April 15-17

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Author: Fatima Ebrahimi
Requested Type: Poster
Submitted: 2019-02-22 13:41:05

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Contact Info:
PPPL-Princeton University
C site T 152 Princeton Plasma
Princeton, NJ   08543
US

Abstract Text:
Magnetic reconnection is expected to be important during burst-like events in tokamaks, such as ELMs or transient vertical displacement events. [F. Ebrahimi Phys. Plasmas 24, 056119 (2017)] Time-evolving edge current sheets, which were first identified during nonlinear 3-D MHD NIMROD simulations [F. Ebrahimi Phys. Plasmas 23, 120705 (2016)], could become unstable on the poloidal Alfvenic time scale, and could break the axisymmetric current to form edge current-driven filaments. A self-consistent nonlinear MHD simulation showed current-carrying structures radially extend from the closed flux region to the region of open field lines in the SOL. We further investigate the stability of halo current and the formation of reconnecting edge peeling-driven filaments. First, we show that as the plasma is vertically displaced, edge halo current-sheet becomes MHD peeling-tearing unstable and forms non-axisymmetric coherent edge current filament structures. Similar to fast reconnection due to axisymmetric plasmoids [Ebrahimi, Raman, Phys. Rev. Lett. 114, 205003 (2015)], we find that the growth rate of these edge filamentary structures becomes independent of Lundquist number. Second, we investigate the maximum flux closure during transient CHI in the presence of non-axisymmetic 3-D magnetic fluctuations. We numerically examine two major effects 1) the role of three-dimensional magnetic fluctuations on the plasmoid-mediated flux closure and 2) the effect of toroidal field on the 3-D stability during transient CHI. Large-volume flux closure was obtained even in the presence of non-axisymmetric edge magnetic fluctuations. It was also found that the 3-D physics response is drastically different for simulations at higher toroidal field and complete stabilization of non-axisymmetic fluctuations were achieved at higher toroidal flux. Supported by DOE-SC0010565, DE-AC02-09CH11466.

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