Modeling of ExB effects on tungsten re-deposition and transport in the DIII-D divertor

Nichols, J. H.; Abrams, T.; Chrobak, C. P.; Donovan, D. C.; Duran, J. D.; Elder, J. D.; Rudakov, D. L.; Stangeby, P. C.; Unterberg, E. A.; Wampler, W. R.; Watkins, J. G.; Zamperini, S. A.

doi:10.1088/1741-4326/ac14e6

Title: Modeling of ExB effects on tungsten re-deposition and transport in the DIII-D divertor

Journal Article · Thu Aug 05 00:00:00 EDT 2021 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ac14e6· OSTI ID:1812359

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^[2];

^[3]; Donovan, D. C. ^[4]; Duran, J. D. ^[4]; Elder, J. D. ^[5];

^[6]; Stangeby, P. C. ^[5];

^[7];

^[8]; Watkins, J. G. ^[8]; Zamperini, S. A. ^[4]

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
General Atomics, La Jolla, CA (United States)
General Atomics, La Jolla, CA (United States); Commonwealth Fusion Systems, Cambridge, MA (United States)
Univ. of Tennessee, Knoxville, TN (United States)
Univ. of Toronto, ON (Canada)
Univ. of California - San Diego, La Jolla, CA (United States)
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Mixed-material DIVIMP-WallDYN modelling, now incorporating ExB drifts, is presented that simultaneously reproduces tungsten (W) erosion and deposition patterns observed during the DIII-D Metal Rings Campaign, in which a toroidally symmetric set of W-coated tiles were installed in the carbon (C) DIII-D divertor. Since most reactor plasma facing component (PFC) designs call for mixed-material environments, including ITER’s W/Be enviroment, the divertor targets will quickly evolve into reconstitued surfaces of multiple elements. This work identifies controlling physics that affects material migration patterns in the divertor, which impact PFC lifetimes and impurity leakage from the divertor to the core. These simulations indicate that radial and poloidal ExB transport dominates over parallel force balance for high-Z impurities such as W in the divertor region of DIII-D. It is demonstrated that ExB drifts are required to reproduce the experimental observation of non-local W and C co-accumulation in a band ~7-9 cm outboard of the outer-strike-point (OSP) W source, for attached Lmode conditions in the unfavorable ion grad-B drift direction. In addition, W gross erosion is localized to the region outboard of the OSP, as the formation of C co-deposits suppresses W erosion at the strike point. Time-dependent simulations with scaled ExB impurity drifts (60% of the OEDGE-calculated drift velocity) and W re-erosion quantitatively reproduce these features, including depth-resolved W/C ratios, within a factor of 2 over ~115 seconds of accumulated plasma exposure. The location of co-deposition regions is shown to be well represented by an analytic leakage model, driven largely by poloidal ExB drifts. Qualitative agreement is also found between campaign-integrated W deposition measurements and simulations for the favorable ion grad-B drift direction, the standard mode of operation for most tokamaks. Furthermore, these results imply that a longterm inward radial migration of material from the outer divertor through the private flux region may occur in future devices.

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Research Organization:: General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Organization:: USDOE Office of Science (SC)

Grant/Contract Number:: FC02-04ER54698; AC05-00OR22725; SC0016318; SC0019256; FG02-07ER54917; NA0003525

OSTI ID:: 1812359

Alternate ID(s):: OSTI ID: 1837857

Journal Information:: Nuclear Fusion, Vol. 61, Issue 9; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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