bluuebunny/crossref_metadata_2025 huggingface dataset:
Green’s function for external excited Bohm–Gross waves
Authors: Randriamboarison O. C. , Décréau P. M. E. , Krasnosel’skikh V. V.
Published: July 2002

Analytical expressions for the impulsive causal Green’s function based on the resolution of the differential equation describing the external excitation of the Bohm and Gross electrostatic wave are derived. The exact solution corresponding to the longitudinal plasma wave is put in the compact form of a two-real-variable Lommel function.
Quasilinear analysis of loss-cone driven weakly relativistic electron cyclotron maser instability
Authors: Ziebell L. F. , Yoon Peter H.
Published: July 2002

This paper presents a quasilinear analysis of the relativistic electron cyclotron maser instability. Two electron populations are assumed: a low-temperature background component and a more energetic loss-cone population. The dispersion relation is valid for any ratio of the energetic to cold populations, and includes thermal and relativistic effects. The quasilinear analysis is based upon an efficient kinetic moment method, in which various moment equations are derived from the particle kinetic equation. A model time-dependent loss-cone electron distribution function is assumed, which allows one to evaluate the instantaneous linear growth rate as well as the moment kinetic equations. These moment equations along with the wave kinetic equation form a fully self-consistent set of equations which governs the evolution of the particles as well as unstable waves. This set of equations is solved with physical parameters typical of the earth’s auroral zone plasma.
Drift waves in helical symmetry
Authors: Persson M. , Lewandowski J. L. V. , Nordman H.
Published: July 2002

The stable and unstable parts of the spectrum of the cold ion drift wave model are discussed in a helically symmetric stellarator model using a ballooning mode formalism. The presence of different types of eigenmodes is discussed. A study of the dependence of the growth of the modes on mode number, and other parameters, is also presented.
Fast magnetic field penetration into a plasma beam
Authors: Armale Ron , Rostoker Norman
Published: July 2002

In this preliminary theoretical treatment, the magnetic field penetration into a beam of plasma is investigated. Maxwell’s equations and the generalized Ohm’s law, including the Hall term, are combined in a fluid model to produce a nonlinear diffusion equation for the magnetic field. The equation is linearized, and analytically solved in slab and cylindrical geometries. In the cylindrical case, the vector potential is introduced to obtain a lowest order solution of the diffusion equations which are coupled by the Hall term. In both cases, the solution contains whistler wave oscillations and classical diffusion. The whistler waves, which vanish without the Hall term, carry-in the field and determine the penetration time. There is no fast penetration without a component of magnetic field normal to the beam surface. The Hall term also produces a field component parallel to the beam velocity.
Inertia and ion Landau damping of low-frequency magnetohydrodynamical modes in tokamaks
Authors: Bondeson A. , Chu M. S.
Published: July 2002

The inertia and Landau damping of low-frequency magnetohydrodynamical modes are investigated using the drift-kinetic energy principle for the motion along the magnetic field. Toroidal trapping of the ions decreases the Landau damping and increases the inertia for frequencies below (r/R)1/2vthi/qR. The theory is applied to toroidicity-induced Alfvén eigenmodes and to resistive wall modes in rotating plasmas. An explanation of the beta-induced Alfvén eigenmode is given in terms of the Pfirsch–Schlüter-like enhancement of inertia at low frequency. The toroidal inertia enhancement also increases the effects of plasma rotation on resistive wall modes.
Experimentally determined profiles of fast wave current drive in a tokamak
Authors: Forest C. B. , Petty C. C. , Baity F. W. , Chui S. C. , deGrassie J. S. , Kupfer K. , Groebner R. J. , Jaeger E. F. , Murakami M. , Pinsker R. I. , Prater R. , Rice B. W. , Wade M. R. , Whyte D. G.
Published: July 2002

Profiles of the noninductive current, driven by direct electron absorption of fast waves in the ion cyclotron range of frequencies, have been determined for DIII-D tokamak discharges [Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159]. The results clearly indicate the presence of centrally peaked driven current and validate theoretical models of fast wave current drive.
Nonlinear evolution of a narrow stratified velocity-shear layer
Authors: Keskinen M. J.
Published: July 2002

The nonlinear evolution of the Kelvin–Helmholtz instability in a narrow stratified velocity-shear layer has been computed using numerical and analytical techniques. It is found that the Kelvin–Helmholtz instability develops, in the nonlinear regime, in a distinctly different manner in configuration and k space when finite temperature effects are included in the fluid approximation. Vortex generation is inhibited with the vortices becoming striated and anisotropic. In addition, large density and electric field fluctuations are produced in the nonlinear regime.
Free electron laser with longitudinal wiggler and finite magnetic field in a partially filled waveguide
Authors: Mehdian Hassan , Willett Joseph E. , Maraghechi Behrouz , Aktas Yildirim
Published: July 2002

The operative mechanism for a free electron laser with a longitudinal electrostatic wiggler is analyzed. A theory is developed that allows for an arbitrary axial magnetic guide field and arbitrary ratio of the electron beam radius a to the waveguide inner radius R. Dispersion equations for the eigenmodes of a waveguide containing a magnetized electron beam and a formula for the spatial growth rate of parametrically excited eigenmodes are derived. The growth rate, efficiency, radiation wavelength, and required pump wavelength are studied numerically as functions of the ratio a/R. It is shown that excitation of the upper branch or lower branch of an electric–magnetic (EH) waveguide mode can be achieved with suitably chosen values for the system parameters.
Instability heating of a solid fiber Z-pinch
Authors: Riley R. , Scudder D. , Shlachter J. , Lovberg R.
Published: July 2002

A dense Z-pinch formed by the electrical breakdown of solid CD2 fibers in an 800 kA, 100 ns risetime pulse generator has been studied with optical and radiation diagnostics. It has been found that, contrary to calculations based on classical joule heating of the plasma that predict approximate dynamic equilibrium, the pinch always expands explosively while displaying intense m=0 hydromagnetic instability activity. Excellent agreement with the observed expansion rate as well as with measured electron temperatures and neutron yield has been obtained by including in a simulation code the direct heating of ions by turbulence arising from instability growth.
Comparison of detached and radiative divertor operation in Alcator C-Mod
Authors: Goetz J. A. , Kurz C. , LaBombard B. , Lipschultz B. , Niemczewski A. , McCracken G. M. , Terry J. L. , Boivin R. L. , Bombarda F. , Bonoli P. , Fiore C. , Golovato S. , Granetz R. , Greenwald M. , Horne S. , Hubbard A. , Hutchinson I. , Irby J. , Marmar E. , Porkolab M. , Rice J. , Snipes J. , Takase Y. , Watterson R. , Welch B. , Wolfe S. , Christensen C. , Garnier D. , Jablonski D. , Lo D. , Lumma D. , May M. , Mazurenko A. , Nachtrieb R. , O’Shea P. , Reardon J. , Rost J. , Schachter J. , Sorci J. , Stek P. , Umansky M. , Wang Y.
Published: July 2002

The divertor of the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)] routinely radiates a large fraction of the power entering the scrape-off layer. This dissipative divertor operation occurs whether the divertor is detached or not, and large volumetric radiative emissivities, up to 60 MW m−3 in ion cyclotron range of frequency (ICRF) heated discharges, have been measured using bolometer arrays. An analysis of both Ohmic and ICRF-heated discharges has demonstrated some of the relative merits of detached divertor operation versus high-recycling divertor operation. An advantage of detached divertor operation is that the power flux to the divertor plates is decreased even further than its already low value. Some disadvantages are that volumetric losses outside the separatrix in the divertor region are decreased, the neutral compression ratio is decreased, and the penetration efficiency of impurities increases.
Gyrokinetic simulation of isotope effects in tokamak plasmas
Authors: Lee W. W. , Santoro R. A.
Published: July 2002

A three-dimensional (3-D) global gyrokinetic particle code in toroidal geometry has been used for investigating the transport properties of ion temperature gradient (ITG) drift instabilities in tokamak plasmas. Using the isotopes of hydrogen (H+), deuterium (D+) and tritium (T+), it is found that, under otherwise identical conditions, there exists a trend for favorable isotope scaling for the ion thermal diffusivity, i.e., χi decreases with mass. Such a trend, which exists both at the saturation of the instability and also at the fully nonlinear stage, can be understood from the resulting wave number and frequency spectra.
Quasilinear evolution of the weakly relativistic electron cyclotron maser instability
Authors: Ziebell L. F.
Published: July 2002

This paper presents a quasilinear analysis of the relativistic electron cyclotron maser instability in which the self-consistent set of equations governing the evolution of the particle distribution function and the energy spectra of unstable waves is numerically solved for parameters typical of the Earth’s auroral zone plasma, taking into account both resonant and non-resonant diffusions. The results obtained show that only 0.1%∼0.2% of the particle energy is converted into wave energy by the loss cone instability, and also show that the saturation amplitude for the extraordinary mode increases in proportion to the ratio between electron cyclotron frequency and electron plasma frequency, in agreement with previous results obtained with numerical simulations.
Free-boundary, high-beta equilibrium in a large aspect ratio tokamak with nearly circular plasma boundary
Authors: Qin H. , Reiman A.
Published: July 2002

An analytic solution is obtained for free-boundary, high-beta equilibria in large aspect ratio tokamaks with a nearly circular plasma boundary. In the absence of surface currents at the plasma-vacuum interface, the free-boundary equilibrium solution introduces constraints arising from the need to couple to an external vacuum field which is physically realizable with a reasonable set of external field coils. This places a strong constraint on the pressure profiles that are consistent with a given boundary shape at high εβp. The equilibrium solution also provides information on the flux surface topology. The plasma is bounded by a separatrix. Increasing the plasma pressure at fixed total current causes the plasma aperture to decrease in a manner that is described.
Contribution of trapped and untrapped particles to the longitudinal permeability of a toroidal plasma
Authors: Grishanov N. I. , de Azevedo C. A. , de Assis A. S.
Published: July 2002

The contributions of trapped and untrapped particles to the longitudinal permeability of a toroidal plasma are analyzed for radio frequency waves in a wide range of frequencies, mode numbers, and plasma parameters. A collisionless plasma model of an axisymmetric tokamak with circular magnetic surfaces and large aspect ratio is considered. The analytical expressions of the longitudinal permeability elements are obtained by using the kinetic theory of dielectric tensor components, where the Vlasov equation is solved as a boundary-value problem. The radial structures of the imaginary part of the longitudinal permeability (for both the untrapped and trapped particles) are studied for parabolic profiles of plasma density, temperature, and tokamak safety factor. The results of the paper are interesting for the problems of Alfvén (and lower-hybrid) resonance heating and current drive by the Čerenkov dissipation mechanism of the waves in toroidal plasmas.
Spectral content of strong Langmuir turbulence in the beam plasma interaction
Authors: McFarland M. D. , Wong A. Y.
Published: July 2002

The detailed spectral content of strong Langmuir turbulence generated by an electron beam is investigated experimentally in an unmagnetized plasma. It is found that the power spectra of the electrostatic waves follows a consistent, reproducible pattern in which the Langmuir energy is concentrated in high frequencies (410 MHz) immediately following a collapse event, transitions to lower frequencies between events, with collapse taking place at the lowest frequencies (350 MHz). Also, after a collapse event, the electrostatic wave intensity falls by about two orders of magnitude in a microsecond, but then continues to fall over the next approximately 10 μs by an additional factor of 10 before beginning to build toward the next collapse. The spectral width and electron saturation current also exhibit reproducible patterns. Measurements are also performed to determine the low-frequency, ion acoustic spectral content. It is found that the peak of the ion acoustic spectrum scales inversely with the average time between collapse.
Van der Pol behavior of virtual anode oscillations in the sheath around a grid in a double plasma device
Authors: Klostermann H. , Rohde A. , Piel A.
Published: July 2002

Experiments are reported on oscillations that arise in a double plasma device when plasma production is restricted to the source chamber and the separating grid between the two chambers is biased negatively. The free oscillating system shows periodic pulling which is a typical behavior of driven van der Pol type oscillators. The second interacting frequency is identified to be half the ion plasma frequency at the sheath edge on the source side. With the help of particle in cell simulations the concept of virtual anode oscillations (VAO’s) as the underlying oscillation mechanism is investigated and the van der Pol character of these is revealed. When applied to the experimental conditions, the VAO-model predicts correct oscillation frequencies. It gives a new interpretation of the scaling of these with plasma density and grid bias, and is compatible with earlier findings.
Solution of the drift kinetic equation in the regime of weak collisions by stochastic mapping techniques
Authors: Kasilov Sergei V. , Moiseenko Vladimir E. , Heyn Martin F.
Published: July 2002

A new method for solving the drift kinetic equation applicable for non-integrable particle motion is presented. To obtain this goal, the general form of the drift kinetic equation is reduced to a stochastic mapping equation which is valid in the weak collisions regime. This equation describes the evolution of the distribution function on Poincaré cuts of phase space. The proposed Monte Carlo algorithm applied to the stochastic mapping equation turns out to solve the drift kinetic equation much faster than a direct integration of stochastic orbits. It can be applied to study quasilinear effects of radio frequency heating and transport in systems with complex magnetic field geometries such as stellarators, tokamaks with toroidal magnetic field ripples, or ergodic divertors. For systems with axial space symmetry the stochastic mapping equation is shown to reduce to the well-known canonical (bounce) averaged equation. For nonaxisymmetric magnetic fields the bounce averaged equation for trapped particles is recovered.
The magnetized Rayleigh-Taylor instability with a temporally variable gravity
Authors: Winske D.
Published: July 2002

Hybrid simulations with kinetic ions and massless fluid electrons are used to investigate the linear and nonlinear behavior of the Rayleigh-Taylor instability in a collisionless, magnetized plasma in slab geometry with the plasma subject to a time varying gravity. In particular, cases where the sign of gravity is reversed for some time interval are compared with the corresponding case with constant gravity. Consistent with simple theory, the effect of the gravity reversal is to stop the growth of the instability. And when the gravity is restored to its initial direction, the instability resumes at a rate that is commensurate with its earlier value. Several ways to estimate the rate of growth of the thickness of the mixing layer when g⃗ is not constant are suggested and compared with the simulations.
Measurements of laser-plasma instability relevant to ignition hohlraums
Authors: Fernández Juan C. , Bauer Bruno S. , Cobble James A. , DuBois D. F. , Kyrala George A. , Montgomery D. S. , Rose Harvey A. , Vu H. X. , Watt Robert G. , Wilde Bernhard H. , Wilke Mark D. , Wood William M. , Failor Bruce H. , Kirkwood R. , MacGowan B. J.
Published: July 2002

The potential for laser-plasma instability is a serious concern for indirect-drive inertial confinement fusion (ICF), where laser beams illuminate the interior of a cavity (called a hohlraum) to produce x-rays for imploding a fusion capsule symmetrically. The speckled nature of laser beams used in ICF is an important factor in laser-plasma instability processes. For example, models which calculate the spatial growth of convective instability by properly accounting for the laser speckles successfully predict the observed onsets of backscattering due to stimulated Brillouin and Raman scattering instabilities (SBS and SRS). Assuming pump depletion as the only saturation mechanism in these models results in very large predicted levels of SBS and SRS backscattering from the long-scale plasmas expected in ignition hohlraums. However, in the long-scale plasmas studied in the Nova and Trident lasers [E. M. Campbell, Rev. Sci. Instrum. 57, 2101 (1986) and N. K. Moncur et al., Appl. Opt. 34, 4274 (1995)], SRS and SBS are observed to saturate much below the levels expected from pump depletion. While the mechanism of SBS saturation is not understood at present, the observations of SRS saturation are qualitatively understood.
Nonlinear interaction of fast particles with Alfvén waves in toroidal plasmas
Authors: Candy J. , Borba D. , Berk H. L. , Huysmans G. T. A. , Kerner W.
Published: July 2002

A numerical algorithm to study the nonlinear, resonant interaction of fast particles with Alfvén waves in tokamak geometry has been developed. When the instability is sufficiently weak, it is known that the wave-particle trapping nonlinearity will lead to mode saturation before wave–wave nonlinearities are appreciable. The spectrum of linear modes can thus be calculated using a magnetohydrodynamic normal-mode code, then nonlinearly evolved in time in an efficient way according to a two-timescale Lagrangian dynamical wave model. The fast particle kinetic equation, including the effect of orbit nonlinearity arising from the mode perturbation, is simultaneously solved for the deviation, δf=f−f0, from an initial analytic distribution f0. High statistical resolution allows linear growth rates, frequency shifts, resonance broadening effects, and nonlinear saturation to be calculated quickly and precisely. The results have been applied to an International Thermonuclear Experimental Reactor [ITER EDA Doc. Series No. 7 (International Atomic Energy Agency, Vienna, 1996), p. V-32] instability scenario. Results show that weakly damped core-localized modes alone cause negligible alpha transport in these reactor-like plasmas—even with growth rates one order of magnitude higher than expected values. However, the possibility of significant transport in reactor-type plasmas due to weakly unstable global modes remains an open question.
A nonlinear theory of relativistic klystrons connected to a coaxial waveguide
Authors: Uhm Han. S. , Hendricks K. J. , Arman M. J. , Bowers L. , Hackett K. E. , Spencer T. A. , Coleman P. D. , Lemke R. W.
Published: July 2002

A self-consistent nonlinear theory of current modulation in an electron beam propagating through relativistic klystrons connected to a coaxial waveguide is developed. A theoretical model of the beam-energy increase Δγ near the extraction cavity is also developed, based on the self-potential depression. The potential depression κ can be significantly reduced in the vicinity of the extraction cavity from its value at the injection point. In appropriate system parameters, the kinetic-energy increase can easily be more than 50 keV, thereby eliminating the possibility of virtual cathode in the extraction cavity. Properties of the current modulation in a klystron are also investigated, assuming that a regular cylindrical waveguide is connected to a coaxial waveguide at the propagation distance z=z1. Due to proximity of a grounded conductor, the beam’s potential depression κ in the coaxial region is considerably less than that in the regular region. It is shown in the present analysis that amplitude of the current modulation increases drastically as the coaxial inner-conductor approaches the driving cavity. Moreover, the amplitude of the current modulation in the coaxial region changes slowly in comparison with that in the regular region.
Comment on “Dynamic plasma screening effects on semiclassical inelastic electron–ion collisions in dense plasmas” [Phys. Plasmas 4, 21 (1997)]
Authors: Murillo M. S.
Published: July 2002

Jung’s analysis of dynamics screening appears to be flawed by attempting to patch many-body effects into a single-body theory and a more rigorous foundation is necessary. Jung’s result and dynamical screening have been previously analyzed many times.(AIP)
Response to “Comment on ‘Explanation for MARFE formation and subsequent evolution into a detached symmetric plasma edge’ [Phys. Plasmas 3, 2673 (1996)], ‘MARFE impurity density limits in tokamaks with poloidal asymmetry and rotation’ [Phys. Plasmas 3, 3032 (1996)], and ‘MARFE suppression by external edge heating’ ” [Phys. Plasmas 4, 134 (1997)]
Authors: Stacey W. M.
Published: July 2002

One dimensional calculations are appropriate for impurity density limits in Tokamak devices and my analysis agrees with previous calculations for MARFE formation and evolution into a detached plasma edge. (AIP)
Confinement of a neutral plasma using nested electric potential wells
Authors: Ordonez C. A.
Published: July 2002

A self-consistent, two-dimensional analysis is presented on confining a region of neutral plasma with a Penning/Malmberg type plasma trap using a nested well configuration. It is found that a neutral plasma region having disparate electron and ion temperatures or having high charge state ions can be confined with static fields. For confining a neutral region comprised of electrons and equal temperature low charge state ions, a quasistatic approach appears promising.
Response to “Comment on ‘Dynamic plasma screening effects on semiclassical inelastic electron–ion collisions in dense plasmas’ ” [Phys. Plasmas 4, 21 (1997)]
Authors: Jung Young-Dae
Published: July 2002

We used a semiclassical technique to calculate the interaction energy between the electron (velocity v) and the target electron by including the dynamic screening effect and effects on atomic transition processes. This differs from previous work. (AIP)
Explosion of soliton in a multicomponent plasma
Authors: Das G. C. , Sarma Jnanjyoti , Uberoi C.
Published: July 2002

A three-dimensional nonlinear Kadomtsev–Petviashvili (K–P) wave equation is derived to discuss the solitons in multicomponent plasma contaminated with negative ions. A new formalism of the simple wave solution method is developed for finding the soliton behaviors caused by the presence of negative ions in plasmas. It is seen that the nonlinear wave equation leads, in some cases, to an ordinary differential equation and a straight way for solving the soliton propagation in plasmas. The overall observations describe the natures of compressive and rarefactive solitons along with the shock-like wave caused by the interaction of negative ions. Also discussed are the possible controls of the scenarios of soliton behaviors. Moreover it is believed, from present investigations, that the observations of collapses or explosions in solitons could enhance the understanding of the soliton phenomena in laboratory and space plasmas.
Nonlinear saturation of the Rayleigh–Taylor instability
Authors: Das Amita , Mahajan Sangeeta , Kaw Predhiman , Sen Abhijit , Benkadda S. , Verga A.
Published: July 2002

A detailed numerical simulation of the nonlinear state of the Rayleigh–Taylor instability has been carried out. There are three distinct phases of evolution where it is governed by the (i) linear effects, (ii) effects arising from the conventional nonlinear terms and (iii) subtle nonlinear effects arising through the coupling terms. During the third phase of evolution, there is a self-consistent generation of shear flow which saturates the Rayleigh–Taylor instability even in situations (with periodic boundaries) where, in principle, an infinite amount of gravitational energy can be tapped. The Galerkin approximation is presented to provide an understanding of our numerical findings. Last, there is an attempt to provide a comprehensive understanding of the nonlinear state of the Rayleigh–Taylor instability by comparing and contrasting this work with earlier studies.
Generation of the electrostatic field in the pulsar magnetosphere plasma
Authors: Kahniashvili T. A. , Machabeli G. Z. , Nanobashvili I. S.
Published: July 2002

The behavior of a relativistic electron–positron plasma in the pulsar magnetosphere is investigated. The equation of the motion of the magnetospheric plasma is discussed, from which it follows that, if the plasma particle radial velocity Vr>c/√ (where c is the speed of light), the centrifugal acceleration changes its sign and the particle braking begins. The stability of the magnetospheric plasma with respect to the radially oriented potential perturbations is discussed and the possibility of the electrostatic field generation in this plasma along the pulsar magnetic field lines is shown.
Crossed-field secondary emission electron source
Authors: Saveliev Y. M. , Sibbett W. , Parkes D. M.
Published: July 2002

A novel crossed-field secondary-emission (CFSE) electron source that is capable of producing high-current tubular electron beams is described. This new electron source is based on the mechanism of secondary-emission multiplication of electron current in a magnetron-like device having smooth cylindrical electrodes. The input electron current may be as low as a few mA. The multiplication process starts at the negative slope of an applied voltage pulse. After initiation, the current is extracted from the diode region with no regard to the voltage pulse shape and as a consequence, the CFSE electron source can operate in a long pulse mode. At the diode voltage of ∼40 kV for a diode gap of ∼6 mm, the output current reaches a value of more than 100 A.
Flow-shear stabilization of ion temperature gradient-driven instability in a tokamak: Slab theory
Authors: Bai L. , Fukuyama A. , Uchida M.
Published: July 2002

A simple physical model for the flow-shear stabilization of ion temperature gradient (ITG)-driven instability in the presence of dissipative trapped electrons is presented. Reduced fluid equations and magnetic sheared slab geometry are adopted. From analytical analyses and numerical calculations, it was found that the coupling between the sheared flows and non-adiabatic electrons will result in the stabilization of both toroidal sheared flow and poloidal sheared flow on hybrid dissipative trapped electron ITG mode. This implies that the confinement improvement in tokamaks can be obtained not only through the poloidal sheared rotation in the edge region of tokamaks for the H-mode (high-confinement mode), but also through the toroidal sheared rotation in the core region for further confinement improvement associated with internal transport barrier (ITB) and negative shear (or reversed magnetic shear). When the poloidal and toroidal sheared flows are simultaneously considered, it was found that in the presence of poloidal sheared flow, the toroidal sheared flow is a stabilizing or destabilizing effect on hybrid dissipative trapped electron ITG mode according to the relative sign of the poloidal and toroidal sheared flows. However, for sufficiently large value of the toroidal sheared flow, the toroidal sheared flow is always destabilization on the hybrid dissipative electron ITG mode regardless of the relative sign of these sheared flows. These conclusions are consistent with the experimental observations on the Japanese Tokamak-60U (JT-60U) [Y. Koide et al., Phys. Rev. Lett. 72, 3662 (1994)], where large toroidal rotation shear or jump was observed across the surface q=3 (the internal transport barrier location). Toroidal sheared flow stabilization therefore appears to offer favorable prospects for high confinement operation of future fusion reactor.
Exact evaluation of the quadratic response tensor for three-wave interactions in Maxwellian plasmas
Authors: Percival D. J. , Robinson P. A.
Published: July 2002

The quadratic response tensor provides a complete description of second-order wave processes in a nonlinear medium. The first exact expression is derived for the quadratic response tensor of a warm collisionless plasma, whose particles have a nonrelativistic Maxwellian velocity distribution. The exact expression is written in terms of a set of generalized plasma dispersion functions which satisfy simple symmetry properties and recursion relations and which can be expressed in terms of the standard nonrelativistic plasma dispersion function.
Indirect drive experiments utilizing multiple beam cones in cylindrical hohlraums on OMEGA
Authors: Murphy T. J. , Wallace J. M. , Delamater N. D. , Barnes Cris W. , Gobby P. , Hauer A. A. , Lindman E. L. , Magelssen G. , Moore J. B. , Oertel J. A. , Watt R. , Landen O. L. , Amendt P. , Cable M. , Decker C. , Hammel B. A. , Koch J. A. , Suter L. J. , Turner R. E. , Wallace R. J. , Marshall F. J. , Bradley D. , Craxton R. S. , Keck R. , Knauer J. P. , Kremens R. , Schnittman J. D.
Published: July 2002

Current plans for time-dependent control of flux asymmetry in the National Ignition Facility [J. A. Paisner, J. D. Boyes, S. A. Kumpan, and M. Sorem, “The National Ignition Facility Project,” ICF Quart. 5, 110 (1995)] hohlraums rely on multiple beam cones with different laser power temporal profiles in each cone. Experiments with multiple beam cones have begun on the Omega laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] at the University of Rochester. In addition to allowing symmetry experiments similar to those performed on Nova [A. Hauer et al., Rev. Sci. Instrum. 66, 672 (1995)], the Omega facility allows multiple beam cones to be moved independently to confirm our ability to model the resulting implosion image shapes. Results indicate that hohlraum symmetry behaves similarly with multiple rings of beams as with a single ring, but with the weighted beam spot position used to parametrize the beam pointing.
Laboratory simulations of solar prominence eruptions
Authors: Bellan P. M. , Hansen J. F.
Published: July 2002

Spheromak technology is exploited to create laboratory simulations of solar prominence eruptions. It is found that the initial simulated prominences are arched, but then bifurcate into twisted secondary structures which appear to follow fringing field lines. A simple model explains many of these topological features in terms of the trajectories of field lines associated with relaxed states, i.e., states satisfying ∇×B=λB. This model indicates that the field line concept is more fundamental than the flux tube concept because a field line can always be defined by specifying a starting point whereas attempting to define a flux tube by specifying a starting cross section typically works only if λ is small. The model also shows that, at least for plasma evolving through a sequence of force-free states, the oft-used line-tying concept is in error. Contrary to the predictions of line-tying, direct integration of field line trajectories shows explicitly that when λ is varied, both ends of field lines intersecting a flux-conserving plane do not remain anchored to fixed points in that plane. Finally, a simple explanation is provided for the S-shaped magnetic structures often seen on the sun; the S shape is shown to be an automatic consequence of field line arching and the parallelism between magnetic field and current density for force-free states.
Tungsten wire-array Z-pinch experiments at 200 TW and 2 MJ
Authors: Spielman R. B. , Deeney C. , Chandler G. A. , Douglas M. R. , Fehl D. L. , Matzen M. K. , McDaniel D. H. , Nash T. J. , Porter J. L. , Sanford T. W. L. , Seamen J. F. , Stygar W. A. , Struve K. W. , Breeze S. P. , McGurn J. S. , Torres J. A. , Zagar D. M. , Gilliland T. L. , Jobe D. O. , McKenney J. L. , Mock R. C. , Vargas M. , Wagoner T. , Peterson D. L.
Published: July 2002

Here Z, a 60 TW/5 MJ electrical accelerator located at Sandia National Laboratories, has been used to implode tungsten wire-array Z pinches. These arrays consisted of large numbers of tungsten wires (120–300) with wire diameters of 7.5 to 15 μm placed in a symmetric cylindrical array. The experiments used array diameters ranging from 1.75 to 4 cm and lengths from 1 to 2 cm. A 2 cm long, 4 cm diam tungsten array consisting of 240, 7.5 μm diam wires (4.1 mg mass) achieved an x-ray power of ∼200 TW and an x-ray energy of nearly 2 MJ. Spectral data suggest an optically thick, Planckian-like radiator below 1000 eV. One surprising experimental result was the observation that the total radiated x-ray energies and x-ray powers were nearly independent of pinch length. These data are compared with two-dimensional radiation magnetohydrodynamic code calculations.
Multi-Mode transport modeling of the International Thermonuclear Experimental Reactor (ITER)
Authors: Bateman Glenn , Kritz Arnold H. , Kinsey Jon E. , Redd Aaron J.
Published: July 2002

Predictions are made for the performance of the International Thermonuclear Experimental Reactor (ITER) [R. Aymar, V. Chuyanov, M. Huguet, R. Parker, and Y. Shimomura, in Proceedings of the Sixteenth International Atomic Energy Agency Fusion Energy Conference, Montréal, Canada 1996 (International Atomic Energy Agency, Vienna, 1997), Paper IAEA-CN-64/01-1] design using the Multi-Mode model in the time-dependent one- and one-half-dimensional (1-1/2-D) BALDUR [C. E. Singer et al., Comput. Phys. Commun. 49, 275 (1988)] transport code. This model predicts the temperature and density profiles observed in present-day tokamak experiments more closely on the average than other models currently available. Simulations using the Multi-Mode transport model, with its inherent gyro-Bohm scaling, indicate that ITER will ignite, even with edge temperatures as low as 0.25 keV (L-mode, or low-confinement mode, boundary conditions) or with volume averaged density as low as 0.775×1020 m−3 (just below the Greenwald density limit, when Tedge=0.75 keV). The ignition is found to be thermally stable, and the fusion power production is easily controlled by varying plasma density, impurity content, or edge temperatures. The nonequilibrium impurity radiation model used in these simulations predicts that a significant fraction of the fusion power is radiated when conditions are close to marginal ignition.
Amplitude modulation of dust-lattice waves in a plasma crystal
Authors: Amin M. R. , Morfill G. E. , Shukla P. K.
Published: July 2002

It is found that the nonlinear dynamics of amplitude-modulated dispersive dust lattice waves (DLW) is governed by a nonlinear Schrödinger equation. The latter exhibits that a constant amplitude carrier dust lattice wave is modulationally stable, and that the modulated DLW packet propagates in the form of either an envelope dark soliton or an envelope shock. The relevance of our theoretical investigation to simulation studies as well as to a laboratory dusty plasma experiment is pointed out.
Acceleration of energetic ions by nonlinear magnetosonic waves
Authors: Maruyama Kentaro , Bessho Naoki , Ohsawa Yukiharu
Published: July 2002

Interactions of nonthermal energetic ions with nonlinear magnetosonic waves are studied by means of a one-dimensional (one space coordinate and three velocity components), relativistic, electromagnetic particle simulation code with full ion and electron dynamics. It is found that, if ions with gyration speeds much greater than the Alfvén speed encounter a shock wave, some of them can gain great energies. The acceleration takes place when the particle velocity becomes nearly parallel to the transverse electric field in the shock. On the basis of a simple physical picture, the increase in the energy is theoretically obtained. Both the theory and simulation show that the ions with higher energies can obtain greater energies. Thus, in a plasma with strong magnetohydrodynamic turbulence some of the ions could be repeatedly accelerated to higher energies by many nonlinear pulses.
Simulation of instability growth rates on the front and back of laser accelerated planar targets
Authors: Bel’kov S. A. , Mkhitarian L. S. , Vinokurov O. A. , Kochemasov G. G. , Bondarenko S. V. , Wilson D. C. , Hoffman N. M.
Published: July 2002

The ability of an inertial confinement fusion target to achieve ignition and burn depends critically upon controlling the growth of hydrodynamic perturbations originating on the outer ablator surface and the inner deuterium–tritium (DT) ice. The MIMOZA-ND code [Sofronov et al., Voprosy Atomnoy Nauki i Tehniki 2, 3 (1990)] was used to model perturbation growth on both sides of carbon foils irradiated by 0.35 μm light at 1015 W/cm2. When an initial perturbation was applied to a laser irradiated surface, the computational instability growth rates agreed well with the existing theoretical estimates. Perturbations applied to the rear side of the target for wavelengths that are large compared to the thickness (d/Λ≪1) behave similarly to the perturbations at the ablation front. For d/Λ⩾1, the shorter the wave length is, the faster the decrease of the growth rate of the amplitudes at the interface (and the mass flows) as compared to the perturbations at the ablation front. This is due to the Richtmyer–Meshkov instability-induced transverse velocity component. The time of Rayleigh–Taylor instability transition to the nonlinear phase depends on the initial amplitude and is well modeled by an infinitely thin shell approximation. The transverse velocity generated by the Richtmyer–Meshkov instability causes the interaction of Λ=10 μm and Λ=2 μm wavelength modes to differ qualitatively when the perturbations are applied to the ablation front or to the rear side of target.
On transport barriers and low–high mode transitions
Authors: Taylor J. B. , Connor J. W. , Helander P.
Published: July 2002

Transport barriers and transitions between modes of low and high confinement in tokamak plasmas are often attributed to suppression of turbulence by a shear flow related to a plasma gradient, e.g., of density. However, such shear flow is also affected by the second derivative of density. When this is introduced there is no unique relation between flux and gradient—it depends on the source distribution within the plasma and on conditions at the plasma edge (e.g., imposed by the scrape-off layer). This edge gradient must lie within prescribed limits if a stationary plasma profile (which may include an improved confinement zone) is to exist.
Azimuthally symmetric pseudosurface and helicon wave propagation in an inductively coupled plasma at low magnetic field
Authors: Lho T. , Hershkowitz N. , Miller J. , Steer W. , Kim G. H.
Published: July 2002

The mode transition from a capacitively coupled mode (E mode) to an inductively coupled mode (H mode) was observed in an inductive Ar plasma source by applying an axially uniform low B field. The applied fundamental rf was 13.56 MHz and many harmonic components were observed. A beat and standing wave patterns of azimuthally symmetric (m=0 mode) first and second harmonic pseudosurfaces and helicon waves were measured at various densities (n∼9.0×1010–2.2×1011 cm−3) and B fields (12–28 G). Wave propagation mode changes, from pseudosurface to helicon waves and from helicon to pseudosurface waves, were observed at critical conditions, ωc/ω>3.0 and n∼2.2×1011 cm−3.
Kinetic theory of photons in a plasma
Authors: Tsintsadze N. L. , Mendonça J. T.
Published: July 2002

A kinetic equation for the photon gas in a relativistic plasma, neglecting the ions motion is derived. From this equation the fluid equations for the photon gas are obtained and their main properties are discussed. In order to illustrate the potential use of these equations to the study of new physical phenomena, which eventually can occur in relativistic plasmas, they are applied to three distinct situations. First, it is shown that a photon beam propagating in a plasma can excite a beam–plasma instability, similar to that occurring for the well-known case of electron beams. Second, it is shown that a bunch of photons, moving with constant velocity across a homogeneous plasma, can emit radiation similar to the Cherenkov effect associated with charged particles. Finally, the filamentation instability of a photon beam is discussed.
The three-dimensional stability of steady magnetohydrodynamic flows of an ideal fluid
Authors: Vladimirov V. A. , Ilin K. I.
Published: July 2002

The stability of steady magnetohydrodynamic flows of an ideal incompressible fluid to small three-dimensional perturbations is studied. Two new conditions sufficient for linear stability of steady magnetohydrodynamic flows are obtained by the energy method.
Optimum particle range for triggering fast ignition
Authors: Piriz A. R. , Sánchez M. M.
Published: July 2002

An analytic model for the dynamics of fast ignition is developed for the case in which the particle beam heats the fuel by generating a supersonic heat wave. It shows that the beam energy and intensity required for ignition increase with the particle range R. These results, together with previous ones for the subsonic regime of heating, allow for the determination of an optimum particle range value (R≈0.25 g/cm2). By decreasing the range below this value the ignition energy no longer decreases.
Spectroscopic analysis of normal and reversed ion flows in the DIII-D divertor
Authors: Isler R. C. , Brooks N. H. , West W. P. , Leonard A. W. , McKee G. R. , Porter G. D.
Published: July 2002

Flow velocities of C+, C2+, B+, and D+ parallel to the magnetic field in the DIII-D [J. Luxon, P. Anderson, F. Batty et al., Plasma Physics Controlled Nuclear Fusion Research, Proceedings of the 11th International Conference, Tokyo, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] divertor have been measured from Doppler shifts of spectral lines. In general, both normal flows (toward the target plate) and reversed flows (away from the target plate) are observed in the outer scrape-off layer with the reversed flows occurring near the separatrix. Following the transition from attached to partially detached conditions, normal flow velocities generally speed up while in some regions reversed flows are observed to slow down. In high density plasmas, deuteron velocities are reflected in Balmer line emission which originates mainly from atoms which have thermalized by charge exchange or which have been formed by recombination. Low-temperature areas of nearly stagnated deuteron flow have been observed. In these regions recombination should be efficient for neutralizing the divertor plasma.
Quasiaxially symmetric stellarators with three field periods
Authors: Garabedian Paul , Ku Long-Poe
Published: July 2002

Compact hybrid configurations with two field periods have been studied recently as candidates for a proof of principle experiment at the Princeton Plasma Physics Laboratory. This project has led us to the discovery of a family of quasiaxially symmetric stellarators with three field periods that have significant advantages, although their aspect ratios are a little larger. They have reversed shear and perform better in a local analysis of ballooning modes. Nonlinear equilibrium and stability calculations predict that the average beta limit will be at least as high as 4% if the bootstrap current turns out to be as big as that expected in comparable tokamaks. The concept relies on a combination of helical fields and bootstrap current to achieve adequate rotational transform at low aspect ratio.
Non-local collisional relaxation of neoclassical ions in tokamaks
Authors: Wang Shaojie
Published: July 2002

The reduced drift kinetic equation, expressed in terms of three independent constants of motion, has been obtained to investigate the nonlocal behavior of the neoclassical ion transport in tokamaks. It has been shown that the neoclassical ion transport is determined by the behavior of trapped particles at the turning points, with the effects of finite banana width taken into account.
Exponential nonlinear growth of a resistive m=1 island
Authors: Wang Xiaogang , Bhattacharjee A.
Published: July 2002

An analytical model is given for the exponential growth of a m=1 resistive island in the late nonlinear stage of its dynamics, observed in a recent numerical simulation [A. Aydemir, Phys. Rev. Lett. 78, 4406 (1997)]. This late nonlinear exponential growth phase follows the linear exponential growth phase and an early nonlinear algebraic growth phase. It is shown that the transition from the early nonlinear phase of algebraic growth in time to exponential growth occurs due to change in the geometric structure of the current sheet. Analytical predictions are in reasonable accord with simulation results.
Perturbative tests of theoretical transport models using cold pulse and modulated electron cyclotron heating experiments
Authors: Kinsey J. E. , Waltz R. E. , DeBoo J. C.
Published: July 2002

It is difficult to discriminate between various tokamak transport models using standardized statistical measures to assess the goodness of fit with steady-state density and temperature profiles in tokamaks. This motivates consideration of transient transport experiments as a technique for testing the temporal response predicted by models. Results are presented comparing the predictions from the Institute for Fusion Studies—Princeton Plasma Physics Laboratory (IFS/PPPL), gyro-Landau-fluid (GLF23), Multi-mode (MM), Current Diffusive Ballooning Mode (CDBM), and Mixed-shear (MS) transport models against data from ohmic cold pulse and modulated electron cyclotron heating (ECH) experiments. In ohmically heated discharges with rapid edge cooling due to trace impurity injection, it is found that critical gradient models containing a strong temperature ratio (Ti/Te) dependence can exhibit behavior that is qualitatively consistent both spatially and temporally with experimental observation while depending solely on local parameters. On the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], off-axis modulated ECH experiments have been conducted in L-mode (low confinement mode) and the perturbed electron and ion temperature response to multiple heat pulses has been measured across the plasma core. Comparing the predicted Fourier phase of the temperature perturbations, it is found that no single model yielded agreement with both electron and ion phases for all cases. In general, it was found that the IFS/PPPL, GLF23, and MS models agreed well with the ion response, but not with the electron response. The CDBM and MM models agreed well with the electron response, but not with the ion response. For both types of transient experiments, temperature coupling between the electron and ion transport is found to be an essential feature needed in the models for reproducing the observed perturbative response.