Plasma characterization in a repetitively pulsed electron beam diode

Abstract

Electron beam (e-beam) generation in high power vacuum diodes results in anode and cathode plasma formation. It is well documented that expansion of these plasmas into the A-K gap may adversely affect diode performance during the main e-beam pulse. Ionized gases exist after the main pulse and can limit diode performance. For a given repetitively pulsed driver, diode physics will depend largely on the emitter material used in the cathode, the anode material, the electric field E, dE/dt, current density (J), vacuum pumping speed, the pulse width, and the pulse repetition frequency (PRF). For single shots and at a PRF of 1 pulse per second (PPS) taken on the NRL Solid State Pulser, diode plasmas are investigated using dielectric fiber velvet and graphite cathodes. A fiber laser interferometer is used to measure the line density of plasma at the cathode. A gated camera is fielded for nanosecond resolution of plasma emissions at axial positions across the anode-cathode gap.