Excitation of RF oscillations in a discharge with negative differential conductivity

The excitation of oscillations in a discharge with negative differential co nductivity is studied experimentally. The possibility is demonstrated of am plifying oscillations in the cathode dark space at frequencies close to the electron plasma frequency of the positive-column plasma. The phase velocit ies of waves at these frequencies are determined. When the waves pass from the cathode dark space to the discharge positive column, their phase veloci ties decrease; the closer the frequency is to the electron plasma frequency , the more pronounced the decrease in the phase velocity. As the intensity of oscillations increases, the discharge becomes non-steady-state. This is confirmed by the time evolution of the current-voltage characteristic. The shape of the current-voltage characteristic, its splitting, and the rate at which it varies depend on the input RF power. The decrease in the cathode dark space indicates that the ionization processes in the discharge are str ongly influenced by electron plasma oscillations excited due to the collect ive interaction of the electron beam formed at the cathode with the dischar ge plasma. It is these processes that determine the maximum values of both the frequency of the excited oscillations and the power that can be withdra wn from the discharge. (C) 2001 MAIK "Nauka/Interperiodica".