Ion behavior and gas mixing in electron cyclotron resonance plasmas as sources of highly charged ions

This article deals with ion behavior in small open-ended magnetic devices, the electron cyclotron resonance ion sources (ECRIS) that were developed fo r multicharged ion production. The ECRIS are basically ECR-heated plasma co nfinement machines with hot electrons and cold ions. The main parameters of the ion population in ECRIS plasmas are successively analyzed: temperature , collisions, losses, confinement times, followed by the gas mixing effect, a specific technique to improve the performance as an ion source. A series of experiments is described for the systematic analysis of this effect. It is experimentally shown that high charge state optimization by gas mixing results from an ion confinement time improvement due to ion cooling, and re lies on a compromise between three criteria, ion losses, mass effect, and i onization rates. (C) 1999 American Institute of Physics. [S0021-8979(99)008 21-X].