Edge-SOL Plasma Transport Simulation for the KSTAR

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## Edge-SOL Plasma Transport Simulation for the KSTAR

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**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**Contents**• Introduction to KTRAN • Simulation Results • Comparison between carbon and tungsten divertor. • Gas puffing effects • Validation with experimental results • Summary**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 >**Introduction of KTRAN**KTRAN* : Two-dimensional coupled edge transport code * Deok-Kyu Kim, Phys. Plasma, 12, 062504 (2005)**Governing Equations**Continuity Equation Parallel Momentum equation Perpendicular diffusion equation Electron Temperature Equation )+)= )+)=-+ )+)=-+**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**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**Computational parameters**• Computational Domain • Input Parameter SOL plasma Divertor < KSTAR baseline operation mode > ( 35 x 9 ) grid**Results of KTRAN**Carbon Tungsten [m-3] [m-3] Plasmadensity [eV] [eV] Plasma Temperature**Results of KTRAN**Carbon Tungsten [m-3] [m-3] Neutral density [eV] [eV] Neutral Temperature**Results of KTRAN**Carbon Tungsten Max :8.69e18 Max :1.5e18 [m-3] [m-3] Impurity density [W/m2] [W/m2] Power Radiation**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.**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.**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.**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.**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**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.**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.**Results of B2 code**• Ready to compare the KTRAN results with B2 and SOLPS.**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)**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.