Microwave Reflection from Small-Diameter Plasma Columns

Abstract

The scattering cross section of electromagnetic waves incident normally on a small‐diameter plasma column exhibits resonances as a function of plasma density when the waves are polarized at right angles to the axis of the column. The electron density at resonance has been measured, using a microwave cavity technique, in pulsed helium arc discharges, as the frequency of the incident microwaves was varied from 2 to 4 kMc/sec. At resonance, the squared ratio of plasma frequency to incident frequency is found to be independent of frequency and neutral gas pressure, but somewhat dependent on pulse duration. Results are in qualitative agreement with recent analyses of the interaction between electromagnetic fields and thermal plasmas with finite dielectric boundaries.