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May 2012

Volume 19, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 19, 056314 (2012); http://dx.doi.org/10.1063/1.4718594 (12 pages)

I. V. Igumenshchev, W. Seka, D. H. Edgell, D. T. Michel, D. H. Froula, V. N. Goncharov, R. S. Craxton, L. Divol, R. Epstein, R. Follett, J. H. Kelly, T. Z. Kosc, A. V. Maximov, R. L. McCrory, D. D. Meyerhofer, et al.
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back to top Basic Plasma Phenomena, Waves, Instabilities

Magnetohydrodynamic spin waves in degenerate electron-positron-ion plasmas

A. Mushtaq, R. Maroof, Zulfiaqr Ahmad, and A. Qamar

Phys. Plasmas 19, 052101 (2012); http://dx.doi.org/10.1063/1.4714602 (7 pages) | Cited 1 time

Online Publication Date: 16 May 2012

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Low frequency magnetosonic waves are studied in magnetized degenerate electron-positron-ion plasmas with spin effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, and spin magnetization energy, a generalized dispersion relation for oblique magnetosonic waves is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. For three different values of angle θ, the generalized dispersion relation is reduced to three different relations under the low frequency magnetohydrodynamic assumptions. It is found that the effect of quantum corrections in the presence of positron concentration significantly modifies the dispersive properties of these modes. The importance of the work relevant to compact astrophysical bodies is pointed out.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Hamiltonian magnetohydrodynamics: Helically symmetric formulation, Casimir invariants, and equilibrium variational principles

T. Andreussi, P. J. Morrison, and F. Pegoraro

Phys. Plasmas 19, 052102 (2012); http://dx.doi.org/10.1063/1.4714761 (8 pages) | Cited 4 times

Online Publication Date: 16 May 2012

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The noncanonical Hamiltonian formulation of magnetohydrodynamics (MHD) is used to construct variational principles for continuously symmetric equilibrium configurations of magnetized plasma, including flow. In particular, helical symmetry is considered, and results on axial and translational symmetries are retrieved as special cases of the helical configurations. The symmetry condition, which allows the description in terms of a magnetic flux function, is exploited to deduce a symmetric form of the noncanonical Poisson bracket of MHD. Casimir invariants are then obtained directly from the Poisson bracket. Equilibria are obtained from an energy-Casimir principle and reduced forms of this variational principle are obtained by the elimination of algebraic constraints.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
02.10.-v Logic, set theory, and algebra
02.30.Xx Calculus of variations
02.50.Ey Stochastic processes

Coupling between whistler waves and slow-mode solitary waves

A. Tenerani, F. Califano, F. Pegoraro, and O. Le Contel

Phys. Plasmas 19, 052103 (2012); http://dx.doi.org/10.1063/1.4717764 (10 pages) | Cited 1 time

Online Publication Date: 18 May 2012

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The interplay between electron- and ion-scale phenomena is of general interest for both laboratory and space plasma physics. In this paper, we investigate the linear coupling between whistler waves and slow magnetosonic solitons through two-fluid numerical simulations. Whistler waves can be trapped in the presence of inhomogeneous external fields such as a density hump or hole where they can propagate for times much longer than their characteristic time scale, as shown by laboratory experiments and space measurements. Space measurements have detected whistler waves also in correspondence to magnetic holes, i.e., to density humps with magnetic field minima extending on ion-scales. This raises the interesting question of how ion-scale structures can couple to whistler waves. Slow magnetosonic solitons share some of the main features of a magnetic hole. Using the ducting properties of an inhomogeneous plasma as a guide, we present a numerical study of whistler waves that are trapped and transported inside propagating slow magnetosonic solitons.
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52.35.Sb Solitons; BGK modes
52.65.-y Plasma simulation
02.60.Cb Numerical simulation; solution of equations
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Modeling the propagation of whistler-mode waves in the presence of field-aligned density irregularities

A. V. Streltsov, J. Woodroffe, W. Gekelman, and P. Pribyl

Phys. Plasmas 19, 052104 (2012); http://dx.doi.org/10.1063/1.4719710 (9 pages) | Cited 2 times

Online Publication Date: 23 May 2012

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We present a numerical study of propagation of VLF whistler-mode waves in a laboratory plasma. Our goal is to understand whistler propagation in magnetic field-aligned irregularities (also called channels or ducts). Two cases are examined, that of a high-frequency (ω>Ωce/2) whistler in a density depletion duct and that of a low-frequency (ω<Ωce/2) whistler in a density enhancement. Results from a numerical simulation of whistler wave propagation are compared to data from the UCLA Los Angeles Physics Teachers Alliance Group plasma device and whistler propagation in pre-existing density depletion and density enhancement ducts is demonstrated.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
94.30.Tz Electromagnetic wave propagation
52.65.-y Plasma simulation
52.72.+v Laboratory studies of space- and astrophysical-plasma processes

Perturbative analysis of sheared flow Kelvin–Helmholtz instability in a weakly relativistic magnetized electron fluid

Sita Sundar, Amita Das, and Predhiman Kaw

Phys. Plasmas 19, 052105 (2012); http://dx.doi.org/10.1063/1.4719712 (5 pages)

Online Publication Date: 23 May 2012

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In the interaction of intense lasers with matter/plasma, energetic electrons having relativistic energies get created. These energetic electrons can often have sheared flow profiles as they propagate through the plasma medium. In an earlier study [Phys. Plasmas 17, 022101 (2010)], it was shown that a relativistic sheared electron flow modifies the growth rate and threshold condition of the conventional Kelvin—Helmholtz instability. A perturbative analytic treatment for the case of weakly relativistic regime has been provided here. It provides good agreement with the numerical results obtained earlier.
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52.27.Ny Relativistic plasmas
52.40.Mj Particle beam interactions in plasmas
52.30.-q Plasma dynamics and flow
52.20.Fs Electron collisions
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Gyrosymmetry: Global considerations

J. W. Burby and H. Qin

Phys. Plasmas 19, 052106 (2012); http://dx.doi.org/10.1063/1.4719700 (8 pages) | Cited 1 time

Online Publication Date: 24 May 2012

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In the guiding center theory, smooth unit vectors perpendicular to the magnetic field are required to define the gyrophase. The question of global existence of these vectors is addressed using a general result from the theory of characteristic classes. It is found that there is, in certain cases, an obstruction to global existence. In these cases, the gyrophase cannot be defined globally. The implications of this fact on the basic structure of the guiding center theory are discussed. In particular, it is demonstrated that the guiding center asymptotic expansion of the equations of motion can still be performed in a globally consistent manner when a single global convention for measuring gyrophase is unavailable. The latter fact is demonstrated directly by deriving a new expression for the guiding-center Poincaré-Cartan form exhibiting no dependence on the choice of perpendicular unit vectors.
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52.65.Tt Gyrofluid and gyrokinetic simulations

Magnetothermal instability in laser plasmas including hydrodynamic effects

J. J. Bissell, R. J. Kingham, and C. P. Ridgers

Phys. Plasmas 19, 052107 (2012); http://dx.doi.org/10.1063/1.4718639 (11 pages) | Cited 2 times

Online Publication Date: 29 May 2012

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The impact of both density gradients and hydrodynamics on the evolution of the field compressing magnetothermal instability is considered [J. J. Bissell et al., Phys. Rev. Lett. 105, 175001 (2010)]. Hydrodynamic motion is found to have a limited effect on overall growth-rates; however, density gradients are shown to introduce an additional source term corresponding to a generalised description of the field generating thermal instability [D. Tidman and R. Shanny, Phys. Fluids 17, 1207 (1974)]. The field compressing and field generating source terms are contrasted, and the former is found to represent either the primary or sole instability mechanism for a range of conditions, especially those with Hall parameter χ>10-1. The generalised theory is compared to numerical simulation in the context of a recent nano-second gas-jet experiment [D. H. Froula et al., Phys. Rev. Lett. 98, 135001 (2007)] and shown to be in good agreement: exhibiting peak growth-rates and wavelengths of order 10 ns1 and 50 μm, respectively. The instability’s relevance to other experimental conditions, including those in inertial confinement fusion (I.C.F.) hohlraums, is also discussed.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z Laser inertial confinement
52.75.-d Plasma devices
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
back to top Nonlinear Phenomena, Turbulence, Transport

Electron kappa distribution and steady-state Langmuir turbulence

Peter H. Yoon

Phys. Plasmas 19, 052301 (2012); http://dx.doi.org/10.1063/1.4710515 (6 pages) | Cited 3 times

Online Publication Date: 4 May 2012

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In a recent pair of papers, the present author discussed a self-consistent theory of asymptotically steady-state electron distribution function and Langmuir turbulence intensity in one [P. H. Yoon, Phys. Plasmas 18, 122303 (2011)] and three [P. H. Yoon, Phys. Plasmas 19, 012304 (2012)] dimensions. The resulting electron distribution function is a type of kappa distribution that features a non-Maxwellian energetic tail component. However, while the one-dimensional solution is rigorously correct, the three-dimensional solution, which was obtained using the cylindrical coordinate representation, contains two features that may be inconsistent for field-free plasmas. One is the assumption that the resonance condition can be approximated by ω-k·v ≈ ω-k∥v∥. Needless to say, this is not the most general condition. The second inconsistency is that while the electron distribution is isotropic in velocity, the Langmuir turbulence intensity depends on the wave propagation direction. While these features may not be too unrealistic in the presence of an implicit ambient magnetic field, they certainly cannot be correct if the plasma is genuinely unmagnetized. In the present paper, we rectify such shortcomings by properly reformulating the problem using a spherical coordinate system in a truly free-field plasma.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Ra Plasma turbulence

Effect of nonthermal electrons on oblique electrostatic excitations in a magnetized electron-positron-ion plasma

H. Alinejad

Phys. Plasmas 19, 052302 (2012); http://dx.doi.org/10.1063/1.4714609 (6 pages) | Cited 4 times

Online Publication Date: 14 May 2012

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The linear and nonlinear propagation of ion-acoustic waves are investigated in a magnetized electron-positron-ion (e-p-i) plasma with nonthermal electrons. In the linear regime, the propagation of two possible modes and their evolution are studied via a dispersion relation. In the cases of parallel and perpendicular propagation, it is shown that these two possible modes are always stable. Then, the Korteweg-de Vries equation describing the dynamics of ion-acoustic solitary waves is derived from a weakly nonlinear analysis. The influence on the solitary wave characteristics of relevant physical parameters such as nonthermal electrons, magnetic field, obliqueness, positron concentration, and temperature ratio is examined. It is observed that the increasing nonthermal electrons parameter makes the solitary structures much taller and narrower. Also, it is revealed that the magnetic field strength makes the solitary waves more spiky. The present investigation contributes to the physics of the nonlinear electrostatic ion-acoustic waves in space and laboratory e-p-i plasmas in which wave damping produces an electron tail.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes
02.10.-v Logic, set theory, and algebra
52.25.-b Plasma properties

Tripolar vortex formation in dense quantum plasma with ion-temperature-gradients

Anisa Qamar, Ata-ur-Rahman, and Arshad M. Mirza

Phys. Plasmas 19, 052303 (2012); http://dx.doi.org/10.1063/1.4714648 (5 pages) | Cited 1 time

Online Publication Date: 16 May 2012

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We have derived system of nonlinear equations governing the dynamics of low-frequency electrostatic toroidal ion-temperature-gradient mode for dense quantum magnetoplasma. For some specific profiles of the equilibrium density, temperature, and ion velocity gradients, the nonlinear equations admit a stationary solution in the form of a tripolar vortex. These results are relevant to understand nonlinear structure formation in dense quantum plasmas in the presence of equilibrium ion-temperature and density gradients.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties

Hexagonal superlattice pattern consisting of colliding filament pairs in a dielectric barrier discharge

Lifang Dong, Ben Li, Ning Lu, Xinchun Li, and Zhongkai Shen

Phys. Plasmas 19, 052304 (2012); http://dx.doi.org/10.1063/1.4717466 (5 pages) | Cited 2 times

Online Publication Date: 17 May 2012

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Colliding-pairs hexagonal superlattice pattern (CPHSP) is studied in a dielectric barrier discharge system. The evolution of CPHSP bifurcating from a hexagonal pattern to chaos is shown. The phase diagrams of CPHSP as a function of discharge parameters are given. From a series of pictures taken by a high speed video camera, collisions between two spots are observed and the superposition of many collisions results in each big spot presenting four small spots on long time scales. Measurements of the correlation between filaments indicate that the pattern is an interleaving of four different transient hexagonal sublattices. Depending on the discharging sequence, the forces exerted on one colliding spot are discussed briefly.
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52.20.-j Elementary processes in plasmas
52.25.Gj Fluctuation and chaos phenomena
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.-s Electric discharges

Energy spectrum, dissipation, and spatial structures in reduced Hall magnetohydrodynamic

L. N. Martin, P. Dmitruk, and D. O. Gomez

Phys. Plasmas 19, 052305 (2012); http://dx.doi.org/10.1063/1.4717728 (6 pages) | Cited 1 time

Online Publication Date: 18 May 2012

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We analyze the effect of the Hall term in the magnetohydrodynamic turbulence under a strong externally supported magnetic field, seeing how this changes the energy cascade, the characteristic scales of the flow, and the dynamics of global magnitudes, with particular interest in the dissipation. Numerical simulations of freely evolving three-dimensional reduced magnetohydrodynamics are performed, for different values of the Hall parameter (the ratio of the ion skin depth to the macroscopic scale of the turbulence) controlling the impact of the Hall term. The Hall effect modifies the transfer of energy across scales, slowing down the transfer of energy from the large scales up to the Hall scale (ion skin depth) and carrying faster the energy from the Hall scale to smaller scales. The final outcome is an effective shift of the dissipation scale to larger scales but also a development of smaller scales. Current sheets (fundamental structures for energy dissipation) are affected in two ways by increasing the Hall effect, with a widening but at the same time generating an internal structure within them. In the case where the Hall term is sufficiently intense, the current sheet is fully delocalized. The effect appears to reduce impulsive effects in the flow, making it less intermittent.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence
52.65.-y Plasma simulation
02.60.Cb Numerical simulation; solution of equations
52.25.Fi Transport properties

Quasi-periodic behavior of ion acoustic solitary waves in electron-ion quantum plasma

Biswajit Sahu, Swarup Poria, Uday Narayan Ghosh, and Rajkumar Roychoudhury

Phys. Plasmas 19, 052306 (2012); http://dx.doi.org/10.1063/1.4714804 (6 pages)

Online Publication Date: 30 May 2012

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The ion acoustic solitary waves are investigated in an unmagnetized electron-ion quantum plasmas. The one dimensional quantum hydrodynamic model is used to study small as well as arbitrary amplitude ion acoustic waves in quantum plasmas. It is shown that ion temperature plays a critical role in the dynamics of quantum electron ion plasma, especially for arbitrary amplitude nonlinear waves. In the small amplitude region Korteweg-de Vries equation describes the solitonic nature of the waves. However, for arbitrary amplitude waves, in the fully nonlinear regime, the system exhibits possible existence of quasi-periodic behavior for small values of ion temperature.
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52.35.Sb Solitons; BGK modes
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Effect of poloidal asymmetries on impurity peaking in tokamaks

A. Mollén, I. Pusztai, T. Fülöp, Ye. O. Kazakov, and S. Moradi

Phys. Plasmas 19, 052307 (2012); http://dx.doi.org/10.1063/1.4719711 (11 pages) | Cited 5 times

Online Publication Date: 30 May 2012

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Poloidal impurity asymmetries are frequently observed in tokamaks. In this paper, the effect of poloidal asymmetry on electrostatic turbulent transport is studied, including the effect of the E×B drift. Collisions are modeled by a Lorentz operator, and the gyrokinetic equation is solved with a variational approach. The impurity transport is shown to be sensitive to the magnetic shear and changes sign for s≳0.5 in the presence of inboard accumulation. The zero-flux impurity density gradient (peaking factor) is shown to be rather insensitive to collisions in both ion temperature gradient and trapped electron mode driven cases. Our results suggest that the asymmetry (both the location of its maximum and its strength) and the magnetic shear are the two most important parameters that affect the impurity peaking.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Vy Impurities in plasmas
52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
back to top Magnetically Confined Plasmas, Heating, Confinement

Gauge properties of the guiding center variational symplectic integrator

J. Squire, H. Qin, and W. M. Tang

Phys. Plasmas 19, 052501 (2012); http://dx.doi.org/10.1063/1.4714608 (7 pages) | Cited 2 times

Online Publication Date: 14 May 2012

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Variational symplectic algorithms have recently been developed for carrying out long-time simulation of charged particles in magnetic fields [H. Qin and X. Guan, Phys. Rev. Lett. 100, 035006 (2008); H. Qin, X. Guan, and W. Tang, Phys. Plasmas (2009); J. Li, H. Qin, Z. Pu, L. Xie, and S. Fu, Phys. Plasmas 18, 052902 (2011)]. As a direct consequence of their derivation from a discrete variational principle, these algorithms have very good long-time energy conservation, as well as exactly preserving discrete momenta. We present stability results for these algorithms, focusing on understanding how explicit variational integrators can be designed for this type of system. It is found that for explicit algorithms, an instability arises because the discrete symplectic structure does not become the continuous structure in the t→0 limit. We examine how a generalized gauge transformation can be used to put the Lagrangian in the “antisymmetric discretization gauge,” in which the discrete symplectic structure has the correct form, thus eliminating the numerical instability. Finally, it is noted that the variational guiding center algorithms are not electromagnetically gauge invariant. By designing a model discrete Lagrangian, we show that the algorithms are approximately gauge invariant as long as A and φ are relatively smooth. A gauge invariant discrete Lagrangian is very important in a variational particle-in-cell algorithm where it ensures current continuity and preservation of Gauss’s law [J. Squire, H. Qin, and W. Tang (to be published)].
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52.65.-y Plasma simulation
02.30.Xx Calculus of variations
02.60.Jh Numerical differentiation and integration
FREE

Kinetic damping of resistive wall modes in ITER

I. T. Chapman, Y. Q. Liu, O. Asunta, J. P. Graves, T. Johnson, and M. Jucker

Phys. Plasmas 19, 052502 (2012); http://dx.doi.org/10.1063/1.4714877 (10 pages)

Online Publication Date: 15 May 2012

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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 β 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.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.50.Gj Plasma heating by particle beams
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons

Auxiliary ECR heating system for the gas dynamic trap

A. G. Shalashov, E. D. Gospodchikov, O. B. Smolyakova, P. A. Bagryansky, V. I. Malygin, and M. Thumm

Phys. Plasmas 19, 052503 (2012); http://dx.doi.org/10.1063/1.4717757 (8 pages) | Cited 2 times

Online Publication Date: 16 May 2012

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Physics aspects of a new system for electron cyclotron resonance heating (ECRH) at the magnetic mirror device Gas Dynamic Trap (GDT, Budker Institute, Novosibirsk) are discussed. This system based on two 400 kW/54.5 GHz gyrotrons is aimed at increasing the electron temperature up to the range 250–350 eV for improved energy confinement of hot ions. The key physical issue of the GDT magnetic field topology is that conventional ECRH geometries are not accessible. The proposed solution is based on a peculiar effect of radiation trapping in inhomogeneous magnetized plasma. Under specific conditions, oblique launch of gyrotron radiation results in generation of right-hand-polarized (R) electromagnetic waves propagating with high N|| in the vicinity of the cyclotron resonance layer, which leads to effective single-pass absorption of the injected microwave power. In the present paper, we investigate numerically an optimized ECRH scenario based on the proposed mechanism of wave propagation and discuss the design of the ECRH system, which is currently under construction at the Budker Institute.
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52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
02.60.-x Numerical approximation and analysis
52.25.Xz Magnetized plasmas
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Drift wave dispersion relation for arbitrarily collisional plasma

Justin R. Angus and Sergei I. Krasheninnikov

Phys. Plasmas 19, 052504 (2012); http://dx.doi.org/10.1063/1.4714614 (7 pages) | Cited 3 times

Online Publication Date: 17 May 2012

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The standard local linear analysis of drift waves in a plasma slab is generalized to be valid for arbitrarily collisional electrons by considering the electrons to be governed by the drift-kinetic equation with a BGK-like (Bhatnagar-Gross-Krook) collision operator. The obtained dispersion relation reduces to that found from collisionless kinetic theory when the collision frequency is zero. Electron temperature fluctuations must be retained in the standard fluid analysis in order to obtain good quantitative agreement with our general solution in the highly collisional limit. Any discrepancies between the fluid solution and our general solution in this limit are attributed to the limitations of the BGK collision operator. The maximum growth rates in both the collisional and collisionless limits are comparable and are both on the order of the fundamental drift wave frequency. The main role of the destabilizing mechanism is found to be in determining the parallel wave number at which the maximum growth rate will occur. The parallel wave number corresponding to the maximum growth rate is set by the wave-particle resonance condition in the collisionless limit and transitions to being set by the real frequency being on the order of the rate for electrons to diffuse a parallel wavelength in the collisional limit.
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52.35.Kt Drift waves
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.20.Fs Electron collisions
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties

On the delayed gas breakdown in a ringing theta-pinch with bias magnetic field

Warner C. Meeks and Joshua L. Rovey

Phys. Plasmas 19, 052505 (2012); http://dx.doi.org/10.1063/1.4717731 (7 pages)

Online Publication Date: 17 May 2012

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A single particle model and particle-in-cell simulations are used to elucidate the breakdown physics in a ringing theta-pinch with a bias magnetic field. Previous experimental results show that gas breakdown occurs when the bias magnetic field is nullified by the theta-pinch magnetic field. The analyses presented here agree with the experimental results and show that electron kinetic energy does not exceed the ionization threshold of deuterium until the net magnetic field is approximately zero. Despite the presence of a strong electric field, the gyromotion of electrons within the bias magnetic field prevents them from gaining energy necessary to ionize the gas. Parametric analysis of the peak electron energy as a function of the bias and pre-ionization magnetic fields reveals that: (1) when the bias magnetic field is ≈97% of the pre-ionization magnetic field, peak electron energies are highly erratic resulting in poor overall ionization, and (2) full ionization with repeatable behavior requires a pre-ionization to bias magnetic field ratio of approximately 2 to 1 or higher.
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52.55.Ez Theta pinch
52.65.Rr Particle-in-cell method
52.25.Jm Ionization of plasmas

Measurements of the runaway electron energy during disruptions in the tokamak TEXTOR

M. Forster, K. H. Finken, M. Lehnen, O. Willi, Y. Xu, and TEXTOR Team

Phys. Plasmas 19, 052506 (2012); http://dx.doi.org/10.1063/1.4717759 (10 pages) | Cited 1 time

Online Publication Date: 18 May 2012

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Calorimetric measurements of the total runaway electron energy are carried out using a reciprocating probe during induced TEXTOR disruptions. A comparison with the energy inferred from runaway energy spectra, which are measured with a scintillator probe, is used as an independent check of the results. A typical runaway current of 100 kA at TEXTOR contains 30 to 35 kJ of runaway energy. The dependencies of the runaway energy on the runaway current, the radial probe position, the toroidal magnetic field and the predisruptive plasma current are studied. The conversion efficiency of the magnetic plasma energy into runaway energy is calculated to be up to 26%.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Fa Tokamaks, spherical tokamaks

Impact of screening of resonant magnetic perturbations in three dimensional edge plasma transport simulations for DIII-D

H. Frerichs, D. Reiter, O. Schmitz, P. Cahyna, T. E. Evans, Y. Feng, and E. Nardon

Phys. Plasmas 19, 052507 (2012); http://dx.doi.org/10.1063/1.4714616 (7 pages) | Cited 3 times

Online Publication Date: 22 May 2012

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The impact of resonant magnetic perturbations (RMPs) on the plasma edge can be analyzed in detail by three dimensional computer simulations, which take the underlying magnetic field structure as input. Previously, the “vacuum approximation” has been used to calculate the magnetic field structure although plasma response effects may result in a screening (or even an amplification) of the external perturbations. Simulation results for an ITER similar shape plasma at the DIII-D tokamak are presented for the full vacuum perturbation field and an ad hoc screening case in comparison to the unperturbed configuration. It is shown that the RMP induced helical patterns in the plasma edge and on the divertor target shrink once screening is taken into account. However, a flat temperature profile is still found in the “open field line domain” inside the separatrix, while the “density pump out effect” found in the vacuum RMP case is considerably weakened.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation

Rotation of tokamak halo currents

Allen H. Boozer

Phys. Plasmas 19, 052508 (2012); http://dx.doi.org/10.1063/1.4717721 (7 pages) | Cited 1 time

Online Publication Date: 23 May 2012

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During tokamak disruptions, halo currents, which can be tenths of the total plasma current, can flow at the plasma edge along the magnetic field lines that intercept the chamber walls. Non-axisymmetric halo currents are required to maintain force balance as the plasma kinks when the edge safety factor drops to about two in a vertical displacement event. The plasma quickly assumes a definite toroidal velocity va(r) with respect to that of the magnetic kink, vk, where va(r) is set by the radial electric field required for ambipolarity. The plasma velocity, vpl = va+vk, near the edge is influenced by the interaction with neutrals and with the potential in the halo required for quasi-neutrality on open magnetic field lines, and the plasma velocity in the core is influenced by external error fields. When plasma effects dominate magnetic locking, the magnetic kink should rotate at a diamagnetic speed of either the edge or the core. If the magnetic field lines of the halo plasma intercept the wall at locations of very different electrical conductivity, the toroidal rotation of the halo currents can intermittently stall at wall locations of high conductivity. Such stalling is seen in experiments. The toroidal phase difference between the stalled halo currents and the kink, which is expected to rotate smoothly, must satisfy δϕ<±π/2. A concern cited by ITER engineers is that the time varying force of the rotating halo could substantially increase the disruption loads on in-vessel components.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties

Scrape-off layer tokamak plasma turbulence

N. Bisai, R. Singh, and P. K. Kaw

Phys. Plasmas 19, 052509 (2012); http://dx.doi.org/10.1063/1.4718714 (7 pages) | Cited 1 time

Online Publication Date: 24 May 2012

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Two-dimensional (2D) interchange turbulence in the scrape-off layer of tokamak plasmas and their subsequent contribution to anomalous plasma transport has been studied in recent years using electron continuity, current balance, and electron energy equations. In this paper, numerically it is demonstrated that the inclusion of ion energy equation in the simulation changes the nature of plasma turbulence. Finite ion temperature reduces floating potential by about 15% compared with the cold ion temperature approximation and also reduces the radial electric field. Rotation of plasma blobs at an angular velocity about 1.5×105 rad/s has been observed. It is found that blob rotation keeps plasma blob charge separation at an angular position with respect to the vertical direction that gives a generation of radial electric field. Plasma blobs with high electron temperature gradients can align the charge separation almost in the radial direction. Influence of high ion temperature and its gradient has been presented.
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52.35.Ra Plasma turbulence
52.65.-y Plasma simulation
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.40.Hf Plasma-material interactions; boundary layer effects
back to top Inertially Confined Plasmas, High Energy Density Plasma Science, Warm Dense Matter

The quantum equations of state of plasma under the influence of a weak magnetic field

N. A. Hussein, D. A. Eisa, and M. G. Eldin

Phys. Plasmas 19, 052701 (2012); http://dx.doi.org/10.1063/1.4704794 (6 pages) | Cited 1 time

Online Publication Date: 9 May 2012

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The aim of this paper is to calculate the magnetic quantum equations of state of plasma, the calculation is based on the magnetic binary Slater sum in the case of low density. We consider only the thermal equilibrium plasma in the case of nλab3≪1, where λab2 = math is the thermal De Broglie wave length between two particles. The formulas contain the contributions of the magnetic field effects. Using these results we compute the magnetization and the magnetic susceptibility. Our equation of state is compared with others.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
05.70.Ce Thermodynamic functions and equations of state

Tendency of spherically imploding plasma liners formed by merging plasma jets to evolve toward spherical symmetry

J. T. Cassibry, M. Stanic, S. C. Hsu, F. D. Witherspoon, and S. I. Abarzhi

Phys. Plasmas 19, 052702 (2012); http://dx.doi.org/10.1063/1.4714606 (9 pages) | Cited 5 times

Online Publication Date: 14 May 2012

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We have performed three-dimensional (3D) simulations using smoothed particle hydrodynamics (SPH) in order to study the effects of discrete plasma jets on the processes of plasma liner formation, implosion on vacuum, and expansion. It was found that the pressure histories of the inner portion of the liner from 3D SPH simulations with a uniform liner and with 30 discrete plasma jets were qualitatively and quantitatively similar from peak compression through the complete stagnation of the liner. The 3D simulations with a uniform liner were first benchmarked against results from one-dimensional radiation-hydrodynamic simulations [T. J. Awe et al., Phys. Plasmas 18, 072705 (2011)]. Two-dimensional plots of the pressure field show that the discrete jet SPH case evolves towards a profile that is almost indistinguishable from the SPH case with a uniform liner, thus indicating that non-uniformities due to discrete jets are smeared out by late stages of the implosion. The processes of plasma liner formation and implosion on vacuum were shown to be robust against Rayleigh-Taylor instability growth. Finally, interparticle mixing for a liner imploding on vacuum was investigated. The mixing rate was found to be very small until after the peak compression for the 30 jet simulations.
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52.75.-d Plasma devices
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.-y Plasma simulation
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