THE CATHODE SPOT PLASMA IN LOW-CURRENT AIR AND VACUUM BREAK ARCS

The radiation from active cathode spots in air and vacuum break arcs w as investigated by different experimental techniques: streak camera re cording, time-resolved and time-integrated spectroscopy. Spot rotation has been found with two frequencies omega1 = 2 x 10(5) Hz and omega2 = 4-6 x 10(7) Hz, and two characteristic radial velocities V1 = 21 m s -1 and V2 = 130 m s-1. From spectroscopic measurements, degeneration o f the upper excited atom states is deduced, corresponding to a strong non-ideality of the cathode spot plasma with consequences for the part icle density (N > 10(28) M-3).