Measurements of the current density in arc cathode spots from the Zeeman splitting of emission lines

Copper resonance lines from low-current break arcs in a vacuum and in air have been registered with a spectral resolution <0.015 nm. Two typical profile types have been found: Stark-broadened single lines and lines split into several components. The first type is ascribed to radiation from the plasma column outside the spots, whereas the split lines are associated with the actual spot. Looking side-on, only the first profile type could be observed. In a vacuum, the Doppler shift of these lines indicates a directed velocity of (1.5-4.5)*10 4 ms -1 . Looking end-on through a cathode hole both types of line could be distinguished. Interpreting the line splitting by the Zeeman effect, the authors conclude that there is an arc spot current density >10 11 Am -2 in a vacuum as well as in air.