The Infinity Two Stellarator Fusion Pilot Plant baseline plasma physics design

In this set of talks, we provide an assessment of the Infinity Two Fusion Pilot Plant (FPP) baseline plasma physics design. Infinity Two is a four-field period, aspect ratio A = 10, quasi-isodynamic stellarator with improved confinement appealing to a max-J approach, elevated plasma density and high magnetic field ( = 9 T). At the envisioned operating point (800 MW DT fusion), the configuration has robust magnetic surfaces based on MHD equilibrium calculations and is stable to both local and global MHD instabilities. The configuration has excellent confinement properties with small neoclassical transport and low bootstrap current (Ibootstrap 2 kA). Calculations of collisional alpha particle confinement show small energy losses to the first wall (< 1.5%) and stable energetic particle/Alfven eigenmodes at high density. Low turbulent transport is produced using a combination of density profile control consistent with pellet fueling and reduced stiffness to turbulent transport via three-dimensional shaping. Transport simulations with the T3D-GX-SFINCS code suite with self-consistent turbulent and neoclassical transport predict that the Pfusion = 800 MW operating point is attainable with high fusion gain (Q = 40) at volume averaged electron densities of = 2 X 1020 m-3, below the Sudo density limit. Additional transport calculations show ignited solutions are available at slightly higher density (<n e = 2.2 X 10 20 m -3 ) with P fusion = 1.5 GW. The magnetic configuration is defined by a magnetic coil set with sufficient room for an island divertor, shielding and blanket solutions with tritium breeding ratios (TBR) above unity. An optimistic estimate for the gas-cooled solid breeder designed Helium Cooled Pebble Bed is TBR ~ 1.3. Infinity Two satisfies the physics requirements of a stellarator fusion pilot plant.