A CW radiofrequency ion source for production of negative hydrogen ion beams for cyclotrons

摘要

A CW 13.56 MHz radiofrequency-driven ion source RADIS for production of H~- and D~- beams is under development for replacing the filament-driven ion source of the MCC30/15 cyclotron. The RF ion source has a 16-pole multicusp plasma chamber, an electromagnet-based magnetic filter and an external planar spiral RF antenna behind an AlN window. The extraction is a 5-electrode system with an adjustable puller electrode voltage for optimizing the beam formation, a water-cooled electron dump electrode and an accelerating einzel lens. At 2650 W of RF power, the source produces 1 mA of H~- (2.6 mA/cm~2), which is the intensity needed at injection for production of 200 μA H~+ with the filament-driven ion source. A simple pepperpot device has been developed for characterizing the beam emittance. Plans for improving the power efficiency with the use of a new permanent magnet front plate is discussed.