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

Nuclear Fushion

article

G.S. Xu¹  B.N. Wan¹  Y.F. Wang¹  X.Q. Wu¹  Xi Chen³  Y.-K. Martin Peng²  H.Y. Guo¹  K.H. Burrell³  A.M. Garofalo³  T.H. Osborne³  R.J. Groebner³  H.Q. Wang¹  R. Chen¹  N. Yan¹  L. Wang¹  S.Y. Ding¹  L.M. Shao¹  G.H. Hu¹  Y.L. Li¹  H. Lan¹  Q.Q. Yang¹  L. Chen¹  Y. Ye¹  J.C. Xu¹  J. Li¹ 

[1] Institute of Plasma Physics, Chinese Academy of Sciences;University of Science and Technology of China;General Atomics

关键词: E × B flow shear;    QH-mode;    EHO;    low-n kink/peeling mode;    DIII-D;   

DOI  :  10.1088/1741-4326/aa7975

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

A new model for the edge harmonic oscillations (EHOs) in the quiescent H-mode regime has been developed, which successfully reproduces the recent observations in the DIII-D tokamak. In particular, at highE    ×    Bflow shear only a few low- nkink modes remain unstable at the plasma edge, consistent with the EHO behavior, while at lowE    ×    Bflow shear, the unstable mode spectrum is significantly broadened, consistent with the low- nbroadband electromagnetic turbulence behavior. The model is based on a new mechanism for destabilizing low- nkink/peeling modes by theE    ×    Bflow shear, which underlies the EHOs, separately from the previously found Kelvin–Helmholtz drive. We find that the differential advection of mode vorticity by shearedE    ×    Bflows modifies the 2D 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 at the plasma edge where the magnetic shear is also strong. This destabilization is also shown to be independent of the sign of the flow shear, as observed experimentally, and has not been taken into account in previous pedestal linear stability analyses. Verification of the veracity of this EHO mechanism will require analysis of the nonlinear evolution of low- nkink/peeling modes so destabilized in the linear regime.

【 授权许可】

Unknown