Compact microwave ion source for extremely low energy ion irradiation system

The performance of a compact microwave ion source developed for extremely low energy ion extraction was measured. The ion source was modified to be fitted for the ion extraction at the voltage lower than 100 V. The current–voltage characteristics, mass spectrum, absolute ion energy, and energy spread of argon ion beam were estimated with a sector magnet. The results showed that the mass spectrum showed a clear separation of singly charged ions and doubly charged ions even at the extraction voltage of 4 V. Mass separated Ar+ current of 0.5 nA at 4 V extraction was obtained. An excess ion energy due to presence of plasma potential was 14 eV at the pressure of 5×10−3 Pa, and 66 eV at 9×10−4 Pa. Energy spread was narrower than 12 eV, from rough estimate of the mass spectrum. These results summarize that the present ion source can be used for extremely low energy ion irradiation system.