Production of highly charged ions in the RIKEN 18 GHz ECR ion source using an electrode in two modes

We placed an axially movable electrode into the plasma chamber of the 18 GHz RIKEN ECR ion source in order to produce higher intensity of multiply charged ions and to study how the electrode effects the highly charged ion (HCI) production. We found that the effect of the electrode strongly depends on the local plasma parameters, mainly on the electrode initial floating potential. At lower floating potential, we need to increase the plasma density by means of biasing the electrode and injecting electrons into the plasma. The electrode operates as an electron source (Electron Donor or ED mode). At higher floating potential, the electrode works by changing the plasma potential. The best result is obtained when the electrode remains at floating potential (Plasma Tuner or PT mode). These two modes were checked and successfully found both in the continuous and in the pulsed mode operation. In both (ED and PT) modes, we generated higher HCI currents than without the electrode. In the PT mode, we successfully obtained 300 eμA of Ar11+ at 15 kV extraction voltage