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Author: Bin Chen
Requested Type: Pre-Selected Invited
Submitted: 2017-03-16 14:21:51

Co-authors: X.Q. Xu, T.Y. Xia, N.M. Li, M. Porkolab, E. Edlund, B. LaBombard, J. Terry, J.W. Hughes and M.Y. Ye

Contact Info:
Lawrence Livermore National Laboratory
7000 East Avenue
Livermore, California   94551
USA

Abstract Text:
The high confinement (H mode) regime is a highly desirable mode of operation in future fusion reactors. Significant progress has been made experimentally in recent years towards understanding ELM free operating conditions in the Enhanced Dα H-mode with unprecedented details. Work is presently proceeding with improved BOUT++ model to improve the understanding of the role of quasi-coherent modes in controlling edge transport, with self-consistent calculation of the electric field across the separatrix into the SOL.
For the C-Mod EDA H-mode discharges, the BOUT++ 6-field two-fluid nonlinear simulations show a reasonable agreement of turbulence and edge transport behavior: a) The simulated QCMs show consistent characteristics of the frequency versus poloidal wave number spectra of the electromagnetic fluctuations when compared with experimental measurements; b) The mode structures at the outer midplane and the radial mode frequency spectra of the nonlinear simulations show that the QCMs originate inside the separatrix, not in the SOL, and the saturated fluctuations have a radial location generally consistent with prior characterization from reflectometry; c) Linear spectrums analysis is consistent with the nonlinear phase relationship calculation which indicates the dominance of resistive-ballooning modes and drift-Alfven wave instabilities. Finally, based on the experimentally measured plasma density and temperature profiles inside the separatrix, the self-consistent electric field is calculated across the separatrix using plasma transport equations with the sheath potential in the SOL. With the self-consistent electric field, instead of force balanced electric field, the spectrum of broadband turbulence changed somewhat and typically the QCM frequency is reduced. The impact of electric field on the QCM and turbulent transport will be presented via a scan of electric field.

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