Measurement of anode surface temperature during a high-current vacuum arc

Anode surface temperature was measured during a 3.8-kA-peak-current 7.2-ms-duration discharge between 2.5-cm-diam Ni electrodes spaced 9 mm apart. The temperature was determined by measurements of the spectral radiance of the anode in the 0.6–1.0-μm spectral region by means of a Si photovoltaic detector and narrow-band interference filters. The spectral radiance was related to anode surface temperature through the Planck radiation law. The major uncertainty in the measurement was the uncertainty of the emissivity. The actual temperature could be bracketed, however, by assuming alternatively the lowest published emissivity and unity emissivity. Prior to high-voltage arcing onset at 2.7 kA, the anode surface temperature was below 1500 °K. After high-voltage arcing onset the surface temperature rose very rapidly, reaching an equilibrium temperature of approximately 2900 °K.