A seminar given by
Dr. Haruhisa Nakano, Associate professor at the National Institute for Fusion Science, Gifu (Japan)
Neutral Beam Injection at the stellarator LHD (Large Helical Device)
Abstract: Improvement of deuterium injection power in the negative-ion-based NBIs (n-NBIs, Neutral Beam Injectors) for the Large Helical Device (LHD) are reported. Co-extracted electron current at acceleration of deuterium negative ions (D− ions) limits the injection power. The electron current is reduced by decreasing the extraction gap, and the injected D− current evaluated from the injection power increased from 46 to 55 A. Greater electron reduction was achieved by installing a structure named an ‘electron fence’ (EF), with which D− beam power was successfully improved from 2.0 MW to 3.0 MW. The injection power in three configurations − without EF, with EF of 5 mm and 7 mm distance from the plasma grid (PG) surface − have been compared in both cases of hydrogen and deuterium operations, and it was found that the configuration with the EF of 5 mm distance was the best to satisfy the performance for both of hydrogen and deuterium injections. Although the co-extracted electron current is reduced in the negative ion sources applied for JT-60SA and ITER by utilizing the PG filter, it is possible to achieve more effective electron reduction by combining the PG filter and the EF.
The rise or fall of antihydrogen: the GBAR* experiment at CERN