Modification of low-frequency instabilities with high-frequency pump waves

The influence of a large amplitude electric field oscillating near the upper hybrid frequency two (omega(0) similar to omega(uh)) on low-frequency (LF) electrostatic flute type instabilities, where the pump frequency (omega(0)/2 pi) is 2.45 GHz, is investigated in a pure toroidal plasma. Argon plasma is produced using a hot cathode discharge and microwaves are launched in the ordinary mode. Measurements reveal that the amplitude of the dominant fluctuating component in the cross power spectrum of density and floating potential fluctuations is suppressed for omega(0) < omega(uh), whereas the amplitude of the fluctuations increases in the case omega(0) > omega(uh).