Contributions of the extended ELISE and BATMAN Upgrade test facilities to the roadmap towards ITER NBI

Abstract

ITER’s NBI systems are a first of its kind system with very challenging targets for the RF-driven ion source and the acceleration stage. In a step ladder approach, the ion source test facilities BATMAN Upgrade (BUG) and ELISE support the activities carried out at the Neutral Beam Test Facility (NBTF), Padua, which is equipped with the ion source facility SPIDER and with MITICA being equivalent to the ITER Heating Neutral Beam injector (HNB), capable of operating at the full power and pulse length of the ITER HNBs. The contributions of the prototype ion source at BUG (1/8 scale) and the size scaling experiment ELISE (1/2 size ITER source) to the roadmap are manifold: for hydrogen operation the ion source performance is demonstrated in several sequential 1000 s pulses, whereas long pulse deuterium operation is limited by the heat load of the co-extracted electrons on the extraction grid. Measures like special magnetic filter field configurations or biasing of surfaces and improved Cs management are identified. Both facilities have recently been extended to full steady state compatibility and very first insights of the ion source performance are already gained. A pulse length of 400 s, as required for the first deuterium campaigns at ITER, seems to be feasible soon, whereas the one hour pulse imposes the highest challenge to overcome. Investigations on beam divergence revealed a divergence at the upper limit of the acceptable value for the HNB. Measurements on the beam uniformity on the scale of beamlet groups and grid segments at ELISE demonstrated a uniformity of better than the required 90%. BUG and ELISE gave input to recent implementations at SPIDER; MITICA and ITER’s NBI. Still open points and challenges are addressed, for which a continuation of the step ladder approach is essential.