OBSERVATIONS OF 2-STREAM COLLISIONAL INSTABILITY DUE TO INTERACTION OF MONOENERGETIC RELATIVISTIC ELECTRON-BEAMS WITH GAS

We have studied experimentally the beam-plasma two-stream dissipative collisional instability of relativistic electron beams (REB) injected into plasma produced by interaction of REB with neutral nitrogen. The gas pressure ranged from 0.02 to 8 Torr. REB (tau = 100 mus, E = 300 k eV, I = 3-15 A) were injected into gas through a pulsed foilless valve . An external magnetic field was not used. A description of the experi mental setup and that of applied diagnostics are presented. In some of the experiments the inner walls of a metallic interaction chamber wer e covered with microwave-absorbent material. We present the experiment al dependence of the critical current of two-stream instability on gas pressure and beam penetration length. We have also measured the distr ibution of microwave emission along the beam axis. The influence of pl asma self-radiation on the instability was observed and is attributed to a feedback. A possible mechanism of the feedback is discussed.