Design and operation of the pellet charge exchange diagnostic for measurement of energetic confined alpha particles and tritons on the Tokamak Fusion Test Reactor

Radially resolved energy and density distributions of the confined a particles in D-T experiments on the Tokamak Fusion Test Reactor (TFTR) are being measured with the pellet charge exchange (PCX) diagnostic. Other energetic ion species can be detected as well, such as tritons produced in D-D plasmas and H, He-3, or tritium rf-driven minority ion tails. The ablation cloud formed by injected low-Z impurity pellets provides the neutralization target for this active charge exchange technique. Because the cloud neutralization efficiency is uncertain, the PCX diagnostic is not absolutely calibrated so only relative density profiles are obtained. A mass and energy resolving E parallel to B neutral particle analyzer (NPA) is used which has eight energy channels covering the energy range of 0.3-3.7 MeV for alpha particles with energy resolution ranging from 5.8% to 11.3% and a spatial resolution of similar to 5 cm. The PCX diagnostic views deeply trapped ions in a narrow pitch angle range around a mean value of upsilon parallel to/upsilon = -0.048+/-10(-3). For D-T operation, the NPA was shielded by a polyethylene-lead enclosure providing 100X attenuation of ambient gamma radiation and 14 MeV neutrons. The PCX diagnostic technique and its application on TFTR are described in detail. (C) 1996 American Institute of Physics.