Burn Control Mechanisms for Power Excursion Mitigation in ITER

The strong increase of the D-T fusion cross-section with increasing plasma temperature in the ITER operating range has long been noted^1-3 as a potential triggering mechanism for positive thermal power excursions, and this possibility remains an issue for ITER^4-7. The efficacy of several inherent and active burn control mechanisms for limiting positive power excursions are explored. Mechanisms being evaluated include line and recombination radiation of seeded impurity ions⁵; MARFEs⁸; direct loss mechanisms such as ion orbit loss (IOL), ELMs, and impurity radiation enhancement by massive gas or pellet injection. We have made calculations to estimate the probable efficacy of such mechanisms in ITER. We find, e.g., that impurity seeding combined with increased massive D gas injection or pellets in the divertor or edge plasma may provide a plausible mechanism to radiate power to terminate a thermal power excursion. Refs: 1) Mills, LA4250, 1970; 2) Mori, Control Nuc Fus, 1105, 1976; 3) Stacey, NucFus 13,843,1973; 4) Borrass, Nuc Fus 31,1035,1991; 5) Mandrekas&Stacey, NucFus35,843,1995; 6) Humphreys, PhysPlas 22,021806,2015; 7) Boyer&Schuster, PPCF 56, 104004(2014); 8) Stacey, FusTech 52, 29 (2007).