Electron Heating by Oblique Injection of Ordinary Mode into Overdense Plasma

Abstract

An electromagnetic wave of ordinary mode (O-mode) at a frequency near the second electron cyclotron harmonic is obliquely incident on an overdense (ω_p>ω) large-volume plasma. Two-dimensional measurements of wave propagations suggest that this is a result of cascade mode conversion, the first conversion being from the O-mode to the X-mode at the critical density (ω=ω_p), and the second conversion being from the X-mode to the Bernstein mode at the upper hybrid resonance. For high-power incidence, electron heating takes place locally around the upper hybrid layer where the intense Bernstein-mode signals are detected. The heating is observed only for ω_p>ω, supporting the theory of cascade mode conversion.