raadu, Michael A.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Gudmundsson, Jon Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Minea, Tiberiu
    Univ Paris Saclay, LPGP, UMR CNRS 8578, Univ Paris Sud, F-91405 Orsay, France..
    Lundin, Daniel
    Univ Paris Saclay, LPGP, UMR CNRS 8578, Univ Paris Sud, F-91405 Orsay, France..
    On three different ways to quantify the degree of ionization in sputtering magnetrons2018In: Plasma sources science & technology (Print), ISSN 0963-0252, E-ISSN 1361-6595, Vol. 27, no 10, article id 105005Article in journal (Refereed)
    Abstract [en]

    Quantification and control of the fraction of ionization of the sputtered species are crucial in magnetron sputtering, and in particular in high-power impulse magnetron sputtering (HiPIMS), yet proper definitions of the various concepts of ionization are still lacking. In this contribution, we distinguish between three approaches to describe the degree (or fraction) of ionization: the ionized flux fraction F-flux, the ionized density fraction F-density, and the fraction a of the sputtered metal atoms that become ionized in the plasma (sometimes referred to as probability of ionization). By studying a reference HiPIMS discharge with a Ti target, we show how to extract absolute values of these three parameters and how they vary with peak discharge current. Using a simple model, we also identify the physical mechanisms that determine F-flux, F-density, and a as well as how these three concepts of ionization are related. This analysis finally explains why a high ionization probability does not necessarily lead to an equally high ionized flux fraction or ionized density fraction.

  • 9.
    Butler, Alexandre
    et al.
    Univ Paris Saclay, LPGP, UMR CNRS 8578, Univ Paris Sud, F-91405 Orsay, France..
    Brenning, Nils
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Univ Paris Saclay, LPGP, UMR CNRS 8578, Univ Paris Sud, F-91405 Orsay, France.;Linköping Univ, Plasma & Coatings Phys Div, IFM Mat Phys, SE-58183 Linköping, Sweden..
    Raadu, Michael A.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Gudmundsson, Jon Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Minea, Tiberiu
    Univ Paris Saclay, LPGP, UMR CNRS 8578, Univ Paris Sud, F-91405 Orsay, France..
    Lundin, Daniel
    Univ Paris Saclay, LPGP, UMR CNRS 8578, Univ Paris Sud, F-91405 Orsay, France..
    On three different ways to quantify the degree of ionization in sputtering magnetrons2018In: Plasma sources science & technology (Print), ISSN 0963-0252, E-ISSN 1361-6595, Vol. 27, no 10, article id 105005Article in journal (Refereed)
    Abstract [en]

    Quantification and control of the fraction of ionization of the sputtered species are crucial in magnetron sputtering, and in particular in high-power impulse magnetron sputtering (HiPIMS), yet proper definitions of the various concepts of ionization are still lacking. In this contribution, we distinguish between three approaches to describe the degree (or fraction) of ionization: the ionized flux fraction F-flux, the ionized density fraction F-density, and the fraction a of the sputtered metal atoms that become ionized in the plasma (sometimes referred to as probability of ionization). By studying a reference HiPIMS discharge with a Ti target, we show how to extract absolute values of these three parameters and how they vary with peak discharge current. Using a simple model, we also identify the physical mechanisms that determine F-flux, F-density, and a as well as how these three concepts of ionization are related. This analysis finally explains why a high ionization probability does not necessarily lead to an equally high ionized flux fraction or ionized density fraction.

  • 10. Chen, L. -J
    et al.
    Wang, S.
    Wilson, L. B. , I I I
    Schwartz, S.
    Bessho, N.
    Moore, T.
    Gershman, D.
    Giles, B.
    Malaspina, D.
    Wilder, F. D.
    Ergun, R. E.
    Hesse, M.
    Lai, H.
    Russell, C.
    Strangeway, R.
    Torbert, R. B.
    Vinas, F. -A
    Burch, J.
    Lee, S.
    Pollock, C.
    Dorelli, J.
    Paterson, W.
    Ahmadi, N.
    Goodrich, K.
    Lavraud, B.
    Le Contel, O.
    Khotyaintsev, Yu.V.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Boardsen, S.
    Wei, H.
    Le, A.
    Avanov, L.
    Electron Bulk Acceleration and Thermalization at Earth's Quasiperpendicular Bow Shock2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 22, article id 225101Article in journal (Refereed)
    Abstract [en]

    Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating. © 2018 American Physical Society.

  • 11.
    Denton, R. E.
    et al.
    Dartmouth Coll, Dept Phys & Astron, Hanover, NH 03755 USA..
    Sonnerup, B. U. O.
    Dartmouth Coll, Thayer Sch Engn, Hanover, NH 03755 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Hasegawa, H.
    JAXA, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Phan, T. -D
    Strangeway, R. J.
    Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Ergun, R. E.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Torbert, R. B.
    Univ New Hampshire, Inst Study Earth Oceans & Space, Durham, NH 03824 USA..
    Burch, J. L.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA..
    Vines, S. K.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX USA.;Johns Hopkins Univ, Appl Phys Lab, Johns Hopkins Rd, Laurel, MD USA..
    Determining L-M-N Current Sheet Coordinates at the Magnetopause From Magnetospheric Multiscale Data2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 3, p. 2274-2295Article in journal (Refereed)
    Abstract [en]

    We discuss methods to determine L-M-N coordinate systems for current sheet crossings observed by the Magnetospheric Multiscale (MMS) spacecraft mission during ongoing reconnection, where e(L) is the direction of the reconnecting component of the magnetic field, B, and e(N) is normal to the magnetopause. We present and test a new hybrid method, with e(L) estimated as the maximum variance direction of B (MVAB) and e(N) as the direction of maximum directional derivative of B, and then adjust these directions to be perpendicular. In the best case, only small adjustment is needed. Results from this method, applied to an MMS crossing of the dayside magnetopause at 1305:45UT on 16 October 2015, are discussed and compared with those from other methods for which e(N) is obtained by other means. Each of the other evaluations can be combined with e(L) from MVAB in a generalized hybrid approach to provide an L-M-N system. The quality of the results is judged by eigenvalue ratios, constancy of directions using different data segments and methods, and expected sign and magnitude of the normal component of B. For this event, the hybrid method appears to produce e(N) accurate to within less than 10 degrees. We discuss variance analysis using the electric current density, J, or the J x B force, which yield promising results, and minimum Faraday residue analysis and MVAB alone, which can be useful for other events. We also briefly discuss results from our hybrid method and MVAB alone for a few other MMS reconnection events. Plain Language Summary We discuss methods for determining coordinate systems in order to study magnetic reconnection events at the magnetopause, the boundary between the ionized gas in the region of space dominated by the Earth's magnetic field and the ionized gas coming from the solar wind. We introduce a new method that combines results from multiple methods in order to determine the three coordinate directions in space. We demonstrate this method by applying it to an event observed by the Magnetospheric Multiscale spacecraft on 16 October 2015 and at other times.

  • 12.
    Eastwood, J. P.
    et al.
    Imperial Coll London, Blackett Lab, London, England..
    Mistry, R.
    Imperial Coll London, Blackett Lab, London, England..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Schwartz, S. J.
    Imperial Coll London, Blackett Lab, London, England.;Univ Colorado, Dept Astrophys & Planetary Sci, LASP, Boulder, CO 80309 USA..
    Ergun, R. E.
    Univ Colorado, Dept Astrophys & Planetary Sci, LASP, Boulder, CO 80309 USA..
    Drake, J. F.
    Univ Maryland, Dept Phys, College Pk, MD 20742 USA.;Univ Maryland, Inst Phys Sci & Technol, College Pk, MD 20742 USA..
    Oieroset, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Stawarz, J. E.
    Imperial Coll London, Blackett Lab, London, England..
    Goldman, M. V.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Haggerty, C.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA.;Univ Chicago, Dept Astron & Astrophys, 5640 S Ellis Ave, Chicago, IL 60637 USA..
    Shay, M. A.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Gershman, D. J.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Torbert, R. B.
    Univ Chicago, Dept Astron & Astrophys, 5640 S Ellis Ave, Chicago, IL 60637 USA.;Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Guide Field Reconnection: Exhaust Structure and Heating2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 10, p. 4569-4577Article in journal (Refereed)
    Abstract [en]

    Magnetospheric Multiscale observations are used to probe the structure and temperature profile of a guide field reconnection exhaust similar to 100 ion inertial lengths downstream from the X-line in the Earth's magnetosheath. Asymmetric Hall electric and magnetic field signatures were detected, together with a density cavity confined near 1 edge of the exhaust and containing electron flow toward the X-line. Electron holes were also detected both on the cavity edge and at the Hall magnetic field reversal. Predominantly parallel ion and electron heating was observed in the main exhaust, but within the cavity, electron cooling and enhanced parallel ion heating were found. This is explained in terms of the parallel electric field, which inhibits electron mixing within the cavity on newly reconnected field lines but accelerates ions. Consequently, guide field reconnection causes inhomogeneous changes in ion and electron temperature across the exhaust.

  • 13.
    Ekeroth, Sebastian
    et al.
    Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden..
    Munger, E. Peter
    Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden..
    Boyd, Robert
    Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden..
    Ekspong, Joakim
    Umea Univ, Dept Phys, SE-90187 Umea, Sweden..
    Wagberg, Thomas
    Umea Univ, Dept Phys, SE-90187 Umea, Sweden..
    Edman, Ludvig
    Umea Univ, Dept Phys, SE-90187 Umea, Sweden..
    Brenning, Nils
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden.
    Helmersson, Ulf
    Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden..
    Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 5, p. 3132-3137Article in journal (Refereed)
    Abstract [en]

    Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 mu m thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H-2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm(2).

  • 14. Ergun, R. E.
    et al.
    Goodrich, K. A.
    Wilder, F. D.
    Ahmadi, N.
    Holmes, J. C.
    Eriksson, S.
    Stawarz, J. E.
    Nakamura, R.
    Genestreti, K. J.
    Hesse, M.
    Burch, J. L.
    Torbert, R. B.
    Phan, T. D.
    Schwartz, S. J.
    Eastwood, J. P.
    Strangeway, R. J.
    Le Contel, O.
    Russell, C. T.
    Argall, M. R.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Chen, L. J.
    Cassak, P. A.
    Giles, B. L.
    Dorelli, J. C.
    Gershman, D.
    Leonard, T. W.
    Lavraud, B.
    Retino, A.
    Matthaeus, W.
    Vaivads, A.
    Magnetic Reconnection, Turbulence, and Particle Acceleration: Observations in the Earth's Magnetotail2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 8, p. 3338-3347Article in journal (Refereed)
    Abstract [en]

    We report observations of turbulent dissipation and particle acceleration from large-amplitude electric fields (E) associated with strong magnetic field (B) fluctuations in the Earth's plasma sheet. The turbulence occurs in a region of depleted density with anti-earthward flows followed by earthward flows suggesting ongoing magnetic reconnection. In the turbulent region, ions and electrons have a significant increase in energy, occasionally >100 keV, and strong variation. There are numerous occurrences of |E| >100 mV/m including occurrences of large potentials (>1 kV) parallel to B and occurrences with extraordinarily large J · E (J is current density). In this event, we find that the perpendicular contribution of J · E with frequencies near or below the ion cyclotron frequency (fci) provide the majority net positive J · E. Large-amplitude parallel E events with frequencies above fci to several times the lower hybrid frequency provide significant dissipation and can result in energetic electron acceleration.

  • 15.
    Eriksson, Elin
    et al.
    Swedish Inst Space Phys, Uppsala, Sweden.;Uppsala Univ, Dept Phys & Astron, Uppsala, Sweden..
    Vaivads, Andris
    Swedish Inst Space Phys, Uppsala, Sweden..
    Graham, Daniel B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Divin, Andrey
    Swedish Inst Space Phys, Uppsala, Sweden.;St Petersburg State Univ, Dept Phys, St Petersburg, Russia..
    Khotyaintsev, Yuri V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Yordanova, Emiliya
    Swedish Inst Space Phys, Uppsala, Sweden..
    Andre, Mats
    Swedish Inst Space Phys, Uppsala, Sweden..
    Giles, Barbara L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, Craig J.
    Denali Sci LLC, Healy, AK USA..
    Russell, Christopher T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Le Contel, Olivier
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Ecole Polytech,CNRS,Lab Phys Plasmas, Paris, France..
    Torbert, Roy B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Ergun, Robert E.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Electron Energization at a Reconnecting Magnetosheath Current Sheet2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 16, p. 8081-8090Article in journal (Refereed)
    Abstract [en]

    We present observations of electron energization within a sub-ion-scale magnetosheath current sheet (CS). A number of signatures indicate ongoing reconnection, including the thickness of the CS (similar to 0.7 ion inertial length), nonzero normal magnetic field, Hall magnetic fields with electrons carrying the Hall currents, and electron heating. We observe localized electron acceleration and heating parallel to the magnetic field at the edges of the CS. Electrostatic waves observed in these regions have low phase velocity and small wave potentials and thus cannot provide the observed acceleration and heating. Instead, we find that the electrons are accelerated by a parallel potential within the separatrix regions. Similar acceleration has been reported based on magnetopause and magnetotail observations. Thus, despite the different plasma conditions in magnetosheath, magnetopause, and magnetotail, the acceleration mechanism and corresponding heating of electrons is similar. Plain Language Summary Magnetic reconnection is an important physical energy conversion process in astrophysical and laboratory plasmas. The easiest place to analyze magnetic reconnection is in near-Earth space. Due to lack of sufficient electron resolution of previous spacecraft missions, there are many unanswered questions regarding electron heating and acceleration processes at small scales. In particular, the regime where thermal pressure dominates over magnetic pressure, the most common state of plasmas in the Universe, is little explored. In this letter we study such a regime using the four-spacecraft Magnetospheric Multiscale mission. We analyze a reconnecting current sheet in the magnetosheath. We show that electrons are energized by a parallel potential, similar to what has been observed in the different plasma regimes the magnetopause and magnetotail. Thus, despite different plasma conditions, a similar acceleration mechanism and corresponding heating of electrons is occurring in all these regions.

  • 16.
    Futaana, Yoshifumi
    et al.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Barabash, Stas
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Wieser, Martin
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Wurz, Peter
    Univ Bern, Bern, Switzerland..
    Hurley, Dana
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Horanyi, Mihaly
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Mall, Urs
    Max Planck Inst Solar Syst Res, Gottingen, Germany..
    Andre, Nicolas
    Univ Toulouse, CNRS, IRAP, Toulouse, France..
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Oberst, Juergen
    German Aerosp Ctr, Berlin, Germany..
    Retherford, Kurt
    Southwest Res Inst, San Antonio, TX USA..
    Coates, Andrew
    UCL, Mullard Space Sci Lab, London, England..
    Masters, Adam
    Imperial Coll London, London, England..
    Wahlund, Jan-Erik
    Swedish Inst Space Phys, Uppsala, Sweden..
    Kallio, Esa
    Aalto Univ, Helsinki, Finland..
    SELMA mission: How do airless bodies interact with space environment? The Moon as an accessible laboratory2018In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 156, p. 23-40Article in journal (Refereed)
    Abstract [en]

    The Moon is an archetypal atmosphere-less celestial body in the Solar System. For such bodies, the environments are characterized by complex interaction among the space plasma, tenuous neutral gas, dust and the outermost layer of the surface. Here we propose the SELMA mission (Surface, Environment, and Lunar Magnetic Anomalies) to study how airless bodies interact with space environment. SELMA uses a unique combination of remote sensing via ultraviolet and infrared wavelengths, and energetic neutral atom imaging, as well as in situ measurements of exospheric gas, plasma, and dust at the Moon. After observations in a lunar orbit for one year, SELMA will conduct an impact experiment to investigate volatile content in the soil of the permanently shadowed area of the Shackleton crater. SELMA also carries an impact probe to sound the Reiner-Gamma mini-magnetosphere and its interaction with the lunar regolith from the SELMA orbit down to the surface. SELMA was proposed to the European Space Agency as a medium-class mission (M5) in October 2016. Research on the SELMA scientific themes is of importance for fundamental planetary sciences and for our general understanding of how the Solar System works. In addition, SELMA outcomes will contribute to future lunar explorations through qualitative characterization of the lunar environment and, in particular, investigation of the presence of water in the lunar soil, as a valuable resource to harvest from the lunar regolith.

  • 17.
    Giagkiozis, Stefanos
    et al.
    Univ Sheffield, Automat Control & Syst Engn, Sheffield, S Yorkshire, England..
    Wilson, Lynn B.
    NASA, Goddard Space Flight Ctr, Heliophys Sci Div, Greenbelt, MD USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Le Contel, Olivier
    Univ Paris Sud, Sorbonne Univ, CNRS, Lab Phys Plasmas,UMR7648,Ecole Polytech,Observ Pa, Paris, France..
    Ergun, Robert E.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Gershman, Daniel J.
    NASA, Goddard Space Flight Ctr, Fields & Particles, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Mirioni, Laurent
    Sorbonne Univ UPMC Paris Sud 11, LPP, CNRS, Ecole Polytech, Palaiseau, France..
    Moore, Thomas E.
    NASA, Goddard Space Flight Ctr, Heliophys Sci Div, Greenbelt, MD USA..
    Strangeway, Robert J.
    Univ Calif Los Angeles, Dept Geophys & Planetary Phys, Los Angeles, CA 90024 USA.;Univ Calif Los Angeles, Earth & Space Sci, Los Angeles, CA USA..
    Statistical Study of the Properties of Magnetosheath Lion Roars2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 7, p. 5435-5451Article in journal (Refereed)
    Abstract [en]

    Lion roars are narrowband whistler wave emissions that have been observed in several environments, such as planetary magnetosheaths, the Earth's magnetosphere, the solar wind, downstream of interplanetary shocks, and the cusp region. We present measurements of more than 30,000 such emissions observed by the Magnetospheric Multiscale spacecraft with high-cadence (8,192 samples/s) search coil magnetometer data. A semiautomatic algorithm was used to identify the emissions, and an adaptive interval algorithm in conjunction with minimum variance analysis was used to determine their wave vector. The properties of the waves are determined in both the spacecraft and plasma rest frame. The mean wave normal angle, with respect to the background magnetic field (B-0), plasma bulk flow velocity (V-b), and the coplanarity plane (V-b x B-0) are 23 degrees, 56 degrees, and 0 degrees, respectively. The average peak frequencies were similar to 31% of the electron gyrofrequency (omega(ce)) observed in the spacecraft frame and similar to 18% of omega(ce) in the plasma rest frame. In the spacecraft frame, similar to 99% of the emissions had a frequency < omega(ce), while 98% had a peak frequency < 0.72 omega(ce) in the plasma rest frame. None of the waves had frequencies lower than the lower hybrid frequency, omega. From the probability density function of the electron plasma beta(e), the ratio between the electron thermal and magnetic pressure, similar to 99.6% of the waves were observed with beta(e) < 4 with a large narrow peak at 0.07 and two smaller, but wider, peaks at 1.26 and 2.28, while the average value was similar to 1.25.

  • 18.
    Giono, Gabriel
    et al.
    Rostock Univ IAP, Leibniz Inst Atmospher Phys, Kuhlungsborn, Germany.;KTH Royal Inst Technol, Sch Elect Engn, Dept Space & Plasma Phys, Stockholm, Sweden..
    Strelnikov, Boris
    Rostock Univ IAP, Leibniz Inst Atmospher Phys, Kuhlungsborn, Germany..
    Asmus, Heiner
    Rostock Univ IAP, Leibniz Inst Atmospher Phys, Kuhlungsborn, Germany..
    Staszak, Tristan
    Rostock Univ IAP, Leibniz Inst Atmospher Phys, Kuhlungsborn, Germany..
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Luebken, Franz-Josef
    Rostock Univ IAP, Leibniz Inst Atmospher Phys, Kuhlungsborn, Germany..
    Photocurrent modelling and experimental confirmation for meteoric smoke particle detectors on board atmospheric sounding rockets2018In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 11, no 9, p. 5299-5314Article in journal (Refereed)
    Abstract [en]

    Characterising the photoelectron current induced by the Sun's UV radiation is crucial to ensure accurate daylight measurements from particle detectors. This article lays out the methodology used to address this problem in the case of the meteoric smoke particle detectors (MSPDs), developed by the Leibniz Institute of Atmospheric Physics in Kuhlungsborn (IAP) and flown on board the PMWEs (Polar Mesosphere Winter Echoes) sounding rockets in April 2018. The methodology focuses on two complementary aspects: modelling and experimental measurements. A detailed model of the MSPD photocurrent was created based on the expected solar UV flux, the atmospheric UV absorption as a function of height by molecular oxygen and ozone, the photoelectric yield of the material coating the MSPD as a function of wavelength, the index of refraction of these materials as a function of wavelength and the angle of incidence of the illumination onto the MSPD. Due to its complex structure, composed of a central electrode shielded by two concentric grids, extensive ray-tracing calculations were conducted to obtain the incidence angles of the illumination on the central electrode, and this was done for various orientations of the MSPD in respect to the Sun. Results of the modelled photocurrent at different heights and for different materials, as well as for different orientations of the detector, are presented. As a pre-flight confirmation, the model was used to reproduce the experimental measurements conducted by Robertson et al. (2014) and agrees within an order of magnitude. An experimental setup for the calibration of the MSPD photocurrent is also presented. The photocurrent induced by the Lyman-alpha line from a deuterium lamp was recorded inside a vacuum chamber using a narrowband filter, while a UV-sensitive photodiode was used to monitor the UV flux. These measurements were compared with the model prediction, and also matched within an order of magnitude. Although precisely modelling the photocurrent is a challenging task, this article quantitatively improved the understanding of the photocurrent on the MSPD and discusses possible strategies to untangle the meteoric smoke particles (MSPs) current from the photocurrent recorded in-flight.

  • 19.
    Graham, D. B.
    et al.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Vaivads, A.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Khotyaintsev, Yu. V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Andre, M.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Le Contel, O.
    Univ Paris Sud, UPMC Univ Paris 06, Observ Paris, LPP,UMR7648,CNRS,Ecole Polytech, Paris, France..
    Malaspina, D. M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Wilder, F. D.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Large-Amplitude High-Frequency Waves at Earth's Magnetopause2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 4, p. 2630-2657Article in journal (Refereed)
    Abstract [en]

    Large-amplitude waves near the electron plasma frequency are found by the Magnetospheric Multiscale (MMS) mission near Earth's magnetopause. The waves are identified as Langmuir and upper hybrid (UH) waves, with wave vectors either close to parallel or close to perpendicular to the background magnetic field. The waves are found all along the magnetopause equatorial plane, including both flanks and close to the subsolar point. The waves reach very large amplitudes, up to 1Vm(-1), and are thus among the most intense electric fields observed at Earth's magnetopause. In the magnetosphere and on the magnetospheric side of the magnetopause the waves are predominantly UH waves although Langmuir waves are also found. When the plasma is very weakly magnetized only Langmuir waves are likely to be found. Both Langmuir and UH waves are shown to have electromagnetic components, which are consistent with predictions from kinetic wave theory. These results show that the magnetopause and magnetosphere are often unstable to intense wave activity near the electron plasma frequency. These waves provide a possible source of radio emission at the magnetopause.

  • 20.
    Graham, D. B.
    et al.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Vaivads, A.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Khotyaintsev, Yu, V
    Swedish Inst Space Phys, Uppsala, Sweden..
    Eriksson, A. , I
    Andre, M.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Malaspina, D. M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Enhanced Escape of Spacecraft Photoelectrons Caused by Langmuir and Upper Hybrid Waves2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7534-7553Article in journal (Refereed)
    Abstract [en]

    The spacecraft potential is often used to infer rapid changes in the thermal plasma density. The variations in spacecraft potential associated with large-amplitude Langmuir and upper hybrid waves are investigated with the Magnetospheric Multiscale (MMS) mission. When large-amplitude Langmuir and upper hybrid waves are observed, the spacecraft potential increases. The changes in spacecraft potential are shown to be due to enhanced photoelectron escape from the spacecraft when the wave electric fields reach large amplitude. The fluctuations in spacecraft potential follow the envelope function of the Langmuir and upper hybrid waves. Comparison with the high-resolution electron moments shows that the changes in spacecraft potential associated with the waves are not due to density perturbations. Indeed, using the spacecraft potential as a density probe leads to unphysically large density fluctuations. In addition, the changes in spacecraft potential are shown to increase as density decreases: larger spacecraft potential changes are observed in the magnetosphere, than in the magnetosheath and solar wind. These results show that external electric fields can lead to unphysical results when the spacecraft potential is used as a density probe. The results suggest that fluctuations in the spacecraft potential alone cannot be used to determine whether nonlinear processes associated with Langmuir and upper hybrid waves, such as the ponderomotive force and three-wave decay, are occurring.

  • 21.
    Grodent, Denis
    et al.
    Univ Liege, STAR Inst, Lab Phys Atmospher & Planetaire, Liege, Belgium..
    Bonfond, B.
    Univ Liege, STAR Inst, Lab Phys Atmospher & Planetaire, Liege, Belgium..
    Yao, Z.
    Univ Liege, STAR Inst, Lab Phys Atmospher & Planetaire, Liege, Belgium..
    Gerard, J-C
    Radioti, A.
    Univ Liege, STAR Inst, Lab Phys Atmospher & Planetaire, Liege, Belgium..
    Dumont, M.
    Univ Liege, STAR Inst, Lab Phys Atmospher & Planetaire, Liege, Belgium..
    Palmaerts, B.
    Univ Liege, STAR Inst, Lab Phys Atmospher & Planetaire, Liege, Belgium..
    Adriani, A.
    INAF, Ist Astrofis & Planetol Spaziali, Rome, Italy..
    Badman, S. V.
    Univ Lancaster, Phys Dept, Lancaster, England..
    Bunce, E. J.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Clarke, J. T.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA..
    Connerney, J. E. P.
    NASA, Goddard Space Flight Ctr, Planetary Magnetospheres Lab, Solar Syst Explorat Div, Greenbelt, MD USA..
    Gladstone, G. R.
    Southwest Res Inst, Dept Space Sci, San Antonio, TX USA..
    Greathouse, T.
    Southwest Res Inst, Dept Space Sci, San Antonio, TX USA..
    Kimura, T.
    RIKEN, Wako, Saitama, Japan..
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Mauk, B. H.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    McComas, D. J.
    Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA..
    Nichols, J. D.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Orton, G. S.
    CALTECH, Jet Prop Lab, Pasadena, CA USA..
    Roth, Lorenz
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Saur, J.
    Univ Cologne, Inst Geophys & Meteorol, Cologne, Germany..
    Valek, P.
    Southwest Res Inst, Dept Space Sci, San Antonio, TX USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX USA..
    Jupiter's Aurora Observed With HST During Juno Orbits 3 to 72018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 5, p. 3299-3319Article in journal (Refereed)
    Abstract [en]

    A large set of observations of Jupiter's ultraviolet aurora was collected with the Hubble Space Telescope concurrently with the NASA-Juno mission, during an eight-month period, from 30 November 2016 to 18 July 2017. These Hubble observations cover Juno orbits 3 to 7 during which Juno in situ and remote sensing instruments, as well as other observatories, obtained a wealth of unprecedented information on Jupiter's magnetosphere and the connection with its auroral ionosphere. Jupiter's ultraviolet aurora is known to vary rapidly, with timescales ranging from seconds to one Jovian rotation. The main objective of the present study is to provide a simplified description of the global ultraviolet auroral morphology that can be used for comparison with other quantities, such as those obtained with Juno. This represents an entirely new approach from which logical connections between different morphologies may be inferred. For that purpose, we define three auroral subregions in which we evaluate the auroral emitted power as a function of time. In parallel, we define six auroral morphology families that allow us to quantify the variations of the spatial distribution of the auroral emission. These variations are associated with changes in the state of the Jovian magnetosphere, possibly influenced by Io and the Io plasma torus and by the conditions prevailing in the upstream interplanetary medium. This study shows that the auroral morphology evolved differently during the five similar to 2week periods bracketing the times of Juno perijove (PJ03 to PJ07), suggesting that during these periods, the Jovian magnetosphere adopted various states.

  • 22.
    Gunnarsson, Rickard
    et al.
    Linkoping Univ, Dept Phys, Plasma & Coating Phys, S-58183 Linkoping, Sweden..
    Brenning, Nils
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Linkoping Univ, Dept Phys, Plasma & Coating Phys, S-58183 Linkoping, Sweden.
    Boyd, Robert Deric
    Linkoping Univ, Dept Phys, Plasma & Coating Phys, S-58183 Linkoping, Sweden..
    Helmersson, Ulf
    Linkoping Univ, Dept Phys, Plasma & Coating Phys, S-58183 Linkoping, Sweden..
    Nucleation of titanium nanoparticles in an oxygen-starved environment. I: experiments2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 45, article id 455201Article in journal (Refereed)
    Abstract [en]

    A constant supply of oxygen has been assumed to be necessary for the growth of titanium nanoparticles by sputtering. This oxygen supply can arise from a high background pressure in the vacuum system or from a purposely supplied gas. The supply of oxygen makes it difficult to grow metallic nanoparticles of titanium and can cause process problems by reacting with the target. We here report that growth of titanium nanoparticles in the metallic hexagonal titanium (alpha Ti) phase is possible using a pulsed hollow cathode sputter plasma and adding a high partial pressure of helium to the process instead of trace amounts of oxygen. The helium cools the process gas in which the nanoparticles nucleate. This is important both for the first dimer formation and the continued growth to a thermodynamically stable size. The parameter region, inside which the synthesis of nanoparticles is possible, is mapped out experimentally and the theory of the physical processes behind this process window is outlined. A pressure limit below which no nanoparticles were produced was found at 200 Pa, and could be attributed to a low dimer formation rate, mainly caused by a more rapid dilution of the growth material. Nanoparticle production also disappeared at argon gas flows above 25 sccm. In this case, the main reason was identified as a gas temperature increase within the nucleation zone, giving a too high evaporation rate from nanoparticles (clusters) in the stage of growth from dimers to stable nuclei. These two mechanisms are in depth explored in a companion paper. A process stability limit was also found at low argon gas partial pressures, and could be attributed to a transition from a hollow cathode discharge to a glow discharge.

  • 23.
    Gunnarsson, Rickard
    et al.
    Linkoping Univ, Dept Phys, Plasma Coating Phys, S-58183 Linkoping, Sweden..
    Brenning, Nils
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Linkoping Univ, Dept Phys, Plasma Coating Phys, S-58183 Linkoping, Sweden.
    Ojamae, Lars
    Linkoping Univ, Dept Phys, Plasma Coating Phys, S-58183 Linkoping, Sweden..
    Kalered, Emil
    Linkoping Univ, Dept Phys, Plasma Coating Phys, S-58183 Linkoping, Sweden..
    Raadu, Michael Allan
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Helmersson, Ulf
    Linkoping Univ, Dept Phys, Plasma Coating Phys, S-58183 Linkoping, Sweden..
    Nucleation of titanium nanoparticles in an oxygen-starved environment. II: theory2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 45, article id 455202Article in journal (Refereed)
    Abstract [en]

    The nucleation and growth of pure titanium nanoparticles in a low-pressure sputter plasma has been believed to be essentially impossible. The addition of impurities, such as oxygen or water, facilitates this and allows the growth of nanoparticles. However, it seems that this route requires such high oxygen densities that metallic nanoparticles in the hexagonal alpha Ti-phase cannot be synthesized. Here we present a model which explains results for the nucleation and growth of titanium nanoparticles in the absent of reactive impurities. In these experiments, a high partial pressure of helium gas was added which increased the cooling rate of the process gas in the region where nucleation occurred. This is important for two reasons. First, a reduced gas temperature enhances Ti-2 dimer formation mainly because a lower gas temperature gives a higher gas density, which reduces the dilution of the Ti vapor through diffusion. The same effect can be achieved by increasing the gas pressure. Second, a reduced gas temperature has a 'more than exponential' effect in lowering the rate of atom evaporation from the nanoparticles during their growth from a dimer to size where they are thermodynamically stable, r*. We show that this early stage evaporation is not possible to model as a thermodynamical equilibrium. Instead, the single-event nature of the evaporation process has to be considered. This leads, counter intuitively, to an evaporation probability from nanoparticles that is exactly zero below a critical nanoparticle temperature that is size-dependent. Together, the mechanisms described above explain two experimentally found limits for nucleation in an oxygen-free environment. First, there is a lower limit to the pressure for dimer formation. Second, there is an upper limit to the gas temperature above which evaporation makes the further growth to stable nuclei impossible.

  • 24.
    Hajihoseini, H.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Science Institute, University of Iceland, Dunhaga 3, IS-107, Reykjavik, Iceland.
    Kateb, M.
    Ingvarsson, S.
    Gudmundsson, J. T.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Science Institute, University of Iceland, Dunhaga 3, IS-107, Reykjavik, Iceland.
    Effect of substrate bias on properties of HiPIMS deposited vanadium nitride films2018In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 663, p. 126-130Article in journal (Refereed)
    Abstract [en]

    We report on the effect of varying the substrate bias on the morphology, composition, structural, and electrical properties of vanadium nitride films deposited by high power impulse magnetron sputtering (HiPIMS). The optimum substrate bias is found to be −50 V, which gives the highest film density, the lowest electrical resistivity, and the lowest surface roughness at the highest deposition rate. We demonstrate how increasing the substrate bias voltage leads to a highly textured film. The preferred orientation of the film changes from (111) to (200) as the substrate bias voltage is increased. An X-ray pole scan shows that the (111) plane grows parallel to the SiO2 substrate when the substrate is grounded while it is gradually replaced by the (200) plane as the substrate bias voltage is increased up to −200 V. The lowest electrical resistivity is measured as 48.4 μΩ cm for the VN film deposited under substrate bias of −50 V. This is among the lowest room temperature values that have been reported for a VN film. We found that the nitrogen concentration presents a decline by 6.5 percentage points as the substrate bias is changed from ground to −200 V. 

  • 25. Hamrin, M.
    et al.
    Gunell, H.
    Lindkvist, J.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Ergun, R. E.
    Giles, B. L.
    Bow Shock Generator Current Systems: MMS Observations of Possible Current Closure2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 242-258Article in journal (Refereed)
    Abstract [en]

    We use data from the first two dayside seasons of the Magnetospheric Multiscale (MMS) mission to study current systems associated with quasi-perpendicular bow shocks of generator type. We have analyzed 154 MMS bow shock crossings near the equatorial plane. We compute the current density during the crossings and conclude that the component perpendicular to the shock normal (J) is consistent with a pileup of the interplanetary magnetic field (IMF) inside the magnetosheath. For predominantly southward IMF, we observe a component J(n) parallel (antiparallel) to the normal for GSM gamma > 0 (<0), and oppositely directed for northward IMF. This indicates current closure across the equatorial magnetosheath, and it is observed for IMF clock angles near 0 degrees and 180 degrees. To our knowledge, these are the first observational evidence for bow shock current closure across the magnetosheath. Since we observe no clear signatures of vertical bar J(perpendicular to)vertical bar decreasing toward large vertical bar Y vertical bar we suggest that the main region of current closure is further tailward, outside MMS probing region. For IMF clock angles near 90 degrees, we find indications of the current system being tilted toward the north-south direction, obtaining a significant J(z) component, and we suggest that the current closes off the equatorial plane at higher latitudes where the spacecraft are not probing. The observations are complicated for several reasons. For example, variations in the solar wind and the magnetospheric currents and loads affect the closure, and J(n) is distributed over large regions, making it difficult to resolve inside the magnetosheath proper.

  • 26.
    Karlsson, Tomas
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Plaschke, Ferdinand
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Hietala, Heli
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, 603 Charles E Young Dr East,Slichter Hall 6844D, Los Angeles, CA 90095 USA..
    Archer, Martin
    Queen Mary Univ London, Sch Phys & Astron, London E1 4NS, England..
    Blanco-Cano, Xochitl
    Univ Nacl Autonoma Mexico, Inst Geofis, Ciudad Univ, Cdmx, Mexico..
    Kajdic, Primoz
    Univ Nacl Autonoma Mexico, Inst Geofis, Ciudad Univ, Cdmx, Mexico..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Gershman, Daniel J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Investigating the anatomy of magnetosheath jets - MMS observations2018In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 36, no 2, p. 655-677Article in journal (Refereed)
    Abstract [en]

    We use Magnetosphere Multiscale (MMS) mission data to investigate a small number of magnetosheath jets, which are localized and transient increases in dynamic pressure, typically due to a combined increase in plasma velocity and density. For two approximately hour-long intervals in November, 2015 we found six jets, which are of two distinct types. (a) Two of the jets are associated with the magnetic field discontinuities at the boundary between the quasi-parallel and quasi-perpendicular magnetosheath. Straddling the boundary, the leading part of these jets contains an ion population similar to the quasi-parallel magnetosheath, while the trailing part contains ion populations similar to the quasi-perpendicular magnetosheath. Both populations are, however, cooler than the surrounding ion populations. These two jets also have clear increases in plasma density and magnetic field strength, correlated with a velocity increase. (b) Three of the jets are found embedded within the quasi-parallel magnetosheath. They contain ion populations similar to the surrounding quasi-parallel magnetosheath, but with a lower temperature. Out of these three jets, two have a simple structure. For these two jets, the increases in density and magnetic field strength are correlated with the dynamic pressure increases. The other jet has a more complicated structure, and no clear correlations between density, magnetic field strength and dynamic pressure. This jet has likely interacted with the magnetosphere, and contains ions similar to the jets inside the quasi-parallel magnetosheath, but shows signs of adiabatic heating. All jets are associated with emissions of whistler, lower hybrid, and broadband electrostatic waves, as well as approximately 10 s period electromagnetic waves with a compressional component. The latter have a Poynting flux of up to 40 mu Wm(-2) and may be energetically important for the evolution of the jets, depending on the wave excitation mechanism. Only one of the jets is likely to have modified the surrounding magnetic field into a stretched configuration, as has recently been reported in other studies. None of the jets are associated with clear signatures of either magnetic or thermal pressure gradient forces acting on them. The different properties of the two types also point to different generation mechanisms, which are discussed here. Their different properties and origins suggest that the two types of jets need to be separated in future statistical and simulation studies.

  • 27.
    Kateb, Movaffaq
    et al.
    Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Hajihoseini, Hamidreza
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland.
    Gudmundsson, Jon Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland.
    Ingvarsson, Snorri
    Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Comparison of magnetic and structural properties of permalloy Ni80Fe20 grown by dc and high power impulse magnetron sputtering2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 28, article id 285005Article in journal (Refereed)
    Abstract [en]

    We study the microstructure and magnetic properties of Ni80Fe20 thin films grown by high power impulse magnetron sputtering (HiPIMS), and compare with films grown by dc magnetron sputtering (dcMS). The films were grown under a tilt angle of 35 degrees to identical thickness of 37 nm using both techniques, at different pressure (0.13-0.73 Pa) and substrate temperature (room temperature and 100 degrees C). All of our films display effective in-plane uniaxial anisotropy with square easy axis and linear hard axis magnetization traces. X-ray diffraction reveals that there is very little change in grain size within the pressure and temperature ranges explored. However, variations in film density, obtained by x-ray reflectivity measurements, with pressure have a significant effect on magnetic properties such as anisotropy field (H-k) and coercivity (H-c). Depositions where adatom energy is high produce dense films, while low adatom energy results in void-rich films with higher H-k and H-c. The latter applies to our dcMS deposited films at room temperature and high pressure. However, the HiPIMS deposition method gives higher adatom energy than the dcMS and results in dense films with low H-k and H-c. The surface roughness is found to increase with increased pressure, in all cases, however it showed negligible contribution to the increase in H-k, and H-c.

  • 28. Le Contel, O.
    et al.
    Nakamura, R.
    Breuillard, H.
    Argall, M. R.
    Graham, D. B.
    Fischer, D.
    Retino, A.
    Berthomier, M.
    Pottelette, R.
    Mirioni, L.
    Chust, T.
    Wilder, F. D.
    Gershman, D. J.
    Varsani, A.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Khotyaintsev, Yu. V.
    Norgren, C.
    Ergun, R. E.
    Goodrich, K. A.
    Burch, J. L.
    Torbert, R. B.
    Needell, J.
    Chutter, M.
    Rau, D.
    Dors, I.
    Russell, C. T.
    Magnes, W.
    Strangeway, R. J.
    Bromund, K. R.
    Wei, H. Y.
    Plaschke, F.
    Anderson, B. J.
    Le, G.
    Moore, T. E.
    Giles, B. L.
    Paterson, W. R.
    Pollock, C. J.
    Dorelli, J. C.
    Avanov, L. A.
    Saito, Y.
    Lavraud, B.
    Fuselier, S. A.
    Mauk, B. H.
    Cohen, I. J.
    Turner, D. L.
    Fennell, J. F.
    Leonard, T.
    Jaynes, A. N.
    Lower Hybrid Drift Waves and Electromagnetic Electron Space-Phase Holes Associated With Dipolarization Fronts and Field-Aligned Currents Observed by the Magnetospheric Multiscale Mission During a Substorm2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 12, p. 12236-12257Article in journal (Refereed)
    Abstract [en]

    We analyze two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on 10 August 2016. The first event corresponds to a fast dawnward flow with an antiparallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing and with a smaller lower hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet we cannot rule out the possibility that the drift waves are produced by the antiparallel current associated with the fast flows, leaving the source for the electron holes unexplained.

  • 29.
    Li, Jinxing
    et al.
    Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA 90095 USA..
    Bortnik, Jacob
    Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA 90095 USA..
    An, Xin
    Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA 90095 USA..
    Li, Wen
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA..
    Russell, Christopher T.
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA..
    Zhou, Meng
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA USA..
    Berchem, Jean
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA USA..
    Zhao, Cong
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA..
    Wang, Shan
    Univ Maryland, Astron Dept, College Pk, MD 20742 USA..
    Torbert, Roy B.
    Univ New Hampshire, Inst Study Earth Oceans & Space, Durham, NH 03824 USA..
    Le Contel, Olivier
    Univ Paris Sud, Sorbonne Univ, Lab Phys Plasmas, CNRS,Ecole Polytech,Observat Paris, Paris, France..
    Ergun, Robert E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Pollock, Craig J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Local Excitation of Whistler Mode Waves and Associated Langmuir Waves at Dayside Reconnection Regions2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 17, p. 8793-8802Article in journal (Refereed)
    Abstract [en]

    In the Earth's dayside reconnection boundary layer, whistler mode waves coincide with magnetic field openings and the formation of the resultant anisotropic electrons. Depending on the energy range of anisotropic electrons, whistlers can grow at frequencies in the upper and/or lower band. Observations show that whistler mode waves modulate Langmuir wave amplitude as they propagate toward the X line. Observations of whistler mode wave phase and Langmuir waves packets, as well as coincident electron measurements, reveal that whistler mode waves can accelerate electrons via Landau resonance at locations where E(parallel to)is antiparallel to the wave propagation direction. The accelerated electrons produce localized beams, which subsequently drive the periodically modulated Langmuir waves. The close association of those two wave modes reveals the microscale electron dynamics in the exhaust region, and the proposed mechanism could potentially be applied to explain the modulation events observed in planetary magnetospheres and in the solar wind. Plain Language Summary The Sun's and Earth's magnetic field can merge and reconnect on dayside magnetopause. Using measurements from NASA's MMS spacecraft, we report that a class of electromagnetic wave, named whistler mode wave, coincides with the reconnected magnetic field lines. Besides, those whistlers are observed to modulate the electric field oscillations, known as Langmuir waves. Using high-resolution wave and particle measurements, we explain that the whistlers are locally excited when electrons from both sides of the magnetopause mix and form an unstable distribution. The modulated Langmuir waves are generated due to localized electron acceleration, which occurs when the velocity of electrons matches that of whistlers in the direction along the magnetic field. The whistler mode waves and associated Langmuir waves can be used as an additional tool to remotely sense the occurrence of magnetic reconnections.

  • 30.
    Lindkvist, J.
    et al.
    Umea Univ, Dept Phys, Umea, Sweden..
    Hamrin, M.
    Umea Univ, Dept Phys, Umea, Sweden..
    Gunell, H.
    Umea Univ, Dept Phys, Umea, Sweden.;Royal Belgian Inst Space Aeron BIRA IASB, Brussels, Belgium..
    Nilsson, H.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Wedlund, C. S.
    Univ Oslo, Dept Phys, Oslo, Norway..
    Kallio, E.
    Aalto Univ, Dept Elect & Nanoengn, Espoo, Finland..
    Mann, I.
    Univ Tromso, Dept Phys & Technol, Tromso, Norway..
    Pitkanen, T.
    Umea Univ, Dept Phys, Umea, Sweden..
    Karlsson, Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Energy conversion in cometary atmospheres Hybrid modeling of 67P/Churyumov-Gerasimenko2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A81Article in journal (Refereed)
    Abstract [en]

    Aims. We wish to investigate the energy conversion between particles and electromagnetic fields and determine the location where it occurs in the plasma environment of comets. Methods. We used a hybrid plasma model that included photoionization, and we considered two cases of the solar extreme ultraviolet flux. Other parameters corresponded to the conditions of comet 67P/Churyumov-Gerasimenko at a heliocentric distance of 1.5 AU. Results. We find that a shock-like structure is formed upstream of the comet and acts as an electromagnetic generator, similar to the bow shock at Earth that slows down the solar wind. The Poynting flux transports electromagnetic energy toward the inner coma, where newly born cometary ions are accelerated. Upstream of the shock-like structure, we find local energy transfer from solar wind ions to cometary ions. We show that mass loading can be a local process with a direct transfer of energy, but also part of a dynamo system with electromagnetic generators and loads. Conclusions. The energization of cometary ions is governed by a dynamo system for weak ionization, but changes into a large conversion region with local transfer of energy directly from solar wind protons for high ionization.

  • 31. Liu, C. M.
    et al.
    Fu, H. S.
    Vaivads, A.
    Khotyaintsev, Y. V.
    Gershman, D. J.
    Hwang, K-J
    Chen, Z. Z.
    Cao, D.
    Xu, Y.
    Yang, J.
    Peng, F. Z.
    Huang, S. Y.
    Burch, J. L.
    Giles, B. L.
    Ergun, R. E.
    Russell, C. T.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Le Contel, O.
    Electron Jet Detected by MMS at Dipolarization Front2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 2, p. 556-564Article in journal (Refereed)
    Abstract [en]

    Using MMS high-resolution measurements, we present the first observation of fast electron jet (V-e similar to 2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale comparable to the DF thickness (similar to 0.9 d(i)), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E x B drift motion; it contributes significantly to the current system at the DF, including a localized ring-current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron-jet-driven current (E.j(e) approximate to 2 E.j(i)), rather than the ion current suggested in previous studies.

  • 32.
    Madsen, B.
    et al.
    Univ Oslo, Dept Phys, Oslo, Norway.;Tech Univ Denmark, Lyngby, Denmark..
    Wedlund, C. Simon
    Univ Oslo, Dept Phys, Oslo, Norway..
    Eriksson, A.
    Swedish Inst Space Phys IRFU, Uppsala, Sweden..
    Goetz, C.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Karlsson, Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Gunell, H.
    Royal Belgian Inst Space Aeron BIRA IASB, Brussels, Belgium.;Umea Univ, Dept Phys, Umea, Sweden..
    Spicher, A.
    Univ Oslo, Dept Phys, Oslo, Norway..
    Henri, P.
    Lab Phys & Chim Environm & Espace LPC2E, Orleans, France..
    Vallieres, X.
    Lab Phys & Chim Environm & Espace LPC2E, Orleans, France..
    Miloch, W. J.
    Univ Oslo, Dept Phys, Oslo, Norway..
    Extremely Low-Frequency Waves Inside the Diamagnetic Cavity of Comet 67P/Churyumov-Gerasimenko2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 9, p. 3854-3864Article in journal (Refereed)
    Abstract [en]

    The European Space Agency/Rosetta mission to comet 67P/Churyumov-Gerasimenko has provided several hundred observations of the cometary diamagnetic cavity induced by the interaction between outgassed cometary particles, cometary ions, and the solar wind magnetic field. Here we present the first electric field measurements of four preperihelion and postperihelion cavity crossings on 28 May 2015 and 17 February 2016, using the dual-probe electric field mode of the Langmuir probe (LAP) instrument of the Rosetta Plasma Consortium. We find that on large scales, variations in the electric field fluctuations capture the cavity and boundary regions observed in the already well-studied magnetic field, suggesting the electric field mode of the LAP instrument as a reliable tool to image cavity crossings. In addition, the LAP electric field mode unravels for the first time extremely low-frequency waves within two cavities. These low-frequency electrostatic waves are likely triggered by lower-hybrid waves observed in the surrounding magnetized plasma. Plain Language Summary As sunlight heats a comet nucleus, frozen volatile gases sublimate are ionized and interact with the solar wind and its embedded magnetic field, inducing a dynamical plasma environment around the comet. With the cornerstone European mission Rosetta and its 2years of near-continuous orbiting of comet 67P/Churyumov-Gerasimenko, the origin, structure, and evolution of this environment are only starting to be unveiled. Exciting are the numerous crossings of the diamagnetic cavity, the innermost plasma region from which the solar wind magnetic field is excluded. Whilst the magnetic field structure of the cavity crossings is well studied, the related electric field activity remains until now unexplored. Studying the electric field with the Langmuir probes onboard Rosetta, we find that whereas the large-scale electric field structure agrees well with the observed magnetic field behavior during cavity crossings, unexpected short-lived low-frequency electric field signals manifest themselves within the cavity. We interpret these as electrostatic waves triggered by a modulating of the cavity boundary caused by observed electrostatic waves at the same frequency in the surrounding magnetized plasma. This unravels a new aspect of the electromagnetic activity in the inner cometary environment, which is crucial for our understanding of the comet-solar wind-induced plasma environment.

  • 33.
    Man, H. Y.
    et al.
    Nanchang Univ, Sch Sci, Dept Phys, Nanchang, Jiangxi, Peoples R China.;Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China..
    Zhou, M.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China..
    Deng, X. H.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China..
    Fu, H. S.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Zhong, Z. H.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China.;Nanchang Univ, Sch Resources Environm & Chem Engn, Nanchang, Jiangxi, Peoples R China..
    Chen, Z. Z.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    In Situ Observation of Magnetic Reconnection Between an Earthward Propagating Flux Rope and the Geomagnetic Field2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 17, p. 8729-8737Article in journal (Refereed)
    Abstract [en]

    It has been proposed that, in the near-Earth magnetotail, earthward propagating flux ropes can merge with the Earth's dipole magnetic field and dissipate its magnetic energy. However, the reconnection diffusion region related to this process has not been identified. Here we report the first in situ observation of magnetic reconnection between an earthward propagating flux rope and the closed magnetic field lines connecting to Earth. Magnetospheric Multiscale (MMS) spacecraft crossed a vertical current sheet between the leading edge of the flux rope (negative B-Z) and the geomagnetic field (positive B-Z). The subion-scale current sheet, super-Alfvenic electron outflow, Hall magnetic and electric field, conversion of magnetic energy to plasma energy (J.E > 0), and magnetic null were observed during the crossing. All the above signatures indicate that MMS detected the reconnection diffusion region. This result is also relevant to other planets with intrinsic magnetosphere. Plain Language Summary Magnetic reconnection is an essential source process in space weather. Reconnection produces many magnetic structures, such as the magnetic flux ropes and reconnection fronts, and ejects them away from the reconnection site. These structures interact with the surrounding space environment during its propagation, which may have great geomagnetic effects. A highly asymmetric earthward propagating magnetic flux rope is often observed in the Earth's magnetotail. It has long been suggested that this asymmetrical magnetic flux rope is formed due to the flux erosion of the earthward part of the flux rope by magnetic reconnection between the flux rope and the geomagnetic field. Despite various theoretical and numerical simulation studies, there has been no observational evidence to confirm this scenario. This paper reports the first observation of magnetic reconnection occurring at the earthward front of a flux rope in the Earth's magnetotail, confirming the previous theoretical predictions and explaining the formation of the asymmetric flux rope which is often observed in the near-Earth magnetotail.

  • 34.
    Nakamura, Rumi
    et al.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Varsani, Ali
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Genestreti, Kevin J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Le Contel, Olivier
    UPMC Univ Paris 06, Univ Paris Sud, Observ Paris, Ecole Polytech,CNRS,Lab Phys Plasmas, Paris, France..
    Nakamura, Takuma
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Baumjohann, Wolfgang
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Nagai, Tsugunobu
    Tokyo Inst Technol, Earth & Planetary Sci, Tokyo, Japan..
    Artemyev, Anton
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Birn, Joachim
    Space Sci Inst, Boulder, CO USA..
    Sergeev, Victor A.
    St Petersburg State Univ, Earths Phys Dept, St Petersburg, Russia..
    Apatenkov, Sergey
    St Petersburg State Univ, Earths Phys Dept, St Petersburg, Russia..
    Ergun, Robert E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Fuselier, Stephen A.
    Southwest Res Inst, San Antonio, TX USA..
    Gershman, Daniel J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, Barbara J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Khotyaintsev, Yuri V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Magnes, Werner
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Mauk, Barry
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Petrukovich, Anatoli
    RAS, Space Res Inst IKI, Moscow, Russia..
    Russell, Christopher T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Stawarz, Julia
    Imperial Coll London, Dept Phys, London, England..
    Strangeway, Robert J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Anderson, Brian
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Bromund, Ken R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Cohen, Ian
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Fischer, David
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Jaynes, Allison
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Kepko, Laurence
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le, Guan
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Plaschke, Ferdinand
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Reeves, Geoff
    CSES, LANL, Los Alamos, NM USA..
    Singer, Howard J.
    NOAA, Space Weather Predict Ctr, Boulder, CO USA..
    Slavin, James A.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Torbert, Roy B.
    Southwest Res Inst, San Antonio, TX USA.;Univ New Hampshire, Inst Study Earth Oceans & Space, Durham, NH 03824 USA..
    Turner, Drew L.
    Aerosp Corp, Space Sci Dept, POB 92957, Los Angeles, CA 90009 USA..
    Multiscale Currents Observed by MMS in the Flow Braking Region2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 2, p. 1260-1278Article in journal (Refereed)
    Abstract [en]

    We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold ExB drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.

  • 35.
    Nilsson, H.
    et al.
    Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden.;Lulea Univ Technol, Dept Comp Sci Elect & Space Engn, Rymdcampus 1, S-98128 Kiruna, Sweden..
    Gunell, H.
    Belgian Inst Space Aeron, Ave Circulaire 3, B-1180 Brussels, Belgium.;Umea Univ, Dept Phys, S-90187 Umea, Sweden..
    Karlsson, Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Brenning, Nils
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Henri, P.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, UMR 7328, Orleans, France..
    Goetz, C.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Eriksson, A. I.
    Swedish Inst Space Phys, Angstrom Lab, Lagerhyddsvagen 1, Uppsala, Sweden..
    Behar, E.
    Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden.;Lulea Univ Technol, Dept Comp Sci Elect & Space Engn, Rymdcampus 1, S-98128 Kiruna, Sweden..
    Wieser, G. Stenberg
    Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden..
    Vallieres, X.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, UMR 7328, Orleans, France..
    Size of a plasma cloud matters The polarisation electric field of a small-scale comet ionosphere2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A50Article in journal (Refereed)
    Abstract [en]

    Context. The cometary ionosphere is immersed in fast flowing solar wind. A polarisation electric field may arise for comets much smaller than the gyroradius of pickup ions because ions and electrons respond differently to the solar wind electric field. Aims. A situation similar to that found at a low activity comet has been modelled for barium releases in the Earth's ionosphere. We aim to use such a model and apply it to the case of comet 67P Churyumov-Gerasimenko, the target of the Rosetta mission. We aim to explain the significant tailward acceleration of cometary ions through the modelled electric field. Methods. We obtained analytical solutions for the polarisation electric field of the comet ionosphere using a simplified geometry. This geometry is applicable to the comet in the inner part of the coma as the plasma density integrated along the magnetic field line remains rather constant. We studied the range of parameters for which a significant tailward electric field is obtained and compare this with the parameter range observed. Results. Observations of the local plasma density and magnetic field strength show that the parameter range of the observations agree very well with a significant polarisation electric field shielding the inner part of the coma from the solar wind electric field. Conclusions. The same process gives rise to a tailward directed electric field with a strength of the order of 10% of the solar wind electric field. Using a simple cloud model we have shown that the polarisation electric field, which arises because of the small size of the comet ionosphere as compared to the pick up ion gyroradius, can explain the observed significant tailward acceleration of cometary ions and is consistent with the observed lack of influence of the solar wind electric field in the inner coma.

  • 36.
    Oimatsu, S.
    et al.
    Kyoto Univ, Grad Sch Sci, Kyoto, Japan..
    Nose, M.
    Kyoto Univ, Grad Sch Sci, Kyoto, Japan..
    Teramoto, M.
    Nagoya Univ, Inst Space Earth Environm Res, Nagoya, Aichi, Japan..
    Yamamoto, K.
    Kyoto Univ, Grad Sch Sci, Kyoto, Japan..
    Matsuoka, A.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Tokyo, Japan..
    Kasahara, S.
    Univ Tokyo, Grad Sch Sci, Tokyo, Japan..
    Yokota, S.
    Osaka Univ, Grad Sch Sci, Suita, Osaka, Japan..
    Keika, K.
    Univ Tokyo, Grad Sch Sci, Tokyo, Japan..
    Le, G.
    NASA, Heliophys Sci Div, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Nomura, R.
    Japan Aerosp Explorat Agcy, Environm Test Technol Unit, Tokyo, Japan..
    Fujimoto, A.
    Kyushu Univ, Int Ctr Space Weather Sci & Educ, Fukuoka, Fukuoka, Japan..
    Sormakov, D.
    Arctic & Antarctic Res Inst, St Petersburg, Russia..
    Troshichev, O.
    Arctic & Antarctic Res Inst, St Petersburg, Russia..
    Tanaka, Y. -M
    Shinohara, M.
    Kagoshima Coll, Natl Inst Technol, Kagoshima, Japan..
    Shinohara, I.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Tokyo, Japan..
    Miyoshi, Y.
    Nagoya Univ, Inst Space Earth Environm Res, Nagoya, Aichi, Japan..
    Slavin, J. A.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Ergun, R. E.
    Univ Colorado, Dept Astrophys & Planetary Sci, Denver, CO 80202 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Drift-Bounce Resonance Between Pc5 Pulsations and Ions at Multiple Energies in the Nightside Magnetosphere: Arase and MMS Observations2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 15, p. 7277-7286Article in journal (Refereed)
    Abstract [en]

    A Pc5 wave is observed by the Exploration of energization and Radiation in Geospace Arase satellite in the inner magnetosphere (L similar to 5.4-6.1) near postmidnight (L-magnetic local time similar to 1.8-2.5 hr) during the storm recovery phase on 27 March 2017. Its azimuthal wave number (m-number) is estimated using two independent methods with satellites and ground observations to be -8 to -15. The direct measurement of the m-number enables us to calculate the resonance energy. The flux oscillations of H+ and O+ ions at >= 56.3 keV are caused by drift resonance and those of O+ ions at <= 18.6 keV by bounce resonance. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. The enhancement of the O+/H+ flux ratio at <= 18.6 keV indicates selective acceleration of O+ ions through bounce resonance. Plain Language Summary Geomagnetic pulsations are magnetic fluctuations excited by solar wind or plasma instabilities in the magnetosphere. Pc5 waves are continuous geomagnetic pulsations with a period of 150-600 s. A Pc5 wave was observed in the inner magnetosphere during a magnetic storm on 27 March 2017. It propagated westward with a wave number of 8 to 15 and resonated with charged particles, resulting in oscillations of the H+ and O+ ion fluxes at >= 56.3 keV and the O+ ion fluxes at <= 18.6 keV. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. At the same time, the O+/H+ flux ratio at <= 18.6 keV enhanced corresponding to the O+ ion flux oscillations, which indicates selective acceleration of O+ ions through resonances.

  • 37. Palmroth, M.
    et al.
    Hietala, H.
    Plaschke, F.
    Archer, M.
    Karlsson, Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Blanco-Cano, X.
    Sibeck, D.
    Kajdic, P.
    Ganse, U.
    Pfau-Kempf, Y.
    Battarbee, M.
    Turc, L.
    Magnetosheath jet properties and evolution as determined by a global hybrid-Vlasov simulation2018In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 36, no 5, p. 1171-1182Article in journal (Refereed)
    Abstract [en]

    We use a global hybrid-Vlasov simulation for the magnetosphere, Vlasiator, to investigate magnetosheath high-speed jets. Unlike many other hybrid-kinetic simulations, Vlasiator includes an unscaled geomagnetic dipole, indicating that the simulation spatial and temporal dimensions can be given in SI units without scaling. Thus, for the first time, this allows investigating the magnetosheath jet properties and comparing them directly with the observed jets within the Earth's magnetosheath. In the run shown in this paper, the interplanetary magnetic field (IMF) cone angle is 30°, and a foreshock develops upstream of the quasi-parallel magnetosheath. We visually detect a structure with high dynamic pressure propagating from the bow shock through the magnetosheath. The structure is confirmed as a jet using three different criteria, which have been adopted in previous observational studies. We compare these criteria against the simulation results. We find that the magnetosheath jet is an elongated structure extending earthward from the bow shock by ∼ 2.6 RE, while its size perpendicular to the direction of propagation is ∼ 0.5R/E. We also investigate the jet evolution and find that the jet originates due to the interaction of the bow shock with a high-dynamic-pressure structure that reproduces observational features associated with a short, large-amplitude magnetic structure (SLAMS). The simulation shows that magnetosheath jets can develop also under steady IMF, as inferred by observational studies. To our knowledge, this paper therefore shows the first global kinetic simulation of a magnetosheath jet, which is in accordance with three observational jet criteria and is caused by a SLAMS advecting towards the bow shock. 

  • 38.
    Panarese, A.
    et al.
    Univ Bari, Dept Chem, I-70126 Bari, Italy.;CNR, Inst Nanotechnol NANOTEC, I-70126 Bari, Italy..
    Bruno, D.
    CNR, Inst Nanotechnol NANOTEC, I-70126 Bari, Italy..
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. st Nazl Fis Nucl, Sez Napoli, I-80126 Naples, Italy..
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Longo, S.
    Univ Bari, Dept Chem, I-70126 Bari, Italy.;CNR, Inst Nanotechnol NANOTEC, I-70126 Bari, Italy..
    de Angelis, U.
    Ist Nazl Fis Nucl, Sez Napoli, I-80126 Naples, Italy..
    Molecular dynamics calculation of the spectral densities of plasma fluctuations2018In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, no 3, article id 905840308Article in journal (Refereed)
    Abstract [en]

    Spectral densities of plasma fluctuations are calculated for the thermal case using classical molecular dynamics (MD) assuming Coulomb interactions and a short-range cutoff radius. The aim of the calculation is to verify limits and performances of such calculations in the light of possible generalizations, e.g. collisional or non-ideal plasmas. Results are presented for ideal, collisionless, fully ionized thermal plasmas. Comparison with the analytical theory reveals a generally satisfactory agreement with possibility for improvement when more strict numerical parameters are used albeit with a strong increase in computational cost. The largest deviations have been observed in the vicinity of the weakly damped eigenmodes. The agreement is strong in other parts of the spectrum, where Landau damping is prominent, and overcomes the effects stemming from the excess collisionality and coupling as well as from the exclusion of short-range collisions.

  • 39.
    Phan, T. D.
    et al.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Eastwood, J. P.
    Imperial Coll London, Blackett Lab, London, England..
    Shay, M. A.
    Univ Delaware, Newark, DE USA..
    Drake, J. F.
    Univ Maryland, College Pk, MD 20742 USA..
    Sonnerup, B. U. O.
    Dartmouth Coll, Hanover, NH 03755 USA..
    Fujimoto, M.
    JAXA, ISAS, Sagamihara, Kanagawa, Japan..
    Cassak, P. A.
    West Virginia Univ, Morgantown, WV USA..
    Oieroset, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Durham, NH 03824 USA..
    Rager, A. C.
    Catholic Univ Amer, Washington, DC 20064 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C.
    Denali Sci, Healy, AK USA..
    Pyakurel, P. S.
    Univ Delaware, Newark, DE USA..
    Haggerty, C. C.
    Univ Delaware, Newark, DE USA..
    Khotyaintsev, Y.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys & Planetol, Toulouse, France..
    Saito, Y.
    JAXA, ISAS, Sagamihara, Kanagawa, Japan..
    Oka, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Retino, A.
    Ecole Polytech, CNRS, Paris, France..
    Le Contel, O.
    Ecole Polytech, CNRS, Paris, France..
    Argall, M. R.
    Univ New Hampshire, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Moore, T. E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Wilder, F. D.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Russell, C. T.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath2018In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 557, no 7704, p. 202-+Article in journal (Refereed)
    Abstract [en]

    Magnetic reconnection in current sheets is a magnetic-to-particle energy conversion process that is fundamental to many space and laboratory plasma systems. In the standard model of reconnection, this process occurs in a minuscule electron-scale diffusion region(1,2). On larger scales, ions couple to the newly reconnected magnetic-field lines and are ejected away from the diffusion region in the form of bi-directional ion jets at the ion Alfven speed(3-5). Much of the energy conversion occurs in spatially extended ion exhausts downstream of the diffusion region(6). In turbulent plasmas, which contain a large number of small-scale current sheets, reconnection has long been suggested to have a major role in the dissipation of turbulent energy at kinetic scales(7-11). However, evidence for reconnection plasma jetting in small-scale turbulent plasmas has so far been lacking. Here we report observations made in Earth's turbulent magnetosheath region (downstream of the bow shock) of an electron-scale current sheet in which diverging bi-directional super-ion-Alfvenic electron jets, parallel electric fields and enhanced magnetic-to-particle energy conversion were detected. Contrary to the standard model of reconnection, the thin reconnecting current sheet was not embedded in a wider ion-scale current layer and no ion jets were detected. Observations of this and other similar, but unidirectional, electron jet events without signatures of ion reconnection reveal a form of reconnection that can drive turbulent energy transfer and dissipation in electron-scale current sheets without ion coupling.

  • 40.
    Pitkanen, T.
    et al.
    Shandong Univ, Inst Space Sci, Weihai, Peoples R China.;Umea Univ, Dept Phys, Umea, Sweden..
    Kullen, Anita
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Royal Inst Technol, Sch Elect Engn, Space & Plasma Phys, Stockholm, Sweden..
    Shi, Q. Q.
    Shandong Univ, Inst Space Sci, Weihai, Peoples R China..
    Hamrin, M.
    Umea Univ, Dept Phys, Umea, Sweden..
    De Spiegeleer, A.
    Umea Univ, Dept Phys, Umea, Sweden..
    Nishimura, Y.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA..
    Convection Electric Field and Plasma Convection in a Twisted Magnetotail: A THEMIS Case Study 1-2 January 20092018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7486-7497Article in journal (Refereed)
    Abstract [en]

    We investigate THEMIS satellite measurements made in a tail-aligned constellation during a time interval on 1-2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic fieldB(y)-driven magnetotail twisting. We find evidence for that the orientation of the convection electric field in the tail is twist-mode dependent. For earthward flow and a negative twist (induced tail B-y < 0), the electric field is found to have northward E-z and tailward E-x components. During a positive twist (induced tail B-y > 0), the directions of E-z and E-x are reversed. The E-y component shows the expected dawn-to-dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi-collinear field is observed irrespective to the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn-dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemispherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserve further investigation.

  • 41.
    Pitkanen, T.
    et al.
    Shandong Univ, Inst Space Sci, Weihai, Peoples R China.;Umea Univ, Dept Phys, Umea, Sweden..
    Kullen, Anita
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Shi, Q. Q.
    Shandong Univ, Inst Space Sci, Weihai, Peoples R China..
    Hamrin, M.
    Umea Univ, Dept Phys, Umea, Sweden..
    De Spiegeleer, A.
    Umea Univ, Dept Phys, Umea, Sweden..
    Nishimura, Y.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA..
    Convection Electric Field and Plasma Convection in a Twisted Magnetotail: A THEMIS Case Study 1-2 January 20092018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7486-7497Article in journal (Refereed)
    Abstract [en]

    We investigate THEMIS satellite measurements made in a tail-aligned constellation during a time interval on 1-2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic fieldB(y)-driven magnetotail twisting. We find evidence for that the orientation of the convection electric field in the tail is twist-mode dependent. For earthward flow and a negative twist (induced tail B-y < 0), the electric field is found to have northward E-z and tailward E-x components. During a positive twist (induced tail B-y > 0), the directions of E-z and E-x are reversed. The E-y component shows the expected dawn-to-dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi-collinear field is observed irrespective to the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn-dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemispherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserve further investigation.

  • 42. Plainaki, C.
    et al.
    Cassidy, T. A.
    Shematovich, V. I.
    Milillo, A.
    Wurz, P.
    Vorburger, A.
    Roth, Lorenz
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Galli, A.
    Rubin, M.
    Blöcker, A.
    Brandt, P. C.
    Crary, F.
    Dandouras, I.
    Jia, X.
    Grassi, D.
    Hartogh, P.
    Lucchetti, A.
    McGrath, M.
    Mangano, V.
    Mura, A.
    Orsini, S.
    Paranicas, C.
    Radioti, A.
    Retherford, K. D.
    Saur, J.
    Teolis, B.
    Towards a Global Unified Model of Europa’s Tenuous Atmosphere2018In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 214, no 1, article id 40Article, review/survey (Refereed)
    Abstract [en]

    Despite the numerous modeling efforts of the past, our knowledge on the radiation-induced physical and chemical processes in Europa’s tenuous atmosphere and on the exchange of material between the moon’s surface and Jupiter’s magnetosphere remains limited. In lack of an adequate number of in situ observations, the existence of a wide variety of models based on different scenarios and considerations has resulted in a fragmentary understanding of the interactions of the magnetospheric ion population with both the moon’s icy surface and neutral gas envelope. Models show large discrepancy in the source and loss rates of the different constituents as well as in the determination of the spatial distribution of the atmosphere and its variation with time. The existence of several models based on very different approaches highlights the need of a detailed comparison among them with the final goal of developing a unified model of Europa’s tenuous atmosphere. The availability to the science community of such a model could be of particular interest in view of the planning of the future mission observations (e.g., ESA’s JUpiter ICy moons Explorer (JUICE) mission, and NASA’s Europa Clipper mission). We review the existing models of Europa’s tenuous atmosphere and discuss each of their derived characteristics of the neutral environment. We also discuss discrepancies among different models and the assumptions of the plasma environment in the vicinity of Europa. A summary of the existing observations of both the neutral and the plasma environments at Europa is also presented. The characteristics of a global unified model of the tenuous atmosphere are, then, discussed. Finally, we identify needed future experimental work in laboratories and propose some suitable observation strategies for upcoming missions.

  • 43.
    Plaschke, F.
    et al.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Karlsson, T.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Goetz, C.
    Braunschweig Inst Technol, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Moestl, C.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Richter, I.
    Braunschweig Inst Technol, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Eriksson, A.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Behar, E.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Goldstein, R.
    Southwest Res Inst, San Antonio, TX USA..
    First observations of magnetic holes deep within the coma of a comet2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 618, article id A114Article in journal (Refereed)
    Abstract [en]

    The Rosetta spacecraft of the European Space Agency made ground-breaking observations of comet 67P/Churyumov-Gerasimenko and of its cometary environment. We search for magnetic holes in that environment, i.e., significant depressions in the magnetic field strength, measured by the Rosetta fluxgate Magnetometer (MAG) in April and May 2015. In that time frame of two months, we identified 23 magnetic holes. The cometary activity was intermediate and increasing because Rosetta was on the inbound leg toward the Sun. While in April solar wind protons were still observed by Rosetta near the comet, in May these protons were already mostly replaced by heavy cometary ions. Magnetic holes have frequently been observed in the solar wind. We find, for the first time, that magnetic holes exist in the cometary environment even when solar wind protons are almost absent. Some of the properties of the magnetic holes are comparable to those of solar wind holes; they are associated with density enhancements, sometimes associated with co-located current sheets and fast solar wind streams, and are of similar scales. However, particularly in May, the magnetic holes near the comet appear to be more processed, featuring shifted density enhancements and, sometimes, bipolar signatures in magnetic field strength rather than simple depressions. The magnetic holes are of global size with respect to the coma. However, at the comet, they are compressed owing to magnetic field pile-up and draping so that they change in shape. There, the magnetic holes become of comparable size to heavy cometary ion gyroradii, potentially enabling kinetic interactions.

  • 44.
    Plaschke, F.
    et al.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Karlsson, Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Goetz, C.
    Braunschweig Inst Technol, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Moestl, C.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Richter, I.
    Braunschweig Inst Technol, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Eriksson, A.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Behar, E.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Goldstein, R.
    Southwest Res Inst, San Antonio, TX USA..
    First observations of magnetic holes deep within the coma of a comet2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 618, article id A114Article in journal (Refereed)
    Abstract [en]

    The Rosetta spacecraft of the European Space Agency made ground-breaking observations of comet 67P/Churyumov-Gerasimenko and of its cometary environment. We search for magnetic holes in that environment, i.e., significant depressions in the magnetic field strength, measured by the Rosetta fluxgate Magnetometer (MAG) in April and May 2015. In that time frame of two months, we identified 23 magnetic holes. The cometary activity was intermediate and increasing because Rosetta was on the inbound leg toward the Sun. While in April solar wind protons were still observed by Rosetta near the comet, in May these protons were already mostly replaced by heavy cometary ions. Magnetic holes have frequently been observed in the solar wind. We find, for the first time, that magnetic holes exist in the cometary environment even when solar wind protons are almost absent. Some of the properties of the magnetic holes are comparable to those of solar wind holes; they are associated with density enhancements, sometimes associated with co-located current sheets and fast solar wind streams, and are of similar scales. However, particularly in May, the magnetic holes near the comet appear to be more processed, featuring shifted density enhancements and, sometimes, bipolar signatures in magnetic field strength rather than simple depressions. The magnetic holes are of global size with respect to the coma. However, at the comet, they are compressed owing to magnetic field pile-up and draping so that they change in shape. There, the magnetic holes become of comparable size to heavy cometary ion gyroradii, potentially enabling kinetic interactions.

  • 45.
    Proto, A.
    et al.
    Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Gudmundsson, Jon Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland.
    The role of surface quenching of the singlet delta molecule in a capacitively coupled oxygen discharge2018In: Plasma sources science & technology (Print), ISSN 0963-0252, E-ISSN 1361-6595, Vol. 27, no 7, article id 074002Article in journal (Refereed)
    Abstract [en]

    We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 to explore the influence of the surface quenching of the singlet delta metastable molecule O-2(a(1)Delta(g)) on the electron heating mechanism, and the electron energy probability function (EEPF), in a single frequency capacitively coupled oxygen discharge. When operating at low pressure (10 mTorr) varying the surface quenching coefficient in the range 0.000 01-0.1 has no influence on the electron heating mechanism and electron heating is dominated by drift-ambipolar (DA) heating in the plasma bulk and electron cooling is observed in the sheath regions. As the pressure is increased to 25 mTorr the electron heating becomes a combination of DA-mode and alpha-mode heating, and the role of the DA-mode decreases with decreasing surface quenching coefficient. At 50 mTorr, electron heating in the sheath region dominates. However, for the highest quenching coefficient there is some contribution from the DA-mode in the plasma bulk, but this contribution decreases to almost zero and pure alpha-mode electron heating is observed for a surface quenching coefficient of 0.001 or smaller.

  • 46.
    Ratynskaia, S.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Tolias, P.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    De Angeli, M.
    CNR, Ist Fis Plasma, I-20125 Milan, Italy..
    Rohde, V.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Herrmann, A.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Ripamonti, D.
    CNR, Inst Condensed Matter Chem & Energy Technol, I-20125 Milan, Italy..
    Riva, G.
    CNR, Inst Condensed Matter Chem & Energy Technol, I-20125 Milan, Italy..
    Thorén, E.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Vignitchouk, L.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Sieglin, B.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Krieger, K.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Neu, R.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Interaction of metal dust adhered on castellated substrates with the ELMy H-mode plasmas of ASDEX-Upgrade2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 10, article id 106023Article in journal (Refereed)
    Abstract [en]

    Castellated substrates with adhered micron dust have been exposed in the outer ASDEX-Upgrade divertor to ELMy H-mode discharges. Beryllium proxy (chromium, copper) and refractory metal (tungsten, molybdenum) dust has been deposited on the plasma-facing and plasma-shadowed sides of the monoblocks as well as the bottom of the gaps. Interaction with time-averaged transient heat loads up to 5 MWm(-2) led to dust remobilization, clustering, melting and wetting-induced coagulation. The amount of dust released in the vessel has been quantified and remobilized dust trajectories inferred. Gaps can efficiently trap locally adhered dust, but dust detaching from adjacent monoblocks does not preferentially move inside the gaps implying that they do not constitute a dust accumulation site. Heat transfer simulations of melting events are also reported taking into account heat constriction due to the finite contact area and the presence of surface roughness.

  • 47.
    Saur, Joachim
    et al.
    Univ Cologne, Inst Geophys & Meteorol, Albertus Magnus Pl, D-50923 Cologne, Germany..
    Fischer, Christian
    Univ Cologne, Inst Geophys & Meteorol, Albertus Magnus Pl, D-50923 Cologne, Germany..
    Wennmacher, Alexandre
    Univ Cologne, Inst Geophys & Meteorol, Albertus Magnus Pl, D-50923 Cologne, Germany..
    Feldman, Paul D.
    Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA..
    Roth, Lorenz
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Strobel, Darrell F.
    Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA.;Johns Hopkins Univ, Dept Earth & Planetary Sci, Baltimore, MD 21218 USA..
    Reiners, Ansgar
    Georg August Univ, Inst Astrophys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    The UV Spectrum of the Ultracool Dwarf LSR J1835+3259 Observed with the Hubble Space Telescope2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 859, no 1Article in journal (Refereed)
    Abstract [en]

    An interesting question about ultracool dwarfs recently raised in the literature is whether their emission is purely internally driven or partially powered by external processes similar to planetary aurora known from the solar system. In this work, we present Hubble Space Telescope observations of the energy fluxes of the M8.5 ultracool dwarf LSR J1835+3259 throughout the ultraviolet (UV). The obtained spectra reveal that the object is generally UV-fainter compared with other earlier-type dwarfs. We detect the Mg II doublet at 2800 angstrom and constrain an average flux throughout the near-UV. In the far-UV without Ly alpha, the ultracool dwarf is extremely faint with an energy output at least a factor of 250 smaller as expected from auroral emission physically similar to that on Jupiter. We also detect the red wing of the Lya emission. Our overall finding is that the observed UV spectrum of LSR J1835 vertical bar 3259 resembles the spectrum of mid/late-type M-dwarf stars relatively well, but it is distinct from a spectrum expected from Jupiter-like auroral processes.

  • 48. Slav, A.
    et al.
    Palade, C.