MACH CONE STRUCTURE GENERATION BY THE INTERACTION OF A SHORT MICROWAVE PULSE WITH A PLASMA

When a non-uniform unmagnetized plasma is irradiated by a short microw ave pulse with length of the order of an ion-wave period, the travelli ng wavepacket of the electron plasma wave, and nonlinear large-amplitu de waves (delta n/n(0) approximate to 40%) in an ion-wave regime have been observed. The observed large-amplitude waves typically have two f requencies. The higher-frequency wave is an ion wakefield excited by t he travelling wavepacket of the electron plasma wave, while the lower- frequency mode, also called a density cavity streamer, can be interpre ted as a pseudowave induced by the supersonic ion bunch with a typical energy of 25 eV produced at the resonance layer. The experimental res ults are in reasonable agreement with a theoretical model based on the Mach cone structure.