Initial results of the 2.45 GHz excitation of the superconducting ECR ion source in its high-B modea)

Abstract

The ‘‘frequency squared scaling’’ law, relied upon to enhance the production of high charge state ions from electron cyclotron resonance (ECR) ion sources, indicates that low frequencies of operation may not be viable for production of high ion densities, and hence for the production of high charge state ions. The superconducting electron cyclotron resonance ion source (SCECR) at the National Superconducting Cyclotron Laboratory is a fully superconducting, hexapole stabilized tandem mirror ECR ion source with a multimode microwave cavity. When operated at its optimized high magnetic field (high-B) mode at 6.4 GHz, the high charge state current output of the SCECR approaches all existing ECR ion sources, including higher requency ECR ion sources (ECRIS). In this study, the SCECR is operated at 2.45 GHz in its high-B mode that is scaled down for that frequency of operation. Initial results with oxygen and argon ion production at 2.45 GHz are presented. It is demonstrated that the SCECR can produce a plasma from which multiply charged ions of up to O7+ and Ar13+ can be extracted with ion current intensities comparable to several higher frequency ECRIS. This study concludes that 2.45 GHz is indeed a viable frequency for production of moderate intensities of multiply charged ions. This may lead to a simpler, and more cost effective microwave apparatus, with a less demanding magnetic field configuration.