Latest results from the Cadarache 1 MV SINGAP experiment

The SINGle Aperture—SINgle GAP (SINGAP) acceleration concept has been developed as a simplified alternative to the Multi-Aperture, Multi-Grid (MAMuG) acceleration of the ITER Neutral Beam reference design. The objective of the present experiments is to demonstrate reliable multi-second acceleration of a D− beam to 1 MeV (∼100 mA, 200 A/m2), relevant to the ITER neutral beam injection (NBI) requirements. During the previous studies it has been demonstrated that the SINGAP concept works and good quality 860 keV H− beams (43 mA, 1 s) and 630 keV D− beams (106 mA, 1 s) have been produced. In the present R&D programme another attempt has been made to reach the full beam energy and increase the extracted beam current density with a refurbished 1 MV epoxy insulator/bushing. Refurbishment had become necessary after the top two of the nine epoxy rings making up the insulator had been perforated and carbonised due to high voltage discharges. The best results achieved during the present campaign are 914 keV D− beams (58 mA, 1 s) with a D− current density of 30 A/m2 and 600 keV D− beams (76 mA, 1 s) with a D− current density of 70 A/m2. These results are world records. The beam optics is largely as expected from the modelling with the Vector Fields OPERA 3D code.