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In a previous paper by Tahir and Long [Phys. Fluids 29, 1282 (1986)] it was shown that radiation energy transport can compensate for the range shortening effects in ion-beam inertial confinement fusion (ICF) plasma. Implosion results of a high-gain, ion-beam driven, reactor-size ICF target including radiation effects were also reported. These implosion simulations were carried out under an assumption of a complete thermodynamic equilibrium between the radiation field and the electrons. This assumption, however, is only applicable in optically thick media and is thus valid in the compression phase of ICF targets only. In the burn phase the radiation field is totally decoupled from the electrons and the above approximation breaks down. A three-temperature model described in another paper by Tahir et al. [J. Appl. Phys. 60, 898 (1986)] is a much better model for such a regime. Using this three-temperature model, the ignition and burn of the target reported in the Tahir–Long paper have been recalculated and these improved results are presented here. The importance of the inverse Compton effect and the α-particle transport in inertial fusion burn plasmas is also discussed. [ABSTRACT FROM AUTHOR]

In a previous paper by Long and Tahir [Phys. Fluids 29, 275 (1986) ], the motion of plane targets irradiated by ion beams whose energy deposition was assumed to be independent of the ion energy, and the temperature and density of the plasma, was analyzed. In this paper, the analytic solution is extended in order to include the effects of a temperature- and densitydependent energy deposition as a result of electron excitation, an improved equation of state, thermal ionization, a pulse shape, and radiation losses. The change in the energy deposition with temperature and density leads to range shortening and an increased power deposition in the target. It is shown how the analytic theory can be used to analyze experiments to measure the enhanced energy deposition. In order to further analyze experiments, numerical simulations are presented which include the plasma-induced effects on the energy deposition. It is shown that since the change in the range is a result of both a decrease in density and an increase in temperature, it is not possible to separate these two effects in present experiments. Therefore, the experiments which measure the time-dependent energy of the ions emerging from the back side of a plane target do not as yet measure the energy loss as a function of the density and temperature of the plasma or of the energy of the ion, but only an averaged loss over certain ranges of these physical quantities. [ABSTRACT FROM AUTHOR]

In a recent paper [E. Zawaideh, F. Najmabadi, and R. W. Conn, Phys. Fluids 29, 463 (1986)] a new set of generalized two-fluid equations is derived that describes plasma transport along the field lines of a space- and time-dependent magnetic field. These equations are valid for collisional to weakly collisional plasmas; they reduce to the conventional fluid equations of Braginskii [S. I. Braginskii, Reviews of Plasma Physics, edited by M. A. Leontovich (Consultants Bureau, New York, 1965), Vol. 1, p. 205] for highly collisional plasmas. An important feature of these equations is that the anisotropy in the ion pressure is explicitly included. In this paper, these generalized transport equations are applied to a model problem of plasma flow through a magnetic mirror field. The profiles of the plasma parameters (density, flow speed, and pressures) are numerically calculated for plasmas in different collisionality regimes. These profiles are explained by examining the competing terms in the transport equation. The pressure anisotropy is found to profoundly impact the plasma flow behavior. As a result, the new generalized equations predict flow behavior more accurately than the conventional transport equations. A large density and pressure drop is predicted as the flow passes through a magnetic mirror. Further, the new equations uniquely predict oscillations in the density profile, an effect missing in results from the conventional equations. [ABSTRACT FROM AUTHOR]

Bissell and Johnson [Phys. Fluids 30, 779 (1987)] have calculated the electrostatic potential variation in the sheath and presheath regions of a collisionless plasma in which the source of ions is assumed to be Maxwellian. To do this, they imposed the generalized Bohm criterion as a boundary condition. In this paper the plasma equation is solved numerically without imposing the Bohm criterion as a boundary condition. The results compare well with their results. In addition, the ion distribution function throughout the plasma region is calculated. Because of this particular source model, the ion distribution at the center of the plasma has a spiked non-Maxwellian shape. [ABSTRACT FROM AUTHOR]

The propagation of plasmoids (neutralized ion beams) in a vacuum transverse magnetic field has been studied in the University of California, Irvine laboratory for several years [Phys. Fluids 24, 739 (1981); 25, 730, 2353 (1982); 26, 2276 (1983); J. Appl. Phys. 64, 73 (1988)]. These experiments have confirmed that the plasmoid propagates by the E X B drift in a low beta and high beta plasmoid beam (0.01 <β < 300), where β is the ratio of beam kinetic energy to magnetic field energy. The polarization electric field E arises from the opposite deflection of the plasmoid ions and electrons, because of the Lorentz force, and allows the plasmoid to propagate undeflected at essentially the initial plasmoid velocity. In these experiments, plasmoids (150 keV, 5 kA, 50-100 A/cm², 1 µsec) were injected into transverse fields of B[sub t] = 0-400 G. Anomalously fast penetration of the transverse magnetic field has been observed as in the "Porcupine" experiments [J. Geophys. Res. 91, 10,183 (1987)]. The most recent experiments are aimed at studying the plasmoid propagation dynamics and losses in the presence of a background, magnetized plasma which is intended to short the induced polarization electric field and stop the beam. Background plasma was generated by TiH[sub 4] plasma guns fired along B[sub t] to produce a plasma density, n[sub p] = 10[sup 12] - 10[sup 14] cm[sup -3]. Preliminary results indicate that the beam propagation losses increase with the background plasma density; compared to vacuum propagation, roughly a 50% reduction in ion current density was noted 70 cm downstream from the anode for n[sub p] ∼ 10[sup 13] cm[sup -3]. Principal diagnostics include magnetically insulated Faraday cups, floating potential probes, calorimeters, microwave interferometer, and thermal-witness paper. [ABSTRACT FROM AUTHOR]

In this paper a study of stimulated Raman scattering (SRS) from relatively planar plasmas irradiated with short-wavelength (0.53 µm) laser light is reported. The Novette Laser Facility [Laser Part. Beams 3, 173 (1985)] produced several kilojoules of light in 1 nsec, which allowed it to irradiate a large spot with enough intensity to produce significant Raman scattering. These experiments measured the fluence, angular distribution, spectrum, and timing of the Raman light, as a function of the average laser intensity. Reductions in the Raman fluence at low laser intensity are attributed to collisional damping. The measured SRS fluence was larger than that predicted from convective amplification of bremsstrahlung noise, as calculated using the average properties of the laser beam and the plasma. Possible contributions to the observed scattering from enhanced noise, Raman scattering within filaments, and the absolute Raman instability at density extrema are discussed. [ABSTRACT FROM AUTHOR]

The high-frequency dielectric tensor for a cold, multispecies, current-carrying plasma is derived in straight-tokamak geometry, including both toroidal and poloidal magnetic fields in the equilibrium. Propagation and resonant absorption of lower hybrid waves in an inhomogeneous plasma column are investigated. The earlier treatment of Grossman and Weitzner [Phys. Fluids 27, 1699 (1984)] of the resonant-layer solutions, power absorption and energy partition, and accessibility of the lower hybrid wave is generalized to include the effects of mode propagation parallel to the magnetic field and of an equilibrium plasma current. In particular, the density gradient coupled to the finite poloidal mode number and parallel wavenumber allows the lower hybrid wave to reach the hybrid layer, unlike the case of an infinite homogeneous plasma. Finally, the eigenvalue problem is solved for a homogeneous plasma column carrying zero current, and surrounded by a vacuum region delimited by a perfectly conducting shell. The spectrum of both axisymmetric and nonaxisymmetric lower hybrid oscillations is obtained for parameters characterizing the tokamak at Saha Institute for Nuclear Physics [in Proceedings of the IVth National Conference on Plasma Science and Technology (Institute for Plasma Research, Bhat, India, 1987), Paper M-25]. [ABSTRACT FROM AUTHOR]

In this paper a kinetic theory of the boundary layer of a weakly ionized plasma in contact with a perfectly absorbing wall is presented. The ion kinetics is governed by charge exchange collisions with neutrals of finite temperature; the collision frequency is constant. Based on the assumption that the Debye length is small compared with all other lengths of the system, a self-consistent two scale (presheath–sheath) analysis is performed. In contrast to Emmert’s analysis [Phys. Fluids 23, 803 (1980)] of the corresponding collision-free system, the sheath edge shows the usual field singularity. It is shown that in the case where the electron and neutral temperatures are of the same order a large fraction of ions enters the sheath with a multiple of the electron thermal energy. [ABSTRACT FROM AUTHOR]

In this paper a one-dimensional, time-dependent model is described for the analysis of railgun plasma armatures. The model assumes that the armature is isothermal, and that the electrical conductivity and degree of ionization in the plasma are uniform and constant in time. The model is applied to the analysis of three problems—armature initiation, armature response to a change in current, and armature response to a change in mass. In each case, the perturbation induces damped oscillations in the armature length and projectile acceleration about the corresponding steady-state values. The period of the oscillations is, for early times, approximately equal to 3leq/a0, where leq is the equilibrium armature length corresponding to the steady-state solution and a0 is the acoustic propagation velocity in the plasma. The exponential decay time for the cases studied ranges from 140 to 200 μsec. Although most calculations are completely numerical, a partly analytic, limiting-case perturbation solution of the governing equations is also carried out. This analysis suggests why the same oscillation period is obtained in all three cases. The impact of transient phenomena on gun performance and diagnostics, as well as plans for additional analyses, are discussed. [ABSTRACT FROM AUTHOR]

The theory of resistive evolution of plasmas is extended to include plasmas with imperfect magnetic surfaces, that is, plasmas having magnetic field lines that wander stochastically. In resistive evolution theory the plasma is assumed to be always in mechanical equilibrium and the evolution occurs by allowing the magnetic flux constraints determining the equilibrium to change, which happens on a resistive time scale. In this paper a formalism is created to describe magnetic field line structure in a general way in order to evaluate the field line integrals that are the magnetic flux constraints. The equations expressing evolution of these flux constraints, along with the plasma mechanical equilibrium equations, are a mathematical model that can be solved to determine the evolution of the plasma. An immediate result of this model is that, for plasmas with stochastic magnetic field lines, the current density has a filamentary structure, giving a self-consistent source of the stochasticity. A simple two-field-line model of the reversed field pinch is discussed. [ABSTRACT FROM AUTHOR]

In this paper a formula is derived for the ponderomotive force of electromagnetic fields in collisionless and inhomogeneous plasma when the temperature varies slowly in space and time. This result, compared to the current formula for the isothermal case, has an additional term that involves the temperature gradient. The new result is valid in anisotropic medium and better suited for application to both laboratory and space plasma situations in which the plasma is anisotropic. [ABSTRACT FROM AUTHOR]

Linear waves superimposed on an arbitrary basic state in ideal magnetohydrodynamics (MHD) are studied by an asymptotic expansion valid for short wavelengths. It has not been necessary to introduce any assumption beyond the usual regularity assumptions on the arbitrarily given solution which represents the basic state in this paper; it may even be time dependent. The theory also allows for a gravitational potential; it may therefore be applied both in astrophysics and in problems related to thermonuclear fusion. The linearized equations for the perturbations of the basic state are found in the form of a symmetric hyperbolic system. This symmetric hyperbolic system is shown to possess characteristics of nonuniform multiplicity, which implies that waves of different types may interact. In particular, it is shown that mass, Alfvén, and slow magnetoacoustic waves will persistently interact in the exceptional case where the local wavenumber vector is perpendicular to the magnetic field. The equations describing this interaction are found in the form of a weakly coupled hyperbolic system. This weakly coupled hyperbolic system is studied in a number of special cases and detailed analytic results are obtained for some such cases. The results show that the interaction of the waves may be one of the major causes of instability of the basic state. It seems beyond doubt that the interacting waves contain the physically relevant parts of the waves, which often are referred to as ballooning modes, including Suydam and Mercier modes. [ABSTRACT FROM AUTHOR]

By following the moment approach of neoclassical transport theory and introducing a vector field D determined by the magnetic field, flux-friction relations in arbitrary closed-end plasmas are derived. Unlike the conventional ones, which are based on the flux coordinates, the new formulas can be used with any coordinate system. They are therefore more convenient for systems with complicated magnetic axes, such as DRAKON’s [in Controlled Fusion and Plasma Physics, 1981, Proceedings of the 10th European Conference, Moscow (European Physical Society, Budapest, 1981), Vol. 1, paper E-8; in Plasma Physics and Controlled Nuclear Fusion Research, 1982, Proceedings of the 9th International Conference, Baltimore (IAEA, Vienna, 1983), Vol. 3, p. 159], for which coordinates that follow the magnetic axes are more natural than the flux coordinates. As a simple application, the Pfirsch–Schlüter fluxes are obtained for arbitrary closed-end plasmas. In particular, the Pfirsch–Schlüter fluxes of nonaxisymmetric toroidal systems and DRAKON’s are calculated, showing that the Pfirsch–Schlüter fluxes of DRAKON’s are in general smaller than those of toroidal systems. The ambipolar potential and the parallel flows in the Pfirsch–Schlüter regime are also determined for arbitrary closed-end plasmas. The fluxes associated with the parallel flows are generally negligible in this regime. [ABSTRACT FROM AUTHOR]

A one-dimensional electrostatic particle simulation code has been used to study a plasma streaming across a uniform magnetic field in vacuum. It is found that the plasma may be convected across the magnetic field even if the density is less than the critical density nc necessary to maintain steady propagation. For all densities studied, polarization charge layers are formed, but they do not become steady for plasmas with n/nc<. For plasma densities at n

The anomalous Doppler instability is investigated for two-dimensional velocity distributions f(v||,v⊥) appropriate for lower-hybrid current drive. In this case, in contrast to the runaway electron problem, this mode becomes unstable at high density when the ratio ω2pe/ ω2ce is sufficiently large. Increasing the maximum velocity v2 of the rf (radio-frequency) plateau, v1≤v|| ≤v2, is also a destabilizing influence. In this paper expressions are given for the growth rate of the electrostatic waves obeying the dispersion relation ω=ωpe (1+ω2pe/ ω2ce)-1/2 k||/k, employing both analytic expressions for f(v||,v⊥) and numerical solutions for f from the two-dimensional Fokker–Planck equation. The analytical and numerical results are in close agreement. [ABSTRACT FROM AUTHOR]

In this paper the nonlinear problem of the free boundary equilibrium of a plasma inside a conducting circular shell has been solved analytically in the high beta limit. The unknown function describing the plasma shape has been expanded in a Volterra functional series, the functional analogous to the Taylor series. The hierarchy of the linear integral equations obtained from the expansion is, at least in principle, analytically solvable, so that the solution of each equation can be given in a closed form. The analytical computations have been carried out up to the fourth order and the results compared with numerical computations. [ABSTRACT FROM AUTHOR]

In this paper an investigation of the parametric process is presented in which a high-power whistler wave decays into another whistler wave and a low-frequency kinetic Alfvén wave (mixed mode), viz., the stimulated Brillouin scattering of a whistler. The dominant coupling in the equation for the scattered whistler arises from the electron motion along the static magnetic field in the low-frequency wave and the partially electrostatic nature of the kinetic Alfvén wave. On the other hand, interaction of two whistler waves leads to a component of the ponderomotive force along the static magnetic field. This component is responsible for the electrostatic part of the kinetic Alfvén wave. Explicit expressions for the growth rate and threshold power are given. At a pump power of ∼ 1 kW, the growth time of this parametric process comes out to be ∼ 5 μsec for the parameters of the mirror device. For the magnetospheric parameters, the convective threshold electric field is ∼0.3 mV/m. [ABSTRACT FROM AUTHOR]

This paper examines the linear theory of electrostatic waves and instabilities in an unmagnetized, homogeneous Vlasov plasma. The first configuration considered is that of a stable plasma with three Maxwellian components: electrons, positive ions, and negative ions. The dispersion properties of the lightly damped ion modes are studied as a function of relative electron density and relative component temperatures. The second configuration considered is that of a tenuous electron-ion beam with drift speed rob streaming through a negative/positive ion plasma. If the beam is very tenuous, an electron beam instability satisfying ω[sub r] ... kv[sub ob], is excited; if the beam is more dense, the instability becomes Buneman-like with parabolic dispersion. The thresholds and maximum growth rates of these instabilities are described as functions of the beam density and drift speed. [ABSTRACT FROM AUTHOR]

In this paper a hybrid particle–fluid simulation code is used to examine the large-scale (λ∼c/ωpi) low-frequency (ω∼ωci) formation and evolution of a collisonless shock in two dimensions where the shock is caused by a plasma slug of finite thickness traveling perpendicular to the ambient magnetic field in the presence of a uniform background plasma. During the evolution of the shock structure, background ions are energized in the perpendicular direction and then isotropized. The isotropization process is associated with the presence of large-amplitude, primarily electromagnetic, waves propagating parallel to the ambient magnetic field that are created by the self-consistent plasma interaction. High Mach number shocks are found to be inherently two-dimensional objects. [ABSTRACT FROM AUTHOR]

When an ion beam is propagated through a plasma, the question of charge neutralization is critical to its propagation. This paper considers such a problem where the plasma is magnetized with the magnetic field perpendicular to the beam. The plasma-number density and beamnumber density are assumed comparable. This problem is reduced to a two-dimensional model and solved. It is shown that it should be possible to attain charge neutralization if the beam density is properly varied along itself. [ABSTRACT FROM AUTHOR]

In this paper computer simulation results showing that radiation can compensate for range shortening in ion-beam inertial fusion targets are presented. Simulation results of ablation, compression, ignition, burn, and hydrodynamic stability of a heavy ion-beam-driven, reactor-size, inertial confinement fusion (ICF) target including radiation transport are also reported. In this target design the fuel is protected against radiative preheat by a high-Z, high-ρ lead radiation shield, and the fuel is separated from the radiation shield by a low-Z, low-ρ lithium cushion. This avoids mixing of the lead from the radiation shield into the fuel at the end of the implosion. The target is driven by 10 GeV Bi++ ions, and it yields an output energy of ∼690 MJ for an imput energy of ∼4.56 MJ, so that the overall target gain is ∼152. The peak power in the input pulse is 500 TW. [ABSTRACT FROM AUTHOR]

For a pure electron plasma in a sufficiently strong magnetic field, there is a many-electron adiabatic invariant which constrains the collisional dynamics. For the case of a uniform magnetic field, the adiabatic invariant is the total kinetic energy associated with the electron velocity components that are perpendicular to the magnetic field (i.e., ∑j mv2j⊥ /2). Were the adiabatic invariant an exact constant of the motion, no exchange of energy would be possible between the parallel and the perpendicular degrees of freedom, and the plasma could acquire and maintain two different temperatures, T|| and T⊥. However, an adiabatic invariant is not strictly conserved. In the present case, each collision produces an exponentially small exchange of energy between the parallel and the perpendicular degrees of freedom, and these act cumulatively in such a way that T|| and T⊥ relax to a common value. This paper provides a calculation of the equipartition rate. [ABSTRACT FROM AUTHOR]

General solutions of Maxwell's equations in cylindrical coordinates contain special solutions which satisfy the electromagnetic boundary conditions on toroidal surfaces. It is possible to choose the meridional cross section of these surfaces. The method of finding these special solutions is described in this paper. The results for E[sub φ] may be used for current-driving calculations and E[sub r], E[sub z] may be useful for heating investigation of tokamaks. [ABSTRACT FROM AUTHOR]

This paper considers the nonlinear interaction of a background warm plasma with intense, circularly polarized radiation along an external magnetic field. It is shown that the couplings of the adiabatic particle as well as the hydrodynamic plasma motions with the radiation field can lead to localized wave-envelope packets. The resulting self-consistent equilibria consist of finiteamplitude electron density perturbations which are nonlinearly driven by electromagnetic fields. [ABSTRACT FROM AUTHOR]

In the literature, the emission of radiation at 2ωe , where ωe denotes the electron plasma frequency, is usually explained as having been produced by the nonlinear interaction of two Langmuir waves via a backscattering process. Since the emission is frequently observed in solar radio bursts, the mechanism has attracted considerable theoretical interest. In the present paper a model is proposed based on a synchrotron-maser instability excited by a hollow beam of moderately relativistic electrons in a plasma, in which the plasma frequency is much higher than the gyrofrequency. An important conclusion is that, as a result of this instability, unpolarized electromagnetic waves with frequencies near 2ωe may be amplified. [ABSTRACT FROM AUTHOR]

The importance of error magnetic fields is that, if large enough, they cause the destruction of magnetic surfaces. In this paper error fields in a cylindrical plasma are described by nonlinear tearing mode theory, which deals with plasma equilibria having concentrated currents flowing along closed magnetic field lines. Because of the small spatial scale of the current distribution, resistive diffusion is significant even for small resistivity and, in certain cases, causes instability. An energy principle exists and is discussed. This conceptual framework is used in a study of the stability of zero pressure equilibria toward spontaneous generation of error fields, relevant for the reversed field pinch program. Cylindrical Ohmic states are shown to be extremely unstable. Relaxed states (having flattened current profiles) have much better stability. Both completely relaxed states of the Taylor type and partially relaxed Robinson-type states are studied. A new class of metal-liner stabilized profiles is found, which offers one explanation for the apparent stability observed in experiments with distant conducting shells. The possibility that relaxed states have weakly stochastic magnetic field lines is discussed. [ABSTRACT FROM AUTHOR]