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

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Bastiaan J. Braams and Charles F. F. Karney

Phys. Fluids B 1, 1355 (1989); http://dx.doi.org/10.1063/1.858966 (14 pages) | Cited 29 times

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The collision operator for a relativistic plasma is reformulated in terms of an expansion in spherical harmonics. In this formulation the collision operator is expressed in terms of five scalar potentials that are given by one‐dimensional integrals over the distribution function. This formulation is used to calculate the electrical conductivity of a uniform electron–ion plasma with infinitely massive ions.

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52.27.Ny	Relativistic plasmas
52.25.Fi	Transport properties
52.20.Fs	Electron collisions

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High‐frequency noise on antennas in plasmas

R. L. Stenzel

Phys. Fluids B 1, 1369 (1989); http://dx.doi.org/10.1063/1.858967 (12 pages) | Cited 19 times

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Fluctuations in plasmas at frequencies near the electron plasma frequency (ω_p ) have been measured with in situ wire antennas. Such observations are important to the understanding of basic plasma properties (discrete versus collective effects) and the use of antennas in plasmas. The experiments are performed in a large (1 m diameter ×2 m) pulsed dc discharge and afterglow plasma (n_e<10¹² cm⁻³, kT_e<5 eV) with a weak axial magnetic field (B₀=5 G). The fluctuations are detected from wire antennas (length L≫radius a≳Debye length λ_D) with a low‐noise microwave receiver. The observations reveal three different physical processes that determine the noise spectra: (i) single particle shot noise, (ii) collective oscillations by bounded sheath–plasma resonances, and (iii) noise enhancements by longitudinal plasma waves. The first phenomenon (shot noise) gives rise to broadband noise (ωω_p) on both electric and magnetic antennas. In the evanescent regime (ω<ω_p) , the shot noise is induced by random electron motions through distances of, at most, a collisionless skin layer (c/ω_p) around the antenna. Recalling that electron transit‐time effects cause absorption of waves in a collisionless skin layer (known as ‘‘anomalous’’ skin absorption) the present observation of a collisionless skin emission effect can also be understood by the equivalence of blackbody absorption and emission coefficients. The second phenomenon (sheath–plasma resonance) is observed as a narrow resonant enhancement in the shot noise below cutoff (ω<ω_p) on electric antennas surrounded by sheaths or dielectrics. The series sheath–plasma resonance, usually identified from reflection/absorption measurements with incident waves, is established here, for the first time, as a feature of thermal emission spectra from antennas. The third phenomenon (plasma dielectric ϵ_(ω,k)→0) produces a broad noise enhancement at ω≳ω_p on electric antennas.

It can only be observed in the open‐loop voltage of dipoles measured with a high‐impedance transformer between antenna and 50Ω transmission line. The enhanced noise is electrostatic, randomly polarized, but not significantly enhanced by the presence of energetic electron tails. Existing theories can describe the new observations qualitatively but not quantitatively.

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52.40.Fd	Plasma interactions with antennas; plasma-filled waveguides
52.25.Os	Emission, absorption, and scattering of electromagnetic radiation
52.40.Hf	Plasma-material interactions; boundary layer effects
52.70.-m	Plasma diagnostic techniques and instrumentation

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Gyrokinetic energy conservation and Poisson‐bracket formulation

A. Brizard

Phys. Fluids B 1, 1381 (1989); http://dx.doi.org/10.1063/1.858968 (4 pages) | Cited 21 times

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An integral expression for the gyrokinetic total energy of a magnetized plasma, with general magnetic field configuration perturbed by fully electromagnetic fields, was recently derived through the use of a gyrocenter Lie transformation. It is shown that the gyrokinetic energy is conserved by the gyrokinetic Hamiltonian flow to all orders in perturbed fields. An explicit demonstration that a gyrokinetic Hamiltonian containing quadratic nonlinearities preserves the gyrokinetic energy up to third order is given. The Poisson‐bracket formulation greatly facilitates this demonstration with the help of the Jacobi identity and other properties of the Poisson brackets.

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52.25.Dg	Plasma kinetic equations
52.35.Kt	Drift waves

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The behavior of magneto‐acoustic‐gravity waves near the cusp resonance in a lossless, compressible, isothermal, stratified, electrically conducting, and uniformly magnetized atmosphere. I. Mode conversion approach

Leon P. J. Kamp

Phys. Fluids B 1, 1385 (1989); http://dx.doi.org/10.1063/1.858969 (11 pages) | Cited 2 times

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In the present paper the propagation of (internal) magneto‐acoustic‐gravity waves is analyzed in a compressible, isothermal, stratified, electrically conducting atmosphere that is permeated by a uniform, nearly horizontal magnetic field. The conversion, near the so‐called cusp resonance of a long acoustic‐gravity wave into a short slow magneto‐acoustic wave, is demonstrated by means of boundary layer theory based on the smallness of the vertical component of the magnetic field. The magneto‐acoustic wave subsequently carries the energy off upward, which in the limit of a horizontal magnetic field would be fed into the cusp resonance ad infinitum. This gives rise to singular fields. The scaling of the tendency toward singular behavior of a field quantity with the obliqueness of the magnetic field is discussed, as well as the partial reflection of the long acoustic‐gravity wave.

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47.65.-d	Magnetohydrodynamics and electrohydrodynamics
47.35.-i	Hydrodynamic waves
41.20.Jb	Electromagnetic wave propagation; radiowave propagation
92.90.+x	Other topics in hydrospheric and atmospheric geophysics (restricted to new topics in section 92)

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Wave‐dynamical analysis of conversion and absorption of oblique extraordinary and Bernstein modes near the second electron‐cyclotron harmonic

V. Petrillo, G. Lampis, C. Maroli, and C. Riccardi

Phys. Fluids B 1, 1396 (1989); http://dx.doi.org/10.1063/1.858970 (9 pages) | Cited 5 times

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The propagation and absorption of oblique second‐harmonic electron‐cyclotron waves in a plasma slab are studied by means of propagation equations directly deduced from the Vlasov–Maxwell system. An electromagnetic wave injected from the vacuum into the plasma can be transformed into a quasielectrostatic forward mode, which, in turn, is converted into a Bernstein backward wave. The occurrence of this double conversion process and the global absorption and reflection are analyzed, and the dependence of these phenomena on the plasma parameters and on the wave characteristics is investigated.

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52.35.Hr	Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.50.Gj	Plasma heating by particle beams

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Time evolution from linear to nonlinear stages in magnetohydrodynamic parametric instabilities

M. Hoshino and M. L. Goldstein

Phys. Fluids B 1, 1405 (1989); http://dx.doi.org/10.1063/1.858971 (11 pages) | Cited 19 times

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The nonlinear evolution of the magnetohydrodynamic (MHD) parametric instability of wave fluctuations propagating along an unperturbed magnetic field is investigated. Both a magnetohydrodynamic perturbation‐theoretical approach and a nonlinear MHD simulation are used. It is shown that high harmonic waves are rapidly excited by wave–wave coupling, and that the wave spectrum evolves from a state containing a small number of degrees of freedom in k space to one which contains a large number of degrees of freedom. It is found that the spectral evolution prior to nonlinear saturation is well described by the perturbation theory. During this stage, the ratio of the growth rate of the nth harmonic wave to the linear growth rate of the fundamental wave is n. The nonlinear saturation stage is characterized by a frequency shift of the fundamental wave that destroys the wave–wave resonance condition which, in turn, causes the wave amplitude to cease its growth.

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52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Ra	Plasma turbulence
52.65.-y	Plasma simulation

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Anomalous transport arising from nonlinear resistive pressure‐driven modes in a plasma

Satoshi Hamaguchi

Phys. Fluids B 1, 1416 (1989); http://dx.doi.org/10.1063/1.858972 (15 pages) | Cited 20 times

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Anomalous transport caused by fluctuations of resistive pressure‐driven modes is discussed within the framework of magnetohydrodynamics (MHD). The nonlinear‐reduced equations describing fluctuations localized near a particular magnetic field line are derived for tokamak and reversed‐field‐pinch (RFP) plasmas, taking into account nonzero viscosity and heat conductivity. For an ideally stable but resistively slightly unstable plasma, the anomalous transport is caused particularly by convective motions. The convection is studied as bifurcation from the linearly unstable equilibrium and the expression of the anomalous transport in a tokamak plasma is obtained as a function of the mean pressure gradient near the critical point. In order to evaluate the effects of the convection on the anomalous transport under various conditions, the reduced equations are also solved numerically. It is found that Nusselt number, that is, the ratio of the total heat conductivity including the anomalous heat transport to the classical collisional heat conductivity, is significantly large under some conditions. This partially accounts for the large heat losses in controlled thermonuclear fusion devices.

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52.25.Fi	Transport properties
52.25.Gj	Fluctuation and chaos phenomena
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)

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Ideal stability of cylindrical plasma in the presence of mass flow

A. Bondeson and R. Iacono

Phys. Fluids B 1, 1431 (1989); http://dx.doi.org/10.1063/1.858973 (13 pages) | Cited 25 times

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The ideal stability of cylindrical plasma with mass flows is investigated using the guiding center plasma (GCP) model of Grad [Proceedings of the Symposium on Electromagnetic and Fluid Dynamics of Gaseous Plasmas (Polytechnic Inst. of Brooklyn, New York, 1961), p. 37]. For rotating plasmas, the kinetic treatment of the parallel motion in GCP gives significantly different results from the fluid models, where the pressures are obtained from equations of state. In particular, GCP removes the resonance with slow magnetoacoustic waves and the loss of stability that occurs in magnetohydrodynamics (MHD) for near‐sonic flows. Because of the strong kinetic damping of the sound waves in an isothermal plasma, the slow waves have little influence on plasma stability in GCP at low beta. In the large aspect ratio, low‐beta tokamak ordering, Alfvénic flows are needed to change the ideal GCP stability significantly. At lowest order in the inverse aspect ratio, flow can be favorable or unfavorable for stability of local modes depending on the profiles, but external kinks are always destabilized by flow if the velocity vanishes at the edge. For high‐beta, reversed field pinch equilibria, numerical computations show that flow can be stabilizing for local modes, but external modes are destabilized by flow. In three dimensions, the MHD equilibrium problem becomes hyperbolic for arbitrarily small flows across the magnetic field, whereas the GCP equilibrium equation remains elliptic for sub‐Alfvénic flows.

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52.35.Dm	Sound waves
52.30.-q	Plasma dynamics and flow
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Dy	General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.

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Resistive ballooning modes in the second region of stability

Jin‐Yong Kim and Duk‐In Choi

Phys. Fluids B 1, 1444 (1989); http://dx.doi.org/10.1063/1.858974 (5 pages) | Cited 4 times

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A recent study suggested that the resistive ballooning modes are largely stable in the second region of the ideal ballooning stability, unlike in the first region. This problem is reexamined here by numerically solving the full resistive mode equation. It is shown that in the second region there are unstable resistive ballooning modes with larger growth rates compared to those in the first region. This behavior is shown to be caused by the fact that the curvature force significantly influences the dynamics in the resistive region, and the mode is mainly driven unstable from the resistive region and not from the ideal region through Δ′.

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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.)

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Stability of toroidicity‐induced drift waves in divertor tokamaks

S. Briguglio, F. Romanelli, C. M. Bishop, J. W. Connor, and R. J. Hastie

Phys. Fluids B 1, 1449 (1989); http://dx.doi.org/10.1063/1.859201 (10 pages) | Cited 6 times

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The stability of toroidicity‐induced drift waves in a tokamak equilibrium with magnetic separatrix is studied both analytically and numerically. In particular, the task of a proper determination of the complex ballooning parameter θ₀ is performed by solving the stationarity condition for the eigenvalue. Results show qualitative dependence on the location of the x point in the meridian plane. Specifically, locating the x point in the equatorial plane, both on the outside and on the inside of the plasma, causes a deepening of the well structure in the potential for the eigenmode, thereby enforcing the inhibition of the shear damping and the marginal stability result obtained in the circular magnetic surfaces case. On the other hand, the location of the x point at the top of the plasma produces a flattening of the well and restores the shear damping, yielding stabilization of the mode. A new quasimarginally stable branch, corresponding to modes localized around the x point, is shown to exist at high values of the separatrix parameter k and x‐point location close to the equatorial plane.

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52.35.Kt

Drift waves

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Neoclassical resonant‐plateau transport in the noncircular equipotential surface of a tandem mirror

I. Katanuma, Y. Kiwamoto, K. Ishii, K. Yatsu, and S. Miyoshi

Phys. Fluids B 1, 1459 (1989); http://dx.doi.org/10.1063/1.858975 (4 pages) | Cited 14 times

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Neoclassical resonant‐plateau transport in a minimum‐B anchored tandem mirror is calculated in an experimentally observed case where a flux tube of equipotential contours is not circular at the central cell.

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28.52.Av	Theory, design, and computerized simulation
52.55.-s	Magnetic confinement and equilibrium
52.25.Fi	Transport properties

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Numerical simulation of laser–target interaction and blast wave formation

John L. Giuliani, Margaret Mulbrandon, and Ellis Hyman

Phys. Fluids B 1, 1463 (1989); http://dx.doi.org/10.1063/1.858976 (14 pages) | Cited 11 times

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A numerical hydrodynamics chemistry model to simulate the laser–target interaction experiment at the Naval Research Laboratory’s PHAROS [Laser Interaction and Related Plasma Phenomena (Plenum, New York, 1986), Vol. 7, p. 857] is presented. Both laser–target and debris–background interactions are modeled, solving mass continuity, total momentum, and separate ion and electron internal energy equations. The model is appropriate for background densities≥1 Torr. To accurately treat both the early‐time planar ablation and the later spherical expansion of the blast wave, as well as the rear‐side shock front, an oblate spheroidal coordinate system was adopted. The aluminum target ablates into and interacts with an ambient nitrogen gas, filling the facility chamber. The simulation models the target continuously from the solid state to the state of a highly ionized nonequilibrium plasma, including all charge states of aluminum and all charge states of the nitrogen background. The laser beam has a wavelength of 1 μ, a ∼5 nsec full width at half‐maximum (FWHM), an intensity at the target surface ∼10¹³ W/cm², and total energy varying from 20–100 J. The model accurately reproduces the measured time‐of‐flight profile and the mass of ablated aluminum. Expansion of the blast wave in the model follows the ideal Sedov relation until radiation losses force a deviation due to a failure in the constant energy assumption. In the shock wave region the simulations show electron density of a few times 10¹⁸ cm⁻³, temperatures ranging from 10–20 eV, and dominant nitrogen species of N⁺³ and N⁺⁴, all in agreement with experimental measurement. A calculated profile of electron density both in the shock and in the cavity region agree closely with experiment and imply an average aluminum charge state of 11 times ionized in the cavity out to late times, as predicted by the simulation described in this paper.

The simulation suggests, also, that observed rear‐side structuring is a result of a deceleration Rayleigh–Taylor instability. The model is capable of providing detailed predictions, which are presented, as to profiles of charge states, densities, and temperatures as a function of time; these predictions are not yet tested by experimental measurement.

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52.38.-r	Laser-plasma interactions
52.35.Tc	Shock waves and discontinuities
52.65.-y	Plasma simulation

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The implosion of a two‐layer spherical shell target

A. R. Piriz

Phys. Fluids B 1, 1477 (1989); http://dx.doi.org/10.1063/1.858977 (6 pages) | Cited 4 times

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An analytical model is developed to describe the parameters of the fuel and the pusher at peak compression when a two‐layer spherical shell target is imploded by a single pressure pulse. The entropy generated by shock waves during the implosion is calculated and an approximate description of the process of central hot spot formation is given. The stagnation stage of a compressible shell is described and scaling laws for the final stage are found. Comparisons with available simulation data are presented and the effect of the thermal conduction in the formation of the central spark is discussed.

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52.65.-y	Plasma simulation
52.50.Lp	Plasma production and heating by shock waves and compression

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The Pierce diode with an external circuit. I. Oscillations about nonuniform equilibria

William S. Lawson

Phys. Fluids B 1, 1483 (1989); http://dx.doi.org/10.1063/1.858925 (10 pages) | Cited 19 times

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The nonuniform (nonlinear) equilibria of the classical (short circuit) Pierce diode and the extended (series RLC external circuit) Pierce diode are described, and the spectrum of oscillations (stable and unstable) about these equilibria are worked out. It is found that only the external capacitance alters the equilibria, though all elements alter the spectrum. In particular, the introduction of an external capacitor destabilizes some equilibria that are marginally stable without the capacitor. Computer simulations are performed to test the theoretical predictions for the case of an external capacitor only. It is found that most equilibria are correctly predicted by theory, but that the continuous set of equilibria of the classical Pierce diode at Pierce parameters (α=ω_pL/v₀) that are multiples of 2π are not observed. This appears to be a failure of the simulation method under the rather singular conditions rather than a failure of the theory.

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52.75.-d	Plasma devices
52.65.-y	Plasma simulation

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The Pierce diode with an external circuit. II. Chaotic behavior

William S. Lawson

Phys. Fluids B 1, 1493 (1989); http://dx.doi.org/10.1063/1.859199 (9 pages) | Cited 16 times

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The existence of the strange attractor discovered by Godfrey [Phys. Fluids 30, 1553 (1987)] in the neighborhood of α=3π for the Pierce diode is verified, and his numerical results are refined. The theory of Feigenbaum for the sequence of period‐doubling bifurcations [J. Stat. Phys. 19, 25 (1975)] is tested with good agreement, despite the strong assumptions made by that theory. The evolution of this attractor is then followed as an external capacitance is introduced, producing a family of bifurcation diagrams. Examination of these diagrams produces one result that should be of interest to mathematical physicists: The existence of an unstable equilibrium in the neighborhood of the strange attractor is strongly implicated in both the existence and destruction of the attractor. The reversibility of the equations of evolution is also discussed, but no clear‐cut conclusion is reached.

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52.75.-d	Plasma devices
05.45.-a	Nonlinear dynamics and chaos
52.65.-y	Plasma simulation

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Evolution of bounded beam–plasma interactions in a one‐dimensional particle simulation

I. J. Morey and R. W. Boswell

Phys. Fluids B 1, 1502 (1989); http://dx.doi.org/10.1063/1.858926 (9 pages) | Cited 4 times

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A particle‐in‐cell code has been used to study the electron beam–plasma interaction, with n_b<n_p, in a bounded one‐dimensional system. Sheaths form on the boundaries because electrons leave the system as a result of the beam–plasma interaction heating the plasma electrons. The ions are chosen to be immobile since most time scales are too short for ion motion. The sheaths reflect waves and beam electrons, so that the interaction rapidly reaches a nonlinear stage. Standing waves have been observed. Despite this, the rate at which the beam–plasma interaction heats the plasma is found to agree with linear and quasilinear theory for weak beams in long systems, except when n_b≳n_p/4 or the interaction length, L≳3v_b/f_pe.

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52.65.-y	Plasma simulation
52.40.Mj	Particle beam interactions in plasmas
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

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A millimeter and submillimeter wavelength free‐electron laser

D. A. Kirkpatrick, G. Bekefi, A. C. DiRienzo, H. P. Freund, and A. K. Ganguly

Phys. Fluids B 1, 1511 (1989); http://dx.doi.org/10.1063/1.858927 (8 pages) | Cited 12 times

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Measurements of millimeter and submillimeter wavelength emission (240 GHz<ω/2π<470 GHz) from a free‐electron laser are reported. The laser operates as a superradiant amplifier and without an axial guide magnetic field; focusing and transport of the electron beam through the wiggler interaction region are achieved by means of the bifilar helical wiggler field itself. Approximately 18 MW of rf power has been observed at a frequency of 470 GHz, corresponding to an electronic efficiency of 0.8%. Frequency spectra are measured with a grating spectrometer and show linewidths Δω/ω∼2%–4%. The experimental results are in very good agreement with nonlinear numerical simulations.

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41.60.Cr	Free-electron lasers
52.59.Px	Hard X-ray sources

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Plasma distribution models in a rotating magnetic dipole and refilling of plasmaspheric flux tubes

J. Lemaire

Phys. Fluids B 1, 1519 (1989); http://dx.doi.org/10.1063/1.858928 (7 pages) | Cited 7 times

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Rotating stars or planets like Earth are sometimes surrounded by a dipolar magnetic field distribution. The thermal plasma forming a corona or an ionosphere around these astrophysical objects diffuses upward along the magnetic field lines and forms a toroidal region filled with this thermal plasma, like the terrestrial plasmasphere. The field‐aligned distribution of this thermal ionospheric plasma is controlled by the gravitational and pseudocentrifugal potential distribution. One can distinguish two extreme types of plasma distribution in this field‐aligned potential: the diffusive equilibrium distribution and the exospheric equilibrium distribution corresponding, respectively, (i) to a saturated, and (ii) to an almost depleted, magnetic flux tube. As a result of pitch angle scattering by Coulomb collisions, an increasing number of ions escaping from the ionosphere are stored in trapped orbits. These trapped particles have magnetic mirror points at high altitudes, i.e., in the low‐density exospheric region. Also as a result of collisions, the field‐aligned density distributions irreversibly evolve from exospheric equilibrium with a highly anisotropic pitch angle (cigarlike) distribution to a diffusive equilibrium distribution characterized by an isotropic pitch angle distribution. It is shown that the suprathermal ions become anisotropic much more slowly than ions of energies smaller than 1 eV.

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94.30.cv	Plasmasphere
94.20.dl	Topside region
94.20.wh	Ionosphere/magnetosphere interactions
96.12.Jt	Atmospheres

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Radiation transport effects in heavy‐ion beam–target interaction studies: Measurement of target opacity and beam conversion efficiency

N. A. Tahir and R. C. Arnold

Phys. Fluids B 1, 1526 (1989); http://dx.doi.org/10.1063/1.858929 (13 pages) | Cited 7 times

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In this paper detailed simulations are presented of radiation‐hydrodynamic response of gaseous cylindrical targets irradiated with heavy‐ion beams that will be produced at the Gesellschaft für Schwerionenforschung, Darmstadt, using a heavy‐ion synchrotron (SIS) [Heavy Ion Fusion, AIP Conference Proceedings No. 152 (AIP, New York, 1986), p. 23]. The purpose of this work is to explore material conditions for which the thermal radiation effects can be maximized. This is desirable in order to study a number of interesting and important effects including maximization of conversion efficiency of the ion beam energy to thermal radiation and measurement of the target opacity in the SIS experiments. It is expected that the SIS beams will produce a specific deposition power of 10 TW/g. The simulations in this paper show that a temperature of the order of 10 eV could be achieved by the SIS beams using homogeneous, cylindrical Xe targets. It has been shown that with the help of these computer simulations one should be able to measure the target opacity in these experiments within a factor of 3. Also these calculations show that in the SIS experiments one should be able to have a 50% conversion efficiency using a Xe target under optimum conditions. It has been found that the radiation effects will be optimized in the SIS experiments if the initial target density is of the order of 10⁻³ g/cm³. If the initial density is too high (of the order of 10⁻¹ g/cm³ or more), hydrodynamic effects will dominate, while, on the other hand, if the initial density is too low (of the order of 10⁻⁴ g/cm³ or less), the electron thermal conductivity will take over.

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52.40.Mj	Particle beam interactions in plasmas
52.58.-c	Other confinement methods

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Sharp boundary analysis of electrostatic flute modes

Don S. Lemons

Phys. Fluids B 1, 1539 (1989); http://dx.doi.org/10.1063/1.858930 (3 pages) | Cited 1 time

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A linear, electrostatic, stability analysis of a magnetized cross‐field drifting plasma with a sharp boundary is presented. The analysis corrects an error in a previously published sharp boundary theory [Phys. Fluids 19, 882 (1976)] and extends another theory [Geophys. Res. Lett. 14, 60 (1987)] to include finite electron mass and non‐neutral perturbations. The instability’s long wavelength structure is associated with the classical flute instability, while the peak of the growth rate curve, at much shorter wavelengths, is a Buneman‐like instability.

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52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Kt	Drift waves

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Magnetic condensation instability in nonuniform unmagnetized plasmas

P. K. Shukla

Phys. Fluids B 1, 1541 (1989); http://dx.doi.org/10.1063/1.858931 (3 pages)

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It is shown that an impurity radiation cooling can give rise to a novel magnetic condensation thermal instability in nonuniform unmagnetized electron plasmas. The resulting enhanced magnetic fluctuations can be responsible for the magnetic turbulence in unmagnetized plasmas.

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52.35.Hr	Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Ra	Plasma turbulence
52.27.Jt	Nonneutral plasmas

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An exact nonlinear cylindrical surface wave solution

L. Stenflo and M. Y. Yu

Phys. Fluids B 1, 1543 (1989); http://dx.doi.org/10.1063/1.858932 (2 pages) | Cited 16 times

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An exact solution for strongly nonlinear electrostatic surface waves on a cylindrical boundary of a plasma medium is presented. The effective nonlinear dielectric constant turns out to be dependent upon the geometry as well as the electric field amplitude.

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52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
68.03.Kn	Dynamics (capillary waves)
68.05.-n	Liquid-liquid interfaces
73.50.Mx	High-frequency effects; plasma effects

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Long‐term development of elongated tokamak plasmas after failure of feedback stabilization

Torkil H. Jensen and Ming S. Chu

Phys. Fluids B 1, 1545 (1989); http://dx.doi.org/10.1063/1.858933 (3 pages) | Cited 7 times

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Tokamaks with cross sections elongated in the axial direction are subject to an instability that basically involves an axial displacement of the plasma. This instability can be stabilized by a feedback circuit. This Brief Communication deals with the long‐term development of the plasma after a failure of the feedback circuit during an otherwise normal discharge. The short‐term (linear) development of such a plasma was considered earlier by Yokomizo et al. [Nucl. Fusion 23, 1593 (1983)]. During the long‐term development, the plasma makes intimate contact with the surrounding conducting shell (vacuum vessel). The timescale for this development is long compared to the Alfvèn time, so that it is appropriate to consider the plasma in a magnetohydrodynamic (MHD) equlibrium which evolves slowly. This equilibrium (assumed axisymmetric) is unusual in that currents and forces are exchanged between the shell and the plasma. The dynamics of the equilibrium is determined by Ohmic dissipation associated with the plasma currents and the toroidal and poloidal currents of the shell. For a ‘‘typical’’ large tokamak, it is found that dissipation in the shell may dominate. Modeling of such long‐term development may be important because the forces acting on the shell due to the shell currents may be large. It may be important that dissipation in the plasma can be neglected or that it is small in such modeling since the uncertainty of the results, due to uncertainties associated with the plasma, is absent or may be small.

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