Phys. Fluids B (1984-1993) - Physics of Plasmas

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Calculation of β_I and l_i for three‐dimensional plasma configurations

S. P. Hirshman

Phys. Fluids B 5, 3119 (1993); http://dx.doi.org/10.1063/1.860647 (3 pages) | Cited 2 times

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The Shafranov equilibrium formulas for tokamaks relate volume‐averaged thermal pressure and magnetic pressure to integrals of the measurable poloidal magnetic field energy at the plasma surface. Similar integral relations are derived that are valid for a general, three‐dimensional plasma confinement geometry.

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

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Thermal magnetic fluctuations of whistlers in a Maxwellian plasma

G. Golubyatnikov and R. L. Stenzel

Phys. Fluids B 5, 3122 (1993); http://dx.doi.org/10.1063/1.860648 (5 pages) | Cited 7 times

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Thermal fluctuations have been measured with a magnetic loop antenna inside a large afterglow plasma in the regime of whistler waves (f≲f_ce≂30 MHz≪f_pe≂3000 MHz; Ar, 2×10⁻⁴ Torr, 1 m diam×2.5 m length). The magnetic fluctuations math

_(ω) exhibit a 1/f‐like spectrum for whistlers (f<f_ce), no resonant enhancement at the electron cyclotron frequency f_ce, and a flat spectrum in the evanescent regime (f_ce<f≪f_pe). Thus the observed fluctuations are neither described by blackbody radiation laws ( math

∝ω) nor by cyclotron emission (lines at nf_ce), but resemble the decaying Alfvénic fluctuation spectrum calculated by Cable and Tajima [Phys. Rev. A 46, 3413 (1992)].

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52.25.Gj	Fluctuation and chaos phenomena
52.35.Ra	Plasma turbulence
52.25.Os	Emission, absorption, and scattering of electromagnetic radiation
52.70.Ds	Electric and magnetic measurements

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Transient ion resonance instability

J. Fajans

Phys. Fluids B 5, 3127 (1993); http://dx.doi.org/10.1063/1.860649 (9 pages) | Cited 9 times

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A trapped pure electron plasma column can be unstable if the plasma column is contaminated by a small number of oppositely charged ions. This instability was analyzed by Levy, Daugherty, and Buneman [Phys. Fluids, 12, 2616 (1969)] for the case of trapped ions. The instability is analyzed here for the case of untrapped ions. The analysis is inherently nonlinear, and growth results from averaging over the ion initial conditions. Several significant differences exist between the two cases, including, for the latter, growth over a much broader parameter region and linear (secular) rather than exponential growth. The predictions of the analysis are compared to the results from a recent experiment on the instability.

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52.27.Jt	Nonneutral plasmas
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Mj	Particle beam interactions in plasmas

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Universal instability in an electron hole filled with negative ions

Nicholas A. Krall

Phys. Fluids B 5, 3136 (1993); http://dx.doi.org/10.1063/1.860650 (4 pages)

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The stability of a layer of negative ions imbedded in a magnetized charge neutral plasma is analyzed. Universal instabilities are found to persist, even in the absence of a net current or net density gradient. Experiments which inject negative ions into the ionosphere may have observed such fluctuations.

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52.35.-g

Waves, oscillations, and instabilities in plasmas and intense beams

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The effects of elastic scattering in neutral atom transport

D. N. Ruzic

Phys. Fluids B 5, 3140 (1993); http://dx.doi.org/10.1063/1.860651 (8 pages) | Cited 12 times

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Neutral atom elastic collisions are one of the dominant interactions in the edge of a high recycling diverted plasma. Starting from the quantum interatomic potentials, the scattering functions are derived for H on H⁺, H on H₂, and He on H₂ in the energy range of 0.1–1000 eV following classical scattering theory and an impact parameter formulation. Potentials for both the gerade and ungerade electronic wavefunctions were included. An algorithm for the addition of these reactions to the degas [J. Comput. Phys. 46, 309 (1982)] code is presented and used to simulate three test problems: (1) the transport of neutral atoms through a dilute edge plasma, (2) the penetration of neutral atoms into a dense plasma from a divertor plate, and (3) the transmittance of neutral atoms through a pump duct. In all three cases the inclusion of elastic scattering has a significant influence on the neutral atom density, temperature, and flux to the walls.

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34.50.-s

Scattering of atoms and molecules

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Wave collapse at the lower‐hybrid resonance

V. D. Shapiro, V. I. Shevchenko, G. I. Solov’ev, V. P. Kalinin, R. Bingham, R. Z. Sagdeev, M. Ashour‐Abdalla, J. Dawson, and J. J. Su

Phys. Fluids B 5, 3148 (1993); http://dx.doi.org/10.1063/1.860652 (15 pages) | Cited 43 times

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The modulational instability and collapse of waves in the vicinity of the lower‐hybrid resonance including both magnetosonic and lower‐hybrid waves are investigated by analytical and numerical methods. The mechanism leading to the modulational instability is the nonlinear coupling of lower‐hybrid waves with the much lower‐frequency quasineutral density perturbations via the ponderomotive force. The result is a filamentation of the high‐frequency field producing elongated, cigar‐shaped nonlinear wave packets aligned along the magnetic field with the plasma expelled outside (cavities). The analytical self‐similar solutions describing cavity collapse are obtained and compared with the results of numerical simulation for both two‐ and three‐dimensional cavity geometries. It is shown that in three‐dimensional solutions the transverse, with respect to the magnetic field, contraction remains prevailing. The possibility of ion acceleration as the result of the lower‐hybrid collapse is discussed and detailed comparison is made with the observations of the phenomena in the auroral ionosphere.

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52.35.Ra

Plasma turbulence

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Nonlinear evolution of a strongly sheared cross‐field plasma flow

H. Romero and G. Ganguli

Phys. Fluids B 5, 3163 (1993); http://dx.doi.org/10.1063/1.860653 (19 pages) | Cited 9 times

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A study is presented of the nonlinear evolution of a magnetized plasma in which a localized electron cross‐field flow is present. The peak velocity of the flow is denoted by V₀; L_E represents the flow’s shear scale length; and the regime ρ_e<L_E<ρ_i is considered, where ρ_i and ρ_e denote the ion and electron Larmor radii, respectively. It is shown that if the shear frequency ω_s=V₀/L_E is larger than the lower‐hybrid frequency, ω_LH, then the system dynamics is dominated by the onset of the electron–ion‐hybrid (EIH) mode which leads to the formation of coherent (vortexlike) structures in the electrostatic potential of the ensuing lower‐hybrid waves. The wavelength of these structures is on the order of L_E, and correlates well with that predicted by the linear theory of the EIH mode. Since the characteristic wavelength is longer than ρ_e, the corresponding phase velocity is low enough that there results significant direct resonant ion acceleration perpendicular to the confining magnetic field. When ω_s≳3ω_LH, the system exhibits significant anomalous viscosity (typically an order of magnitude larger than that due to Coulomb collisions), which increases as the shear frequency is increased. As ω_s is reduced below ω_LH, shear effects are no longer dominant and a smooth transition takes place in which the system dynamics is governed by the short wavelength (on the order of ρ_e) lower‐hybrid drift instability.

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52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
94.30.cq	MHD waves, plasma waves, and instabilities
52.65.-y	Plasma simulation
52.35.Ra	Plasma turbulence

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Ion kinetic simulations of the formation and propagation of a planar collisional shock wave in a plasma

F. Vidal, J. P. Matte, M. Casanova, and O. Larroche

Phys. Fluids B 5, 3182 (1993); http://dx.doi.org/10.1063/1.860654 (9 pages) | Cited 10 times

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Ion kinetic simulations of the formation and propagation of planar shock waves in a hydrogen plasma have been performed at Mach numbers 2 and 5, and compared to fluid simulations. At Mach 5, the shock transition is far wider than expected on the basis of comparative fluid calculations. This enlargement is due to hot ions streaming from the hot plasma into the cold plasma and is found to be limited by the electron preheating layer, essentially because electron–ion collisions slow down these energetic ions very effectively in the cold upstream region. Double‐humped ion velocity distributions formed in the transition region, which are particularly prominent during the shock formation, are found not to be unstable to any electrostatic mode, due to electron Landau damping. At Mach numbers of 2 and below, no such features are seen in velocity space, and there is very little difference between the profiles from the kinetic and fluid simulations.

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52.35.Tc	Shock waves and discontinuities
52.25.Fi	Transport properties
52.65.-y	Plasma simulation
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

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The enhancement of edge turbulence in tokamaks by a limiter current

A. V. Nedospasov

Phys. Fluids B 5, 3191 (1993); http://dx.doi.org/10.1063/1.860655 (4 pages) | Cited 9 times

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The results indicating that enhanced electrostatic potential fluctuations had been observed in the scrape‐off layer, due to biasing, were published recently. The qualitative explanation of these experimental results as an effect of current owing to the flute instability with the dissipation into the sheath layer near the surfaces is presented in this paper. The possibility of controlling the edge turbulence by a limiter current is shown.

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52.35.Ra	Plasma turbulence
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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Ideal magnetohydrodynamics: Global mode analysis of three‐dimensional plasma configurations

Carolin Schwab

Phys. Fluids B 5, 3195 (1993); http://dx.doi.org/10.1063/1.860656 (12 pages) | Cited 51 times

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The global magnetohydrodynamic (MHD) stability of three‐dimensional (3‐D) toroidal plasmas, investigated here by the ideal MHD energy principle formulated in magnetic coordinates, is studied by a Finite‐Element‐Fourier code, the Code for the Analysis of the Stability of 3‐D equilibria (CAS3D) [Theory of Fusion Plasmas, Varenna 1990 (Editrice Compositori, Bologna, 1990), p. 667]. A first survey of the stability properties of 3‐D equilibria clarifies structural characteristics of global MHD modes, such as the existence of separable mode families and the possibility of annihilating all compression terms, i.e., the fluid and the field compression, for the minimizing perturbation.

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52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.-y	Plasma simulation
52.55.Jd	Magnetic mirrors, gas dynamic traps

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Poloidal variation of viscous forces in the banana collisionality regime

J. P. Wang and J. D. Callen

Phys. Fluids B 5, 3207 (1993); http://dx.doi.org/10.1063/1.860965 (10 pages) | Cited 10 times

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The poloidal variation of the parallel viscous and heat viscous forces are determined for the first time using a rigorous Chapman–Enskog‐like approach that has been developed recently. It is shown that the poloidal variation is, like the poloidal distribution of the trapped particles, concentrated on the outer edge (large major radius side) of the tokamak.

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51.10.+y	Kinetic and transport theory of gases
52.25.Dg	Plasma kinetic equations
52.55.Fa	Tokamaks, spherical tokamaks
52.30.-q	Plasma dynamics and flow

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Collective transport of alpha particles due to Alfvén wave instability

B. N. Breizman, H. L. Berk, and H. Ye

Phys. Fluids B 5, 3217 (1993); http://dx.doi.org/10.1063/1.860657 (10 pages) | Cited 26 times

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Recently a new point of view has been developed for describing saturation of discrete modes excited by weak sources. The method applies to the evolution of energetic particles in the beam plasma instability as well as to the description of how alpha particles evolve when they destabilize Alfvén waves under reactor conditions. Over a wide range of parameters the system produces pulsations, where there are relatively brief bursts of wave energy separated by longer intervals of quiescence. There are two types of pulsations: benign and explosive. In the benign phase, valid when particle motion is not stochastic, the distribution function is close to that predicted by classical transport theory, and the instability saturates when the wave trapping frequency equals the expected linear growth rate. If the field amplitude in a burst reaches the level where orbit stochasticity occurs, the quasilinear diffusion causes rapid transfer of particle energy to wave energy and rapid flattening of the particle distribution function. The bursting phase is followed by a relatively long quiescent time interval, where the source provides the necessary free energy to regenerate the cycle. The critical issue is whether the instability develops to a high enough level to produce stochastic diffusion. In general, this question can be assessed by using mapping methods to obtain criteria of overlapping of orbit resonances. If overlap occurs, then the modes will saturate at a high level, which will result in significant anomalous transport effects. This picture is consistent with recent observations of energetic beam losses in tokamak experiments due to Alfvén mode excitation.

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52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.-y	Plasma simulation

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Profile stabilization of tilt mode in a field‐reversed configuration

John W. Cobb, T. Tajima, and Daniel C. Barnes

Phys. Fluids B 5, 3227 (1993); http://dx.doi.org/10.1063/1.860658 (12 pages) | Cited 14 times

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The possibility of stabilizing the tilt mode in field‐reversed configurations without resorting to explicit kinetic effects such as large ion orbits is investigated. Various pressure profiles, P(Ψ), are chosen, including ‘‘hollow’’ profiles, where current is strongly peaked near the separatrix. Numerical equilibria are used as input for an initial value simulation, which uses an extended magnetohydrodynamic (MHD) model that includes viscous and Hall terms. Tilt stability is found for specific hollow profiles when accompanied by high values of separatrix beta, β_sep. The stable profiles also have moderate to large elongation, racetrack separatrix shape, and lower values of math

, average ratio of Larmor radius to device radius. The stability is unaffected by changes in viscosity, but the neglect of the Hall term does cause stable results to become marginal or unstable. Implications for interpretation of recent experiments are discussed.

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52.65.-y	Plasma simulation
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.)
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)

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Suppression of m=2 islands by electron cyclotron heating in the Texas Experimental Tokamak: Experiment and theory

D. C. Sing, M. E. Austin, D. L. Brower, J. Y. Chen, R. F. Gandy, C. X. Yu, X.‐H. Wang, A. Bhattacharjee, and D. D. Schnack

Phys. Fluids B 5, 3239 (1993); http://dx.doi.org/10.1063/1.860659 (7 pages) | Cited 14 times

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Electron cyclotron heating (ECH) is used to suppress m=2 magnetohydrodynamic (MHD) oscillations in the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)]. The location of ECH power deposition is controlled by a movable antenna. The MHD activity is suppressed when the ECH beam is directed close to the q=2 surface. The experiment is simulated using a three‐dimensional resistive MHD code in cylindrical geometry. For fixed plasma current, the saturated m=2 island width is found to depend on the value of the safety factor at the magnetic axis (q₀). The simulation suggests that the observed saturated m=2 island in the pre‐ECH plasma, which typically occupies 25% of the minor radius, corresponds to q₀∼1.3. The suppression of the island in the presence of ECH is attributed to current profile modification. In some discharges, the m=2 activity does not resume even after the ECH pulse is turned off.

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52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.50.Gj	Plasma heating by particle beams
52.55.Fa	Tokamaks, spherical tokamaks

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Atomic physics effects on tokamak edge drift‐tearing modes

T. S. Hahm

Phys. Fluids B 5, 3246 (1993); http://dx.doi.org/10.1063/1.860660 (6 pages)

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The effects of ionization and charge exchange on the linear stability of drift‐tearing modes are analytically investigated. In particular, the linear instability threshold Δ^Th, produced by ion sound wave coupling [Phys. Rev. Lett. 40, 1500 (1978)] is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semicollisional regime, both ionization and charge exchange act as drag on the ion parallel velocity [Phys. Fluids B 4, 2567 (1992)], and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

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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)
52.25.Gj	Fluctuation and chaos phenomena
52.55.Fa	Tokamaks, spherical tokamaks

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Two novel applications of bootstrap currents: Snakes and jitter stabilization

A. Thyagaraja and F. A. Haas

Phys. Fluids B 5, 3252 (1993); http://dx.doi.org/10.1063/1.860661 (9 pages) | Cited 4 times

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Both neoclassical theory and certain turbulence theories of particle transport in tokamaks predict the existence of bootstrap (i.e., pressure‐driven) currents. Two new applications of this form of noninductive current are considered in this work. In the first, an earlier model of the nonlinearly saturated m=1 tearing mode is extended to include the stabilizing effect of a bootstrap current inside the island. This is used to explain several observed features of the so‐called ‘‘snake’’ reported in the Joint European Torus (JET) [R. D. Gill, A. W. Edwards, D. Pasini, and A. Weller, Nucl. Fusion 32, 723 (1992)]. The second application involves an alternating current (ac) form of bootstrap current, produced by pressure‐gradient fluctuations. It is suggested that a time‐dependent (in the plasma frame), radio‐frequency (rf) power source can be used to produce localized pressure fluctuations of suitable frequency and amplitude to implement the dynamic stabilization method for suppressing gross modes in tokamaks suggested in a recent paper [A. Thyagaraja, R. D. Hazeltine, and A. Y. Aydemir, Phys. Fluids B 4, 2733 (1992)]. This method works by ‘‘detuning’’ the resonant layer by rapid current/shear fluctuations. Estimates made for the power source requirements both for small machines such as COMPASS and for larger machines like JET suggest that the method could be practically feasible. This ‘‘jitter’’ (i.e., dynamic) stabilization method could provide a useful form of active instability control to avoid both gross/disruptive and fine‐scale/transportive instabilities, which may set severe operating/safety constraints in the reactor regime. The results are also capable, in principle, of throwing considerable light on the local properties of current generation and diffusion in tokamaks, which may be enhanced by turbulence, as has been suggested recently by several researchers.

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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.)
52.55.Fa	Tokamaks, spherical tokamaks

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Production of superthermal electrons and ion cyclotron waves in a reversed‐field‐pinch plasma

Z. Yoshida, A. Hasegawa, and M. Wakatani

Phys. Fluids B 5, 3261 (1993); http://dx.doi.org/10.1063/1.860662 (6 pages) | Cited 8 times

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Production of superthermal electrons through kinetic interactions with electromagnetic fluctuations is studied to account for observations of fast electrons and ion cyclotron waves in reversed field pinch plasmas. Low‐frequency Alfvénic (torsional) modes can interact with electrons through the Landau resonance when the wavelength perpendicular to the magnetic field is as small as the ion gyroradius. Such kinetic Alfvén waves induce simultaneous diffusion (double diffusion) in the coordinate and velocity spaces, and produce a field aligned superthermal electron beam in the edge region. Microinstabilities are driven by the electron‐beam and ion cyclotron waves are excited. Through these precesses the fluctuation energy in the low‐frequency regime may be transported to the ion cyclotron frequency regime.

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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.Ez	Theta pinch
52.35.Ra	Plasma turbulence
52.25.Gj	Fluctuation and chaos phenomena

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Magnetohydrodynamic stability studies of supershot plasmas

M. H. Hughes, M. W. Phillips, and E. D. Fredrickson

Phys. Fluids B 5, 3267 (1993); http://dx.doi.org/10.1063/1.860663 (9 pages) | Cited 4 times

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Slowly growing magnetohydrodynamic (MHD) instabilities are usually detected experimentally in supershot plasmas in the Tokamak Fusion Test Reactor [in Plasma Physics and Controlled Nuclear Fusion Research 1986, Kyoto (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 75] (TFTR). These instabilities, when they occur, result in deterioration of the confinement and limit the attainable β. Using initial profile data from transport analysis of specific high β supershot plasmas, the predictions of the single fluid, linear MHD stability model are studied and compared with the experimental observations. It is shown that, in the highest β plasmas achieved, the pressure gradients in the interior are such that the absence of the 1/1 mode is difficult to reconcile with the single fluid MHD model if the safety factor, q<1. On the assumption that q exceeds unity everywhere, it is found that supershot plasmas are predicted to be unstable or near marginal to small toroidal mode number, pressure‐driven instabilities of the ballooning variety. When finite plasma resistivity is included in the analysis the range of parameters over which these instabilities are excited is significantly extended.

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52.30.-q	Plasma dynamics and flow
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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On self‐consistent ray‐tracing and Fokker–Planck modeling of the hard x‐ray emission during lower‐hybrid current drive in tokamaks

João P. Bizarro, Yves Peysson, Paul T. Bonoli, Joël Carrasco, Thierry Dudok de Wit, Vladimir Fuchs, Gia T. Hoang, Xavier Litaudon, Didier Moreau, Christine Pocheau, and Issie P. Shkarofsky

Phys. Fluids B 5, 3276 (1993); http://dx.doi.org/10.1063/1.860664 (8 pages) | Cited 17 times

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A detailed investigation is presented on the ability of combined ray‐tracing and Fokker–Planck calculations to predict the hard x‐ray (HXR) emission during lower‐hybrid (LH) current drive in tokamaks when toroidally induced ray stochasticity is important. A large number of rays is used and the electron distribution function is obtained by self‐consistently iterating the appropriate power deposition and Fokker–Planck calculations. It is shown that effects due to radial diffusion of suprathermal electrons and to radiation scattering by the inner wall can be significant. The experimentally observed features of the HXR emission are fairly well predicted, thus confirming that combined ray‐tracing and Fokker–Planck codes are capable of correctly modeling the physics of LH current drive in tokamaks.

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52.70.La	X-ray and γ-ray measurements
52.50.Gj	Plasma heating by particle beams
42.15.Dp	Wave fronts and ray tracing
52.65.-y	Plasma simulation

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Theory of kinetic ballooning modes excited by energetic particles in tokamaks

Shih‐Tung Tsai and Liu Chen

Phys. Fluids B 5, 3284 (1993); http://dx.doi.org/10.1063/1.860624 (7 pages) | Cited 67 times

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Resonant excitations of kinetic ballooning modes by the energetic ions/alpha particles in tokamaks have been analyzed theoretically. The theoretical analysis includes finite‐size orbit effects of both circulating and trapped particles. With energetic particle contributions suppressed in the singular inertial layer, an analytic dispersion relation can then be derived via an asymptotic matching analysis. The dispersion relation, in particular, demonstrates the existence of two types of modes; that is, the magnetohydrodynamic gap mode and the energetic‐particle continuum mode. Specific expressions for real frequencies, growth rates and threshold conditions are also derived for a model slowing‐down beam ion distribution function.

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52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa	Tokamaks, spherical tokamaks

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Numerical simulation of bootstrap current

Yanlin Wu and R. B. White

Phys. Fluids B 5, 3291 (1993); http://dx.doi.org/10.1063/1.860625 (8 pages) | Cited 9 times

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The neoclassical theory of bootstrap current in toroidal systems is calculated in magnetic flux coordinates and confirmed by numerical simulation. The effects of magnetic ripple, loop voltage, and magnetic and electrostatic perturbations on bootstrap current for the cases of zero and finite plasma pressure are studied. The numerical results are in reasonable agreement with analytical estimates.

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52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Gj	Fluctuation and chaos phenomena
52.25.Fi	Transport properties
52.35.Ra	Plasma turbulence

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Theory of pseudoclassical confinement and transition to L mode

K. Itoh, S.‐I. Itoh, M. Yagi, A. Fukuyama, and M. Azumi

Phys. Fluids B 5, 3299 (1993); http://dx.doi.org/10.1063/1.860626 (5 pages) | Cited 8 times

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A theory of the self‐sustained turbulence is developed for resistive plasma in toroidal devices. Pseudoclassical confinement is obtained in the low‐temperature limit. As temperature increases, the current diffusivity prevails upon resistivity, and the turbulence nature changes so as to recover the L‐mode transport. Comparison with experimental observation on this transition is made. The Hartmann number is also given.

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52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Ra	Plasma turbulence
52.55.Pi	Fusion products effects (e.g., alpha-particles, etc.), fast particle effects

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Space and time behavior of parametric instabilities for a finite pump wave duration in a bounded plasma

Philippe Mounaix, Denis Pesme, Wojciech Rozmus, and Michel Casanova

Phys. Fluids B 5, 3304 (1993); http://dx.doi.org/10.1063/1.860627 (15 pages) | Cited 45 times

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The space and time behavior of the decay waves is computed analytically in the regime of standard parametric decay. The plasma is assumed to be homogeneous and bounded. The pump wave has a finite pulse duration. The propagation of the pump wave is taken into account, its depletion is ignored. The parametric growth is solved in terms of fluctuating initial and boundary conditions corresponding to thermal noise at equilibrium. Fluctuating source terms, representing noise emission, are accordingly retained in the coupled mode equations. The initial stage of parametric growth is investigated in detail; the time from which the asymptotic concept of absolute or convective instability applies is computed. The connection between the Manley–Rowe and flux conservation relations is discussed.

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52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.38.Bv	Rayleigh scattering; stimulated Brillouin and Raman scattering
52.40.Db	Electromagnetic (nonlaser) radiation interactions with plasma
52.38.-r	Laser-plasma interactions

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Stimulated Brillouin scattering in picosecond time scales: Experiments and modeling

H. A. Baldis, D. M. Villeneuve, B. La Fontaine, G. D. Enright, C. Labaune, S. Baton, Ph. Mounaix, D. Pesme, M. Casanova, and W. Rozmus

Phys. Fluids B 5, 3319 (1993); http://dx.doi.org/10.1063/1.860628 (9 pages) | Cited 35 times

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This paper presents an experimental and theoretical study of stimulated Brillouin scattering (SBS) in laser produced plasma using a laser pump with a duration of 8–10 psec. The experiments were performed in a preformed plasma to minimize the flow velocity and have the same plasma conditions over a large range of laser intensities. The reflectivity was then compared to theoretical results over an intensity range of 10¹³–2×10¹⁵ W/cm². A short pulse was used so that the SBS was in the temporally growing regime and saturation was not an issue.

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52.38.-r	Laser-plasma interactions
52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
42.65.Es	Stimulated Brillouin and Rayleigh scattering

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X‐ray spectroscopy of high‐energy density inertial confinement fusion plasmas

C. J. Keane, B. A. Hammel, D. R. Kania, J. D. Kilkenny, R. W. Lee, A. L. Osterheld, L. J. Suter, R. C. Mancini, C. F. Hooper, and N. D. Delamater

Phys. Fluids B 5, 3328 (1993); http://dx.doi.org/10.1063/1.860964 (9 pages) | Cited 40 times

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Analysis is presented of K‐ and L‐shell spectra obtained from Ar and Xe dopants seeded into the fuel region of plastic capsules indirectly imploded using the Nova laser. Stark broadening measurements of the n=3‐1 lines in H‐ and He‐like Ar (Ar Ly‐β and He‐β, respectively) are used to infer fuel electron density, while spatially averaged fuel electron temperature is deduced from the ratio of the intensities of these lines. Systematic variations in Ar spectral features are observed as a function of drive conditions. A spectral postprocessing code has been developed to simulate experimental spectra by taking into account spatial gradients and line transfer effects, and shows good agreement with experimental data. It is shown that correct modeling of the x‐ray emission requires a proper treatment of the coupled radiative transfer and kinetics problem. Continuum lowering effects are shown not to affect diagnostic line ratios, within the confines of a simple model. A recently developed diagnostic based on fitting measured line profiles of Ar He‐β and its associated dielectronic satellites to theory is shown to provide a simultaneous measure of electron temperature and electron density. L‐shell Xe spectroscopy is under development as an electron temperature and electron‐density diagnostic. Density and temperature sensitive ratios of spectral features each consisting of many lines have been identified. Observed Xe spectra from imploded cores show the same qualitative behavior with temperature, as predicted by model calculations of Xe emission spectra. Stark broadening of Ne‐like Xe 4‐2 lines appears viable as an electron density diagnostic for N_e∼10²⁵ cm⁻³ and is under continuing investigation. (Based on the invited paper 8I3 at the 1992 APS/DPP annual meeting [Bull. Am. Phys. Soc. 37, 1553 (1992)].)

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