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

Abstract

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 conditionsmore » 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.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1512600
Alternate Identifier(s):
OSTI ID: 1464582
Report Number(s):
LLNL-JRNL-741509
Journal ID: ISSN 0031-9007; PRLTAO; 891209
Grant/Contract Number:  
AC52-07NA27344; FC02-04ER54698; 17-ERD-020
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 121; Journal Issue: 7; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

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., and Wang, H. Q. E×B Flux Driven Detachment Bifurcation in the DIII-D Tokamak. United States: N. p., 2018. Web. doi:10.1103/PhysRevLett.121.075001.
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. E×B Flux Driven Detachment Bifurcation in the DIII-D Tokamak. United States. doi:10.1103/PhysRevLett.121.075001.
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., and Wang, H. Q. Wed . "E×B Flux Driven Detachment Bifurcation in the DIII-D Tokamak". United States. doi:10.1103/PhysRevLett.121.075001. https://www.osti.gov/servlets/purl/1512600.
@article{osti_1512600,
title = {E×B Flux Driven Detachment Bifurcation in the DIII-D Tokamak},
author = {Jaervinen, A. E. and Allen, S. L. and Eldon, D. and Fenstermacher, M. E. and Groth, M. and Hill, D. N. and Leonard, A. W. and McLean, A. G. and Porter, G. D. and Rognlien, T. D. and Samuell, C. M. and Wang, H. Q.},
abstractNote = {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.},
doi = {10.1103/PhysRevLett.121.075001},
journal = {Physical Review Letters},
number = 7,
volume = 121,
place = {United States},
year = {2018},
month = {8}
}

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Works referenced in this record:

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    Works referencing / citing this record:

    First experimental tests of a new small angle slot divertor on DIII-D
    journal, July 2019