Concerning the Types of Cathode Spots

The kinds of electrical-arc cathode spots described in literature are analyzed. Division of spots into two types qualitatively different in nature-explosive spots and thermal spots-is proposed. The observed microsecond oscillations of the brightness of a rapidly moving spot are interpreted in terms of heat accumulation in the cathode and random motion of the spot. The transition of the spot to a thermal region is analyzed and the lifetime of nonstationary thermal spots is shown to be proportional to their size squared.