Measurement of ion parameters during a forced switching off of current in vacuum

This paper presents the results of ion parameters measured during a forced current commutation of a diffuse vacuum arc, aimed at evaluating the role of ions in discharges occurring rarely after the counterpulse commutation process, in a contact arrangement corresponding to a low-voltage vacuum switch. A sinusoidal half-wave current was interrupted near its amplitude of 400 A with a counterpulse of rise velocities 2.4 and 32 A//spl mu/s. In this way, a forced switching off of dc current was modeled. A retarding field analyzer was used for ion parameter measurements at the forced commutation process. Ion potentials up to 100 V were measured at the current zero moment, and the average decay times of ions after current zero were in the range from a few microseconds up to 30 /spl mu/s as a function of observed ion potential. The measured values of decay times show the rather negligible role of ions in the discharge process after the counterpulse commutation in the examined contact arrangement. The rise time of the countercurrent is proposed as a factor in the successful forced current commutation under these conditions, and values up to a few amperes per microsecond of countercurrent rise velocity can be considered as the limit value.