Collisional effects in the region of the electron cyclotron frequency on electromagnetic wave propagation in plasmas

Abstract

Electromagnetic wave propagation in plasmas in the region of the electron cyclotron frequency has been investigated at a frequency of 9.2 Gc in a helium afterglow plasma. The behaviour of the wave is characterized by small phase changes and high attenuation rates for the right-hand circularly polarized wave while there is no significant variation in the left-hand wave as the frequency passes through the electron cyclotron frequency. Measurements show a reversal in phase of the wave passing through the plasma as the electron density is increased. This phenomena occurs only for the right-hand circularly polarized wave at frequencies very near but just above the electron cyclotron frequency. Collisional effects based on cold-plasma theory can account for this behaviour which may be a very sensitive way of measuring certain plasma parameters. At frequencies just below the electron cyclotron frequency extremely small electron densities (as low as 0.002 of the critical density) affect the right -hand wave and can be detected. The attenuation of e-m waves in the region about the electron cyclotron frequency agrees well with cold-plasma theory for low electron densities.