Robustness and Flexibility in NCSX: Global Ideal MHD Stability and Energetic Particle Transport

Abstract

Concerns about the flexibility and robustness of a compact quasiaxial stellarator design are addressed by studying the effects of varied pressure and iota profiles. For thirty related equilibrium configurations the global, ideal magnetohydrodynamic (MHD) stability is evaluated as well as energetic particle transport. It is found that tokamak intuition is useful to understanding the MHD stability, with pressure gradient driving terms and shear stabilization controlling both the N=0 and N=1 unstable modes. Global kink modes are generated by steeply peaked profiles and edge localized modes are found for plasmas with edge iota above 0.5. Energetic particle transport is not strongly dependent on these changes of pressure and iota profiles, although a weak inverse dependence on pressure peaking through the magnetic axis Shafranov shift is found. While good transport and MHD stability are not anticorrelated in these 30 equilibria, stability depends on a delicate balance of the pressure and shear stabilization forces.