Conductivity and ion density of a plasma channel induced by a mildly relativistic electron beam from a gas-filled diode

Conductivity and ion density of a plasma channel induced by a mildly relativistic electron beam (300 kV, similar to 2 kA, 10-50 ns) have been experimentally investigated under various gas pressures. Pressures of filling gas (air) in this experiment ranged from 10 mTorr to 100 mTTorr. The net currents of the beam-induced plasma channel were measured by four Rogowski coils located along the propagating region, while the electron beam currents were measured by a Faraday cup. The inductive plasma currents observed at the above pressure regimes have been characterized by magnetic decay time. Plasma-channel conductivity and ion density induced by the beam are measured along the propagating axial positions under various gas pressures. The numerical result of the ion density is also obtained at the charge neutralization time when the ion density is just the same as the electron beam density, and the digitizing experimental data of the beam current I-b(T) and voltage V-d(t) have been used. As expected, in both numerical and experimental results the ion density increases to a peak value of about 3.0 x 10(11) cm(-3) and 3.3 x 10(11) cm(-3), respectively, at 50 mTorr and slowly decreases for both cases as the gas pressure increases from 50 mTorr to 100 mTorr. Moreover, the results of ion density predicted by the theoretical model developed here are also found to be in remarkably good agreement with experimental and numerical results at pressure regimes from 10 mTorr to 100 mTTorr. (C) 1998 American Institute of Physics.