Development of a rf negative-ion source for ITER neutral beam injection

The development at IPP of a large-area rf source for negative hydrogen ions, an official EFDA task agreement, aims to demonstrate ITER-relevant source parameters. This implies a current density of 20mAcm−2 accelerated D− at a source-filling pressure of <0.3Pa, an electron to ion ratio of <1, and for pulse lengths of up to 1h. The principle suitability concerning current density, pressure, and electron content has been demonstrated with the test facility Bavarian Test Machine for Negative Ions but with only small extraction area (70cm2) and for pulse length of <6s. The further development concentrates now on long pulse operation at the test stand Multi-Ampere Negative Ion Test Unit (MANITU), which became operational this spring. For source size extension from 70to1000cm2 MANITU and a third test facility, currently under development, called RADI will be used. This article will report on the latest results of the work in progress. A critical issue for ITER is reliable source operation at high current densities. Therefore the procedure used to obtain in a reproducible manner source operation at the ITER target values will be detailed and discussed.