Pulsewidth and rising time of relativistic electron beam in gas-filled diode

The pulsewidth and rising time of a mildly relativistic electron beam (300 kV, 1-3 kA) passing through a gas-filled diode region are investigated experimentally under various gas pressures P. The pulsewidth and rising time of a relativistic electron beam (REB) were controlled by adjusting the gas pressures P of the diode region. The pulsewidth and rising time of the relativistic electron beam are experimentally found to scale as P-0.807+/-0.054 and P-0.770+/-0.056, respectively. The REB pulsewidth and rising time are shown to have the same scaling law, within the experimental error range as a function of pressure. In particular, the empirical scaling law of the REB pulsewidth is in remarkably good agreement with the numerical scaling law P-0.809+/-0.069 of the full-space charge neutralization time t(s), at which the ion density n(i) is just equal to the electron beam density n(b) at the diode region under a given gas pressure P. It also is found that ion density n(i)(s) at the full space-charge neutralization time t(s) has quite a similar profile in terms of pressure P to that of the REB peak current detected by a Faraday cup.