Introduction of cesium vapor into the arc chamber of a high-brightness H−/D− volume source and resulting beam characteristics (abstract)

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Abstract
Addition of cesium vapor to H−/D− multicusp volume sources has been shown to result in significantly increased extracted ion current density. However, using a cesium oven, the initial introduction of Cs vapor causes high-voltage breakdowns that persist for extended periods. In the extreme case, source operation may no longer be possible without shutting down and thoroughly cleaning source components. If operation can be recovered, the increase in extracted ion current density persists for many days, usually until filament burn-out or other failure unrelated directly to Cs introduction. We have refined the procedure for Cs introduction to produce less catastrophic initial source operation and shorter recovery times to consistent operation. The new procedure has produced consistent H− currents of 35–42 mA at 30 keV. Higher currents, up to 64 mA, have been achieved for short periods soon after recovery. These data were obtained for a 6.4-mm-diam emission aperture using a modified Pierce geometry. In this paper, the new procedure for introduction of Cs will be described with the associated recovery characteristics. This paper will compare the emittance changes as a function of H− current, equivalent current, and plasma electrode bias. The behavior of the output over many days and shutdown-operation-shutdown cycles also will be described.

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