Electron Temperature and Probe Floating Potentials in a Plasma of the Low-Current Vacuum Arc

Measurements of the electron temperature and of floating potentials are presented, as obtained utilizing Langmuir probes situated in the plasma of a low-current (120-360-A) vacuum arc on copper electrodes. The ring-shaped probes were located coaxially to the axis of the electrode assembly at different angles ψS from the cathode surface normal. Probe characteristics were obtained at varying probe bias voltage, generated from the 100-Hz half-sinusoidal voltage source. The electron temperature, far away from the cathode spot, in the region of direct radial plasma flux, is 2.1 eV for 120 A and 2.8-3.5 eV for 230 A. Floating potentials are functions . Uf = f(ψS) and diminish distinctly if ψS < ψA, where ψA is the semi-angle of the anode. The analysis was carried out assuming a shifted Maxwellian ion velocity distribution. Characterristic parmeters vio and α were evaluated from the derived floating potential equation.