Magnetohydrodynamic equilibrium and stability properties of the Infinity Two fusion pilot plant

The magnetohydrodynamic (MHD) equilibrium and stability properties of the Infinity Two fusion pilot plant baseline plasma physics design are presented. The configuration is a four-field period, aspect ratio A = 10 quasi-isodynamic stellarator optimised for excellent confinement at elevated density and high magnetic field B = 9 T. Magnetic surfaces exist in the plasma core in vacuum and retain good equilibrium surface integrity from vacuum to an operational β = 1.6 %, the ratio of the volume average of the plasma and magnetic pressures, corresponding to 800 MW deuterium–tritium fusion operation. Neoclassical calculations show that a self-consistent bootstrap current of the order of ∼1 kA slightly increases the rotational transform profile by less than 0.001. The configuration has a magnetic well across its entire radius. From vacuum to the operating point, the configuration exhibits good ballooning stability characteristics, exhibits good Mercier stability across most of its minor radius and it is stable against global low-n MHD instabilities up to β = 3.2 %.