RF WAVES IN NONEQUILIBRIUM-PLASMA ACCELERATOR.

The wave intensity has been measured over the frequency range 500-3000 MHz in an electrodynamic discharge intended for accelerating plasma, both in the cross section and along the length of the plasma stream. The experiments show that the energy density of the rf waves exceeds the thermal level by 4-5 orders of magnitude. The estimated phase velocities of the excited waves correspond to the velocities of the fast electrons in the cathode region of the discharge. A mechanism of an rf instability involving fast electrons in the discharge is discussed; this mechanism agrees qualitatively with the experimental results.