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

Journal Article · Tue Jul 18 00:00:00 EDT 2017 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/aa7975· OSTI ID:1437716

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.

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.

• Research Organization: General Atomics, San Diego, CA (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• Grant/Contract Number: FC02-04ER56498; 2013GB106000; 2015GB101000; 2013GB107000; FC02-04ER54698
• OSTI ID: 1437716
• Alternate ID(s): OSTI ID: 1406246
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Vol. 57 Journal Issue: 8; ISSN 0029-5515
• Publisher: IOP Publishing
• Country of Publication: IAEA
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
E x B flow shear
QH-mode
EHO
low-n kink/peeling mode
ELM control
DIII-D