Beam performance of negative-ion based NBI system for JT-60

The negative-ion based NBI system (N-NBI) for JT-60 is being operated for a high energy neutral beam injection into the JT-60 plasma, in parallel with increasing the beam power. The estimation of the beam characteristics is v ery important for the enhancement and optimization of the beam power. The f ollowing four items have been used as the characterization of the beam: neu tron yield from the beamline, beam divergence, heat load on the beamline co mponents and beam profile on the armor plate in the tokamak Vacuum vessel. Since the beam power accelerated in the ion source is proportional to the n eutron yield in the beamline components, the operation status of deuterium negative ion current can be monitored easily. The beam divergence estimated at the drift duct and ion dumps, and the heat load on the beamline compone nts are used for the optimization of the ion source operation parameters an d the evaluation of neutral beam injection power. The beam divergence measu red at the drift duct is 4 mrad in the horizontal direction, 6 mrad in the vertical, which are in agreement with the design value of 5 mrad. The depos ition profile on the armor plate is used for monitoring of the neutral beam profile. (C) 2000 Published by Elsevier Science B.V. All rights reserved.