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  • 101. Bohm, Martin
    et al.
    Brenning, Nils
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Dynamic trapping of electrons in the porcupine ionospheric ion beam experiment1992In: Advances in Space Research, ISSN 02731177, Vol. 12, p. 9-14Article in journal (Refereed)
    Abstract [en]

    Electrons are needed to maintain quasineutrality in a case where positive ions are injected across the magnetic field into a limited volume in a magnetized plasma. In the absence of collisions, a positive potential builds up and traps the electrons which enter the region along the magnetic field. If the added density of ions exceeds the ambient density, large potential differences along the magnetic field can be maintained this way. The process explains several features of the Porcupine xenon ion beam injection experiment, where strong magnetic-field-aligned electric fields were measured in the vicinity of a xenon ion beam which was injected into the ambient ionosphere from a spinning subpayload. © 1992.

  • 102.
    Bolmgren, Karl
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Time dependence of average structure size and precipitation energy in pulsating aurora2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Pulsating aurora is low intensity aurora appearing in limited structures with quasiperiodicalmodulations in intensity. The highly energetic electron precipitation associatedwith pulsating aurora has been shown to cause chemical changes as far downas the mesosphere, causing ozone depletion. The drivers involved in generating pulsatingaurora are not fully known, and efforts have been made to model many of thesuggested mechanisms. In order to evaluate these results observational constraintson the temporal and spatial characteristics of pulsating aurora are necessary.Previous studies have noted that the pulsating area tends to decrease over timefrom studying single pulsating patches. This study examines a large set of all-skycamera data comprising approximately 400 image series with pulsating aurora fromthe MIRACLE network in northern Fennoscandia in order to determine the time dependenceof the average size and precipitation energy in pulsating aurora. The 20 stime resolution of the all-sky images makes it challenging to identify spatial boundariesof the pulsating structures whose periods have a typical range of 2-20 s. Twomethods are implemented here, with the same results showing a gradual decreasein average size. No relationship between UT and size is clear. The electron precipitationenergies are inferred from the peak emission height and 557,7 nm/427,8 nmintensity ratio, and seem not to be directly related pulsating structure size. Thepeak emission height shows a constant average energy following an initial increasefollowing the onset of the pulsating aurora, and the intensity ratio suggests a constantaverage electron precipitation energy.

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  • 103.
    Bonanomi, N.
    et al.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Univ Milano Bicocca, Milan, Italy.;CNR, Ist Fis Plasma P Caldirola, Milan, Italy.;Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany.;Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    Impact of electron-scale turbulence and multi-scale interactions in the JET tokamak2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 12, article id 124003Article in journal (Refereed)
    Abstract [en]

    Experimental observations in JET tokamak plasmas and gyrokinetic simulations point to an important role, for electron heat transport, of electron-scale instabilities and of their interaction with ion-scale instabilities. Since these effects are maximized for strong electron heating and ion-scale modes close to marginal stability, these findings are of high relevance for ITER plasmas, featuring both conditions. Gyrokinetic and quasi-linear transport models accounting for multi-scale effects are assessed against JET experimental results.

  • 104.
    Bonanomi, N.
    et al.
    -.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics. KTH, Fusion Plasma Phys, EES, SE-10044 Stockholm, Sweden..
    Zychor, I.
    et al.,
    Effects of nitrogen seeding on core ion thermal transport in JET ILW L-mode plasmas2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 2, article id 026028Article in journal (Refereed)
    Abstract [en]

    A set of experiments was carried out in JET ILW (Joint European Torus with ITER-Like Wall) L-mode plasmas in order to study the effects of light impurities on core ion thermal transport. N was puffed into some discharges and its profile was measured by active Charge Exchange diagnostics, while ICRH power was deposited on- and off-axis in (He-3) - D minority scheme in order to have a scan of local heat flux at constant total power with and without N injection. Experimentally, the ion temperature profiles are more peaked for similar heat fluxes when N is injected in the plasma. Gyro-kinetic simulations using the GENE code indicate that a stabilization of Ion Temperature Gradient driven turbulent transport due to main ion dilution and to changes in T-e/T-i and s/q is responsible of the enhanced peaking. The quasi-linear models TGLF and QuaLiKiz are tested against the experimental and the gyro-kinetic results.

  • 105.
    Bonanomi, N.
    et al.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Univ Milano Bicocca, Milan, Italy.;CNR, Inst Plasma Phys P Caldirola, Milan, Italy.;Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics. KTH, Fusion Plasma Phys, EES, SE-10044 Stockholm, Sweden..
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Light impurity transport in JET ILW L-mode plasmas2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 3, article id 036009Article in journal (Refereed)
    Abstract [en]

    A series of experimental observations of light impurity profiles was carried out in JET (Joint European Torus) ITER-like wall (ILW) L-mode plasmas in order to investigate their transport mechanisms. These discharges feature the presence of He-3, Be, C, N, Ne, whose profiles measured by active Charge Exchange diagnostics are compared with quasi-linear and non-linear gyro-kinetic simulations. The peaking of He-3 density follows the electron density peaking, Be and Ne are also peaked, while the density profiles of C and N are flat in the mid plasma region. Gyro-kinetic simulations predict peaked density profiles for all the light impurities studied and at all the radial positions considered, and fail predicting the flat or hollow profiles observed for C and N at mid radius in our cases.

  • 106.
    Bonelli, F.
    et al.
    KIT, Inst Tech Phys, Vacuum Dept, Karlsruhe, Germany.;Karlsruhe Inst Technol, POB 3640, D-76021 Karlsruhe, Germany..
    Varoutis, S.
    KIT, Inst Tech Phys, Vacuum Dept, Karlsruhe, Germany.;Karlsruhe Inst Technol, POB 3640, D-76021 Karlsruhe, Germany..
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics. KTH, Fusion Plasma Phys, EES, SE-10044 Stockholm, Sweden..
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Self-consistent coupling of DSMC method and SOLPS code for modeling tokamak particle exhaust2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 6, article id 066037Article in journal (Refereed)
    Abstract [en]

    In this work, an investigation of the neutral gas flow in the JET sub-divertor area is presented, with respect to the interaction between the plasma side and the pumping side. The edge plasma side is simulated with the SOLPS code, while the sub-divertor area is modeled by means of the direct simulation Monte Carlo (DSMC) method, which in the last few years has proved well able to describe rarefied, collisional flows in tokamak sub-divertor structures. Four different plasma scenarios have been selected, and for each of them a user-defined, iterative procedure between SOLPS and DSMC has been established, using the neutral flux as the key communication term between the two codes. The goal is to understand and quantify the mutual influence between the two regions in a self-consistent manner, that is to say, how the particle exhaust pumping system controls the upstream plasma conditions. Parametric studies of the flow conditions in the sub-divertor, including additional flow outlets and variations of the cryopump capture coefficient, have been performed as well, in order to understand their overall impact on the flow field. The DSMC analyses resulted in the calculation of both the macroscopic quantities-i.e. temperature, number density and pressure-and the recirculation fluxes towards the plasma chamber. The consistent values for the recirculation rates were found to be smaller than those according to the initial standard assumption made by SOLPS.

  • 107.
    Bordogna, Marco Tito
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Fidjeland, Leo
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fjällid, Markus
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Galrinho, Miguel
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Haponen, Anders
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hou, Anton
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kristmundsson, Darri
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Lárusdóttir, Ólafía
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lejon, Marcus
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Lindh, Marcus
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lozano, Emilio
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Magnusson, Patrick
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Myleus, Andreas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Oakes, Ben D.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    MUSCAT experiment: active free falling units for in situ measurements of temperature and density in the middle atmosphere2013In: European Space Agency: (Special Publication) ESA SP / [ed] L. Ouwehand, ESTEC, Noordwijk, The Netherlands: ESA Communications , 2013, p. 575-582Conference paper (Other academic)
    Abstract [en]

    The main scientific objective of the MUSCAT Experimentis to develop a technique to reconstruct temperatures and density profiles in the middle atmosphere using active spherical probes. The MUSCAT experiment was launched on May 9, 2013 on the REXUS-13 sounding rocket from Esrange, in northern Sweden. The experiment ejected four probes that collected raw GPS signal. The experiment design and preliminary results are presented here.

  • 108.
    Bourdelle, C.
    et al.
    CEA, IRFM, F-13108 St Paul Les Durance, France.;CEA, IRFM, F-13108 St Paul Les Durance, France..
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Fast H isotope and impurity mixing in ion-temperature-gradient turbulence2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 7, article id 076028Article in journal (Refereed)
    Abstract [en]

    In ion-temperature-gradient (ITG) driven turbulence, the resonance condition leads to ion particle turbulent transport coefficients significantly larger than electron particle turbulent transport coefficients. This is shown in nonlinear gyrokinetic simulations and explained by an analytical quasilinear model. It is then illustrated by JETTO-QuaLiKiz integrated modelling. Large ion particle transport coefficients implies that the ion density profiles are uncorrelated to the corresponding ion source, allowing peaked isotope density profiles even in the absence of core source. This also implies no strong core accumulation of He ash. Furthermore, the relaxation time of the individual ion profiles in a multi-species plasma can be significantly faster than the total density profile relaxation time which is constrained by the electrons. This leads to fast isotope mixing and fast impurity transport in FM regimes. In trapped-electron- mode (TEM) turbulence, in presence of electron heating about twice the ion heating, the situation is the inverse: ion particle turbulent transport coefficients are smaller than their electron counterpart.

  • 109. Bowman, C.
    et al.
    Dickinson, D.
    Horvath, L.
    Lunniss, A. E.
    Wilson, H. R.
    Cziegler, I.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Gibson, K.
    Kirk, A.
    Lipschultz, B.
    Maggi, C. F.
    Roach, C. M.
    Saarelma, S.
    Snyder, P. B.
    Thornton, A.
    Wynn, A.
    Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 1, article id 016021Article in journal (Refereed)
    Abstract [en]

    The pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal between ELMs is analysed for 1.4 MA, 1.7 T, low triangularity, delta = 0.2, discharges with the ITER-like wall, finding that the pressure gradient typically tracks the ideal magneto-hydrodynamic ballooning limit, consistent with a role for the kinetic ballooning mode. Furthermore, the pedestal width is often influenced by the region of plasma that has second stability access to the ballooning mode, which can explain its sometimes complex evolution between ELMs. A local gyrokinetic analysis of a second stable flux surface reveals stability to kinetic ballooning modes; global effects are expected to provide a destabilising mechanism and need to be retained in such second stable situations. As well as an electronscale electron temperature gradient mode, ion scale instabilities associated with this flux surface include an electro-magnetic trapped electron branch and two electrostatic branches propagating in the ion direction, one with high radial wavenumber. In these second stability situations, the ELM is triggered by a peeling-ballooning mode; otherwise the pedestal is somewhat below the peeling-ballooning mode marginal stability boundary at ELM onset. In this latter situation, there is evidence that higher frequency ELMs are paced by an oscillation in the plasma, causing a crash in the pedestal before the peeling-ballooning boundary is reached. A model is proposed in which the oscillation is associated with hot plasma filaments that are pushed out towards the plasma edge by a ballooning mode, draining their free energy into the cooler plasma there, and then relaxing back to repeat the process. The results suggest that avoiding the oscillation and maximising the region of plasma that has second stability access will lead to the highest pedestal heights and, therefore, best confinement-a key result for optimising the fusion performance of JET and future tokamaks, such as ITER.

  • 110.
    Bramsäter, Robin
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Topography and morphology analysis of marine nanoparticles and a pedagogical study of representations used for improving a high school experiment2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Arctic Summer Cloud Ocean Study expedition took place during the autumn of 2008 and brought back water and air samples. One theory was that marine particles were shot into the atmosphere by bubble bursting and, while in the atmosphere, acted as cloud condensation nuclei. Particles collected from the subsurface water, surface microlayer and just above the surface had their topography and morphology analyzed using a scanning electron microscope. Due to a lack of EDS analysis it's impossible to say for sure if the particles found were the same found in previous studies, just that it is highly likely that they are. No evidence against the marine particles being able to act as cloud condensation nuclei was found but the data gathered was not sufficient to strengthen the theory either.

    The scanning electron microscope was also used in a pedagogical study, analyzing how operators with different knowledge and prior experience interact with the microscope's images. These results as well as knowledge gained from literature studies were used to improve a high school experiment regarding centripetal acceleration. The main issue with the experiment was that what the students learned performing the experiment was not the same as the theoretical models the teachers wished the students to learn. The reason for this was because the experimental equipment lacked the centripetal model's external representations such as force arrows. If a simulator would be incorporated into the lab centripetal acceleration representations could be visualized and a clearer connection between experiment and theory could be made.

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    fulltext
  • 111.
    Brenning, Nils
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    An Appendix to the Paper Te determination in low-density plasmas from the HeI 3889 Å and 5016 Å line intensities1981Report (Other academic)
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    fulltext
  • 112.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Axnas, I.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lundin, D.
    Helmerson, U.
    A bulk plasma model for dc and HiPIMS magnetrons2008In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 17, no 4Article in journal (Refereed)
    Abstract [en]

    A plasma discharge model has been developed for the bulk plasma (also called the extended presheath) in sputtering magnetrons. It can be used both for high power impulse magnetron sputtering (HiPIMS) and conventional dc sputtering magnetrons. Demonstration calculations are made for the parameters of the HiPIMS sputtering magnetron at Link "oping University, and also benchmarked against results in the literature on dc magnetrons. New insight is obtained regarding the structure and time development of the currents, the electric fields and the potential profiles. The transverse resistivity eta(perpendicular to) has been identified as having fundamental importance both for the potential profiles and for the motion of ionized target material through the bulk plasma. New findings are that in the HiPIMS mode, as a consequence of a high value of eta(perpendicular to), (1) there can be an electric field reversal that in our case extends 0.01-0.04m from the target, (2) the electric field in the bulk plasma is typically an order of magnitude weaker than in dc magnetrons, (3) in the region of electric field reversal the azimuthal current is diamagnetic in nature, i.e. mainly driven by the electron pressure gradient, and actually somewhat reduced by the electron Hall current which here has a reversed direction and (4) the azimuthal current above the racetrack can, through resistive friction, significantly influence the motion of the ionized fraction of the sputtered material and deflect it sideways, away from the target and towards the walls of the magnetron.

  • 113.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Axnas, I.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tennfors, E.
    Koepke, M.
    Radiation from an electron beam in a magnetized plasma: Whistler mode wave packets2006In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 111, no A11Article in journal (Refereed)
    Abstract [en]

    Experimental studies are reported of oscillations and radiation that is spontaneously excited by an electron beam which is shot along a diverging magnetic field into a plasma from a hot cathode. In the present study we focus on oscillations below the electron gyrofrequency, where we find that whistler mode radiation appears in the form of bursts, or wave packets, each with typically 0.1-1 mu s time duration, and which together cover typically a few percent of the full time. Wave packets are found in a broad frequency range of 7-40 MHz, while each individual wave packet is dominated by a single frequency. There is propagation along two routes: at the group velocity resonance cone angle, away from the central channel where the waves are excited, and in a channel along the magnetic field. Features of the whistler mode wave packets that are studied include (1) the statistics of amplitudes, frequencies, and time durations; (2) the propagation and decay of wave packets with different frequencies; (3) the group and phase velocities; and (4) how the wave packet production varies with the energy, and the current density, in the electron beam.

  • 114.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Axnäs, Ingvar
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Koepke, Mark
    KTH.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tennfors, Einar
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Radiation from an electron beam in magnetized plasma: excitation of a whistler mode wave packet by interacting, higher-frequency, electrostatic-wave eigenmodes2017In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, no 12, article id 124006Article in journal (Refereed)
    Abstract [en]

    Infrequent, bursty, electromagnetic, whistler-mode wave packets, excited spontaneously in the laboratory by an electron beam from a hot cathode, appear transiently, each with a time duration tau around similar to 1 mu s. The wave packets have a center frequency f(W) that is broadly distributed in the range 7 MHz < f(W) < 40 MHz. They are excited in a region with separate electrostatic (es) plasma oscillations at values of f(hf), 200 MHz < f(hf) < 500 MHz, that are hypothesized to match eigenmode frequencies of an axially localized hf es field in a well-defined region attached to the cathode. Features of these es-eigenmodes that are studied include: the mode competition at times of transitions from one dominating es-eigenmode to another, the amplitude and spectral distribution of simultaneously occurring es-eigenmodes that do not lead to a transition, and the correlation of these features with the excitation of whistler mode waves. It is concluded that transient coupling of es-eigenmode pairs at f(hf) such that vertical bar f(1, hf) - f(2, hf)vertical bar = f(W) < f(ge) can explain both the transient lifetime and the frequency spectra of the whistler-mode wave packets (f(W)) as observed in lab. The generalization of the results to bursty whistler-mode excitation in space from electron beams, created on the high potential side of double layers, is discussed.

  • 115.
    Brenning, Nils
    et al.
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Haerendel, G.
    Kelley, M.C.
    Marklund, Göran
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Pfaff, R.
    Providakes, J.
    Stenbaek-Nielsen, H.C.
    Swenson, C.
    Torbert, R.
    Wescott, E.M.
    Interpretation of the Electric Fields Measured in an Ionospheric Critical Ionization Velocity Experiment1991In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 96, p. 9719-9733Article in journal (Refereed)
    Abstract [en]

    This paper deals with the quasi-dc electric fields measured in the CRIT I ionospheric release experiment, which was launched from Wallops Island on May 13, 1986. The purpose of the experiment was to study the critical ionization velocity (CIV) mechanism in the ionosphere. Two identical barium shaped charges were fired from distances of 1.99 km and 4.34 km towards a main payload, which made full three-dimensional measurements of the electric field inside the streams. There was also a subpayload separated from the main payload by a couple of kilometers along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in CIV is investigated in the light of the CRIT I results. It is concluded that both the “homogeneous” and the “ionizing front” models probably apply, but in different parts of the stream. It is also possible that electrons are directly accelerated by a magnetic-field-aligned component of the electric field; the quasi-dc electric field observed within the streams had a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. The coupling between the ambient ionosphere and the ionized barium stream in CRIT I was more complicated than is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes. One interpretation of the quasi-dc electric field data is that the internal electric fields of the streams were not greatly modified by magnetic-field-aligned currents, i.e., a state was established where the transverse currents were to a first approximation divergence-free. It is argued that this interpretation can explain both a reversal of the strong explosion-directed electric field in burst 1 and the absence of such a reversal in burst 2.

  • 116.
    Brenning, Nils
    et al.
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Haerendel, G.
    Kelley, M.C.
    Marklund, Göran
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Pfaff, R.
    Providakes, J.
    Stenbaek-Nielsen, H.C.
    Swenson, C.
    Torbert, R.B.
    Wescott, E.M.
    Critical ionization velocity interaction in the CRIT I rocket experiment1990In: Advances in Space Research, ISSN 02731177, Vol. 10, p. 63-66Article in journal (Refereed)
    Abstract [en]

    In the rocket experiment CRIT I, launched from Wallops Island on 13 May 1986, two identical Barium shaped charges were fired from distances of 1.3 km and 3.6 km towards the main experiment payload, which was separated from a sub-payload by a couple of km along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in ionospheric critical velocity experiments is investigated in the light of the CRIT I results. It is concluded that both the "homogeneous" and the "ionizing front" models can be applied, in different parts of the stream. It is also possible that a third, entirely different, mechanism may contribute to the electron heating. This mechanism involves direct energization of electrons in the magnetic-field-aligned component of the DC electric field. © 1989.

  • 117.
    Brenning, Nils
    et al.
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Haerendel, G.
    Kelley, M.C.
    Marklund, Göran
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Pfaff, R.
    Providakes, J.
    Stenbaek-Nielsen, H.C.
    Swenson, C.
    Wescott, E.M.
    Electrodynamic interaction between the CRIT I ionized barium streams and the ambient ionosphere1990In: Advances in Space Research, ISSN 02731177, Vol. 10, p. 67-70Article in journal (Refereed)
    Abstract [en]

    In the CRIT I Critical Velocity experiment, launched from Wallops Island on 13 May, 1986, two fast barium streams were ejected by means of shaped charges. Their electrodynamic interaction with the ambient ionosphere is discussed. An outstanding feature of the DC electric field observed within the streams was a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. One interpretation of the DC electric field data is that the internal electric fields of the streams is not greatly modified by Birkeland currents, i.e. a state is established, where the transverse currents are to a first approximation divergence-free. It is argued that this interpretation can explain why a reversal of the strong explosion-directed electric field was observed in the first explosion but not in the second (more distant one). © 1989.

  • 118.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. Linköping University, Sweden; Université Paris-Sud, France.
    Gudmundsson, Jon Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lundin, D.
    Minea, T.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. Université Paris-Sud, France.
    Helmersson, U.
    The role of Ohmic heating in dc magnetron sputtering2016In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 25, no 6, article id 065024Article in journal (Refereed)
    Abstract [en]

    Sustaining a plasma in a magnetron discharge requires energization of the plasma electrons. In this work, Ohmic heating of electrons outside the cathode sheath is demonstrated to be typically of the same order as sheath energization, and a simple physical explanation is given. We propose a generalized Thornton equation that includes both sheath energization and Ohmic heating of electrons. The secondary electron emission yield gamma(SE) is identified as the key parameter determining the relative importance of the two processes. For a conventional 5 cm diameter planar dc magnetron, Ohmic heating is found to be more important than sheath energization for secondary electron emission yields below around 0.1.

  • 119.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. Laboratoire de Physique des Gaz et Plasmas—LPGP, UMR 8578 CNRS, Université Paris-Saclay, France; Plasma and Coatings Physics Division, IFM-Materials Physics, Linköping University, Sweden.
    Gudmundsson, Jon Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. Laboratoire de Physique des Gaz et Plasmas—LPGP, UMR 8578 CNRS, Université Paris-Sud, Université Paris-Saclay, France; Science Institute, University of Iceland, Dunhaga 3, IS-107 Reykjavik, Iceland.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Petty, T. J.
    Universite Paris Sud.
    Minea, Tiberiu
    Unicersite Paris Sud.
    Lundin, Daniel
    Universite Paris Sud.
    A unified treatment of self-sputtering, process gas recycling, and runaway for high power impulse sputtering magnetrons2017In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 26, no 12, article id 125003Article in journal (Refereed)
    Abstract [en]

    The combined processes of self-sputter (SS)-recycling and process gas recycling in high power impulse magnetron sputtering (HiPIMS) discharges are analyzed using the generalized recycling model (GRM). The study uses experimental data from discharges with current densities from the direct current magnetron sputtering range to the HiPIMS range, and using targets with self-sputter yields Y-SS from approximate to 0.1 to 2.6. The GRM analysis reveals that, above a critical current density of the order of J(crit) approximate to 0.2 A cm(-2), a combination of self-sputter recycling and gas-recycling is generally the case. The relative contributions of these recycling mechanisms, in turn, influence both the electron energy distribution and the stability of the discharges. For high self-sputter yields, above Y-SS approximate to 1, the discharges become dominated by SS-recycling, contain few hot secondary electrons from sheath energization, and have a relatively low electron temperature T-e. Here, stable plateau values of the discharge current develop during long pulses, and these values increase monotonically with the applied voltage. For low self-sputter yields, below Y-SS approximate to 0.2, the discharges above J(crit) are dominated by process gas recycling, have a significant sheath energization of secondary electrons and a higher T-e, and the current evolution is generally less stable. For intermediate values of YSS the discharge character gradually shifts between these two types. All of these discharges can, at sufficiently high discharge voltage, give currents that increase rapidly in time. For such cases we propose that a distinction should be made between 'unlimited' runaway and 'limited' runaway: in unlimited runaway the current can, in principle, increase without a limit for a fixed discharge voltage, while in limited runaway it can only grow towards finite, albeit very high, levels. For unlimited runway Y-SS > 1 is found to be a necessary criterion, independent of the amount of gas-recycling in the discharge.

  • 120.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Huo, Chunqing
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lundin, Daniel
    Plasma and Coatings Physics Division, Linköping, Sweden.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Vitelaru, Catalin
    Stancu, Gabriel
    Minea, Tiberiu
    Helmersson, Ulf
    Understanding deposition rate loss in high power impulse magnetron sputtering: I. Ionization-driven electric fields2012In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 21, no 2, p. 025005-Article in journal (Refereed)
    Abstract [en]

    The lower deposition rate for high power impulse magnetron sputtering (HiPIMS) compared with direct current magnetron sputtering for the same average power is often reported as a drawback. The often invoked reason is back-attraction of ionized sputtered material to the target due to a substantial negative potential profile, sometimes called an extended presheath, from the location of ionization toward the cathode. Recent studies in HiPIMS devices, using floating-emitting and swept-Langmuir probes, show that such extended potential profiles do exist, and that the electric fields E-z directed toward the target can be strong enough to seriously reduce ion transport to the substrate. However, they also show that the potential drops involved can vary by up to an order of magnitude from case to case. There is a clear need to understand the underlying mechanisms and identify the key discharge variables that can be used for minimizing the back-attraction. We here present a combined theoretical and experimental analysis of the problem of electric fields E-z in the ionization region part of HiPIMS discharges, and their effect on the transport of ionized sputtered material. In particular, we have investigated the possibility of a 'sweet spot' in parameter space in which the back-attraction of ionized sputtered material is low. It is concluded that a sweet spot might possibly exist for some carefully optimized discharges, but probably in a rather narrow window of parameters. As a measure of how far a discharge is from such a window, a Townsend product Pi(Townsend) is proposed. A parametric analysis of Pi(Townsend) shows that the search for a sweet spot is complicated by the fact that contradictory demands appear for several of the externally controllable parameters such as high/low working gas pressure, short/long pulse length, high/low pulse power and high/low magnetic field strength.

  • 121.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hurtig, T.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Conditions for plasmoid penetration across abrupt magnetic barriers2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 1Article in journal (Refereed)
    Abstract [en]

    The penetration of plasma clouds, or plasmoids, across abrupt magnetic barriers (of the scale less than a few ion gyro radii, using the plasmoid directed velocity) is studied. The insight gained earlier, from detailed experimental and computer simulation investigations of a case study, is generalized into other parameter regimes. It is concluded for what parameters a plasi-noid should be expected to penetrate the magnetic barrier through self-polarization, penetrate through magnetic expulsion, or be rejected from the barrier. The scaling parameters are n(e), upsilon(o), B-perpendicular to, m(i), T-i, and the width w of the plasmoid. The scaling is based on a model for strongly driven, nonlinear magnetic field diffusion into a plasma which is a generalization of the earlier laboratory findings. The results are applied to experiments earlier reported in the literature, and also to the proposed application of impulsive penetration of plasmoids from the solar wind into the Earth's magnetosphere.

  • 122.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lundin, Daniel
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Alfven's critical ionization velocity observed in high power impulse magnetron sputtering discharges2012In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, no 9, p. 093505-Article in journal (Refereed)
    Abstract [en]

    Azimuthally rotating dense plasma structures, spokes, have recently been detected in several high power impulse magnetron sputtering (HiPIMS) devices used for thin film deposition and surface treatment, and are thought to be important for plasma buildup, energizing of electrons, as well as cross-B transport of charged particles. In this work, the drift velocities of these spokes are shown to be strongly correlated with the critical ionization velocity, CIV, proposed by Alfven. It is proposed as the most promising approach in combining the CIV and HiPIMS research fields is to focus on the role of spokes in the process of electron energization.

  • 123.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lundin, Daniel
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Minea, T.
    Costin, C.
    Vitelaru, C.
    Spokes and charged particle transport in HiPIMS magnetrons2013In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 46, no 8, p. 084005-Article in journal (Refereed)
    Abstract [en]

    Two separate scientific communities are shown to have studied one common phenomenon, azimuthally rotating dense plasma structures, also called spokes, in pulsed-power E x B discharges, starting from quite different approaches. The first body of work is motivated by fundamental plasma science and concerns a phenomenon called the critical ionization velocity, CIV, while the other body of work is motivated by the applied plasma science of high power impulse magnetron sputtering (HiPIMS). Here we make use of this situation by applying experimental observations, and theoretical analysis, from the CIV literature to HiPIMS discharges. For a practical example, we take data from observed spokes in HiPIMS discharges and focus on their role in charged particle transport, and in electron energization. We also touch upon the closely related questions of how they channel the cross-B discharge current, how they maintain their internal potential structure and how they influence the energy spectrum of the ions? New particle-in-cell Monte Carlo collisional simulations that shed light on the azimuthal drift and expansion of the spokes are also presented.

  • 124.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Merlino, R. L.
    Lundin, D.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Helmersson, U.
    Faster-than-Bohm Cross-B Electron Transport in Strongly Pulsed Plasmas2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 22Article in journal (Refereed)
    Abstract [en]

    We report the empirical discovery of an exceptionally high cross-B electron transport rate in magnetized plasmas, in which transverse currents are driven with abruptly applied high power. Experiments in three different magnetic geometries are analyzed, covering several orders of magnitude in plasma density, magnetic field strength, and ion mass. It is demonstrated that a suitable normalization parameter is the dimensionless product of the electron (angular) gyrofrequency and the effective electron-ion momentum transfer time, omega(ge)tau(EFF), by which all of diffusion, cross-resistivity, cross-B current conduction, and magnetic field diffusion can be expressed. The experiments show a remarkable consistency and yield close to a factor of 5 greater than the Bohm-equivalent values of diffusion coefficient D-perpendicular to, magnetic-diffusion coefficient D-B, Pedersen conductivity sigma(P), and transverse resistivity eta(perpendicular to).

  • 125.
    Breton, S.
    et al.
    Culham Sci Ctr, EUROfus Consortium, JET, Abingdon OX14 3DB, Oxon, England.;CEA, IRFM, F-13108 St Paul Les Durance, France.;CEA, IRFM, F-13108 St Paul Les Durance, France..
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics. KTH, Fusion Plasma Phys, EES, SE-10044 Stockholm, Sweden..
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    High Z neoclassical transport: Application and limitation of analytical formulae for modelling JET experimental parameters2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 1, article id 012303Article in journal (Refereed)
    Abstract [en]

    Heavy impurities, such as tungsten (W), can exhibit strongly poloidally asymmetric density profiles in rotating or radio frequency heated plasmas. In the metallic environment of JET, the poloidal asymmetry of tungsten enhances its neoclassical transport up to an order of magnitude, so that neoclassical convection dominates over turbulent transport in the core. Accounting for asymmetries in neoclassical transport is hence necessary in the integrated modeling framework. The neoclassical drift kinetic code, NEO [E. Belli and J. Candy, Plasma Phys. Controlled Fusion P50, 095010 (2008)], includes the impact of poloidal asymmetries on W transport. However, the computational cost required to run NEO slows down significantly integrated modeling. A previous analytical formulation to describe heavy impurity neoclassical transport in the presence of poloidal asymmetries in specific collisional regimes [C. Angioni and P. Helander, Plasma Phys. Controlled Fusion 56, 124001 (2014)] is compared in this work to numerical results from NEO. Within the domain of validity of the formula, the factor for reducing the temperature screening due to poloidal asymmetries had to be empirically adjusted. After adjustment, the modified formula can reproduce NEO results outside of its definition domain, with some limitations: When main ions are in the banana regime, the formula reproduces NEO results whatever the collisionality regime of impurities, provided that the poloidal asymmetry is not too large. However, for very strong poloidal asymmetries, agreement requires impurities in the Pfirsch-Schluter regime. Within the JETTO integrated transport code, the analytical formula combined with the poloidally symmetric neoclassical code NCLASS [W. A. Houlberg et al., Phys. Plasmas 4, 3230 (1997)] predicts the same tungsten profile as NEO in certain cases, while saving a factor of one thousand in computer time, which can be useful in scoping studies. The parametric dependencies of the temperature screening reduction due to poloidal asymmetries would need to be better characterised for this faster model to be extended to a more general applicability.

  • 126.
    Breton, S.
    et al.
    JET, Culham Sci Ctr, EUROfus Consortium, Abingdon OX14 3DB, Oxon, England.;CEA, IRFM, F-13108 St Paul Les Durance, France.;CEA, IRFM, F-13108 St Paul Les Durance, France..
    Bourdelle, C.
    JET, Culham Sci Ctr, EUROfus Consortium, Abingdon OX14 3DB, Oxon, England.;CEA, IRFM, F-13108 St Paul Les Durance, France.;CEA, IRFM, F-13108 St Paul Les Durance, France..
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    First principle integrated modeling of multi-channel transport including Tungsten in JET2018In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 9, article id 096003Article in journal (Refereed)
    Abstract [en]

    For the first time, over five confinement times, the self-consistent flux driven time evolution of heat, momentum transport and particle fluxes of electrons and multiple ions including Tungsten (W) is modeled within the integrated modeling platform JFTTO (Romanelli et al 2014 Plasma Fusion Res. 9 1-4), using first principle-based codes: namely, QuaLiKiz (Bourdelle et al 2016 Plasma Phys. Control. Fusion 58 014036) for turbulent transport and NEO (Belli and Candy 2008 Plasma Phys. Control. Fusion 50 95010) for neoclassical transport. For a JET-ILW pulse, the evolution of measured temperatures, rotation and density profiles are successfully predicted and the observed W central core accumulation is obtained. The poloidal asymmetries of the W density modifying its neoclassical and turbulent transport are accounted for. Actuators of the W core accumulation are studied: removing the central particle source annihilates the central W accumulation whereas the suppression of the torque reduces significantly the W central accumulation. Finally, the presence of W slightly reduces main ion heat turbulent transport through complex nonlinear interplays involving radiation, effective charge impact on ITG and collisionality.

  • 127. Breuillard, H.
    et al.
    Le Contel, O.
    Retino, A.
    Chasapis, A.
    Chust, T.
    Mirioni, L.
    Graham, D. B.
    Wilder, F. D.
    Cohen, I.
    Vaivads, Andris
    Khotyaintsev, Yu V.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Burch, J. L.
    Torbert, R. B.
    Ergun, R. E.
    Goodrich, K. A.
    Macri, J.
    Needell, J.
    Chutter, M.
    Rau, D.
    Dors, I.
    Russell, C. T.
    Magnes, W.
    Strangeway, R. J.
    Bromund, K. R.
    Plaschke, F.
    Fischer, D.
    Leinweber, H. K.
    Anderson, B. J.
    Le, G.
    Slavin, J. A.
    Kepko, E. L.
    Baumjohann, W.
    Mauk, B.
    Fuselier, S. A.
    Nakamura, R.
    Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 14, p. 7279-7286Article in journal (Refereed)
    Abstract [en]

    Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (approximate to 500km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales.

  • 128. Brezinsek, S.
    et al.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zaplotnik, R.
    et al.,
    Plasma-wall interaction studies within the EUROfusion consortium: Progress on plasma-facing components development and qualification2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 11, article id 116041Article in journal (Refereed)
    Abstract [en]

    The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful operation of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading facilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualification and specification of plasma-facing components, and by modelling codes that simulate edge-plasma conditions and the plasma-material interaction as well as the study of fundamental processes. WP PFC addresses these critical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel) with respect to heat-load capabilities (transient and steady-state heat and particle loads), lifetime estimates (erosion, material mixing and surface morphology), and safety aspects (fuel retention, fuel removal, material migration and dust formation) particularly for quasi-steady-state conditions. Alternative scenarios and concepts (liquid Sn or Li as PFCs) for DEMO are developed and tested in the event that the conventional solution turns out to not be functional. Here, we present an overview of the activities with an emphasis on a few key results: (i) the observed synergistic effects in particle and heat loading of ITER-grade W with the available set of exposition devices on material properties such as roughness, ductility and microstructure; (ii) the progress in understanding of fuel retention, diffusion and outgassing in different W-based materials, including the impact of damage and impurities like N; and (iii), the preferential sputtering of Fe in EUROFER steel providing an in situ W surface and a potential first-wall solution for DEMO.

  • 129.
    Brändström, B. U. E.
    et al.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Enell, C. F.
    Widell, O.
    Hansson, T.
    Whiter, N.
    Mäkinen, S.
    Mikhaylova, D.
    Axelsson, K.
    Sigernes, F.
    Gulbrandsen, N.
    Schlatter, N. M.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Gjendem, A. G.
    Cai, L.
    Reistad, J. P.
    Daae, M.
    Demissie, T. D.
    Andalsvik, Y. L.
    Roberts, O.
    Poluyanov, S.
    Chernouss, S.
    Results from the intercalibration of optical low-light calibration sources 20112012In: Geoscientific Instrumentation, Methods and Data Systems, ISSN 2193-0856, E-ISSN 2193-0864, Vol. 1, p. 43-51Article in journal (Refereed)
    Abstract [en]

    Following the 38th Annual European Meeting on Atmospheric Studies by Optical Methods in Siuntio in Finland, an intercalibration workshop for optical low light calibration sources was held in Sodankylä, Finland. The main purpose of this workshop was to provide a comparable scale for absolute measurements of aurora and airglow. All sources brought to the intercalibration workshop were compared to the Fritz Peak reference source using the Lindau Calibration Photometer built by Wilhelm Barke and Hans Lauche in 1984. The results were compared to several earlier intercalibration workshops. It was found that most sources were fairly stable over time, with errors in the range of 5–25%. To further validate the results, two sources were also intercalibrated at UNIS, Longyearbyen, Svalbard. Preliminary analysis indicates agreement with the intercalibration in Sodankylä within about 15–25%.

  • 130. Burch, J. L.
    et al.
    Torbert, R. B.
    Phan, T. D.
    Chen, L. -J
    Moore, T. E.
    Ergun, R. E.
    Eastwood, J. P.
    Gershman, D. J.
    Cassak, P. A.
    Argall, M. R.
    Wang, S.
    Hesse, M.
    Pollock, C. J.
    Giles, B. L.
    Nakamura, R.
    Mauk, B. H.
    Fuselier, S. A.
    Russell, C. T.
    Strangeway, R. J.
    Drake, J. F.
    Shay, M. A.
    Khotyaintsev, Yu. V.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Wilder, F. D.
    Young, D. T.
    Torkar, K.
    Goldstein, J.
    Dorelli, J. C.
    Avanov, L. A.
    Oka, M.
    Baker, D. N.
    Jaynes, A. N.
    Goodrich, K. A.
    Cohen, I. J.
    Turner, D. L.
    Fennell, J. F.
    Blake, J. B.
    Clemmons, J.
    Goldman, M.
    Newman, D.
    Petrinec, S. M.
    Trattner, K. J.
    Lavraud, B.
    Reiff, P. H.
    Baumjohann, W.
    Magnes, W.
    Steller, M.
    Lewis, W.
    Saito, Y.
    Coffey, V.
    Chandler, M.
    Electron-scale measurements of magnetic reconnection in space2016In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 352, no 6290, p. 1189-+Article, review/survey (Refereed)
    Abstract [en]

    Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

  • 131. Bykov, I.
    et al.
    Rudakov, D. L.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angeli, M.
    Hollmann, E. M.
    McLean, A. G.
    Lasnier, C. J.
    Riva, G.
    Modification of adhered dust on plasma-facing surfaces due to exposure to ELMy H-mode plasma in DIII-D2017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 379-385Article in journal (Refereed)
    Abstract [en]

    Transient heat load tests have been conducted in the lower divertor of DIII-D using DiMES manipulator in order to study the behavior of dust on tungsten Plasma Facing Components (PFCs) during ELMy H-mode discharges. Samples with pre- adhered, pre- characterized dust have been exposed at the outer strike point (OSP) in a series of discharges with varied intra-(inter-) ELM heat fluxes. We used C dust because of its high sublimation temperature and non-metal properties. Al dust as a surrogate for Be and W dust were employed as relevant to that in the ITER divertor. The poor initial thermal contact between the substrate and the particles led to overheating, sublimation and shrinking of the carbon dust, and wetting induced coagulation of Al dust. Little modification of the W dust was observed. An enhanced surface adhesion and improvement of the thermal contact of C and Al dust were the result of exposure. A post mortem "adhesive tape" sampling showed that 70% of Al, <5% of W and C particles could not be removed from the surface owing to the improved adhesion. Al and C but not W particles that could be lifted had W inclusions indicating damage to the substrate. This suggests that non destructive methods may be inefficient for removal of dust in ITER.

  • 132.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ogata, Douglas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Collection of mobile dust in the T2R reversed field pinch2012In: Nukleonika, ISSN 0029-5922, E-ISSN 1508-5791, Vol. 57, no 1, p. 55-60Article in journal (Refereed)
    Abstract [en]

    Intensive plasma-wall interactions in fusion devices result in the impurity production and the formation of films of redeposited material, debris and dust. In present day devices, with short pulses, the mobile dust does not pose any serious operational problems, but it is a matter of serious concern for ITER and for later power producing devices with a high duty cycle. We report results of a dust collection experiment carried out at the T2R reversed field pinch device and related heavy impurity flux measurements. Dust and impurities were collected on passive Si surface probes and on ultralow density silica aerogel collectors. The advantage of the latter method is the possibility of nondestructive capture of the micron- and submicron-sized dust particles. The toroidal and radial deposition fluxes of dust particles and impurities are estimated and discussed in the light of the dominant forces acting on the dust.

  • 133.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Litnovsky, A.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Time resolved collection and characterization of dust particles moving in the TEXTOR scrape-off layer2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, no Suppl., p. S681-S685Article in journal (Refereed)
    Abstract [en]

    Moving dust has been collected in the SOL of TEXTOR in a time-resolved way with silica aerogel collectors [1-3]. The collectors were exposed to the toroidal particle flux in NBI heated discharges during the startup and flat top phase. Intrinsic dust was collected in several discharges. Other discharges were accompanied with injection of known amounts of pre-characterized dust (W, C flakes and C microspheres) from a position toroidally 120° away from the collector. Particle flux, composition and dust size distribution have been determined with SEM and EDX. Calibration allowed particle velocity estimates to be made. Upper limits for the deuterium content of individual dust grains have been determined by NRA.

  • 134.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Banon, Jean-Philippe
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Transport asymmetry and release mechanisms of metal dust in the reversed-field pinch configuration2014In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, no 3, p. 035014-Article in journal (Refereed)
    Abstract [en]

    Experimental data on dust resident in the EXTRAP T2R reversed-field pinch are reported. Mobile dust grains are captured in situ by silicon collectors, whereas immobile grains are sampled post mortem from the wall by adhesive tape. The simulation of collection asymmetries by the MIGRAINe dust dynamics code in combination with the experimental results is employed to deduce some characteristics of the mechanism of intrinsic dust release. All evidence suggests that re-mobilization is dominant with respect to dust production.

  • 135.
    Calabro, G.
    et al.
    Univ Tuscia, Dept Econ Engn Soc & Business Org DEIm, Largo Univ Snc, I-01100 Viterbo, Italy.;ENEA C R Frascati, Unit Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Minucci, S.
    Univ Tuscia, Dept Econ Engn Soc & Business Org DEIm, Largo Univ Snc, I-01100 Viterbo, Italy.;Univ Napoli Federico II, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Bergsåker, Henric
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Divertor currents optimization procedure for JET-ILW high flux expansion experiments2018In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 129, p. 115-119Article in journal (Refereed)
    Abstract [en]

    This paper deals with a divertor coil currents optimized procedure to design High Flux Expansion (HFE) configurations in the JET tokamak aimed to study the effects of flux expansion variation on the radiation fraction and radiated power re-distribution. A number of benefits of HFE configuration have been experimentally demonstrated on TCV, EAST, NSTX and DIII-D tokamaks and are under investigation for next generation devices, as DEMO and DTT. The procedure proposed here exploits the linearized relation between the plasma-wall gaps and the Poloidal Field (PF) coil currents. Once the linearized model is provided by means of CREATE-NL code, the divertor coils currents are calculated using a constrained quadratic programming optimization procedure, in order to achieve HFE configuration. Flux expanded configurations have been experimentally realized both in ohmic and heated plasma with and without nitrogen seeding. Preliminary results on the effects of the flux expansion variation on total power radiation increase will be also briefly discussed.

  • 136. Cao, D.
    et al.
    Fu, H. S.
    Cao, J. B.
    Wang, T. Y.
    Graham, D. B.
    Chen, Z. Z.
    Peng, F. Z.
    Huang, S. Y.
    Khotyaintsev, Y. V.
    Andre, M.
    Russell, C. T.
    Giles, B. L.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Torbert, R. B.
    Ergun, R. E.
    Le Contel, O.
    Burch, J. L.
    MMS observations of whistler waves in electron diffusion region2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 9, p. 3954-3962Article in journal (Refereed)
    Abstract [en]

    Whistler waves that can produce anomalous resistivity by affecting electrons' motion have been suggested as one of the mechanisms responsible for magnetic reconnection in the electron diffusion region (EDR). Such type of waves, however, has rarely been observed inside the EDR so far. In this study, we report such an observation by Magnetospheric Multiscale (MMS) mission. We find large-amplitude whistler waves propagating away from the X line with a very small wave-normal angle. These waves are probably generated by the perpendicular temperature anisotropy of the -300eV electrons inside the EDR, according to our analysis of dispersion relation and cyclotron resonance condition; they significantly affect the electron-scale dynamics of magnetic reconnection and thus support previous simulations.

  • 137.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Dark mammoth trunks in the merging galaxy NGC 1316 and a mechanism of cosmic double helices2010In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 327, no 2, p. 267-278Article in journal (Refereed)
    Abstract [en]

    NGC 1316 is a giant, elliptical galaxy containing a complex network of dark, dust features. The morphology of these features has been examined in some detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is found that most of the features are constituted of long filaments. There also exist a great number of dark structures protruding inwards from the filaments. Many of these structures are strikingly similar to elephant trunks in H ii regions in the Milky Way Galaxy, although much larger. The structures, termed mammoth trunks, generally are filamentary and often have shapes resembling the letters V or Y. In some of the mammoth trunks the stem of the Y can be resolved into two or more filaments, many of which showing signs of being intertwined. A model of the mammoth trunks, related to a recent theory of elephant trunks, is proposed. Based on magnetized filaments, the model is capable of giving an account of the various shapes of the mammoth trunks observed, including the twined structures.

  • 138.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Model of outgrowths in the spiral galaxies NGC 4921 and NGC 7049 and the origin of spiral arms2013In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 343, no 2, p. 689-712Article in journal (Refereed)
    Abstract [en]

    NGC 4921 and 7049 are two spiral galaxies presenting narrow, distinct dust features. A detailed study of the morphology of those features has been carried out using Hubble Space Telescope archival images. NGC 4921 shows a few but well-defined dust arms midway to its centre while NGC 7049 displays many more dusty features, mainly collected within a ring-shaped formation. Numerous dark and filamentary structures, called outgrowths, are found to protrude from the dusty arms in both galaxies. The outgrowths point both outwards and inwards in the galaxies. Mostly they are found to be V-shaped or Y-shaped with the branches connected to dark arm filaments. Often the stem of the Y appears to consist of intertwined filaments. Remarkably, the outgrowths show considerable similarities to elephant trunks in H ii regions. A model of the outgrowths, based on magnetized filaments, is proposed. The model provides explanations of both the shapes and orientations of the outgrowths. Most important, it can also give an account for their intertwined structures. It is found that the longest outgrowths are confusingly similar to dusty spiral arms. This suggests that some of the outgrowths can develop into such arms. The time-scale of the development is estimated to be on the order of the rotation period of the arms or shorter. Similar processes may also take place in other spiral galaxies. If so, the model of the outgrowths can offer a new approach to the old winding problem of spiral arms.

  • 139.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Twisted Crab fingers revisited2015In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 357, no 1, article id 47Article in journal (Refereed)
    Abstract [en]

    Narrowband images of the Crab Nebula captured by the Hubble Space Telescope have earlier shown that the nebula does not only present a network of broad, bright filaments crossing the nebula but also numerous so-called fingers mostly pointing inwards. Using archival Hubble images we have in some detail studied the morphology of a great number of such fingers. This scrutiny has revealed that practically all the fingers are made up of filaments. Most of the larger fingers show overall shapes that are similar to either of the two letters V and Y. In many of these fingers it is also possible to see internal details. Interestingly, a number of the larger, Y-shaped fingers turn out to have a stem that consists of intertwined filaments. By contrast with this, the smaller fingers usually appear only as diffuse and sometimes incomplete pegs. In none of the smaller fingers is it possible to find any plain, internal structure. The observational results obtained are compared with the properties of a previously proposed model of the fingers. The model suggests that the fingers have evolved out of magnetized filaments. The evolution should lead to fingers with overall shapes that are similar to either a V or a Y, very much in agreement with the observations. In addition to this, the model prescribes that the stems of the Y-shaped fingers should be made up of intertwined filaments. From all these points of agreement we conclude that the properties of the fingers observed lend strong support to the model.

  • 140.
    Carnevale, D.
    et al.
    Univ Roma Tor Vergata, Dept Ing Civile & Informat, Rome, Italy..
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Runaway electron beam control2019In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, no 1, article id 014036Article in journal (Refereed)
    Abstract [en]

    Post-disruption runaway electron (RE) beams in tokamaks with large current can cause deep melting of the vessel and are one of the major concerns for ITER operations. Consequently, a considerable effort is provided by the scientific community in order to test RE mitigation strategies. We present an overview of the results obtained at FTU and TCV controlling the current and position of RE beams to improve safety and repeatability of mitigation studies such as massive gas (MGI) and shattered pellet injections (SPI). We show that the proposed RE beam controller (REB-C) implemented at FTU and TCV is effective and that current reduction of the beam can be performed via the central solenoid reducing the energy of REs, providing an alternative/parallel mitigation strategy to MGI/SPI. Experimental results show that, meanwhile deuterium pellets injected on a fully formed RE beam are ablated but do not improve RE energy dissipation rate, heavy metals injected by a laser blow off system on low-density flat-top discharges with a high level of RE seeding seem to induce disruptions expelling REs. Instabilities during the RE beam plateau phase have shown to enhance losses of REs, expelled from the beam core. Then, with the aim of triggering instabilities to increase RE losses, an oscillating loop voltage has been tested on RE beam plateau phase at TCV revealing, for the first time, what seems to be a full conversion from runaway to ohmic current. We finally report progresses in the design of control strategies at JET in view of the incoming SPI mitigation experiments.

  • 141.
    Carralero, D.
    et al.
    EURATOM, Max Planck Inst Plasmaphys, D-14476 Garching, Germany.;Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Olivares, Pablo Vallejos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushun
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics. KTH, Fusion Plasma Phys, EES, SE-10044 Stockholm, Sweden..
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Recent progress towards a quantitative description of filamentary SOL transport2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 5, article id 056044Article in journal (Refereed)
    Abstract [en]

    A summary of recent results on filamentary transport, mostly obtained with the ASDEX-Upgrade tokamak (AUG), is presented and discussed in an attempt to produce a coherent picture of scrape-off layer (SOL) filamentary transport. A clear correlation is found between L-mode density shoulder formation in the outer midplane and a transition between the sheath-limited and the inertial filamentary regimes. Divertor collisionality is found to be the parameter triggering the transition. A clear reduction of the ion temperature takes place in the far SOL after the transition, both for the background and the filaments. This coincides with a strong variation of the ion temperature distribution, which deviates from Gaussianity and becomes dominated by a strong peak below 5 eV. The filament transition mechanism triggered by a critical value of collisionality seems to be generally applicable to inter-ELM H-mode plasmas, although a secondary threshold related to deuterium fueling is observed. EMC3-EIRENE simulations of neutral dynamics show that an ionization front near the main chamber wall is formed after the shoulder formation. Finally, a clear increase of SOL opacity to neutrals is observed, associated with the shoulder formation. A common SOL transport framework is proposed to account for all these results, and their potential implications for future generation devices are discussed.

  • 142. Carter, J. A.
    et al.
    Milan, S. E.
    Fear, R. C.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hairston, M. R.
    Dayside reconnection under interplanetary magnetic field B-y-dominated conditions: The formation and movement of bending arcs2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 4, p. 2967-2978Article in journal (Refereed)
    Abstract [en]

    Based upon a survey of global auroral images collected by the Polar Ultraviolet Imager, Kullen etal. (2002) subdivided polar cap auroral arcs into a number of categories, including that of bending arcs. We are concerned with those bending arcs that appear as a bifurcation of the dayside auroral oval and which subsequently form a spur intruding into the polar cap. Once formed, the spur moves poleward and antisunward over the lifetime of the arc. We propose that dayside bending arcs are ionospheric signatures of pulses of dayside reconnection and are therefore part of a group of transient phenomena associated with flux transfer events. We observe the formation and subsequent motion of a bending arc across the polar cap during a 30 min interval on 8 January 1999, and we show that this example is consistent with the proposed model. We quantify the motion of the arc and find it to be commensurate with the convection flows observed by both ground-based radar observations and space-based particle flow measurements. In addition, precipitating particles coincident with the arc appear to occur along open field lines, lending further support to the model.

  • 143. Castaldo, C.
    et al.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angeli, M.
    de Angelis, U.
    On the feasibility of electro-optical detection of dust-impact ionization in tokamaks2010In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 52, no 10, p. 105003-Article in journal (Refereed)
    Abstract [en]

    The feasibility of the optical and electrical detection of dust-impact ionization events in the scrape-off layers of tokamak plasmas is evaluated. It is shown that the expected light emission and the charge released during a dust impact on a biased target can be measured above the light emission and the charge collected due to the background plasma. A scheme of an electro-optical probe for diagnostics of fast dust particles is proposed.

  • 144. Castaldo, C.
    et al.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Pericoli, V.
    Rypdal, K.
    De Angelis, U.
    Morfill, G. E.
    Pieroni, L.
    Capobianco, G.
    De Angeli, M.
    Gabellieri, L.
    Giovannozzi, E.
    Maddaluno, G.
    Marmolino, C.
    Orsitto, F.
    Romano, A.
    Rufoloni, A.
    Tuccillo, A. A.
    Fast dust particles in tokamak plasmas: Detection and effects2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, European Physical Society , 2007, no 2, p. 848-851Conference paper (Refereed)
  • 145. Castaldo, C.
    et al.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Pericoli, V.
    de Angelis, U.
    Rypdal, K.
    Pieroni, L.
    Giovannozzi, E.
    Maddaluno, G.
    Marmolino, C.
    Rufoloni, A.
    Tuccillo, A.
    Kretschmer, M.
    Morfill, G. E.
    Diagnostics of fast dust particles in tokamak edge plasmas2007In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, no 7, p. L5-L9Article in journal (Refereed)
    Abstract [en]

    The use of electrostatic probes as a diagnostic tool of the dust particles in the tokamak edge plasmas is investigated. Probe measurements of electrostatic fluctuations in the scrape-off layer of the Frascati Tokamak Upgrade revealed that some features of the signals can be explained only by a local non-propagating phenomenon. These signal features are shown to be both in qualitative and quantitative agreement with ionization, and consequent extra charge collected by the probes, due to the impact of micrometre-sized dust at a velocity of the order of 10 km s(- 1). Electron microscope analysis of the probe surface yielded direct support for such an interpretation.

  • 146. Cattell, C.
    et al.
    Breneman, A.
    Colpitts, C.
    Dombeck, J.
    Thaller, S.
    Tian, S.
    Wygant, J.
    Fennell, J.
    Hudson, M. K.
    Ergun, Robert
    Russell, C. T.
    Torbert, Roy
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Burch, J.
    Dayside response of the magnetosphere to a small shock compression: Van Allen Probes, Magnetospheric MultiScale, and GOES-132017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 17, p. 8712-8720, article id L074895Article in journal (Refereed)
    Abstract [en]

    Observations from Magnetospheric MultiScale (similar to 8 Re) and Van Allen Probes (similar to 5 and 4 Re) show that the initial dayside response to a small interplanetary shock is a double-peaked dawnward electric field, which is distinctly different from the usual bipolar (dawnward and then duskward) signature reported for large shocks. The associated ExB flow is radially inward. The shock compressed the magnetopause to inside 8 Re, as observed by Magnetospheric MultiScale (MMS), with a speed that is comparable to the ExB flow. The magnetopause speed and the ExB speeds were significantly less than the propagation speed of the pulse from MMS to the Van Allen Probes and GOES-13, which is consistent with the MHD fast mode. There were increased fluxes of energetic electrons up to several MeV. Signatures of drift echoes and response to ULF waves also were seen. These observations demonstrate that even very weak shocks can have significant impact on the radiation belts. Plain Language Summary Very fast moving clouds of charged particles are ejected from the Sun when it is active. Shock waves often develop at the cloud front as it plows through the solar wind. When the shock hits the Earth's magnetic field, it can push the Earth's magnetic shield inside the distance where many communication and weather satellites orbit. The energy associated with the shock can also very rapidly increase the energy of electrons trapped in the Earth's magnetic field in the Van Allen Radiation belts. These electrons can damage satellites. We have used four satellites arrayed at different locations on the dayside of the Earth's magnetic field to show, for the first time, that small shocks have a different effect than the large shocks that are usually studied but that even small shocks can produce relativistic electrons.

  • 147. Chasapis, A.
    et al.
    Matthaeus, W. H.
    Parashar, T. N.
    Lecontel, O.
    Retinò, A.
    Breuillard, H.
    Khotyaintsev, Y.
    Vaivads, Andris
    Lavraud, B.
    Eriksson, E.
    Moore, T. E.
    Burch, J. L.
    Torbert, R. B.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ergun, R. E.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Goodrich, K. A.
    Wilder, F. D.
    Chutter, M.
    Needell, J.
    Rau, D.
    Dors, I.
    Russell, C. T.
    Le, G.
    Magnes, W.
    Strangeway, R. J.
    Bromund, K. R.
    Leinweber, H. K.
    Plaschke, F.
    Fischer, D.
    Anderson, B. J.
    Pollock, C. J.
    Giles, B. L.
    Paterson, W. R.
    Dorelli, J.
    Gershman, D. J.
    Avanov, L.
    Saito, Y.
    Electron Heating at Kinetic Scales in Magnetosheath Turbulence2017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 836, no 2, article id 247Article in journal (Refereed)
    Abstract [en]

    We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth's magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet.

  • 148. Chen, L. -J
    et al.
    Hesse, M.
    Wang, S.
    Gershman, D.
    Ergun, R. E.
    Burch, J.
    Bessho, N.
    Torbert, R. B.
    Giles, B.
    Webster, J.
    Pollock, C.
    Dorelli, J.
    Moore, T.
    Paterson, W.
    Lavraud, B.
    Strangeway, R.
    Russell, C.
    Khotyaintsev, Y.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Avanov, L.
    Electron diffusion region during magnetopause reconnection with an intermediate guide field: Magnetospheric multiscale observations2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 5, p. 5235-5246Article in journal (Refereed)
    Abstract [en]

    An electron diffusion region (EDR) in magnetic reconnection with a guide magnetic field approximately 0.2 times the reconnecting component is encountered by the four Magnetospheric Multiscale spacecraft at the Earth's magnetopause. The distinct substructures in the EDR on both sides of the reconnecting current sheet are visualized with electron distribution functions that are 2 orders of magnitude higher cadence than ever achieved to enable the following new findings: (1) Motion of the demagnetized electrons plays an important role to sustain the reconnection current and contributes to the dissipation due to the nonideal electric field, (2) the finite guide field dominates over the Hall magnetic field in an electron-scale region in the exhaust and modifies the electron flow dynamics in the EDR, (3) the reconnection current is in part carried by inflowing field-aligned electrons in the magnetosphere part of the EDR, and (4) the reconnection electric field measured by multiple spacecraft is uniform over at least eight electron skin depths and corresponds to a reconnection rate of approximately 0.1. The observations establish the first look at the structure of the EDR under a weak but not negligible guide field.

  • 149. Chernouss, S.
    et al.
    Alpatov, V.
    Demekhov, A.
    Deehr, C.
    Brandström, U.
    Widell, O.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Koustov, A.
    Pirjola, R.
    Sergienko, T.
    Sandahl, I.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Project "Development of the Methodology of Experiment and Technical Support for Studies of the Flow Cyclotron Maser in the Earth's Magnetosphere by Creating an Artificial Ionization Cloud From a Geophysical Rocket"2012In: Óptica Pura y Aplicada, ISSN 0030-3917, E-ISSN 2171-8814, Vol. 45, no 1, p. 45-49Article in journal (Refereed)
    Abstract [en]

    Investigation of the wave particle interaction in the magnetosphere and ionosphere by controllable experiment in near Earth space is in focus of modern space geophysics. We propose to stimulate auroral precipitation by changing parameters of the Flow Cyclotron Maser (FCM) and test the FCM model itself. One of the main goals of the project is inducing of artificial pulsating aurora.

  • 150.
    Chosson, Gaël
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Miniaturization of a spacecraft magnetometer using multichip module technique2008Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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