Current clamping in a long pulse electron beam-gas interaction

Current clamping (constant current behavior) was observed in measurements of the current drawn by a metal plate acting as a beam collector for long-pulse (300 ns) electron beam, propagating a short distance through low-pressure gas (40-1000 mtorr). When the clamping occurs, oscillations in the beam collector current are reduced, resulting in a flat current pulse. Good agreement is found with a model which considers the impedance of the plasma produced by the electron beam in parallel with the inductance of the beam-collector current path. The current clamping occurs when the plasma impedance is smaller than the inductive impedance of the beam-collector current path