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Dec 2000

Volume 7, Issue 12, pp. 4797-5271

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Destabilizing effect of thermal conductivity on the Rayleigh–Taylor instability in a plasma

D. D. Ryutov

Phys. Plasmas 7, 4797 (2000); http://dx.doi.org/10.1063/1.1321316 (4 pages) | Cited 10 times

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It is shown that the Rayleigh–Taylor instability in a compressible medium is not necessarily stabilized by thermal conductivity. It is pointed out that one can use the destabilization effect for in situ measurements of thermal conductivity in high-energy-density experiments. The other consequence is generation of small-scale turbulence in supernovae, giving rise to significant turbulent viscosity. © 2000 American Institute of Physics.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.57.-z Laser inertial confinement
47.20.Bp Buoyancy-driven instabilities (e.g., Rayleigh-Benard)
97.60.Bw Supernovae

Tokamak, reversed field pinch and intermediate structures as minimum-dissipative relaxed states

R. Bhattacharyya, M. S. Janaki, and B. Dasgupta

Phys. Plasmas 7, 4801 (2000); http://dx.doi.org/10.1063/1.1324660 (4 pages) | Cited 10 times

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The principle of minimum energy dissipation rate is utilized to develop a unified model for relaxation in toroidal discharges. The Euler–Lagrange equation for such relaxed states is solved in toroidal coordinates for an axisymmetric torus by expressing the solutions in terms of Chandrasekhar–Kendall (C–K) eigenfunctions analytically continued in the complex domain. The C–K eigenfunctions are hypergeometric functions that are solutions of the scalar Helmholtz equation in toroidal coordinates in the large-aspect-ratio approximation. Equilibria are constructed by assuming the total current J = 0 at the edge. This yields the eigenvalues for a given aspect-ratio. The most novel feature of the present model is that solutions allow for tokamak, low-q as well as reversed field pinch-like behavior with a change in the eigenvalue characterizing the relaxed state. © 2000 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.55.Ez Theta pinch
52.30.-q Plasma dynamics and flow
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back to top Basic Plasma Phenomena, Waves, Instabilities

The diocotron spectrum of a toroidal non-neutral plasma

S. N. Bhattacharyya

Phys. Plasmas 7, 4805 (2000); http://dx.doi.org/10.1063/1.1319334 (7 pages) | Cited 4 times

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The equilibrium and stability of a toroidal non-neutral plasma of low density has been studied numerically. The equilibrium is computed using the variational moment method, while linear stability is computed using a Fourier representation in the poloidal coordinate and a finite difference approximation in the radial coordinate. The computation has been carried out for various configurations to obtain frequencies of stable modes and the growth rate of instabilities. © 2000 American Institute of Physics.
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52.27.Jt Nonneutral plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
02.70.Bf Finite-difference methods

Limit of temperature anisotropy relaxation by ion cyclotron waves: A statistical theory

Tadas K. Nakamura

Phys. Plasmas 7, 4812 (2000); http://dx.doi.org/10.1063/1.1321015 (4 pages) | Cited 4 times

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The ion velocity distribution resulting from ion anisotropy reduction by the growth of ion cyclotron waves has been investigated by the use of a Maximum Entropy Principle. The anisotropy is reduced due to waves induced by an electromagnetic instability, but the system saturates before a completely isotropic Maxwellian distribution is realized, and a nonzero level of anisotropy remains in the final state. This is because the scattering process has a restriction; waves do not alter particle energy in the wave rest frame. Taking this restriction into account as an additional constraint, the final state is calculated by maximizing the entropy. The results show that the upper bound of the plasma β and anisotropy are inversely correlated, which is quantitatively in agreement with recent studies on satellite observations, numerical simulations, and laboratory experiments. © 2000 American Institute of Physics.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.25.Kn Thermodynamics of plasmas

Variational principle for nonlinear gyrokinetic Vlasov–Maxwell equations

Alain J. Brizard

Phys. Plasmas 7, 4816 (2000); http://dx.doi.org/10.1063/1.1322063 (7 pages) | Cited 32 times

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A new variational principle for the nonlinear gyrokinetic Vlasov–Maxwell equations is presented. This Eulerian variational principle uses constrained variations for the gyrocenter Vlasov distribution in eight-dimensional extended phase space and turns out to be simpler than the Lagrangian variational principle recently presented by H. Sugama [Phys. Plasmas 7, 466 (2000)]. A local energy conservation law is then derived explicitly by the Noether method. In future work, this new variational principle will be used to derive self-consistent, nonlinear, low-frequency Vlasov–Maxwell bounce-gyrokinetic equations, in which the fast gyromotion and bounce-motion time scales have been eliminated. © 2000 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
03.50.De Classical electromagnetism, Maxwell equations

Relativistic magnetohydrodynamics revisited

Alfredo Sandoval-Villalbazo and Leopoldo S. García-Colín

Phys. Plasmas 7, 4823 (2000); http://dx.doi.org/10.1063/1.1322064 (8 pages) | Cited 3 times

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Magnetohydrodynamics is discussed within the framework of irreversible thermodynamics. The nonrelativistic version is reviewed by introducing the electromagnetic field as an external force. Results are discussed and emphasis is placed on the fact that the transport equations, being of a parabolic type, violate causality. The relativistic version is next considered using Kaluza’s ideas about unifying fields in terms of the corresponding space–time curvature for a given metric. The outcome of this approach is rewarding. The conservation equations follow in a direct way as well as the entropy balance equation with an entropy production whose form suggests the type of constitutive equations that are consistent with its semipositive character. Further, the resulting transport equations are of a hyperbolic type in agreement with causality. Therefore, relativistic magnetohydrodynamics is placed within a thermodynamic framework consistent with the second law. © 2000 American Institute of Physics.
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04.40.-b Self-gravitating systems; continuous media and classical fields in curved spacetime
04.50.-h Higher-dimensional gravity and other theories of gravity
05.70.Ln Nonequilibrium and irreversible thermodynamics
back to top Nonlinear Phenomena, Turbulence, Transport

Hole equilibria in Vlasov–Poisson systems: A challenge to wave theories of ideal plasmas

H. Schamel

Phys. Plasmas 7, 4831 (2000); http://dx.doi.org/10.1063/1.1316767 (14 pages) | Cited 113 times

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A unified description of weak hole equilibria in collisionless plasmas is given. Two approaches, relying on the potential method rather than on the Bernstein, Greene, Kruskal method and associated with electron and ion holes, respectively, are shown to be equivalent. A traveling wave solution is thereby uniquely characterized by the nonlinear dispersion relation and the “classical” potential V(ϕ), which determine the phase velocity and the spectral decomposition of the wave structure, respectively. A new energy expression for a hole carrying plasma is found. It is dominated by a trapped particle contribution occurring one order earlier in the expansion scheme than the leading term in conventional schemes based on a truncation of Vlasov’s equation. Linear wave theory— reconsidered by taking the infinitesimal amplitude limit—is found to be deficient, as well. Neither Landau nor van Kampen modes and their general superpositions can adequately describe these trapped particle modes due to an incorrect treatment of resonant particles for phase velocities in the thermal range. It is therefore concluded that wave theories in their present form, dictated by linearity, are not yet properly shaped to describe the dynamics of ideal plasmas (and fluids) correctly. © 2000 American Institute of Physics.
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52.35.Sb Solitons; BGK modes

Kinetic modeling of a one-dimensional, bounded plasma in the ambipolar regime

Monojoy Goswami and H. Ramachandran

Phys. Plasmas 7, 4845 (2000); http://dx.doi.org/10.1063/1.1318356 (6 pages)

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In this paper we present a self-consistent kinetic simulation of a diffusion dominated bulk plasma region. Collisions have been modeled by a velocity-dependent Krook collision operator. The technique is capable of handling large systems—the results presented here are for systems 100λmfp in extent—yet retains the details of the edge physics present. The distribution functions for the trapped and the transiting orbits and their moments are obtained. The density and potential profiles inside the bulk shows overall agreement with ambipolar predictions. The kinetic equivalent of DA is obtained and compared to the fluid prediction. The validity of the code and the observed deviations from fluid treatments are discussed. © 2000 American Institute of Physics.
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51.10.+y Kinetic and transport theory of gases
52.25.Dg Plasma kinetic equations
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.65.-y Plasma simulation

Finger instability in radiatively driven dusty plasmas

Andreas Schröer and Yuri Shchekinov

Phys. Plasmas 7, 4851 (2000); http://dx.doi.org/10.1063/1.1318357 (7 pages)

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In this work the dynamics of a three-fluid plasma consisting of electrons, ions and charged dust particles are considered. The plasma is illuminated by a radiation field, which, through absorbtion, accelerates the dust particles. By direct and Coulomb collisions the gained momentum is partially transmitted to electrons and ions. A steady state can be achieved by an external gravitational field acting against the radiation. After presenting the steady-state flow, linear perturbations of dynamical variables with the wave vector perpendicular to the radiation flux are considered. A linear analysis is performed by reducing the full three-fluid description to a suitable one-fluid system of equations, assuming the plasma to be quasineutral and omitting plasma species separation. It is demonstrated that when the drag force between ions and dust particles is a decreasing function of their relative velocity, the steady state is unstable against the formation of parallel layered streams with high and low relative flow velocities, i.e., multiple current sheets. The temporal evolution of this instability is then investigated by means of numerical simulations in the framework of a complete three-fluid model. © 2000 American Institute of Physics.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
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.)

Generalized weak turbulence theory

Peter H. Yoon

Phys. Plasmas 7, 4858 (2000); http://dx.doi.org/10.1063/1.1318358 (14 pages) | Cited 30 times

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In this article we present the derivation of a generalized weak turbulence kinetic equation for unmagnetized collisionless plasmas in a uniform medium. For the sake of simplicity the present formulation assumes longitudinal electrostatic interaction only, and the effects of spontaneous thermal fluctuations are ignored. In spite of these simplifications, the present formalism represents a generalization of the existing weak turbulence theory in that a nonlinear eigenmode excited in a turbulent plasma with frequency close to twice the plasma frequency is incorporated into the discussion. Traditional weak turbulence theory emphasizes various linear and nonlinear interactions among wave modes in quiescent plasmas (i.e., Langmuir and ion-sound waves). In contrast, the present formalism describes linear and nonlinear interactions among Langmuir, ion-sound, and the new nonlinear eigenmode. Nonlinear wave kinetic equations for these modes are systematically derived, and the particle kinetic equation which generalizes the well known quasilinear diffusion equation, is also derived. © 2000 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Ra Plasma turbulence

Electromagnetic vortices in streaming pair plasmas

J. Vranješ, M. Kono, E. Lazzaro, and M. Lontano

Phys. Plasmas 7, 4872 (2000); http://dx.doi.org/10.1063/1.1318359 (6 pages) | Cited 12 times

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Two coupled nonlinear equations for a perturbed electromagnetic field in an electron–positron streaming plasma which is placed in a nonuniform magnetic field are derived and solved analytically, yielding stationary solutions in the form of vortices consisting of monopolar and quadrupolar parts. It is shown that vortices are created in and carried by a specific given linear shear flow profile and a given nonuniformity of the magnetic shear. © 2000 American Institute of Physics.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Sb Solitons; BGK modes

Theory of Langmuir wave generation in the presence of Alfvén wave turbulence in an electron-positron plasma: Case III

H. Kakati, K. S. Goswami, and S. Bujarbarua

Phys. Plasmas 7, 4878 (2000); http://dx.doi.org/10.1063/1.1287420 (4 pages)

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The plasma maser interaction of a test Langmuir wave in the presence of Alfvén wave turbulence is studied theoretically in a magnetized electron-positron (e-p) plasma, where the turbulence is produced by both electron and positron temperature anisotropies. Langmuir waves are generated without the necessity of an electron or positron beam component. The growth takes place in the direction of propagation of the Alfvén waves. © 2000 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Ra Plasma turbulence
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Kn Thermodynamics of plasmas

Simulation studies of heavy ion heating by current-driven instabilities

M. Toida, T. Maeda, I. Shiiba, A. Sugishima, and Y. Ohsawa

Phys. Plasmas 7, 4882 (2000); http://dx.doi.org/10.1063/1.1321017 (7 pages) | Cited 5 times

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Nonlinear evolution of current-driven instabilities and associated energy transport among different particle species are studied by means of a two-dimensional, electrostatic, particle simulation code with full ion and electron dynamics. The plasma is assumed to consist of hydrogen (H) and helium (He) ions and electrons with the electron temperature larger than the ion temperatures; the electrons drift along a uniform magnetic field with an initial speed equal to the thermal speed. Then, simulations show that after the development of ion acoustic waves and fundamental H cyclotron waves, second harmonic waves are destabilized due to the change in the electron velocity distribution function parallel to the magnetic field, fe(v∥). Even though the linear theory based on the initial conditions predicts that the second harmonics are only marginally unstable, they eventually grow to the largest amplitudes and heat He ions more significantly than H ions. The instabilities of these three kinds of modes with different phase velocities give rise to flattening of fe(v∥) over a region larger than the thermal speed. © 2000 American Institute of Physics.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.25.Fi Transport properties

Scaling properties of three-dimensional isotropic magnetohydrodynamic turbulence

Dieter Biskamp and Wolf-Christian Müller

Phys. Plasmas 7, 4889 (2000); http://dx.doi.org/10.1063/1.1322562 (12 pages) | Cited 86 times

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A comprehensive picture of three-dimensional (3D) isotropic magnetohydrodynamic (MHD) turbulence is presented based on the first 5123-mode numerical simulations performed. Both temporal and spatial scaling properties are studied. For finite magnetic helicity H the energy decay is governed by the constancy of H and the decrease of the ratio of kinetic and magnetic energy Γ = EK/EM. A simple model consistent with a series of simulation runs predicts the asymptotic decay laws E ∼ t−1/2, EK ∼ t−1. For nonhelical MHD turbulence, H ≃ 0, the energy decays faster, E ∼ t−1. The energy spectrum follows a k−5/3 law, clearly steeper than k−3/2 previously found in 2D MHD turbulence. The scaling exponents of the structure functions are consistent with a modified She–Leveque model ζpMHD = p/9+1−(1/3)p/3, which corresponds to a basic Kolmogorov scaling and sheet-like dissipative structures. The difference between the 3D and the 2D behavior can be related to the eddy dynamics in 3D and 2D hydrodynamic turbulence. © 2000 American Institute of Physics.
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47.27.Gs Isotropic turbulence; homogeneous turbulence
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.27.E- Turbulence simulation and modeling

Role of collective effects in dominance of scattering off thermal ions over Langmuir wave decay: Analysis, simulations, and space applications

Iver H. Cairns

Phys. Plasmas 7, 4901 (2000); http://dx.doi.org/10.1063/1.1319638 (15 pages) | Cited 15 times

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Langmuir waves driven to high levels by beam instabilities are subject to nonlinear processes, including the closely related processes of scattering off thermal ions (STI) and a decay process in which the ion response is organized into a product ion acoustic wave. Calculations of the nonlinear growth rates predict that the decay process should always dominate STI, creating two paradoxes. The first is that three independent computer simulation studies show STI proceeding, with no evidence for the decay at all. The second is that observations in space of type III solar radio bursts and Earth’s foreshock, which the simulations were intended to model, show evidence for the decay proceeding but no evidence for STI. Resolutions to these paradoxes follow from the realization that a nonlinear process cannot proceed when its growth rate exceeds the minimum frequency of the participating waves, since the required collective response cannot be maintained and the waves cannot respond appropriately, and that a significant number of e-foldings and wave periods must be contained in the time available. It is shown that application of these “collective” and “time scale” constraints to the simulations explains why the decay does not proceed in them, as well as why STI proceeds in specific simulations. This appears to be the first demonstration that collective constraints are important in understanding nonlinear phenomena. Furthermore, applying these constraints to space observations, it is predicted that the decay should proceed (and dominate STI) in type III sources and the high beam speed regions of Earth’s foreshock for a specific range of wave levels, with a possible role for STI alone at slightly higher wave levels. Deeper in the foreshock, for slower beams and weaker wave levels, the decay and STI are predicted to become ineffective. Suggestions are given for future testing of the collective constraint and an explanation for why waves in space are usually much weaker than in the simulations. © 2000 American Institute of Physics.
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52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.65.-y Plasma simulation
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
96.50.Ry Discontinuities

Electro-acoustic damping effects on the parametric decays of electromagnetic waves in electron–positron plasmas

Víctor Muñoz and Luis Gomberoff

Phys. Plasmas 7, 4916 (2000); http://dx.doi.org/10.1063/1.1322065 (7 pages) | Cited 1 time

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Parametric decays of a linearly polarized electromagnetic wave in an electron–positron plasma, including weakly relativistic effects and damping on the electro-acoustic pseudomodes, are studied. The effect of nondissipative Landau damping is simulated through a phenomenological collisional-like term in the fluid equations. It is shown that in general, there are a number of instabilities due to the coupling between electro-acoustic and electromagnetic pseudomodes, and between electromagnetic modes. On the other hand, damping effects reduce the growth rate of these instabilities and increase the instability range. It is also shown that there are no threshold effects on any of the decay modes. © 2000 American Institute of Physics.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
51.60.+a Magnetic properties

Strong narrow-band electron cyclotron emission from a mirror plasma heated by electron cyclotron waves

K. Ito, Y. Kiwamoto, T. Saito, and Y. Tatematsu

Phys. Plasmas 7, 4923 (2000); http://dx.doi.org/10.1063/1.1322556 (8 pages) | Cited 1 time

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Strong electromagnetic radiation is observed in a narrow band slightly above the frequency of a heating wave that is absorbed by electrons near the electron cyclotron resonance layer in a magnetic beach. The frequency spectrum consists of a sharp component and a broad background, which is enhanced by more than 30 dB and 10 dB, respectively, above the radiation of thermal electrons. This observation is explained in terms of cyclotron radiation emitted by electrons, localized in a magnetic mirror, that are resonantly heated and bunched by a strong monochromatic wave. © 2000 American Institute of Physics.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Gj Plasma heating by particle beams
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
back to top Magnetically Confined Plasmas, Heating, Confinement

The role of thermal instabilities in limiting the density in DIII-D

W. M. Stacey and T. W. Petrie

Phys. Plasmas 7, 4931 (2000); http://dx.doi.org/10.1063/1.1316766 (11 pages) | Cited 13 times

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The mechanisms which apparently govern the maximum achievable density in several DIII-D [Luxon, Anderson, Batty et al., Plasma Physics on Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. 1, p. 159] shots in which different operating procedures were used in building up the density were investigated and compared with the predictions of thermal instability theory. Core MARFEs (multifaceted asymmetric radiation from the edge) followed by a H–L (high-to-low confinement mode) transition limit the density well below the Greenwald limit in continuous gas puffed lower single-null discharges with low triangularity. Similar continuous gas puff fueled discharges with higher triangularity or with pumping in the lower divertor achieve densities at or above the Greenwald value, apparently limited by confinement degradation, without the formation of core MARFEs. Pellet fueled discharges achieve densities up to twice the Greenwald value, limited by global radiative collapse. Thermal instability theory predictions of the limiting core MARFEs, confinement degradation or global radiative collapse are in good agreement with the experimental observations for the shots examined. Evidence for an important role of neutral particles in the plasma edge in core MARFE onset and in confinement degradation was identified. © 2000 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks

Drift mode calculations for the Large Helical Device

G. Rewoldt, L.-P. Ku, W. M. Tang, H. Sugama, N. Nakajima, K. Y. Watanabe, S. Murakami, H. Yamada, and W. A. Cooper

Phys. Plasmas 7, 4942 (2000); http://dx.doi.org/10.1063/1.1317521 (6 pages) | Cited 13 times

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A fully kinetic assessment of the stability properties of toroidal drift modes has been obtained for a case for the Large Helical Device [A. Iiyoshi et al., Nucl. Fusion 39, 1245 (1999)]. This calculation retains the important effects in the linearized gyrokinetic equation, using the lowest-order “ballooning representation” for high toroidal mode number instabilities in the electrostatic limit. Results for toroidal drift waves destabilized by trapped particle dynamics and ion temperature gradients are presented, using three-dimensional magnetohydrodynamic equilibria reconstructed from experimental measurements. The effects of helically trapped particles and helical curvature are investigated. © 2000 American Institute of Physics.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.Tt Gyrofluid and gyrokinetic simulations
52.55.Jd Magnetic mirrors, gas dynamic traps

Effect of poloidal electric field on electron cyclotron current drive in a tokamak geometry

Sanghyuk Lee and C. S. Chang

Phys. Plasmas 7, 4948 (2000); http://dx.doi.org/10.1063/1.1317522 (12 pages)

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Effect of a poloidal electric field on the electron cyclotron current drive is studied in a tokamak geometry. A general discussion of its influence on the electron phase-space dynamics and current drive efficiency is presented. It is shown that the modification to the current drive efficiency increases as the heating location is moved out in the major radius. It is concluded that the modification is only moderate to insignificant (<10% for low magnetic field side heating and <3% for high field side heating) for a poloidal electrostatic potential variation of order inverse aspect ratio under an efficient current drive. © 2000 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.50.Gj Plasma heating by particle beams

Control-matrix approach to stellarator design and control

H. E. Mynick and N. Pomphrey

Phys. Plasmas 7, 4960 (2000); http://dx.doi.org/10.1063/1.1318354 (12 pages) | Cited 3 times

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The full space Z ≡ {Zj = 1,…,Nz} of independent variables defining a stellarator configuration is large. To find attractive design points in this space, or to understand operational flexibility about a given design point, one needs insight into the topography in Z-space of the physics figures of merit Pi which characterize the machine performance, and means of determining those directions in Z-space which give one independent control over the Pi, as well as those which affect none of them, and so are available for design flexibility. The control matrix (CM) approach described here provides a mathematical means of obtaining these. In this work, the CM approach is described and used in studying some candidate Quasi-Axisymmetric (QA) stellarator configurations the National Compact Stellarator Experiment design group has been considering. In the process of the analysis, a first exploration of the topography of the configuration space in the vicinity of these candidate systems has been performed, whose character is discussed. © 2000 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.Fi Transport properties
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Combined kinetic and transport modeling of radiofrequency current drive

R. Dumont, G. Giruzzi, and E. Barbato

Phys. Plasmas 7, 4972 (2000); http://dx.doi.org/10.1063/1.1318355 (11 pages) | Cited 15 times

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A numerical model for predictive simulations of radiofrequency current drive in magnetically confined plasmas is developed. It includes the minimum requirements for a self-consistent description of such regimes, i.e., a three-dimensional kinetic equation for the electron distribution function, one-dimensional heat and current transport equations, and resonant coupling between velocity space and configuration space dynamics, through suitable wave propagation equations. The model finds its full application in predictive studies of complex current profile control scenarios in tokamaks, aiming at the establishment of internal transport barriers by the simultaneous use of various radiofrequency current drive methods. The basic properties of this nonlinear numerical system are investigated and illustrated by simulations applied to reversed magnetic shear regimes obtained by Lower Hybrid and Electron Cyclotron current drive for parameters typical of the Tore Supra tokamak [Equipe Tore Supra, in Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, France, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 1, p. 9]. © 2000 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
52.50.Gj Plasma heating by particle beams

Nonlinear dynamics of feedback modulated magnetic islands in toroidal plasmas

Richard Fitzpatrick and François L. Waelbroeck

Phys. Plasmas 7, 4983 (2000); http://dx.doi.org/10.1063/1.1318360 (13 pages) | Cited 14 times

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An analysis is presented of the dynamics of a helical magnetic island chain embedded in a toroidal plasma, in the presence of an externally imposed, rotating, magnetic perturbation of the same helicity. Calculations are carried out in the large aspect-ratio, zero-β, resistive magnetohydrodynamical limit, and incorporate a realistic treatment of plasma viscosity. There are three regimes of operation, depending on the modulation frequency (i.e., the difference in rotation frequency between the island chain and the external perturbation). For slowly modulated islands, the perturbed velocity profile extends across the whole plasma. For strongly modulated islands, the perturbed velocity profile is localized around the island chain, but remains much wider than the chain. Finally, for very strongly modulated islands, the perturbed velocity profile collapses to a boundary layer on the island separatrix, plus a residual profile which extends a few island widths beyond the separatrix. Analytic expressions are obtained for the perturbed velocity profile, the island equation of motion, and the island width evolution equation in each of these three regimes. The ion polarization correction to the island width evolution equation, which has previously been reported to be stabilizing, is found to be destabilizing in all three regimes. © 2000 American Institute of Physics.
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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.)
52.55.Jd Magnetic mirrors, gas dynamic traps

Numerical study of tilt stability of prolate field-reversed configurations

E. V. Belova, S. C. Jardin, H. Ji, M. Yamada, and R. Kulsrud

Phys. Plasmas 7, 4996 (2000); http://dx.doi.org/10.1063/1.1318929 (11 pages) | Cited 40 times

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Global stability of the field-reversed configuration (FRC) has been investigated numerically using both three-dimensional magnetohydrodynamic and hybrid (fluid electron and δf particle ion) simulations. The stabilizing effects of velocity shear and finite ion Larmor radius (FLR) on the n = 1 internal tilt mode in the prolate FRCs have been studied. Sheared rotation is found to reduce the growth rate, however a large rotation rate with Mach number of M≳1 is required in order for significant reduction in the instability growth rate to occur. Kinetic effects associated with large thermal ion orbits have been studied for different kinetic equilibria. The simulations show that there is a reduction in the tilt mode growth rate due to FLR effects, but complete linear stability has not been found, even when the thermal ion gyroradius is comparable to the distance between the field null and the separatrix. The instability existing beyond the FLR theory threshold could be due to the resonant interaction of the wave with ions whose Doppler shifted frequency matches the betatron frequency. © 2000 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.)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.65.Rr Particle-in-cell method
52.65.Kj Magnetohydrodynamic and fluid equation

A rotating shell and stabilization of the tokamak resistive wall mode

C. G. Gimblett and R. J. Hastie

Phys. Plasmas 7, 5007 (2000); http://dx.doi.org/10.1063/1.1319333 (6 pages) | Cited 7 times

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The finite resistivity of the wall that surrounds any toroidal plasma confinement device can lead to a branch of instabilities known as the resistive wall mode (RWM). Theory indicates that the RWM is potentially activated whenever the plasma equilibrium is unstable with the wall placed at infinity. In particular, advanced tokamak power plant designs require the plasma β to be above the critical value for this condition to be satisfied. Accordingly, it is important to find a method of stabilizing this mode. In this work we describe a method of stabilizing the tokamak RWM that utilizes a secondary rotating conducting shell surrounding the plasma and first wall. This scheme was first thought of for the reversed-field pinch, but must be reexamined for the tokamak as the mode involved has different characteristics. It is shown that provided the second wall is suitably positioned, RWM stabilization of a tokamak is possible even in the absence of plasma rotation. © 2000 American Institute of Physics.
Show PACS
52.55.Fa Tokamaks, spherical tokamaks
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
28.52.Av Theory, design, and computerized simulation
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