Microwave emission from plasmas produced by magnetically confined-electron beams

Microwave emission, in the x-band frequency range (8.2-12.4 GHz), from a thin, large, rectangular sheet plasma has been measured. The plasma electron density was such that the plasma frequency was within or just above this frequency range. The plasma was immersed in an external magnetic field from a set of Helmholz coils. The magnetic field was oriented parallel to the electric field between the anode ground plane and a cylindrical, hollow cathode. The spectrum of the emitted noise was measured for both ordinary mode (P to B) and extraordinary mode (/spl perp/ to B) polarization in the x-band. The emission was strongest at high harmonics of the electron cyclotron frequency. Mechanisms that might produce this noise and its potential use as a diagnostic tool are discussed.