Progress in DIII-D towards validating divertor power exhaust predictions

Jaervinen, A. E.; Allen, S. L.; Eldon, D.; Fenstermacher, M. E.; Groth, M.; Hill, D. N.; Lasnier, C. J.; Leonard, A. W.; McLean, A. G.; Moser, A. L.; Porter, G. D.; Rognlien, T. D.; Samuell, C. M.; Wang, H. Q.; Watkins, J. G.

doi:10.1088/1741-4326/ab7f5c

Progress in DIII-D towards validating divertor power exhaust predictions

Journal Article · Thu Mar 12 00:00:00 EDT 2020 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ab7f5c· OSTI ID:1615893

^[1]; Allen, S. L. ^[1]; Eldon, D. ^[2]; Fenstermacher, M. E. ^[1]; Groth, M. ^[3]; Hill, D. N. ^[2]; Lasnier, C. J. ^[1]; ^[2]; McLean, A. G. ^[1]; Moser, A. L. ^[2]; Porter, G. D. ^[1]; Rognlien, T. D. ^[1]; Samuell, C. M. ^[1]; Wang, H. Q. ^[2]; Watkins, J. G. ^[4]

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
General Atomics, San Diego, CA (United States)
Aalto Univ., Espoo (Finland)
Sandia National Lab. (SNL-CA), Livermore, CA (United States)

In this study, UEDGE simulations highlight the role of cross-field drifts on the onset of detached conditions, and new calibrated divertor vacuum ultra violet (VUV) spectroscopy is used to challenge the predictions of radiative constituents in these simulations. UEDGE simulations for DIII-D H-mode plasmas with the open divertor with the ion ∇B-drift towards the X-point show a bifurcated onset of the low field side (LFS) divertor detachment, consistent with experimentally observed step-like detachment onset (Jaervinen A.E. et al 2018 Phys. Rev. Lett. 121 075001). The divertor plasma in the simulations exhibits hysteresis in upstream separatrix density between attached and detached solution branches. Reducing the drift magnitude by a factor of 3 eliminates the step-like detachment onset in the simulations, confirming the strong role of drifts in the bifurcated detachment onset. When measured local plasma densities and temperatures are within proximity of predicted values in the simulations, there is no shortfall of the local emission of the dominant resonant radiating lines. However, the simulations systematically predict a factor of two lower total integrated radiated power than measured by the bolometer with the difference lost through radial heat flow out of the computational domain. Even though there is no shortfall in the emission of the dominant lines, a shortfall of total radiated power can be caused by underpredicted spatial extent of the radiation front, indicating a potential upstream or divertor transport physics origin for the radiation shortfall, or shortfall of radiated power in the spectrum between the dominant lines. In addition to the underpredicted spatial extent, in detached conditions, the simulations overpredict the peak radiation and dominant carbon lines near the X-point, which can be alleviated by manually increasing divertor diffusivity in the simulations, highlighting the ad hoc cross-field transport as one of the key limitations of the predictive capability of these divertor fluid codes.

View Accepted Manuscript (DOE)

Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: AC52-07NA27344; FC02-04ER54698; AC04-94AL85000

OSTI ID:: 1615893

Alternate ID(s):: OSTI ID: 1615126
OSTI ID: 1616298
OSTI ID: 1778066
OSTI ID: 22805979
OSTI ID: 23013609

Report Number(s):: LLNL-JRNL--780898; 975610

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 5 Vol. 60; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Detachment
Divertor
Drifts
Exhaust
Power
Radiation
UEDGE
VUV spectroscopy

Progress in DIII-D towards validating divertor power exhaust predictions

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