Simulations of electron/electron instabilities: Electromagnetic fluctuations

Electron/electron instabilities arise in collisionless plasmas when the ele ctron velocity distribution consists of two distinct components with a suff iciently large relative drift speed between them. If the less dense beam co mponent is not too tenuous and sufficiently fast, the electron/electron bea m instability is excited over a relatively broad range of frequencies. This instability is often studied in the electrostatic limit, which is appropri ate at omega(e)/\Omega(e)\ much greater than 1, where omega(e) is the elect ron plasma frequency and Omega(e) is the electron cyclotron frequency, but is not necessarily valid at omega(e)/\Omega(e)\ similar to 1. Here linear V lasov dispersion theory has been used and fully electromagnetic particle-in -cell simulations have been run in a spatially homogeneous, magnetized plas ma model at beta(e) much less than 1 and 0.5 less than or equal to omega(e) /\Omega(e)\ less than or equal to 4.0. Theory and simulations (run to times of order 100 omega(e)(-1)) of the electron/electron beam instability show the growth of appreciable magnetic fluctuations at omega(e)/\Omega(e)\ < 2; these waves bear right-hand elliptical magnetic polarization. The simulati ons reproduce the well-known slowing and heating of the beam; at omega(e)/\ Omega(e)\ < 1 this heating is predominantly parallel to the background magn etic field, but as omega(e)/\Omega(e)\ becomes greater than unity the perpe ndicular heating of the beam increases. The simulations also demonstrate th at, for omega(e)/\Omega(e)\ similar to 1, electromagnetic fluctuations impa rt to the more dense electron core component significant heating perpendicu lar to the background magnetic field. (C) 2000 American Institute of Physic s. [S1070-664X(00)00202-0].