Role of microwave frequency on the high charge states buildup in the ECR ion sources

The effect of frequency scaling on the performance of electron cyclotron resonance (ECR) ion sources is predicted by theory but trials to demonstrate this law have not been successful. Controversial experimental data have been published throughout the years, some leading to the idea that the sources working at higher frequencies give higher charge states, while others state that the increase in frequency is ineffective. Recently, theoretical and experimental developments have suggested that the scaling is effective only if the confining field is high enough. The only way to prove this suggestion is to operate the same source at many different frequencies and with the same mirror ratio. Such a test may be adequately carried out on superconducting ECR sources such as the 6.4 GHz SC-ECRIS working at MSU-NSCL or the 14.5 GHz SERSE under construction at LNS (which is the ECR source with the maximum design magnetic field) with different generators, from 2.45 to 30 GHz.