Vacuum arc ion sources:: Charge state enhancement and arc voltage

The Metal Vapor Vacuum ion source (MEVVA) has been developed for the production of ion beams for a wide range of metal ions. The ion charge states for most heavy elements created by the high current MEVVA ion source, which typically generates ions with a mean charge state up to three, have to be elevated to higher charge states for accelerator reasons at the GSI accelerator facility. Several methods are known which elevate charge states. Especially for the generation of U4+ ions a strong magnetic field and a high arc current has been used at GSI. Both methods increase the arc voltage which in turn influences the electron energy distribution and thus the mean ion charge state. Arc voltages have been measured for different settings of arc current, magnetic flux density and discharge geometry indicating the dependencies between these quantities and the arc voltage.