摘要:

A model which treats the formation of wave sidebands on a propagating electron plasma wave in the case where the plasma density is modulated by a low‐frequency perturbation is developed. A new mechanism for production of an asymmetric distribution of sidebands appears, and circumstances under which the original wave may reconstitute itself are described. An experimental study of electrostatic plasma waves in a weakly ionized plasma, where the density is modulated either by external means or by the presence of an unstable drift wave, is in agreement with the model.

ISSN:0031-9171    

DOI:10.1063/1.863918

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An analytic investigation is made of the conductive heat transport properties of a cold plasma blanket, where the heat conductivity has been increased by turbulence due to a current‐convective instability.

ISSN:0031-9171    

DOI:10.1063/1.863919

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

In long pulse, high‐energy experiments (4000 J, 2 nsec, 5×1014W/cm2, 1.064 &mgr;m) at the Shiva laser facility, several percent of the laser light has been observed to be Raman scattered. The spectrum of the Raman‐scattered light was measured from 1.48 to 2.17 &mgr;m. The Raman scattering occurred principally at electron densities much lower than the quarter‐critical electron density. The high‐energy electrons expected in Raman scattering were observed indirectly in these experiments via their bremsstrahlung radiation. Additional experiments show that the Raman instability has a much lower intensity threshold for longer laser pusle length and larger laser spot size. Raman light measurements for 5320 A˚ irradiated disk target experiments are also reported. The light near 2&lgr;0or 1.064 &mgr;m had both a red‐ and blue‐shifted component. At high intensities, Raman scattering also occurred in the very underdense plasma.

ISSN:0031-9171    

DOI:10.1063/1.863920

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A stability analysis is performed for the first nine transverse modes (azimuthal mode number plus radial mode number ⩽3) of a self‐pinched relativistic electron beam propagating in a collisional plasma. Only frequencies &ohgr; in the range &ohgr;&tgr;d≪1 are considered, where &tgr;dis the dipole magnetic decay length. For such modes, the presence of plasma return current is the only destabilizing mechanism. Paraxial flow, space charge neutrality, and a flat radial profile of beam density are also assumed. Within these limitations, an exact analysis of the linearized Vlasov stability problem is carried out in closed form. For each mode, the instability threshold, growth rate, and conditions for oscillatory versus pure growth are determined. For beams with a moderate return current fraction, the hose, sausage, and axial hollowing modes appear to be particularly dangerous.

ISSN:0031-9171    

DOI:10.1063/1.863921

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Recent intense beam experiments in microwave radiation are considered within the context of strong turbulence theory of the beam‐plasma instability. A weak turbulence model for radiation at the plasma fundamental gives qualitatively correct power levels and suggests that the radiation itself is an important dynamical entity in the beam‐plasma instability. Radiation in the region &ohgr;∼2&ohgr;pis weak, in agreement with experiment. Plasma inhomogeneities in the experiment of size approximately 0.3 cm can explain the low‐frequency emission power level, and its dependence on the plasma density and external magnetic field. Understanding these processes may lead to use of radiation as a versatile diagnostic measurement of beam‐plasma systems.

ISSN:0031-9171    

DOI:10.1063/1.863922

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A new model of beam dynamics is presented for treating the resistive hose instability in intense, self‐pinched electron or ion beams. The beam is modeled as a superposition of rigid, independently moving components with different radii. This multicomponent model exhibits the localized resonances and other analytic properties of a Vlasov treatment. The new model is used to calculate the eigenfunctions and the dispersion relation for hose instability of an axially uniform beam propagating in a medium of specified conductivity profile with any specified return current. Wave growth is found to be significantly increased by return current or by a narrow conductivity profile. The results are compared to those of earlier models.

ISSN:0031-9171    

DOI:10.1063/1.863923

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Magnetically insulated gaps have proved useful for the production of high current density ion beams. Although ion flow well beyond conventional space charge limits has been observed, previous theoretical treatments have not predicted such flow enhancement at the magnetic fields typically used. One‐dimensional numerical simulations are presented which demonstrate that trapped electron distributions are accessible that cancel much of the effect of ion space charge. This allows ion flow more than an order of magnitude higher than the Child limit. Two processes that result in modified electron distributions have been investigated; the use of a distributed initial electron source and electron diffusion across insulating field lines (specific instabilities were not studied). In both cases, high flow enhancement can be obtained with relatively small electron loss current.

ISSN:0031-9171    

DOI:10.1063/1.863897

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Randomness of low‐order models of two‐dimensional invicid dynamics is commented. AIP

ISSN:0031-9171    

DOI:10.1063/1.863924

出版商:AIP    

年代:1982

数据来源: AIP