Experiments on plasma interactions with powerful R.F. discharges

Abstract

Linear discharges in a steady axial magnetic field are produced in hydrogen plasmas by means of unconventional line generators. Non-decaying current pulses ranging from 1 to 50 kA at a frequency of 3 MHz. The penetration of the azimuthal oscillating field is observed, and the influence of limiters is investigated. A critical current is found, and this result is compared with the previous theory. Anomalous skin depth results from analysis of the complex wave vector, which shows energy exchanges with the plasma, in addition to the normal Joule heating. Decreasing conductivity at low densities indicates possible turbulent behaviour. An interesting feature of the discharges in the highest power range is the excitation of magnetoacoustic compressional waves at the second harmonic of the axial current with typical resonance effect. This quadratic interaction is explained with a simple model considering the pressure gradient at the plasma boundary.