Cyclotron Harmonic Resonances in an Electrodeless Discharge

Abstract

Electron-cyclotron harmonic resonances in rf-excited, electrodeless, helium discharges have been investigated experimentally. The discharge simulates a plasma slab of relatively uniform electron density in a uniform magnetic field. Measurements were made at 9.15 GHz of both incoherent emission and coherent fundamental wave propagation, the microwaves propagating in a direction perpendicular to the magnetic field and normal to the slab boundaries. Emission resonances were found for both ordinary and extraordinary wave propagation. Precise measurements of the magnetic field at corresponding peaks for the ordinary and extraordinary waves show that the former occur at magnetic fields about 0.3% lower than that of the latter, independent of harmonic number, electron density and pressure. The ordinary wave resonances occur at the cyclotron harmonic within experimental error (0.1%). Resonances were found in the coherent fundamental transmitted and reflected waves and are due to resonance absorption. Their magnetic field positions always occur on the high magnetic field side of the cyclotron harmonic (by as much as 2.5%).