Challenges of production of high current four-fold Bi and Au beams from vacuum arc ion sources at GSI accelerator facility

This work describes recent results of developing high current ion beams of Bi and Au at GSI accelerator facility. Challenges of production of ion beams with required charge state in vacuum arc discharge ion sources are discussed. The difficulties and limitations occurred due to using of pure Bi and Au materials in the cathodes are described. As a feasible solution the use of the mixed cathodes that contain a certain amount of more refractory metal admixed to the desired element is considered. As a significant result, a dramatic improvement in production of high charge state Bi and Au ions using the mixed Bi-Cu (15% Wt.) and Au-Cr (50% Wt.) cathodes, respectively, compare to cathodes from pure elements is presented. Also the results of investigation of the working surface and the material structure of the mixed cathodes using optical and electron microscopes are described. In conclusion, the possibility of optimization of cathode material as well as the next steps in development program are discussed.