Mechanical design of the positioning system for an pff-axis neutral beam

The DIII-D tokamak has 4 neutral beams (NB) for plasma heating, rotation control and current drive. These NBs are all horizontal injection at 19deg offset from radial. Three NBs inject in the co-current direction and one NB injects in the counter current direction. The physics program requires two of the co-current NBs to be converted to allow injection at angles between 0deg and 16.5deg from horizontal by 2013 in order to investigate enhanced off-axis current drive. Each NB will be fully disassembled and it is planned during this task to upgrade thermal performance of internal components to allow for increased pulse length. The positioning system will incorporate 3 hydraulic cylinders to elevate the front and rear of the 35 ton NB. Hydraulic cylinder displacements will be supplied by hydraulic spool valves controlled by a programmable logic controller (PLC). The paper will present the following information for this mechanical positioning system: (1) Design requirements (2) Linkage arrangement (3) Loads evaluation including vacuum and seismic loads (4) Hydraulic circuit including instrumentation.