Overview of the RF source development programme at IPP Garching

The development of a large-area RF source for negative hydrogen ions, an official EFDA task agreement, is aiming at demonstrating ITER-relevant ion source parameters. This implies a current density of 200 A m−2 accelerated D− ions at a source filling pressure of ⩽0.3 Pa and an electron-to-ion ratio of ⩽1 from an extraction area similar to the positive-ion based sources at JET and ASDEX Upgrade and for pulse lengths of up to 1 h. The work is progressing along three lines in parallel: (i) optimization of current densities at low pressure and electron/ion ratio, utilizing small extraction areas (<0.01 m2) and short pulses (<6 s), in this parameter range the ITER requirements are met or even exceeded; (ii) investigation on extended extraction areas (<0.03 m2) and pulse lengths of up to 3600 s and (iii) investigation of a size-scaling on a half-size ITER plasma source. Three different test beds are being used to carry out these investigations in parallel. An extensive diagnostic and modelling programme accompanies the activities. The paper discusses the recent achievements and the status in these three areas of development.