Heat Load Mitigation Studies in the W7 ‐X Stellarator Experiment

ABSTRACT During the experiments at the stellarator Wendelstein 7‐X (W7‐X) with fully water‐cooled plasma‐facing components (PFC), including carbon‐fiber composite (CFC) divertor targets with a thermal load capability of 10 MW/m 2 , high performance was achieved. However, weak design points have also been observed by increasing the heating power and discharge time. This primarily impacts the middle part of the divertor units, as well as some baffle and heat shield areas. These areas receive heat loads that exceed their specifications. The extent to which overloading specific components restricts plasma operation for different magnetic field configurations is shown, and the most critical areas are identified. The effects of using different operational actuators to improve the situation are discussed. However, substantial mitigation of excess heat loads under attached plasma conditions is only achievable through design changes to the divertor and baffle areas. Two different geometric modifications to the plasma‐facing surface (PFS) are proposed to help extend the operational range of the W7‐X with regard to higher heating power, while safeguarding the divertor components.