Status report of the 28GHz superconducting electron cyclotron resonance ion source VENUS (invited)

Abstract

The superconducting versatile electron cyclotron resonance (ECR) ion source for nuclear science (VENUS) is a next generation superconducting ECR ion source designed to produce high-current, high-charge-state ions for the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory. VENUS also serves as the prototype ion source for the rare isotope accelerator (RIA) front end, where the goal is to produce intense beams of medium-charge-state ions. Example beams for the RIA accelerator are 15pμA of Kr17+(260eμA), 12pμA of Xe20+ (240eμA of Xe20+), and 8pμA of U28+(230eμA). To achieve these high currents, VENUS has been optimized for operation at 28GHz, reaching maximal confinement fields of 4 and 3T axially and over 2.2T on the plasma chamber wall radially. After a commissioning phase at 18GHz, the source started the 28GHz operation in the summer of 2004. During that ongoing 28GHz commissioning process, record ion-beam intensities have been extracted. For instance, measured extracted currents for the low to medium charge states were 270eμA of Xe27+ and 245eμA of Bi29+, while for the higher charge states 15eμA of Xe34+, 15eμA of Bi41+, and 0.5eμA of Bi50+ could be produced. Results from the ongoing 28GHz commissioning as well as results using double-frequency heating with 18 and 28GHz for oxygen and xenon are presented. The effect of the minimum B field on the ion source performance has been systematically measured for 18 and 28GHz. In both cases the performance peaked at a minimum B field of about 80% of the resonance field. In addition, a strong dependence of the x-ray flux and energy on the minimum B field value was found.