Transport Analysis of High-Z Impurities Including Sawtooth Effects in a Tokamak System

In fusion reactors, high-Z materials will be used to balance the need to accommodate high heat load on divertor plates against consistency between fusion burning plasmas and plasma facing component (PFC) materials. However, high-Z impurities from these PFCs cause large radiation loss even if the amount of impurities is quite small. High-Z impurity transport analysis including sawtooth effects is carried out using the toroidal transport analysis linkage (TOTAL) code. The Bohm-type anomalous transport model for the core plasma and the anomalous inward flow model for impurity ions are used in addition to neoclassical transport. After comparisons with Joint European Torus (JET) impurity transport data, sawtooth effects on impurity transport in ITER are clarified with a simplified full magnetic reconnection model. The critical levels of impurity concentration in ITER are found to be 4.0 % for carbon, 0.1 % for iron, and 0.008 % for tungsten with respect to electron density. Forming an internal transport barrier (ITB) for electron density can prevent high-Z impurity accumulation. Also, sawtooth oscillation is shown to be beneficial, reducing radiation loss from the plasma core by about 20 %, although it might lead to unfavorable fusion power fluctuation of 10 %.