1. Conference on Computational Physics 30 August 2006 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. Conference on Computational Physics 30 August 2006  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. Introduction

3. Conference on Computational Physics 30 August 2006 Particle conservation: Parallel momentum conservation: Charge conservation: where Energy conservation: where Governing equations

4. Conference on Computational Physics 30 August 2006 Computational domain B T =3.5T

5. Conference on Computational Physics 30 August 2006 Case I : No drift is considered. Case II : Only diamagnetic drift is included. Case III : All drifts are switched on. Simulation conditions

6. Conference on Computational Physics 30 August 2006 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 Total pressure Case ICase IICase III Pa

7. Conference on Computational Physics 30 August 2006 20 40 60 80 100 120 140 160 180 200 220 Electron temperature Case ICase IICase III eV

8. Conference on Computational Physics 30 August 2006 BTBT -5 0 5 10 15 2020 25 BTBT BTBT Electrostatic potential Case IICase IIIReversed field case V

9. Conference on Computational Physics 30 August 2006 1 2 3 4 5 6 7 8 9 x 10 19 /m 3 Plasma density Case ICase IICase III

10. Conference on Computational Physics 30 August 2006 Case II Case III Effect of cross-field drifts on density distribution 1 2 3 4 5 6 7 8 9 x 10 19 /m 3

11. Conference on Computational Physics 30 August 2006 Heat load to divertors

12. Conference on Computational Physics 30 August 2006 Heat load to divertors

13. Conference on Computational Physics 30 August 2006 Total heat load to divertors and wall

14. Conference on Computational Physics 30 August 2006 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.