Beam Optics Study during Long-Pulse MeV-Class Beam Operation for the ITER HNB

Abstract

Neutral beam injectors for ITER require the beam divergence to be less than 7 mrad for both D− and H− negative ion beams. The time evolution of beam optics parameters of ITER-relevant high intensity has not been well understood due to the material capabilities of heat load. In this study, the time evolution of beam divergence has been successfully observed with the ITER-relevant perveance beam parameter for 0.5 MeV and 100 seconds pulse. For this purpose, a beam monitoring system based on a visible camera, which has been newly developed and installed in the MeV Test Facility, is used. As a result of this experiment, it is experimentally found that the time evolution of beam divergence exists even if the Iacc and heat load to beam dump are stable. To reduce the time evolution of beam optics, the feed-back control of Iext is under development in order to suppress the variation of conditions in the ion source.