PSI-ECRIT(S): a hybrid magnetic system with a mirror ratio of 10 for H-like heavy ion production and trapping

S. Biri1, L. Simons2 and D. Hitz3
1 Institute of Nuclear Research (ATOMKI), H-4026 Debrecen, Bem ter 18/C, Hungary
2 Paul Scherrer Institut (PSI), CH-5232 Villigen AG, Switzerland
3 CEA/Grenoble, DRFMC/SI2A, 17 Rue des Martyrs, 38054 Grenoble, France

At the Paul Scherrer Institut ( PSI, Switzerland) an experimental program is started to measure the ground state shift and width of pionic hydrogen. To calibrate the crystal spectrometer X-ray transitions in hydrogen-like heavy ions (e.g. Ar17+) produced by ECR ion sources, are necessary.

In PSI a superconducting cyclotron trap magnet originally developed for high energy experiments will be transformed into an ECR Ion Trap (ECRIT). The SC-magnet can deliver more than 4 Tesla magnetic fields with a mirror ratio of 2. A careful calculation showed this mirror ratio can be increased upto 10 and the trap can operate with frequencies between 5 and 20 GHz. To form a closed resonance zone a relatively large open structure (LBL-AECRU-type) NdFeB hexapole will be applied. The first tests will be performed with 6.4 GHz. Later higher frequencies (10 or 14.5 GHz) and the 2-frequency heating (6.4+10, 6.4+14.5 or 10+14.5) are planned to be applied to get enough quantity of H-like heavy ions.

Since the main goal of this machine is to be a trap no extraction is necessary. However, for the fine-tuning of the plasma for very high charge states might require ion charge state spectrums to be analyzed. If this is the case a simple beamline at negative potential will be built.

The present paper shows the results of the magnetic system calculations in details and summarises the present state of the ECRIT(S) overall design.

Presenting Author : Biri S.
Presentation : Poster
Monday Poster Session at 14:00

Highly Charged Ion Production Using an Electrode in Biased and Floating Modes

S. Biri2, T. Nakagawa1, M. Kidera1, L. Kenez2, A. Valek2 and Y. Yano1

1) The Institute of Physical and Chemical Research (RIKEN) Hirosawa 2-1, Wako, Saitama 351-01, Japan,
2) Institute of Nuclear Research (ATOMKI), H-4026 Debrecen, Bem ter 18/c, Hungary

One of the most popular ways to obtain higher beam intensities in ECR ion sources is to install an electrode (usually disc) into the plasma chamber. Examined this method in detail we found that 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. Only a few (and sometimes contradictionary) information was found on the optimised properties of the electrodes, i.e. position, dimension, shape, material.

In spite of the great success of the "biased-disc" method, the mechanism is still not completely clear. In this contribution, as one step of understanding, we examine what condition we observed the above mentioned two modes. The experiments were performed at the 18 GHz RIKEN and at the 14.5 GHz ATOMKI ECR ion sources.

It was found that effect of the electrode is strongly depends on the local plasma parameters and on the position of the electrode. At certain mirror ratios and electrode positions we needed to negatively bias the electrode and inject electrons into the plasma. The electrode operated as an electron source (Electron Donor ED mode). At higher mirror ratios and other axial positions the electrode works by directly changing the plasma potential dip (Potential Tuner PT mode). These two modes were checked and successfully found both in continuos and in pulsed mode operation. In both (ED and PT) modes we generated higher highly charged ion currents in the RIKEN-ECRIS than without the electrode.

Presenting Author : Biri S.
Presentation : Oral
Tuesday 11:30