Maximal current of a pulsed constricted arc discharge operating in the forevacuum plasma electron source

Abstract

The paper presents results of investigation of maximal current of the pulsed constricted arc discharge generating emission plasma in the forevacuum plasma electron source. Distinctive feature of the forevacuum plasma electron source is the absence of pressure differential between region of formation of emission plasma and the region of acceleration and propagation of electron beam. Therefore, the operating conditions of the constricted arc in the forevacuum plasma source are significantly different from the conditions in the plasma electron sources generating electron beams at pressure 10–3–10–1 Pa. The constriction of the positive column of the arc discharge provides, as it known, to reduce influence of instability and chaotic behavior of the cathode spot of the arc on the formation of emission plasma. In the investigated pressure range 3–20.5 Pa, the maximal current of the constricted arc discharge has been limited either by extinction of the arc or by initiation of the cathode spots on the constricting electrode and transition of the arc operation to the cascade mode. Increase of gas pressure and the use of working gas with larger ionization cross section (e.g. argon) have provided increase of the maximal arc current. The increase in the constricting channel diameter has provided the increase of maximal current and provided lower minimal gas pressure, at which stable operation of the constricted arc ensured. The decrease of length of the constricting channel has provided noticeable increase in the maximal arc current only at gas pressure more than 12 Pa.