Analysis of non-resonant divertor experiments with EMC3-EIRENE in W7-X and HSX

The non-resonant divertor (NRD) concept makes use of chaotic edge magnetic structures. It has been shown to be resilient across changes in plasma current in contrast to the resonant island structure which is typically used in the island divertor approach of the W7-X stellarator [1]. 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. It is shown that the observed strikelines agree with predictions with field line tracing. The heat and particle transport are analyzed with EMC3-EIRENE [2]. Special attention is placed on comparison of the neutral subdivertor pressures between island divertor and NRD scenarios, and on the radiation behavior of impurities in the plasma. These findings in W7-X are compared with modeling results of the HSX stellarator. Through this comparison, we examine the effects manifested from a quasi-isodynamic stellarator (W7-X) to a quasi-helically symmetric device (HSX) which tends to develop higher levels of bootstrap current.

[1] K.A. Garcia et al., Plasma Phys. Contr. Fusion 67, 035011 (2025)

[2] Y. Feng, et al., Contr. Plasma Phys. 54, 426-431 (2014)