An overview of ideal MHD stability calculations for the Quasi-Poloidal Stellarator

An overview of the status of ideal MHD stability calculations for the Quasi-Poloidal Stellarator (QPS) is presented. The primary focus of these calculations has been infinite-$n$ ballooning modes using the COBRAVMEC code. Previously, it was shown that QPS is potentially susceptible to ballooning instabilities for $\left< \beta \right> > 2\%$ and that regions of second stability exist for $\left< \beta \right> > 4\%$ [A. S. Ware, {\it et al.}, Phys. Plasmas {\bf 11}, (2453)]. Recent calculations have examined the possibility of testing ballooning stability in QPS at lower plasma beta. An optimization is underway that targets degraded ballooning stability at $\left< \beta \right> \sim 1\%$ without degrading the neoclassical confinement propoerties. The results of this optimization will be presented. In addition to the infinite-$n$ calculations, previous work has been done on global, finite-$n$ calculations using the TERPSICHORE code. Here, we present a status report on initial attempts to apply both the TERPSICHORE and CAS3D codes to examine global ideal MHD stability for QPS plasmas.