Design of a high-yield H2+ ion source for commissioning of the IFMIF accelerator using a one-dimensional plasma model

It is desirable to minimise the activation of components during the commissioning phase of the IFMIF accelerator and this can be achieved by using a beam of H2+ ions in place of the D+ beam. Having the same charge to mass ratio ensures that the commissioning can be conducted at full power, provided a sufficiently intense source of H2+ ions is available. Ideally, the H2+ beam current should equal that of the IFMIF D+ beam current, 140 mA, with a species fraction of greater than 85% H2+. This paper describes a study to determine the physical processes and ion source design criteria that optimise H2+ yield.Examination of the processes contributing to the yield of H2+ ions in a plasma indicate that extraction should occur as close to the ionisation volume as possible. The most suitable ion source is currently the volume discharge. A one-dimensional plasma model of this source has been developed and is validated against experimental measurements. The model has been used to identify those design criteria that most strongly affect the H2+ yield and has been used to optimise the design of the volume arc source for the production of H2+ ions.