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

The conceptual design of a neutral injector for ITER(EDA) presented he re is based on a combination of established technology and the Europea n negative ion development programme. The injector is based on negativ e ions as the energy required is more than 250 keV, above which the pr oduction of neutral beams from positive ions becomes unrealistic on gr ounds of efficiency. It is proposed to have a negative ion source at a high negative potential, with the ions accelerated up to the ground p otential of the neutralizer via a SINGAP electrostatic accelerator. In the initial design a gas neutralizer is proposed, but a future upgrad e using a plasma neutralizer is clearly possible. The charged fraction of the beam emerging from the neutralizer will be deflected electrost atically onto conventional water-cooled dump plates, and the neutral b eam will fall onto a long pulse copper calorimeter downstream of the r esidual ion dump during beamline commissioning. The necessary low gas pressure in the beamline is maintained by cryo condensation pumps, whi ch will require overnight regeneration.