Effect of broadband microwave radiation on the performance of a conventional B-minimum geometry electron cyclotron resonance ion source

The performances of electron cyclotron resonance ion sources can be enhanced by increasing the physical sizes or numbers of resonant zones embedded within their plasma volumes. Broadband rf power offers a simple, cost effective alternative for increasing the sizes of electron cyclotron resonance (ECR) zones in conventional minimum-B geometry sources over independently powered narrow bandwidth, multiple discrete frequency schemes. In this report, the charge-state enhancing effects of broadband microwave radiation are first demonstrated by comparing the high charge states of Ar ion beams produced by powering a conventional minimum-B geometry, 6.4 GHz ECR ion source with broadband microwave radiation 1200 MHz [full width at half maximum (FWHM)]) with those produced by conventional bandwidth [similar to 1.5 MHz (FWHM)] radiation. The results of these studies show that high-charge-state beams (e.g., Ar11+) can be enhanced by factors > 2 with broadband microwave radiation over those powered with narrow bandwidth radiation at the same power level, with or without voltage applied to the biased disk. The high charge states exhibit an anomalously strong increase in intensity at an optimum pressure with broadband microwave radiation. (c) 2006 American Institute of Physics.