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Description
Divertors are important for particle and heat removal in future stellarator power plants. Currently, three types of stellarator divertors are studied: the island divertor, the helical divertor, and the non-resonant divertor [1]. Where the island divertor and the helical divertor have been studied experimentally in W7-X and LHD, respectively, the non-resonant divertor has mainly been studied theoretically [2].
The non-resonant divertor (NRD) concept makes use of chaotic magnetic structures in the plasma edge. Modelling shows that NRDs are resilient across changes in plasma current and magnetic equilibrium in contrast to the resonant island structure which is typically used in the island divertor approach of the W7-X stellarator [1,3]. Recently, a particular magnetic field configuration in W7-X sharing properties of such a NRD configuration has been identified and experiments in this configuration have been performed. To mitigate coil stresses resulting from the high rotational transform of this configuration, only experiments at reduced magnetic field using purely NBI heating were possible. A first analysis indicates that there are similarities between observed strikelines with infrared cameras and predictions made by EMC3-Lite [4] (which uses an anisotropic heat diffusion model).
The use of NBI heating, however, causes some challenges. It can contribute to strikeline splitting through fast ion heat loads [5] which is not considered in the EMC3-Lite simulation. Furthermore, this NBI causes a steep density profile in the core leading to impurity accumulation. Consequently, the radiated power is dominated by core radiation.
To analyze how the heat and particle transport behaves in the case of edge radiation, EMC3-EIRENE [6] is used. Special attention is placed on grid quality to avoid artificial power leaking and on determination of anomalous transport parameters to obtain agreement between simulations and experiments. This study is a first step towards power and particle exhaust studies in non-resonant divertors.
[1] K.A. Garcia et al., Plasma Phys. Contr. Fusion 67, 035011 (2025)
[2] A.H. Boozer and A. Punjabi, Phys. Plasmas 25, 092505 (2018)
[3] K.A. Garcia et al., Nucl. Fusion 63 (12), 126043 (2023)
[4] Y. Feng, Plasma Phys. Contr. Fusion 64, 125012 (2022)
[5] M.J.H. Cornelissen et al., Plasma Phys. Contr. Fusion 64, 125015 (2022)
[6] Y. Feng, et al., Contr. Plasma Phys. 54, 426-431 (2014)