14 Oct. 2009, S. Masuzaki1/18

Edge Heat Transport in the Helical Divertor Configuration

in LHD

S. Masuzaki, M. Kobayashi, T. Murase, T. Morisaki, N. Ohyabu, H. Yamada, A. Komori and LHD Experiment group

National Institute for Fusion Science

14 Oct. 2009, S. Masuzaki2/18

MOTIVATION

• Understanding of heat and particle transport in edge region is essential for divertor design in fusion reactor.

– Complex field line structure in which stochastic region, islands and laminar region coexist exists in edge region in heliotron-type devices, stellarators and tokamaks with RMP.

– Different mechanism which determines divertor heat and particle flux profiles from poloidal divertor tokamaks may exist.

• In this study, we focus on profiles of heat and particle flux on helical divertor in LHD heliotron.

14 Oct. 2009, S. Masuzaki3/18

OUTLINE

• Edge magnetic field line structure in LHD

• Relation between the structure and profiles of particle and heat load on divertor

• Transport change with Te rise

• Summary

14 Oct. 2009, S. Masuzaki4/18

Edge field line structure in LHD

R R R

R

= 0º = 9º = 18º

Rax=3.6m

Rax=3.75m

•Helical divertor SOL has three dimensional structure.

•In the HD SOL, the stochastic region, islands and laminar layer co-exist.

•The fine structure in the HD SOL varies with the operational magnetic structure.

14 Oct. 2009, S. Masuzaki5/18

Edge field line structure in LHD

R

R

= 0º

Rax=3.6m

Rax=3.75m

1

10

102

103

Lc,

Lk

(m)

1

10

102

103

2.6 2.8 3

Lc,

Lk

(m)

R (m)4.6 4.8 5

R (m)

L c (m

)L c

(m)

14 Oct. 2009, S. Masuzaki6/18

Divertor leg

‚h‚

b‚q‚

eƒAƒ

“ƒeƒ

i

i• W €” z Ê C‚ q‚ ‚ ‚ R D‚ V‚ T‚ Cƒ À‚ O D‚ R‚ Q“j

i• W €” z Ê C‚ q‚ ‚ ‚ R D‚ V‚ T‚ Cƒ À‚ O“j

100

101

102

103

0.7 0.8 0.9 1 1.1 1.2 1.3 1.4

L c (m

)

X (m)

100

101

102

103

104

L c (m

)

Torus center

－ trace CW－ trace CCW

Z

Rax=3.5m

Rax=3.6m

Outer of this line, field lines interrupted by divertor plates or first wall within about ten meter

divertor leg

Z (m)

0.4

0.6

0.8

1

1.2

1.4

0.8 0.9 1 1.1 1.2 1.3 1.4

B (

T)

z(m)

BT

BP

Rax=3.9m

In divertor region, poloidal field component is larger than toroidal one

14 Oct. 2009, S. Masuzaki7/18

Divertor Plate Array

Divertor plate arrays and diagnostics

O utboard Inboard

O utboard

Bottom

Top=0° 36° 72°

LP#1

LP#2LP#3LP#4

LP#5

• Langmuir probes and thermocouples are embedded in divertor plates

• An IR camera observes inboard divertor plates

• 1,700 water cooled graphite tiles

IR camera4.2℃

123.1℃

50

100

Divertor platesPrivat

e region

14 Oct. 2009, S. Masuzaki8/18

Particle Flux Profiles on a Divetor Plate

101

102

103

104

0

0.01

0.02Rax3.75m

Lc (

m)

Iis

(A)

101

102

103

104

105

0

0.01

0.02

0 20 40 60 80 100 120

Rax3.9m

Lc (

m)

Iis

(A)

probe position (mm)

101

102

103

104

0

0.01

0.02Rax3.5m

Lc (

m)

Iis

(A)

101

102

103

104

0

0.01Rax3.53m

Lc (

m)

Iis

(A)

101

102

103

104

0

0.04

0.08

0 20 40 60 80 100 120

Rax3.6m

Lc (

m)

Iis

(A)

probe position (mm)

=0° 36° 72°

Outboard

InboardOutboard

Bottom

Top

Divertor plate array

Probe array

Inward shifted RaxOutward shifted Rax

14 Oct. 2009, S. Masuzaki9/18

Heat Flux Profiles on a Divertor Plate

• Heat flux profiles were reconstructed by using temperature rise profiles at the beginning of NB injection. Semi-infinite assumption was applied neglecting three dimensional heat diffusion.

14 Oct. 2009, S. Masuzaki10/18

Heat and Particle Deposition Profiles on divertor

6040200

-150

-100

-50

0

50

100

150

Toroidal angle, (°)

Pol

oid

al a

ngle

,

(

。

)

Rax=3.75m

6040200

-150

-100

-50

0

50

100

150 Rax=3.6m

2520151050

red

blue

red

blue

Particle deposition patterns on the HD. (=0)(Calculation results of field lines tracing)

inboard

outboard

outboard

bottom

top

Par

ticle

num

ber

(cal

.)

Nor

mal

ized

tem

pera

ture

ris

e

0

50

100

150

0

1

2Rax=3.6m

0

50

100

150

0

1

2

0 10 20 30 40 50 60 70

Rax=3.75m

Toroidal angle (°)

Profile of normalized temperature rise measured by thermocouples, and particle deposition obtained by field line tracing.

=0° 36° 72°

Outboard

InboardOutboard

Top

14 Oct. 2009, S. Masuzaki11/18

Change of heat flux profile during discharge (Rax=3.60m)

• Such change of heat flux profile has been observed frequently.• Particle flux profile is also changed.

t=1.2s

t=2.4s

Divertor plate arrays

First wall

0

6

12

101

102

103

104

020406080100120

Pdiv

(MW/m2) Lc (m)

(a)t=2.4-2.6s

t=1.1-1.3s

position (mm)

0

4

8

0

10

20

n e,b

ar (

101

9 m

-3)

PN

BI (

MW

)

(b)

0

200

400

0

1

2

0 1 2 3 4

Te

, L

CF

S (

eV)

n e,

LC

FS (

101

9 m

-3)

time (s)

(c)

14 Oct. 2009, S. Masuzaki12/18

Application of the 3D edge transport codes : EMC3-EIRENE

Physics standard fluid equations of density, momentum, energy of ion & electron simplified fluid model for impurities (not for present analysis) kinetic model for neutral gas

Geometry

fully 3D for plasma, divertor plates, baffles and wall ergodic or non-ergodic B-field configurations

Numerics

Monte Carlo technique on local field-aligned vectors, piecewise parallel integration for isolation of the small from the large II-transport (/II~10-8) new Reversible Field Line Mapping (RFLM) technique, Finite flux tube coordinates for B-field line interpolation

Coupled self-consistently

14 Oct. 2009, S. Masuzaki13/18

Reproduce of the profile change using EMC3-EIRENE code

• Blue profile in experiment was reproduced by calculation.• Red profile was not well reproduced. But increasing of diffusion

coefficient flatten the profile in calculation.• Heat load decreases with increase diffusion coefficient.

0

6

12

101

102

103

104

0 20 40 60 80 100 120

Pdiv

(MW/m2) Lc (m)

t=2.4-2.6s

t=1.1-1.3s

position (mm)

0

4

8

101

102

103

0 50 100 150

D=0.2 =0.6D=1, =3D=5, =15

Lc

Pdiv

(MW/m2) Lc(m)

position (mm)

6I

experiment calculation

14 Oct. 2009, S. Masuzaki14/18

At 10.5U probe position

• Heat load (and particle load) increases with increase of diffusion coefficient at this position.

• Heat and particle transfer from “long” flux tube to laminar region is enhanced.

0

0.4

0.8

60 80 100 120 140

10.5UD=0.2, =0.6D=1, =3D=5, =15

Pdiv

(MW/m2)

position (mm)calculation

0

0.5

1

0

0.05

0.1

0 1 2 3 4

tota

l Isa

t 6I(

A)

tota

l Isa

t10.5

U(A

)

time (s)

• The ratio of total Isat at 10.5U probe to that at 6I probe increase during the profile change (yellow hatched).

• Consistent with calculation assuming larger D and .

experiment

14 Oct. 2009, S. Masuzaki15/18

In the case of Rax=3.75m

• Profiles of heat and particle flux are not largely changed by plasma conditions.

• In experiment, ratio of peak heat flux on the divertor to heating power is large for relatively low Te discharges (blue line).

• In calculation, the ratio increase with decreasing of D and .

0

1

2

3

4

0 2 4 6 8 10 12

7Iis

Te

*sin

(

MW

/m2 )

PNBI

-Prad

(MW)

6.5e19m-3

213eV

5.6e19m-3

273eV

7.2e19m-3

203eV

2.8e19m-3

336eV

5.4e19m-3

323eV

3.3e19m-3

373eV2.7e19m-3

390eV2.9e19m-3

383eV

1.9e19m-3

406eV

0

1

2

3

0 20 40 60 80 100 120

7I is

Te*s

in

(M

W/m

2)

position (mm)

Divertor heat flux vs. heating powerNe and Te at LCFS are shown for each symbol

0

4

8

10

100

1000

0 50 100 150

D=0.2, =0.6D=1, =3D=5, =15

Lc(m)

Pdiv

(MW/m2) Lc(m)

position (mm)

6IExp.

Cal.

14 Oct. 2009, S. Masuzaki16/18

Less collision looks to enhance the heat transfer from long flux tube to laminar region

• Normalized heat flux vs. collision mean free path (1016Te

2/ne) around the last closed flux surface.

• Decreasing of the normalized heat flux suggests that heat transfer from “long” flux tube to laminar region is enhanced.

0

0.2

0.4

0.6

0 20 40 60 80 100

7IisT

e*sin/(P

nbi-P

rad)

collision mean free path (m)

14 Oct. 2009, S. Masuzaki17/18

Do diffusion coefficients increase with increasing of Te?

Te Isat@6IIsat@10.5U

Te

Te flattening of heat flux profile@6I

Pdiv@6I

Heating power

Pdiv@6I

Heating powerCalculations with increasing D and

Observations in discharges with Rax=3.75m

Observations in discharges with Rax=3.60m

consistent

14 Oct. 2009, S. Masuzaki18/18

Summary

• Profiles of heat and particle load on divertor plates are roughly determined by magnetic field line structure.

– Though the edge field line structure is complex, the profiles can be roughly predicted even in the complex e.

• Heat and particle transfer from “long” flux tube to laminar region look to be enhanced with Te rise rather than increasing collisionality.

14 Oct. 2009, S. Masuzaki19/18

Closed Helical Divertor will be installed (2/10 sections) in 2010

Present divertor Closed divertor

14 Oct. 2009, S. Masuzaki20/18

14 Oct. 2009, S. Masuzaki21/18

Edge Te profiles D and were estimated by fitting of

calculation to experimental data

0

100

200

73141

Te (

eV

)

D = 0.125 m2/s0.25 m2/s0.5 m2/s1.0 m2/s

TS

0

100

200

73161

Te (

eV

)

D = 0.25 m2/s0.5 m2/s1.0 m2/s2.0 m2/s

0

100

200

4.5 4.6 4.7 4.8 4.9

73508

Te (

eV

)

R(m)

D = 0.25 m2/s0.5 m2/s1.0 m2/s

Te,LCFS~200eVne,LCFS~1-1.5E19m-3

D = 0.125 - 0.25 m2/s= 0.375 - 0.5 m2/s

Te,LCFS~400eVne,LCFS~1-1.5E19m-3

D = 0.5 – 1.0 m2/s= 1.5 – 3 m2/s

Te,LCFS~200eV

ne,LCFS~6E19m-3

D = 0.25 - 0.5 m2/s= 0.75 – 1.5 m2/s

These results suggest that the cross-field transport coefficients have temperature dependence, and they also depend on density weakly.