Alpha physics in tokamaks

After briefly reviewing recent experimental and theoretical alpha -particle physics simulation results self-consistent values of the anomalous radial diffusion coefficient D alpha from two related theories and/or numerical simulations of energetic alpha -excited shear Alfven wave turbulence are derived and used in a reduced drift kinetic equation (DKE) for the alpha distribution function F alpha (r,E,t) which contains a diffusion term 1 / r delta rD alpha delta . Since D alpha depends on delta n alpha / delta r through w* alpha the ensuing nonlinear diffusion equation for n alpha (r,t) is solved iteratively with the DKE for F alpha and the effects of D alpha on the alpha -power coupling efficiency eta alpha and the ignition margin are analyzed for an ITER-like device ('ignited operation' of the ITER conceptual design activity (CDA)). From a power balance point of view the resulting D alpha >or approximately=1 m 2 /s appears tolerable, D alpha >3 m 2 /s would yield eta alpha <0.95.