Microwave Absorption in a Plasma Resonator operated with Hydrogen

The permeation of microwave pulses ( / = 9 . 4 G H z . pulse duration: 0 .5-0 .7 ps) through a partially ionized hydrogen plasma is investigated. At supercritical electron densities (line-averaged density: n t = 1.2-1.8 x 10 m~) 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 H^ line intensity, of the electron density, and of the mean electron energy. From these measurements, both the reduced H^ excitation rate and the reduced ionization rate by electron collisions are obtained as functions of the reduced effective field strength in the range 3 0 6 5 Vm 1 Pa 1 .