Error field impact on mode locking and divertor heat flux in NSTX-U

Journal Article · 25 June 2019 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ab22c4 · OSTI ID:1529148

Ferraro, N. M.  ^[1]; Park, J. -K.  ^[1]; Myers, C. E.  ^[2]; Brooks, A. ^[1]; Gerhardt, S. P.  ^[1]; Menard, J. E.  ^[1]; Munaretto, S.  ^[3]; Reinke, M. L.  ^[4]

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1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
3. General Atomics, San Diego, CA (United States)
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

During the 2016 NSTX-U experimental campaign, locked modes in the plasma edge presented clear evidence of the presence of error fields. Extensive metrology and plasma response modeling with IPEC and M3D-C1 have been conducted to understand the various sources of error fields in NSTX-U as built in 2016, and to determine which of these sources have the greatest effect on the plasma. In particular, modeling finds that the error field from misalignment of the toroidal field (TF) coils may have a significant effect on the plasma. The response to the TF error field is shown to depend on the presence of a q = 1 surface, in qualitative agreement with experimental observations. It is found that certain characteristics of the TF error field present new challenges for error field correction. Specifically, the error field spectrum differs significantly from that of coils on the low-field side (such as the NSTX-U error field correction coils), and does not resonate strongly with the dominant kink mode, thus potentially requiring a multi-mode correction. Moreover, to mitigate heat fluxes using poloidal flux expansion, the pitch angle at the divertor plates must be small (~1°). It is shown that uncorrected error fields may result in potentially significant local perturbation to the pitch angle. Estimates for coil alignment tolerances in NSTX-U are derived based on consideration of both heat flux and core resonant fields independently.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
• Grant/Contract Number: AC04-94AL85000; AC02-09CH11466; AC05-00OR22725; SC0012706; FC02-04ER54698
• OSTI ID: 1529148
• Alternate ID(s): OSTI ID: 1532736; OSTI ID: 22808023; OSTI ID: 1594315; OSTI ID: 22929849
• Report Number(s): SAND--2019-2558J; 673251
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 8 Vol. 59; ISSN 0029-5515
• Publisher: IOP ScienceCopyright Statement
• Country of Publication: United States
• Language: English