Critical Gradient Computation with Respect To Stellarator Geometry

Surpassing the critical ion temperature gradient of a stellarator results in the onset of ion-temperature-gradient turbulent transport. Calculating this temperature gradient is important for modelling stellarator transport and temperature profiles. To this end, analytical and numerical methods for analyzing the growth of modes with respect to stellarator geometry are presented and evaluated. A description of the magnetic field and stellarator geometry is computed by VMEC, a magnetohydrodynamic optimizer, and GIST, which calculates drifts from curvature and shear, respectively. The stability of turbulence in the resulting simulation is analyzed by either solving an eigenvalue stability problem [1] or applying the GX gyrofluid turbulence simulation code. The efficiency and accuracy of these methods are discussed.