MHD Evaluation and Analysis of the Infinity Two Stellarator

Type One Energy has produced a large number of configurations that meet the desired requirements for realizing a fusion pilot plant using the stellarator concept [1]. Configurations with favorable properties undergo rigorous physics assessments to then be considered for a high field fusion pilot plant concept. This study presents the assessment of self-consistent neoclassical bootstrap current, global ideal MHD modes and macro-instabilities of the Infinity Two configuration. We show that the configuration displays favorable ballooning stability characteristics, favorable Mercier stability, and is stable against global low-n to global high-n MHD instabilities up to β = 2.5%. Global internal unstable modes emerge at β = 3.5% for high-n modes, but for low-n modes the configuration is still stable at this beta value. We also discuss the stability of the Infinity Two configuration with ferritic inserts. The configuration (with ferritic inserts) at 1150 MW is stable to ideal MHD modes at β = 2.0%.