Phys. Plasmas (1994-Present) - Physics of Plasmas

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Fishbone mode excitation in the ion kinetic regime

Bingren Shi and Guofang Sui

Phys. Plasmas 4, 2785 (1997); http://dx.doi.org/10.1063/1.872445 (3 pages) | Cited 2 times

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By solving the dispersion relation in the ion kinetic regime, it is found that the threshold of the plasma beta value for exciting the ion-fishbone mode is lowered. Thus, for most of the present-day tokamaks where the Bussac criterion [Bussac et al., Phys. Rev. Lett. 35, 1638 (1975)] is not satisfied, it will still be possible to excite the ion-fishbone mode. © 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.)
52.25.Dg	Plasma kinetic equations
52.55.Fa	Tokamaks, spherical tokamaks

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Production of sheared flow during ion cyclotron resonance heating in tokamak plasmas

C. G. Liu, M. Yamagiwa, and S. J. Qian

Phys. Plasmas 4, 2788 (1997); http://dx.doi.org/10.1063/1.872446 (3 pages) | Cited 3 times

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An approach of producing the poloidal ion rotation by using ion cyclotron resonance heating (ICRH) is presented in core tokamak plasmas. The mechanism employed here is inducing a poloidal density inhomogeneity by rf cyclotron heating and then destabilizing the anomalous Stringer spin-up. A criterion for destabilization of the poloidal ion rotation in the presence of a rf wave is given, which depends on the ratio of the characteristic time of inhomogeneous density formation to the ion collision time. The numerical results have shown that the poloidal ion rotation can be destabilized in the present ICRH power level. © 1997 American Institute of Physics.

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52.30.-q	Plasma dynamics and flow
52.50.Gj	Plasma heating by particle beams
52.55.Fa	Tokamaks, spherical tokamaks

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An electrostatic magnetohydrodynamics theory for resistive-viscous helical instabilities of arc discharges

Xiaogang Wang, Jinyuan Liu, Ye Gong, Guobing Li, and Tengcai Ma

Phys. Plasmas 4, 2791 (1997); http://dx.doi.org/10.1063/1.872411 (7 pages) | Cited 4 times

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A simplified linear analysis for resistive-viscous magnetic helical instabilities of arc discharges in a cylindrical plasma is developed. Based on a set of electrostatic magnetohydrodynamic (MHD) equations, resistive-viscous m = 1 modes with an external axial magnetic field are studied. Explicit analytic results are obtained, from which the growth rate and the stability criterion can be shown, and the electrostatic assumption can be justified. In comparison with the previous channel model calculations, this analytic treatment can provide a simplified model for instability estimates, while avoiding artificial assumptions and misorderings in the energy equation. © 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.)
52.80.Mg	Arcs; sparks; lightning; atmospheric electricity
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)

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Effects of various forces on the distribution of particles at the boundary of a dusty plasma

Jin-yuan Liu and J. X. Ma

Phys. Plasmas 4, 2798 (1997); http://dx.doi.org/10.1063/1.872412 (7 pages) | Cited 15 times

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The distribution and suspension of dust particles under the action of electrostatic, gravitational, ion-drag and neutral collision forces are investigated near the boundary of a dusty plasma. It is shown that the competition among the forces results in spatial oscillations (multi-layer) of the particle distribution. For sub-micron grains the ion-drag has a significant effect on the grain dynamics while for micrometer sized grains the gravity quickly dominates over other forces. The effect of the neutral gas flux is to enhance or diminish that of the gravity while the effect of the neutral viscosity is to shift the profile toward the wall. Under the force balance, the particles are suspended in a narrow region with sharp boundaries within the sheath. © 1997 American Institute of Physics.

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52.40.Hf	Plasma-material interactions; boundary layer effects
52.25.Vy	Impurities in plasmas
52.20.-j	Elementary processes in plasmas
95.30.Qd	Magnetohydrodynamics and plasmas

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Electric field spikes formed by electron beam–plasma interaction in plasma density gradients

H. Gunell and T. Löfgren

Phys. Plasmas 4, 2805 (1997); http://dx.doi.org/10.1063/1.872413 (8 pages) | Cited 5 times

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In the electron beam–plasma interaction at an electric double layer the beam density is much higher than in the classical beam–plasma experiments. The wave propagation takes place along the density gradient that is present at the high potential side of the double layer. Such a case is studied experimentally by injecting the electron beam from a plane cathode, without any grids suppressing the gradient, and by particle simulations. The high frequency field concentrates in a sharp “spike” with a half width of the order of one wavelength. The spike is found to be a standing wave surrounded by regions dominated by propagating waves. It forms at a position where its frequency is close to the local plasma frequency. The spike forms also when the electric field is well below the threshold for modulational instability, and long before a density cavity is formed in the simulations. Particle simulations reveal that, at the spike, there is a backward traveling wave that, when it is strongly damped, accelerates electrons back towards the cathode. In a simulation of a homogeneous plasma without the density gradient no spike is seen, and the wave is purely travelling instead of standing. © 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.)
52.25.Kn	Thermodynamics of plasmas
52.40.Mj	Particle beam interactions in plasmas
52.40.Hf	Plasma-material interactions; boundary layer effects

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The dust charging effect on electrostatic ion waves in a dusty plasma with trapped electrons

Y.-N. Nejoh

Phys. Plasmas 4, 2813 (1997); http://dx.doi.org/10.1063/1.872414 (7 pages) | Cited 72 times

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The effect of the dust charging and the influence of the ion density and temperature on electrostatic nonlinear ion waves in a dusty plasma having trapped electrons are investigated by numerical calculation. The nonlinear structure of the dust charging is examined, and it is shown that the characteristics of the dust charge number sensitively depend on the electrostatic potential, Mach number, trapped electron temperature, ion density, and temperature. An increase of the ion temperature decreases the dust charging rate and the propagation speed of ion waves. It turns out that a decrease of the trapped electron temperature increases the charging rate of dust grains. It is found that the existence of ion waves sensitively depends on the ion to electron density ratio. New findings of variable-charge dust grain particles, ion density, and temperature in a dusty plasma with trapped electrons are predicted. © 1997 American Institute of Physics.

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52.25.Vy	Impurities in plasmas
52.25.Kn	Thermodynamics of plasmas
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

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Direct magnetic field measurement of flow dynamics in magnetized coaxial accelerator channels

D. C. Black, R. M. Mayo, and R. W. Caress

Phys. Plasmas 4, 2820 (1997); http://dx.doi.org/10.1063/1.872415 (17 pages) | Cited 3 times

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A miniature magnetic probe array, consisting of ten spatially separated coils, has been used to obtain profile information on the time-varying magnetic field within the 2.54 cm wide flow channel of the Coaxial Plasma Source experiment (CPS-1) [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)] at the North Carolina State University. Two-dimensional (2-D) current profiles within the annular flow channel, which were constructed from the time-varying magnetic field data, reveal several complex features reflecting the influence of gun inductance, the Hall effect, and the applied magnetic field. When an external, electrode linking magnetic field is applied, the evolution of the 2-D current profile shows evidence of an ionizing shock front identified by a narrow current sheet propagating through the channel during the first few microseconds of the discharge. The thickness of this current sheet is on the same order as both the collisional mean-free path and the ion electromagnetic skin depth. In this applied field case, the plasma is prevented from advancing ahead of the current sheet by the applied magnetic field, which turns the ions and electrons without collisions. In the absence of an applied field, plasma is able to advance ahead of the current sheet, where it may initiate ionization downstream before the advance of the ionization front. © 1997 American Institute of Physics.

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52.30.-q	Plasma dynamics and flow
29.20.-c	Accelerators
52.70.Ds	Electric and magnetic measurements
52.75.Di	Ion and plasma propulsion

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Ionization-induced frequency up-shift of a high-power microwave interacting with a plasma

B. Cros, X. Xu, T. Tsukada, N. Yugami, Y. Nishida, and G. Matthieussent

Phys. Plasmas 4, 2837 (1997); http://dx.doi.org/10.1063/1.872416 (8 pages) | Cited 2 times

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The propagation of an intense electromagnetic wave (EMW), of frequency 9 GHz, in an underdense, near critical, inhomogeneous plasma (n_e ⩽ 1.2×10¹² cm⁻³, T_e ≃ 3 eV) leads to an up-shift of the EMW frequency of a few MHz. The injected EMW with power, P₀ ⩽ 250 kW, and with pulse duration of 1 μs, produces additional ionization of the neutral argon gas (n₀ ≃ 6.6×10¹³ cm⁻³) through the heating of plasma electrons. The increase of plasma density, which can reach during the EMW pulse several tens of percents in relative value, leads to a modulation in time of the spatial phase of the EMW. Experimental results for the evolution in space and in time of density, electric field, and frequency shift are compared to a simple nonlinear model of EMW propagation in a plasma, which takes into account the additional ionization due to the absorption of the EMW. © 1997 American Institute of Physics.

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52.40.Db	Electromagnetic (nonlaser) radiation interactions with plasma
52.25.-b	Plasma properties

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Intermittent self-organization: Nonlinear responses of twisting multiple flux tubes

Hisanori Takamaru and Tetsuya Sato

Phys. Plasmas 4, 2845 (1997); http://dx.doi.org/10.1063/1.872417 (8 pages) | Cited 2 times

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A new type of self-organization is presented where a system evolves intermittently and undergoes self-adaptively local maxima and minima of energy state. Numerical study of nonlinear interactions of twisting multiple flux tubes have shown that each flux tube suffers from a helical kink instability, resulting in the formation of a knotted structure. The knotted deformation stimulates reconnection with a neighboring flux tube whereby kinetic and thermal energies are impulsively and markedly released. Repeating reconnection intermittently with surrounding field lines, the whole structure returns to the more or less originally separated flux tubes and thereafter repeats an intermittent and recursive evolution. All these results lead to a working hypothesis that in an open complex nonlinear system where energy is externally and continuously supplied, the system exhibits an intermittent self-organization, self-adapting local maxima and minima of energy state alternatively in temporal evolution. The present work will also forecast this as some essential concept to an energy conversion problem such as solar flares. © 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.)
52.30.-q	Plasma dynamics and flow
95.30.Qd	Magnetohydrodynamics and plasmas
96.60.qe	Flares
52.65.Kj	Magnetohydrodynamic and fluid equation

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Bäcklund transformations and Painlevé analysis: Exact solutions for the nonlinear isothermal magnetostatic atmospheres

A. H. Khater, D. K. Callebaut, and R. S. Ibrahim

Phys. Plasmas 4, 2853 (1997); http://dx.doi.org/10.1063/1.872418 (11 pages) | Cited 10 times

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The equations of magnetohydrostatic equilibria for a plasma in a gravitational field are investigated analytically. For equilibria with one ignorable spatial coordinate, the equations reduce to a single nonlinear elliptic equation for the magnetic potential μ, known as the Grad–Shafranov equation. Specifying the arbitrary functions in the latter equation, one gets the nonlinear elliptic equation. Analytical solutions of the elliptic equation are obtained for the case of a nonlinear isothermal atmosphere in a uniform gravitational field. The solutions are obtained by using the Bäcklund transformations technique and Painlevé analysis, which are adequate for describing parallel filaments of diffuse, magnetized plasma suspended horizontally in equilibrium in a uniform gravitational field. © 1997 American Institute of Physics.

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52.30.-q	Plasma dynamics and flow
41.20.Gz	Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
52.25.-b	Plasma properties

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Passive particle dynamics in a flow exhibiting transition to turbulence

S. Benkadda, P. Gabbai, and G. M. Zaslavsky

Phys. Plasmas 4, 2864 (1997); http://dx.doi.org/10.1063/1.872577 (7 pages) | Cited 12 times

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The behavior of a passive particle in a flow that exhibits bifurcations in the transition to a turbulent regime is investigated. The flow considered is a variant of the Charney–Hasegawa–Mima equation. The scalar particle dynamics is considered for different regimes of the main flow. A regime of anomalous diffusion (hypodiffusion) is observed when the field has few harmonics whereas normal diffusion occurs in the strange attractor regime. The analysis of the singular orbit reveals the presence of traps and flights that control the transport. ©1997 American Institute of Physics.

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47.00.00	Fluid dynamics
05.45.-a	Nonlinear dynamics and chaos
47.55.Kf	Particle-laden flows
47.52.+j	Chaos in fluid dynamics

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Compressible magnetohydrodynamic Kelvin–Helmholtz instability with vortex pairing in the two-dimensional transverse configuration

Akira Miura

Phys. Plasmas 4, 2871 (1997); http://dx.doi.org/10.1063/1.872419 (15 pages) | Cited 28 times

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For a two-dimensional (2-D) transverse configuration, where the plasma motion occurs in a 2-D plane transverse to the magnetic field, the nonlinear evolution of the magnetohydrodynamic (MHD) Kelvin–Helmholtz (K–H) instability is investigated by means of a 2-D MHD simulation for a convective fast magnetosonic Mach number 0.35, which is defined for the total jump of the flow velocity. The compressibility and the nonzero baroclinic vector are shown to violate the conservation of the enstrophy for the 2-D MHD transverse configuration and for the 2-D fluid motion. After the nonlinear saturation of the linearly fastest growing vortices, the vortices continue to coalesce until no more vortex pairing is allowed, owing to a finite length of the simulation system. The plasma inside the vortex is rarefied strongly by the fast magnetosonic rarefaction and each vortex is associated with an eddy current, which is inertia current in nature. The plasma flow velocity is enhanced at the periphery of the vortex and the net momentum transport and shear relaxation by the instability occur as long as the vortex pairing continues. Anomalous viscosity by the K–H instability increases with the vortex pairing and its increase is due to the growth of subharmonic modes. © 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.)
52.30.-q	Plasma dynamics and flow
52.65.Kj	Magnetohydrodynamic and fluid equation

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Formation of wave-front pattern accompanied by current-driven electrostatic ion-cyclotron instabilities

Seiji Ishiguro, Tetsuya Sato, Hisanori Takamaru, and Kunihiko Watanabe

Phys. Plasmas 4, 2886 (1997); http://dx.doi.org/10.1063/1.872613 (7 pages) | Cited 4 times

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Formation of a wave-front pattern accompanied by an electrostatic ion-cyclotron instability driven by electrons drifting along a magnetic field is investigated by two-and-half dimensional particle simulations. A clear spatial wave-front pattern appears as the ion cyclotron wave grows due to the instability. When the electron stream is uniform in the system, an obliquely intersected stripe wave-front pattern is formed. When the stream has a bell-shaped pattern across the magnetic field, a V-shaped stripe wave-front pattern appears. The wave fronts have small angles with the magnetic field lines and propagate from the high-stream region to the low-stream region. © 1997 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.)
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.-y	Plasma simulation

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Rarefactive ion acoustic soliton excitation using a modulated high-frequency sinusoidal wave in a negative ion plasma

Seungjun Yi and Karl E. Lonngren

Phys. Plasmas 4, 2893 (1997); http://dx.doi.org/10.1063/1.872420 (6 pages) | Cited 5 times

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Experiments on the excitation of rarefactive ion acoustic solitons using a fine mesh grid in a negative ion plasma are described. The excitation is novel in that a modulated high-frequency sinusoidal wave voltage signal is applied to the grid. 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.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb	Solitons; BGK modes
52.27.Jt	Nonneutral plasmas

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Magnetohydrodynamic stability of negative central magnetic shear, high pressure (ϵβ_pol≫1) toroidal equilibria

Robert G. Kleva

Phys. Plasmas 4, 2899 (1997); http://dx.doi.org/10.1063/1.872421 (8 pages)

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The magnetohydrodynamic (MHD) stability of negative central magnetic shear toroidal equilibria with q>2 everywhere and ϵβ_pol≫1 is investigated. Here, q is the safety factor of the equilibrium magnetic field in a torus with inverse aspect ratio ϵ, and β_pol is the ratio of the plasma pressure to the pressure in the poloidal magnetic field. At small ϵβ_pol≪1, the elimination of the q = 2 resonant surface in a negative shear equilibrium greatly improves resistive MHD stability as compared to equilibria with a monotonic q-profile containing a q = 2 resonant surface. However, at large ϵβ_pol≫1, the reversal of the central magnetic shear and the elimination of the q = 2 resonant surface does not improve MHD stability. The existence, or non-existence, of rational magnetic surfaces has no impact on MHD stability when ϵβ_pol≫1. Altering the current profile, and with it the q-profile, does not affect MHD stability when ϵβ_pol is no longer small. Stability is not improved by vertical elongation of the plasma in the poloidal plane. The utilization of an external vertical magnetic field to move the magnetic axis in major radius also does not improve MHD stability. © 1997 American Institute of Physics.

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52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa	Tokamaks, spherical tokamaks

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Description of turbulent transport in tokamaks by invariants

V. V. Yankov and J. Nycander

Phys. Plasmas 4, 2907 (1997); http://dx.doi.org/10.1063/1.872422 (13 pages) | Cited 27 times

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In general, turbulent transport drives a plasma toward a state of turbulent equipartition, in which Lagrangian invariants are uniformly distributed. Different invariants decay with different rates, and in tokamaks the frozen-in law of particles in the poloidal magnetic field survives longer than the corresponding law for the toroidal field, assuming that the trapped particles dominate the turbulent transport. Therefore, the plasma profiles depend on the safety factor q(r), and the condition for convection of trapped particles is that the shear dq/dr is positive. There are two ways to suppress this convection and thereby enhance confinement. The first one is to reverse the magnetic shear. The energy of typical trapped particles then increases outward instead of inward, which suppresses instabilities. The second method is to eliminate the trapped ions by poloidal rotation, and thereby create a transport barrier. © 1997 American Institute of Physics.

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52.25.Fi	Transport properties
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.)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

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Plasma transport near the separatrix of a magnetic island

R. D. Hazeltine, P. Helander, and Peter J. Catto

Phys. Plasmas 4, 2920 (1997); http://dx.doi.org/10.1063/1.872423 (8 pages) | Cited 13 times

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The simplest nontrivial model of transport across a magnetic island chain in the presence of collisionless streaming along the magnetic field is solved by a Wiener–Hopf procedure. The solution found is valid provided the boundary layer about the island separatrix is narrow compared to the island width. The result demonstrates that when this assumption is satisfied the flattened profile region is reduced by the boundary layer width. The calculation is similar to the recent work by Fitzpatrick [Phys. Plasmas 2, 825 (1995)] but is carried out in the collisionless, rather than the collisional, limit of parallel transport, and determines the plasma parameters on the separatrix self-consistently. © 1997 American Institute of Physics.

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52.25.Fi	Transport properties
52.40.Hf	Plasma-material interactions; boundary layer effects

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Simultaneous measurement of viscosity and flow velocity in Texas Experimental Tokamak-Upgrade (TEXT-U) edge plasmas by using a Visco-Mach probe

Kyu-Sun Chung and Roger D. Bengtson

Phys. Plasmas 4, 2928 (1997); http://dx.doi.org/10.1063/1.872424 (5 pages) | Cited 5 times

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Shear viscosity [η ≡ α×(mass density)×(diffusivity)] and parallel flow velocity [M_∞× math

] of tokamak edge plasma were simultaneously measured in the Texas Experimental Tokamak-Upgrade (TEXT-U) tokamak by using a “Visco-Mach” probe with the iteration method (VMPI) [K-S. Chung, Nucl. Fusion 34, 1213 (1994)]. The VMPI was composed of two Mach probes measuring two ratios of ion saturation current densities, with the small Mach probe located within the free presheath generated by the large Mach probe (LMP). Radial variations of the normalized shear viscosity, α, and parallel Mach number, M_∞, for typical discharges were deduced from two measured ratios of ion saturation current densities, and plasma density from ion saturation currents by LMP. Here α varied from 0.7 to 1.3 with an estimated error of ±40%, and M_∞ from 0 to 0.2 for 0<r−r_l<4.5 cm, where r_l = 27 cm is the limiter radius. Also, α and M_∞ increased with the radial direction, while cross-field diffusivity (D_⊥) was approximately constant. Here D_⊥ is obtained as ∼ 3D_B, where a typical Bohm diffusivity (D_B) is ∼ 1 m²/s. © 1997 American Institute of Physics.

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52.55.Fa	Tokamaks, spherical tokamaks
52.40.Hf	Plasma-material interactions; boundary layer effects
52.30.-q	Plasma dynamics and flow
52.25.Fi	Transport properties
52.70.Ds	Electric and magnetic measurements
02.60.-x	Numerical approximation and analysis

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Studies of transport scaling and reduction under feedback

J. S. Chiu and A. K. Sen

Phys. Plasmas 4, 2933 (1997); http://dx.doi.org/10.1063/1.872425 (7 pages) | Cited 9 times

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A feedback control system using an ion beam as a remote suppressor has been previously shown to be very effective in suppressing plasma instabilities in the Columbia Linear Machine [G. A. Navratil et al., Plasma Phys. 24, 184 (1982)]. The first experimental measurements for the effect of this feedback system on anomalous particle transport, as determined from the cross-correlation of density and potential fluctuations is presented. It is shown that feedback reduces transport due to a rotational E×B mode by up to a factor of 3 in this experiment. Also, it was found that particle transport scales linearly with fluctuation amplitude and feedback control does not alter this scaling. Last, the experimentally observed scaling of particle transport does not agree with any theoretical predictions. © 1997 American Institute of Physics.

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52.25.Fi	Transport properties
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Mj	Particle beam interactions in plasmas
52.25.Gj	Fluctuation and chaos phenomena
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

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On the stabilization of neoclassical magnetohydrodynamic tearing modes using localized current drive or heating

C. C. Hegna and J. D. Callen

Phys. Plasmas 4, 2940 (1997); http://dx.doi.org/10.1063/1.872426 (7 pages) | Cited 5 times

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The effectiveness of using localized current drive or heating to suppress the formation and growth of neoclassical magnetohydrodynamic (MHD) tearing modes is addressed. The most efficient way to use an auxiliary current source is to cause current to flow in the same direction as the equilibrium bootstrap current and phase the current relative to the magnetic island such that the current is deposited on the O-point of the island. Theoretical estimates for the amount of required current to suppress the formation of a large magnetic island is of order a few percent of the equilibrium current. If the suppression is successful, the magnetic island will saturate at a width of order the radial localization width of the current source. Localized heating at the O-point of the magnetic island can also produce stabilizing effects relative to magnetic island growth. The effects of the driven current or heating can be illustrated by using a phase diagram of the island growth. © 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.)
52.30.-q	Plasma dynamics and flow
52.25.Fi	Transport properties
52.50.Gj	Plasma heating by particle beams

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Measurements on rotating ion cyclotron range of frequencies induced particle fluxes in axisymmetric mirror plasmas

R. Hatakeyama, N. Hershkowitz, R. Majeski, Y. J. Wen, D. B. Brouchous, P. Proberts, R. A. Breun, D. Roberts, M. Vukovic, and T. Tanaka

Phys. Plasmas 4, 2947 (1997); http://dx.doi.org/10.1063/1.872427 (8 pages) | Cited 5 times

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A comparison of phenomenological features of plasmas is made with a special emphasis on radio-frequency induced transport, which are maintained when a set of two closely spaced dual half-turn antennas in a central cell of the Phaedrus-B axisymmetric tandem mirror [J. J. Browning et al., Phys. Fluids B 1, 1692 (1989)] is phased to excite electromagnetic fields in the ion cyclotron range of frequencies (ICRF) with m = −1 (rotating with ions) and m = +1 (rotating with electrons) azimuthal modes. Positive and negative electric currents are measured to flow axially to the end walls in the cases of m = −1 and m = +1 excitations, respectively. These parallel nonambipolar ion and electron fluxes are observed to be accompanied by azimuthal ion flows in the same directions as the antenna-excitation modes m. The phenomena are argued in terms of radial particle fluxes due to a nonambipolar transport mechanism [Hojo and Hatori, J. Phys. Soc. Jpn. 60, 2510 (1991); Hatakeyama et al., J. Phys. Soc. Jpn. 60, 2815 (1991), and Phys. Rev. E 52, 6664 (1995)], which are induced when azimuthally traveling ICRF waves are absorbed in the magnetized plasma column. © 1997 American Institute of Physics.

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52.70.-m

Plasma diagnostic techniques and instrumentation

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Role of finite parallel wave number in low frequency fluctuations in toroidal current less plasma

Rajwinder Kaur, A. K. Singh, and S. K. Mattoo

Phys. Plasmas 4, 2955 (1997); http://dx.doi.org/10.1063/1.872428 (7 pages) | Cited 4 times

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In this paper we present results related to studies of low frequency electrostatic fluctuations in a toroidal plasma of varying length and without a toroidal current. The toroidal length of plasma is varied from fully toroidal (major radius R=45 cm to 278, 212 and 142 cm. The characteristics of fluctuations changed, showing the effect of finite system length on the nature of the fluctuations. The major results are 1 a drastic reduction in the amplitude of fluctuations, 2 this reduction is mainly due to the disappearance of coherent peaks at 3 kHz and its harmonics observed in unbounded system, 3 the presence of a broad coherent feature around 10 kHz, only in bad curvature region, at low magnetic field (200 G) and 4 the appearance of a large number of coherent peaks, in one particular system length, at a higher magnetic field (400 G). These results indicate that the Rayleigh–Taylor instability with finite k_‖ may be excitable in the device. © 1997 American Institute of Physics.

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52.25.Gj	Fluctuation and chaos phenomena
52.55.Fa	Tokamaks, spherical tokamaks
52.55.Jd	Magnetic mirrors, gas dynamic traps
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

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Nonsingular canonical coordinates for the drift Hamiltonian in a magnetic field with a separatrix

Allen H. Boozer

Phys. Plasmas 4, 2962 (1997); http://dx.doi.org/10.1063/1.872429 (5 pages) | Cited 1 time

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Magnetic coordinates are singular on a separatrix. A method is given for transforming to nonsingular coordinates that are closely related to magnetic coordinates and can be used in the canonical coordinates of the Hamiltonian for particle drifts. The case of a magnetic separatrix with a single X point is emphasized and approximate expressions are given for the functions that appear in the drift Hamiltonian. © 1997 American Institute of Physics.

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52.25.Fi	Transport properties
52.55.Fa	Tokamaks, spherical tokamaks

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The dynamics of bifurcating bright-spots in fiber Z-pinch plasmas

J. P. Chittenden, I. H. Mitchell, R. Aliaga-Rossel, J. M. Bayley, F. N. Beg, A. Lorenz, M. G. Haines, and G. Decker

Phys. Plasmas 4, 2967 (1997); http://dx.doi.org/10.1063/1.872444 (5 pages) | Cited 1 time

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Results are presented from the diagnosis of the optical and x-ray emission from “bright-spots” in carbon fiber Z-pinch experiments using the MAGPIE (Mega-Ampere Generator for Plasma Implosion Experiments) generator [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)]. Inhomogeneities evolve very rapidly within the plasma with bright-spots becoming detectable after 15–20 ns. After a short ( ∼ 4 ns) duration formation phase, these bright-spots exhibit highly dynamic behavior. Bifurcation of the bright-spots is observed giving rise to rapid axial motion at 1–3×10⁵ ms⁻¹. The post-bifurcation bright-spots persist for up to 40 ns. Analysis of cross-filtered, time integrated, x-ray pinhole images yield bright-spot parameters during the formation phase (diameter ∼ 80 μm, temperature 250–300 eV, ion number densities ∼ 2×10²⁶ m⁻³). With a spatial resolution of 175 μm, the strong temperature and density gradients within the post-bifurcation spots can be resolved in gated x-ray images with 2 ns exposure times. After the dynamic phase of bright-spot evolution, the pinch enters a quiescent phase where the time scale for evolution is much longer. © 1997 American Institute of Physics.

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52.70.Kz	Optical (ultraviolet, visible, infrared) measurements
52.55.Ez	Theta pinch
52.70.La	X-ray and γ-ray measurements
52.25.Os	Emission, absorption, and scattering of electromagnetic radiation

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Non-relativistic response function for higher harmonic electron cyclotron resonance heating

Y. Tatematsu, Y. Kiwamoto, T. Saito, I. Katanuma, and T. Tamano

Phys. Plasmas 4, 2972 (1997); http://dx.doi.org/10.1063/1.872430 (10 pages) | Cited 1 time

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A response function [Y. Kiwamoto et al., Phys. Plasmas 1, 834 (1994)] for higher harmonic cyclotron resonance heating is constructed through the analysis of electron trajectory under harmonic heating in an inhomogeneous magnetic field. General expressions of orbital displacement and energy gain for higher harmonic resonance are obtained. Phase-averaged energy gain of electrons by n-th harmonic electron cyclotron resonance heating (ECRH) is larger by a factor of n, if the effect of the orbital displacement from the unperturbed orbit is correctly included, than that evaluated based on an unperturbed orbit assuming small k_⊥ρ. The energy gain for finite k_⊥ρ is also obtained. These results are confirmed with a numerical calculation for second harmonics. © 1997 American Institute of Physics.

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