Enhancing the performances of traditional electron cyclotron resonance ion sources with multiple-discrete-frequency microwave radiation

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 creation of a large ECR plasma “volume” permits coupling of more power into the plasma, resulting in the heating of a much larger electron population to higher energies, the effect of which is to produce higher charge-state distributions and higher intensities within a particular charge state than possible in present forms of the ECR source. 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-band-width frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). To demonstrate that the frequency domain technique can be used to enhance the performance of a traditional B-minimum ECR ion source, comparative studies were made to assess the relative performances of the Oak Ridge National Laboratory Caprice ECR ion source, in terms of multiply charged ion-beam generation capabilities, when excited with high-power, single-frequency, or multiple-discrete-frequency microwave radiation, derived from standard klystron and/or TWT technologies. These studies demonstrate that the charge-state populations for Ar q+ and Xeq+ move toward higher values when excited with two and three discrete-frequency, microwave power compared to those observed when single-frequency microwave power is used. For example, 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 compared to those observed for single-frequency plasma excitation. 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 report.

Study of the asymmetric magnetic field confining the plasma in an experimental ECR set-up

“…This was not possible with the formulas used in [5,6], and it is indeed necessary in the studies dealing with particles magnetically confined within these apparatuses. In this way, this study can be also useful to deal with the situations in which the plasma is fed by the superimposition of waves at different frequencies [25][26][27] and that can be tuned [28,29]. Moreover, the study leads to a detailed and accurate description of the dependence on frequency of the resonance surface and its parameters, associated with a given monochromatic electromagnetic wave.…”

“…A broad frequency range has been considered for this analysis. In this way, this study can be also useful to deal with the situations in which the plasma is fed by the superimposition of waves at different frequencies [25][26][27] and that can be tuned [28,29].…”

A New Method for Enhancing the Performances of Conventional B-Geometry ECR Ion Sources

“…[12][13][14] for improving the charge-state distributions from these sources. 6-11) and frequency domain, multiplediscrete frequency techniques (see, e.g., Refs.…”

Towards explanation of the two-frequency heating effect in electron cyclotron ion sources

“…The latter solution seems to be very natural since the most experiments aimed at development of highperformance ECR ion sources have an option of two or more frequency heating as a consequence of gradual upgrade of the heating systems when old sources remain operating together with new ones, at different frequency. In all cases two-frequency heating leads to increase of the source performance, especially the high charge state ion productin [9][10][11][12][13]; in some cases a setup operates normally without a second heating frequency only in an extremely narrow range of parameters [14].…”