Difference in the performances of ECR ion sources when they are fed by klystron-based generator or travelling-wave-tube-based generator

During recent experiments, a different behaviour of the electron cyclotron resonance (ECR) ion source CAESAR was observed at INFN-LNS, when it was operated by means of a travelling-wave-tube-based generator with respect to the standard operation by means of a klystron-based generator. The current available for argon-high charge states was significantly higher in the former case. The same test was repeated with the other source available at LNS, i.e. the superconducting ECR ion source SERSE, with oxygen in place of argon, and the results were similar. ription of the experimental set-up and of the results obtained in the two cases is given in the following.