| This dissertation explores the relaxation and fluctuations of nonequilibrium plasmas in two and three dimensions. It consists of three topics: an analytic study of the two-dimensional Fokker-Planck transport coefficients relevant to computer simulations, a particle simulation study of the relaxation of a hot electron layer, and a calculation of the electromagnetic fluctuations due to a helical electron beam.;The quasilinear fluctuation integral is calculated for a two-dimensional, unmagnetized plasma, and is expressed in terms of Fokker-Planck coefficients. It is found that in two dimensions, the enhanced fluctuations generated by fast electrons lead to anomalously large transport coefficients. In three dimensions, the effect of fluctuations is masked by the dominant collisions, but higher order terms describe processes similar to those in two dimensions, and these terms can become significant for weakly stable plasmas (A. A. Ware, Phys. Fluids B 5, 2769 (1993)). The differences between two and three dimensions are crucial to the interpretation of two-dimensional computer simulations. Such two-dimensional simulations are used to investigate the relaxation of electrons which have large velocities parallel to the external magnetic field, and which are confined to a narrow, magnetic-field-aligned layer. It is found that the primary relaxation mechanism of these electrons is the emission of lower-hybrid waves which are absorbed by the surrounding colder plasma. The relaxation rate is only weakly dependent on the perpendicular temperature of the electrons within the layer. A secondary mechanism, which becomes important when the magnetic field is weak, is binary collisions with other particles both within the layer and outside the layer.;The electromagnetic fluctuations generated by a modulated, free-streaming, helical electron beam, which can be considered the single-particle equivalent of a narrow layer, are calculated and compared to a recent laboratory experiment (R. L. Stenzel and G. Golubyatnikov, Phys. Fluids B 5, 3789 (1993)). The fluctuations of the magnetic field are found to have strong, spatially-localized (evanescent) resonances at harmonics of the electron-cyclotron frequency, in agreement with the experiment. In addition, the beam radiates electrostatic modes near the hybrid frequencies, and electromagnetic modes near the higher electron-cyclotron harmonics (... |
