Low-pressure hollow-cathode glow discharge plasma for broad beam gaseous ion source

Abstract

We have developed a hollow-cathode glow discharge plasma for a dc broad beam ion source. For a broad beam ion source, it is hard to obtain adequate pressure drop between the discharge space and the extraction region. The high-current low-voltage mode of discharge is limited to a pressure about 10−3 Torr, but for stable extraction of ions without breakdown the pressure needs to be at least one order of magnitude lower. To decrease the limited operation pressure for the high-current mode of the hollow-cathode glow, an external electron beam was used. These electrons were generated in a “keep-alive” discharge and are accelerated in the cathode layer of the primary discharge. In this way we successfully decreased the operation pressure to 10−4–3×10−5 Torr, as well as reaching a value of the discharge voltage as low as 80 V. The characteristics of this discharge system are presented, and the influence of external electrons on the discharge parameters is discussed.