Helium transport in advanced tokamak scenarios with internal transport barrier

The results are presented of investigations on advanced scenarios for plasm as of next-generation tokamaks by means of a 11/2-dimensional transport cod e. The role of thermonuclear alpha particles and helium ash is analyzed by a two-group model and by introducing experimentally validated mixed Bohm/gy roBohm models on the assumption that the diffusion of helium ash can be tre ated like the diffusion of bulk plasma ions. Recycling of helium ash is mod eled by introducing a wall source. Results are presented of parameter studi es presenting the equilibrium helium fraction as a function of the recyclin g factor. It is shown that for a given scenario, the fraction of effective helium confinement time and energy confinement time is a time-dependent qua ntity and not a constant, as was assumed in earlier research.