NEUTRAL BEAMS FOR ITER

Neutral beam injection has been the most successful scheme used to hea t magnetically confined plasmas studied in controlled nuclear fusion r esearch, and neutral beams are a candidate to heat to ignition the Int ernational Tokamak Experimental Reactor (ITER). This article describes the system which is presently being designed in Europe, Japan, and Ru ssia, with coordination by the Joint Central Team of ITER at Naka, Jap an. The proposed system consists of three negative ion based neutral i njectors, delivering a total of 50 MW of 1 MeV D-0 to the ITER plasma for pulse length of >1000 s. The proposed injectors each use a single caesiated volume are discharge negative ion source? and a multigrid, m ultiaperture accelerator, to produce about 40 A of 1 MeV D-. This will be neutralized in a subdivided gas neutralizer, which has a conversio n efficiency of about 60%. The charged fraction of the beam emerging f rom the neutralizer is dumped onto the water-cooled surfaces making up the electrostatic residual ion dump. A water-cooled calorimeter can b e moved into the beam path to intercept the neutral beam, allowing com missioning of the injector independent of ITER. (C) 1996 American Inst itute of Physics.