Distributions of alpha particles escaping to the wall during sawtooth oscillations in the Tokamak Fusion Test Reactor

It has been observed experimentally in deuterium-tritium shots of the Tokam ak Fusion Test Reactor (TFTR) [D. J. Grove and D. M. Meade, Nucl. Fusion 25 , 1167 (1985)] that crashes of sawtooth oscillations may result in very inh omogeneous flux of alpha particles to the wall. To explain this phenomenon, both theoretical analysis and numerical simulation have been carried out. It is concluded that the "crash-induced prompt loss,'' i.e., the orbital lo ss of marginally trapped particles arising because of the crash-induced orb it transformation of circulating particles, is responsible for the flux nea r the bottom of the vessel, whereas the crash-induced stochastic diffusion of moderately trapped particles explains the large signal near the equatori al plane of the torus. The calculated poloidal distributions of the integra l alpha flux are in reasonable agreement with experimental data. The energy spectrum of the escaping particles has also been calculated, which can be used for diagnostics of the crash type. (C) 1999 American Institute of Phys ics. [S1070-664X(99)02304-6].