Design of a resilient divertor for HSX*

The Helically Symmetric eXperiment (HSX) is a quasi helically symmetric optimized stellarator at the University of Wisconsin-Madison. To allow higher heating powers, a divertor is required to avoid damage to the vessel wall. Ref. [1] has shown that HSX is suitable for a divertor which is resilient against changes in the magnetic field. This is interesting for future stellarators. Such a resilient divertor is characterized by a stochastic layer between the last closed flux surface (LCFS) and the plasma-facing components. In the current HSX design, there is no space to install such a divertor. Therefore, a complete makeover is proposed. First, a new vessel is designed. Starting from the LCFS, the wall is lofted outwards as much as the coils allow. Field line following with FLARE [2] is used to determine the strike point locations for different equilibria, and shows the resiliency of the strike point location. These locations are used as the initial divertor position and are the starting point of more advanced optimisation using EMC3-Lite [3] and EMC3-EIRENE [4]. 

[1] Bader, A., et al. Physics of Plasmas 24.3 (2017): 032506., [2] Frerichs, H., et al.  Bulletin of the American Physical Society (2015), [3] Feng, Y., et al. Plasma Physics and Controlled Fusion 64.12 (2022): 125012., [4] Feng, Y., et al. Contributions to Plasma Physics 54.4‐6 (2014): 426-431.