Experimental Verification of Electron Cyclotron Damping in a Plasma with Collisional Losses

The right-hand circularly polarized microwave (R wave) propagating along a magnetic field in a plasma is described by the hot-plasma theory near the electron cyclotron resonance where the thermal effect of the electron should be taken into account. The left-hand circularly polarized wave (L wave), which has no resonance, is described by the cold-plasma theory. In this paper, the plasma parameters such as the electron densities and the collision frequencies are measured by the reflection coefficient of the L wave at the plasma boundary. The attenuation constant αc of the R wave is then calculated by the cold-plasma theory from the plasma parameters thus obtained; αc is compared with the attenuation constant αh, measured directly by the R wave. The measurements are performed during the decaying period of the plasma produced in a circular waveguide filled with argon at a pressure of 0.1 Torr. The electron temperature Te deduced from αh/αc is compared with Te independently measured by a double probe. The experimental results of αh/αc indicate a reasonable enhancement of the attenuation of the R wave near the electron cyclotron resonance.