Speaker
Description
Commonwealth Fusion Systems (CFS) is rapidly assembling the SPARC tokamak, with commissioning of many systems already underway. SPARC is a high field (12T), high current (8.7MA) device capable of achieving an energy gain of 11 when operating in H-mode with DT fuel. While the high magnetic field enables high fusion performance, it also results in a narrow heat flux width (between 0.3-0.6mm) due to a poloidal field of ~2.5T at the outer midplane. This narrow heat flux width makes power exhaust a central challenge, as unmitigated H-mode parallel heat fluxes are expected to reach as high as 10 GW/m2.
SPARC utilizes plasma facing components (PFCs) composed of pure tungsten and tungsten heavy alloy (97% W, 2% Ni, 1% Fe), which have been optimized for plasma power exhaust handling. Because the PFCs have the potential to contaminate the core plasma with high-Z sputtered impurities, SPARC will run in a partially or fully detached regime (e.g. XPT, XPR), using Ne, Kr, and Ar as the seeded impurity species. A relatively lean set of diagnostics will be combined with state-of-the-art plasma control techniques to maintain detachment while optimizing for core performance. Later campaigns will prepare for ARC, a 400MWe power plant, by operating SPARC with a neutron compatible diagnostic set.
SPARC edge plasmas are simulated across a wide range of fidelities by CFS and our collaborators. Fast hyperspace scoping is performed using physics models such as the extended Lengyel model and SepOS. Axisymmetric plasma distributions are predicted with a neural network trained on SOLPS runs, which can be connected to the plasma control system. The 3D plasma power exhaust and corresponding 3D PFC state is predicted using the HEAT code. Synthetic diagnostics are used to predict the expected diagnostic signals from thermocouples, cameras, spectroscopy, shunt measurements, and Langmuir probes. Workflows to reconstruct the plasma state from diagnostic data, and to track lifetime consumables (e.g. recrystallization), are under development in preparation for first plasma.
This presentation summarizes ongoing work across the SPARC boundary physics team, along with the challenges expected for operations. It provides a summary of the expected boundary physics regimes that will be observed in SPARC, and outlines the boundary control strategies that will be employed to operate the machine at high performance while preserving the PFCs.