A survey of optimal filament shape in a Japan Proton Accelerator Research Complex H- ion source

Dependence of various shapes of lanthanum hexaboride (LaB(6)) filaments on H(-) ion currents (I_H(-)'s) was examined by using the first Japan Proton Accelerator Research Complex (J-PARC) test ion source. It is almost the same with the J-PARC H(-) ion source (J-PARC-IS) except for the maximum arc current (290 A instead of 400 A). An I_H(-) of 35.2 mA was extracted by using a cylindrical double-spiral LaB(6) filament with a diameter of 29.5 mm and a length of 35.5 mm, which is the same one used in J-PARC-IS. It increased to 43.4 mA with a flat triple-hairpin LaB(6) filament. The I_H(-) is considered to be increased by the enlargement of the high density plasma region near the plasma electrode aperture and the reduction of the LaB(6) filament unemission area located in the high density plasma region.