Suppression of ion-ion instabilities by an external field

The suppression of the ion-ion instability excited in an ion beam-plasma system by an external field is experimentally investigated. We examine the behavior of the instability as a function of both amplitude and frequency of the external field and compare with the theoretical prediction. It is found that there exists a threshold and this threshold amplitude depends on the frequency. We also discuss the effect of the electron temperature and the ion distribution function with the external field on the suppression of the instability. (author)