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  • 1. Aiba, N
    et al.
    Giroud, C
    Honda, M
    Delabie, E
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Saarelma, S
    Hillesheim, J
    Pamela, S
    Wiesen, S
    Maggi, C
    Urano, H
    Drewelow, P
    Leyland, M
    Moulton, D
    Menmuir, S
    Diamagnetic MHD Equations for Plasmas with Fast Flow and its Application to ELM Analysis in JT-60U and JET-ILW2016In: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Conference paper (Refereed)
  • 2. Aiba, N.
    et al.
    Giroud, C.
    Honda, M.
    Delabie, E.
    Saarelma, S.
    Frassinetti, L
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lupelli, I.
    Casson, F. J.
    Pamela, S.
    Urano, H.
    Maggi, C. F.
    Numerical analysis of ELM stability with rotation and ion diamagnetic drift effects in JET2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 12, article id 126001Article in journal (Refereed)
    Abstract [en]

    Stability to the type-I edge localized mode (ELM) in JET plasmas was investigated numerically by analyzing the stability to a peeling-ballooning mode with the effects of plasma rotation and ion diamagnetic drift. The numerical analysis was performed by solving the extended Frieman-Rotenberg equation with the MINERVA-DI code. To take into account these effects in the stability analysis self-consistently, the procedure of JET equilibrium reconstruction was updated to include the profiles of ion temperature and toroidal rotation, which are determined based on the measurement data in experiments. With the new procedure and MINERVA-DI, it was identified that the stability analysis including the rotation effect can explain the ELM trigger condition in JET with ITER like wall (JET-ILW), though the stability in JET with carbon wall (JET-C) is hardly affected by rotation. The key difference is that the rotation shear in JET-ILW plasmas analyzed in this study is larger than that in JET-C ones, the shear which enhances the dynamic pressure destabilizing a peeling-ballooning mode. In addition, the increase of the toroidal mode number of the unstable MHD mode determining the ELM trigger condition is also important when the plasma density is high in JET-ILW. Though such modes with high toroidal mode number are strongly stabilized by the ion diamagnetic drift effect, it was found that plasma rotation can sometimes overcome this stabilizing effect and destabilizes the peeling-ballooning modes in JET-ILW.

  • 3. Aiba, N
    et al.
    Giroud, C
    Honda, M
    Delabie, E
    Saarelma, S
    Lupelli, I
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Maggi, C
    Impact of rotation and ion diamagnetic drift on ELM stability in JET-ILW2016In: 33rd Annual meeting of Japan society of plasma science and nuclear fusion research JSPF, Nov 2016. Japan, 2016Conference paper (Other academic)
  • 4. Aiba, N.
    et al.
    Pamela, S.
    Honda, M.
    Urano, H.
    Giroud, C.
    Delabie, E.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lupelli, I.
    Hayashi, N.
    Huijsmans, G.
    Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas2018In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, no 1, article id 014032Article in journal (Refereed)
    Abstract [en]

    The stability with respect to a peeling-ballooning mode (PBM) was investigated numerically with extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift (omega(*i)), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into account both the rotation and omega(*i) effects in the numerical analysis. When deuterium poloidal rotation is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes the PBM because of an acceleration of rotation and a decrease in omega(*i). The difference in the amount of ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the difference in the linear stability property, due not to the rotation direction but to the plasma density profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and w*i effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.

  • 5. Aijaz, Asim
    et al.
    Sarakinos, Kostas
    Lundin, Daniel
    Brenning, Nils
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Helmersson, Ulf
    A strategy for increased carbon ionization in magnetron sputtering discharges2012In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 23, p. 1-4Article in journal (Refereed)
    Abstract [en]

    A strategy that facilitates a substantial increase of carbon ionization in magnetron sputtering discharges is presented in this work. The strategy is based on increasing the electron temperature in a high power impulse magnetron sputtering discharge by using Ne as the sputtering gas. This allows for the generation of an energetic C+ ion population and a substantial increase in the C+ ion flux as compared to a conventional Ar-HiPIMS process. A direct consequence of the ionization enhancement is demonstrated by an increase in the mass density of the grown films up to 2.8 g/cm(3); the density values achieved are substantially higher than those obtained from conventional magnetron sputtering methods.

  • 6. Aikio, A T
    et al.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Yamauchi, M
    On the origin of the high-altitude electric field fluctuations in the auroral zone1996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no A12, p. 27157-27170Article in journal (Refereed)
    Abstract [en]

    Intense fluctuations in the electric field at high altitudes in the auroral zone are frequently measured by the Viking satellite. We have made an analysis of the origin of electric and magnetic fluctuations in the frequency range of 0.1 - 1 Hz by assuming four different sources for the signals: (I) spatial structures, (2) spatial structures with a parallel potential drop below the satellite, (3) traveling; shear Alfven waves, and (4) interfering shear Alfven waves. We will shaw that these different sources of the signals may produce similar amplitude ratios and phase differences between the perpendicular electric and magnetic fields. Since the different sources have different frequency dependencies, this can be used as an additional test if the signals are broadband. In other cases, additional information is needed, for example, satellite particle measurements or ground; magnetic measurements. The ideas presented in the theory were tested for one Viking eveningside pass over Scandinavia, where ground-based magnetometer and EISCAT radar measurements were available. The magnetic conditions were active during this pass and several interfering shear Alfven waves were found. Also, a spatial structure with a parallel potential drop below the satellite was identified. The magnitude of the 10-km-wide potential drop was at least 2 kV and the upward field-aligned current 26 mu A m(-2) (value mapped to the ionospheric level). The held-aligned conductance was estimated as 1.3 - 2.2x10(-8) S m(-2).

  • 7. Airila, M. I.
    et al.
    Aho-Mantila, L.
    Brezinsek, S.
    Coad, J. P.
    Kirschner, A.
    Likonen, J.
    Matveev, D.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Strachan, J. D.
    Widdowson, A.
    Wiesen, S.
    ERO modelling of local deposition of injected C-13 tracer at the outer divertor of JET2009In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T138, p. 014021-Article in journal (Refereed)
    Abstract [en]

    The 2004 tracer experiment of JET with the injection of (CH4)-C-13 into H-mode plasma at the outer divertor has been modelled with the Monte Carlo impurity transport code ERO. EDGE2D solutions for inter-ELM and ELM-peak phases were used as plasma backgrounds. Local two-dimensional (2D) deposition patterns at the vertical outer divertor target plate were obtained for comparison with post-mortem surface analyses. ERO also provides emission profiles for comparison with radially resolved spectroscopic measurements. Modelling indicates that enhanced re-erosion of deposited carbon layers is essential in explaining the amount of local deposition. Assuming negligible effective sticking of hydrocarbons, the measured local deposition of 20-34% is reproduced if re-erosion of deposits is enhanced by a factor of 2.5-7 compared to graphite erosion. If deposits are treated like the substrate, the modelled deposition is 55%. Deposition measurements at the shadowed area around injectors can be well explained by assuming negligible re-erosion but similar sticking behaviour there as on plasma-wetted surfaces.

  • 8. Airila, M. I.
    et al.
    Jarvinen, A.
    Groth, M.
    Belo, P.
    Wiesen, S.
    Brezinsek, S.
    Lawson, K.
    Borodin, D.
    Kirschner, A.
    Coad, J. P.
    Heinola, K.
    Likonen, J.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Widdowson, A.
    Preliminary Monte Carlo simulation of beryllium migration during JET ITER-like wall divertor operation2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 800-804Article in journal (Refereed)
    Abstract [en]

    Migration of beryllium into the divertor and deposition on tungsten in the final phase of the first ITER-like-wall campaign of JET are modelled with the 3D Monte Carlo impurity transport code ERO. The simulation covers the inner wall and the inner divertor. To generate the plasma background for Monte Carlo tracing of impurity particles, we use the EDGE2D/EIRENE code set. At the relevant regions of the wall, the estimated plasma conditions vary around T-e approximate to 5eV and n(e) 2 x 10(17) m(-3) (far-scrape-off layer; more than 10 cm away from the LCFS). We calculate impurity distributions in the plasma using the main chamber source as a free parameter in modelling and attempt to reproduce inter-ELM spectroscopic BeII line (527 nm) profiles at the divertor. The present model reproduces the level of emission close to the inner wall, but further work is needed to match also the measured emission peak values and ultimately link the modelled poloidal net deposition profiles of beryllium to post mortem data.

  • 9.
    Alaniz, Monica
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Belyayev, Serhiy
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Bergman, David
    Casselbrant, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Honeth, Mark
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Huang, Jiangwei
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Laukkanen, Mikko
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Michelsen, Jacob
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Pronenko, Vira
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Paulson, Malin
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Schlick, Georg
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Valle, Mario
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    The SQUID sounding rocket experiment2011In: Proceedings of the 20th ESA Symposium on European Rocket and Balloon Programmes and Related Research, European Space Agency, 2011, p. 159-166Conference paper (Refereed)
    Abstract [en]

    The objective of the SQUID project is to develop and in flight verify a miniature version of a wire boom deployment mechanism to be used for electric field measurements in the ionosphere. In February 2011 a small ejectable payload, built by a team of students from The Royal Institute of Technology (KTH), was launched from Esrange on-board the REXUS-10 sounding rocket. The payload separated from the rocket, deployed and retracted the wire booms, landed with a parachute and was subsequently recovered. Here the design of the experiment and post fight analysis are presented.

  • 10. Albornoz, N. L. Gonzalez
    et al.
    Schmidt-May, Angnis
    von Strauss, Mikael
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Dark matter scenarios with multiple spin-2 fields2018In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 1, article id 014Article in journal (Refereed)
    Abstract [en]

    We study ghost-free multimetric theories for (N + 1) tensor fields with a coupling to matter and maximal global symmetry group S-N x (Z(2))(N). Their mass spectra contain a massless mode, the graviton, and N massive spin-2 modes. One of the massive modes is distinct by being the heaviest, the remaining (N - 1) massive modes are simply identical copies of each other. All relevant physics can therefore be understood from the case N = 2. Focussing on this case, we compute the full perturbative action up to cubic order and derive several features that hold to all orders in perturbation theory. The lighter massive mode does not couple to matter and neither of the massive modes decay into massless gravitons. We propose the lighter massive particle as a candidate for dark matter and investigate its phenomenology in the parameter region where the matter coupling is dominated by the massless graviton. The relic density of massive spin-2 can originate from a freeze-in mechanism or from gravitational particle production, giving rise to two different dark matter scenarios. The allowed parameter regions are very different from those in scenarios with only one massive spin-2 field and more accessible to experiments.

  • 11. Alfier, A.
    et al.
    Pasqualotto, R.
    Spizzo, G.
    Canton, A.
    Fassina, A.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Electron temperature profiles in RFX-mod2008In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, no 3, p. 035013-Article in journal (Refereed)
    Abstract [en]

    Electron temperature profiles have been measured by the main Thomson scattering ( TS) diagnostic on the RFX-mod reversed field pinch experiment in Padova, Italy. The increased accuracy and spatial and temporal resolution permits one to measure in detail the improvements in T-e profiles, obtained with the active saddle coil system, which allows one to obtain core temperature 30% higher and scaling stronger with plasma current, steeper gradients in the core (+30%) and at the edge (+60%). 1D power balance calculations show that the active control of MHD modes largely reduces the values of electron heat diffusivity along the whole plasma radius, with similar to 50% reduction at the edge and similar to 30% in the core. The resulting electron energy confinement time is doubled. Further improvements occur during quasi-single helicity (QSH) states: the new TS allows one to study in detail the hot island that develops in the core. A characterization of the island electron thermal profile is presented, in terms of width, temperature increase, gradients and asymmetry; the effect on density profile is also discussed. A 2D transport code has been applied to calculate the heat diffusivity inside the magnetic island corresponding to the QSH state, also considering the correlation between temperature increase and pressure gradient with the chaos level around the island. Finally, electron energy confinement time during QSH states is compared with that in MH states.

  • 12.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Annihilation Model of the QSOs1979Report (Other academic)
  • 13.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Comment on H. Arp "The Persistent Problem of Spiral Galaxies"1987Report (Other academic)
  • 14.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Cosmogony as an Extrapolation of Magnetospheric Research1984Report (Other academic)
  • 15.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Cosmology in the Plasma Universe1987Report (Other academic)
  • 16.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Double Layers and Circuits in Astrophysics1986Report (Other academic)
  • 17.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Double radio sources and the new approach to cosmic plasma physics1977Report (Other academic)
  • 18.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Double Radio Sources and the New Approach to Cosmic Plasma Physics1977Report (Other academic)
  • 19.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Electric Current Model of Magnetosphere1979Report (Other academic)
  • 20.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Electric currents in cosmic plasmas1977Report (Other academic)
  • 21.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Magnetospheric Research and the History of the Solar System1984Report (Other academic)
  • 22.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Observations and hypotheses in cosmology1978Report (Other academic)
  • 23.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Origin of the solar system1976Report (Other academic)
  • 24.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Paradigm Transition in Cosmic Plasma Physics1982Report (Other academic)
  • 25.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Plasma Universe1986Report (Other academic)
  • 26.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Rymdforskningen och vår världsbild1982Report (Other academic)
  • 27.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Science and the future of Europe1978Report (Other academic)
  • 28.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Solar System History as Recorded in the Saturnian Ring Structure1983Report (Other academic)
  • 29.
    Alfvén, Hannes
    KTH, Superseded Departments.
    Space Research and Cosmic Plasma Physics1983Report (Other academic)
  • 30.
    Alfvén, Hannes
    et al.
    KTH, Superseded Departments.
    Arrhenius, Gustaf
    Cosmogonic Scenario1985Report (Other academic)
  • 31.
    Alfvén, Hannes
    et al.
    KTH, Superseded Departments.
    Axnäs, Ingvar
    KTH, Superseded Departments.
    Brenning, Nils
    KTH, Superseded Departments.
    Lindqvist, Per-Arne
    KTH, Superseded Departments.
    Further Explorations of Cosmogonic Shadow Effects in the Saturnian Rings1985Report (Other academic)
  • 32.
    Alfvén, Hannes
    et al.
    KTH, Superseded Departments.
    Axnäs, Ingvar
    KTH, Superseded Departments.
    Brenning, Nils
    KTH, Superseded Departments.
    Lindqvist, Per-Arne
    KTH, Superseded Departments.
    Voyager Saturnian Ring Measurements and the Early History of the Solar System1985Report (Other academic)
  • 33.
    Alfvén, Hannes
    et al.
    KTH, Superseded Departments.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments.
    Astrophysics in a Nutshell - from the Telescope to the Sputnik1988Report (Other academic)
  • 34.
    Alfvén, Hannes
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments, Alfvén Laboratory.
    Can the Big Bang Survive in the Space Age?1990Report (Other academic)
  • 35.
    Alm, Love
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cluster investigations of the extent and altitude distribution of the auroral density cavity2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The auroral density cavity constitutes the boundary between the cold, dense ionospheric plasma and the hot, tenuous plasma sheet plasma. The auroral density cavity is characterized by low electron density and particle populations modified by parallel electric fields. Inside the cavity the electron densities can be as much as a factor 100-1000 lower than same altitude outside the cavity.The Cluster mission's wide range of instruments, long lifetime and ability to make multi-spacecraft observations has been very successful. Over its 15 year lifespan, the Cluster satellites have gathered data on auroral density cavities over a large altitude range and throughout an entire solar cycle, providing a vast data material.The extent of the density cavity and acceleration region is large compared to the typical altitude coverage of a satellite crossing the cavity. This makes it difficult to produce a comprehensive altitude/density profile from a single crossing. In order to facilitate comparisons between data from different events, we introduce a new reference frame, pseudo altitude. Pseudo altitude describes the satellites' position relative to the acceleration region, as opposed to relative to the Earth. This pseudo altitude is constructed by dividing the parallel potential drop below the satellite with the total parallel potential drop. A pseudo altitude of 0 corresponds to the bottom of the acceleration region and a pseudo altitude of 1 to the top of the acceleration region. As expected, the pseudo altitude increases with altitude. The electron density exhibits an anti-correlation with the pseudo altitude, the density becomes lower close to the upper edge of the acceleration region. The upper edge of the acceleration region is located between a geocentric altitude of 4.375 and 5.625 RE. Above the upper edge of the acceleration region, the electron density continues to decrease for the entire range of the study, 3.0-6.5 RE. This is much further than the geocentric altitude range of 2-3 RE which is suggested by previous models. We can conclude that the auroral density cavity is not confined by the auroral acceleration region, as suggested by previous models, and may extend all the way to the plasma sheet.

  • 36.
    Alm, Love
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Electron density and parallel electric field distribution of the auroral density cavity2015In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 120, no 11, p. 9428-9441Article in journal (Refereed)
    Abstract [en]

    We present an event study in which Cluster satellites C1 and C3 encounters the flux tube of a stable auroral arc in the pre-midnight sector. C1 observes the mid cavity, while C3 enters the flux tube of the auroral arc at an altitude which is below the acceleration region, before crossing into the top half of the acceleration region. This allows us to study the boundary between the ionosphere and the density cavity, as well as large portion of the upper density cavity. The position of the two satellites, in relation to the acceleration region, is described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellites.The electron density exhibits an anti-correlation with the pseudo altitude, indicating that the lowest electron densities are found near the top of the density cavity. Over the entire pseudo altitude range, the electron density distribution is similar to a planar sheath, formed out of a plasma sheet dominated electron distribution, in response to the parallel electric field of the acceleration region. This indicates that the parallel electric fields on the ionosphere-cavity boundary, as well as the mid cavity parallel electric fields, are part of one unified structure rather than two discrete entities.The results highlight the strong connection between the auroral density cavity and auroral acceleration as well as the necessity of studying them in a unified fashion.

  • 37.
    Andersson, Dag
    KTH, Superseded Departments.
    Double Layer Formation in a Magnetized Mercury Plasma1978Report (Other academic)
  • 38.
    Andersson, Dag
    KTH, Superseded Departments.
    Measurements of electron energy distributions in front of and behind a stationary plasma sheath1976Report (Other academic)
  • 39.
    Andersson, Dag
    et al.
    KTH, Superseded Departments.
    Sörensen, John
    European Space Agency.
    Numerical Double Layer Solutions with Ionization1982Report (Other academic)
  • 40.
    Andersson, Hans
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, Superseded Departments, Alfvén Laboratory.
    Currrent disruptions in a magnetised plasma stream1997Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 41. Andre, M
    et al.
    Norqvist, P
    Andersson, L
    Eliasson, L
    Eriksson, A I
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Erlandson, R E
    Waldemark, J
    Ion energization mechanisms at 1700 km in the auroral region1998In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 103, no A3, p. 4199-4222Article in journal (Refereed)
    Abstract [en]

    Observations obtained by the Freja satellite at altitudes around 1700 km in the high-latitude magnetosphere are used to study ion energization perpendicular to the geomagnetic field. Investigations of ions, electrons, plasma densities, electric and magnetic wave fields, and field-aligned currents are used to study O+ heating mechanisms. Three ion heating events are studied in detail, and 20 events are used in a detailed statistical study. More than 200 events are classified as belonging to one of four major types of ion heating and are ordered as a function of magnetic local time. The most common types of ion heating are associated with broadband low-frequency electric wave fields occurring at all local times. These waves cover frequencies from below one up to several hundred hertz and correspond to the most intense O+ energization. Heating by these waves at frequencies of the order of the O+ gyrofrequency at 25 Hz seems to be the important energization mechanism, causing O+ ion mean energies up to hundreds of eV. The broadband waves are associated with Alfven waves with frequencies up to at least a few hertz and with field-aligned currents. Other types of O+ energization events are less common. During these events the ions are heated by waves near the lower hybrid frequency or near half the proton gyrofrequency. These waves are generated by auroral electrons or in a few cases by precipitating ions.

  • 42. Andriopoulou, M.
    et al.
    Nakamura, R.
    Torkar, K.
    Baumjohann, W.
    Torbert, R. B.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Khotyaintsev, Y. V.
    Dorelli, J.
    Burch, J. L.
    Russell, C. T.
    Study of the spacecraft potential under active control and plasma density estimates during the MMS commissioning phase2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 10, p. 4858-4864Article in journal (Refereed)
    Abstract [en]

    Each spacecraft of the recently launched magnetospheric multiscale MMS mission is equipped with Active Spacecraft Potential Control (ASPOC) instruments, which control the spacecraft potential in order to reduce spacecraft charging effects. ASPOC typically reduces the spacecraft potential to a few volts. On several occasions during the commissioning phase of the mission, the ASPOC instruments were operating only on one spacecraft at a time. Taking advantage of such intervals, we derive photoelectron curves and also perform reconstructions of the uncontrolled spacecraft potential for the spacecraft with active control and estimate the electron plasma density during those periods. We also establish the criteria under which our methods can be applied.

  • 43.
    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.

  • 44. André, Mats
    et al.
    Odelstad, Elias
    Graham, Daniel
    Eriksson, Anders
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Stenberg Wieser, Gabriella
    Vigren, Erik
    Norgren, Cecilia
    Johansson, Fredrik
    Henri, Pierre
    Rubin, M.
    Richter, Ingo
    Lower Hybrid Waves at Comet 67P/Churyumov-Gerasimenko2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469Article in journal (Refereed)
    Abstract [en]

    We investigate the generation of waves in the lower hybrid frequency range by density gradients in the near plasma environment of comet 67P/Churyumov–Gerasimenko. When the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. These waves can transfer energy between ions and electrons and reshape the plasma environment of the comet. We consider cometocentric distances out to a few hundred km. We find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. Overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment.

  • 45. Antoni, V
    et al.
    Cavanazza, R
    Martines, E
    Serianni, G
    Spada, E
    Spolaore, M
    Vianello, N
    Drake, James Robert
    KTH, Superseded Departments, Alfvén Laboratory.
    Bergsåker, Henric
    KTH, Superseded Departments, Alfvén Laboratory.
    Brunsell, Per R
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Regnoli, G
    Turbulent transport and plasma flow in the reversed field pinch2004In: IAEA-CN-116, 2004Conference paper (Refereed)
  • 46.
    Archer, Jenny
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Dynamics and characteristics of blackaurora as observed by high resolution ground-based imagers and radar2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 47.
    Arriaga Trejo, Israel Alejandro
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Numerical Modeling and Evaluation of the Small Magnetometer in Low-Mass Experiment (SMILE)2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Fluxgate magnetometers have played a major role in space missions due to their stability, range of operation and low energy consumption. Their principle of operation is relatively simple and easy to implement, a nonlinear magnetic material is driven into saturation by an alternating excitation current inducing a voltage that is modulated by the external field intended to be measured. With the increasing use of nanosatellites the instruments and payload on board have been reduced considerably in size and weight. The Small Magnetometer in Low-Mass Experiment, SMILE, is a miniaturised triaxial fluxgate magnetometer with volume compensation incorporating efficient signal processing algorithms within a field programmable gate array (FPGA). SMILE was designed in collaboration between the Lviv Centre of Institute of Space Research in Ukraine where the sensor was developed and the Royal Institute of Technology (KTH) in Stockholm, Sweden where the electronics used to operate the instrument were designed and programmed. The characteristic dimensions of the SMILE magnetometer and geometry of its parts make impractical the task to find an analytical expression for the voltages induced in the pick-up coils to evaluate its performance. In this report, the results of numerical simulations of the SMILE magnetometer using a commercial finite element method (FEM) based software are presented. The results obtained are compared with the experimental data available and will serve as a first step to understand the behaviour of the nonlinear components that could lead to improvements of its design in a future.

  • 48. Askinazi, L. G.
    et al.
    Khrebtov, S.
    Komarov, A. D.
    Komev, V. A.
    Krikunov, S. V.
    Krupnik, L. I.
    Lebedev, S. V.
    Rozhdestvensky, V. V.
    Tendler, Michael B.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tukachinsky, A. S.
    Vildjunas, M. I.
    Zhubr, N. A.
    GAM evolution in the H-mode discharge in the TUMAN-3M tokamak2011In: 38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts, 2011, p. 529-532Conference paper (Refereed)
  • 49. Askinazi, L. G.
    et al.
    Kornev, V. A.
    Krikunov, S. V.
    Krupnik, L. I.
    Lebedev, S. V.
    Smirnov, A. I.
    Tendler, Michael
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Tukachinsky, A. S.
    Vildjunas, M. I.
    Zhubr, N. A.
    Radial electric field evolution in various operational modes in the TUMAN-3M tokamak2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 123, p. 012010-Article in journal (Refereed)
    Abstract [en]

    Radial electric field evolution has been studied on the TUAMN-3M tokamak in different modes of operation: ohmic and NBI heating, L- and H-modes, with and without strong MHD activity. Peripheral radial electric field was measured using Langmuire probes, which were inserted up to 2cm inside LCFS, while core plasma potential evolution was measured using HIBP diagnostic. It was found, that in presence of strong MHD activity radial electric field in a vicinity of the island changed sign from negative to positive and could reach up to 4kV/m. Central plasma potential exhibited a positive perturbation of ∼700V during the MHD burst. This positive radial electric field might lead to H-mode termination, both in ohmic and NBI heating cases. Possible mechanism of the positive Er generation, namely the electron losses along ergodized magnetic field lines in the presence of MHD-island, is discussed. The same mechanism might be responsible for the positive potential spikes during a saw-tooth crash, also observed using HIBP. Another phenomenon observed using HIBP was quasi-coherent potential oscillations with the frequency close to one of the GAM. Possible location of these oscillations in the core region r/a ∼ 0.33 is discussed.

  • 50.
    Axnäs, Ingvar
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Brenning, Nils
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Experiments on the Magnetic Field and Neutral Density Limits on CIV Interaction1988Report (Other academic)
1234567 1 - 50 of 1117
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