Beam optic characteristics of neutral beam heating line on HL-2A

The beam optic characteristics of the neutral beam ion source affects the neutral beam injection power. With theoretical calculation and experimental scanning, study on the variation of half width of extraction beam with perveance is carried out. Theoretically, the 1/e half-width of extraction beam at the calorimetric target is obtained with IGUN program simulating trajectory of element beam to the 3 electrodes extraction accelerator on HL-2A device and beam geometry optic program calculating the superposition of every element beam. Experimentally, when the discharge gas is deuterium, the extraction voltage is scanned separately for arc current at 200 A, 300 A and 400 A, and the 1/e half-width of extraction beam is obtained with temperature rise curves measured by thermal couples on the calorimetric target. Theoretical and experimental results show that with the perveance increasing, the beam half width decreases first and then increases gradually. The optimum perveance value keeps almost the same for different beam current by theoretical result, while for arc current at 200, 300 and 400 A, the optimum perveances are 1.6, 1.7 and 1.85 P separately by experimental result.