Vacuum Magnetic Field and Modular Coil System of the Advanced Stellarator Wendelstein VII-AS

The vacuum field and the modular coils of the Advanced Stellarator WENDELSTEIN VII-AS are described. Each of the five field periods contains 9 different twisted coils, one of them with increased dimensions and current to provide sufficient access for neutral beam injection. The standard configuration (8 = 3 T, rotational transform τ= 0.39, aspect ratio ξ 10, low shear, and magnetic well) can be varied by toroidal and vertical fields, or by changing independently the current in the special coils. From a study of magnetic field perturbations some estimates are derived for the admissible coil tolerances.