Effect of wall material on H/sup -/ production in a multicusp source

In this paper, the authors investigate the extracted H/sup -/ beam with different metallic liners installed in a magnetically-filtered multicusp source (15 cm diam by 24 cm long). These metal liners were cleaned in an ultrasonic alcohol bath before installation. To ensure good thermal and electrical contact with the source chamber, two stainless-steel rings were used to force the liner to lay flush against the vessel wall. A steady-state hydrogen plasma was produced by primary electrons emitted from two 0.05-cm-diam tungsten filaments. The entire chamber wall, together with the filter rods, served as the anode for the discharge. During the experiment, the pressure inside the source was maintained at ≅ 1.5 x 10/sup -3/ Torr. A discharge power of 90 V, 1A was employed throughout the experiment to generate a modest hydrogen plasma density of about 4 x 10/sup 10/ cm/sup -3/. The results show that aluminum and copper generate the highest H/sup -/ yield while stainless steel produces the lowest. The H/sup -/ output of other metal liners such as Mo, Ta, W and Au fall between those of Al and stainless steel