On plasma-wave interaction at the frequency above the low hybrid one

The regularities of absorption of electromagnetic waves have been experimentally investigated at the frequencies exceeding the lower hybrid one in a plasma with toroidal geometry of a magnetic field. The experimental facility is a metal toroidal chamber with large and small diameters 43 and 10 cm respectively, placed in a quasi-stationary magnetic field of 3 kOe. The discharge in hydrogen at the pressure p=10-4-10-3 mm Hg is sustained by introducing into the chamber SHF power of 100 W at wavelength of 3 cm satisfying the conditions of the cyclotron and the upper hybrid resonances. The plasma parameters are the following: nsub(e) approximately 1011 cm-3, Tsub(e) approximately 5-10 eV. The HF power under investigation at f=440 MHz and Wsub(max)=2 kW is introduced by pulses of controlled duration by a dipole antenna. It has been revealed that under the hydrogen pressure of 10-3 mm Hg absorption takes place in the exterior part of the discharge, that is apparently connected with the collisional absorption of the surface mode. At lower pressures a decrease of the plasma density is observed under the effect of the HF power. The mechanisms which may provide explanation to the phenomena observed have been discussed