Production of highly charged ions in electron cyclotron resonance ion sources using an electrode in two modes

One of the most known ways to obtain higher beam intensities in electron cyclotron resonance (ECR) ion sources is to install an electrode (usually disk) into the plasma chamber. We found that a majority of the groups observed the beam intensity improvement by supplying a suitable biased voltage to the electrode and an electron current was injected into the plasma. A few groups observed the enhancement, however, when the electrode operated at floating potential—without being an electron donor. In spite of the great success of the “biased disk” method, the mechanism is still not completely clear. In this contribution, as a step toward of understanding, we examined the above mentioned two modes. The experiments were performed at the 18 GHz RIKEN and at the 14.5 GHz ATOMKI ECR ion sources.