Simulation of a plasma-focused electron gun

Summary form only given. Plasma can play an important role in the physics of an electron gun. It can provide an important focusing mechanism, and plasmas are often present in varying densities in many devices designed for vacuum operation. Plasma can also be a source of noise and instability for a microwave beam device. A plasma-focused electron gun is modeled using the PIC code XOOPIC. The plasma is formed via electron impact ionization with an argon background gas at 10/sup -4/ Torr. Electron-neutral interactions are included using a Monte-Carlo model. The gun operates close to the space charge limit, with V=30 kV, I=9A for a 7 mm AK gap. A solenoidal coil with an iron core provides a peak field on axis of B/sub max/=180 G. Argon ions streaming back toward the cathode cause erosion of the surface. Most of the ion flux passes through a 1 mm hole in the center of the cathode. The flux at the cathode surface is characterized, including energy and angle of incidence. In addition, the beam emittance is examined as the plasma builds up to steady state over a microsecond timescale.