Parametric decay instability control by non-monochromatic pumps

Abstract

The wide variety of physical effects accompanying the parametric decay instability driven by the frequency modulated pump is studied experimentally and theoretically. It is shown that pump frequency modulation does not influence the instability when the modulation frequency is much faster than the decay wave transient time in the interaction region. However in the case of slower modulation it is demonstrated that the resonant enhancement and suppression may take place depending on the modulation rate. A scheme of active parametric decay instability feed-back control is proposed. A possibility of deep instability suppression by launching of an additional (small power) pump wave possessing a frequency shifted by the value equal to the frequency separation of ion acoustic eigen modes is demonstrated as well. The recovery of microwave power absorption at the parametric decay instability suppression is shown using measurements of the plasma luminosity and fluxes of accelerated electrons.