Determination of Cr Density After Current Zero in a High-Current Vacuum Arc Considering Anode Plume

Results of broadband absorption spectroscopy in high-current vacuum arcs after current zero (CZ) are presented. Vapor density of atomic Cr is determined within 3 ms after CZ in cases with an anode plume which appears at about 400 μs before CZ and after extinction of anode spot type 2. The anode plume is a cloud of metal vapor which develops on the anode after the extinction of one specific high-current anode mode, namely, anode spot type 2. An ac current pulse of about 7 kA from a high-current generator with operation frequency of 100 Hz was applied. Cr I resonance lines at 425.43, 427.78, and 428.97 nm were chosen for the analysis. The temporal evolution of the ground state density of Cr atoms within first 3 ms after CZ starts with about 2.5 × 10
¹⁸
m
^-3
and decreases almost linearly with 0.65 × 10
¹⁸
m
^-3
/ms. The Cr I densities in cases with and without anode plume corresponding to anode spot type 2 and 1, respectively, are compared at 100 μs after CZ. In cases with anode plume, the metal vapor density is about 60% higher than in cases without plume, although the interrupting current is the same. The general behavior of the copper component is expected to be very similar to that of chromium.