Radially expanding plasma parameters in a hot refractory anode vacuum arc

Electron temperature, plasma density, and plasma potential were measured with a Langmuir probe in the radially expanding plasma streaming from the interelectrode gap of a hot refractory anode vacuum arc. Plasma parameters were measured when the anodic plume was formed, during the first 20 s after arc ignition, at points located 3 to 18 cm from the electrode edge. In addition, the ion energy distribution was determined using a retarding field analyzer. As a function of radial distance, the electron temperature decreased from 1.2 to 0.6 eV, the plasma potential decreased from 3.7 to 1.7 V, and the plasma density decreased from 2.1013 to 1.8.1011 cm−3. The measured mean ion energy per unit charge state increased from 8 eV at an axial distance of 3 cm to 20 eV at 18 cm. The electron temperature and plasma potential decreased with arc duration by about 0.4 and 2 eV, respectively, near the electrode region. The relatively small magnitude of the ion energy observed near the gap may be caused by nonelastic resona...