1 Development of integrated SOL/Divertor code and simulation study in JT-60U/JT-60SA tokamaks H. Kawashima, K. Shimizu, T. Takizuka Japan Atomic Energy Agency Workshop on Edge Transport in Fusion Plasmas, September, Kraków, Poland

2 Contents 1. Introduction 2. Development of integrated SOL/divertor code in JAEA 3. Simulation results 3.1Carbon impurity transport simulation at Xp MARFE on JT- 60U with SOLDOR/NEUT2D/IMPMC code 3.2 Study of divertor pumping for JT-60SA divertor designing with SOLDOR/NEUT2D code 3.3 ELM simulation with PARASOL code 4. Summary

3 ● On the contrary, numerical simulation including A&M processes and PWI effects is essential to predict the SOL/divertor plasmas.  SOLPS5.0(B2.5), UEDGE, EDGE2D, etc Prediction of burning plasmas through “scaling law” and the “non-dimensional experiment” are effective for the core plasma transport. ●SOL/Div. code (SOLDOR/NEUT2D/ IMPMC/PARASOL) has been developed in JAEA. ● Simulations are carried out on the JT- 60U experiments and the JT-60SA divertor designing. 1. Introduction

4 o 2. Development of integrated SOL/Divertor code in JAEA [1] Plasma 2D fluid codeSOLDOR Neutral MC codeNEUT2D ImpurityMC codeIMPMC Particle simulation codePARASOL Investigation of basic physics Analysis  Prediction [1] H. Kawashima, K. Shimizu, T. Takizuka et al., Plasma and Fusion Research 1 (2006) 031.

5 High-resolution oscillation-free scheme in solving fluid equations. Using fine meshes around the divertor targets (≤2 mm). Monte Carlo noise is reduced by the “piling method ” (efficient time average). NEUT2D is optimized on the massive parallel computer SGI ALTIX  Resulting, the steady-state solution can be obtained for 3~4 hours. SOLDOR and NEUT2D codes have been successfully combined. Example of JT-60U meshes

6 Impurity modeling Application of the simplified radiation model (non-coronal model) [3] for fast calculation.  W rad = n e n z L z (T e )  n c / n e = 1~2 % [2] K. Shimizu, T. Takizuka, H. Kawashima, 17 th PSI, 2006; to be published in J. Nucl. Mater. [3] D.E. Post, J. Nucl. Mater (1995) 143. Coupled with MC modeling code IMPMC to treat the impurity A&M process self- consistently by introducing the “new diffusion model” [2]. They can be optionally combined with SOLDOR/NEUT2D code.

7 To verify and establish various physics models (boundary condition, heat conductivity, etc.) applied in fluid plasma simulation, a kinetic approach by particle simulation is required to examine the validity of such physics models.  PARASOL Code An advanced particle simulation code PARASOL (PARticle Advanced simulation for SOL and divertor plasmas) was developed. Motion of charged particles and self- consistent electric field are calculated by the PIC method. Coulomb collisions are simulated by a binary collision model.

8 By PARASOL code, ⑥ Transient behavior of SOL/divertor plasmas after an ELM crash [6,7] ⑦ Asymmetric SOL flow [8] etc. By SOLDOR/NEUT2D/IMPMC(or simple radiation model) code, SOL/divertor simulations at JT-60U experiments ① Analysis of carbon transport at Xp-MARFE [2] ② Characterization of divertor pumping with wall saturation condition [4] ③ Evaluation of geometric effect to improve heat & particle controllability [4] Design study of JT-60SA divertor ④ Study of divertor pumping for effective heat & particle control [1,5] ⑤ Evaluation of heat & particle controllability on two kinds of plasma/divertor configurations [5] Present status of simulation study using the codes [4] H. Kawashima, K. Shimizu, T. Takizuka, et al., 17 th PSI, 2006; to be published in J. Nucl. Mater. [5] H. Kawashima, S. Sakurai, K. Shimizu, et al., Fusion Eng. Des. 81 (2006) [6] T. Takizuka, M. Hosokawa, Contrib. Plasma Phys. 46 (2006) 222. [7] T. Takizuka, M. Hosokawa, 6th Int. Conf. Open Magnetic Systems for Plasma Confinement, 2006, Tsukuba; to be published in Trans. Fusion Sci. Tech. [8] T.Takizuka, M.Hosokawa, K.Shimizu, J.Nucl.Mater (2003) 1331.

9 3.1 Carbon impurity transport simulation at Xp MARFE on JT-60U with SOLDOR/NEUT2D/IMPMC code Attach DetachXp MARFE Divertor detachment is effective for reduction of target heat loads. Core confinement is degraded with generation of Xp MARFE. Carbon impurity transport at Xp MARFE is analyzed by the simulation. [9] S.Konoshima, et al., J.Nucl.Mater (2003) D radiation profiles W rad (MW/m 3 ) Experiment [9]

10 Input parameters Total loss powerQ total = 4 MW Ion flux (r/a=0.95)  ion = 0.25 x10 22 s -1 Gas puff  puff = 0  0.8 x10 22 s -1 Pumping speed S pump = 26 m 3 /s Heat/particle diffusion coefficients  e =  i =1 m 2 /s 、 D = 0.25 m 2 /s C impurity D imp = 1 m 2 /s W rad (MW/m 3 ) Transition to Xp MARFE can be reproduced by increasing the gas puffing (  puff = 0  0.8 x10 22 s -1 ). Attach Detach Xp MARFE Simulation with SOLDOR/NEUT2D/IMPMC code  puff = 0  s -1  puff =0.8 x10 22 s -1

11 Ionization point of carbon The ionization of carbon dissociated from CD4 sputtered by neutrals from the private wall takes place near the X-point due to low electron temperature of ~ 1 eV in the private region. Such carbons cause the high radiation power (≥ 5 MW/m 3 ) near the X-point. Attach Xp MARFE C C C C+C+ These are cleared by applying the MC method and fine mesh in the integration code.

12 JT-60SA:Modification program of JT-60U to establish high  steady-state operation in collisionless regime. Pumping capability in JT-60SA, which is important for particle control at long pulse operation, is evaluated using the SOLDOR/ NEUT2D code with simple radiation model. 3.2 Study of divertor pumping for JT-60SA divertor designing with SOLDOR/NEUT2D code JT-60SA (Super Advanced)

13 E ff ects of slot width and strike point on pumping efficiency Pumping efficiency  pump is evaluated by  narrowing the exhaust slot width (d in, d out ) from 20 to 5 cm by three steps  changing the strike point distance (L in, L out ) from 3 to16 cm by four steps Pumping efficiency  pump is defined as ration of pumping flux to generated flux on the target ;  pump   pump /  d =(  g /  d )  (1-  bf /  g ), where  pump =  g -  bf （ steady state ） Input parameters  ion =1.0 x10 22 s -1  Q total =12 MW  puff = 0 ~ 3.0 x10 22 s -1  S pump = 20 ~ 200 m 3 /s  D = 0.3 m 2 /s,  e =  I = 1 m 2 /s  C imp =1%  d : generated neutral flux at divertor target  g : neutral flux into exhaust chamber through slots  bf : neutral back-flow from the chamber to plasma side  pump : pumping flux (=  g -  bf )

14 Pumping efficiency   increases with small slot width d in/out and large slot view angle  in/out. Increment of  in with decreasing L in/out enhances the incident flux ratio  g /  d and increases the  pump. An approach to effective divertor pumping can be obtained by the parameter survey using the code mobility to advantage. Backflow rate  bf /  g is reduced by narrowing the slot width, resulting the   is increased. Inner divertor S pump =100 m 3 /s outer divertor

ELM simulaton with PARASOL code Transient behavior of SOL/divertor plasmas after an ELM crash 1D SOL/divertor Plasmas & ELM model Uniform B with pitch B x /B=0.2. Recycling rate R  is chosen 0~0.9 in regions L c. Collisionality L // /I mfp0 is chosen 1~50. ELM crash supplies a large number of hotter particles (N ELM =10 5 ) in a short period (  ELM =10 3  t <<  // ~10 5  t). T eELM =2T e0, T iELM =T eELM /2=2T i0. Parameters for stationary phase N i0 =10 5, T i0 /T e0 =1/2, T ec /T e0 =T ic /T i0 =0.1, L s =0.2L, L c =0.2L

16 An ELM event is distinguished the fast time scale related to the electron transit time  //e =L // /2v e and the slow time scale related to the sound-speed transit time  // =L // /2C s. Fast heat transport is affected by collisions. (Not suffered by recycling) Slow behaviour is affected by recycling. (Insensitive to collisions) Characteristics of heat flux to target plate after an ELM crash These are obtained by the particle simulation through the kinetic approach.

17 Self-consistent simulation of neutral or impurity transport by MC method with combination of plasma fluid code. Fast calculation using the massive parallel computer. Plasma fluid modeling is supported by the particle simulation code. 4. Summary  Integrated SOL/Divertor code is developed originally.  Simulation studies are progressed.  Transport of chemical sputtered carbon at the JT-60U Xp MARFE.  Divertor pumping in the design study of JT-60SA divertor.  Transient behavior of after an ELM crash by 1D particle model.  etc.  Future plan  Application of SONIC to the future device such as ITER