High-beta extended MHD simulations of toroidal stellarators

The nonlinear, extended MHD code NIMROD is used to study high-beta, 3D magnetic topology evolution of a toroidal stellarator. The configurations under investigation derive from the geometry of the Compact Toroidal Hybrid (CTH) experiment. However, the vacuum rotational transform profile is artificially raised in an effort to examine the sensitivity of low order rational surfaces and/or magnetic islands. Finite beta plasmas are created using a heating source and anisotropic heat conduction in a manner similar to previous calculations of CTH where the effects of Ohmic current drive were simulated.\footnote{M. G. Schlutt et al, Nucl. Fusion 52, 103023 (2012).} The onset of MHD instabilities and nonlinear consequences are monitored as a function of beta as well as the fragility of the magnetic surfaces.