CONCEPTUAL DESIGN OF A NEUTRAL BEAM SYSTEM FOR A NEXT STEP TOKAMAK

The conceptual design of a neutral injector for ITER(EDA) presented here is based on a combination of established technology and the European negative ion development programme. The injector is based on negative ions as the energy required is more than 250 keV, above which the production of neutral beams from positive ions becomes unrealistic on grounds of efficiency. It is proposed to have a negative ion source at a high negative potential, with the ions accelerated up to the ground potential of the neutralizer via a SINGAP electrostatic accelerator. In the initial design a gas neutralizer is proposed, but a future upgrade using a plasma neutralizer is clearly possible. The charged fraction of the beam emerging from the neutralizer will be deflected electrostatically onto conventional water-cooled dump plates, and the neutral beam will fall onto a long pulse copper calorimeter downstream of the residual ion dump during beamline commissioning. The necessary low gas pressure in the beamline is maintained by cryo condensation pumps, which will require overnight regeneration.