Influence of magnetic configuration properties on kinetic ballooning modes in W7-X

The stability properties of kinetic ballooning modes are investigated for a number of magnetic configurations of the stellarator Wendelstein 7-X. In particular, we consider the effects of the vacuum rotational transform, ι, and the mirror ratio. The analysis sheds light on the interplay between global magnetohydrodynamic configuration properties and local gyrokinetic stability, and is instrumental in the design of high-β(the ratio of kinetic to magnetic pressure) operation scenarios. In particular, it is demonstrated that some Wendelstein 7-X magnetic configurations have a relatively low kinetic ballooning mode threshold.