A one-dimensional numerical hybrid model (Vlasov ions, fluid electrons) which includes all nontrivial field components has been devised and its predictions have been compared with experimental pinch results. The effect of microscopic electron dynamics is included on the average by the specification of (anomalous) resistivity and thermal conductivity coefficients. The model has reproduced the magnetic field profiles observed during the implosion and post implosion phases of several screw pinch experiments. The behavior of the imploding plasma as various physical parameters are changed is discussed. The foot in the front of an experimentally determined density profile of a high density theta pinch is reproduced and shown to be due to a reflected ion beam. For some conditions the formation of a reflected ion beam is found to be dependent upon whether the bias is parallel or antiparallel to the driving field.
When the interplanetary magnetic field is northward, wave‐particle cross‐field transport may contribute to solar wind‐magnetosphere coupling. Such transport is studied here through the use of hybrid computer simulations (particle ions, fluid electrons with nonzero mass) carried out in the x‐y plane of a plasma with a density gradient in the x direction, no average iow speed, and a magnetic field B = B(x)ž. At early times, the lower hybrid drift instability grows on the gradient. However, at times long compared to an ion gyroperiod, the fluctuations coalesce to longer wavelengths in the y‐direction and nondiffusive density x‐profiles emerge which exhibit “plateaus” and “inclusions” qualitatively similar to those observed by ISEE near the magnetopause. These results call into question critical assumptions of quasilinear theories of cross‐field transport by this instability.
The expansion of a plasma slab across an initially uniform magnetic field is simulated by the use of a two-dimensional electromagnetic hybrid (particle ions, fluid electrons of nonzero mass) computer code. The expanding plasma develops magnetic-field-aligned structure on time scales faster than an ion gyroperiod. Through the full duration of the mi/me =100 simulation, the structure wavelength is well predicted by the wavelength at maximum growth rate from the linear Vlasov theory of the lower hybrid drift instability modified by deceleration. At mi/me =400, the late time structure wavelength is about 1.5 times the early time value. At mi/me =1836, the structure wavelength at early times is close to that corresponding to the maximum growth rate of linear theory, while at later times the structure wavelength becomes about twice as long as its early time value. These three results suggest that the ratio of the late time wavelength to the early time value gradually increases with mi/me. Extrapolation of this scaling to larger mi/me values is consistent with structure wavelengths observed in an expanding aluminum plasma experiment [J. Appl. Phys. J. 20, 157 (1981)], as well as the observed wavelength in the expanding barium plasma of the AMPTE magnetotail experiment [J. Geophys. Res. 92, 5777 (1987)].
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