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Transport Simulation for the Scrape-Off Layer and Divertor Plasmas in KSTAR Tokamak

Transport Simulation for the Scrape-Off Layer and Divertor Plasmas in KSTAR Tokamak. S. S. Kim and S. W. Yoon National Fusion Research Center. Introduction.

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Transport Simulation for the Scrape-Off Layer and Divertor Plasmas in KSTAR Tokamak

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  1. Transport Simulation for the Scrape-Off Layer and Divertor Plasmas in KSTAR Tokamak S. S. Kim and S. W. Yoon National Fusion Research Center

  2. Introduction • The control of power and particle exhaust in tokamak edge region is one of the important issues in tokamak physics. The large power loss onto plasma-facing materials such as divertor is critical obstacle to the progress of tokamak toward a fusion reactor. • To resolve this problem, the edge plasma transport should be understood in advance because the heat removal on the divertor through dispersive loss mechanism such as recombination and radiation is mainly governed by the distributions of plasma density and temperature. • In this study, we investigate the characteristics of the edge plasma transport in KSTAR discharges by using B2.5 code, focusing on the effect of cross-field drifts on the plasma transport near the divertor. The drift is believed to affect significantly plasma performance, e.g. it leads to the edge turbulence reduction in the pedestal-gradient regions and causes asymmetries in the divertor plasmas. Our results emphasize the importance of drifts in divertor power dispersal and reduction.

  3. Governing equations Particle conservation: where Parallel momentum conservation: Charge conservation: where Energy conservation:

  4. Computational domain BT=3.5T

  5. Simulation conditions Case I : No drift is considered. Case II : Only diamagnetic drift is included. Case III : All drifts are switched on.

  6. 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 Total pressure Pa Case I Case II Case III

  7. 220 200 180 160 140 120 100 80 60 40 20 Electron temperature eV Case I Case II Case III

  8. 25 20 15 10 BT BT BT 5 0 -5 Electrostatic potential V Case II Case III Reversed field case

  9. 19 x 10 9 8 7 6 5 4 3 2 1 Plasma density /m3 Case I Case II Case III

  10. 19 x 10 9 8 7 6 5 4 3 2 1 Effect of cross-field drifts on density distribution /m3 Case III Case II

  11. Heat load to divertors

  12. Heat load to divertors

  13. Total heat load to divertors and wall

  14. Summary and Future Work • Two-dimensional simulations by using B2.5 code show that the cross-field drifts can affect significantly the edge plasma transport. The and ExB drifts disperse density distribution near the divertor, leading to the reduction of divertor heat load. • The effect of drifts on injected impurities will be investigated for the radiative divertor experiments which are planed for effective removal of heating power in KSTAR. • Parametric study on the drift effects will be carried out by changing transport coefficients.

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