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Jul 1997

Volume 4, Issue 7, pp. 2313-2778

Page 1 of 3 Pages Next Page | Jump to Page

Confinement of a neutral plasma using nested electric potential wells

C. A. Ordonez

Phys. Plasmas 4, 2313 (1997); http://dx.doi.org/10.1063/1.872404 (3 pages) | Cited 10 times

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A self-consistent, two-dimensional analysis is presented on confining a region of neutral plasma with a Penning/Malmberg type plasma trap using a nested well configuration. It is found that a neutral plasma region having disparate electron and ion temperatures or having high charge state ions can be confined with static fields. For confining a neutral region comprised of electrons and equal temperature low charge state ions, a quasistatic approach appears promising. © 1997 American Institute of Physics.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.25.Kn Thermodynamics of plasmas

Enhanced reverse shear bifurcation in tokamak

K. Avinash, P. K. Kaw, and R. Singh

Phys. Plasmas 4, 2316 (1997); http://dx.doi.org/10.1063/1.872236 (3 pages) | Cited 3 times

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A transport bifurcation model for enhanced reverse shear (ERS) mode recently observed in tokamaks is given. The model includes effects due to evolution of magnetic shear and bootstrap current. It is shown that these effects substantially reduce the power threshold for ERS transition. © 1997 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.30.-q Plasma dynamics and flow
05.45.-a Nonlinear dynamics and chaos

Crossed-field secondary emission electron source

Y. M. Saveliev, W. Sibbett, and D. M. Parkes

Phys. Plasmas 4, 2319 (1997); http://dx.doi.org/10.1063/1.872614 (3 pages) | Cited 13 times

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A novel crossed-field secondary-emission (CFSE) electron source that is capable of producing high-current tubular electron beams is described. This new electron source is based on the mechanism of secondary-emission multiplication of electron current in a magnetron-like device having smooth cylindrical electrodes. The input electron current may be as low as a few mA. The multiplication process starts at the negative slope of an applied voltage pulse. After initiation, the current is extracted from the diode region with no regard to the voltage pulse shape and as a consequence, the CFSE electron source can operate in a long pulse mode. At the diode voltage of ∼ 40 kV for a diode gap of ∼ 6 mm, the output current reaches a value of more than 100 A.
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07.77.Ka Charged-particle beam sources and detectors
41.75.Fr Electron and positron beams

Linear stability of the collisionless, large Larmor radius Z-pinch

P. G. F. Russell, T. D. Arber, M. Coppins, and J. Scheffel

Phys. Plasmas 4, 2322 (1997); http://dx.doi.org/10.1063/1.872237 (9 pages) | Cited 14 times

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The Vlasov fluid model is used to study the m = 0 and m = 1 internal and free boundary modes in a collisionless, large Larmor radius Z pinch. Two methods (initial value and variational) are employed, and give good agreement. The growth rate can be reduced from its zero Larmor radius value by a factor of up to 10 for m = 1, and up to 3 for m = 0. Stability thresholds and the role of resonant ions are discussed. © 1997 American Institute of Physics.
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52.55.Ez Theta pinch
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.)
52.25.Fi Transport properties
FREE

Dust acoustic waves in a direct current glow discharge

C. Thompson, A. Barkan, N. D’Angelo, and R. L. Merlino

Phys. Plasmas 4, 2331 (1997); http://dx.doi.org/10.1063/1.872238 (5 pages) | Cited 147 times

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An experimental investigation of dust acoustic (DA) waves in a dc glow discharge plasma is described. The glow discharge is formed between a 3 cm anode disk and the grounded walls of a 60 cm diameter vacuum chamber which is filled with nitrogen gas at a pressure of about 100 mTorr. Dust located on a tray in the chamber is attracted into the plasma where it is trapped electrostatically. The dust acoustic waves were produced by applying a modulation signal (5–40 Hz) to the anode. The wavelength of the DA waves was measured from single frame video images of scattered light from the dust grains. The measured dispersion relation is compared with theoretical predictions. © 1997 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Hc Glow; corona
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.25.Vy Impurities in plasmas

Impulsive and transient excitation of Bohm–Gross waves in a dissipative plasma

Orélien C. Randriamboarison

Phys. Plasmas 4, 2336 (1997); http://dx.doi.org/10.1063/1.872239 (12 pages) | Cited 3 times

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Based on the resolution of the partial differential equation describing the external excitation of the Bohm–Gross longitudinal wave, analytical expressions for causal responses of a dissipative macroscopic plasma are derived. Both impulsive and harmonic solutions representing the spatial Green’s functions of the radiation problem are given. These exact responses of the plasma, expressed in terms of two-variable Lommel functions, are then used to gain some better understanding of the excitation and dynamics of the well-known thermal wave. Special attention is paid to the resonant excitation case. Intrinsic characteristics of the secular behavior of the radiated signal are illustrated and analyzed. It is shown that the proffered algebraic solutions constitute a generalization of previous results inferred from an asymptotic representation of the Green’s functions, or from the familiar steady state harmonic approach. © 1997 American Institute of Physics.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Plasma equations in general relativity

Klaus Elsässer and Sergey Popel

Phys. Plasmas 4, 2348 (1997); http://dx.doi.org/10.1063/1.872575 (9 pages) | Cited 5 times

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Vlasov’s equation and the ideal multifluid equations are considered in manifestly covariant form. In the latter case, a thermodynamic closure (locally the first law of thermodynamics) leads to a generalized Kelvin/Helmholtz theorem. In the former case, the local dispersion relation for Langmuir waves in a strong gravitational field is derived and solved. © 1997 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Kn Thermodynamics of plasmas
04.00.00 General relativity and gravitation
52.27.Ny Relativistic plasmas

A model for particle acceleration in lower hybrid collapse

John M. Retterer

Phys. Plasmas 4, 2357 (1997); http://dx.doi.org/10.1063/1.872217 (8 pages) | Cited 4 times

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A model for particle acceleration during the nonlinear collapse of lower hybrid waves is described. Using the Musher-Sturman wave equation to describe the effects of nonlinear processes and a velocity diffusion equation for the particle velocity distribution, the model self-consistently describes the exchange of energy between the fields and the particles in the local plasma. Two-dimensional solutions are presented for the modulational instability of a plane wave and the collapse of a cylindrical wave packet. These calculations were motivated by sounding rocket observations in the vicinity of auroral arcs in the Earth’s ionosphere, which have revealed the existence of large-amplitude lower-hybrid wave packets associated with ions accelerated to energies of 100 eV. The scaling of the sizes of these wave packets is consistent with the theory of lower-hybrid collapse and the observed lower-hybrid field amplitudes are adequate to accelerate the ionospheric ions to the observed energies.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
94.30.cq MHD waves, plasma waves, and instabilities

Stochastic particle transport in a magnetic island due to electrostatic drift waves

Y. Nishimura and M. Azumi

Phys. Plasmas 4, 2365 (1997); http://dx.doi.org/10.1063/1.872218 (11 pages) | Cited 3 times

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The effect of poloidally mode coupled, ballooning type electrostatic drift waves on a magnetic island has been studied both analytically and numerically. It has been shown quantitatively that particle orbits become stochastic and their behavior can be a possible candidate for the radial plasma transport across a magnetic island of a tokamak. The transport is significant in that it takes place even when the flux surface is not destroyed. The mechanism of the stochasticity generation is understood as an overlapping of secondary islands caused by resonance between periodic particle motions in the magnetic island and Fourier modes of E×B drift due to the electrostatic drift waves. The diffusion process perpendicular to magnetic surface has been analyzed by approximating the distribution to the Gaussian type. In addition, local diffusion process in the vicinity of Kolmogorov, Arnold, and Moser surfaces has been discussed. © 1997 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)
52.35.Kt Drift waves
52.55.Fa Tokamaks, spherical tokamaks
02.50.Ey Stochastic processes

Two-dimensional plasma flow past a laser beam

Sandip Ghosal and Harvey A. Rose

Phys. Plasmas 4, 2376 (1997); http://dx.doi.org/10.1063/1.872219 (21 pages) | Cited 13 times

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Analytical results are presented for laser beam deflection rate due to plasma flow when the ponderomotive force (PMF) is static and given. Explicit expressions are obtained in various parameter regimes including that of weak PMF for the case of a coherent (diffraction limited) beam and a beam whose fluctuations are spatially homogeneous, as in the case of a model random phase plate beam. When the Landau damping coefficient, γ0, is negligible and the beam is either coherent and cylindrically symmetric, or random with isotropic fluctuations, the deflection rate is obtained as a closed form function of plasma flow Mach number, M. For finite damping, results are expressed in terms of a universal, one dimensional integral parameterized by M and γ0. For arbitrary PMF and M small, the problem is identified with one in the theory of random dielectric media. © 1997 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.25.Gj Fluctuation and chaos phenomena
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Nonlinear dynamics of an elliptic magnetic stagnation line

C. Wahlberg, H. G. Eriksson, and Z. X. Jiang

Phys. Plasmas 4, 2397 (1997); http://dx.doi.org/10.1063/1.872220 (9 pages) | Cited 1 time

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The nonlinear evolution of the kink instability of a plasma with an elliptic magnetic stagnation line is studied by means of an amplitude expansion of the ideal magnetohydrodynamic (MHD) equations. A cylindrically symmetric plasma with circular field lines is used to model the magnetic field geometry close to the stagnation line. Due to the symmetry with respect to ±z, the linear stability problem of such a system has a two-folded degeneracy, with equal eigenvalues for helical kink perturbations with positive and negative polarization. It is shown that, near marginal stability, the nonlinear evolution of the instability can be described in terms of a two-dimensional potential U(X,Y), where X and Y represent the amplitudes of the perturbations with positive and negative helical polarization. The potential U(X,Y) is found to be nonlinearly stabilizing for all values of the polarization. Furthermore, in addition to the equilibrium point (X,Y) = (0,0), the nonlinear potential has eight equilibrium points in the XY-plane, four corresponding to helical polarization (X or Y = 0) and four to plane polarization (∣X∣ = ∣Y∣). The latter equilibria have the lowest energy, indicating that plane kinks preferably should be formed as the stagnation line instability evolves. The equilibria with helical polarization agree with the bifurcated Z-pinch equilibria obtained by means of a different method in a previous paper [Plasma Phys. Controlled Fusion 35, 551 (1993)]. © 1997 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.)
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.65.Kj Magnetohydrodynamic and fluid equation
52.55.Ez Theta pinch
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra

Van der Pol behavior of virtual anode oscillations in the sheath around a grid in a double plasma device

H. Klostermann, A. Rohde, and A. Piel

Phys. Plasmas 4, 2406 (1997); http://dx.doi.org/10.1063/1.872221 (7 pages) | Cited 23 times

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Experiments are reported on oscillations that arise in a double plasma device when plasma production is restricted to the source chamber and the separating grid between the two chambers is biased negatively. The free oscillating system shows periodic pulling which is a typical behavior of driven van der Pol type oscillators. The second interacting frequency is identified to be half the ion plasma frequency at the sheath edge on the source side. With the help of particle in cell simulations the concept of virtual anode oscillations (VAO’s) as the underlying oscillation mechanism is investigated and the van der Pol character of these is revealed. When applied to the experimental conditions, the VAO-model predicts correct oscillation frequencies. It gives a new interpretation of the scaling of these with plasma density and grid bias, and is compatible with earlier findings. © 1997 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.-y Plasma simulation
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.)
52.75.-d Plasma devices

Quasilinear theory of collisionless electron heating in radio frequency gas discharges

Yu. M. Aliev, I. D. Kaganovich, and H. Schlüter

Phys. Plasmas 4, 2413 (1997); http://dx.doi.org/10.1063/1.872222 (9 pages)

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On the basis of quasilinear kinetic theory, the electron heating of rf discharges is treated for characteristic scale lengths of the heating field much shorter than the electron mean free path. The analysis considers plasmas bounded by walls providing specular reflection. The expressions for the coefficients of electron diffusion in energy space are obtained and analyzed for inductively and capacitively coupled plasmas. Accounting for the oscillatory spatial structure of the penetrating electric field in the regime of anomalous skin effect leads to a decrease of the diffusion coefficient for high, and an increase for low, energy electrons. It is shown that the presence of a second boundary in the case of collisionless plasma slabs results in a similar effect. The formation of energy distribution functions in various regimes of collisionless heating is discussed. The diffusion coefficients are presented taking into account ambipolar electric fields. © 1997 American Institute of Physics.
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52.50.-b Plasma production and heating
52.80.Pi High-frequency and RF discharges
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties

Solution of the drift kinetic equation in the regime of weak collisions by stochastic mapping techniques

Sergei V. Kasilov, Vladimir E. Moiseenko, and Martin F. Heyn

Phys. Plasmas 4, 2422 (1997); http://dx.doi.org/10.1063/1.872223 (14 pages) | Cited 6 times

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A new method for solving the drift kinetic equation applicable for non-integrable particle motion is presented. To obtain this goal, the general form of the drift kinetic equation is reduced to a stochastic mapping equation which is valid in the weak collisions regime. This equation describes the evolution of the distribution function on Poincaré cuts of phase space. The proposed Monte Carlo algorithm applied to the stochastic mapping equation turns out to solve the drift kinetic equation much faster than a direct integration of stochastic orbits. It can be applied to study quasilinear effects of radio frequency heating and transport in systems with complex magnetic field geometries such as stellarators, tokamaks with toroidal magnetic field ripples, or ergodic divertors. For systems with axial space symmetry the stochastic mapping equation is shown to reduce to the well-known canonical (bounce) averaged equation. For nonaxisymmetric magnetic fields the bounce averaged equation for trapped particles is recovered. © 1997 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
52.55.Jd Magnetic mirrors, gas dynamic traps
52.55.Fa Tokamaks, spherical tokamaks
52.20.-j Elementary processes in plasmas

Ion acoustic soliton excitation using a modulated high-frequency sinusoidal wave

Seungjun Yi, Er-Wei Bai, and Karl E. Lonngren

Phys. Plasmas 4, 2436 (1997); http://dx.doi.org/10.1063/1.872224 (7 pages) | Cited 11 times

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Experiments on the excitation of ion acoustic solitons using a fine mesh grid in a normal two component plasma are described. The excitation is novel in that a modulated high-frequency sinusoidal wave voltage signal is applied to the grid. The carrier frequency of the high-frequency sinusoidal wave is above the ion plasma frequency. An interpretation of the velocity modulation and bunching of free streaming ions that pass through the grid to which the signal is applied is given. © 1997 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)

Numerical measurement of turbulent responses in drift-Alfvén turbulence

E. Fernandez and P. W. Terry

Phys. Plasmas 4, 2443 (1997); http://dx.doi.org/10.1063/1.872225 (11 pages) | Cited 3 times

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A drift-Alfvén magnetoturbulence model that augments reduced magnetohydrodynamics with evolution of electron density under parallel compression and fluid advection has been studied numerically. In the Alfvénic regime, measurement of spectral transfer rates, frequency spectra, energy partitions, and the ensemble-averaged turbulent response reveals both Alfvénic and hydrodynamic characteristics. The rms turbulent frequency is Alfvénic, the energies are equipartitioned, and there is a fast, Alfvén-time scale relaxation in the turbulent response. The mean frequency is hydrodynamic, with diamagnetic and eddy straining signatures, and there is an eddy straining decorrelation appearing as a distinct, long time scale branch in the turbulent response. The decay rates and relative fluctuation strengths associated with fast and slow time scale decorrelation are in good agreement with theoretical predictions that posit a Kolmogorov spectrum in the Alfvénic regime. © 1997 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.30.-q Plasma dynamics and flow
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Kt Drift waves

The magnetized Rayleigh-Taylor instability with a temporally variable gravity

D. Winske

Phys. Plasmas 4, 2454 (1997); http://dx.doi.org/10.1063/1.872226 (10 pages) | Cited 4 times

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Hybrid simulations with kinetic ions and massless fluid electrons are used to investigate the linear and nonlinear behavior of the Rayleigh-Taylor instability in a collisionless, magnetized plasma in slab geometry with the plasma subject to a time varying gravity. In particular, cases where the sign of gravity is reversed for some time interval are compared with the corresponding case with constant gravity. Consistent with simple theory, the effect of the gravity reversal is to stop the growth of the instability. And when the gravity is restored to its initial direction, the instability resumes at a rate that is commensurate with its earlier value. Several ways to estimate the rate of growth of the thickness of the mixing layer when math is not constant are suggested and compared with the simulations. © 1997 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.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.-y Plasma simulation

Expansion of the relativistic Fokker-Planck equation including non-linear terms and a non-Maxwellian background

I. P. Shkarofsky

Phys. Plasmas 4, 2464 (1997); http://dx.doi.org/10.1063/1.872227 (18 pages) | Cited 1 time

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The relativistic Fokker-Planck collision term in Braams and Karney [Phys. Fluids B 1, 1355 (1989)] is expanded using Cartesian tensors (equivalent to associated Legendre spherical harmonics) retaining all non-linear terms and an arbitrary zeroth order distribution background. Expressions are given for collision terms between all harmonics and the background distribution in terms of the j and y functions in Braams and Karney. The results reduce to Braams and Karney for the first order harmonic term with a Maxwellian background and to those given by Shkarofsky [Can. J. Phys. 41, 1753 (1963)] in the non-relativistic limit. Expressions for the energy and momentum transfer associated with relativistic Coulomb collisions are given. The fast two dimensional Fokker-Planck solver in Shoucri and Shkarofsky [Comput. Phys. Commun. 82, 287 (1994)] has been extended to include the second order harmonic term. © 1997 American Institute of Physics.
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52.27.Ny Relativistic plasmas
02.30.-f Function theory, analysis
FREE

A gyro-Landau-fluid transport model

R. E. Waltz, G. M. Staebler, W. Dorland, G. W. Hammett, M. Kotschenreuther, and J. A. Konings

Phys. Plasmas 4, 2482 (1997); http://dx.doi.org/10.1063/1.872228 (15 pages) | Cited 295 times

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A physically comprehensive and theoretically based transport model tuned to three-dimensional (3-D) ballooning mode gyrokinetic instabilities and gyrofluid nonlinear turbulence simulations is formulated with global and local magnetic shear stabilization and E×B rotational shear stabilization. Taking no fit coefficients from experiment, the model is tested against a large transport profile database with good agreement. This model is capable of describing enhanced core confinement transport barriers in negative central shear discharges based on rotational shear stabilization. The model is used to make ignition projections from relative gyroradius scaling discharges. © 1997 American Institute of Physics.
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52.25.Fi Transport properties
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.)
52.35.Ra Plasma turbulence
52.65.-y Plasma simulation
52.55.Fa Tokamaks, spherical tokamaks

On the Bernstein–Landau paradox

A. I. Sukhorukov and P. Stubbe

Phys. Plasmas 4, 2497 (1997); http://dx.doi.org/10.1063/1.872229 (11 pages) | Cited 11 times

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The essence of the Bernstein–Landau paradox is that in a stable unmagnetized plasma electrostatic waves exhibit collisionless Landau damping, while in a magnetized plasma the Bernstein modes, perpendicular to the magnetic field, are exactly undamped, independent of the strength of the magnetic field. This problem is the subject of the present study. An analytical solution of the initial value problem for perturbations perpendicular to the magnetic field is given, which is a generalization of the well-known Landau work to magnetized plasmas. By introducing, according to Plemelj’s prescription, plus- and minus-functions, having unique analytical properties, the character of the short-term and long-term plasma response is revealed, showing in the small magnetic field limit Landau damping in the first gyroperiod, followed by recurrence, and exhibiting irregular behavior with no damping at large times. The initial damping rate is seen to be close to the commonly used Landau damping rate for unmagnetized plasmas, however with a significant systematic deviation. A corrected expression for the Landau damping rate is found which yields a perfect description of the initial damping of oscillations perpendicular to a weak magnetic field. An alternative approach, expansion over Bernstein modes, is also employed. It is found that a zero-frequency (convective) mode, revealed earlier in particle simulations, is included in the complete linear treatment. © 1997 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.65.-y Plasma simulation
02.30.-f Function theory, analysis

Numerical observation of turbulence enhanced growth rates

Isidoros Doxas and John R. Cary

Phys. Plasmas 4, 2508 (1997); http://dx.doi.org/10.1063/1.872230 (11 pages) | Cited 15 times

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An enhancement of the velocity diffusion over the quasilinear value is observed in the regime where the autocorrelation time is much smaller than the linear growth time or resonance broadening time. The diffusion enhancement occurs when the resonance broadening time is small compared with the linear growth time. These simulations are self consistent and have enough modes to be in the continuous spectrum limit. That is, even at the initial amplitudes the intermode spacing is sufficiently small that the resonance overlap parameter is large. A possible mechanism for the enhanced diffusion (spontaneous spectrum discretization) is discussed. © 1997 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.-y Plasma simulation
52.25.Fi Transport properties
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.)

Feedback stabilization of the resistive shell mode in a tokamak fusion reactor

Richard Fitzpatrick

Phys. Plasmas 4, 2519 (1997); http://dx.doi.org/10.1063/1.872231 (13 pages) | Cited 18 times

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Stabilization of the “resistive shell mode” is vital to the success of the “advanced tokamak” concept. The most promising reactor relevant approach is to apply external feedback using, for instance, the previously proposed “fake rotating shell” scheme [R. Fitzpatrick and T. H. Jensen, Phys. Plasmas 3, 2641 (1996)]. This scheme, like other simple feedback schemes, only works if the feedback controlled conductors are located inside the “critical radius” at which a perfectly conducting shell is just able to stabilize the ideal external kink mode. In general, this is not possible in a reactor, since engineering constraints demand that any feedback controlled conductors be placed outside the neutron shielding blanket (i.e., relatively far from the edge of the plasma). It is demonstrated that the fake rotating shell feedback scheme can be modified so that it works even when the feedback controlled conductors are located well beyond the critical radius. The gain, bandwidth, current, and total power requirements of such a feedback system for a reactor sized plasma are estimated to be less than 100, a few Hz, a fews tens of kA, and a few MW, respectively. These requirements could easily be met using existing technology. It is concluded that feedback stabilization of the resistive shell mode is possible in a tokamak fusion reactor. © 1997 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.Fa Tokamaks, spherical tokamaks

Plug potential formation in a tandem mirror

I. Katanuma, Y. Kiwamoto, Y. Tatematsu, K. Ishii, T. Saito, K. Yatsu, and T. Tamano

Phys. Plasmas 4, 2532 (1997); http://dx.doi.org/10.1063/1.872232 (12 pages) | Cited 5 times

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It is suggested experimentally that a plug potential forms in a different mechanism from the originally expected scenario in the present tandem mirror [T. Tamano, Phys. Plasmas 2, 2321 (1995)]. That is, the formation requires only electron cyclotron resonance heating experimentally. In this manuscript, therefore, the plug potential with continuous axial profile is analytically shown to be created with the plausible ion and electron distribution functions in a present tandem mirror, i.e., passing ions, mirror trapped ions in the thermal barrier, passing electrons, ϕ-trapped electrons in a plug potential, and the small amount of ions that are born around the plug region.© 1997 American Institute of Physics.
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28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.50.Gj Plasma heating by particle beams
52.25.Fi Transport properties

Theory of fast ion transport induced by sawtooth oscillations: Overview and new results

Ya. I. Kolesnichenko, V. V. Lutsenko, Yu. V. Yakovenko, and G. Kamelander

Phys. Plasmas 4, 2544 (1997); http://dx.doi.org/10.1063/1.872233 (11 pages) | Cited 12 times

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The work contains both an overview of recent theories and new results on the influence of sawtooth oscillations on the superthermal ions in a tokamak plasma. In particular, new results of numerical simulations of the sawtooth-crash-induced redistribution of fast ions are presented. The results are based on the approach suggested by the authors earlier [Nucl. Fusion 36, 159 (1996)]. Peculiarities of the particle motion during the crash are revealed. Dependence of the behavior of fast ions on their parameters, as well as on tokamak parameters and features of sawteeth, is analyzed. Based on this analysis, a simple picture showing the different effects of sawtooth oscillations on various groups of particles is suggested. © 1997 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)
52.65.-y Plasma simulation
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.)

Radiative and three-body recombination in the Alcator C-Mod divertor

D. Lumma, J. L. Terry, and B. Lipschultz

Phys. Plasmas 4, 2555 (1997); http://dx.doi.org/10.1063/1.872234 (12 pages) | Cited 65 times

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Significant recombination of the majority ion species has been observed in the divertor region of Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] under detached conditions. This determination is made by analysis of the visible spectrum from the divertor, in particular the Balmer series line emission and the observed recombination continuum, including an apparent recombination edge at ∼ 375 nm. The analysis shows that the electron temperature in the recombining plasma is 0.8–1.5 eV. The measured volume recombination rate is comparable to the rate of ion collection at the divertor plates. The dominant recombination mechanism is three-body recombination into excited states (e+e+D+⇒D0+e), although radiative recombination (e+D+⇒D0+hν) contributes ∼ 5% to the total rate. Analysis of the Balmer series line intensities (from nupper = 3 through 10) shows that the upper levels of these transitions are populated primarily by recombination. Thus the brightnesses of the Balmer series (and Lyman series) are directly related to the recombination rate. © 1997 American Institute of Physics.
Show PACS
52.55.Fa Tokamaks, spherical tokamaks
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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