MEASUREMENTS OF CONFINED ALPHAS AND TRITONS IN THE MHD QUIESCENT COREOF TFTR PLASMAS USING THE PELLET CHARGE-EXCHANGE DIAGNOSTIC

The energy distributions and radial density profiles of the fast confi ned trapped alpha particles in DT experiments on TFTR are being measur ed in the energy range 0.5-3.5 MeV using the pellet charge exchange (P CX) diagnostic. A brief description of the measurement technique which involves active neutral particle analysis using the ablation cloud su rrounding an injected impurity pellet as the neutralizer is presented. This paper focuses on alpha and triton measurements in the core of MH D quiescent TFTR discharges where the expected classical slowing-down and pitch angle scattering effects are not complicated by stochastic r ipple diffusion and sawtooth activity. In particular, the first measur ement of the alpha slowing-down distribution up to the birth energy, o btained using boron pellet injection, is presented. The measurements a re compared with predictions using either the TRANSP Monte Carlo code and/or a Fokker-Planck Post-TRANSP processor code, which assumes that the alphas and tritons are well confined and slow down classically. Bo th the shape of the measured alpha and triton energy distributions and their density ratios are in good agreement with the code calculations . We can conclude that the PCX measurements are consistent with classi cal thermalization of the fusion-generated alphas and tritons.