摘要:

The effect of the anisotropic pressure of a hot‐electron plasma on ballooning‐interchange and compressional‐Alfve´n modes is investigated. General eigenmode equations for these modes are derived in the eikonal and high phase velocity limits with finite gyroradius effects retained. A local dispersion relation is obtained in the flute limit for an isotropic Maxwellian background plasma with a bi‐Maxwellian hot‐electron population. Stability is investigated both analytically and numerically for this high phase velocity and/or high precessional frequency model.

ISSN:0031-9171    

DOI:10.1063/1.864032

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Several recent studies of ELMO Bumpy Torus (EBT) stability show that conflicting results can emerge when different distribution functions for the hot‐electron component are used. In this paper the role of the distribution function is established by examining the stability of various modes with the aid of two models. In the ‘‘slab’’ model where the magnetic field curvature is simulated by a gravitational force it is shown that the stability of the compressional Alfve´n wave is insensitive to the distribution function while the interacting interchange mode is sensitive. In the ‘‘local’’ approximation in which the curvature effects enter in a natural way it is seen that the interchange modes are insensitive so long as the anisotropy of the hot electrons is large, while other modes reflect dependence on the distribution function. Finally it is demonstrated that in the ‘‘deep well’ case the results for both modes are independent of the model and of the distribution function.

ISSN:0031-9171    

DOI:10.1063/1.864033

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A systematic survey is made of free‐boundary, large‐orbit ion ring equilibria for the case where the distribution function is narrowly peaked at a given value of the single‐particle energy (H) and the canonical angular momentum (P&thgr;). Suitably normalized, such equilibria depend on only two free parameters. The survey covers essentially all of the parameter space where field‐reversed equilibria exist. Results are presented as contour plots in the (P¯,H¯) plane of various physical quantities. The results may be reinterpreted so as to apply to relativistic electron rings on which there are experimental observations.

ISSN:0031-9171    

DOI:10.1063/1.864034

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The dispersion relation for a relativistic electron beam in a plasma, in the absence of an external magnetic field, is derived. It is shown that the plasma oscillations excited by the beam are linearly coupled to the electromagnetic TM mode.

ISSN:0031-9171    

DOI:10.1063/1.864035

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The filamentation instability of an intense electron beam propagating through a collisional plasma is examined. The effects of the transverse energy and of the pinch force (self‐pinch as well as an applied magnetic field) are included. It is assumed that the characteristic perpendicular wavelength of the perturbations is much less than the beam radius. The stability analysis is carried out for the beam electron distribution in which all beam electrons have the same energy in rotating frames and a Lorentzian distribution in axial canonical momentum. From the stability analysis, it is found that the transverse energy and the pinch force strongly stabilize the instability. Moreover, the axial momentum spread plays a major stabilizing role.

ISSN:0031-9171    

DOI:10.1063/1.864036

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The two‐plasmon instability in warm inhomogeneous plasma for a normally incident pump is considered. The complex eigenfrequencies of the absolute instability are obtained by reducing the linearized fluid equations to a Schro¨dinger equation in wavenumber space. These eigenvalues are obtained in several ways. One is by combining a perturbation expansion in powers of the reciprocal scale length with WKB theory. The resulting algebraic equations are solved by three analytical approximations and by direct numerical solution. A second way is by analysis of the Schro¨dinger equation using an interactive WKB computer code. A third way is by the use of a shooting code. These methods are all used and compared for threshold curves and growth rates above threshold. Some eigenfunction forms are also obtained. The threshold is near (v0/ve)2k0 L=3, and varies weakly with &bgr;&bartil;v4e/v20c2, rising from near 2 to about 4 over six decades of variation of &bgr;. The corresponding critical value of (ky/k0)2is near 0.2/&bgr; over this range. Above threshold, there is a smooth variation of the growth rate with (ky/k0)2, peaking at some intermediate value. The perturbation method is in good agreement there with more exact calculations. Experimental implications of these results are discussed.

ISSN:0031-9171    

DOI:10.1063/1.864037

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Vlasov simulations of stimulated Raman scattering (SRS) are presented, both for low laser irradiance when the plasma waves remain linear and for high laser irradiance when particle trapping occurs. At low irradiance the energy in scattered radiation and in plasma kinetic energy approach values given by the Manley–Rowe relations. At high irradiance the effective damping rate of the plasma waves is greatly increased over the Landau damping rate while electron trapping is occurring. A relativistic model for electron trapping has been developed. It yields expressions for the number and maximum energy of the trapped electrons and the threshold for their production. Forward SRS dominates at high plasma temperatures and produces faster trapped electrons compared to backward SRS.

ISSN:0031-9171    

DOI:10.1063/1.864038

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The reduction in Rayleigh–Taylor instability growth rate because of density inhomogeneity in an incompressible ablatively accelerated plasma is calculated over a very wide range of physical parameters. In the low‐wavenumber regime, the effect of the density gradient is to give a significant (about a factor of 2) reduction in growth rate as seen in fluid simulations.

ISSN:0031-9171    

DOI:10.1063/1.864039

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The analysis of Shkarofsky on hot‐electron transport is extended to include a variable degree of collisionality and gradient scale length. An extended version of the method of Shvartsetal. [Phys. Rev. Lett.47, 247 (1981)] is used whereby the perturbed electron velocity distribution is limited in magnitude to the unperturbed part when the former becomes larger than the latter. A Maxwellian distribution is adopted for the hot electrons. For the cold electrons, either a Maxwellian, [exp(−v2/v2c)], or an exp(−v5/v5c) variation is used. The heat flow has coefficients proportional to gradients in cold‐ and hot‐electron density, to gradients in cold‐ and hot‐electron temperature, and the free‐streaming contribution. These contributions are summed for two sample sets of scale lengths. One set of results shows that in an intermediate range of collisionality, heat inhibition occurs, in that the flux limiter is decreasing substantially below the free‐streaming value, rather than increasing monotonically towards the collisionless regime.

ISSN:0031-9171    

DOI:10.1063/1.864040

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Numerical simulations are performed on the interaction of double‐step laser pulses and solid planar targets. These double‐step laser pulses are routinely generated in the laboratory. The simulations show that compressions of 10 to 16 can be obtained in aluminum when the shock waves, generated by the first and second laser pulse steps, collide within the target. Optimization of the laser pulse shape results in the compression, to this magnitude, of approximately 10 &mgr;m of Al target for durations of about 0.5 nsec. Utilization of shaped laser pulses in conjunction with impedance mismatched targets that cause shock reflection or with opposing laser beams that cause oppositely directed shock collisions can result in compressions of 30 to 40.

ISSN:0031-9171    

DOI:10.1063/1.864041

出版商:AIP    

年代:1983

数据来源: AIP