3D-simulation studies of the modified magnetic multipole structure for an electron cyclotron resonance ion source P. Suominen * , O. Tarvainen, H. Koivisto Department of Physics, University of Jyv€askyl€a, Survontie 9, P.O. Box 35, FIN-40014 Jyv€askyl€a, Finland Received 31 March 2004; received in revised form 12 May 2004 Abstract Experiments have shown that efficient operation of an electron cyclotron resonance ion source requires that the magnetic field fulfills the so-called scaling laws. In most cases the requirements for the radial magnetic field, i.e. the strength of the magnetic multipole are the most difficult to satisfy. This is due to the fact that the multipole is usually produced from permanent magnets, which makes a value of 1.3 T feasible. One possible solution to increase the multipole field is the so-called Modified MultiPole Structure (JYFL-MMPS). This new idea makes it possible to in- crease the magnetic field at the places where the plasma flux is in contact with the plasma chamber wall. In this article we will present detailed three-dimensional magnetic field simulations of the JYFL-MMPS. Ó 2004 Elsevier B.V. All rights reserved. PACS: 07.77.K Keywords: Magnetic multipole; Electron cyclotron resonance ion source; JYFL-MMPS; 3D simulation 1. Introduction Modern Electron Cyclotron Resonance Ion Sources (ECRIS) [1] have a complex magnetic structure in which the plasma is confined. The inventor of the ECR ion source, R. Geller, pro- posed scaling laws [2], which show that the inten- sity of the ion beams extracted from an ECRIS depends strongly on the microwave frequency, i.e. I q / x 2 , where I q is the beam intensity of charge state q and x is the microwave frequency. Exper- iments have shown that the performance of ECR ion source follows very closely the aforementioned behavior (see for example [3]). Consequently, the most effective way to obtain higher charge states and higher beam currents is to use a microwave frequency as high as possible. However, that re- quires very strong magnetic fields. The so-called B-minimum structure [1], needed for efficient operation of an ECRIS, is produced by the combination of a solenoid and a multipolar magnetic field (normally hexapole). The optimum magnetic field structure can be studied using su- perconducting ECRIS’s in which both the solenoid and the multipole field can be adjusted. The first tests for the optimum configuration were carried * Corresponding author. Tel.: +358-50-305-2292; fax: +358- 14-260-2351. E-mail address: pekka.a.suominen@phys.jyu.fi (P. Suomi- nen). 0168-583X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.05.031 Nuclear Instruments and Methods in Physics Research B 225 (2004) 572–578 www.elsevier.com/locate/nimb