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Title: E × B flow shear drive of the linear low- n modes of EHO in the QH-mode regime [ E × B flow shear drive of EHO in the QH-mode regime]

A new mechanism is identified for driving the edge harmonic oscillations (EHOs) in the quiescent H-mode (QH-mode) regime, where a strong E × B flow shear destabilizes low-n kink/peeling modes, separately from the previously found Kelvin-Helmholtz drive. We find that the differential advection of mode vorticity by sheared E × B flows modifies the two-dimensional pattern of mode electrostatic potential perpendicular to the magnetic field lines, which in turn causes a radial expansion of the mode structure, an increase of field line bending away from the mode rational surface, and a reduction of inertial stabilization. This enhances the kink drive as the parallel wavenumber increases significantly away from the rational surface where the magnetic shear is also strong. A newly developed model reproduces the observations that at high E × B flow shear only a few low-n modes remain unstable, consistent with the EHO behavior, while at low E × B flow shear the unstable mode spectrum is significantly broadened, consistent with the low-n broadband electromagnetic turbulence behavior observed recently in the DIII-D tokamak. This destabilization is also shown to be independent of the sign of the flow shear, as observed experimentally, and has not been taken into 2 /more » 46 account in previous pedestal linear stability analyses. Verification of the veracity of this EHO mechanism will require analysis of the nonlinear evolution of low-n kink/peeling modes so destabilized in the linear regime.« less
Authors:
 [1] ;  [2] ;  [1] ;  [2] ; ORCiD logo [3] ;  [4] ;  [5] ;  [3] ;  [3] ;  [3] ;  [3] ;  [5] ; ORCiD logo [2] ;  [2] ;  [2] ; ORCiD logo [2] ;  [2] ;  [2] ;  [2] ;  [2] more »;  [1] ; ORCiD logo [1] ;  [1] ;  [1] ;  [1] « less
  1. Chinese Academy of Sciences, Hefei (People's Republic of China); Univ. of Science and Technology of China, Hefei (People's Republic of China)
  2. Chinese Academy of Sciences, Hefei (People's Republic of China)
  3. General Atomics, San Diego, CA (United States)
  4. Univ. of Science and Technology of China, Hefei (People's Republic of China)
  5. Chinese Academy of Sciences, Hefei (People's Republic of China); General Atomics, San Diego, CA (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698; FC02-04ER56498; 2013GB106000; 2015GB101000; 2013GB107000
Type:
Published Article
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; E x B flow shear; QH-mode; EHO; low-n kink/peeling mode; ELM control; DIII-D
OSTI Identifier:
1437716
Alternate Identifier(s):
OSTI ID: 1406246

Xu, G. S., Wan, B. N., Wang, Y. F., Wu, X. Q., Chen, Xi, Martin Peng, Y. -K., Guo, H. Y., Burrell, K. H., Garofalo, A. M., Osborne, T. H., Groebner, R. J., Wang, H. Q., Chen, R., Yan, N., Wang, L., Ding, S. Y., Shao, L. M., Hu, G. H., Li, Y. L., Lan, H., Yang, Q. Q., Chen, L., Ye, Y., Xu, J. C., and Li, J.. E × B flow shear drive of the linear low-n modes of EHO in the QH-mode regime [E × B flow shear drive of EHO in the QH-mode regime]. United States: N. p., Web. doi:10.1088/1741-4326/aa7975.
Xu, G. S., Wan, B. N., Wang, Y. F., Wu, X. Q., Chen, Xi, Martin Peng, Y. -K., Guo, H. Y., Burrell, K. H., Garofalo, A. M., Osborne, T. H., Groebner, R. J., Wang, H. Q., Chen, R., Yan, N., Wang, L., Ding, S. Y., Shao, L. M., Hu, G. H., Li, Y. L., Lan, H., Yang, Q. Q., Chen, L., Ye, Y., Xu, J. C., & Li, J.. E × B flow shear drive of the linear low-n modes of EHO in the QH-mode regime [E × B flow shear drive of EHO in the QH-mode regime]. United States. doi:10.1088/1741-4326/aa7975.
Xu, G. S., Wan, B. N., Wang, Y. F., Wu, X. Q., Chen, Xi, Martin Peng, Y. -K., Guo, H. Y., Burrell, K. H., Garofalo, A. M., Osborne, T. H., Groebner, R. J., Wang, H. Q., Chen, R., Yan, N., Wang, L., Ding, S. Y., Shao, L. M., Hu, G. H., Li, Y. L., Lan, H., Yang, Q. Q., Chen, L., Ye, Y., Xu, J. C., and Li, J.. 2017. "E × B flow shear drive of the linear low-n modes of EHO in the QH-mode regime [E × B flow shear drive of EHO in the QH-mode regime]". United States. doi:10.1088/1741-4326/aa7975.
@article{osti_1437716,
title = {E × B flow shear drive of the linear low-n modes of EHO in the QH-mode regime [E × B flow shear drive of EHO in the QH-mode regime]},
author = {Xu, G. S. and Wan, B. N. and Wang, Y. F. and Wu, X. Q. and Chen, Xi and Martin Peng, Y. -K. and Guo, H. Y. and Burrell, K. H. and Garofalo, A. M. and Osborne, T. H. and Groebner, R. J. and Wang, H. Q. and Chen, R. and Yan, N. and Wang, L. and Ding, S. Y. and Shao, L. M. and Hu, G. H. and Li, Y. L. and Lan, H. and Yang, Q. Q. and Chen, L. and Ye, Y. and Xu, J. C. and Li, J.},
abstractNote = {A new mechanism is identified for driving the edge harmonic oscillations (EHOs) in the quiescent H-mode (QH-mode) regime, where a strong E × B flow shear destabilizes low-n kink/peeling modes, separately from the previously found Kelvin-Helmholtz drive. We find that the differential advection of mode vorticity by sheared E × B flows modifies the two-dimensional pattern of mode electrostatic potential perpendicular to the magnetic field lines, which in turn causes a radial expansion of the mode structure, an increase of field line bending away from the mode rational surface, and a reduction of inertial stabilization. This enhances the kink drive as the parallel wavenumber increases significantly away from the rational surface where the magnetic shear is also strong. A newly developed model reproduces the observations that at high E × B flow shear only a few low-n modes remain unstable, consistent with the EHO behavior, while at low E × B flow shear the unstable mode spectrum is significantly broadened, consistent with the low-n broadband electromagnetic turbulence behavior observed recently in the DIII-D tokamak. This destabilization is also shown to be independent of the sign of the flow shear, as observed experimentally, and has not been taken into 2 / 46 account in previous pedestal linear stability analyses. Verification of the veracity of this EHO mechanism will require analysis of the nonlinear evolution of low-n kink/peeling modes so destabilized in the linear regime.},
doi = {10.1088/1741-4326/aa7975},
journal = {Nuclear Fusion},
number = 8,
volume = 57,
place = {United States},
year = {2017},
month = {7}
}