H- ion beam extraction from a transformer coupled plasma source with triode extraction system

A continuous-mode H- ion source has been developed in SNU by using rf transformer coupled plasma source for long lifetime. Recently, its plasma confinement has been improved by modifying the main cusp magnet system that covers rf antenna and plasma electrode regions. The extraction system has also been upgraded to triode extraction system, where permanent magnets in dipole configuration are embedded in extraction electrode to provide additional magnetic field for filtering out fast electrons. Electrode shape, extraction hole size, and gap distance are optimized for high beam currents with low emittance by using PBGUNS code. With new configuration, H- beam currents of up to 1.67 mA with 1.7 kW, 13.56 MHz rf power are extracted in a continuous mode. Low e/H- ratios down to 8 are achieved by increasing total filtering field strength up to 190 G