A Systematic Comparison of Intense-Mode Vacuum Arc Between CuCr and AgWC Electrode by Using Various Optical Diagnostics

Abstract

Interelectrode phenomena related to intense-mode vacuum arc interruption were systematically compared between CuCr and AgWC electrodes by using various optical techniques mainly including two-color pyrometry for anode temperature determination after current zero, optical emission spectroscopy for the plasma composition assessment, and a Shack–Hartmann method for simultaneous 2-D electron and metal vapor density imaging. At the current peak, the widths of the radial electron density distributions for CuCr were narrower than those for AgWC. The electron density for CuCr was 3–5 times higher than that for AgWC. At current zero, the metal vapor density for CuCr was slightly lower than that for AgWC, which was specifically demonstrated for CuCr by a locally reduced metal vapor density below the minimum detectable limit of 1020 m−3. During and after the arcing time, mixing ratios of the copper vapor existing in the CuCr gap was about two times higher than expected from the CuCr electrode composition. After current zero, the decaying time constants of the metal vapor densities on the anode surfaces were Cr < Cu < Ag. This order was consistent with the decaying time constants of the anode evaporation rates estimated from the anode temperature measurement. The consistency suggests that the supplying process of the metal vapor after the intense vacuum arc interruption was the evaporation of the anode surfaces.