The process of the plasma discharge due to an electron beam is experimentally investigated. A pulse (∼540 &mgr;s) of an electron beam (0.5–1.5 keV, ≤20 mA) is injected into argon gas (5×10−5–5×10−4Torr) in a magnetic field (50–300 G). The discharge based on a gas break down occurs cascade‐likely in time. The gas beak down with some steps is explained by the two stream instability of an electron beam‐plasma system, from the observation of the temporal evolution of the frequency spectra (0–3.0 GHz) of the instability and the measurement of the temporal plasma density and temperature. ©1996 American Institute of Physics.