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# The effects of edge magnetic structure on particle fueling and exhaust in the HSX and W7-X stellarators

## Publication Details Click to collapse Cite/Export

• Creator by Laurie A. Stephey
• Format Books
• Publication
• 2017
• Physical Details
• xix, 147 leaves : illustrations (some color) ; 29 cm
• OCLC on1085512855, on1101195707

## Summary

• In this study, both experimental and numerical techniques have been used to study particle behavior in response to changes in the edge magnetic field (i.e.~inserting and removing edge islands) at the Helically Symmetric eXperiment (HSX) and Wendelstein-7X (W7-X) stellarators. At HSX, the two magnetic configurations studied were the Edge-Islands and the No-Edge-Islands configurations. Measurements of the effective hydrogen particle confinement time, $\tau_{p,H}^*$, and the effective helium particle confinement time, $\tau_{p,He-II}^*$, were a factor of 1.5 and 1.6 longer, respectively, in the Edge-Islands configuration. A complete hydrogen particle balance yielded particle confinement times $\tau_{p,H}$ a factor of 1.3 longer in the Edge-Islands configuration. EMC3-EIRENE fueling efficiency calculations yielded values of 0.70 in the Edge-Islands configuration and 0.87 in the No-Edge-Islands configuration, a factor of 1.2 difference. At W7-X, the two magnetic configurations studied were the Increased Iota and the Standard configurations. Measurements of $\tau_{p,He-I}^*$ and $\tau_{p,He-II}^*$ were a factor of 1.5 and 1.2 longer, respectively, in the Increased Iota configuration. A complete hydrogen particle balance yielded values of $\tau_{p,H}$ that were approximately the same in both configurations. Similarly, EMC3-EIRENE fueling efficiency calculations yielded values approximately the same in both configurations. These results indicate that the edge magnetic structure can have a significant impact on the particle fueling and exhaust, but only if the change in edge structure is made in the ionization source region. In HSX, when the 8/7 island chain was inserted in the peak ionization source region in the Edge-Islands configuration, the 8/7 islands were able to decouple the plasma source from the confinement region through locally peaked temperatures at the island X-point (creating a private flux region in the same way that a divertor does). This led to reduced fueling efficiencies and increased global particle confinement times. For this same reason, moving the islands in W7-X did not result in major changes in particle fueling and exhaust, because the islands were not located in the ionization source region.