Results of the Cadarache 1 MeV D− “SINGAP” Experiment

The objective of the experiment is to demonstrate the acceleration of a long pulse 100 m A D − ion beam in a simplified electrostatic accelerator concept. In contrast to the ITER injector reference design, multiple beamlets are pre-accelerated to about 50 keV, then merged and post-accelerated to 1 MeV into one SIN Gle AP erture (at high voltage) using one SIN gle GAP (“SINGAP”). The beam is dumped onto a uni-directional thermal conductivity CFC graphite target allowing infrared-calorimetric beam profile measurements. The experiment is supported by 3d beam trajectory calculations. Conditioning without beam to 1 MV was achieved after the first 10 days of operation. This required only 35 min of integrated voltage on-time. During voltage application, an intense field-emitted electron current (up to 120 mA of “dark current”) is observed. This current can be strongly reduced by conditioning and pressure increase. H − beams of good quality were produced at a level of 910 keV, 40 mA, 1 s pulse. The only problem encountered was the perforation by breakdowns of one of the 9 insulator rings (epoxy) which constitute the 1 MV bushing. After repairing this insulator, the high voltage operation could be restarted without major difficulties. The damage of the insulator is due to a defect in the manufacturing process and does not impair the qualities of the SINGAP concept.