Tungsten filament material and cesium dynamic equilibrium effects on a surface converter ion source

We present results on two different aspects that affect surface converter H(-) ion source performance: tungsten filament material and converter/wall temperature control. On the tungsten material aspect, evidence that filament grain size affects the source performance as well as filament failure modes is shown. Materials with impurity contents that hinder grain growth during conditioning or operation are to be avoided in order to increase the filament lifetime. Regarding the temperature control of the converter and plasma chamber walls, we present results of increased current output of up to 2.5 mA (15%). This is explained by generating increased cesium vapor pressure leading to enhanced sputtering of H(-) ions.