Speaker
Description
Large area diodes under high vacuum (1e-6 Torr) can exhibit similar characteristics to pressurized arcs via several mechanisms such as stimulated emission of ions, thermal ion emission, and bipolar ion flow. Generally these diodes are under high electric field stresses (above 200kV/cm) where field emission of electrons from the cathode are expected. The ions in each mechanism above are liberated from the anode by the intense electron beam. This work demonstrates a diode in which an intense electron beam is shown to liberate secondary (stimulated or knock-on) ions from adsorbed contaminants (e.g. water, oil, etc.) that causes the electron beam to pinch. The pinch then leads to anode spot-heating, which yields thermal ion emission. This is a positive feedback problem that is eventually limited by bipolar flow. In this work, bipolar flow is undesirable as this is typically accompanied by damage to the anode, but was nonetheless observed in experiment. Electromagnetic particle-in-cell simulations performed in EMPIRE yield insight into these ion generation processes, and ultimately into experimental results.
