High Performance of Neutral Beam Injectors for Extension of LHD Operational Regime

High-power negative and positive ion-based neutral beam injectors (NBIs) are operated with high reliability in the Large Helical Device (LHD). The total injection power is >20 MW, and such high-power beams are available every 3 min. The high performance of the LHD NBI system has extended the LHD parameter regime to levels equivalent to those obtained in large tokamaks. Three negative NBIs inject a total power of 16 MW with an energy of 180 keV, which is the world’s highest power from a negative NBI system (H−), and one positive NBI (H+) injects 7 MW at 40 keV. The injection duration can be extended beyond 1 min with reduced power from the negative and positive NBIs, and long-pulse plasmas are successfully sustained with the NBIs. The structure and performance of the LHD NBI system is reviewed.