Use of multiple-discrete-frequency microwave radiation to enhance the performances of traditional B-minimum electron cyclotron resonance ion sources

Abstract

The performances of electron cyclotron resonance (ECR) ion sources, in terms of high-charge-state yields and intensities within a particular charge-state, can be enhanced by increasing the physical sizes of the ECR zones in relation to the sizes of their plasma volumes. The ECR plasma “volumes” of traditional B-minimum ECR sources can be increased by injecting broadband microwave radiation (multiple-discrete frequency, variable frequency, or broad-bandwidth frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). In this work, comparisons were made of the charge-state distributions of Arq+ and Xeq+ extracted from the ORNL Caprice ECR ion source, when excited with single frequency and multiple-discrete-frequency microwave radiation, derived from standard klystron and/or TWT technologies. The charge-state populations for Arq+ and Xeq+ move toward higher values when excited with modest power from two and three discrete frequency, microwave radiation compared to those generated with power from single-frequency radiation. For three-frequency plasma excitation, the most probable charge state for Xe is increased by one charge-state unit while the beam intensities for charge-states higher than the most probable are increased by factors of ∼3 over those for the single frequency plasma case. The results of these measurements along with details on the modifications to the injection system required to couple the microwave radiation into the plasma volume of the Caprice source will be presented in this article.