Effects of Micro-turbulence on the Removal of Helium Ash in Deuterium–Tritium Plasmas

Abstract

Avoiding the accumulation of helium ash in the plasma core is a critical issue for future fusion reactors such as International Thermonuclear Experimental Reactor and China Fusion Engineering Test Reactor. The effects of micro-turbulence, including ion temperature gradient (ITG), parallel velocity shear (PVS) and collisionless trapped electron mode (CTEM) turbulence, on the removal of helium ash are briefly reviewed. We study how helium ash affects ITG and PVS instabilities based on our previous theoretical works, and compare the corresponding results with CTEM instability. The parametric dependence of ash flux is illustrated by calculating the turbulent flux and the corresponding transport coefficients. It indicates that long wavelength electrostatic micro-turbulence is favorable for removing helium ash, especially when its density profile is steeper than that of electrons. The outward flux of helium ash becomes larger for the temperature of helium ash being slightly higher than that of background plasmas ( $${T}_{z}>{T}_{e}={T}_{i}$$ ). Isotopic effects are favorable (unfavorable) for exhausting helium ash through PVS and CTEM (ITG) turbulence. In addition, the ambipolarity of turbulent transport fluxes between electrons, ions and helium ash is self-consistently verified, and its implication on the simultaneous transport of both helium ash and D–T ions is discussed.