Possibilities for further optimizing the H-/D- RF source

RF sources for the production of positive hydrogen ions have been successfully developed at IPP for the AUG and the W7AS neutral beam heating system. A collaboration on high frequency ion source development for negative hydrogen ions between CEA Cadarache and IPP Garching had been started in 1996 with first results reported in 1998. Compared to arc sources RF sources have less parts, requiring just a source body, an RF coil, and a matching transformer and are therefore cheaper to build and basically maintenance free in operation. The simple design is potentially quite beneficial for ITER with its remote handling requirements. In contrast to the arc sources RF sources do not require regular maintenance to replace worn out filaments. Furthermore it is being speculated, that the arc current of the arc sources might contribute to the plasma non-uniformity observed in the large arc sources. Since September 2002 the development of the RF source is being supported by an EFDA contract aimed at demonstrating that the ITER requirements can be met. The ITER targets for current density, source pressure, and co-extracted electron fraction could already be achieved or exceeded. Further improvements are mainly aiming at improved efficiency and reliability. The present paper is to some extent of a speculative nature with the aim to provoke discussions under the workshop participants. (author)