Effect of an external RF field on the beam-plasma discharge in a magnetic field

The effect of an RF field on a steady-state beam-plasma discharge with a pl ane electrode placed parallel to a sheetlike electron beam is studied exper imentally. The plasma parameters were measured by a single probe, and the e lectron distribution function was determined with the use of an electrostat ic analyzer. The energy and current of the electron beam were E-B = 2.5 keV and J(B) = 0.05-1.5 A, respectively. The working pressure was p = 2 x 10(- 5)-10(-3) torr. The frequency of the external RF field was 13.56 MHz. Both the steady-state regimes in which the RF field had no effect on the plasma parameters and regimes with a pronounced effect of the RF field were observ ed. The experiments show that the regime of the discharge depends strongly on the plasma density and the magnetic field. The parametric instability is studied theoretically in the weak-turbulence approximation. It is shown th at, due to the decay nature of the spectrum of plasma oscillations, the ons et of instability is accompanied by the transfer of the energy of fluctuati ons over the spectrum, from the pump frequency toward its harmonics. (C) 20 00 MAIK "Nauka/Interperiodica".