Divertor leg control of a quasi-symmetry stellarator with external coils and its consequences for transport

A control method of the divertor configuration using external saddle loop coils is investigated for a quasi-symmetry stellarator device. Multiple coils are used to modify the divertor configuration while keeping the rotational transform distribution in the core region the same. The external coils successfully shrink the core plasma region and extend the divertor legs. From the transport analysis with the EMC3-EIRENE code, it is confirmed that the dependence of the electron temperature of the core plasma on the position of the plasma-facing walls is weakened by the extension of the divertor legs. The increase of the divertor particle flux and the increase of energy loss due to radiation and charge exchange processes are also confirmed.