Beam Injection in the TMX-U Central Cell

摘要

Results pertaining to the recently modified beam-injection arrangement in the central cell of TMX-U are presented here. These modifications followed our observation that beam atoms injected perpendicular to the magnetic axis between the first two magnet-coil gaps give rise to trapped ions with midplane pitch angles lying in the intervals 68 degrees < theta < 78 degrees and 59 degrees < theta < 65 degrees . These pitch-angle intervals are similar in value to the earlier arrangement of beams injected at the midplane at pitch angles of 58 and 70 degrees. Normal injection at an off-midplane position has two advantages when compared with off-normal injection at the midplane. First, the unattenuated beam can be dumped in the first-injector region rather than in the plasma region. Second, the beams can be oriented with their long dimension horizontal rather than vertical. The first point allows a large improvement in central-cell vacuum conditions during beam injection, and the second provides improved beam-trapping efficiency in the core plasma. For the new beam-injection arrangement, we also displaced the beam-injection profiles vertically by one ion gyroradius to increase energy deposition at small radii. The advantages gained by the new beam orientation are considered in detail. (ERA citation 10:015468)