Formation time and heating mechanism of arc cathode craters in vacuum

摘要: With clean cathodes in UHV it is shown experimentally that (i) the arc craters are formed successively and displaced without spatial interruption, (ii) there only a few active at one instant for currents below spot-splitting limit (generally 1-2), (iii) crater formation much faster than compatible with heat conduction time scale, amounting to nanoseconds. From these observations measured values of radii times heating mechanism estimated. The calculations show Joule insufficient explain short therefore ion impact concluded be dominant process. Also this energy source effective by thin layers well defined thickness (about 0.1 mu m) which removed immediately after melting. Therefore, melting front proceeds into interior conduction. This model explains high losses cathode as Daalder (1977), also reason spot movement.