Visual observations on the high−current transition from the constricted to the diffuse MPD arc mode

Abstract

High−speed movies of the continuous change through the high−current transition region from a retrograde constricted MPD arc discharge to a diffuse MPD discharge have been obtained. The occurrence of the high−current diffuse discharge is governed by the behavior of the cathode spots with increasing current and magnetic field. Besides obtaining a relatively uniform discharge distribution between the electrodes with the diffuse arc mode, three other important properties are that (1) the retrograde moving cathode spots distribute uniformly over the cathode when the uniform discharge is obtained, (2) the arc voltage decreases, and (3) the arc voltage noise is greatly reduced.