Particle fueling and exhaust in the Wendelstein 7-X island divertor

Author / Creator

Kremeyer, Thierry, author

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Online

Physical

Summary

A single-reservoir particle balance for the main species hydrogen has been established for Wendelstein 7-X (W7-X). This has enabled the quantitative characterization of the particle sources and sin...

A single-reservoir particle balance for the main species hydrogen has been established for Wendelstein 7-X (W7-X). This has enabled the quantitative characterization of the particle sources and sinks in the standard Island Divertor configuration for the first time. Findings from attached to first results for detached divertor scenarios after boronization are presented. Fueling efficiencies, flux balances and source locations were measured and used to infer the total particle confinement time. Perturbative gas injection experiments served to measure the effective particle confinement time [greek letter tau][subscript p][superscript *]. Combining both confinement times provides access to the overall recycling coefficient [R]. Hydrogen and helium particle inventories have been addressed and the knowledge of particle sources and sinks provides insight into the capability of the magnetic island size and shape to control exhaust features. The global particle balance revealed that no significant difference in the fueling efficiencies from up- and downstream gas fueling was found for H, and that overall the fueling efficiency of He was about 60 % higher. The recycling fluxes of the divertor and wall were found to govern the particle source. It was shown that in attached scenarios, 57 % of recycled particles came from the divertor, while the remainder of the overall recycling flux source was distributed between the baffle (9 %), heat shield (22 %) and steel panels (12 %). [greek letter tau][subscript p] values in the range of 100 - 120 ms, depending on the exact density, were extracted for these discharges. First assessment of detached divertor conditions shows that the fueled particle flux was fully balanced by the pumped flux with a constant wall source. The particle confinement time [greek letter tau][subscript p] doubled to levels of 250 ms for these discharges. This is a result of a decrease of the overall recycling flux at an increased density level in equilibrium between sources and sinks. Acknowledgements: This work was funded in part by the Department of Energy under grant DE-SC0014210.

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