OBSERVATION OF TEMPORAL PLASMA-WAVE ECHOES IN AN ION-WAVE REGIME

Temporal echoes in an ion-wave regime are observed in microwave-plasma interaction experiments. When two short microwave pulses (tau less-th an-or-equal-to 1/f(pi), where tau is the pulse width and f(pi) is ion plamsa frequency) are applied successively, one after another, in the nonuniform magnetic-field-free plasma, waves in ion plasma frequency r ange and plasma density cavity (caviton) are excited at the critical l ayer of the resonance absorption. After the waves damp out by Landau d amping, temporal echoes appear in both the critical layer and underden se region. In the overdense region, however, no echo appears in the pr esent experiments. The results are explained by the theoretical predic tion given by Gould, O'Neil, and Malmberg