THE USE OF PELLET DIAGNOSTICS FOR THE STUDY OF THERMONUCLEAR ALPHA-PARTICLES IN THE TFTR TOKAMAK

An alpha particle diagnostic technique based on impurity-pellet inject ion into tokamak plasma is described. This technique has been develope d in collaboration with the Princeton Plasma Physics Laboratory, Gener al Atomic, and Ioffe Institute for Physics and Technology and has been used in the TFTR tokamak. When lithium or boron pellets are injected into tokamak plasma, some fraction of a particles are neutralized in t he ablation cloud due to two-step single electron capture or double el ectron capture. Outward fluxes of neutralized a particles in the MeV e nergy range are analyzed by the Gemma-2 high-energy analyzer, which wa s developed in the Ioffe Institute for Physics and Technology. This di agnostic has been used in DT experiments in the TFTR tokamak and provi ded measurements of the local energy spectra and radial distributions of a particles in the 0.5-3.5 MeV energy range. Results of the measure ments of energy spectra and radial distributions of confined a particl es in the TFTR, influence of sawtooth oscillations on the a particle d istribution, and evidence for the radial redistribution of a particles in the presence of the toroidal Alfven modes induced by a particles a re presented. Possible ways of implementing a particle diagnostics wit h the use of pellets in the ITER are also discussed.