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In a significant step for nuclear fusion research, Florian Effenberg et al. have demonstrated the first effective use of impurity seeding for radiative power exhaust in the island divertor of the Wendelstein 7-X stellarator. Detailed in the journal Nuclear Fusion, the study presents the results of using neon (Ne) and nitrogen (N2) gases to achieve a controlled reduction of heat loads on the plasma-facing components.
Published with the citation (F. Effenberg et al 2019 Nucl. Fusion 59 106020, DOI 10.1088/1741-4326/ab32c4), the paper explains how seeding with Ne and N2 led to an 80% increase in radiative power losses and a two-thirds reduction in divertor heat loads. This was accomplished by injecting the gases into one of the stellarator’s five magnetic islands.
The study observed sustained edge radiation with Ne and a correlated response of line emission and plasma parameters to N2 puff duration. Furthermore, the seeding process was shown to dampen SOL flows, indicating a reduction in convective heat fluxes.
Significantly, the experimental results were compared with EMC3-EIRENE modeling for both Ne and N2 seeding scenarios. The models were used to predict the behavior of these gases in the plasma, and the close correlation between the predictions and the experimental results adds robustness to the findings.
The controlled experiment and its correlation with the predictive models indicate that impurity seeding can be a feasible strategy for managing the heat flux in the complex three-dimensional magnetic field structures of stellarators. Despite some loss in plasma energy and density, these effects were mitigated with controlled fueling, maintaining stable plasma conditions. This development is crucial for ensuring the longevity and stability of plasma-facing components in stellarator fusion reactors.
The paper has been published in Nuclear Fusion: F. Effenberg et al 2019 Nucl. Fusion 59 106020 DOI 10.1088/1741-4326/ab32c4
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