Operation of the GTS-LHC ECR Ion Source in Afterglow With Varying Klystron Frequency

The GTS-LHC ECR ion source delivers lead ions for the CERN heavy ion programme at the LHC and the SPS fixed target physics. The source is normally operated with a main microwave frequency of 14.5 GHz in the afterglow mode. As part of the consolidation the microwave generator was replaced with a klystron based generator that allows free variation of the operating frequency in a range of 14.0 - 14.5 GHz. The aim of this study was to see how the lead charge state Pb²⁹⁺, which is the main ion species produced for experiments, is influenced by the different frequencies. Variations in performance were observed (beam intensity and beam stability), but no frequencies were found that would provide significant performance improvements compared to normal operation at 14.5 GHz. The results in general suggest that for the GTS-LHC ion source the optimal operating frequency depends on the overall source tuning and the influence of varying the main frequency is comparable to adjusting the other tuning parameters.