Prospects for charge-exchange-recombination-based measurements on International Thermonuclear Experimental Reactor using a helium diagnostic neutral beam

Several important measurements in the International Thermonuclear Experimen tal Reactor (ITER) diagnostic mission, including the primary one of core he lium ash density, are expected to be addressed using active spectroscopic t echniques. These methods rely on the use of a dedicated diagnostic neutral beam (DNB) which has been optimized for the dual requirements of beam penet ration and charge exchange cross section. For hydrogenic beams, this result s in an optimal beam energy of similar to 100 keV/amu. Signal-to-noise esti mates using realistic geometries and the existing ITER profile and equilibr ium data have confirmed the stringent requirements on beam quality and inte nsity to satisfy the stated ITER measurement precisions. In this article we consider the use of a neutral helium DNB for making active spectroscopic m easurements on ITER, since helium beams offer better penetration in dense p lasma for a given energy, and the prospects for given source performance ma y also be improved. Drawbacks include the more difficult absolute calibrati on of the beam density profile as well as the fundamental problem of unique ly identifying the source (fusion-based ash, beam core fuelling, or edge DN B neutralizer/source efflux) of the observed He charge-exchange recombinati on line in order to unambiguously characterize core helium buildup and conf inement on ITER. (C) 1999 American Institute of Physics. [S0034-6748(99)650 01-8].