Bootstrap current, magnetic islands and ballooning stability in W7-X

Computational modeling is used to calculate the expected bootstrap current in the Wendelstein 7-X stellarator and determine the impact of this current on the magnetic surfaces and ballooning stability. Pressure, density and temperature profiles have been selected to match the profiles anticipated in W7-X. Finite-$\beta$, free-boundary equilibria have been obtained with the VMEC code and analyzed for bootstrap current (BOOTSJ), ballooning stability (COBRAVMEC) and magnetic structure (SIESTA). The bootstrap current can impact the rotational transform profile and thus, the location of magnetic islands near the edge of W7-X. The possibility of controlling the rotational transform profile using planar coils is examined.