The plasma in RF driven negative hydrogen ion sources is sustained via inductive coupling with large power levels of up to 100 kW and low frequencies around 1 MHz. This leads to currents of around 100 A flowing over the RF coil and corresponding voltages in the kV range. The associated risk of arcing limits the reliability of the whole ion source. The required power level can be reduced via optimizing the RF power transfer efficiency, which is typically only in the range of 50 to 60%. For enabling a fundamental insight into the RF coupling mechanisms at the operational parameters of the ion sources, a self-consistent fluid model has been set up (details of the model are presented in the contribution to this conference by D. Zielke et al.). The model was successfully validated with experimental measurements at the BATMAN Upgrade test bed. Optimization studies revealed that the RF power transfer efficiency can be improved to 90% by increasing the driver length and the RF frequency.
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