Parameters of Constricted Arc for the Pulsed Forevacuum Plasma Electron Source

Abstract

The paper presents results of investigation of special features and parameters of pulsed constricted arc discharge that is used to produce extended emission plasma for the forevacuum plasma electron source. Such electron source generates large-radius pulsed electron beam in the so-called forevacuum pressure range of 5–15 Pa. The contraction of the positive column of the arc provides, as it known, more stable parameters of the discharge plasma and makes its parameters independent of the instability and chaotic behavior of the cathode spot of the arc. It is also known, that maximal stable parameters of the constricted arc are limited by formation of cathode spots on the intermediated constricting electrode and transition of the arc to the cascade mode. A distinctive feature of the contracted arc in the forevacuum pressure range is the absence of pressure differential between the cathode and anode parts of the discharge. Nevertheless, even in the isobaric mode, there are also all characteristic properties of the constricted arc. A distinctive feature of the forevacuum constricted arc is more strong dependence of the maximal arc current and the duration of stable pulse duration on the pressure and type of operating gas. So, for example, for helium stable mode of operation of the constricted arc has not been achieved. When using heavier gases with larger ionization cross section, such as argon or nitrogen, the problem of the stability of the contracted arc discharge in the forevacuum pressure range has been solved. The possibility of using the constricted arc in the pulsed forevacuum plasma electron source has been successfully demonstrated.