Princeton Plasma Physics Laboratory, Princeton, NJ USA

Motivations for advanced divertor system and materials research in next-step fusion facilities and NSTX Upgrade

Abstract: 

A Fusion Nuclear Science Facility (FNSF) could play an important role in the development of fusion energy by providing the nuclear environment needed to develop fusion materials and components. The spherical tokamak (ST) is a leading candidate for an FNSF due to its potentially high neutron wall loading and modular configuration. Further, recent studies point to the interesting finding that the optimal aspect ratio for a compact R=3m high-temperature Superconducting (HTS) FNSF / pilot plant may be near A = 2 which is an unexplored configuration in the present fusion program. These compact FNSF/Pilot Plant configurations challenge the material limits of solid plasma facing components for heat removal and motivate the consideration of advanced divertor magnetic field geometries to better dissipate power. Fast-flowing liquid-metal divertor systems offer the potential to handle significantly higher power loads, and low-recycling liquids (namely lithium) may provide a means for improving energy confinement and active removal of main-ion hydrogenic species, impurities, and possibly dust.  Near-term and longer-term research directions and plans for the National Spherical Torus Experiment Upgrade (NSTX-U) at PPPL in support of the above divertor and materials research areas will also be described.