skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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]

Abstract

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:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1406246
Grant/Contract Number:
FC02-04ER54698
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
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

Citation Formats

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., 2017. 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. https://www.osti.gov/servlets/purl/1406246.
@article{osti_1406246,
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
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • The semicollisional layer equations governing the linear stability of small mode number tearing modes in a low beta, large aspect ratio, tokamak equilibrium are derived from an expansion of the gyrokinetic equation. In this analysis only the cases where the ion Larmor radius is either much less than, or much greater than, the layer width are considered. Both the electrons and the ions are assumed to lie in the banana collisionality regime. One interesting feature of the derived layer equations, in the limit of small ion Larmor radius, is a substantial reduction in the effective collisionality of the system duemore » to neoclassical ion dynamics. Next, using a shooting code, a dispersion relation is obtained from the layer equations in the limits of small ion Larmor radius and a vanishingly small fraction of trapped particles. As expected, strong semicollisional stabilization of the mode is found, but, in addition, a somewhat weaker destabilizing effect is obtained in the transition region between the collisional and semicollisional regimes.« less
  • The close relationship between the locked mode (LM) and pulsed poloidal current drive (PPCD) regime in a reversed-field pinch device is described. If the modes lock close to the shell gap then the LM is enhanced and there is a high probability that the PPCD will not improve plasma performance. The physical reason will be discussed. If the position of the locked mode is far from the shell gap then the PPCD is effective with a high probability. LM energy is reduced and the more the LM energy decreases, the better the plasma performance.
  • The nonlinear growth for the m/ngreater than or equal to2 resistive tearing mode is studied in the case when the rational surface q(r/sub 0/) = m/n falls in a regime of weak magnetic shear, q'(r/sub 0/)approx. =0. The island width is determined self-consistently from the nonlinear, zero-helicity component of the perturbed magnetic flux that provides the local shear. It is found that the magnetic perturbation keeps growing exponentially in the nonlinear regime on a hybrid resistive-Alfvenic time scale, while the island width and the vorticity grow on a much slower time scale. Accordingly, much faster release of magnetic energy resultsmore » for modes growing near minima of hollow q profiles.« less
  • The effect of a subsonic toroidal flow on the linear magnetohydrodynamic stability of a tokamak plasma surrounded by an external resistive wall is studied. A complex non-self-adjoint eigenvalue problem for the stability of general kink and tearing modes is formulated, solved numerically, and applied to high {beta} tokamaks. Results indicate that toroidal plasma flow, in conjunction with dissipation in the plasma, can open a window of stability for the position of the external wall. In this window, stable plasma beta values can significantly exceed those predicted by the Troyon scaling law with no wall. Computations utilizing experimental data indicate goodmore » agreement with observations.« less
  • A single parameter has been developed that predicts the highly nonlinear state of a microgravity flow with a confidence of up to 95% in differentiating slug flow from other regimes for different fluids of radically different properties such as air/water and Freon-11, -12, and -114. The authors have also shown that by taking the best data available based on current knowledge, it was possible to predict the flow regime in experiments with an accuracy of at least 85%, whether the flow was slug or bubbly, slug/annular and annular flow.