Thermal analysis of EAST neutral beam injectors for long-pulse beam operation

Two sets of neutral beam injectors (NBI-1 and NBI-2) have been mounted on EAST tokamak since 2014. NBI-1 and NBI-2 are co-direction and counter-direction, respectively. As in-depth physics and engineering study of EAST, the ability of long pulse beam injection should be required in the NBI system. For neutral beam injector, the most important and difficult thing, which should be overcome, is heat removal capacity of heat loaded components for long pulse beam extraction. In this article, the thermal state of the components of EAST NBI is investigated using water flow calorimetry and thermocouple temperatures. Results show that (1) operation parameters have an obvious influence on the heat deposited on the inner components of beamline, (2) suitable operation parameter can decrease the head loading effectively and obtain longer beam pulse length; (3) under the cooling water pressure of 0.25MPa, the predicted maximum beam pulse length will be up to 260 s with 50keV beam energy by a duty factor of 0.5. The results present that in this regard the EAST NBI-1 system has the ability of long pulse beam injection.