TRANSP Simulations of Alpha Parameters and Ash in ITER
Authors: R. V. Budny, D. C. McCune, M. H. Redi, J. Schivell, and R. M. Wieland
The TRANSP code is used to construct comprehensive, self-consistent models for ITER discharges. Plasma parameters for two discharges from the ITER ÒInterim DesignÓ database producing 1.5 GW fusion power with a plasma current of 21 MA and 20 toroidal field coils generating 5.7 T are studied. Steady state profiles for Tion, Te, ne, Zeff, and Prad from the database are specified. TRANSP models the full up/down asymmetric plasma boundary within the separatrix. Effects of high-energy neutral beam injection, sawteeth mixing, toroidal field ripple, and helium ash transport are included. Results are given for the fusion rate, fusion alpha orbits, and parameters describing effects such as alpha particle slowing down, the heating of electrons and thermal ions, and the thermalization rates. The neutral beam deposition is predicted to peak near the half radius, and the average beam ion energy is predicted to be half the injected energy. Sawtooth mixing is predicted to broaden the fast alpha profile. The toroidal ripple losses rate of alpha energy is estimated to be 3% before sawtooth crashes and considerably higher immediately following crashes. Assumptions for the thermal He transport and the He recycling coefficient at the boundary are discussed. If the He recycling coefficient at the separatrix is ³ 0.95 and the inward pinch is negligible, the relatively flat database profiles imply that to obtain 1.5 GW of fusion power, the ash diffusivity must be much larger than that measured in current Tokamak experiments.