摘要:

Numerical techniques have been used to study the intensity pattern of a high‐frequency electromagnetic wave near the critical density for conditions typical of laser fusion plasmas. The investigation considered nonlinear density profiles, collisional absorption, and finite bandwidth effects. Using the results of these calculations as a guide, elementary analytic models were developed to describe the behavior of the intensity pattern. Results of the numerical and analytic methods indicate the following: (i) For a nonlinear but monotonic density profile, the swelling factor can be related to the Airy function pattern by a simple scale factor; (ii) for collisional absorption below 50%, a linear relation holds between the intensity and the absorption; (iii) for laser bandwidth &Dgr;&ohgr;/&ohgr;0<15%, the intensity is reduced in a manner similar to that associated with collisional absorption. Within the ranges given, accuracy of the analytic models is within 10% of the numerical results. These semiquantitative models provide simple, useful tools for estimating the intensity patterns near the critical density.

ISSN:0031-9171    

DOI:10.1063/1.862011

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A general theory of finite amplitude envelope Langmuir solitons is presented. Comparison with recent beam‐plasma experiments suggests identification of the observed localized structures with these solitons.

ISSN:0031-9171    

DOI:10.1063/1.861998

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Based on scaled version of the equations of ideal magnetohydrodynamics it is shown how to construct a steady flow with a shock in a mirror. The upstream state is supersonic, but essentially arbitrary. The shock must be Mach number one on axis although the Mach number may rise rapidly off axis. The shock is extremely effective in converting the directed streaming energy of flow into randomized thermal energy. Such flow patterns may be of interest in very long theta pinches where quasi‐steady flow may obtain or in plasma gun devices where the gun injects a plasma along a magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.861999

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A functional analytic approach to the linearized collisionless Vlasov equation is presented utilizing a resolvent integration technique on the resolvent of the transport operator evaluated at a particular point. Formulae for the eigenfunction expansion are found for cases in which the plasma disperion function &Lgr; has first and second order zeroes. Special care is taken in the study of real zeroes of &Lgr; culminating in new results for this case. For a simple zero of &Lgr; with nonvanishing imaginary part the van Kampen–Case discrete modes are reproduced. The results are used to obtain the solution to the initial value problem.

ISSN:0031-9171    

DOI:10.1063/1.862000

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The parametric decay of an intense, coherent electromagnetic wave into subluminous electrostatic waves and scattered electromagnetic waves in a homogeneous plasma is studied, with particular attention to the effects of relativistic electron temperature. A mode coupling formalism is developed, from which growth rates for stimulated Raman and Brillouin backscattering in one dimension, and for modulational Raman forward scattering, are derived.

ISSN:0031-9171    

DOI:10.1063/1.862012

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The behavior of the lower hybrid drift instability is investigated in the low drift velocity regime by including the effects of the magnetic field on the ions. It is found that the mode is transformed from the nonresonant lower hybrid drift instability to the resonant ion cyclotron drift instability as the drift velocityVddecreases and is finally stabilized whenVd/Vti∼ (me/mi)1/2.

ISSN:0031-9171    

DOI:10.1063/1.862013

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The nonlinear response of a plasma subject to an intense, spatially localized rf field has been investigated experimentally. In a uniform quiescent magnetoplasma of densityne≳109cm−3, temperaturekTe≃5kTi≃1 eV, and magnetic fieldB0∼100 G, a resonance cone (&ohgr;/&ohgr;c≃0.1; where &ohgr;cis the electron cyclotron frequency) is established which converges away from a circular exciter to reach a maximum amplitude at the remote cone apex. When an rf burst of intensity &egr;0Erf2/nekTe≲O(1) is applied, a strong density depression (&dgr;ne/ne≃40%) is formed in the focal region on a time scale (∼1 &mgr;sec) short compared with a collision time. Fast ion bursts [(1/2)mvi2≃35 eV≳100kTi], large amplitude ion acoustic waves, but negligible electron temperature increases are observed. Density and resonance cone field interact nonlinearly and in time develop a state of turbulence. Ion heating (&Dgr;Ti/Ti≃100) dominates over electron heating (&Dgr;Te/Te∼2). The direct measurements of the particle distributions with probes and energy analyzers are supplemented by test wave techniques. Small amplitude ion acoustic, electron plasma, and Bernstein waves are propagated through the region of high rf intensity and the perturbed plasma properties are deduced from the test wave behavior. The observed nonlinear collisionless interactions between particles and intense rf field are qualitatively explained by a model involving the ponderomotive force on electrons and acceleration of ions by space charge fields.

ISSN:0031-9171    

DOI:10.1063/1.862014

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The behavior of a beam plasma system has been modeled with a set of nonlinear rate equations. Solutions of these equations show characteristically different multiple equilibria. The experimental behavior implied by this result is shown to be in agreement with experimental observations.

ISSN:0031-9171    

DOI:10.1063/1.862015

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A Vlasov equilibrium model is developed which can describe a broad class of beam‐plasma systems in an applied field,B0z. The model treats arbitrary density profiles and azimuthal self‐magnetic fields as well as a thermal spread in the momentum of the beam. It is assumed that the electron gyroradius is small but not negligible compared with the beam radius, and that the beam is completely charge neutralized but only fractionally current neutralized. The electron orbit equations are solved and are used to simplify the form of the distribution function and the calculation of its velocity moments. The rotation frequency of the beam and the diamagnetic or paramagnetic properties of such warm beam‐plasma systems are also studied.

ISSN:0031-9171    

DOI:10.1063/1.862016

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The transition of the tearing instability from the collisional to the collisionless regime is investigated kinetically using a Fokker–Planck collision operator to represent electron‐ion collisions. As a function of the collisionality of the plasma, the tearing instability falls into three regions, which are referred to as collisionless, semi‐collisional, and collisional. The width &Dgr; of the singular layer around k⋅B0=0 is limited by electron thermal motion along B0in the collisional and semi‐collisional regimes and is typically smaller than &rgr;i, the ion Larmor radius. Previously accepted theories, which are based on the assumption &Dgr;≫&rgr;i, are found to be valid only in the collisional regime. The effects of density and temperature gradients on the instabilities are also studied. The tearing instability is only driven by the temperature gradient in the collisional and semi‐collisional regimes. Numerical calculations indicate that the semi‐collisional tearing instability is particularly relevant to present day high temperature tokamak discharges.

ISSN:0031-9171    

DOI:10.1063/1.862017

出版商:AIP    

年代:1977

数据来源: AIP