Fusion Science and Technology / Volume 44 / Number 4 / December 2003 / Pages 776-790
An alternative residual ion removal concept for the ITER neutral beam system is presented. It consists of magnetic deflection of the residual ions to in-line ion dumps. The target plates are hit from one side and form a 0.5-m-wide opening to the beam. First calculations show that for the most severe case of a 3-mrad beam, the maximum power load can be kept below 15 MW/m2, using a different horizontal focal length. However, this different beamlet optic increases the beam peak power density changing the plasma deposition profile and increasing the shine-through power during low-density operation. First calculations showed that using a passive screening, the additional stray field created by the magnet could be kept below the required 1 gauss within the neutralizer. The overall beamline transmission increases by ~10% (i.e., an additional 1.7-MW injected power for each beamline for a 3-mrad beam) due to the open structure of the magnet and the ion dumps. Furthermore, the concept offers a larger operating window regarding beam alignment, divergence, steering, and transmission, and it avoids creating accelerated secondary electrons.