30 August 2006

Conference on Computational Physics

Transport Simulation for the Scrape-Off Layer and Divertor Plasmas in KSTAR Tokamak

S. S. Kim and S. W. Yoon

National Fusion Research Center

30 August 2006

Conference on Computational Physics

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

30 August 2006

Conference on Computational Physics

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30 August 2006

Conference on Computational Physics

Computational domain

Korea-Japan CUP 2001

Workshop on the Atomic and Molecular Processes in Plasmas and the Database

3/34

KSTAR (Korea Superconducting Tokamak Advanced Research)

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Z (m

)R (m)

BT=3.5T

30 August 2006

Conference on Computational Physics

Parameter Value

Input power 4 MW

Plasma density at core boundary 31019 m-3

Anomalous particle diffusivity 2 m2/sec

Anomalous thermal diffusivity 4 m2/sec

Recycling coefficient at wall and divertor 1.0

Leakage factor in private region by pumping 0.3 %

Decay length at wall boundary 0.03 m

Case I : No drift is considered.Case II : Only diamagnetic drift is included.Case III : All drifts are switched on.

Simulation conditions

anD

an

30 August 2006

Conference on Computational Physics

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

Total pressure

Case I Case II Case III

Pa

30 August 2006

Conference on Computational Physics

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

R (m)Z

(m

)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

20

40

60

80

100

120

140

160

180

200

220

Electron temperature

Case I Case II Case III

eV

30 August 2006

Conference on Computational Physics

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

BT

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

-5

0

5

10

15

20

25

BTBT

Electrostatic potential

Case II Case III Reversed field case

V

drift B drift B

30 August 2006

Conference on Computational Physics

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

R (m)

Z (

m)

1.2 1.4 1.6 1.8 2 2.2

-1

-0.5

0

0.5

1

1

2

3

4

5

6

7

8

9

x 10 19

/m3

Plasma density

Case I Case II Case III

30 August 2006

Conference on Computational Physics

R (m)

Z (

m)

1.2 1.3 1.4 1.5 1.6 1.7 1.80.7

0.8

0.9

1

1.1

1.2

1.3

1.4

R (m)

Z (

m)

1.2 1.3 1.4 1.5 1.6 1.7 1.8

-1.4

-1.3

-1.2

-1.1

-1

-0.9

-0.8

-0.7

R (m)

Z (

m)

1.2 1.3 1.4 1.5 1.6 1.7 1.8

-1.4

-1.3

-1.2

-1.1

-1

-0.9

-0.8

-0.7

R (m)

Z (

m)

1.2 1.3 1.4 1.5 1.6 1.7 1.80.7

0.8

0.9

1

1.1

1.2

1.3

1.4

Case II Case IIIdrift B drift BE

Effect of cross-field drifts on density distribution

1

2

3

4

5

6

7

8

9

x 10 19

/m3

30 August 2006

Conference on Computational Physics

R (m)

Z (

m)

1.2 1.3 1.4 1.5 1.6 1.7 1.80.7

0.8

0.9

1

1.1

1.2

1.3

1.4

R (m)

Z (

m)

1.2 1.3 1.4 1.5 1.6 1.7 1.8

-1.4

-1.3

-1.2

-1.1

-1

-0.9

-0.8

-0.7

-0.05 0.00 0.05 0.100.0

0.2

0.4

0.6

0.8

private region

Hea

t ful

x on

div

erto

r (M

W/m

2 )

Distance from striking point (m)

Case I Case II Case III

-0.15 -0.10 -0.05 0.00 0.05 0.10 0.150.0

0.1

0.2

0.3

0.4

0.5

private region

Hea

t ful

x on

div

erto

r (M

W/m

2 )

Distance from striking point (m)

Case I Case II Case III

-0.15 -0.10 -0.05 0.00 0.05 0.10 0.150.0

0.1

0.2

0.3

0.4

0.5

private region

Hea

t ful

x on

div

erto

r (M

W/m

2 )

Distance from striking point (m)

Case I Case II Case III

-0.05 0.00 0.05 0.100.0

0.2

0.4

0.6

0.8

private region

Hea

t ful

x on

div

erto

r (M

W/m

2 )

Distance from striking point (m)

Case I Case II Case III

Heat load to divertors

30 August 2006

Conference on Computational Physics

R (m)

Z (

m)

1.2 1.3 1.4 1.5 1.6 1.7 1.80.7

0.8

0.9

1

1.1

1.2

1.3

1.4

R (m)

Z (

m)

1.2 1.3 1.4 1.5 1.6 1.7 1.8

-1.4

-1.3

-1.2

-1.1

-1

-0.9

-0.8

-0.7

Heat load to divertors

-0.15 -0.10 -0.05 0.00 0.05 0.10 0.150.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

private region

Hea

t ful

x on

div

erto

r (M

W/m

2 )

Distance from striking point (m)

Case I Case II Case III

-0.05 0.00 0.05 0.100.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

private region

Hea

t ful

x on

div

erto

r (M

W/m

2 )

Distance from striking point (m)

Case I Case II Case III

-0.15 -0.10 -0.05 0.00 0.05 0.10 0.150.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

private region

Hea

t ful

x on

div

erto

r (M

W/m

2 )

Distance from striking point (m)

Case I Case II Case III

-0.05 0.00 0.05 0.100.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

private region

Hea

t ful

x on

div

erto

r (M

W/m

2 )

Distance from striking point (m)

Case I Case II Case III

/sm 2 /s,m 1 22 ananD

30 August 2006

Conference on Computational Physics

Total heat load (MW)

Case I Case II Case III

Divertor 1.30 0.97 0.89

Wall 1.91 2.06 2.02

Divertor 2.38 1.82 1.52

Wall 1.12 1.26 1.17

Total heat load to divertors and wall

/sm 4

/sm 22

2

an

anD

/sm 2

/sm 12

2

an

anD

30 August 2006

Conference on Computational Physics

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.

B