Status report of the ECR ion sources at the KVI

Abstract: At the moment three ECR ion sources are in operation at the KVI. One of these is being used as the ionizer section of the polarized ion (protons and deuterons) source POLIS; it runs at 2.5 GHz. In this paper the emphasis will be on the other two ECRISs, both being used for the production of highly charged ions. ECRIS3 is connected to the AGOR super-conducting Cyclotron. Beams of 12, 13C6+, 14N7+, 15N5+, 16O6+, 8+, 36Ar11+, 12+, 14+, 40Ar8+ and 3He2+, 4He2+ have been produced at various source voltages (16 - 29 kV), corresponding to a range of beam energies for experiments. The source is operating satisfactorily with sufficiently high beam intensities. Gas mixing is important for the high charge states of argon, where the best results have been obtained with 18O as a mixing gas. Since the AGOR cyclotron is used for the larger fraction of available beam time with (polarized) protons, the ECRIS3 set up is quite often available for test runs. ECRIS4 is connected to the five experimental set-ups of the Atomic Physics group. It is very intensively used to deliver all kinds of high and low charged ions (all "gaseous"), in the mass range of A=1 - 131, at source voltages ranging from 1-25 kV. This source is equipped with the strong Hallbach type hexapole magnet; the implications are subject of a separate paper. The performance for O7+ and Ar14+ beams is about a factor 5 lower as compared to the currents of ECRIS3. Interchanging the central part (i.e. hexapole magnet, pole plugs and vacuum chamber) results in interchanging the properties of the two sources. In the new situation, time for upgrading is available. A substantial improvement was obtained by reshaping the (axial) magnet configuration. This was realized on the one hand by the installation of a coil with reversed current between the two major coils; this resulted in a reduction of the minimum axial field by 10 % and at the same time in a substantially increase of the ECR resonance zone length. In this way the performance of the two sources has become much closer. On the other hand, by reshaping the pole plugs, according to model calculations, the two field maxima could be increased by about 10 %. Results of magnetic field calculations and measurements, and output currents will be shown.