Radially expanding plasma parameters in a hot refractory anode vacuum arc

Electron temperature, plasma density, and plasma potential were measured wi th a Langmuir probe in the radially expanding plasma streaming from the int erelectrode gap of a hot refractory anode vacuum are. Plasma parameters wer e measured when the anodic plume was formed, during the first 20 s after ar e ignition, at points located 3 to 18 cm from the electrode edge. In additi on, the ion energy distribution was determined using a retarding field anal yzer. 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 t he plasma density decreased from 2.10(13) to 1.8.10(11) cm(-3). The measure d mean ion energy per unit charge state increased from 8 eV at an axial dis tance of 3 cm to 20 eV at 18 cm. The electron temperature and plasma potent ial decreased with are duration by about 0.4 and 2 eV, respectively, near t he electrode region. The relatively small magnitude of the ion energy obser ved near the gap may be caused by nonelastic resonance charge exchange scat tering of the cathode jet ions on atoms that are reevaporated from the anod e. The observed ion acceleration at larger distances from the gap is caused by the gradient in the electron pressure caused by the plasma expansion fr om the interelectrode gap into the ambient vacuum. (C) 2000 American Instit ute of Physics. [S0021-8979(00)03424-1].