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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, 11-13 September, Kraków, Poland

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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

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●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

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o

2. Development of integrated SOL/Divertor code in JAEA[1]

Plasma 2D fluid code SOLDOR Neutral MC code NEUT2D ImpurityMC code IMPMC Particle simulation code PARASOL Investigation of

basic physics

AnalysisPrediction

[1] H. Kawashima, K. Shimizu, T. Takizuka et al., Plasma and Fusion Research 1 (2006) 031.

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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 3900.

Resulting, the steady-state solution can be obtained for 3~4 hours.

SOLDOR and NEUT2D codes have been successfully combined.

2.5 3.0 3.5 4.0 4.5R (m)

-1.0

0.0

1.0

2.5 3.0 3.5 4.0 4.5

-1.0

0.0

1.0

Nj=120

Exhaustchamber

x10

Ni=37(r/a=0.95)

Example of JT-60U meshes

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Impurity modeling

Application of the simplified radiation model (non-coronal model) [3] for fast calculation.

　 Wrad = ne nz Lz(Te)

　 nc / ne = 1~2 %

[2] K. Shimizu, T. Takizuka, H. Kawashima, 17th PSI, 2006; to be published in J. Nucl. Mater.

[3] D.E. Post, J. Nucl. Mater. 220-222 (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.

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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.

v//

fe

diffusion to high energy

divertor plate

x

Importance of collisions

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By PARASOL code,⑥Transient behavior of SOL/divertor plasmas after an ELM crash[6,7]

⑦Asymmetric SOL flow [8]

etc.

By SOLDOR/NEUT2D/IMPMC(or simple radiation model) code, SOL/divertor simulations at JT-60U experiments

①Analysis of carbon transport at Xp-MARFE[2]

Characterization of divertor pumping with wall saturation condition[4] Evaluation of geometric effect to improve heat & particle

controllability[4]

Design study of JT-60SA divertor

①Study of divertor pumping for effective heat & particle control[1,5]

②Evaluation 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., 17th PSI, 2006; to be published in J. Nucl. Mater.[5] H. Kawashima, S. Sakurai, K. Shimizu, et al., Fusion Eng. Des. 81 (2006) 1613.[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. 313-316 (2003) 1331.

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3.1 Carbon impurity transport simulation at Xp MARFE on JT-60U with SOLDOR/NEUT2D/IMPMC code

Attach Detach Xp 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.313-316 (2003) 888..

2D radiation profilesWrad

(MW/m3)

Experiment [9]

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　　 Input parameters•Total loss power Qtotal = 4 MW Ion flux• (r/a=0.95) ion = 0.25 x1022s-1

•Gas puff puff = 00.8 x1022s-1 Pumping speed• Spump = 26 m3/s•Heat/particle diffusion coefficients e = i =1 m2/s 、 D = 0.25 m2/s•C impurity Dimp = 1 m2/s

Wrad (MW/m3)

Transition to Xp MARFE can be reproduced by increasing the gas puffing (puff = 00.8 x1022s-1).

Attach Detach Xp MARFE

Simulation with SOLDOR/NEUT2D/IMPMC code

puff = 0s-1 puff =0.8 x1022s-1

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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/m3) near the X-point.

2.8 2.9 3 3.1 3.2 3.3 3.4

R (m)

D chemical wxdr_54

Attach2.8 2.9 3 3.1 3.2 3.3 3.4

R (m)

D chemical wxdr_53

Xp MARFE

CC

C

C+

These are cleared by applying the MC method and fine mesh in the integration code.

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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)

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Effects of slot width and strike point on pumping efficiency

Pumping efficiency pump is evaluated by

narrowing the exhaust slot width(din , dout) from 20 to 5 cm by three steps

changing the strike point distance (Lin , Lout) 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 x1022 s-1 Qtotal=12 MW• puff = 0 ~ 3.0 x1022 s-1 Spump = 20 ~ 200 m3/sD = 0.3 m2/s, e = I = 1 m2/s Cimp=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 )

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Pumping efficiency increases with small slot width din/out and large slot view angle in/out.

Increment of in with decreasing Lin/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 ratebf/g is reduced by narrowing the slot width, resulting the is increased.Inner divertor

Spump=100 m3/s

outer divertor

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3.3 ELM simulaton with PARASOL codeTransient behavior of SOL/divertor plasmas after an ELM crash

1D SOL/divertor Plasmas & ELM model

Uniform B with pitch Bx/B=0.2.

Recycling rate R is chosen 0~0.9 in regions Lc.

Collisionality L///Imfp0 is chosen 1~50.

ELM crash supplies a large number of hotter particles (NELM=105) in a short period (ELM

=103t << //~105t).TeELM=2Te0, TiELM=TeELM/2=2Ti0.

Parameters for stationary phaseNi0=105, Ti0/Te0=1/2, Tec/Te0=Tic/Ti0=0.1, Ls=0.

2L, Lc=0.2L

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An ELM event is distinguished the fast time scale related to the electron transit time //e=L///2ve and the slow time scale related to the sound-speed transit time //=L///2Cs.

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.

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• 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 MARF

E. 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