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Author: Nami Li
Requested Type: Poster
Submitted: 2017-03-16 17:44:26

Co-authors: X.Q. Xu, T.M. Wilks, B. Gui, X.T. Xiao, J.Z. Sun, D.Z. Wang

Contact Info:
Lawrence Livermore National Laboratory
5720 East Ave.
Livermore, CA   94550
USA

Abstract Text:
The transition from the L-mode to the improved H-mode confinement regime is often associated with an increased Er. Along with the L-H transition, changes in the edge Er are also correlated with changes in many edge phenomena such as rotation, transport, SOL and divertor heat flux width scaling, and the suppression of ELMs. Therefore, it is important to develop a self-consistent physical model for the Er and its influence on the plasma.
The steady state Er is self-consistently calculated by coupling the plasma transport and two-field model within the BOUT++ framework with sheath boundary conditions (SBC) on the divertor surface. Based on the experimentally measured plasma density, temperature, and flow profiles inside the separatrix, the effective particle and heat diffusivities can be determined from transport equation with sources from inner radial boundary. By extrapolating the transport coefficients into SOL, the self-consistent Er then can be calculated across the saparatrix with the sheath boundary conditions, along with the plasma density, temperature and parallel flow profiles in the SOL.
Based on this self-consistent calculation in the C-mod discharges, with a given SBC, the profiles of density and temperature are evolved in the SOL. With the evolved profiles, inside the separatrix, the Er is determined by the force balance with no net flow, while in the SOL, the thermal sheath potential is formed on the divertor plates, and it affects the electric field even far from the sheath region. A larger positive Er is formed in the SOL compared with no SBC. In the plasma edge, ion orbit loss and corresponding return currents determine the radial ion particle fluxes, which in turn provide torques that, in part, determine the rotation velocities and Er. So the intrinsic co-rotation caused by the ion orbit loss mechanism [1] is implemented in the parallel momentum transport equation. Its impact on the calculation of Er will be presented.

Comments:
[1] T. M. Wilks and W. M. Stacey, Phys. Plasmas 23, 122505 (2016)
*This work was performed under the auspices of the U.S. DoE by LLNL under Contract No. DE-AC52-07NA27344.