Upper hybrid emission from a magnetized gas discharge plasma

Abstract

Measurements are presented of electromagnetic radiation emitted perpendicular to a strong magnetic field in a gas discharge. The discharge plasma is characterized by electron densities in the range 1010-3*1012 cm-3, an electron temperature of approximately 2 eV, and a dilute energetic electron tail extending out to the discharge voltage (<or approximately=200 V). Emission measurements are made in the frequency range 12-18 GHz. It is shown that the emission is predominantly in the extraordinary mode, originates at the upper hybrid layer in the radially inhomogeneous plasma, and is generated by the energetic electron tail. Combined with earlier detailed measurements of the energetic electron properties it is shown that the emitted power varies linearly with the hot electron density in the vicinity of the upper hybrid radius and varies as the 3/2 power of the tail temperature. Absolute power estimates are provided to link the authors measurements to the fundamental emission parameters. There are indications that tunneling of radiation is not playing a role in these experiments, but this conclusion requires a lot of further study.