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  • 1. Abdelsalam, UM
    et al.
    Moslem, WM
    Shukla, Padma Kant
    Umeå University, Faculty of Science and Technology, Department of Physics. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Nonlinear Physics Centre & Center for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für Extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto Superior Técnico, 1049-001 Lisbon, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, UK; SUPA Department of Physics, University of Strathclyde, Glasgow G 40NG, UK; School of Physics, Faculty of Science & Agriculture, University of Kwazulu-Natal, Durban 4000, South Africa; Department of Physics, CITT, Islamabad, Pakistan.
    Localized electrostatic excitations in a Thomas-Fermi plasma containing degenerate electrons2008In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, no 5, article id 052303Article in journal (Refereed)
    Abstract [en]

    By using the Thomas-Fermi electron density distribution for quantum degenerate electrons, the hydrodynamic equations for ions, and the Poisson equation, planar and nonplanar ion-acoustic solitary waves in an unmagnetized collisionless plasma are investigated. The reductive perturbation method is used to derive cylindrical and spherical Korteweg-de Vries equations. Numerical solutions of the latter are presented. The present results can be useful in understanding the features of small but finite amplitude localized ion-acoustic solitary pulses in a degenerate plasma.

  • 2. Adhikary, N C
    et al.
    Misra, Amar P
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bailung, H
    Chutia, J
    Ion-beam driven dust ion-acoustic solitary waves in dusty plasmas2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 4, article id 044502Article in journal (Refereed)
    Abstract [en]

    The nonlinear propagation of small but finite amplitude dust ion-acoustic waves (DIAWs) in an ion-beam driven plasma consisting of Boltzmannian electrons, positive ions, and stationary negatively charged dust grains is studied by using the standard reductive perturbation technique. It is shown that there exist two critical values (γc1) and (γc2) of ion beam to ion phase velocity ratio (γ), above and below which the beam generated solitons are not possible. The effects of the parameters, namely, γ, the ratio of the ion beam to plasma ion density (μi), the dust to ion density ratio (μd), and the ion beam to plasma ion mass ratio (μ) on both the amplitude and width of the stationary DIAWs, are analyzed numerically, and applications of the results to laboratory ion beam as well as space plasmas (e.g., auroral plasmas) are explained.

  • 3. Ali, S
    et al.
    Moslem, W.M.
    Shukla, P.K.
    Umeå University, Faculty of Science and Technology, Physics.
    Schlickeiser, R.
    Linear and nonlinear ion-acoustic waves in an unmagnetized electron-positron-ion quantum plasma2007In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, p. 82307-Article in journal (Refereed)
  • 4. Ali, S
    et al.
    Shukla, Padma K
    Umeå University, Faculty of Science and Technology, Department of Physics. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck Institut für extraterrestrische Physik, D-85741 Garching, Germany, GoLP/Instituto Superior Técnico, 1049-001 Lisbon, Portugal, Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom, and Department of Physics, University of Strathclyde, Glasgow, Scotland, United Kingdom .
    Dust acoustic solitary waves in a quantum plasma2006In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 2, article id 022313Article in journal (Refereed)
    Abstract [en]

    By employing one-dimensional quantum hydrodynamic (QHD) model for a three species quantum plasma, nonlinear properties of dust acoustic solitary waves are studied. For this purpose a Korteweg-de Vries (KdV) equation is derived, incorporating quantum corrections. The quantum mechanical effects are also examined numerically both on the profiles of the amplitude and the width of dust acoustic solitary waves. It is found that the amplitude remains constant but the width shrinks for different values of a dimensionless electron quantum parameter H-e=root(Z(d0)h(2)omega(2)(pd))/m(e)m(d)C(d)(4), where Z(d0) is the dust charge state, h is the Planck constant divided by 2 pi, omega(pd) is the dust plasma frequency, m(e) (m(d)) is the electron (dust) mass, and C-d is the dust acoustic speed.

  • 5. Ali, S
    et al.
    Shukla, Padma Kant
    Umeå University, Faculty of Science and Technology, Department of Physics. Institut für Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck Institut für extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto Superior Técnico, 1049-001 Lisbon, Portugal; Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom; Department of Physics, University of Strathclyde, Glasgow, Scotland, United Kingdom.
    Dispersion properties of compressional electromagnetic waves in quantum dusty magnetoplasmas2006In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 5, article id 052113Article in journal (Refereed)
    Abstract [en]

    A new dispersion relation for low-frequency compressional electromagnetic waves is derived by employing quantum magnetohydrodynamic model and Maxwell equations in cold quantum dusty magnetoplasmas. The latter is composed of inertialess electrons, mobile ions, and immobile charged dust particulates. The dispersion relation for the low-frequency compressional electromagnetic modes is further analyzed for the waves propagating parallel, perpendicular, and oblique to the external magnetic field direction. It is found theoretically and numerically that the quantum parameter alpha(q)=(n(i0)/n(e0))h(2)/(4m(e)m(i)) affects the real angular frequencies and the phase speeds of the compressional electromagnetic modes. Here, n(i0) (n(e0)) is the equilibrium number density of the ions (electrons), m(e) (m(i)) is the electron (ion) mass, and h is the Plank constant divided by 2 pi.

  • 6. Amole, C.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Butler, E.
    Capra, A.
    Cesar, C. L.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Little, A.
    Madsen, N.
    McKenna, J. T. K.
    Menary, S.
    Napoli, S. C.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sarid, E.
    Shields, C. R.
    Silveira, D. M.
    So, C.
    Stracka, S.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Zhmoginov, A.
    Friedland, L.
    Experimental and computational study of the injection of antiprotons into a positron plasma for antihydrogen production2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 4, p. 043510-Article in journal (Refereed)
    Abstract [en]

    One of the goals of synthesizing and trapping antihydrogen is to study the validity of charge-parity-time symmetry through precision spectroscopy on the anti-atoms, but the trapping yield achieved in recent experiments must be significantly improved before this can be realized. Antihydrogen atoms are commonly produced by mixing antiprotons and positrons stored in a nested Penning-Malmberg trap, which was achieved in ALPHA by an autoresonant excitation of the antiprotons, injecting them into the positron plasma. In this work, a hybrid numerical model is developed to simulate antiproton and positron dynamics during the mixing process. The simulation is benchmarked against other numerical and analytic models, as well as experimental measurements. The autoresonant injection scheme and an alternative scheme are compared numerically over a range of plasma parameters which can be reached in current and upcoming antihydrogen experiments, and the latter scheme is seen to offer significant improvement in trapping yield as the number of available antiprotons increases.

  • 7.
    Annibaldi, Silvia Valeria
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bonomo, F.
    Pasqualotto, R.
    Spizzo, G.
    Alfier, A.
    Buratti, P.
    Piovesan, P.
    Terranova, D.
    Strong transport reduction in the helical core of the reversed-field pinch2007In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, no 11, p. 112515-Article in journal (Refereed)
    Abstract [en]

    An explanation of the strong heating observed in the core of a reversed-field pinch in the quasi-single-helicity state is presented. A magnetic island is formed, in which the heat transport coefficient is much smaller than in the surrounding chaotic sea, because of the formation of well defined magnetic surfaces. The values of the thermal conductivity obtained with the M1TEV [F. Porcelli , Phys. Rev. Lett 82, 1458 (1999)] two-dimensional transport code are in very good agreement with the estimates of the ion diffusion coefficient inside the island, given by a Hamiltonian guiding center code. Moreover, the values of thermal conductivity are in the tokamak range, and are consistent with the peak temperatures measured in the Reversed Field eXperiment [P. Sonato , Fusion Eng. Des. 66-68, 161 (2003)] at Consorzio RFX, Padova, Italy. The effect of the island width and the different powers deposited inside the island on the final temperature peak are also investigated.

  • 8. Badziak, J
    et al.
    Mishra, G
    Gupta, N K
    Holkundkar, Amol
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Generation of ultraintense proton beams by multi-ps circularly polarized laser pulses for fast ignition-related applications2011In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, no 5, article id 053108Article in journal (Refereed)
    Abstract [en]

    A scheme of generation of ultraintense proton beams relevant for proton fast ignition (PFI) which employs multi-ps, circularly polarized laser pulse irradiating a thick (≥ 10 μm) H-rich target is proposed and examined using one-dimensional particle-in cell-simulations. It is shown that a 5-ps laser pulse of intensity ∼ (2–5) × 1020W/cm2 irradiating the target of the areal proton density ∼ 2 × 1020cm−2 can produce – with a high energetic efficiency – a proton beam (plasma block) of parameters (intensity, energy fluence, pulse duration, proton energy spectrum) close to those required for PFI. At a fixed total laser energy, the proton beam parameters can be controlled and fitted to the PFI requirements by changing the laser intensity (energy fluence) and/or the target thickness as well as by using a shaped (curved) target inserted into a guiding cone.

  • 9. Bains, AS
    et al.
    Misra, Amar P
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Saini, NS
    Gill, TS
    Modulational instability of ion-acoustic wave envelopes in magnetized quantum electron-positron-ion plasmas2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 1, article id 012103Article in journal (Refereed)
    Abstract [en]

    The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schroumldinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (mu), the normalized ion-cyclotron frequency (omega(c)) as well as the ratio (H) of the "plasmonic energy density" to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing mu or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.

  • 10.
    Bergman, Jan
    et al.
    Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden.
    Eliasson, Bengt
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Erratum:: "Linear wave dispersion laws in unmagnetized relativistic plasma: Analytical and numerical results" [Phys. Plasmas 8, 1482 (2001)]2009In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, no 12, p. 129902-Article in journal (Refereed)
  • 11.
    Bergman, Jan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Space Plasma Physics.
    Eliasson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing.
    Linear wave dispersion laws in unmagnetized relativistic plasma: Analytical and numerical results2001In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 8, p. 1482-1492Article in journal (Refereed)
  • 12. Beurskens, M N A
    et al.
    Osborne, T H
    Schneider, P A
    Wolfrum, E
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Groebner, R
    Lomas, P
    Nunes, I
    Saarelma, S
    Scannell, R
    Snyder, P B
    Zarzoso, D
    Balboa, I
    Bray, B
    Brix, M
    Flanagan, J
    Giroud, C
    Giovannozzi, E
    Kempenaars, M
    Loarte, A
    de la Luna, E
    Maddison, G
    Maggi, C F
    McDonald, D
    Pasqualotto, R
    Saibene, G
    Sartori, R
    Solano, E
    Walsh, M
    Zabeo, L
    Team, D I I I-D
    Team, ASDEX Upgrade
    Contributors, J E T-E F D A
    H-mode pedestal scaling in DIII-D, ASDEX Upgrade, and JET2011In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, no 5Article in journal (Refereed)
    Abstract [en]

    Multidevice pedestal scaling experiments in the DIII-D, ASDEX Upgrade (AUG), and JET tokamaks are presented in order to test two plasma physics pedestal width models. The first model proposes a scaling of the pedestal width Delta/a proportional to rho*(1/2) to rho* based on the radial extent of the pedestal being set by the point where the linear turbulence growth rate exceeds the E x B velocity. In the multidevice experiment where rho* at the pedestal top was varied by a factor of four while other dimensionless parameters where kept fixed, it has been observed that the temperature pedestal width in real space coordinates scales with machine size, and that therefore the gyroradius scaling suggested by the model is not supported by the experiments. The density pedestal width is not invariant with rho* which after comparison with a simple neutral fuelling model may be attributed to variations in the neutral fuelling patterns. The second model, EPED1, is based on kinetic ballooning modes setting the limit of the radial extent of the pedestal region and leads to Delta(psi) proportional to beta p(1/2). All three devices show a scaling of the pedestal width in normalised poloidal flux as Delta(psi) proportional to beta p(1/2), as described by the kinetic ballooning model; however, on JET and AUG, this could not be distinguished from an interpretation where the pedestal is fixed in real space. Pedestal data from all three devices have been compared with the predictive pedestal model EPED1 and the model produces pedestal height values that match the experimental data well.

  • 13. Bhowmik, C.
    et al.
    Bhowmik, A. P.
    Shukla, P.K.
    Umeå University, Faculty of Science and Technology, Physics.
    Oblique modulation of electron-acoustic waves in a Fermi electron-ion plasma2007In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, p. 122107-Article in journal (Refereed)
  • 14.
    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.

  • 15.
    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.

  • 16.
    Bret, Antoine
    et al.
    Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
    Dieckmann, Mark E
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Hierarchy of instabilities for two counter-streaming magnetized pair beams: Influence of field obliquity2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 6, article id 062105Article in journal (Refereed)
    Abstract [en]

    The hierarchy of unstable modes when two counter-streaming pair plasmas interact over a flow-aligned magnetic field has been recently investigated [Phys. Plasmas 23, 062122 (2016)]. The analysis is here extended to the case of an arbitrarily tilted magnetic field. The two plasma shells are initially cold and identical. For any angle θ ∈ [0, π/2] between the field and the initial flow, the hierarchy of unstable modes is numerically determined in terms of the initial Lorentz factor of the shells γ0, and the field strength as measured by a parameter denoted σ. For θ = 0, four different kinds of mode are likely to lead the linear phase. The hierarchy simplifies for larger θ's, partly because the Weibel instability can no longer be cancelled in this regime. For θ > 0.78 (44°) and in the relativistic regime, the Weibel instability always govern the interaction. In the non-relativistic regime, the hierarchy becomes θ-independent because the interaction turns to be field-independent. As a result, the two-stream instability becomes the dominant one, regardless of the field obliquity.

  • 17.
    Bret, Antoine
    et al.
    ETSI Ind Univ Castilla-La Mancha.
    Dieckmann, Mark E
    Ruhr-University Bochum.
    Ions motion effects on the full unstable spectrum in relativistic electron beam plasma interaction2008In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, no 1, p. 012104-1-12104-13Article in journal (Refereed)
    Abstract [en]

    A relativistic fluid model is implemented to assess the role of the ions motion in the linear phase of relativistic beam plasma electromagnetic instabilities. The all unstable wave vector spectrum is investigated, allowing us to assess how ion motions modify the competition between every possible instability. Beam densities up to the plasma one are considered. Due to the fluid approach, the temperatures must remain small, i.e., nonrelativistic. In the cold limit, ions motion affect the most unstable mode when the beam gamma factor bM/mi, being the beam to plasma density ratio, i the ion charge, M their mass, and m the electrons. The return current plays an important role by prompting Buneman-type instabilities which remain in the nonrelativistic regime up to high beam densities. Nonrelativistic temperatures only slightly affect these conclusions, except in the diluted beam regime where they can stabilize the Buneman modes.

  • 18.
    Bret, Antoine
    et al.
    ETSI Industriales Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
    Dieckmann, Mark E
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Relativistic electron beam driven instabilities in the presence of an arbitrarily oriented magnetic field2008In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, no 6, p. 062102-1-Article in journal (Refereed)
    Abstract [en]

    The electromagnetic instabilities driven by a relativistic electron beam, which moves through a magnetized plasma, are analyzed with a cold two-fluid model. It allows for any angle B between the beam velocity vector and the magnetic field vector and considers any orientation of the wavevector in the two-dimensional plane spanned by these two vectors. If the magnetic field is strong, the two-stream instability dominates if B=0 and the oblique modes grow faster at larger B. A weaker magnetic field replaces the two-stream modes with oblique modes as the fastest-growing waves. The threshold value separating both magnetic regimes is estimated. A further dimensionless parameter is identified, which determines whether or not the wavevector of the most unstable wave is changed continuously, as B is varied from 0 to /2. The fastest growing modes are always found for a transverse propagation of the beam with B=/2, irrespective of the magnetic field strength. ©2008 American Institute of Physics

  • 19.
    Bret, Antoine
    et al.
    ETSI Ind. Univ Castilla La Mancha, Spain.
    Dieckmann, Mark E
    Ruhr-University Bochum.
    Deutsch, Claude
    Phys Gaz Plasmas Lab CNRS-Orsay, France.
    Oblique electromagnetic instabilities for a hot relativistic beam interacting with a hot and magnetized plasma2006In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 8, p. 082109-1-082109-8Article in journal (Refereed)
    Abstract [en]

    The temperature-dependent fluid model from Phys. Plasmas 13, 042106 (2006) is expanded in order to explore the oblique electromagnetic instabilities, which are driven by a hot relativistic electron beam that is interpenetrating a hot and magnetized plasma. The beam velocity vector is parallel to the magnetic-field direction. The results are restricted to nonrelativistic temperatures. The growth rates of all instabilities but the two-stream instability can be reduced by a strong magnetic field so that the distribution of unstable waves becomes almost one dimensional. For high beam densities, highly unstable oblique modes dominate the spectrum of unstable waves as long as omega(c)/omega(p)less than or similar to 2 gamma(3/2)(b), where omega(c) is the electron gyrofrequency, omega(p) is the electron plasma frequency, and gamma(b) is the relativistic factor of the beam. A uniform stabilization over the entire k space cannot be achieved.

  • 20.
    Bret, Antoine
    et al.
    Universidad de Castilla-La Mancha, Spain.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    How large can the electron to proton mass ratio be in particle-in-cell simulations of unstable systems?2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 3, p. 032109-Article in journal (Refereed)
    Abstract [en]

    Particle-in-cell simulations are widely used as a tool to investigate instabilities that develop between a collisionless plasma and beams of charged particles. However, even on contemporary supercomputers, it is not always possible to resolve the ion dynamics in more than one spatial dimension with such simulations. The ion mass is thus reduced below 1836 electron masses, which can affect the plasma dynamics during the initial exponential growth phase of the instability and during the subsequent nonlinear saturation. The goal of this article is to assess how far the electron to ion mass ratio can be increased, without changing qualitatively the physics. It is first demonstrated that there can be no exact similarity law, which balances a change in the mass ratio with that of another plasma parameter, leaving the physics unchanged. Restricting then the analysis to the linear phase, a criterion allowing to define a maximum ratio is explicated in terms of the hierarchy of the linear unstable modes. The criterion is applied to the case of a relativistic electron beam crossing an unmagnetized electron-ion plasma.

  • 21.
    Bret, Antoine
    et al.
    ETSI Ind Univ Castilla-La Mancha.
    Gremillet, Laurent
    CEA, DAM, DIF, 91297 Arpajon, France.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Multidimensional electron beam-plasma instabilities in the relativistic regime2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 12, p. 120501-1-120501-36Article, review/survey (Refereed)
    Abstract [en]

    The interest in relativistic beam-plasma instabilities has been greatly rejuvenated over the past two decades by novel concepts in laboratory and space plasmas. Recent advances in this long-standing field are here reviewed from both theoretical and numerical points of view. The primary focus is on the two-dimensional spectrum of unstable electromagnetic waves growing within relativistic, unmagnetized, and uniform electron beam-plasma systems. Although the goal is to provide a unified picture of all instability classes at play, emphasis is put on the potentially dominant waves propagating obliquely to the beam direction, which have received little attention over the years. First, the basic derivation of the general dielectric function of a kinetic relativistic plasma is recalled. Next, an overview of two-dimensional unstable spectra associated with various beam-plasma distribution functions is given. Both cold-fluid and kinetic linear theory results are reported, the latter being based on waterbag and Maxwell–Jüttner model distributions. The main properties of the competing modes (developing parallel, transverse, and oblique to the beam) are given, and their respective region of dominance in the system parameter space is explained. Later sections address particle-in-cell numerical simulations and the nonlinear evolution of multidimensional beam-plasma systems. The elementary structures generated by the various instability classes are first discussed in the case of reduced-geometry systems. Validation of linear theory is then illustrated in detail for large-scale systems, as is the multistaged character of the nonlinear phase. Finally, a collection of closely related beam-plasma problems involving additional physical effects is presented, and worthwhile directions of future research are outlined.

  • 22.
    Brodin, G.
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nonlinear dynamics of a cold collisional electron plasma2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 12, article id 124505Article in journal (Refereed)
    Abstract [en]

    We study the influence of collisions on the dynamics of a cold non-relativistic plasma. It is shown that even a comparatively small collision frequency can significantly change the large amplitude wave solution. Published by AIP Publishing.

  • 23.
    Brodin, G.
    et al.
    Umea Univ, Dept Phys, SE-90187 Umea, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Nonlinear dynamics of large amplitude modes in a magnetized plasma2014In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, p. 122301-Article in journal (Refereed)
    Abstract [en]

    We derive two equations describing the coupling between electromagnetic and electrostaticoscillations in one-dimensional geometry in a magnetized cold and non-relativistic plasma. The nonlinear interaction between the wave modes is studied numerically. The effects of the external magnetic field strength and the initial electromagneticpolarization are of particular interest here. New results can, thus, be identified.

  • 24.
    Brodin, G.
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Three-wave coupling coefficients for perpendicular wave propagation in a magnetized plasma2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 10, article id 104503Article in journal (Refereed)
    Abstract [en]

    The resonant interaction between three waves in a uniform magnetized plasma is reconsidered. Starting from previous kinetic expressions, we limit our investigation to waves propagating perpendicularly to the external magnetic field. It is shown that reliable results can only be obtained in the two-dimensional case, i.e., when the wave vectors have both x and y components. (C) 2015 AIP Publishing LLC.

  • 25.
    Brodin, Gert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Marklund, Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Spin solitons in magnetized pair plasmas2007In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, no 11, p. 2107-4 sidorArticle in journal (Refereed)
    Abstract [en]

    A set of fluid equations, taking into account the spin properties of the electrons and positrons in a magnetoplasma, are derived. The magnetohydrodynamic limit of the pair plasma is investigated. It is shown that the microscopic spin properties of the electrons and positrons can lead to interesting macroscopic and collective effects in strongly magnetized plasmas. In particular, it is found that new Alfvénic solitary structures, governed by a modified Korteweg–de Vries equation, are allowed in such plasmas. These solitary structures vanish if the quantum spin effects are neglected. Our results should be of relevance for astrophysical plasmas, e.g., in pulsar magnetospheres, as well as for low-temperature laboratory plasmas.

  • 26.
    Brodin, Gert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stenflo, L.
    Nonlinear dynamics of a cold collisional electron plasma2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 12, article id 124505Article in journal (Refereed)
    Abstract [en]

    We study the influence of collisions on the dynamics of a cold non-relativistic plasma. It is shown that even a comparatively small collision frequency can significantly change the large amplitude wave solution.

  • 27.
    Brodin, Gert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stenflo, L.
    Nonlinear dynamics of large amplitude modes in a magnetized plasma2014In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, no 12, article id 122301Article in journal (Refereed)
    Abstract [en]

    We derive two equations describing the coupling between electromagnetic and electrostatic oscillations in one-dimensional geometry in a magnetized cold and non-relativistic plasma. The nonlinear interaction between the wave modes is studied numerically. The effects of the external magnetic field strength and the initial electromagnetic polarization are of particular interest here. New results can, thus, be identified. 

  • 28.
    Brodin, Gert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stenflo, L.
    Three-wave coupling coefficients for perpendicular wave propagation in a magnetized plasma2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 10, article id 104503Article in journal (Refereed)
    Abstract [en]

    The resonant interaction between three waves in a uniform magnetized plasma is reconsidered. Starting from previous kinetic expressions, we limit our investigation to waves propagating perpendicularly to the external magnetic field. It is shown that reliable results can only be obtained in the two-dimensional case, i.e., when the wave vectors have both x and y components. 

  • 29.
    Brunsell, Per. R.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Malmberg, Jenny-Ann
    KTH, Superseded Departments, Alfvén Laboratory.
    Yadikin, Dimitry
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Resistive wall modes in the EXTRAP T2R reversed-field pinch2003In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 10, p. 3823-Article in journal (Refereed)
    Abstract [en]

    Resistive wall modes (RWM) in the reversed field pinch are studied and a detailed comparison of experimental growth rates and linear magnetohydrodynamic (MHD) theory is made. RWM growth rates are experimentally measured in the thin shell device EXTRAP T2R [P. R. Brunsell , Plasma Phys. Controlled Fusion 43, 1 (2001)]. Linear MHD calculations of RWM growth rates are based on experimental equilibria. Experimental and linear MHD RWM growth rate dependency on the equilibrium profiles is investigated experimentally by varying the pinch parameter Theta=B-theta(a)/<B-phi> in the range Theta=1.5-1.8. Quantitative agreement between experimental and linear MHD growth rates is seen. The dominating RWMs are the internal on-axis modes (having the same helicity as the central equilibrium field). At high Theta, external nonresonant modes are also observed. For internal modes experimental growth rates decrease with Theta while for external modes, growth rates increase with Theta. The effect of RWMs on the reversed-field pinch plasma performance is discussed.

  • 30. Brunsell, Per R.
    et al.
    Olofsson, K. E. J.
    Frassinetti, L.
    Drake, James R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Resistive wall mode feedback control in EXTRAP T2R with improved steady-state error and transient response2007In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, no 10Article in journal (Refereed)
  • 31.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Marchiori, Giuseppe
    Feedback stabilization of resistive wall modes in a reversed-field pinch2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 9, p. 092508-Article in journal (Refereed)
    Abstract [en]

    An array of saddle coils having Nc =16 equally spaced positions along the toroidal direction has been installed for feedback control of resistive wall modes (RWMs) on the EXTRAP T2R reversed-field pinch [P. R. Brunsell, H. Bergsaker, M. Cecconello, Plasma Phys. Controlled Fusion 43, 1457 (2001)]. Using feedback, multiple nonresonant RWMs are simultaneously suppressed for three to four wall times. Feedback stabilization of RWMs results in a significant prolongation of the discharge duration. This is linked to a better sustainment of the plasma and tearing mode toroidal rotation with feedback. Due to the limited number of coils in the toroidal direction, pairs of modes with toroidal mode numbers n, n′ that fulfill the condition ∫n- n′ ∫ = Nc are coupled by the feedback action from the discrete coil array. With only one unstable mode in a pair of coupled modes, the suppression of the unstable mode is successful. If two modes are unstable in a coupled pair, two possibilities exist: partial suppression of both modes or, alternatively, complete stabilization of one target mode while the other is left unstable.

  • 32.
    Bychkov, Vitaly
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Modestov, Mikhail
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Marklund, Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Magnetohydrodynamic instability in plasmas with intrinsic magnetization2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 11, p. 112107-112112Article in journal (Refereed)
    Abstract [en]

    From a magnetofluid description with intrinsic magnetization, a new plasma instability is obtained. The plasma magnetization is produced by the collective electron spin. The instability develops in a nonuniform plasma when the electron concentration and temperature vary along an externally applied magnetic field. Alfvén waves play an important role in the instability. The instability properties are numerically investigated for a particular example of an ultrarelativistic degenerate plasma in exploding white dwarfs.

  • 33.
    Bychkov, Vitaly
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Modestov, Mikhail
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Marklund, Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The Darrieus-Landau instability in fast deflagration and laser ablation2008In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, no 3, p. 032702-Article in journal (Refereed)
    Abstract [en]

    The problem of the Darrieus-Landau instability at a discontinuous deflagration front in a compressible flow is solved. Numerous previous attempts to solve this problem suffered from the deficit of boundary conditions. Here, the required additional boundary condition is derived rigorously taking into account the internal structure of the front. The derived condition implies a constant mass flux at the front; it reduces to the classical Darrieus-Landau condition in the limit of an incompressible flow. It is demonstrated that in general the solution to the problem depends on the type of energy source in the flow. In the common case of a strongly localized source, compression effects make the Darrieus-Landau instability considerably weaker. Particularly, the instability growth rate is reduced for laser ablation in comparison to the classical incompressible case. The instability disappears completely in the Chapman-Jouguet regime of ultimately fast deflagration.

  • 34.
    Bychkov, Vitaly
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Modestov, Mikhail
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Marklund, Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The structure of weak shocks in quantum plasmas2008In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, no 3, p. 032309-032322Article in journal (Refereed)
    Abstract [en]

    The structure of a weak shock in a quantum plasma is studied, taking into account both dissipation terms due to thermal conduction and dispersive quantum terms due to the Bohm potential. Unlike quantum systems without dissipations, even a small thermal conduction may lead to a stationary shock structure. In the limit of zero quantum effects, the monotonic Burgers solution for the weak shock is recovered. Still, even small quantum terms make the structure nonmonotonic with the shock driving a train of oscillations into the initial plasma. The oscillations propagate together with the shock. The oscillations become stronger as the role of Bohm potential increases in comparison with thermal conduction. The results could be of importance for laser-plasma interactions, such as inertial confinement fusion plasmas, and in astrophysical environments, as well as in condensed matter systems.

  • 35.
    Candelaresi, Simon
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Astronomy.
    Hubbard, Alexander
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Brandenburg, Axel
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Astronomy.
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Magnetic helicity transport in the advective gauge family2011In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, no 1, p. 012903-Article in journal (Refereed)
    Abstract [en]

    Magnetic helicity fluxes are investigated in a family of gauges in which the contribution from ideal magnetohydrodynamics takes the form of a purely advective flux. Numerical simulations of magnetohydrodynamic turbulence in this advective gauge family exhibit instabilities triggered by the build-up of unphysical irrotational contributions to the magnetic vector potential. As a remedy, the vector potential is evolved in a numerically well behaved gauge, from which the advective vector potential is obtained by a gauge transformation. In the kinematic regime, the magnetic helicity density evolves similarly to a passive scalar when resistivity is small and turbulent mixing is mild, i.e., when the fluid Reynolds number is not too large. In the dynamical regime, resistive contributions to the magnetic helicity flux in the advective gauge are found to be significant owing to the development of small length scales in the irrotational part of the magnetic vector potential.

  • 36. Carolipio, E. M.
    et al.
    Heidbrink, W. W.
    Cheng, C. Z.
    Chu, M. S.
    Fu, G. Y.
    Jaun, André
    KTH, Superseded Departments, Alfvén Laboratory.
    Spong, D. A.
    Turnbull, A. D.
    White, R. B.
    The toroidicity-induced Alfven eigenmode structure in DIII-D: Implications of soft x-ray and beam-ion loss data2001In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 8, no 7, p. 3391-3401Article in journal (Refereed)
    Abstract [en]

    The internal structure of the toroidicity-induced Alfven eigenmode (TAE) is studied by comparing soft x-ray profile and beam ion loss data taken during TAE activity in the DIII-D tokamak [W. W. Heidbrink , Nucl. Fusion 37, 1411 (1997)] with predictions from theories based on ideal magnetohydrodynamic (MHD), gyrofluid, and gyrokinetic models. The soft x-ray measurements indicate a centrally peaked eigenfunction, a feature which is closest to the gyrokinetic model's prediction. The beam ion losses are simulated using a guiding center code. In the simulations, the TAE eigenfunction calculated using the ideal MHD model acts as a perturbation to the equilibrium field. The predicted beam ion losses are an order of magnitude less than the observed similar to6%-8% losses at the peak experimental amplitude of deltaB(r)/B(0)similar or equal to2-5x10(-4).

  • 37. Cazzola, E.
    et al.
    Curreli, D.
    Markidis, Stefano
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Lapenta, G.
    On the ions acceleration via collisionless magnetic reconnection in laboratory plasmas2016In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 23, no 11, article id 112108Article in journal (Refereed)
    Abstract [en]

    This work presents an analysis of the ion outflow from magnetic reconnection throughout fully kinetic simulations with typical laboratory plasma values. A symmetric initial configuration for the density and magnetic field is considered across the current sheet. After analyzing the behavior of a set of nine simulations with a reduced mass ratio and with a permuted value of three initial electron temperatures and magnetic field intensity, the best ion acceleration scenario is further studied with a realistic mass ratio in terms of the ion dynamics and energy budget. Interestingly, a series of shock wave structures are observed in the outflow, resembling the shock discontinuities found in recent magnetohydrodynamic simulations. An analysis of the ion outflow at several distances from the reconnection point is presented, in light of possible laboratory applications. The analysis suggests that magnetic reconnection could be used as a tool for plasma acceleration, with applications ranging from electric propulsion to production of ion thermal beams. © 2016 Author(s).

  • 38. Cazzola, E.
    et al.
    Innocenti, M. E.
    Markidis, Stefano
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz). KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Goldman, M. V.
    Newman, D. L.
    Lapenta, G.
    On the electron dynamics during island coalescence in asymmetric magnetic reconnection2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 9, article id 092901Article in journal (Refereed)
    Abstract [en]

    We present an analysis of the electron dynamics during rapid island merging in asymmetric magnetic reconnection. We consider a doubly periodic system with two asymmetric transitions. The upper layer is an asymmetric Harris sheet of finite width perturbed initially to promote a single reconnection site. The lower layer is a tangential discontinuity that promotes the formation of many X-points, separated by rapidly merging islands. Across both layers, the magnetic field and the density have a strong jump, but the pressure is held constant. Our analysis focuses on the consequences of electron energization during island coalescence. We focus first on the parallel and perpendicular components of the electron temperature to establish the presence of possible anisotropies and non-gyrotropies. Thanks to the direct comparison between the two different layers simulated, we can distinguish three main types of behavior characteristic of three different regions of interest. The first type represents the regions where traditional asymmetric reconnections take place without involving island merging. The second type of regions instead shows reconnection events between two merging islands. Finally, the third regions identify the regions between two diverging island and where typical signature of reconnection is not observed. Electrons in these latter regions additionally show a flat-top distribution resulting from the saturation of a two-stream instability generated by the two interacting electron beams from the two nearest reconnection points. Finally, the analysis of agyrotropy shows the presence of a distinct double structure laying all over the lower side facing the higher magnetic field region. This structure becomes quadrupolar in the proximity of the regions of the third type. The distinguishing features found for the three types of regions investigated provide clear indicators to the recently launched Magnetospheric Multiscale NASA mission for investigating magnetopause reconnection involving multiple islands.

  • 39. Chapman, I. T.
    et al.
    Liu, Y. Q.
    Asunta, O.
    Graves, J. P.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Jucker, M.
    Kinetic damping of resistive wall modes in ITER2012In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, no 5, p. 052502-Article in journal (Refereed)
    Abstract [en]

    Full drift kinetic modelling including finite orbit width effects has been used to assess the passive stabilisation of the resistive wall mode (RWM) that can be expected in the ITER advanced scenario. At realistic plasma rotation frequency, the thermal ions have a stabilising effect on the RWM, but the stability limit remains below the target plasma pressure to achieve Q = 5. However, the inclusion of damping arising from the fusion-born alpha particles, the NBI ions, and ICRH fast ions extends the RWM stability limit above the target beta for the advanced scenario. The fast ion damping arises primarily from finite orbit width effects and is not due to resonance between the particle frequencies and the instability.

  • 40. Chen, Li-Jen
    et al.
    Bessho, Naoki
    Lefebvre, Bertrand
    Vaith, Hans
    Asnes, Arne
    Santolik, Ondrej
    Fazakerley, Andrew
    Puhl-Quinn, Pamela
    Bhattacharjee, Amitava
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Daly, Patrick
    Torbert, Roy
    Multispacecraft observations of the electron current sheet, neighboring magnetic islands, and electron acceleration during magnetotail reconnection2009In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, no 5, p. 056501-Article in journal (Refereed)
    Abstract [en]

    Open questions concerning structures and dynamics of diffusion regions and electron acceleration in collisionless magnetic reconnection are addressed based on data from the four-spacecraft mission Cluster and particle-in-cell simulations. Using time series of electron distribution functions measured by the four spacecraft, distinct electron regions around a reconnection layer are mapped out to set the framework for studying diffusion regions. A spatially extended electron current sheet (ecs), a series of magnetic islands, and bursts of energetic electrons within islands are identified during magnetotail reconnection with no appreciable guide field. The ecs is collocated with a layer of electron-scale electric fields normal to the ecs and pointing toward the ecs center plane. Both the observed electron and ion densities vary by more than a factor of 2 within one ion skin depth north and south of the ecs, and from the ecs into magnetic islands. Within each of the identified islands, there is a burst of suprathermal electrons whose fluxes peak at density compression sites [L.-J. Chen , Nat. Phys. 4, 19 (2008)] and whose energy spectra exhibit power laws with indices ranging from 6 to 7.3. These results indicate that the in-plane electric field normal to the ecs can be of the electron scale at certain phases of reconnection, electrons and ions are highly compressible within the ion diffusion region, and for reconnection involving magnetic islands, primary electron acceleration occurs within the islands.

  • 41.
    Dahlin, Jon-Erik
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Scheffel, Jan
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    A novel feedback algorithm for simulating controlled dynamics and confinement in the advanced reversed-field pinch2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 6, p. 062502-Article in journal (Refereed)
    Abstract [en]

    In the advanced reversed-field pinch (RFP), the current density profile is externally controlled to diminish tearing instabilities. Thus the scaling of energy confinement time with plasma current and density is improved substantially as compared to the conventional RFP. This may be numerically simulated by introducing an ad hoc electric field, adjusted to generate a tearing mode stable parallel current density profile. In the present work a current profile control algorithm, based on feedback of the fluctuating electric field in Ohm's law, is introduced into the resistive magnetohydrodynamic code DEBSP [D. D. Schnack and D. C. Baxter, J. Comput. Phys. 55, 485 (1984); D. D. Schnack, D. C. Barnes, Z. Mikic, D. S. Marneal, E. J. Caramana, and R. A. Nebel, Comput. Phys. Commun. 43, 17 (1986)]. The resulting radial magnetic field is decreased considerably, causing an increase in energy confinement time and poloidal beta. It is found that the parallel current density profile spontaneously becomes hollow, and that a formation, being related to persisting resistive g modes, appears close to the reversal surface.

  • 42.
    Daldorff, L. K. S.
    et al.
    University of Michigan.
    Pecseli, H. L.
    University of Oslo.
    Trulsen, J. K.
    University of Oslo.
    Ulriksen, M. I.
    Norwegian Water Resources and Energy Directorate.
    Eliasson, B.
    Ruhr University Bochum.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines2011In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, no 5, p. 052107-Article in journal (Refereed)
    Abstract [en]

    Observations by, for instance, the EISCAT Svalbard Radar (ESR) demonstrate that the symmetry of the naturally occurring ion line in the polar ionosphere can be broken by an enhanced, nonthermal, level of fluctuations (naturally enhanced ion-acoustic lines, NEIALs). It was in many cases found that the entire ion spectrum can be distorted, also with the appearance of a third line, corresponding to a propagation velocity significantly slower than the ion acoustic sound speed. It has been argued that selective decay of beam excited primary Langmuir waves can explain some phenomena similar to those observed. We consider a related model, suggesting that a primary nonlinear process can be an oscillating two-stream instability, generating a forced low frequency mode that does not obey any ion sound dispersion relation. At later times, the decay of Langmuir waves can give rise also to enhanced asymmetric ion lines. The analysis is based on numerical results, where the initial Langmuir waves are excited by a cold dilute electron beam. By this numerical approach, we can detect fine details of the physical processes, in particular, demonstrate a strong space-time intermittency of the electron waves in agreement with observations. Our code solves the full Vlasov equation for electrons and ions, with the dynamics coupled through the electrostatic field derived from Poissons equation. The analysis distinguishes the dynamics of the background and beam electrons. This distinction simplifies the analysis for the formulation of the weakly nonlinear analytical model for the oscillating two-stream instability. The results have general applications beyond their relevance for the ionospheric observations.

  • 43. Daldorff, LKS
    et al.
    Pecseli, HL
    Trulsen, JK
    Ulriksen, MI
    Eliasson, Bengt
    Stenflo, Lennart
    Department of Physics, Linköping University, SE-58183 Linköping, Sweden .
    Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines2011In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, no 15, p. 052107-052114Article in journal (Refereed)
    Abstract [en]

    Observations by, for instance, the EISCAT Svalbard Radar (ESR) demonstrate that the symmetry of the naturally occurring ion line in the polar ionosphere can be broken by an enhanced, nonthermal, level of fluctuations (naturally enhanced ion-acoustic lines, NEIALs). It was in many cases found that the entire ion spectrum can be distorted, also with the appearance of a third line, corresponding to a propagation velocity significantly slower than the ion acoustic sound speed. It has been argued that selective decay of beam excited primary Langmuir waves can explain some phenomena similar to those observed. We consider a related model, suggesting that a primary nonlinear process can be an oscillating two-stream instability, generating a forced low frequency mode that does not obey any ion sound dispersion relation. At later times, the decay of Langmuir waves can give rise also to enhanced asymmetric ion lines. The analysis is based on numerical results, where the initial Langmuir waves are excited by a cold dilute electron beam. By this numerical approach, we can detect fine details of the physical processes, in particular, demonstrate a strong space-time intermittency of the electron waves in agreement with observations. Our code solves the full Vlasov equation for electrons and ions, with the dynamics coupled through the electrostatic field derived from Poisson's equation. The analysis distinguishes the dynamics of the background and beam electrons. This distinction simplifies the analysis for the formulation of the weakly nonlinear analytical model for the oscillating two-stream instability. The results have general applications beyond their relevance for the ionospheric observations.

  • 44. de Angelis, U.
    et al.
    Regnoli, G.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Long-range attraction of negatively charged dust particles in weakly ionized dense dust clouds2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 4, p. 043702-Article in journal (Refereed)
    Abstract [en]

    The new Plasma Kristall Experiment (PK-4) is scheduled to fly on the International Space Station in 2012 with one of the experiments designed to investigate the existence of two fluid phases and a critical point in complex plasmas. A crucial issue is the parameter regime where the critical point could be found and this requires, as a first step, knowledge of the parameter range where dust-dust attraction can exist. This problem is addressed in the present work, extending previous works on long-range screening and attraction of negatively charged dust particles in plasmas. The roles of nonlinearities, ion-neutral collisions, electron dynamics, and plasma source on the depth and long-range behavior of the attractive well are established and the impact of these results on the PK-4 experiments is discussed.

  • 45. de Angelis, Umberto
    et al.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Effects of dust particles in plasma kinetics; ion dynamics time scales2012In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, no 7, p. 073701-Article in journal (Refereed)
    Abstract [en]

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

  • 46. Deca, J.
    et al.
    Lapenta, G.
    Marchand, R.
    Markidis, Stefano
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Spacecraft charging analysis with the implicit particle-in-cell code iPic3D2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 10, p. 102902-Article in journal (Refereed)
    Abstract [en]

    We present the first results on the analysis of spacecraft charging with the implicit particle-in-cell code iPic3D, designed for running on massively parallel supercomputers. The numerical algorithm is presented, highlighting the implementation of the electrostatic solver and the immersed boundary algorithm; the latter which creates the possibility to handle complex spacecraft geometries. As a first step in the verification process, a comparison is made between the floating potential obtained with iPic3D and with Orbital Motion Limited theory for a spherical particle in a uniform stationary plasma. Second, the numerical model is verified for a CubeSat benchmark by comparing simulation results with those of PTetra for space environment conditions with increasing levels of complexity. In particular, we consider spacecraft charging from plasma particle collection, photoelectron and secondary electron emission. The influence of a background magnetic field on the floating potential profile near the spacecraft is also considered. Although the numerical approaches in iPic3D and PTetra are rather different, good agreement is found between the two models, raising the level of confidence in both codes to predict and evaluate the complex plasma environment around spacecraft.

  • 47. Di Siena, A.
    et al.
    Görler, T.
    Doerk, H.
    Bilato, R.
    Citrin, J.
    Johnson, T.
    KTH, School of Electrical Engineering (EES). VR Association.
    Schneider, M.
    Poli, E.
    Non-Maxwellian fast particle effects in gyrokinetic GENE simulations2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 4, article id 042304Article in journal (Refereed)
    Abstract [en]

    Fast ions have recently been found to significantly impact and partially suppress plasma turbulence both in experimental and numerical studies in a number of scenarios. Understanding the underlying physics and identifying the range of their beneficial effect is an essential task for future fusion reactors, where highly energetic ions are generated through fusion reactions and external heating schemes. However, in many of the gyrokinetic codes fast ions are, for simplicity, treated as equivalent-Maxwellian-distributed particle species, although it is well known that to rigorously model highly non-thermalised particles, a non-Maxwellian background distribution function is needed. To study the impact of this assumption, the gyrokinetic code GENE has recently been extended to support arbitrary background distribution functions which might be either analytical, e.g., slowing down and bi-Maxwellian, or obtained from numerical fast ion models. A particular JET plasma with strong fast-ion related turbulence suppression is revised with these new code capabilities both with linear and nonlinear gyrokinetic simulations. It appears that the fast ion stabilization tends to be less strong but still substantial with more realistic distributions, and this improves the quantitative power balance agreement with experiments. 

  • 48. Dieckmann, M. E.
    et al.
    Folini, D.
    Walder, R.
    Romagnani, L.
    d'Humieres, E.
    Bret, A.
    Karlsson, T.
    Ynnerman, A.
    Emergence of MHD structures in a collisionless PIC simulation plasma2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 9, article id 094502Article in journal (Refereed)
    Abstract [en]

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

  • 49.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Alejo, Aaron
    Centre for Plasma Physics, Queen's University Belfast, Belfast, UK..
    Sarri, Gianluca
    Centre for Plasma Physics, Queen's University Belfast, Belfast, UK..
    Folini, Doris
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, Lyon, France.
    Walder, Rolf
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, Lyon, France.
    One-dimensional thermal pressure-driven expansion of a pair cloud into an electron-proton plasma2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 5, article id 064502Article in journal (Refereed)
    Abstract [en]

    Recently, a filamentation instability was observed when a laser-generated pair cloud interacted with an ambient plasma. The magnetic field it drove was strong enough to magnetize and accelerate the ambient electrons. It is of interest to determine if and how pair cloud-driven instabilities can accelerate ions in the laboratory or in astrophysical plasma. For this purpose, the expansion of a localized pair cloud with the temperature 400 keV into a cooler ambient electron-proton plasma is studied by means of one-dimensional particle-in-cell simulations. The cloud's expansion triggers the formation of electron phase space holes that accelerate some protons to MeV energies. Forthcoming lasers might provide the energy needed to create a cloud that can accelerate protons.

  • 50.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Doria, Domenico
    School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, United Kingdom.
    Ahmed, Hamad
    School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, United Kingdom.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Sarri, Gianluca
    School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, United Kingdom.
    Folini, Doris
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Lyon, France.
    Walder, Rolf
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Lyon, France.
    Bret, Antoine
    ETSI Industriales, Universidad de Castilla-La Mancha, Ciudad Real, Spain.
    Borghesi, Marco
    School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, United Kingdom.
    Expansion of a radial plasma blast shell into an ambient plasma2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 9, article id 094501Article in journal (Refereed)
    Abstract [en]

    The expansion of a radial blast shell into an ambient plasma is modeled with a particle-in-cell simulation. The unmagnetized plasma consists of electrons and protons. The formation and evolution of an electrostatic shock is observed, which is trailed by ion-acoustic solitary waves that grow on the beam of the blast shell ions in the post-shock plasma. In spite of the initially radial symmetric outflow, the solitary waves become twisted and entangled and, hence, they break the radial symmetry of the flow. The waves and their interaction with the shocked ambient ions slow down the blast shell protons and bring the post-shock plasma closer to equilibrium.

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