Whistler Wave Excitation by an Electron Beam in a Laboratory Plasma.*

A. Burke, V. Pivovarov, S.K. Ride, V.D. Shapiro; (UCSD Department of Physics and California Space Institute, La Jolla, CA 92093) and Walter Gekelman; (UCLA Department of Physics, 15-70 Rehab, 1000 Veteran Avenue, Los Angeles, CA 90095; 310- 206-1772)

We propose a scenario for radiation of electromagnetic whistlers in a laboratory plasma for the case of a 1keV electron beam and the plasma parameters of the LAPD device (He, n=4 X 10^12/cm^3, B=500-2500G, plasma length=10m, diameter=50cm). We show that the interaction can result in the instability of electrostatic waves driven by Cherenkov resonance between the waves and the beam. A linear stability analysis was carried out for two limiting cases, a wide and a narrow electron beam; the wave excitation is shown to develop at typical distances on the order of 1 meter. Nonlinear evolution of the instability was investigated by a combination of analytical and numerical methods. Electron beam energy is efficiently transformed into the electrostatic mode. The mechanism of electromagnetic mode generation is then dipole radiation from the electron beam, which is strongly bunched as a result of the electrostatic instability. The efficiency of radiation is a strong function of the ratio of the electron beam velocity to electron Alfvén velocity (). A corresponding laboratory experiment is in progress to investigate this mechanism and other mechanisms of whistler excitation, and to guide future electron beam experiments and applications in space. The preliminary results of this experiment will be presented at the July '95 IUGG meeting in Boulder, Colorado.

*Work supported by ONR and the California Space Institute