E×B Flux Driven Detachment Bifurcation in the DIII-D Tokamak

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

doi:10.1103/PhysRevLett.121.075001

Title: $E \times B$ Flux Driven Detachment Bifurcation in the DIII-D Tokamak

Journal Article · 31 July 2018 · Physical Review Letters

DOI: https://doi.org/10.1103/PhysRevLett.121.075001 · OSTI ID:1512600

Jaervinen, A. E. ^[1]; Allen, S. L. ^[1]; Eldon, D. ^[1]; Fenstermacher, M. E. ^[1]; Groth, M. ^[1]; Hill, D. N. ^[1]; Leonard, A. W. ^[1]; McLean, A. G. ^[1]; Porter, G. D. ^[1]; Rognlien, T. D. ^[1]; Samuell, C. M. ^[1]; Wang, H. Q. ^[1]

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

A bifurcative step transition from low-density, high-temperature, attached divertor conditions to high-density, low-temperature, detached divertor conditions is experimentally observed in DIII-D tokamak plasmas as density is increased. The step transition is only observed in the high confinement mode and only when the B × ∇B drift is directed towards the divertor. Here, this work reports for the first time a theoretical explanation and numerical simulations that qualitatively reproduce this bifurcation and its dependence on the toroidal field direction. According to the model, the bifurcation is primarily driven by the interdependence of the E × B -drift fluxes, divertor electric potential structure, and divertor conditions. In the attached conditions, strong potential gradients in the low field side (LFS) divertor drive E × B -drift flux towards the high field side divertor, reinforcing low density, high temperature conditions in the LFS divertor leg. At the onset of detachment, reduction in the potential gradients in the LFS divertor leg reduce the E × B -drift flux as well, such that the divertor plasma evolves nonlinearly to high density, strongly detached conditions. Experimental estimates of the E × B -drift fluxes, based on divertor Thomson scattering measurements, and their dependence on the divertor conditions are qualitatively consistent with the numerical predictions. Finally, the implications for divertor power exhaust and detachment control in the next step fusion devices are discussed.

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

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA)

Grant/Contract Number:: AC52-07NA27344

OSTI ID:: 1512600

Alternate ID(s):: OSTI ID: 1464582

Report Number(s):: LLNL-JRNL--741509; 891209

Journal Information:: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 7 Vol. 121; ISSN 0031-9007; ISSN PRLTAO

Publisher:: American Physical Society (APS)Copyright Statement

Country of Publication:: United States

Language:: English

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Thermionic Cooling of the Target Plasma to a Sub-eV Temperature Campanell, M. D.; Johnson, G. R. Physical Review Letters, Vol. 122, Issue 1 https://doi.org/10.1103/physrevlett.122.015003	journal	January 2019
DIII-D research towards establishing the scientific basis for future fusion reactors Petty, C. C. Nuclear Fusion, Vol. 59, Issue 11 https://doi.org/10.1088/1741-4326/ab024a	journal	June 2019
Neutral density estimation in the ASDEX upgrade divertor from deuterium emissivity measurements during detachment and shoulder formation Agostini, M.; Vianello, N.; Carraro, L. Plasma Physics and Controlled Fusion, Vol. 61, Issue 11 https://doi.org/10.1088/1361-6587/ab4122	journal	September 2019
Summary of the 27th IAEA Fusion Energy Conference in the categories of EX/W, EX/D, and ICC Ida, K. Nuclear Fusion, Vol. 59, Issue 11 https://doi.org/10.1088/1741-4326/ab3811	journal	September 2019
First experimental tests of a new small angle slot divertor on DIII-D Guo, H. Y.; Wang, H. Q.; Watkins, J. G. Nuclear Fusion, Vol. 59, Issue 8 https://doi.org/10.1088/1741-4326/ab26ee	journal	July 2019
Divertor detachment and asymmetry in H-mode operation with an ITER-like tungsten divertor in EAST Liu, J. B.; Wang, L.; Guo, H. Y. Nuclear Fusion, Vol. 59, Issue 12 https://doi.org/10.1088/1741-4326/ab4639	journal	October 2019

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