Mechanical design for modification of a neutral beam for off-axis injection

Abstract

DIII-D is planning to implement off-axis neutral beam current drive by neutral beam injection through a midplane port at angles up to 15° from horizontal. To accommodate the beam-line tilting, the following modifications are planned: (1) move the beam line away from the tokamak by 0.39 m to allow for a 0.68 m inside diameter welded bellows of necessary length to provide 15° of vertical motion between the vessel port and the beam line; (2) reduce the vertical height of the injected beam from 0.48 m to 0.43 m to provide clearance for the inclined beam as it passes through the length of the vessel port; (3) add a linkage system between the front of the beam line and the tokamak to restrain the NB against the vacuum loading from the bellows while maintaining zero roll about the axis of the beam line as it is moved about a virtual pivot axis; (4) add a forward and two rear vertical actuators for raising and lowering the beam line (These actuators require coordinated position control to rotate the NB about a virtual pivot axis.); (5) incorporate lateral restraint to comply with seismic requirements.