Edge-SOL Plasma Transport Simulation for the KSTAR

1. The 6th Japan-Korea Workshop on Theory and Simulation of Magnetic Fusion Plasmas 28~29 July 2011 Edge-SOL Plasma Transport Simulation for the KSTAR Seung Bo Shima, Jin-Woo Parkb, HyunsunHanc, Hae June Leea, Yong-Su Nab, Jin Yong Kimc aPusan National University, Busan, Korea bSeoul National University, Seoul, Korea cNational Fusion Research Institute, Daejon, Korea

2. Contents • Introduction to KTRAN • Simulation Results • Comparison between carbon and tungsten divertor. • Gas puffing effects • Validation with experimental results • Summary

3. Advent of KTRAN • Steady state two-dimensional coupled transport code for plasma, neutral and impurity particles • Consists of three major modules that calculate plasma, neutral and impurity transports, respectively • Self-consistent description in transport phenomena in the edge region • Atomic interactions included • (ionization, charge-exchange, recombination, elastic collision) • Realistic wall configuration adaptable • Empirical formula for surface reflection and reaction rate coefficients < Schematic diagram of a lower half of the edge region of a D-shaped tokamak >

4. Introduction of KTRAN KTRAN* : Two-dimensional coupled edge transport code * Deok-Kyu Kim, Phys. Plasma, 12, 062504 (2005)

5. Governing Equations Continuity Equation Parallel Momentum equation Perpendicular diffusion equation Electron Temperature Equation )+)= )+)=-+ )+)=-+

6. Impurity data for Carbon Radiation rate coefficient of carbon depending on the electron temperature. Reflection rate coefficients of deuterium ion incident on the carbon target . Physical sputtering yields by the impact of deuterium and carbon on the graphite target . Rate coefficients of electron impact ionization of carbon in variousionization Rate coefficients of radiative recombination of carbon in various ionization

7. Impurity data for Tungsten Radiation rate coefficient of tungsten depending on the electron temperature. Reflection rate coefficients of deuterium ion incident on the tungsten target . Physical sputtering yields by the impact of deuterium and tungsten on the tungsten target . Rate coefficients of electron impact ionization of tungsten in variousionization Rate coefficients of radiative recombination of tungsten in various ionization

8. Computational parameters • Computational Domain • Input Parameter SOL plasma Divertor < KSTAR baseline operation mode > ( 35 x 9 ) grid

9. Results of KTRAN Carbon Tungsten [m-3] [m-3] Plasmadensity [eV] [eV] Plasma Temperature

10. Results of KTRAN Carbon Tungsten [m-3] [m-3] Neutral density [eV] [eV] Neutral Temperature

11. Results of KTRAN Carbon Tungsten Max :8.69e18 Max :1.5e18 [m-3] [m-3] Impurity density [W/m2] [W/m2] Power Radiation

12. Heat flux on the divertor Carbon Tungsten • Heat flux on the tungsten divertor decreased slightly compared with carbon divertor.. • As input power increased, increase of Heat flux on the carbon divertor is bigger than tungsten divertor.

13. Reduction of Heat Flux by Gas Puffing • Puffing gas: Deuterium and Argon • Puffing gas energy: Maxwellian distribution at thermal energy (0.026eV) D Ar Puffing Puffing • Argon gases are transported by friction and thermal gradient force. • Deuterium gases are transported by collision with other particles and finally ionized or leaked out.

14. Reduction of Heat Flux by Gas Puffing • Deuterium puffing • Argon puffing • Considerable reduction of peak heat flux at the divertor target plates was found to occur when the both gas puffing rate exceeds a certain threshold value • (~ 1.0 x 1020 /s for deuterium and ~ 5.0 x 1018 /s for argon). • As puffing gas flux density increases, heat flux is reduced and the location of peak heat flux point moves outward.

15. Transition of Carbon Impurity Distribution No puffing 6.4 x 1020 /s The amount of carbon density is decreased as deuterium gas is increased. When the puffing rate is reached 6.4 x 1020 /s, the peak heat flux is about 5 MW/m2 (engineering limit), carbon peak density is lowered by 25 % compared to the one without puffing. The decreased carbon impurity in SOL and divertor region will be expected to enhance the performance of steady state operation.

16. Simulation Conditions for NSTX • Computational Domain • Input Parameter and assumption <NSTX shot 128797, 543 ms> * B.J.Lee et al.,FusionSci.Technol.. 37,110, 2000 ( 31 x 17 ) grid

17. Computational Results for NSTX Plasma Density Neutral Density Plasma Temperature Neutral Temperature • Plasma density is accumulated in front of the divertor target due to the neutral-plasma recycling effect. Resulting mainly from charge-exchange reaction with the background plasma, neutrals could have high energy about 160 eV.

18. Electron Density Profile at Midplane • For the density at separatrix, • nsep = 6.79 x 1018 m-3, is set by interpolation between the diagnostic points. : Error bar • With D⊥ = 1 m2/s, ce,⊥ = 1 m2/s, • it agrees well with the experimental one.

19. Results of B2 code • Ready to compare the KTRAN results with B2 and SOLPS.

20. Comparison with SOLPS Electron Temperature Tungsten density Plasma density M.Toma et al.”First steps towards the coupling of the IMPGYRO and SOLPS Codes to Analyze Tokamak Plasmas with Tungsten Impurities”, contrib. plasma phys. 50,392(2010)

21. Summary • The 2-D modeling of SOL and divertorregion in KSTAR is performed with the KTRAN code. • In case of tungsten divertor, plasma and impurity density lowered than carbon divertor. But, power radiation increased which emitted from impurity. • As the puffing gas flux density increases more thana certain value (~ 1.0 x 1020 /s for deuterium and ~ 5.0 x 1018 /s for argon), peak heat flux is significantly reduced and the location of the peak heat flux moves outward from the strike point. • The density profile and peak heat flux of NSTX experiments is well-reproduced. • I plan to compare the KTRAN result with B2 and SOLPS.