Multicusp ion source with external rf antenna for production of protons

Abstract

Proton beams are needed in neutral-beam injection for diagnostic development of an internal magnetic field measurement. High proton fraction, low axial energy spread, current density in excess of 30 mA/cm2, and a parallel ion beam with cw operation are the requirements for the ion source/extraction system. A multicusp-type ion source with an external rf antenna was constructed at Lawrence Berkeley National Laboratory. A proton fraction of 85% and proton current density of 32 mA/cm2 were achieved at 1.8 kW of rf power. Plasma parameters were measured with a rf compensated Langmuir probe.