After briefly reviewing recent experimental and theoretical alpha -particle physics simulation results self-consistent values of the anomalous radial diffusion coefficient Dalpha 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 Falpha (r,E,t) which contains a diffusion term 1/r delta rDalpha delta . Since Dalpha depends on delta nalpha / delta r through w* alpha the ensuing nonlinear diffusion equation for nalpha (r,t) is solved iteratively with the DKE for Falpha and the effects of Dalpha 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 Dalpha >or approximately=1 m2/s appears tolerable, Dalpha >3 m2/s would yield eta alpha <0.95.