Integrated Simulation Of Turbulence And Heat Flux On Tokamak Edge Plasma Based On BOUT++

The heat flux distributions on divertor targets are serious concerns for the steady-state operation of the future magnetic confinement fusion devices under High-confinement mode(H-mode).Where there exists a large amount of power that flows across the last closed flux surface and goes toward the divertor target,which leads to corrosion and damage on the divertor or other material surfaces.Recently,an international experimental effort on multi-machines to characterize scrape-off layer(SOL)width in H-mode discharges was carried out.This database yields a nearly linear inverse dependence of SOL width on plasma current.According to this scaling law,the SOL width of ITER would be less than 1 mm,which implies a much worse divertor condition for the fu-ture fusion reactors.It's crucial to reveal the main physical mechanisms that determine the SOL width from the theoretical side.Besides,a more reasonable physical model needs to be established to validate the scaling law obtained from the experiment.Then the SOL width of the future fusion devices can be predicted,which becomes more and more important in the field of fusion research.And it needs to be studied and solved in this paper.To achieve these goals,the electromagnetic turbulence model of BOUT++ will be used.Based on this model,the characteristics of turbulent transport are studied on the regions of pedestal and SOL.Based on the self-consistent turbulence simulations,the heat transport in the entire boundary region can be described more reasonably.In general,this research is divided into three parts:First of all,the radial electric field(Er)is self-consistently calculated by using the newly developed BOUT++ transport module;Then the characteristics of the edge turbulent transport in the C-Mod enhanced D?(EDA)H-mode discharges are explored based on the six-field two-fluid turbulence module with two kinds of different Er models;Finally,the discussion of the main physical mechanisms involving the quasi-coherent modes(QCMs)and the SOL width is given.In this paper,the turbulence fluid model is used to study the transport behavior in the tokamak edge plasma,which shows a reasonable agreement of simulation results with the experimental data.It's beneficial to improve the basic physical under-standing of the turbulent modes and the resulting heat transport:1)The simulation results of the C-Mod EDA H-mode discharges demonstrate that the QCMs are dominated by resistive-ballooning modes and drift-Alfven wave instabilities,and the coexistence with the broadband turbulence in the edge plasma.They are originated from peak gradients in the pedestal with the nature of blobby transport and resistive-ballooning mode type structure.Radially,the QCMs are oscillating around the Er minimum near the separatrix.Additionally,we find that the Te fluctuation across separatrix is enhanced by the magnetic flutter.It's generally consistent with measurement of the fluctuation level and the mode spectra from the simulations;2)Based on the success of simulation in getting the QCMs and broadband turbulence,we reproduced the divertor heat flux footprint measured by the IR camera.The inverse dependence of SOL width on the plasma current Ip is validated by the turbulence fluid simulations.In addition,the sensitivity studies of the heat flux width to different physical assumptions and effects are conducted together with the theoretical analysis,which indicates Er is one of the most important parameters setting the SOL width;3)In order to make a further under-standing of the underling physics determining the SOL width,the self-consistent Er is calculated from the plasma transport equations with the sheath potential across the entire poloidal cross section.Based on the Er scan,we find that the reduced radial electric field E,.leads to the enhanced radial SOL transport and larger heat flux width.The inverse dependence of SOL width on Ip is reproduced from the perspective of turbulence transport.The related results can be used to interpret the experimental boundary phenomena and to provide data of the boundary turbulent heat transport for the design of future fusion reactors.