| dc.description |
We present a spectroscopic study of the temporal evolution of a new type of hot-anode vacuum arc discharge. This arc begins as a multi-cathode-spot vacuum arc (MCS) operating for 150 - 200 s duration at 175 or 340 A DC current and is eventually sustained by the metal vapour (originating from the cold copper cathode) that is re-evaporated from a non-consumable and thermally isolated hot graphite anode, located 10 mm away from the cathode. The hot anode acts indirectly as the plasma source by evaporating and/or reflecting the cathode material condensed on it. Spectral lines of Cu I, Cu II and Cu III in the visible were investigated as a function of time near the cathode, near the anode and in the middle of the electrode gap. Line intensity measurement was performed with 40 ms time resolution and 0.4 mm spatial resolution. Time-resolved excited-state densities were determined from the calculated radial distribution. The anodic plasma plume was observed to develop and reach the cathode within approximately 30 and 15 s for arc currents of 175 and 340 A, respectively. The calculated near-anode density of the Cu I level increased from approximately to within 30 s for a 175 A arc. The distribution temperature derived from a Boltzmann diagram was found to be 0.6 eV, approximately. The electron temperature derived from saturated Cu I lines was found to be close to 1 eV during steady-state operation. |
