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Dec 1995

Volume 2, Issue 12, pp. 4381-4665

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Ideal magnetohydrodynamic stability in the presence of a resistive wall

S. N. Bhattacharyya

Phys. Plasmas 2, 4381 (1995); http://dx.doi.org/10.1063/1.870994 (8 pages) | Cited 3 times

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Using the Galerkin method, the equations governing the linear stability of an ideal plasma in the presence of a thin resistive wall is reduced to a standard matrix eigenvalue problem. This can be used to compute the entire spectrum of normal modes. Stability is shown to be governed by an energy principle. As an application, the Galerkin formulation is used to study the stability of an elliptical cross‐section straight tokamak, surrounded by a thin resistive wall, to rigid vertical displacements. The Galerkin formulation is also generalized to include equilibrium mass flow of the plasma and allow for arbitrary thickness of the resistive wall. Stability is again shown to be governed by an energy principle. © 1995 American Institute of Physics.  
Show PACS
52.30.-q Plasma dynamics and flow
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Fa Tokamaks, spherical tokamaks

Quasi‐equilibria: A special class of time‐dependent solutions of the two‐dimensional magnetohydrodynamic equations

T. Neukirch

Phys. Plasmas 2, 4389 (1995); http://dx.doi.org/10.1063/1.870995 (11 pages) | Cited 3 times

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A special method is presented to construct exact time‐dependent solutions of the two‐dimensional ideal magnetohydrodynamic (MHD) equations for which plasma elements experience no acceleration. The momentum equation then contains the time merely parametrically and assumes the structure of an equilibrium equation. For a special form of the pressure profile p(A), for which the corresponding quasi‐equilibrium equation is a completely integrable non‐linear elliptic equation that is invariant under conformal transformations, these invariance properties are then used to determine the possible time‐dependences of the solutions. Contrary to the common use of the term quasi‐equilibrium arbitrarily large plasma velocities are allowed in the present treatment. In polar coordinates, the time evolution turns out to be self‐similar in the radial coordinate, but it is in general not self‐similar in the azimuthal coordinate. The adiabatic exponent of the plasma is found to be equal to one, which means that the plasma is isothermal. Explicit examples of solutions are discussed. © 1995 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

New parallel velocity shear instability

John M. Finn

Phys. Plasmas 2, 4400 (1995); http://dx.doi.org/10.1063/1.870996 (13 pages) | Cited 11 times

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Analytic and numerical results on the linear theory of a new instability driven by shear in the parallel velocity v∥′ will be presented. This instability exists in the presence of parallel velocity shear and field line curvature. It also requires either parallel viscosity—the full Braginskii stress tensor [S. I. Braginskii, in Reviews of Plasma Physics, edited by M. A. Leontovich (Consultants Bureau, New York, 1965), Vol. 1, p. 205]—or parallel compression. The mode exists in an electromagnetic version, where it can enhance the growth rate of an unstable resistive magnetohydrodynamic (MHD) mode or cause an otherwise stable resistive mode to grow. In its electromagnetic form it is global (matches to an ideal MHD outer region) and can influence modes responsible for disruptions; it can also lead to anomalous transport by stochastic field lines as well as by E×B advection. The instability also exists in an electrostatic form for short wavelengths. For most reasonable edge plasma parameters the effect of parallel compression dominates that of parallel viscosity. The properties of this mode, specifically its growth rate and localization width, are compared with those of the usual v∥′ mode [N. D’Angelo, Phys. Fluids 8, 1748 (1965)]. The importance of this mode in edge fluctuations and on more global resistive MHD is discussed. © 1995 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence

Wave emission by resonance crossing

E. R. Tracy, A. N. Kaufman, and Y.‐M. Liang

Phys. Plasmas 2, 4413 (1995); http://dx.doi.org/10.1063/1.870997 (7 pages) | Cited 6 times

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The emission of collective waves by a moving charged particle in a nonuniform medium is discussed. Emission occurs in a nonuniform medium when the local dispersion relation of the collective wave is satisfied. This is a form of resonance crossing. Using the Weyl symbol calculus, a local expansion of the collective wave equation driven by the particle source is derived in the neighborhood of the crossing. The collective wave dispersion manifold and the gyroballistic wave dispersion manifold can be used as a pair of local coordinates in the neighborhood of the resonance crossing, which greatly simplifies the analysis. This change of representation is carried out using a metaplectic transform (a generalization of the fourier transform). The Wigner function of the emitted wave field is then computed in the new coordinates. The Wigner function is a phase space scalar, hence the numerical value is invariant under linear canonical transformations. This invariance is invoked to finally arrive at the Wigner function in the original (physical) coordinates. The wave‐action and ‐energy emission rates are then computed from the Wigner function. © 1995 American Institute of Physics.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
41.60.-m Radiation by moving charges
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Modulational interaction between drift waves and trapped ion convective cells: A paradigm for the self‐consistent interaction of large‐scale sheared flows with small‐scale fluctuations

V. B. Lebedev, P. H. Diamond, V. D. Shapiro, and G. I. Soloviev

Phys. Plasmas 2, 4420 (1995); http://dx.doi.org/10.1063/1.870998 (12 pages) | Cited 39 times

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The linear and nonlinear dynamics of modulational interaction between small‐scale drift waves and large‐scale trapped ion convective cells are investigated. This example is a paradigm of the more general problem of describing the self‐consistent interaction of small‐scale fluctuations with mean sheared flows. The growth rate of modulational instability is determined by spectral properties of drift waves and can exceed the linear growth rate of the trapped ion mode. An anisotropic spectrum of drift waves is always modulationally unstable. The spatial orientation of the convective cell pattern and structure (i.e., shear strength) is determined by drift wave spectrum anisotropy and propagation direction. In the presence of a sheared magnetic field, which pins small‐scale drift waves to mode rational surfaces, the modulational growth rate becomes intrinsically anisotropic, on account of the modified radial structure of drift waves. © 1995 American Institute of Physics.
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52.35.Kt Drift waves
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Ra Plasma turbulence

Transverse ion acceleration and ion conic formation in a divergent‐field laboratory plasma

M. Zintl, R. McWilliams, and N. Wolf

Phys. Plasmas 2, 4432 (1995); http://dx.doi.org/10.1063/1.870999 (10 pages) | Cited 13 times

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The results of laboratory experiments at the University of California at Irvine are presented in which multidimensional ion velocity distributions in the presence of radio‐frequency (RF) waves and a spatially divergent external magnetic field are observed. A plasma volume is subjected to either local or nonlocal electrostatic turbulence, which in turn is responsible for accelerating the ions transverse to the confining magnetic field. The ions flow away from the source of turbulence in a spatially decreasing magnetic field, where the μ ∇B force and magnetic‐moment conservation work to distort the heated distribution. Laser‐induced‐fluorescence (LIF) signals, measured downstream from the plasma source with the aid of optical tomography techniques, reveal substantial ion heating and conic formation. © 1995 American Institute of Physics.
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52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
94.20.wj Wave/particle interactions
94.20.wc Plasma motion; plasma convection; particle acceleration

Nonlinear dynamics of twisted magnetic flux tubes

Yun‐Tung Lau

Phys. Plasmas 2, 4442 (1995); http://dx.doi.org/10.1063/1.871000 (9 pages) | Cited 3 times

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The nonlinear response of an axisymmetric magnetic flux tube under the influence of an azimuthal twist force is studied. For a constant twist force, the tube approaches an inertial collapse phase in finite time. The competing pinch and magnetic pressure forces cause radial oscillation during the collapse. The plasma pressure is negligible in the process. When the tube is subject to a random twist, each end of the tube absorbs angular momentum preferentially in the direction of the initial field line winding. Thus again, the tube is twisted up and collapses in finite time. For typical solar parameters, the collapse time is a few tens of the coronal Alfvén time. Both magnetic and kinetic energy increase explosively near the collapse as a result of the twist. The tube contracts to about one‐tenth of its original size before reaching the kink threshold twist angle. © 1995 American Institute of Physics.
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96.60.-j Solar physics
96.60.P- Corona
52.65.Kj Magnetohydrodynamic and fluid equation

Fluid model of collisionless plasma with finite Larmor radius effects

A. I. Smolyakov, I. O. Pogutse, and A. Hirose

Phys. Plasmas 2, 4451 (1995); http://dx.doi.org/10.1063/1.871001 (4 pages) | Cited 6 times

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A closed set of moment equations for the plasma density, velocity and pressure is proposed by imposing linear closure for the heat flux and viscosity. The formulation is valid for arbitrary finite Larmor radius parameter k⊥ρ (k⊥ is the perpendicular wave vector, ρ is the particle Larmor radius) and retains main convective nonlinearities. Reduced moment equations relevant to the drift‐wave modes are derived in the low frequency limit (ω≪ωB, ωB is the particle cyclotron frequency). © 1995 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
52.25.Gj Fluctuation and chaos phenomena
52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence

Nonlinear magnetohydrodynamic dynamo

Robert G. Kleva and J. F. Drake

Phys. Plasmas 2, 4455 (1995); http://dx.doi.org/10.1063/1.871002 (7 pages) | Cited 4 times

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The self‐consistent nonlinear evolution and saturation of the dynamo, including the back reaction of the magnetic field on the flow through the Lorentz J×B force, is investigated via simulation of the fully compressible magnetohydrodynamic (MHD) equations. The saturated state is found to be highly turbulent. The energy in the saturated magnetic field is only a small fraction of the kinetic energy in the flow which drives the dynamo. However, as the collision frequency decreases and the Reynolds number R increases, the ratio of magnetic to kinetic energy in the saturated state increases gradually. The nonlinear viscosity generated by the turbulent fluctuations rises rapidly relative to the collisional viscosity as R increases, such that the total transport of momentum remains virtually unchanged as the collisional viscosity is reduced. The scale lengths of the magnetic and velocity fluctuations both decrease as R increases, so that the scale size of the magnetic field remains comparable to the scale size of the flow. © 1995 American Institute of Physics.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.30.-q Plasma dynamics and flow

Relativistic shock waves in an electron–positron plasma

Levan N. Tsintsadze

Phys. Plasmas 2, 4462 (1995); http://dx.doi.org/10.1063/1.871003 (8 pages) | Cited 24 times

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The equations describing the detailed structure of radiation electromagnetic hydrodynamics for a relativistically hot electron–positron plasma are derived. Various discontinuities are studied by these equations. It is shown that the dependence of the electron (positron) mass on the temperature changes the structure of discontinuities, including shock waves, both qualitatively and quantitatively. Steady radiative shocks are considered, which can arise in steady flows, and which also can be used to describe the propagation of shocks when the shock thickness is very small as compared to the characteristic length over which the ambient medium changes significantly. First, the magnetohydrodynamic shock wave is treated as a discontinuity and jump relations, which relate the equilibrium states of the upstream and downstream plasma far from the front, are derived. Then the structure of the front itself is considered and tangential, contact (or entropy) and rotational discontinuities are investigated. © 1995 American Institute of Physics.
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52.27.Ny Relativistic plasmas
52.35.Tc Shock waves and discontinuities
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Formation and evolution of envelope shocks of ion plasma waves

Tadao Honzawa, Takao Hoshina, and Yoshifumi Saitou

Phys. Plasmas 2, 4470 (1995); http://dx.doi.org/10.1063/1.871004 (6 pages) | Cited 2 times

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It is experimentally shown that envelope shocks of low frequency ion plasma waves are formed in a plasma. If the wave amplitude is large enough, a broad packet form of externally excited ion plasma wave first steepens at its leading edge. Thereafter, the wave envelope near the edge evolves into a series of wave packets, forming an envelope shock. A precursor due to reflected ions is also observed ahead of the shock. © 1995 American Institute of Physics.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Tc Shock waves and discontinuities
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

An analytical solution of finite‐amplitude solitary kinetic Alfvén waves

De‐Jin Wu, De‐Yu Wang, and Carl‐Gunne Fälthammar

Phys. Plasmas 2, 4476 (1995); http://dx.doi.org/10.1063/1.871005 (6 pages) | Cited 32 times

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An analytical solution of finite‐amplitude solitary kinetic Alfvén waves (SKAWs) in a low‐β (β≪me/mi≪1) plasma is presented. This solution has been compared with the solution of the Korteweg–de Vries (KdV) equation in the small‐amplitude limit. It is found that the KdV soliton solution is valid only for the maximum relative density perturbation Nm<0.1. For the larger Nm, the exact analytical solution shows that the SKAWs have a much wider structure and much stronger perturbed fields than the KdV solitons with the same Nm. Moreover, the relations between the width and the amplitude of SKAWs are also considerably different from that of the KdV solitons. In addition, the possibility for applying these results to some events observed from the Freja scientific satellite is discussed. (The Freja is a Swedish–German scientific project for the investigation of ionospheric and magnetospheric plasmas, and the Freja satellite was launched on a Long‐March II rocket of China on October 6, 1992.) © 1995 American Institute of Physics.
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52.35.Sb Solitons; BGK modes
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
93.30.Sq Polar regions
94.30.Tz Electromagnetic wave propagation

Rarefaction waves, solitons, and holes in a pure electron plasma

J. D. Moody and C. F. Driscoll

Phys. Plasmas 2, 4482 (1995); http://dx.doi.org/10.1063/1.871006 (12 pages) | Cited 16 times

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The propagation of holes, solitons, and rarefaction waves along the axis of a magnetized pure electron plasma column is described. The time dependence of the radially averaged density perturbation produced by the nonlinear waves is measured at several locations along the plasma column for a wide range of plasma parameters. The rarefaction waves are studied by measuring the free expansion of the plasma into a vacuum. A new hydrodynamic theory is described that quantitatively predicts the free expansion measurements. The rarefaction is initially characterized by a self‐similar plasma flow, resulting in a perturbed density and velocity without a characteristic length scale. The electron solitons show a small increase in propagation speed with increasing amplitude and exhibit electron bursts. The holes show a decrease in propagation speed with increasing amplitude. Collisions between holes and solitons show that these objects pass through each other undisturbed, except for a small offset. © 1995 American Institute of Physics.
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52.35.Sb Solitons; BGK modes
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Interface localized instabilities in resistive magnetohydrodynamics

D. Lortz and G. O. Spies

Phys. Plasmas 2, 4494 (1995); http://dx.doi.org/10.1063/1.871007 (5 pages) | Cited 1 time

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Modes localized at a plasma–vacuum interface are studied in plane slab equilibria by using resistive magnetohydrodynamics. Such modes are unstable whenever the current density and the magnetic field are not perpendicular to each other in the interface. The perturbations have no radial nodes but large mode numbers in the other two directions. The instability occurs for a wide range of angles between the nodal lines and the magnetic field lines in the interface and does not depend on the presence of a mode resonant surface. © 1995 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Hamiltonian approach to the magnetostatic equilibrium problem

Massimo Tessarotto, John L. Johnson, and Lin Jin Zheng

Phys. Plasmas 2, 4499 (1995); http://dx.doi.org/10.1063/1.871008 (14 pages) | Cited 8 times

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The purpose of this paper is to investigate the classical scalar‐pressure magnetostatic equilibrium problem for nonsymmetric configurations in the framework of a Hamiltonian approach. Requiring that the equilibrium admits locally a family of nested toroidal magnetic surfaces, the Hamiltonian equations describing the magnetic flux lines in such a subdomain are obtained for a general canonical curvilinear coordinate system. The properties of such a coordinate system are investigated and a representation of the magnetic field is obtained. Its basic feature is that the magnetic field must fulfill suitable periodicity constraints to be imposed on arbitrary rational magnetic surfaces for general nonsymmetric toroidal equilibria, i.e., it is quasisymmetric. Implications for the existence of magnetostatic equilibria are pointed out. In particular, it is proven that a generalized equilibrium equation exists for such quasisymmetric equilibria, which extends the Grad–Shafranov equation to fully three‐dimensional configurations. As an application, a representation is obtained for generalized helically symmetric equilibrium, extending the definition given by Nührenberg and Zille [Phys. Lett. A 129, 113 (1988)]. Since the new representation overcomes the inconsistency exhibited by the previous representation near the magnetic axis, pointed out by Garren and Boozer [Phys. Fluids B 3, 2805, 2822 (1991)], it appears potentially useful to interpret the numerical findings of quasihelical equilibria obtained so far. © 1995 American Institute of Physics.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.

Implosions, equilibria, and stability of rotating, radiating Z‐pinch plasmas

A. L. Velikovich and J. Davis

Phys. Plasmas 2, 4513 (1995); http://dx.doi.org/10.1063/1.871467 (8 pages) | Cited 4 times

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The effects of uniform rotation on the dynamics, equilibria and stability of cylindrically symmetric, radiating Z‐pinch plasmas are studied. Rotation changes the Bennett and Pease–Braginskii equilibria qualitatively, eliminating radiative collapse for both quasisteady and dynamic plasmas. In particular, a steady rotating plasma column can support any current above the Pease–Braginskii value, with Ohmic heating balanced by radiative losses. Stabilizing effect of rotation on the m=0 mode of Rayleigh–Taylor instability of a hollow plasma shell was found for long perturbation wavelengths. © 1995 American Institute of Physics.
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52.55.Ez Theta pinch
52.30.-q Plasma dynamics and flow
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Stabilization of resistive wall modes by slow plasma rotation

Allen H. Boozer

Phys. Plasmas 2, 4521 (1995); http://dx.doi.org/10.1063/1.871009 (12 pages) | Cited 33 times

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External kinks that drive magnetic islands inside a plasma can be stabilized by a resistive wall for even a slow plasma rotation. It is shown that only a subclass of ideal kinks avoid driving islands and stabilization by slow rotation. In addition, the separatrix of a tokamak divertor causes external kink instabilities to have resonant surfaces within the plasma and drive islands. Consequently, tokamaks with a hot divertor scrape‐off layer may be more stable to resistive wall modes than tokamaks with limiters. It is shown that the calculation and description of the stability of wall modes is greatly simplified by the use of the inductance, resistance, and torque associated with a surface current. © 1995 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.-q Plasma dynamics and flow
52.55.Fa Tokamaks, spherical tokamaks
52.35.Dm Sound waves

Self‐similarity of stochastic magnetic field lines near the X‐point

S. S. Abdullaev and G. M. Zaslavsky

Phys. Plasmas 2, 4533 (1995); http://dx.doi.org/10.1063/1.871010 (9 pages) | Cited 34 times

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The properties of magnetic field line trajectories near a separatrix are studied and the renormalization invariance of the Hamiltonian of the system near the X‐point is considered in relation to the perturbation amplitude. To describe the footprint of intersections of the trajectories with an arbitrarily positioned plane, the shifted separatrix map is derived and applied to the analysis of the magnetic field lines dynamics in the stochastic layer and to the magnetic footprint. The numerical simulations confirm the renormalization invariance of the field line equations, surface of section of the field line trajectories, and magnetic footprint obtained by the shifted separatrix map for a simple Hamiltonian system, which is topologically equivalent to the single null poloidal divertor of a tokamak. © 1995 American Institute of Physics.
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45.05.+x General theory of classical mechanics of discrete systems
47.52.+j Chaos in fluid dynamics
52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.
52.55.Fa Tokamaks, spherical tokamaks

Current diffusion and toroidal electric field response to a non‐Ohmic current drive

C. Litwin

Phys. Plasmas 2, 4542 (1995); http://dx.doi.org/10.1063/1.871011 (9 pages) | Cited 5 times

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Resistive current diffusion and inductive electric field evolution in response to an auxiliary current drive are analyzed for conditions typical for tokamak operation. Special emphasis is placed on a localized current drive. Relaxation time scales for a broad range of conductivity profiles are calculated, using the Wentzel–Kramer–Brillouin (WKB) approximation, and compared with numerical solutions. Validity of the effective circuit model is discussed. © 1995 American Institute of Physics.
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52.25.Fi Transport properties
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.50.Gj Plasma heating by particle beams
52.55.Fa Tokamaks, spherical tokamaks

Analysis of loop voltage evolution in current drive experiments in the Phaedrus‐T tokamak

C. Litwin, N. Hershkowitz, S. Wukitch, T. Intrator, M. Vukovic, D. Brouchous, R. Breun, and M. Harper

Phys. Plasmas 2, 4551 (1995); http://dx.doi.org/10.1063/1.871012 (4 pages) | Cited 2 times

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The loop voltage response in the low‐frequency current drive experiments is analyzed in order to extract information about the current drive profile and efficiency. © 1995 American Institute of Physics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.50.Gj Plasma heating by particle beams
52.55.Fa Tokamaks, spherical tokamaks

Nonlinear evolution of the alpha‐particle‐driven toroidicity‐induced Alfvén eigenmode

Yanlin Wu, Roscoe B. White, Yang Chen, and M. N. Rosenbluth

Phys. Plasmas 2, 4555 (1995); http://dx.doi.org/10.1063/1.871013 (8 pages) | Cited 14 times

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A fast and efficient numerical algorithm using energy conservation is developed to study the interaction of high‐energy particles with a toroidicity‐induced Alfvén eigenmode (TAE). A Hamiltonian guiding center code is used to simulate the alpha particle motion and a nonlinear δf scheme is employed to calculate the wave‐particle energy exchange. The code is benchmarked using the bump‐on‐tail problem and simulation results agree with analytical estimates. For a single TAE mode, the particle radial excursion is much less than the spacing between the resonances produced by the poloidal harmonics for International Thermonuclear Experimental Reactor parameters. Resonant particles that lose their energy to the wave can become trapped poloidally, but transfer to a loss orbit through this mechanism does not occur. Modification of the particle distribution leading to mode saturation is observed. © 1995 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.65.Tt Gyrofluid and gyrokinetic simulations

Plasma flow resulting from electron cyclotron resonance heating on a magnetic hill

E. B. Hooper

Phys. Plasmas 2, 4563 (1995); http://dx.doi.org/10.1063/1.871014 (7 pages) | Cited 4 times

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The flow of low collisionality plasma down a magnetic hill during electron cyclotron resonance heating is analyzed using a particle‐in‐cell code that follows both the electron and ion guiding centers. The analysis is applied to the formation of an ion beam by plasma expansion in a magnetic nozzle, of interest for plasma thrusters and other applications. The ambipolar electric potential that accelerates the ions is enhanced by effects of the magnetic forces on the electrons that are heated perpendicular to the magnetic field. Comparison with flow in the presence of isotropic heating demonstrates an increase in the efficiency of the particle and energy fluxes down the field relative to those that flow up the field to a wall at a large mirror ratio. The increases are reduced somewhat if particles recycle near the wall, but are still significant.
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52.50.Dg Plasma sources
52.50.Gj Plasma heating by particle beams
52.65.Rr Particle-in-cell method

Analysis of electron cyclotron current drive using neoclassical Fokker–Planck code without bounce‐average approximation

H. Takase

Phys. Plasmas 2, 4570 (1995); http://dx.doi.org/10.1063/1.871015 (5 pages) | Cited 2 times

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A new three‐dimensional relativistic Fokker–Planck code (poloidal angle and two dimensions in momentum space) has been developed for the analysis of electron cyclotron current drive (ECCD) in tokamak plasmas. This numerical code takes into consideration trapped electron effects without using the bounce‐average approximation. Simulations have been carried out using the code, and the results were compared with those of a bounce‐averaged Fokker–Planck code. There are differences in the current drive efficiencies calculated by the two codes, and this difference is shown to be caused by a change in electron velocity parallel to the magnetic field due to the inhomogeneous magnetic field. © 1995 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
52.50.Gj Plasma heating by particle beams
52.55.Fa Tokamaks, spherical tokamaks
52.65.Ff Fokker-Planck and Vlasov equation

Theory of isolated, small‐scale magnetic islands in a high temperature tokamak plasma

J. W. Connor and H. R. Wilson

Phys. Plasmas 2, 4575 (1995); http://dx.doi.org/10.1063/1.871016 (11 pages) | Cited 20 times

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A theory for the existence of noninteracting small‐scale, ‘‘drift’’ magnetic islands in a high temperature tokamak plasma is presented. This situation contrasts with that discussed by Rebut and Hugon [Plasma Phys. Controlled Fusion 33, 1085 (1991)] which involves a background ‘‘sea’’ of magnetic turbulence caused by island overlap. The islands are driven by the effect of finite ion Larmor radius on the particle drifts and they propagate with a velocity comparable to the diamagnetic velocity. In contrast with the work of Smolyakov [Plasma Phys. Controlled Fusion 35, 657 (1993)] collisions are assumed to be rare. Although the saturated island size is independent of the collision frequency in the model discussed here, collisions play a crucial role in determining the frequency of the magnetic islands. An estimate is made of the anomalous heat transport which results from the fluctuations in the electrostatic potential associated with these magnetic islands. The predicted thermal diffusivity has several, but not all, of the characteristics of the Rebut–Lallia–Watkins transport model. © 1995 American Institute of Physics.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects

The perpendicular electron energy flux driven by magnetic fluctuations in the edge of the Texas Experimental Tokamak

G. Fiksel, Roger D. Bengtson, S. C. Prager, and A. J. Wootton

Phys. Plasmas 2, 4586 (1995); http://dx.doi.org/10.1063/1.871017 (3 pages) | Cited 8 times

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A fast bolometer was used for direct measurements of parallel electron energy flux in the edge of the Texas Experimental Tokamak (TEXT‐U) [K. W. Gentle, Nucl. Technol. Fusion 1, 479 (1981)]. The fluctuating component of the parallel electron energy flux, combined with a measurement of magnetic fluctuations, provides an upper limit to the perpendicular electron flux. This magnetically driven energy flux cannot account for the observed energy flux. © 1995 American Institute of Physics.
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52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
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  1. On the mechanism for edge localized mode mitigation by supersonic molecular beam injection
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