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  • 251.
    De Angeli, M.
    et al.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Lazzaro, E.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Vignitchouk, Ladislas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Castaldo, C.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Apicella, M. L.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Gervasini, G.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Giacomi, G.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Giovannozzi, E.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Granucci, G.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Iafrati, M.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Iraji, D.
    Amirkabir Univ Technol, Energy Engn & Phys Dept, Tehran, Iran..
    Maddaluno, G.
    ENEA, CR Frascati, I-00044 Rome, Italy..
    Riva, G.
    CNR, Ist Chim Mat Condensata & Tecnol Energia, Via R Cozzi 53, I-20125 Milan, Italy..
    Uccello, A.
    CNR, Ist Sci & Tecnol Plasmi, Milan, Italy..
    Pre-plasma remobilization of ferromagnetic dust in FTU and possible interference with tokamak operations2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 10, artikel-id 106033Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental evidence of the pre-plasma remobilization of ferromagnetic dust in FTU is presented. Thomson scattering data and IR camera observations document the occurrence of intrinsic dust remobilization prior to discharge start-up and allow for a rough calculation of the average mobilized dust density. Exposures of calibrated extrinsic non-magnetic and ferromagnetic dust to sole magnetic field discharges reveal that the magnetic moment force is the main mobilizing force, as confirmed by theoretical estimates. Pre-plasma remobilization probabilities are computed for varying dust sizes. The impact of prematurely remobilized dust on the breakdown and burn-through start-up phases is investigated together with the discharge termination induced once the plasma plateau is established.

  • 252. De Angeli, M.
    et al.
    Tolias, Panagiotis
    Ratynskaia, Svetlana V.
    Ripamonti, D.
    Riva, G.
    Bardin, S.
    Morgan, T.
    De Temmerman, G.
    Remobilization of tungsten dust from castellated plasma-facing components2017Ingår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 536-540Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Studies of tungsten dust remobilization from castellated plasma-facing components can shed light to whether gaps constitute a dust accumulation site with important implications for monitoring but also removal. Castellated structures of ITER relevant geometry that contained pre-adhered tungsten dust of controlled deposition profile have been exposed in the Pilot-PSI linear device. The experiments were performed under steady state and transient plasma conditions, as well as varying magnetic field topologies. The results suggest that dust remobilization from the plasma-facing monoblock surface can enhance dust trapping in the gaps and that tungsten dust is efficiently trapped inside the gaps.

  • 253. de Angelis, Umberto
    et al.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Effects of dust particles in plasma kinetics; ion dynamics time scales2012Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, nr 7, s. 073701-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The self-consistent kinetic theory of dusty plasmas [V. N. Tsytovich and U. de Angelis, Phys. Plasmas 6, 1093 (1999)] is extended to frequency regimes relevant for ion dynamics, accounting for both constant and fluctuating plasma sources. In contrast to earlier models, binary plasma collisions are no longer neglected with respect to collisions with dust; hence, the model developed here is also valid for low dust densities. Expressions are found for the system's permittivity, the ion collision integral, and the spectral densities of ion density fluctuations. The structure of the ion kinetic equation is analyzed, and applications of the model for both astrophysical and laboratory environments are discussed.

  • 254. de la Luna, E
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lomas, P
    Maggi, C
    Brezinsek, S
    Challis, C
    Nunes, I
    Rimini, F
    Type I ELM characterization in JET with the ITER-like wall2015Ingår i: 15th International Workshop on H-mode Physics and Transport Barriers, 19-21 October 2015. Garching, Germany, 2015Konferensbidrag (Övrigt vetenskapligt)
  • 255. de la Luna, E
    et al.
    Rimini, F
    Lomas, P
    Sips, A
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Amicucci, L
    Drewelow, P
    Flanagan, J
    Nunes, I
    Saarelma, S
    Recent Results on High-Triangularity H-Mode Studies in JET-ILW2016Ingår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferensbidrag (Refereegranskat)
  • 256. De Temmerman, G.
    et al.
    Doerner, R. P.
    John, P.
    Lisgo, S.
    Litnovsky, A.
    Marot, L.
    Porro, S.
    Petersson, P.
    Rubel, Marek J.
    Rudakov, D. L.
    Van Rooij, G.
    Westerhout, J.
    Wilson, J. I. B.
    Interactions of diamond surfaces with fusion relevant plasmas2009Ingår i: Physica scripta. T, ISSN 0281-1847, Vol. T138, s. 014013-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The outstanding thermal properties of diamond and its low reactivity towards hydrogen may make it an attractive plasma-facing material for fusion and calls for a proper evaluation of its behaviour under exposure to fusion-relevant plasma conditions. Micro and nanocrystalline diamond layers, deposited on Mo and Si substrates by hot filament chemical vapour deposition (CVD), have been exposed both in tokamaks and in linear plasma devices to measure the erosion rate of diamond and study the modification of the surface properties induced by particle bombardment. Experiments in Pilot-PSI and PISCES-B have shown that the sputtering yield of diamond (both physical and chemical) was a factor of 2 lower than that of graphite. Exposure to detached plasma conditions in the DIII-D tokamak have evidenced a strong resistance of diamond against erosion under those conditions.

  • 257. De Temmerman, G.
    et al.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Coad, J. P.
    Pitts, R. A.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Mirror test for ITER: Optical characterisation of metal mirrors in divertor tokamaks2005Ingår i: 32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets: Europhysics Conference Abstracts, 2005, s. 586-589Konferensbidrag (Refereegranskat)
  • 258. Deca, Jan
    et al.
    Divin, Andrey
    Wang, Xu
    Lembege, Bertrand
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST). KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Horanyi, Mihaly
    Lapenta, Giovanni
    Three-dimensional full-kinetic simulation of the solar wind interaction with a vertical dipolar lunarmagnetic anomaly2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 9, s. 4136-4144Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A detailed understanding of the solar wind interaction with lunar magnetic anomalies (LMAs) is essential to identify its implications for lunar exploration and to enhance our physical understanding of the particle dynamics in a magnetized plasma. We present the first three-dimensional full-kinetic electromagnetic simulation case study of the solar wind interaction with a vertical dipole, resembling a medium-size LMA. In contrast to a horizontal dipole, we show that a vertical dipole twists its field lines and cannot form a minimagnetosphere. Instead, it creates a ring-shaped weathering pattern and reflects up to 21% (four times more as compared to the horizontal case) of the incoming solar wind ions electrostatically through the normal electric field formed above the electron shielding region surrounding the cusp. This work delivers a vital piece to fully comprehend and interpret lunar observations, as we find the amount of reflected ions to be a tracer for the underlying field structure.

  • 259. Dejarnac, R.
    et al.
    Podolnik, A.
    Komm, M.
    Arnoux, G.
    Coenen, J. W.
    Devaux, S.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gunn, J. P.
    Matthews, G. F.
    Pitts, R. A.
    Numerical evaluation of heat flux and surface temperature on a misaligned JET divertor W lamella during ELMs2014Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 12, s. 123011-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of experiments has been performed on JET to investigate the dynamics of transient melting due to edge localized modes (ELMs). The experiment employs a deliberately misaligned lamella in one module of the JET bulk tungsten outer divertor, allowing the combination of stationary power flux and ELMs to transiently melt the misaligned edge. During the design of the experiment a number of calculations were performed using 2D particle-in-cell simulations and a heat transfer code to investigate the influence on the deposited power flux of finite Larmor radius effects associated with the energetic ELM ions. This has been performed using parameter scans inside a range of pedestal temperatures and densities to scope different experimentally expected ELM energies. On the one hand, we observe optimistic results, with smoothing of the heat flux due to the Larmor gyration on the protruding side of the lamella which sees the direct parallel flux-the deposited power tends to be lower than the nominal value expected from geometric magnetic field line impact over a distance smaller than 2 Larmor radii, a finding which is always valid during ELMs for such a geometry. On the other hand, the fraction of the flux not reaching the directly wetted side is transferred and spread to the top surface of the lamella. The hottest point of the lamella (corner side/top) does not always benefit from the gain from the Larmor smoothing effect because of an enhanced power deposition from the second contribution.

  • 260.
    Del Ferraro, Gino
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Aurell, Erik
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. Aalto University, Finland.
    Dynamic message-passing approach for kinetic spin models with reversible dynamics2015Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 92, nr 1, artikel-id 010102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method to approximately close the dynamic cavity equations for synchronous reversible dynamics on a locally treelike topology is presented. The method builds on (a) a graph expansion to eliminate loops from the normalizations of each step in the dynamics and (b) an assumption that a set of auxilary probability distributions on histories of pairs of spins mainly have dependencies that are local in time. The closure is then effectuated by projecting these probability distributions on n-step Markov processes. The method is shown in detail on the level of ordinary Markov processes (n = 1) and outlined for higher-order approximations (n > 1). Numerical validations of the technique are provided for the reconstruction of the transient and equilibrium dynamics of the kinetic Ising model on a random graph with arbitrary connectivity symmetry.

  • 261.
    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, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    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 Data2018Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 3, s. 2274-2295Artikel i tidskrift (Refereegranskat)
    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.

  • 262. Di Siena, A.
    et al.
    Görler, T.
    Doerk, H.
    Bilato, R.
    Citrin, J.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Schneider, M.
    Poli, E.
    Impact of realistic fast ion distribution function in gyrokinetic GENE simulations2017Ingår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Understanding the stabilising mechanism of fast particles on plasma turbulence is an essential task for a fusion reactor, where the energetic particles can constitute a significant fraction of the main ions. While the consideration of equivalent Maxwellian distributed fast ions in the simulations has greatly improved the agreement with experiments, fast ion electromagnetic stabilization seems to be somewhat over-estimated. Power balance is usually reached only with increased plasma gradients. However, it is well known that to rigorously model highly non thermalised particles, a non-Maxwellian background distribution function is needed. To this aim, a previous study on a particular JET plasma has been revised and analysed with the gyrokinetic code GENE. Fast particles have been modelled with a number of different analytic and numerical distributions. The latter have been imported from the modelling tools NEMO/SPOT and SELFO. 

  • 263. Dieckmann, M. E.
    et al.
    Folini, D.
    Walder, R.
    Romagnani, L.
    d'Humieres, E.
    Bret, A.
    Karlsson, T.
    Ynnerman, A.
    Emergence of MHD structures in a collisionless PIC simulation plasma2017Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, nr 9, artikel-id 094502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The expansion of a dense plasma into a dilute plasma across an initially uniform perpendicular magnetic field is followed with a one-dimensional particle-in-cell simulation over magnetohydrodynamics time scales. The dense plasma expands in the form of a fast rarefaction wave. The accelerated dilute plasma becomes separated from the dense plasma by a tangential discontinuity at its back. A fast magnetosonic shock with the Mach number 1.5 forms at its front. Our simulation demonstrates how wave dispersion widens the shock transition layer into a train of nonlinear fast magnetosonic waves.

  • 264. Divin, A.
    et al.
    Semenov, V.
    Korovinskiy, D.
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC. KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Deca, J.
    Olshevsky, V.
    Lapenta, G.
    A new model for the electron pressure nongyrotropy in the outer electron diffusion region2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 20, s. 10565-10573Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a new model to describe the electron pressure nongyrotropy inside the electron diffusion region (EDR) in an antiparallel magnetic reconnection scenario. A combination of particle-in-cell simulations and analytical estimates is used to identify such a component of the electron pressure tensor in the rotated coordinates, which is nearly invariant along the outflow direction between the X line and the electron remagnetization points in the outer EDR. It is shown that the EDR two-scale structure (inner and outer parts) is formed due to superposition of the nongyrotropic meandering electron population and gyrotropic electron population with large anisotropy parallel to the magnetic field upstream of the EDR. Inside the inner EDR the influence of the pressure anisotropy can largely be ignored. In the outer EDR, a thin electron layer with electron flow speed exceeding the E x B drift velocity is supported by large-momentum flux produced by the electron pressure anisotropy upstream of the EDR. We find that this fast electron exhaust flow with |V(e)xB|>|E| is in fact a constituent part of the EDR, a finding which will steer the interpretation of the Magnetospheric Multiscale Mission (MMS) data.

  • 265.
    Doddapaneni, Venkatesh
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Gati, Rudolf
    ABB Switzerland.
    Toprak, Muhammet S.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Funktionella material, FNM.
    Engineered PMMA-CuO nanocomposites for improving the electric arc interruption process in electrical switching applicationsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Polymer-based nanocomposites (PNCs) display fascinating functionalities to be useful in electrical switching applications like circuit breakers, switch gears, etc. These PNCs are fabricated by incorporating nanoparticles (NPs) into a polymer by in-situ polymerization. When the PNCs interrupt the high energetic fault currents generate between the two contacts in a circuit breaker, they outgas (ablation) chemical species and cooling gases, which change the thermodynamic properties of the arcing environment leading to quench the electrical arcs quickly. Two PNCs are fabricated with different wt% of oleic acid modified CuO NPs and a polymer matrix i.e. poly methyl methacrylate (PMMA). These PNCs are tested with the electrical arcs of a prospective current of 1.6 kA generated in the test-setup. The electrical signals (arc current and voltage) and computed dissipated enegy i.e., ∫𝑖(𝑡)𝑉(𝑡)𝑑𝑡 help to understand the effect of PNCs on the electrical arcs. In addition to that, the computed joule integral and mass loss of the PNCs due to outgassing is reported. The re-depositions of the chemical species are analyzed by using Fourier transform infrared spectroscopy (FTIR) and the morphological changes on the surface of outgassed PNCs are analyzed by using scanning electron microscopy (SEM). These results help to understand the effect of PNCs on the arc interruption process in circuit breakers.

  • 266.
    Drake, J R
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Brunsell, P R
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Brzozowski, J H
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Cecconello, M
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Gravestijn, R M
    KTH, Tidigare Institutioner, Fysik.
    Malmberg, J-A
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Sallander, E
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    First results from the EXTRAP T2R RFP experiment2001Ingår i: Europhysics Conf. Abstracts Vol 25A, 2001, s. 457-460Konferensbidrag (Refereegranskat)
  • 267.
    Drake, James Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bolzonella, T.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Baruzzo, T. M.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Guo, S. C.
    Igochine, V.
    Liu, Y. Q.
    Marchiori, G.
    Paccagnella, R.
    Rubinacci, G.
    Soppelsa, A.
    Villone, F.
    Yadikin, D.
    Martin, P.
    Zohm, H.
    Reversed-Field Pinch Contributions to Resistive Wall Mode Physics and Control2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Optimal feedback control of resistive-wall modes (RWM) is of common interest for toroidal fusionconcepts that use conducting walls for stabilization of ideal MHD modes. From the RWM control point of view,the RFP situation is in many respects similar to the advanced tokamak situation in the presence of very lowplasma rotation, where the most effective stabilizing mechanism is the feedback action of a set of active coils.Results from EXTRAP T2R (Sweden) and RFX-mod (Italy) RFP experiments have shown that full feedbackcontrol of multiple RWMs is possible and their deleterious effects can be completely suppressed. However it isnow important to optimize the RWM control systems both for the RFP and tokamak configuration for futureimplementation. Important aspects of optimization are effective mode identification and tracking capability,avoidance of the harmful effects of sideband modes (aliasing) in the control spectrum, minimized powerrequirements and robust controller stability. The paper describes collaborative work carried out on the two RFPexperiments. Controller models based on the mode harmonic control concept and on a state-space multipleinputmultiple-output intelligent shell concept are studied. Progress in development of optimal control schemesare presented both through experimental studies and simulations.

  • 268.
    Drake, James Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Yadikin, Dmitriy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hedqvist, Anders
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Menmuir, Sheena
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Experiments on feedback control of multiple resistive wall modes comparing different active coil arrays and sensor types2006Ingår i: IAEA-F1-CN-149, 2006, s. Paper EX/P8-11-Konferensbidrag (Refereegranskat)
  • 269.
    Drake, James Robert
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Brunsell, Per R
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Yadikin, Dmitriy
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Cecconello, Marco
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, Jenny-A.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Gregoratto, D
    Paccagnella, R
    Bolzonella, T
    Manduchi, G
    Marrelli, L
    Ortolani, S
    Spizzo, G
    Zanca, P
    Bondeson, A
    Liu, Y Q
    Experimental and theoretical studies of active control of resistive wall mode growth in the EXTRAP T2R reversed-field pinch2004Ingår i: IAEA-CN-116, 2004, s. Paper EX/P2-20-Konferensbidrag (Refereegranskat)
  • 270.
    Duguet, Yohann
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Larsson, B. Robin J.
    Towards minimal perturbations in transitional plane Couette flow2010Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 82, nr 2, s. 026316-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For parallel shear flows, transition to turbulence occurs only for perturbations of sufficiently large amplitude. It is therefore relevant to study the shape, amplitude, and dynamics of the least energetic initial disturbances leading to transition. We suggest a numerical approach to find such minimal perturbations, applied here to the case of plane Couette flow. The optimization method seeks such perturbations at initial time as a linear combination of a finite number of linear optimal modes. The energy threshold of the minimal perturbation for a Reynolds number Re=400 is only 2% less than for a pair of symmetric oblique waves. The associated transition scenario shows a long transient approach to a steady state solution with special symmetries. Modal analysis shows how the oblique-wave mechanism can be optimized by the addition of other oblique modes breaking the flow symmetry and whose nonlinear interaction generates spectral components of the edge state. The Re dependence of energy thresholds is revisited, with evidence for a O(Re(-2))-scaling for both oblique waves and streamwise vortices scenarios.

  • 271.
    Dumont, R. J.
    et al.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Mailloux, J.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Aslanyan, V
    MIT, PSFC, 175 Albany St, Cambridge, MA 02039 USA..
    Baruzzo, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Challis, C. D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Coffey, I
    Queens Univ, Dept Pure & Appl Phys, Belfast BT7 1NN, Antrim, North Ireland..
    Czarnecka, A.
    Inst Plasma Phys & Laser Microfus, Hery St 23, PL-00908 Warsaw, Poland..
    Delabie, E.
    Oak Ridge Natl Lab, Oak Ridge, TN USA..
    Eriksson, J.
    Uppsala Univ, Dept Phys & Astron, SE-75119 Uppsala, Sweden..
    Faustin, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Ferreira, J.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Fitzgerald, M.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Garcia, J.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Giacomelli, L.
    Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Giroud, C.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Hawkes, N.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Jacquet, Ph
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Joffrin, E.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Keeling, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    King, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Kiptily, V
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Lomanowski, B.
    Aalto Univ, POB 14100, FIN-00076 Aalto, Finland..
    Lerche, E.
    Ass EUROFUS Belgian State, LPP ERM KMS, TEC Partner, Brussels, Belgium..
    Mantsinen, M.
    Barcelona Supercomp Ctr, Barcelona, Spain.;ICREA, Barcelona, Spain..
    Meneses, L.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Menmuir, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    McClements, K.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Moradi, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Nabais, F.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Nocente, M.
    Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Patel, A.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Patten, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Puglia, P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Scannell, R.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Sharapov, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Solano, E. R.
    CIEMAT, Lab Nacl Fus, Madrid, Spain..
    Tsalas, M.
    FOM Inst DIFFER, NL-3430 BE Nieuwegein, Netherlands.;ITER Org, Route Vinon Sur Verdon, F-13067 St Paul Les Durance, France..
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Weisen, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Scenario development for the observation of alpha-driven instabilities in JET DT plasmas2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 8, artikel-id 082005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In DT plasmas, toroidal Alfven eigenmodes (TAEs) can be made unstable by the alpha particles resulting from fusion reactions, and may induce a significant redistribution of fast ions. Recent experiments have been conducted in JET deuterium plasmas in order to prepare scenarios aimed at observing alpha-driven TAEs in a future JET DT campaign. Discharges at low density, large core temperatures associated with the presence of internal transport barriers and characterised by good energetic ion confinement have been performed. ICRH has been used in the hydrogen minority heating regime to probe the TAE stability. The consequent presence of MeV ions has resulted in the observation of TAEs in many instances. The impact of several key parameters on TAE stability could therefore be studied experimentally. Modeling taking into account NBI and ICRH fast ions shows good agreement with the measured neutron rates, and has allowed predictions for DT plasmas to be performed.

  • 272. Dunne, M
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Poetzel, S
    Reimold, F
    Wischmeier, M
    Wolfrum, E
    Bernerdt, M
    The Role of the Density Profile Location on Pedestal Stability in ASDEX-Upgrade2016Ingår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferensbidrag (Refereegranskat)
  • 273. Dunne, M. G.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Beurskens, M. N. A.
    Cavedon, M.
    Fietz, S.
    Fischer, R.
    Giannone, L.
    Huijsmans, G. T. A.
    Kurzan, B.
    Laggner, F.
    McCarthy, P. J.
    McDermott, R. M.
    Tardini, G.
    Viezzer, E.
    Willensdorfer, M.
    Wolfrum, E.
    Global performance enhancements via pedestal optimisation on ASDEX Upgrade2017Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 2, artikel-id 025010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Results of experimental scans of heating power, plasma shape, and nitrogen content are presented, with a focus on global performance and pedestal alteration. In detailed scans at low triangularity, it is shown that the increase in stored energy due to nitrogen seeding stems from the pedestal. It is also shown that the confinement increase is driven through the temperature pedestal at the three heating power levels studied. In a triangularity scan, an orthogonal effect of shaping and seeding is observed, where increased plasma triangularity increases the pedestal density, while impurity seeding (carbon and nitrogen) increases the pedestal temperature in addition to this effect. Modelling of these effects was also undertaken, with interpretive and predictive models being employed. The interpretive analysis shows a general agreement of the experimental pedestals in separate power, shaping, and seeding scans with peeling-ballooning theory. Predictive analysis was used to isolate the individual effects, showing that the trends of additional heating power and increased triangularity can be recoverd. However, a simple change of the effective charge in the plasma cannot explain the observed levels of confinement improvement in the present models.

  • 274. Dunne, M. G.
    et al.
    Potzel, S.
    Reimold, F.
    Wischmeier, M.
    Wolfrum, E.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Beurskens, M.
    Bilkova, P.
    Cavedon, M.
    Fischer, R.
    Kurzan, B.
    Laggner, F. M.
    McDermott, R. M.
    Tardini, G.
    Trier, E.
    Viezzer, E.
    Willensdorfer, M.
    The role of the density profile in the ASDEX-Upgrade pedestal structure2017Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 1, artikel-id 014017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental evidence for the impact of a region of high density localised in the high-field side scrape-off layer (the HFSHD) on plasma confinement is shown in various dedicated experiments on ASDEX Upgrade (AUG). Increasing main ion fuelling is shown to increase the separatrix density and shift the density profile outwards. Predictive pedestal modelling of this shift indicates a 25% decrease in the attainable pedestal top pressure, which compares well with experimental observations in the gas scan. Since the HFSHD can be mitigated by applying nitrogen seeding, a combined scan in fuelling rate, heating power, and nitrogen seeding is presented. Significant increases in the achievable pedestal top pressure are observed with seeding, in particular at high heating powers, and are correlated with inward shifted density profiles and a reduction of the HFSHD and separatrix density. Interpretive linear stability analysis also confirms the impact of a radially shifted pressure profile on peeling-ballooning stability, with an inward shift allowing access to higher pressure gradients and pedestal widths.

  • 275. Dunne, M
    et al.
    Poetzel, S
    Wischmeier, M
    Wolfrum, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Reimold, F
    Predictive  modelling  of  the  impact  of  a  radiative  divertor  on pedestal  con nement  on  ASDEX  Upgrade2015Ingår i: 57rd Meeting of the APS Division of Plasma Physics, November 2015, Savannah, USA, 2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In future devices, tailoring of the edge density profile and radiation profile for power exhaust control via a deuterium gas puff and extrinsic impurity seeding will be necessary. It has been observed on present day machines that high D fuelling can reduce the plasma stored energy while adding impurity seeding can act to improve confinement by up to 40{\%}. This study presents a combination of observations and modelling completed on AUG with the aim of determining the mechanisms behind the confinement degradation with a gas puff and improvement with impurity seeding. In particular, predictive modelling, based on the EPED pedestal model, has been extensively used. Alterations of the temperature and density at the separatrix are found to have large impacts on pedestal stability. Measured changes in divertor properties are used to inform the direction and magnitude of these alterations, with experimentally relevant confinement changes being recovered via pressure profile shifts.

  • 276. Dunne, M
    et al.
    Potzel, S
    Remold, F
    Viezzer, E
    Wischmeier, M
    Wolfrum, E
    Bernerdt, M
    Beurskens, M
    Cavedon, M
    Fischer, R
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kurzan, B
    The role of the density profile in the ASDEX-Upgrade pedestal structure2016Ingår i: 43th European Physical Society (EPS) Conference on Plasma Physics. July 4 – July 8, 2016, 2016Konferensbidrag (Refereegranskat)
  • 277. Dzanko, Matija
    et al.
    Mikac, Branko
    Furdek, Marija
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Dedicated path protection for optical networks based on function programmable nodes2018Ingår i: Optical Switching and Networkning Journal, ISSN 1573-4277, E-ISSN 1872-9770, Vol. 27, s. 79-87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to the constantly increasing volumes and tightening reliability requirements of network traffic, survivability is one of the key concerns in optical network design. Optical "white box" nodes based on the Architecture on Demand (AoD) paradigm allow for self-healing of nodal component failures due to their architectural flexibility and the ability to employ idle components for failure recovery. By incorporating node-level survivability with network-level protection from link failures, resiliency of optical networks can be significantly improved. To this end, we propose a survivable routing algorithm for AoD-based networks called Dedicated Path Protection with Enforced Fiber Switching (DPP-EFS), which combines self-healing at the node level with dedicated path protection at the network level. The algorithm aims at improving the self-healing capabilities of the nodes by increasing the percentage of fiber switching (FS). Namely, fiber-switched lightpaths require a minimal amount of processing within the node (i.e. only signal switching), while other aspects of processing (e.g. demultiplexing, bandwidth virtualization) and the related components (i.e. demultiplexers, splitters, wavelength selective switches) remain unused and may be used as redundancy. On the other hand, lightpaths that are not eligible for FS have to be re-routed to alternative, longer paths in order to allow for FS between certain ports within the node. Therefore, the proposed algorithm pursues an advantageous trade-off between the increase of the number of idle components which can be used as redundancy at the node level and the unwanted length increase of lightpaths re-routed to render components redundant. For particular cases when DPP-EFS is not able to reduce the mean down time (MDT) in the network merely by increasing the percentage of fiber switching, we propose an algorithm for Dedicated Path Protection with Fixed Shortest Path routing and added Redundancy (DPP-FSP-RED) which adds additional spare components at strategic nodes to ensure that all connections have at least one redundant node component along their path. Simulation results show a significant reduction in MDT with minimal extra capital expenses.

  • 278. Eastwood, J. P.
    et al.
    Phan, T. D.
    Cassak, P. A.
    Gershman, D. J.
    Haggerty, C.
    Malakit, K.
    Shay, M. A.
    Mistry, R.
    Oieroset, M.
    Russell, C. T.
    Slavin, J. A.
    Argall, M. R.
    Avanov, L. A.
    Burch, J. L.
    Chen, L. J.
    Dorelli, J. C.
    Ergun, R. E.
    Giles, B. L.
    Khotyaintsev, Y.
    Lavraud, B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Moore, T. E.
    Nakamura, R.
    Paterson, W.
    Pollock, C.
    Strangeway, R. J.
    Torbert, R. B.
    Wang, S.
    Ion-scale secondary flux ropes generated by magnetopause reconnection as resolved by MMS2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 4716-4724Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New Magnetospheric Multiscale (MMS) observations of small-scale (similar to 7 ion inertial length radius) flux transfer events (FTEs) at the dayside magnetopause are reported. The 10 km MMS tetrahedron size enables their structure and properties to be calculated using a variety of multispacecraft techniques, allowing them to be identified as flux ropes, whose flux content is small (similar to 22 kWb). The current density, calculated using plasma and magnetic field measurements independently, is found to be filamentary. Intercomparison of the plasma moments with electric and magnetic field measurements reveals structured non-frozen-in ion behavior. The data are further compared with a particle-in-cell simulation. It is concluded that these small-scale flux ropes, which are not seen to be growing, represent a distinct class of FTE which is generated on the magnetopause by secondary reconnection.

  • 279.
    Edberg, Terry
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Evaluation and optimization of the SMILE fluxgate magnetometer2007Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The report shows the development during the last six months of the SMILE fluxgate magnetometer from a basic platform into a first generation magnetometer. The purpose of the SMILE project is to develop a miniaturized digital fluxgate magnetometer for the Nanospace project. The Nanospace project is collaboration by KTH and IRF Uppsala with the goal to develop a nano satellite platform.

    The FPGA programming has been improved to include a functional correlation loop, 13 bit DACs and a parallel and a serial interface with several output modes. The timing of the processes in the FPGA has been improved making it more robust. Some critical changes to the analogue parts has also been made.

    The LEMI sensors have been tested in a number of ways to increase the understanding of their characteristics. The magnetometer has also been calibrated at the Nurmijärvi geophysical observatory in Finland.

  • 280.
    Elfsberg, Mattias
    et al.
    FOI.
    Hurtig, Tomas
    FOI.
    Möller, Cecilia
    FOI.
    Nyholm, Sten E.
    FOI.
    Experimental studies on a coaxial vircator, designed for operation in TE11 mode2011Ingår i: Proc. of Pulse Power Conference (PPC 2011), 2011, Vol. 38, nr 1, s. 811-814Konferensbidrag (Refereegranskat)
    Abstract [en]

    Experiments on a coaxial vircator have been performed. A vircator is a narrow band high power microwave source without any external generated magnetic field [1]. A coaxial vircator is an advantageous design of a microwave radiation source for a compact HPM-system. With a limited size and outer diameter it is possible to use a larger emitting area compared to an axial design. A conventional coaxial vircator will generate the radiation in TM01 mode, due to its geometrical properties. For a compact HPM-system, radiation in TE11 mode is preferred when the radiated energy needs to be focused on a specific target. For operation in TE11 mode a sectioned emitter can be used rather than a circumcircular. The efficiency of the vircator can be greatly improved by optimizing the geometry of the vircator housing. The impedance of the pulsed power supply driving the vircator and the impedance of the vircator, depending on the A-K gap and amount of emitting material, is also important for maximizing the vircator efficiency. For the experiments reported on, the vircator was driven by a 500 kV/500 J compact Marx generator that can be operated repetitively at 10 Hz. For these experiments, the Marx generator was operating in single shot mode. During the experiments presented here, a couple of geometrical features were varied as well as the applied voltage. Their influence on the radiated field strength, dominating frequency and bandwidth are reported on and discussed.

  • 281.
    Elfsberg, Mattias
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Möller, Cecilia
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Hurtig, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Larsson, Anders
    Swedish Defence Research Agency (FOI) Defence & Security, Systems and Technology, Grindsjön Research Centre, Tumba, Sweden.
    Nyholm, Sten
    Swedish Defence Research Agency (FOI) Defence & Security, Systems and Technology, Grindsjön Research Centre, Tumba, Sweden.
    Experimental Studies of Anode and Cathode Materials in a Repetitive Driven Axial Vircator2008Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 36, s. 688-693Artikel i tidskrift (Refereegranskat)
    Abstract [en]

     Repetitive use of a high-power microwave (HPM) radiation source implies strong erosion on cathode and anode materials. Electrode material endurance has been studied in a series of experiments with an axial vircator powered by a compact Marx generator. The Marx generator operated in a 10 Hz repetitive mode with a burst of ten pulses. Velvet and graphite was used as electron-emitting materials, and they showed markedly different pulse characteristics. Three different anode materials were used; stainless steel mesh, stainless steel wires and molybdenum wires, which all had different influence on the pulse characteristics.

  • 282.
    Emmoth, Birger
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Kreter, A.
    Hallén, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Jakubowski, M.
    Lehnen, M.
    Litnovsky, A.
    Petersson, P.
    Philipps, V.
    Possnert, G.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Schweer, B.
    Sundelin, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Unterberg, B.
    Wienhold, P.
    In-situ measurements of carbon and deuterium deposition using the fast reciprocating probe in TEXTOR2009Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 390-91, s. 179-182Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Silicon samples were exposed in the scrape-off layer of the TEXTOR plasma using a fast reciprocating probe, with the aim of studying carbon deposition and deuterium retention during Dynamic Ergodic Divertor (DED) operation. Separate samples were exposed for 300 ms at the flat-top phase of neutral beam heated discharges. The exposure conditions were varied on a shot-to-shot basis by external magnetic perturbations generated by the DED in the m/n = 3/1, DC regime, base configuration. Nuclear Reaction Analysis (NRA) was used to characterise collector sample surfaces after their exposure. Enhanced concentrations of both carbon and deuterium (C 3-10 x 10(16) at./cm(2), D 8-60 x 10(15) at./cm(2)) were found. The D/C ratio was less than unity which indicates that most of the carbon and deuterium were co-deposited. Carbon e-folding lengths of about 2 cm were found on both toroidal sides of the probe independent of DED perturbations.

  • 283. Ergun, R. E.
    et al.
    Tucker, S.
    Westfall, J.
    Goodrich, K. A.
    Malaspina, D. M.
    Summers, D.
    Wallace, J.
    Karlsson, M.
    Mack, J.
    Brennan, N.
    Pyke, B.
    Withnell, P.
    Torbert, R.
    Macri, J.
    Rau, D.
    Dors, I.
    Needell, J.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olsson, Göran F.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Cully, C. M.
    The Axial Double Probe and Fields Signal Processing for the MMS Mission2016Ingår i: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 199, nr 1-4, s. 167-188Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The Axial Double Probe (ADP) instrument measures the DC to similar to 100 kHz electric field along the spin axis of the Magnetospheric Multiscale (MMS) spacecraft (Burch et al., Space Sci. Rev., 2014, this issue), completing the vector electric field when combined with the spin plane double probes (SDP) (Torbert et al., Space Sci. Rev., 2014, this issue, Lindqvist et al., Space Sci. Rev., 2014, this issue). Two cylindrical sensors are separated by over 30 m tip-to-tip, the longest baseline on an axial DC electric field ever attempted in space. The ADP on each of the spacecraft consists of two identical, 12.67 m graphite coilable booms with second, smaller 2.25 m booms mounted on their ends. A significant effort was carried out to assure that the potential field of the MMS spacecraft acts equally on the two sensors and that photo- and secondary electron currents do not vary over the spacecraft spin. The ADP on MMS is expected to measure DC electric field with a precision of similar to 1 mV/m, a resolution of similar to 25 mu V/m, and a range of similar to 1 V/m in most of the plasma environments MMS will encounter. The Digital Signal Processing (DSP) units on the MMS spacecraft are designed to perform analog conditioning, analog-to-digital (A/D) conversion, and digital processing on the ADP, SDP, and search coil magnetometer (SCM) (Le Contel et al., Space Sci. Rev., 2014, this issue) signals. The DSP units include digital filters, spectral processing, a high-speed burst memory, a solitary structure detector, and data compression. The DSP uses precision analog processing with, in most cases, > 100 dB in dynamic range, better that -80 dB common mode rejection in electric field (E) signal processing, and better that -80 dB cross talk between the E and SCM (B) signals. The A/D conversion is at 16 bits with similar to 1/4 LSB accuracy and similar to 1 LSB noise. The digital signal processing is powerful and highly flexible allowing for maximum scientific return under a limited telemetry volume. The ADP and DSP are described in this article.

  • 284.
    Ericsson, Anders
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    On the properties of magnetic pulsations in the solar wind2005Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 285. Eriksson, A. I.
    et al.
    Engelhardt, I. A. D.
    Andre, M.
    Bostrom, R.
    Edberg, N. J. T.
    Johansson, F. L.
    Odelstad, E.
    Vigren, E.
    Wahlund, J. -E
    Henri, P.
    Lebreton, J. -P
    Miloch, W. J.
    Paulsson, J. J. P.
    Wedlund, C. Simon
    Yang, L.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Jarvinen, R.
    Broiles, T.
    Mandt, K.
    Carr, C. M.
    Galand, M.
    Nilsson, H.
    Norberg, C.
    Cold and warm electrons at comet 67P/Churyumov-Gerasimenko2017Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, artikel-id A15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce. Aims. Our aim is to demonstrate the existence of cold electrons in the inner coma of comet 67P/Churyumov-Gerasimenko and show filamentation of this plasma. Methods. In situ measurements of plasma density, electron temperature and spacecraft potential were carried out by the Rosetta Langmuir probe instrument, LAP. We also performed analytical modelling of the expanding two-temperature electron gas. Results. LAP data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5-10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order -10 V. Conclusions. The warm (5-10 eV) electron population observed throughout the mission is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming filaments that we observe as pulses.

  • 286.
    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, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Electron Energization at a Reconnecting Magnetosheath Current Sheet2018Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 16, s. 8081-8090Artikel i tidskrift (Refereegranskat)
    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.

  • 287.
    Eriksson, Elin
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Graham, Daniel. B.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Yordanova, Emiliya
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Hietala, H.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA USA..
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Avanov, L. A.
    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.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lavraud, B.
    CNRS, IRAP, Toulouse, France..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Saito, Y.
    JAXA, Chofu, Tokyo, Japan..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C.
    Torbert, R.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Ergun, R.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Strong current sheet at a magnetosheath jet: Kinetic structure and electron acceleration2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 10, s. 9608-9618Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Localized kinetic-scale regions of strong current are believed to play an important role in plasma thermalization and particle acceleration in turbulent plasmas. We present a detailed study of a strong localized current, 4900 nA m(-2), located at a fast plasma jet observed in the magnetosheath downstream of a quasi-parallel shock. The thickness of the current region is similar to 3 ion inertial lengths and forms at a boundary separating magnetosheath-like and solar wind-like plasmas. On ion scales the current region has the shape of a sheet with a significant average normal magnetic field component but shows strong variations on smaller scales. The dynamic pressure within the magnetosheath jet is over 3 times the solar wind dynamic pressure. We suggest that the current sheet is forming due to high velocity shears associated with the jet. Inside the current sheet we observe local electron acceleration, producing electron beams, along the magnetic field. However, there is no clear sign of ongoing reconnection. At higher energies, above the beam energy, we observe a loss cone consistent with part of the hot magnetosheath-like electrons escaping into the colder solar wind-like plasma. This suggests that the acceleration process within the current sheet is similar to the one that occurs at shocks, where electron beams and loss cones are also observed. Therefore, electron beams observed in the magnetosheath do not have to originate from the bow shock but can also be generated locally inside the magnetosheath.

  • 288.
    Eriksson, Elin
    et al.
    Uppsala universitet, Institutionen för fysik och astronomi.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri. V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyayintsev, V. M.
    Taras Shevchenko Natl Univ Kyiv, Dept Theoret Phys, Kiev, Ukraine..
    Andre, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Statistics and accuracy of magnetic null identification in multispacecraft data2015Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, s. 6883-6889Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Complex magnetic topologies are ubiquitous in astrophysical plasmas. Analyzing magnetic nulls, regions of vanishing magnetic field, is one way to characterize 3-D magnetic topologies. Magnetic nulls are believed to be important in 3-D reconnection and turbulence. In the vicinity of a null, plasma particles become unmagnetized and can be accelerated to high energies by electric fields. We present the first statistical study of the occurrence of magnetic nulls and their types in the Earth's nightside magnetosphere. We are able to identify the nulls both in the tail and in the magnetopause current sheets. On average, we find one null for every few current sheet crossings. We show that the type identification of magnetic nulls may be sensitive to local fluctuations in the magnetic field. We develop and demonstrate a method to estimate the reliability of the magnetic null type identification.

  • 289. Eriksson, J.
    et al.
    Nocente, M.
    Binda, F.
    Cazzaniga, C.
    Conroy, S.
    Ericsson, G.
    Giacomelli, L.
    Gorini, G.
    Hellesen, C.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hjalmarsson, A.
    Jacobsen, A. S.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kiptily, V.
    Koskela, T.
    Mantsinen, M.
    Salewski, M.
    Schneider, M.
    Sharapov, S.
    Skiba, M.
    Tardocchi, M.
    Weiszflog, M.
    Dual sightline measurements of MeV range deuterons with neutron and gamma-ray spectroscopy at JET2015Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 12, artikel-id 123026Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observations made in a JET experiment aimed at accelerating deuterons to the MeV range by third harmonic radio-frequency (RF) heating coupled into a deuterium beam are reported. Measurements are based on a set of advanced neutron and gamma-ray spectrometers that, for the first time, observe the plasma simultaneously along vertical and oblique lines of sight. Parameters of the fast ion energy distribution, such as the high energy cut-off of the deuteron distribution function and the RF coupling constant, are determined from data within a uniform analysis framework for neutron and gamma-ray spectroscopy based on a one-dimensional model and by a consistency check among the individual measurement techniques. A systematic difference is seen between the two lines of sight and is interpreted to originate from the sensitivity of the oblique detectors to the pitch-angle structure of the distribution around the resonance, which is not correctly portrayed within the adopted one dimensional model. A framework to calculate neutron and gamma-ray emission from a spatially resolved, two-dimensional deuteron distribution specified by energy/pitch is thus developed and used for a first comparison with predictions from ab initio models of RF heating at multiple harmonics. The results presented in this paper are of relevance for the development of advanced diagnostic techniques for MeV range ions in high performance fusion plasmas, with applications to the experimental validation of RF heating codes and, more generally, to studies of the energy distribution of ions in the MeV range in high performance deuterium and deuterium-tritium plasmas.

  • 290. Eriksson, L. -G
    et al.
    Hellsten, Torbjörn A K
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Holmström, Kerstin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas Joe
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brzozowski, Jerzy H.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Nave, F.
    Ongena, J.
    Zastrow, K. -D
    Simulation of fast ion contribution to toroidal rotation in ICRF heated jet plasmas2008Ingår i: EPS Conf. Plasma Phys., EPS - Europhys. Conf. Abstr., 2008, nr 3, s. 1679-1682Konferensbidrag (Refereegranskat)
  • 291. Eriksson, L. -G
    et al.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Nave, F.
    Brzozowski, Jerzy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Holmström, Kerstin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ongena, J.
    Zastrow, K. -D
    Toroidal rotation in RF heated JET plasmas2007Ingår i: RADIO FREQUENCY POWER IN PLASMAS, 2007, Vol. 933, s. 59-62Konferensbidrag (Refereegranskat)
    Abstract [en]

    Experiments have been carried out on JET aimed at studying rotation in RF heated plasmas with low external momentum input. Both plasmas with Ion Cyclotron Resonance Frequency (ICRF) heating and Lower Hybrid Current Drive (LHCD) have been investigated. The rotation profiles are measured by Charge Exchange recombination spectroscopy, using short diagnostic Neutral Beam Injection (NBI) pulses. Moreover, the temporal evolution of the central rotation could in some cases be deduced from MHD activity. While most of the measurements were focussed on ICRF heating, the profiles measured in plasmas with LHCD are interesting since they are the first reported from JET in such plasmas. In particular, they allowed for studies of rotation in RF heated plasmas with q>1. The experimental results are presented together with an analysis of the torque from ICRF heated fast ions.

  • 292. Eriksson, L. G.
    et al.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Mayoral, M. L.
    Coda, S.
    Sauter, O.
    Buttery, R. J.
    McDonald, D.
    Hellsten, Torbjörn A. K.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Mantsinen, M. J.
    Mueck, A.
    Noterdaeme, J. M.
    Santala, M.
    Westerhor, E.
    de Vries, P.
    On ion cyclotron current drive for sawtooth control2006Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, nr 10, s. S951-S964Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments using ion cyclotron current drive (ICCD) to control sawteeth are presented. In particular, discharges demonstrating shortening of fast ion induced long sawteeth reported in (Eriksson et al 2004 Phys. Rev. Lett. 92 235004) by ICCD have been analysed in detail. Numerical simulations of the ICCD driven currents are shown to be consistent with the experimental observations. They support the hypothesis that an increase in the magnetic shear, due to the driven current, at the surface where the safety factor is unity was the critical factor for the shortening of the sawteeth. In view of the potential utility of ICCD, the mechanisms for the current drive have been further investigated experimentally. This includes the influence of the averaged energy of the resonating ions carrying the current and the spectrum of the launched waves. The results of these experiments are discussed in the light of theoretical considerations.

  • 293.
    Eriksson, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Characteristics of transpolar auroral arcs based on data from the Viking satellite1996Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 294.
    Eriksson, Stefan
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Blomberg, Lars G.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ivchenko, Nickolay V.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field2001Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 19, nr 6, s. 649-653Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The cross-polar potential drop Phi (pc), and the low-latitude asymmetric geomagnetic disturbance field, as indicated by the mid-latitude ASY-H magnetic index, are used to study the average magnetospheric response to the solar wind forcing for southward interplanetary magnetic field conditions. The state of the solar wind is monitored by the ACE spacecraft and the ionospheric convection is measured by the double probe electric field instrument on the Astrid-2 satellite. The solar wind-magnetosphere coupling is examined for 77 cases in February and from mid-May to mid-June 1999 by using the interplanetary magnetic field B-z component and the reconnection electric field. Our results show that the maximum correlation between Phi (pc) and the reconnection electric field is obtained approximately 25 min after the solar wind has reached a distance of II R-E from the Earth, which is the assumed average position of the magnetopause. The corresponding correlation for ASY-H shows two separate responses to the reconnection electric field, delayed by about 35 and 65 min, respectively. We suggest that the combination of the occurrence of a large magnetic storm on 18 February 1999 and the enhanced level of geomagnetic activity which peaks at Kp = 7(-) may explain the fast direct response of ASY-H to the solar wind at 35 min, as well as the lack of any clear secondary responses of Phi (pc) to the driving solar wind at time delays longer than 25 min.

  • 295.
    Eriksson, Stefan
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Blomberg, Lars G.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Weimer, D. R.
    Comparing a spherical harmonic model of the global electric field distribution with Astrid-2 observations2002Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, nr A11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    [1] Electric field measurements provided by the double probe instrument on the Astrid-2 satellite are compared with the empirical Weimer electric field model for all magnetic local times, except between 11 and 13 MLT, and poleward of 55degrees corrected geomagnetic latitude (CGLat). We focus the model evaluation on its ability to predict the latitudinal locations of the convection reversal boundaries for two-cell convection patterns and to estimate the magnitude of the electric field above 55degrees CGLat. A total number of 780 polar cap passes are employed from the Northern Hemisphere between January and July 1999. The measured average electric field magnitude in the dawn-dusk meridian plane above 55degrees CGLat is generally 25% larger than the predicted field independent of the interplanetary magnetic field (IMF) direction. The model shows a better correspondence with the observed electric field for southward IMF than for northward IMF, with most cases centered around B-z = -1.5 nT and r = 0.88. However, the agreement for northward IMF is promising, and a few examples are shown to corroborate this fact. The observed and predicted convection reversal boundary locations along the satellite track for southward IMF are on the average found 2-3degrees CGLat apart in the dawn-dusk meridian plane but may be as far apart as 9degrees CGLat. An initial investigation of the relative timing of a 20-min averaging window for the IMF along the 20-25 min polar cap crossing suggests that a time-dependent transfer function may be found that applies a higher weight to the input solar wind data early in the pass and a lower weight later in the pass for an IMF window that corresponds to the first half of the crossing and the opposite weight versus time dependence for an IMF window corresponding to the last half of the crossing.

  • 296.
    Eriksson, Stefan
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Bonnell, J. W.
    Blomberg, Lars G.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R. E.
    Marklund, Göran T.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Carlson, C. W.
    Lobe cell convection and field-aligned currents poleward of the region 1 current system2002Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, nr A8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    [1] We present a case and statistical study of plasma convection in the Northern Hemisphere during summer conditions using electric field, magnetic field, and particle data taken during dawn-dusk directed orbits of the FAST satellite. To our knowledge, this set provides the most comprehensive combination of data as yet presented in support of lobe cell convection from an ionospheric perspective this far from the noon sector. In particular, we study the current systems and convection patterns for all passes in July 1997 that show evidence for six large-scale field-aligned currents (FACs) rather than the usual system of four FACs associated with the region 1/region 2 current systems. A total of 71 passes out of 232 in the study had the extra pair of FACs. The extra pair of FACs in 30 of the 71 cases lies either on the dawnside or on the duskside of the noon-midnight meridian, and their position is strongly correlated with the polarity of the IMF By (negative and positive, respectively). This is consistent with the IMF dependence of a three-cell convection pattern of coexisting merging, viscous, and lobe-type convection cells. The occurrence of the asymmetric FAC pair was also strongly linked to conditions of IMF |B-y/B-z | > 1. The extra pair of FACs in these cases was clearly associated with the lobe cell of the three-cell convection system. The remaining 41 cases had the pair of FACs straddling the noon-midnight meridian. The extra pair of FACs was often (20 cases out of 30) observed at magnetic local times more than three hours away from noon, rather than being confined to regions near noon and the typical location of the cusp. Such a current system consisting of a pair of FACs poleward of the nearest region 1 current is consistent with the IMF B-y-dependent global MHD model developed by Ogino et al. [1986] for southward IMF conditions, as well as with other magnetospheric and ionospheric convection models that include the effects of merging occuring simultaneously at both low-latitude dayside and high-latitude lobe and flank magnetopause reconnection sites. Finally, the presence of the additional FACs and three-cell convection well away from noon show that the entire dayside ionosphere is affected by IMF-dependent processes, rather than only a limited region around noon.

  • 297.
    Eriksson, Stefan
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Ergun, R. E.
    Carlson, C. W.
    Peria, W.
    The Cross-Polar Potential Drop and its Correlation to the Solar Wind2000Ingår i: Journal of Geophysical Research - Space Physics, ISSN 0148-0227, Vol. 105, s. 18639-18653Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The cross-polar potential drop Phi(pc) as derived from the FAST satellite is used to study the average magnetospheric response to changes in the solar wind as monitored by the Wind spacecraft. The coupling of the solar wind with the magnetosphere is examined using the interplanetary magnetic field (IMF) B-z, the model reconnection electric field vB(t)sin(k)(theta/2) for k=3, 4, and the Akasofu-Perreault epsilon parameter. Initial results comprising 37 cases of Phi(pc) show one major response of the magnetosphere to the solar wind forcing at 15 min time lag followed by two minor pulses at 55 min and 105 min, respectively, during times when the IMF polarity was mainly southward and the geomagnetic activity was moderate to low. Phi(pc) shows a very good correlation with typical models of the reconnection electric field at 15 min time lag, reaching a maximum linear correlation coefficient of r=0.95 for vB(t)sin(3)(theta/2). In order to reach an understanding of the importance of individually calculated correlation coefficients, we introduce the statistical. bootstrap algorithm of Efron and Tibshirani [1993], which allows us to estimate a correlation coefficient standard error. In defining a quality measure based on this method, the significance coefficient s, we are able to interpret a resulting correlation coefficient time lag series in terms of a linear prediction filter similar to earlier techniques. The results on the magnetospheric response for Phi(pc) are further compared with those obtained using the geomagnetic indices Dst, SYM-H, and ASY-H. The similar magnetospheric response to the solar wind electric field for Phi(pc) and ASY-H at time delays of more than 40 min together with a high correlation coefficient between Phi(pc) and ASY-H suggest that these magnetospheric parameters couple to one another. The average dynamic response of the ionospheric convection to the solar wind electric field is in essential agreement with those reported by Klimas et al. [1994] on a normal magnetospheric mode with a recurrence frequency of 50 min.

  • 298.
    Eriksson, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Multi-point Measurements of Ultra Low Frequency Waves in the Terrestrial Magnetosphere2007Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Waves in the mHz frequency range are prominent features of the terrestrial magnetosphere. In this frequency range the waves have wavelengths comparable to the lengths of the geomagnetic field lines. The waves are then standing waves along closed field lines with endpoints in the southern and northern ionosphere. Waves play an important role in the distribution of energy in the magnetosphere and mHz waves can accelerate electrons to MeV energies and have been proposed as driving mechanism for auroral arcs. They can also be used as diagnostic tools for determining the plasma density. There are two important classes of these low frequency waves. One has large azimuthal wavelength and is usually associated with driving mechanisms outside the magnetosphere, such as the Kelvin-Helmholtz instability at the magnetopause. The other has small azimuthal wavelength and is associated with plasma instabilities inside the magnetosphere. Both types of waves are studied in this thesis with a slight emphasis on the large azimuthal wavelength waves. For the type of wave with large azimuthal wavelength there is however, a considerable debate about the driving mechanism. One recently suggested driver is coherent magnetohydrodynamic waves in the solar wind. Part of this thesis studies this experimentally and we conclude that, at least on some occasions, this driving mechanism comes into play. The Cluster satellites are used to study the morphology of the waves. We demonstrate the ability of Cluster to determine the azimuthal wave number of the waves and also how the structure along the magnetic field lines can be determined. This gives information regarding the harmonic number of the standing waves, which in turn says something about the driver of the waves. We also look at possible excitation mechanisms for the small azimuthal wavelength waves.

  • 299.
    Eriksson, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Resonant Waves in the Terrestrial Magnetosphere2005Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Waves in the mHz frequency range are a prominent feature in the terrestrial magnetosphere. In this frequency range the waves have wavelengths comparable to the lengths of the geomagnetic field lines. The waves are then standing waves along closed field lines with endpoints in the southern and northern ionosphere. Waves play an important role in the distribution of energy in the magnetosphere and mHz waves can accelerate electrons to MeV energies and have been proposed as a driver of auroral arcs. They can also be used as a diagnostic tool for determining the plasma density. There are two important classes of these low frequency waves. One has large azimuthal wavelength and is usually associated with driving mechanisms outside the magnetosphere, such as the Kelvin-Helmholtz instability at the magnetopause. The other has small azimuthal wavelength and is associated with plasma instabilities inside the magnetosphere. Both types of waves are studied in this thesis with an emphasis on the small azimuthal wavelength waves. For the type of wave with large azimuthal wavelength there is however, a considerable debate about the driving mechanism. One recently suggested driver is coherent magnetohydrodynamic waves in the solar wind. Part of this thesis studies this experimentally and we conclude that, at least on some occasions, this driving mechanism come into play. The Cluster satellites are used to study the morphology of the waves. We demonstrate the ability of Cluster to determine the azimuthal wave number of the waves and also how the structure along the magnetic field lines can be determined. This gives information regarding the harmonic number of the standing waves, which in turn says something about the driver of the waves. We also look at possible excitation mechanisms for the small azimuthal wavelength waves.

  • 300.
    Eriksson, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Wave pulsations in the magnetosphere and their dependence on the solar wind2003Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
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