Neutral beam injection into the JIPP T-II Stellarator

Neutral beam injection experiments are carried out in JIPP T-II, which is a hybrid device of stellarator and tokamak. Two neutral beam injectors are equipped tangentially in the direction of parallel (co-injection) and anti-parallel (counter-injection) to the plasma current. Neutral hydrogen beams of 22 keV, 60 kW (co-injection) and 30 kW (counter-injection) are injected into the ohmically heated stellarator plasma and also into the tokamak plasma. The bulk ion heating efficiency for co-injection is around 1.6 eV/kW in the case of stellarator and 1.9 eV/kW in the case of tokamak, while the heating efficiencies for counter-injection are about 1.6 eV/kW in both cases. The difference between the tokamak and the stellarator is considered to be caused by the enhanced orbit loss due to the helical ripples in the stellarator