Measurement of loss of DT fusion products using scintillator detectors in TFTR (invited)

A poloidal array of MeV ion loss probes previously used to measure DD fusion product loss has been upgraded to measure the loss of alpha particles from DT plasmas in the Tokamak Fusion Test Reactor (TFTR). The following improvements to the system have been made in preparation for the use of tritium in TFTR: (1) relocation of detectors to a neutron-shielded enclosure in the basement to reduce neutron-induced background signals; (2) replacement of ZnS:Cu (P31) scintillators in the probes with the Y3Al5O12:Ce (P46) variety to minimize damage and assure linearity at the fluxes anticipated from DT plasmas; and (3) shielding of the fiber optic bundles which carry the light from the probes to the detectors to reduce neutron- and gamma-induced light within them. In addition to the above preparations, the probes have been absolutely calibrated for alpha particles by using the Van de Graaf accelerator at Los Alamos National Laboratory. Alpha particle losses from DT plasmas have been observed, and losses at the detector 90° below the midplane are consistent with first orbit loss.