Microwave Absorption in a Plasma Resonator operated with Hydrogen

Abstract

The permeation of microwave pulses (ƒ = 9.4 GHz,pulse duration: 0.5-0.7 μs) through a partially ionized hydrogen plasma is investigated. At supercritical electron densities (line-averaged density: ne= 1.2-1.8 x 1018 m-3) a resonant enhancement of the wave amplitude is observed between the plasma column and the metallic end reflector of the waveguide. Local measurements of the electric field strength in the cut-off layer next to the end reflector are correlated with the transient behaviour of the Hβ line intensity, of the electron density, and of the mean electron energy. From these measurements, both the reduced Hβ excitation rate and the reduced ionization rate by electron collisions are obtained as functions of the reduced effective field strength in the range 30 - 65 Vm-1 Pa-1.