Effects of Particle Transport on Helium Ash Accumulation and Sustained Ignition in the International Thermonuclear Experimental Reactor

The buildup of helium ash has been studied in a series of simulations with the BALDUR transport code in the proposed International Thermonuclear Experimental Reactor (ITER) experiment at low density = 8.3 × 10¹⁹/m⁻³. Sustained ignition is found to be possible only for R_He < 0.5 → 0.9, with lower values required at lower edge densities. Using radially dependent thermal diffusivities that were scaled from Joint European Torus (JET) values, the effects of particle transport coefficients and edge recycling on helium poisoning of ignition are studied. A sustained ignition is obtained when the exhaust of helium from the edge plasma is allowed to exceed 10% of the helium flux into the edge plasma from the core plasma, and the ratio of particle (helium ion) to thermal diffusivities, D/χ, is > ¼. The simulations include the effects of sawtooth oscillations, radiative as well as conductive energy loss channels, and density profile variations.