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Optimization of the snowflake divertor for power and particle exhaust on NSTX–U

Author(s): Vail, PJ; Izacard, O; Kolemen, Egemen

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Abstract: In this paper, simple analytical modeling and numerical simulations performed with the multi-fluid edge transport code UEDGE are used to identify optimal snowflake divertor (SFD) configurations for heat flux mitigation and sufficient cryopumping performance on the National Spherical Torus eXperiment Upgrade (NSTX–U). A model is presented that describes the partitioning of sheath-limited SOL power and particle exhaust in the SFD as a result of diffusive transport to multiple activated strike points. The model is validated against UEDGE predictions and used to analyze a database of 70 SFD-minus equilibria. The optimal location for the entrance to a divertor cryopumping system on NSTX–U is computed for enabling sufficient pumping performance with acceptable power loading in a variety of SFD-minus configurations. UEDGE simulations of one promising equilibrium from the database indicate that a significant redistribution of power to the divertor legs occurs as a result of neutral particle removal near one of the SFD-minus strike points in the outboard scrape-off layer. It is concluded that pump placement at the optimal location is advantageous as the large number of compatible equilibria reduces the precision required of real-time SFD configuration control systems and enables acceptable divertor solutions even if UEDGE-predicted power redistribution slightly reduces the achievable pumping performance.
Publication Date: 2019
Citation: Vail, PJ, Izacard, O, Kolemen, E. (2019). Optimization of the snowflake divertor for power and particle exhaust on NSTX–U. Nuclear Materials and Energy, 19 (516 - 523. doi:10.1016/j.nme.2019.03.003
DOI: doi:10.1016/j.nme.2019.03.003
Pages: 516 - 523
Type of Material: Journal Article
Journal/Proceeding Title: Nuclear Materials and Energy
Version: Final published version. This is an open access article.

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