Latest achievements of the negative ion beam test facility ELISE

Abstract

The negative ion source test facility ELISE represents an important step in the European R&D roadmap for the neutral beam injection (NBI) systems of ITER. Its aim is to consolidate the design and to gain early experimental experience with a large and modular Radio Frequency (RF) negative ion source and an ITER like extraction system of the same width but half the height of the ITER source (0.9 × 1 m2). H− and D− beams can be extracted and accelerated up to 60 kV for 10 s every ∼150 s out of the continuously operating plasma source.For short plasma pulses (10 s), the extracted negative ion current densities in hydrogen have almost reached the ITER requirement (329 A/m2 H‾, 286 A/m2 D‾). Also the required long pulse source operation up to 1000 s (H-)/3600 s (D-) could be demonstrated on ELISE with repetitive beam blips, but with reduced current densities. The main limitations are the amount and temporal stability of co-extracted electrons, especially in deuterium operation. This co-extracted electron current has to remain below the extracted ion current to avoid thermal overloading of the extraction grid. Magnetic field configurations, electric potentials of source surfaces close to the extraction system and caesium management are under investigation as tools for source performance optimization. Furthermore RF issues such as heating of source components, RF breakdowns and RF matching have been solved for high power source operation.