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Jan 2002

Volume 9, Issue 1, pp. 1-384

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Direction of ion ∇B drift and power threshold in high confinement mode in diverted tokamaks

K. C. Shaing

Phys. Plasmas 9, 1 (2002); http://dx.doi.org/10.1063/1.1428326 (3 pages) | Cited 12 times

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An explanation of the dependence of the power threshold on the direction of the ion ∇B drift in diverted tokamaks is presented by using the high confinement mode (H-mode) theory based on the orbit loss triggered electric field bifurcation and the subsequent turbulence suppression. Here, B is the magnetic field strength. It is shown that ion collisionality, which defines the onset of the orbit loss, depends on the direction of the ion ∇B drift. Through this dependence, the power threshold also depends on the direction of the ion ∇B drift. A possible method to test this explanation experimentally is suggested. © 2002 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.20.-j Elementary processes in plasmas
28.52.Av Theory, design, and computerized simulation
02.30.Oz Bifurcation theory
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back to top Basic Plasma Phenomena, Waves, Instabilities

Modeling of complex plasmas under micro-gravity conditions

G. Morfill and V. N. Tsytovich

Phys. Plasmas 9, 4 (2002); http://dx.doi.org/10.1063/1.1413227 (13 pages) | Cited 15 times

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Computer modeling of complex (dusty) plasmas under micro-gravity conditions is performed. It is shown that several requirements are necessary to obtain almost homogeneous self-confining micro-particle structures: (a) The ion and electron densities at the center of the structure should exceed certain critical values; (b) the rate of ionization should be less than a certain critical value; and (c) the micro-particle structures surrounded by walls should be separated from the wall by a dust void. It is found that in the optimum case up to 6×106 micro-particles can be confined in the structure. For that the ion flux in the center part of the structure should be almost convective. Less than 103 micro-particles can be confined without optimal tuning of the parameters. The void surrounding the micro-particle structure has specific properties determined both by the particle cloud and the wall conditions. The void’s properties are found to be crucial for the properties of the particle cloud. © 2002 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals

Potential profiles obtained from applied dust cloud perturbations

Edward Thomas

Phys. Plasmas 9, 17 (2002); http://dx.doi.org/10.1063/1.1419254 (4 pages) | Cited 4 times

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This paper details an experimental investigation of the local potential structure within a cloud of suspended microparticles—a “dusty” or “complex” plasma—using particle image velocimetry (PIV) techniques. Applied perturbations, synchronized to the PIV measurements, are used to force a cloud of suspended microparticles to become unconfined. From the free-streaming motion of the particles during the loss of confinement and subsequent reformation of the dust cloud, an analysis of the potential is performed. Furthermore, a new method of analyzing the potential structure from the motion of free-streaming microparticles in the plasma is presented. © 2002 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.80.Hc Glow; corona
52.25.Fi Transport properties

Structural and thermodynamic properties of spin-polarized fluid hydrogen

Hong Xu and Jean-Pierre Hansen

Phys. Plasmas 9, 21 (2002); http://dx.doi.org/10.1063/1.1421372 (7 pages) | Cited 1 time

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The “orbital-free” two-component density functional theory introduced previously [H. Xu and J. P. Hansen, Phys. Rev. E 57, 211 (1998)] is extended to the study of the proton–proton and proton–electron pair correlations in a spin-polarized hydrogen plasma as a function of density and temperature. An approximate formula is suggested to compute the free energy of the plasma phase, and applied to the investigation of the plasma-insulator transition of spin-polarized fluid hydrogen. © 2002 American Institute of Physics.
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61.20.-p Structure of liquids
31.15.E- Density-functional theory
64.70.-p Specific phase transitions

Accurate measurements of the pitch-angle scattering of beam ions

W. W. Heidbrink

Phys. Plasmas 9, 28 (2002); http://dx.doi.org/10.1063/1.1423622 (7 pages) | Cited 7 times

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The pitch-angle scattering rate of a dilute population of 75 keV deuterium ions is measured in a well-diagnosed, relatively quiet, magnetically-confined deuterium plasma. Neutral particle diagnostics detect the fast-ion density in velocity space following a short 10 ms pulse of injected beam ions. The data are compared to the classical theory of diffusion in velocity space caused by many, small-angle, Coulomb-scattering events. Within uncertainties of ≲15%, the data confirm the classical theory. © 2002 American Institute of Physics.
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52.70.Nc Particle measurements
52.40.Mj Particle beam interactions in plasmas

Nonstationary closure relations of the collisionless fluid equations

A. Bendib, G. Matthieussent, and F. Bouzid

Phys. Plasmas 9, 35 (2002); http://dx.doi.org/10.1063/1.1418019 (12 pages) | Cited 5 times

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An analytical method to solve the time-dependent linearized Vlasov equation is carried out by making use of the method developed recently in the literature [K. Bendib and A. Bendib, Phys. Plasmas 6, 1500 (1999)]. The distribution function is computed with respect to the continued fractions and the collisionless transport coefficients are deduced. These transport coefficients have been used to close the fluid equations and it has been checked that the fluid and the kinetic response functions coincide very accurately for arbitrary normalized phase velocities ξ = ω/mathkvt, where ω and k are the frequency and the wave number of the plasma modes and vt is the thermal velocity. The collisionless fluid equations have been expressed with respect to a phenomenological ratio of specific heats Γ(ξ) and a fluid damping rate ν(ξ), which include the kinetic effects. They are used to study the dispersion relation of the Langmuir waves and of the thermal filamentation instability. © 2002 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
52.38.Hb Self-focussing, channeling, and filamentation in plasmas

Resistive pressure-gradient-driven instabilities in the transition regime to fully developed turbulence

L. Garcia, B. A. Carreras, and V. E. Lynch

Phys. Plasmas 9, 47 (2002); http://dx.doi.org/10.1063/1.1430252 (8 pages) | Cited 7 times

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Numerical calculations of resistive pressure-gradient-driven turbulence in toroidal geometry for tokamak plasma edge parameters have been carried out in the unstable regime below the threshold for fully developed turbulence. This threshold is at a β value of about three times the linear stability threshold. In this regime, the toroidal mode number spectrum in the stationary state is dominated by a single toroidal mode. The dominant mode may intermittently fluctuate among a narrow range of possible values. © 2002 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.Ra Plasma turbulence
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.55.Fa Tokamaks, spherical tokamaks
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Hf Plasma-material interactions; boundary layer effects
back to top Nonlinear Phenomena, Turbulence, Transport

The properties of fast and slow oblique solitons in a magnetized plasma

J. F. McKenzie and T. B. Doyle

Phys. Plasmas 9, 55 (2002); http://dx.doi.org/10.1063/1.1418721 (9 pages) | Cited 23 times

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This work builds on a recent treatment by McKenzie and Doyle [Phys. Plasmas 8, 4367 (2001)], on oblique solitons in a cold magnetized plasma, to include the effects of plasma thermal pressure. Conservation of total momentum in the direction of wave propagation immediately shows that if the flow is supersonic, compressive (rarefactive) changes in the magnetic pressure induce decelerations (accelerations) in the flow speed, whereas if the flow is subsonic, compressive (rarefactive) changes in the magnetic pressure induce accelerations (decelerations) in the flow speed. Such behavior is characteristic of a Bernoulli-type plasma momentum flux which exhibits a minimum at the plasma sonic point. The plasma energy flux (kinetic plus enthalpy) also shows similar Bernoulli-type behavior. This transonic effect is manifest in the spatial structure equation for the flow speed (in the direction of propagation) which shows that soliton structures may exist if the wave speed lies either (i) in the range between the fast and Alfven speeds or (ii) between the sound and slow mode speed. These conditions follow from the requirement that a defined, characteristic “soliton parameter” m exceeds unity. It is in this latter slow soliton regime that the effects of plasma pressure are most keenly felt. The equilibrium points of the structure equation define the center of the wave. The structure of both fast and slow solitons is elucidated through the properties of the energy integral function of the structure equation. In particular, the slow soliton, which owes its existence to plasma pressure, may have either a compressive or rarefactive nature, and exhibits a rich structure, which is revealed through the spatial structure of the longitudinal speed and its corresponding transverse velocity hodograph. © 2002 American Institute of Physics.
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52.35.Sb Solitons; BGK modes
52.30.-q Plasma dynamics and flow
52.25.Dg Plasma kinetic equations

Transport cross sections relevant to cool hydrogen plasmas bounded by graphite

D. R. Schultz and P. S. Krstić

Phys. Plasmas 9, 64 (2002); http://dx.doi.org/10.1063/1.1419056 (7 pages) | Cited 9 times

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Atomic collision quantities relevant to transport in hydrogen plasmas bounded by graphite walls are considered. Fully quantal, ab initio calculations of the differential and integral elastic scattering cross sections for H+, D+, and T+ colliding with C at center of mass energies between 0.1 and 200 eV are described. The computed elastic cross section and its transport moments, the momentum transfer, and viscosity cross sections, are compared with those from a simple analytical model (the Massey–Mohr approximation) and with a three-body classical scattering approach in order to extend the data to higher collision energies. For energies typical of the edge plasma, the elastic scattering cross section is found to be as much as 10 times larger than that estimated from the widely used analytical approximation. The highly accurate quantal results are also tabulated and made available to the plasma science community through the world wide web. © 2002 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Fi Transport properties
31.15.A- Ab initio calculations
52.25.Kn Thermodynamics of plasmas

Theory of the momentum flux probability distribution function for drift wave turbulence

Eun-jin Kim and P. H. Diamond

Phys. Plasmas 9, 71 (2002); http://dx.doi.org/10.1063/1.1421616 (7 pages) | Cited 16 times

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An analytical theory of the tails of the probability distribution function (PDF) for the local Reynolds stress (R) is given for forced Hasegawa–Mima turbulence. The PDF tail is treated as a transition amplitude from an initial state, with no fluid motion, to final states with different values of R due to nonlinear coherent structures in the long time limit. With the modeling assumption that the nonlinear structure is a modon (an exact solution of a nonlinear Hasegawa–Mima equation) in space, this transition amplitude is determined by an instanton. An instanton is localized in time and can be associated with bursty and intermittent events which are thought to be responsible for PDF tails. The instanton is found via a saddle-point method applied to the PDF, represented by a path integral. It implies the PDF tail for R with the specific form exp[−cR3/2], which is a stretched, non-Gaussian exponential. © 2002 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.35.Kt Drift waves
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Fractional kinetics for relaxation and superdiffusion in a magnetic field

A. V. Chechkin, V. Yu. Gonchar, and M. Szydłowski

Phys. Plasmas 9, 78 (2002); http://dx.doi.org/10.1063/1.1421617 (11 pages) | Cited 43 times

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Fractional Fokker–Planck equation is proposed for the kinetic description of relaxation and superdiffusion processes in constant magnetic and random electric fields. It is assumed that the random electric field acting on a test charged particle is isotropic and possesses non-Gaussian Levy stable statistics. These assumptions provide one with a straightforward possibility to consider formation of anomalous stationary states and superdiffusion processes, both properties are inherent to strongly nonequilibrium plasmas of solar systems and thermonuclear devices. The fractional kinetic equation is solved, the properties of the solution are studied, and analytical results are compared with those of numerical simulation based on the solution of the Langevin equations with a noise source having Levy stable probability density. It is found, in particular, that the stationary states are essentially non-Maxwellian ones and, at the diffusion stage of relaxation, the characteristic displacement of a particle grows superdiffusively with time and is inversely proportional to the magnetic field. © 2002 American Institute of Physics.
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05.10.Gg Stochastic analysis methods (Fokker-Planck, Langevin, etc.)
05.40.Fb Random walks and Levy flights

Analysis of cancellation in two-dimensional magnetohydrodynamic turbulence

L. Sorriso-Valvo, V. Carbone, A. Noullez, H. Politano, A. Pouquet, and P. Veltri

Phys. Plasmas 9, 89 (2002); http://dx.doi.org/10.1063/1.1420738 (7 pages) | Cited 12 times

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A signed measure analysis of two-dimensional intermittent magnetohydrodynamic turbulence is presented. This kind of analysis is performed to characterize the scaling behavior of the sign-oscillating flow structures, and their geometrical properties. In particular, it is observed that cancellations between positive and negative contributions of the field inside structures are inhibited for scales smaller than the Taylor microscale, and stop near the dissipative scale. Moreover, from a simple geometrical argument, the relationship between the cancellation exponent and the typical fractal dimension of the structures in the flow is obtained. © 2002 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
05.45.Df Fractals

Generation of harmonic Langmuir mode by beam-plasma instability

Rudi Gaelzer, Luiz F. Ziebell, and Peter H. Yoon

Phys. Plasmas 9, 96 (2002); http://dx.doi.org/10.1063/1.1421371 (15 pages) | Cited 11 times

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In this article, numerical solutions of the generalized weak turbulence equation [P. H. Yoon, Phys. Plasmas 7, 4858 (2000)] are carried out. In the generalized weak turbulence theory, the generation of the 2ωpe-harmonic Langmuir mode is treated as a fundamental process in turbulent beam-plasma interaction process, in addition to, and concomitant to, the well-known nonlinear processes such as Langmuir and ion-sound mode coupling and wave-particle interactions. The present numerical analysis shows that the harmonic mode, which is a solution to a nonlinear dispersion equation, hence a “nonlinear” eigenmode, grows primarily due to an induced emission process, which is a “linear” wave-particle interaction process. The harmonic Langmuir mode generation has been observed since the late 1960s in laboratory experiments, simulations, and in space. However, adequate and quantitative theoretical explanation has not been forthcoming. The present work represents a step toward an understanding of such a phenomenon. © 2002 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
back to top Magnetically Confined Plasmas, Heating, Confinement

On the problem of negative dissipation of fast waves at the fundamental ion cyclotron resonance and the accuracy of absorption estimates

F. Castejón, S. S. Pavlov, and D. G. Swanson

Phys. Plasmas 9, 111 (2002); http://dx.doi.org/10.1063/1.1421075 (7 pages) | Cited 2 times

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Negative dissipation appears when ion cyclotron resonance (ICR) heating at first harmonic in a thermal plasma is estimated using some numerical schemes. The causes of the appearance of such a problem are investigated analytically and numerically in this work showing that the problem is connected with the accuracy with which the absorption coefficient at the first ICR harmonic is estimated. The corrections for the absorption estimation are presented for the case of quasiperpendicular propagation of fast wave in this frequency range. A method to solve the problem of negative dissipation is presented and, as a result, an enhancement of absorption is found for reactor-size plasmas. © 2002 American Institute of Physics.
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52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
28.52.Av Theory, design, and computerized simulation

Stratified shear flows in a model of turbulence-shear flow interaction

D. del-Castillo-Negrete and B. A. Carreras

Phys. Plasmas 9, 118 (2002); http://dx.doi.org/10.1063/1.1421076 (10 pages) | Cited 11 times

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In magnetically confined plasmas there is evidence of localized regions of improved confinement. These regions are usually associated with shear flows with radial structure, and an important problem is to understand how such flows emerge. To address this problem a reaction–diffusion type model of turbulence-shear flow interaction that incorporates the mechanism of turbulence suppression by shear, and parameterizes turbulent transport as a nonlinear diffusivity is considered. The fixed points of the model correspond to the L (low confinement) and H (high confinement) modes of the system, and it is shown that for a range of parameter values the H-mode fixed point has a finite-k instability. Numerical results show that this instability leads, in the nonlinear regime, to the formation of stratified shear layers and jets in which bands of intense shear and suppressed turbulence alternate with bands of low shear and enhanced turbulence. Approximate analytical solutions of the model corresponding to high-confinement modes with radial structure are presented. © 2002 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.55.-s Magnetic confinement and equilibrium
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Effect of rotation on H-mode transport in DIII–D via changes in the E×B velocity shear

C. C. Petty, M. R. Wade, J. E. Kinsey, D. R. Baker, and T. C. Luce

Phys. Plasmas 9, 128 (2002); http://dx.doi.org/10.1063/1.1421077 (9 pages) | Cited 20 times

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The effect of rotation on the heat and particle transport is measured in the DIII–D tokamak [Fusion Technol. 8, 441 (1985)] for high-confinement mode (H-mode) plasmas with edge localized modes. In a novel experiment, transport is compared for nearly identical scans of the relative gyroradius in co- and counter-rotating plasmas. Since the plasma profiles are the same, the difference in the transport scaling can be attributed to changes in the sheared E×B flow caused by the shift in the toroidal plasma velocity. The ion heat and particle transport are found to be sensitive to the change in the rotation direction and magnitude whereas the electron heat transport is not. Simulations using a gyroLandau-fluid drift wave transport model show that the variation in the ion heat transport for co/counter rotation is due to changes in the E×B shear stabilization, but the electrons appear to be governed by a different transport mechanism. © 2002 American Institute of Physics.
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52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
52.65.Tt Gyrofluid and gyrokinetic simulations

Three-dimensional codes to design stellarators

Paul R. Garabedian

Phys. Plasmas 9, 137 (2002); http://dx.doi.org/10.1063/1.1419252 (13 pages) | Cited 6 times

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Equilibrium, stability, and transport in stellarators can be studied theoretically by running large computer codes. Some of the codes have excellent resolution, and experimental data have been used to validate the results of numerical calculations. An analysis has been made of recent measurements from the Large Helical Device experiment in Japan to see how they compare with the theory [A. Komori, H. Yamada, O. Kaneko et al., Plasma Phys. Control. Fusion 42, 1165 (2000)]. Observations of confinement time at low collisionality like that in a reactor agree well with estimates using a quasineutrality algorithm to determine the electric potential. A nonlinear magnetohydrodynamic calculation of stability for various pressure profiles gives predictions of the beta limit that are consistent with the observations. Correlation of the theory with measurements justifies using the codes as a tool to design quasisymmetric configurations for a modular stellarator experiment promising better performance at reactor conditions.© 2002 American Institute of Physics.
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52.25.Fi Transport properties
52.55.Jd Magnetic mirrors, gas dynamic traps

In search of zonal flows using cross-bispectrum analysis in the boundary plasma of the Hefei Tokamak-7

G. S. Xu, B. N. Wan, and M. Song

Phys. Plasmas 9, 150 (2002); http://dx.doi.org/10.1063/1.1419255 (5 pages) | Cited 15 times

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Langmuir probes have been used to measure the electrostatic Reynolds stress and the floating potential fluctuation in the boundary plasma of the Hefei Tokamak-7 (HT-7) [J. Li, B. N. Wan, and J. S. Mao, Plasma Phys. Controlled Fusion 42, 135 (2000)]. The cross bispectrum of 〈mathrmathθmathf〉 indicates the existence of difference-frequency nonlinear phase coupling and the generation of fluctuations near the geodesic acoustic mode frequency. The inverse cascade process might be linked to the generation of zonal flows by small-scale electrostatic drift-wave turbulence. © 2002 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.70.Ds Electric and magnetic measurements
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.55.Fa Tokamaks, spherical tokamaks

Nonlinear magnetohydrodynamical effects in precessional fishbone oscillations

A. Ödblom, B. N. Breizman, S. E. Sharapov, T. C. Hender, and V. P. Pastukhov

Phys. Plasmas 9, 155 (2002); http://dx.doi.org/10.1063/1.1421373 (12 pages) | Cited 11 times

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The role of magnetohydrodynamic nonlinearities in precessional m = n = 1 fishbone oscillations has been analyzed analytically and numerically. The work is based on the reduced magnetohydrodynamic (MHD) equations including a linear energetic particle drive model. When the energetic particle pressure is close to the instability threshold, the top-hat linear eigenmode profile of the ideal MHD m = 1 radial displacement splits up into a two-step structure around the q = 1 flux surface, due to the finite frequency ω of the mode. The width of the individual steps is a factor γ/ω smaller than the distance between them, where γ is the growth rate of the mode. We find that the MHD nonlinearities modify the mode structure further, and produce explosive nonlinear growth, accompanied by frequency chirping, for modes that are near the instability threshold. The results are quite different for fishbone oscillations that are excited well above the stability threshold. The growth rates of these linearly fast growing modes decreases nonlinearly and the MHD nonlinearities are stabilizing in this limit. The nonlinear MHD effects are important when the plasma displacement is comparable to, or larger than, the scale length of the fishbone structure. © 2002 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.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Enhancement of mode-converted electron Bernstein wave emission during National Spherical Torus Experiment H-mode plasmas

G. Taylor, P. C. Efthimion, B. Jones, B. P. LeBlanc, and R. Maingi

Phys. Plasmas 9, 167 (2002); http://dx.doi.org/10.1063/1.1423336 (4 pages) | Cited 13 times

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A sudden, threefold increase in emission from fundamental electrostatic electron Bernstein waves (EBW) which mode convert and tunnel to the electromagnetic X-mode has been observed during high energy and particle confinement (H-mode) transitions in the National Spherical Torus Experiment (NSTX) plasma [M. Ono, S. Kaye, M. Peng et al., in Proceedings of the 17th IAEA Fusion Energy Conference (IAEA, Vienna, Austria, 1999), Vol. 3, p. 1135]. The mode-converted EBW emission viewed normal to the magnetic field on the plasma midplane increases when the density profile steepens in the vicinity of the mode conversion layer, which is located in the plasma scrape off. The measured conversion efficiency during the H-mode is consistent with the calculated EBW to X-mode conversion efficiency derived using edge density data. Calculations indicate that there may also be a small residual contribution to the measured X-mode electromagnetic radiation from polarization-scrambled, O-mode emission, converted from EBWs. © 2002 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Control of a global motion on field-reversed configuration

K. Fujimoto, A. Hoshikawa, S. Ohmura, T. Takahashi, Y. Nogi, and Y. Ohkuma

Phys. Plasmas 9, 171 (2002); http://dx.doi.org/10.1063/1.1416880 (6 pages) | Cited 10 times

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An n = 1 mode global motion on a field-reversed configuration (FRC) plasma is observed by means of a newly developed optical system. The deviation of the FRC from the coil axis reaches 20%–40% of the plasma radius. In order to push back the FRC to the equilibrium position, a multipole field (quadrupole or hexapole field) is applied. The n = 1 motion can be easily controlled by the quadrupole field, the critical field strength of which is required to be about 15% of the confinement field. It is found that the n = 2 rotational instability can also be stabilized by strength of the same order. The critical strength for the n = 1 motion is theoretically obtained from a model such that the driving energy of the motion given at the formation phase balances with the work done by the multipole field. The theoretical estimation agrees within a factor of 2 with the experimental results. © 2002 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.58.Lq Z-pinches, plasma focus, and other pinch devices
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.)

Comparing simulation of plasma turbulence with experiment

David W. Ross, Ronald V. Bravenec, William Dorland, Michael A. Beer, G. W. Hammett, George R. McKee, Raymond J. Fonck, Masanori Murakami, Keith H. Burrell, Gary L. Jackson, and Gary M. Staebler

Phys. Plasmas 9, 177 (2002); http://dx.doi.org/10.1063/1.1424925 (8 pages) | Cited 13 times

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The direct quantitative correspondence between theoretical predictions and the measured plasma fluctuations and transport is tested by performing nonlinear gyro-Landau-fluid simulations with the GRYFFIN (or ITG) code [W. Dorland and G. W. Hammett, Phys. Fluids B 5, 812 (1993); M. A. Beer and G. W. Hammett, Phys. Plasmas 3, 4046 (1996)]. In an L-mode reference discharge in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], which has relatively large fluctuations and transport, the turbulence is dominated by ion temperature gradient (ITG) modes. Trapped electron modes and impurity drift waves also play a role. Density fluctuations are measured by beam emission spectroscopy [R. J. Fonck, P. A. Duperrex, and S. F. Paul, Rev. Sci. Instrum. 61, 3487 (1990)]. Experimental fluxes and corresponding diffusivities are analyzed by the TRANSP code [R. J. Hawryluk, in Physics of Plasmas Close to Thermonuclear Conditions, edited by B. Coppi, G. G. Leotta, D. Pfirsch, R. Pozzoli, and E. Sindoni (Pergamon, Oxford, 1980), Vol. 1, p. 19]. The shape of the simulated wave number spectrum is close to the measured one. The simulated ion thermal transport, corrected for E×B low shear, exceeds the experimental value by a factor of 1.5 to 2.0. The simulation overestimates the density fluctuation level by an even larger factor. On the other hand, the simulation underestimates the electron thermal transport, which may be accounted for by modes that are not accessible to the simulation or to the BES measurement. © 2002 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.65.Tt Gyrofluid and gyrokinetic simulations
52.55.Fa Tokamaks, spherical tokamaks
52.25.Gj Fluctuation and chaos phenomena
52.25.Vy Impurities in plasmas
52.35.Kt Drift waves
52.70.-m Plasma diagnostic techniques and instrumentation

Formation and steady-state maintenance of field reversed configuration using rotating magnetic field current drive

H. Y. Guo, A. L. Hoffman, R. D. Brooks, A. M. Peter, Z. A. Pietrzyk, S. J. Tobin, and G. R. Votroubek

Phys. Plasmas 9, 185 (2002); http://dx.doi.org/10.1063/1.1426102 (16 pages) | Cited 43 times

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Rotating magnetic fields (RMF) have been used to both form and maintain field reversed configurations (FRC) in quasisteady state. These experiments differ from steady-state rotamaks in that the FRCs are similar to those formed in theta-pinch devices, that is elongated and confined inside a flux conserver. The RMF creates an FRC by driving an azimuthal current which reverses an initial positive bias field. The FRC then expands radially, compressing the initial axial bias flux and raising the plasma density, until a balance is reached between the RMF drive force and the electron–ion friction. This generally results in a very high ratio of separatrix to flux conserver radius. The achievable final conditions are compared with simple analytic models to estimate the effective plasma resistivity. The RMF torque on the electrons is quickly transferred to the ions, but ion spin-up is limited in these low density experiments, presumably by ion-neutral friction, and does not influence the basic current drive process. However, the ion rotation can result in a rotating n=2 distortion if the separatrix radius is too far removed from the plasma tube wall. © 2002 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.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Ez Theta pinch
52.58.Lq Z-pinches, plasma focus, and other pinch devices

Long mean-free path collisional stability of electromagnetic modes in axisymmetric closed magnetic field configurations

Andrei N. Simakov, R. J. Hastie, and Peter J. Catto

Phys. Plasmas 9, 201 (2002); http://dx.doi.org/10.1063/1.1424309 (11 pages) | Cited 8 times

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An axially symmetric plasma confined by a poloidal magnetic field with closed field lines is considered. A kinetic analysis of electromagnetic modes is performed for an “intermediate collisionality” ordering in which the particle collision frequency is much smaller than the transit or bounce frequency, but much larger than the mode, magnetic drift, and diamagnetic drift frequencies. A second order integrodifferential ballooning equation for electromagnetic modes is derived, which describes “high-frequency” ideal magnetohydrodynamic (MHD) and “low-frequency” entropy modes. The equation recovers the corresponding ideal MHD ballooning equation for the mode frequency greater than the magnetic drift and diamagnetic drift frequencies, and generalizes the results of an earlier electrostatic treatment of the entropy mode to arbitrary plasma beta. Ion gyrorelaxation collisional modifications to the entropy mode are also evaluated for arbitrary plasma beta and specific results are presented for both a point dipole and Z pinch. © 2002 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.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.20.-j Elementary processes in plasmas
52.25.Dg Plasma kinetic equations
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.59.Qy Wire array Z-pinches

Resistive wall instabilities and tearing mode dynamics in the EXTRAP T2R thin shell reversed-field pinch

J.-A. Malmberg and P. R. Brunsell

Phys. Plasmas 9, 212 (2002); http://dx.doi.org/10.1063/1.1426101 (10 pages) | Cited 11 times

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Observations of resistive wall instabilities and tearing mode dynamics in the EXTRAP T2R thin shell (τw = 6 ms) reversed field pinch are described. A nonresonant mode (m = 1,n = −10) with the same handedness as the internal field grows nearly exponentially with an average growth time of about 2.6 ms (less than 1/2 of the shell time) consistent with linear stability theory. The externally nonresonant unstable modes (m = 1,n>0), predicted by linear stability theory, are observed to have only low amplitudes (in the normal low-Θ operation mode of the device). The radial field of the dominant internally resonant tearing modes (m = 1,n = −15 to n = −12) remain low due to spontaneous fast mode rotation, corresponding to angular phase velocities up to 280 krad/s. Phase aligned mode structures are observed to rotate toroidally with an average angular velocity of 40 krad/s, in the opposite direction of the plasma current. Toward the end of the discharge, the radial field of the internally resonant modes grows as the modes slow down and become wall-locked, in agreement with nonlinear computations. Fast rotation of the internally resonant modes has been observed only recently and is attributed to a change of the front-end system (vacuum vessel, shell, and TF coil) of the device. © 2002 American Institute of Physics.
Show PACS
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
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