MHD and neoclassical properties of the Infinity Two Stellarator

In this talk we summarize the magnetohydrodynamic (MHD) equilibrium and stability properties of the Infinity Two fusion pilot plant, a four-field period, aspect ratio 𝐴=10 quasi-isodynamic stellarator optimized for excellent confinement at elevated density and high magnetic field 𝐵=9𝑇 [1]. Nested magnetic flux surfaces exist in the plasma core in vacuum and retain good equilibrium surface integrity from vacuum to its operational points of 800 MW and 1500 MW deuterium-tritium fusion power, corresponding to volume average plasma to magnetic pressures of 𝛽=1.6% and 2.0%, respectively. Neoclassical calculations show that the self-consistent bootstrap current is small (less than a few kA) and only slightly modifies the rotational transform profile. The configuration has a magnetic well across its entire radius. From vacuum to the operating points, 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% [2].



[1] Schmitt, J.C. et al. “Magnetohydrodynamic Equilibrium and Stability Properties of the Infinity Two Fusion Pilot Plant.” Journal of Plasma Physics 91.3 (2025): E88.

[2] Davila, N.M. et al. “MHD Evaluation and Analysis of the Infinity Two Stellarator”, this conference.