Importance of heavy ion bombardment for H− formation in surface conversion sources

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Abstract
The interaction between the plasma and the converter in a surface conversion negative ion source is studied. The converter consists of a porous tungsten button, through which liquid cesium diffuses towards the surface. This scheme results in a low cesium density in the discharge. Xe+ and Ar+ ions are used to simulate the sputtering effect of Cs+ ion bombardment of the converter. The extracted H− beam energy profile and the conversion efficiency appeared to depend strongly on the heavy ion flux to the converter surface. The total H− current increases with an order of magnitude with increasing heavy ion flux. A maximum current density of 8 mA/cm2 of H− ions has been extracted.