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r=0.8 r=0.65 plasma confin r=0.5 ct fort champ ct faible cham OV/4-4 3D effects of edge magnetic field configuration on divertor/SOL transport and optimization possibilities for a future reactor M. Kobayashi 1 , Y. Feng 2 , O.

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SLIDE 1

25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

3D effects of edge magnetic field configuration on divertor/SOL transport and optimization possibilities for a future reactor

  • M. Kobayashi1, Y. Feng2, O. Schmitz3, K. Ida1, T.E. Evans4, H. Frerichs3, F.L. Tabares5, Y. Liang6, Y. Corre7,
  • Ph. Ghendrih7, G. Ciraolo7, A. Bader3, Y. Xu8, H.Y. Guo4,9, J.W. Coenen6, D. Reiter6, Z.Y. Cui8, U. Wenzel2,
  • N. Asakura10, N. Ohno11, D. Tafalla5, S. Morita1, S. Masuzaki1, B.J. Peterson1, K. Itoh1 and H. Yamada1

1 National Institute for Fusion Science,322-6 Oroshi-cho, Toki 509-5292, Japan 2 Max-Planck-Institute fuer Plasmaphysik, D-17491 Greifswald, Germany 3 University of Wisconsin – Madison, WI, USA 4 General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA 5 Laboratorio Nacional de Fusion. Ciemat, Madrid, Spain 6 Forschungszentrum Jülich GmbH Institut für Energie- und Klimaforschung – Plasmaphysik, Jülich, Germany 7 IRFM, CEA Cadarache ST Paul Lez Durance, France 8 Southwestern Institute of Physics, P. O. Box 432, Chengdu 610041, China 9 Institute of Plasma Physics, CAS, Hefei, China 10 Japan Atomic Energy Agency, Rokkasho, Aomori 039-3212, Japan 11 Nagoya University, Nagoya 464–8603, Japan 25th IAEA Fusion Energy Conference (FEC 2014)

  • St. Petersburg, Russia, 13-18 October 2014

1

OV/4-4

r=0.5 r=0.65 r=0.8

plasma confiné côté fort champ côté faible cham
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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Introduction: background, motivation & goal

  • Helical devices: Divertor optimization in 3D magnetic configuration is inevitable
  • Tokamak devices: 2D axi-symmetric configuration + symmetry breaking perturbation

 3D configuration For edge transport control (Tore Supra, TEXTOR-DED), ELM mitigation/suppression (DIII-D, JET, AUG,

MAST, NSTX…, ITER)

  • Recent progress of 3D numerical transport codes, systematic experiments, accumulation of

experimental data

  • Identification of 3D effects on SOL/divertor transport, physical interpretation & key

parameters that control the effects, will be useful for divertor optimization in future reactors, taking full advantage of 3D configurations. Multi-machine comparison between tokamak and helical devices. Impacts of 3D configuration on the divertor functions.

2

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Outline of the talk 1.Introduction 2.Definition of 3D effects 3.Impact on divertor density regime 4.Impact on impurity transport 5.Impact on detachment control 6.Summary

3

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Transport in 2D axi-symmetric configuration

//-transport is dominant to deliver plasma quantity from upstream to divertor plates.

          

2 // t

B B

4

Divertor plates //  ┴

1 . ~

t

B B

8 5 //

10 ~ 10   

Toroidal Poloidal

Several degrees

B field lines

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Magnetic field structure & “3D effects”

3D effects: Competition between // and ⊥ transport, which originates from structural/topological change of magnetic field lines, such as openness of stochastic field lines, or formation of magnetic island.

3D effect emerges

          ~

2 // t r

B B

Divertor plates //

Field lines (stochastic, opened)

 ┴ r  //  ┴

5

┴ //

r

Flux surface (magnetic island)

3 4

10 ~ 10

 

t r

B B

8 5 //

10 ~ 10   

B field is prescribed for present analysis.  Self-consistent inclusion of dynamics of B field change due to plasma response is future work.

OV/2-3 K.Ida et al. (Monday) EX/1-3 T. Evans et al. (Tuesday)

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

6

Impact on divertor density regime

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

7

  • Y. Feng et al., PPCF 44 (2002) 611.
  • S. Masuzaki et al., JNM 313-316 (2003) 852.

Absence of high recycling regime prior to detachment in the 3D configurations

  • M. Clever et al., Nucl. Fusion 52 (2012) 054005.

In helical devices as well as tokamaks with RMP, the modest density dependence is often observed.

3 up div

n n 

2 

up div

n T

High recycling in 2D tokamaks 1 ~

up div

n T

1 ~ up div

n n 

The modest dependence in 3D configuration

10

1

10

2

1 10 nup (1019 m-3)

LHD TEXTOR-DED (m/n=6/2)

10

  • 1

10 1 10 nup (1019 m-3)

W7-AS LHD TEXTOR-DED (m/n=6/2)

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

nup (m-3)

1018 1019 1020

Tup, Tdown (eV) Tdown Tup

10 100 1000 (b) fm0=5

nup (1020 m-3) ndown (1020 m-3)

With

1.0 0.8 0.6 0.4 0.2 1.0 0.8 0.6 0.4 0.2 (a)

Effects of enhanced ⊥ interaction of momentum transport on divertor regime

8

  • Y. Feng et al., Nucl. Fusion 46 (2006) 807.

3D configuration (e.g. stochastic layer, ID)

+V// -V//

Divertor plate Divertor plate

poloidal radial

Open field lines

//-Momentum loss due to counter flows

ndown is suppressed

2 // // // m m m m

f V L D  

 

  

  • loss of //-Momentum

//-Temperature drop Tup/Tdown becomes small 2D axi-symmetric divertor

Pressure conservation along flux tube

Divertor plate

poloidal

+V//

(+ f)

  • V//

(- f) radial

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Multi-machine comparison for divertor density regime

  • Replacement of //-energy flux with ⊥ -flux

 reduction of //-conduction energy

2 // // // m m m

V L D   

 

5 . 2 2 //

) / (

e e t r e e e

T B B n q q  

 

m: ⊥ characteristic scale length for momentum loss (e.g. ~2pa/m)

  • ⊥ loss of //-Momentum

 //-pressure drop

div LCFS

p p 

9

Possible Impacts on divertor functions due to the absence of high recycling regime: Pumping efficiency ↓, physical sputtering ↑, detach. onset density ↑ (!?)

collisional collisionless

t r B

B /

large Large Large magnetic shear

a

Large m

6 // 2 //

10 4

  

                 

e e m m

q q  

Operation domain for high recycling regime

 LCFS div

n n 

e e q

q

//

/

 m m

  /

// TEXTOR-DED (m/n=12/4)

DIII-D (m/n≈10/3) LHD (m/n~5/10, strong shear) W7-AS (m/n=9/5) Tore Supra (m/n=18/6) W7-X (m/n=5/5) ITER (m/n~10/3) TEXTOR-DED (m/n=3/1) HSX

(m/n=4/4) (m/n=7/8) TEXTOR-DED (m/n=6/2)

3)   ( ) 3 (  

High recycling No High recycling

10

  • 4

10

  • 3

10

  • 2

10

  • 1

10 10

1

10

  • 3

10

  • 2

10

  • 1

10 10

1

q_perp_e / q_//_e mid

Can be avoided in detached phase Preferable for core performance

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

10

Impact on Impurity screening

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

0.5 1 2 2.5 3 3.5

19

  • 3

11

  • Y. Corre et al., Nucl. Fusion 47 (2007) 119.

Tore Supra

Impurity screening has been observed in many devices with edge stochastic layer

Experiments with density scan shows better screening at high density (low Te)

  • M. Lehnen et al., PPCF 47 (2005) B237.

TEXTOR-DED

C concentration (%)

ne (1019 m-3)

5 10 15 0.5 1 ne edge (1019 m-3) 0.5 1 2 4 6 8

19

  • 3

(m/n=3/1) LHD ne (1019 m-3)

CVI/ne (a.u.) (~ nC5+)

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Interpretation of the impurity screenings: key parameters

  • With Br, outward plasma flow (V//) is enhanced

 particle confinement time ↓  recycling ↑  friction force ↑

 

 D L V B B D D

t r st // // 2

) / (

5 . 2 2 //

) / (

i i t r i i i

T B B n q q  

 

  • Replacement of //-energy flux (q//) with ⊥-flux (q⊥) for ion

  thermal force ↓

  

i i i i

T T q

// 5 . 2 //

//-transport model for impurity momentum

Friction force

.... 6 . 2

// 2 // // //

      

i s z i z z z

T Z V V m t V m 

Ion thermal force

s core SOL LCFS Divertor Ti VII Recycling Thermal Friction

i

T

//

12

  • Y. Feng et al., NF 46 (2006) 807.

//

q

q

r

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

0.1 1 10 2 4 6 8 10 Better screening

C in core C source CV+CVI CIII+CIV ∝

13

SOL thickness dependence of impurity screening: thicker stochastic SOL  better screening already at low density

LHD Thin stochastic layer Thick stochastic layer

M.B. Chowdhuri et al., Phys. Plasmas 16 (2009) 062502.

  • Thicker stochastic layer/SOL ( ) relative to neutral

impurity penetration ( )  better screening

SOL st

imp

 

 imp SOL st

  /

ne (1019 m-3)

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SLIDE 14

25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Multi-machine comparison for impurity screening at high density range

Operation domain of upper half of density range  impurity screening is usually observed at high density

14

Further study: Quantification of screening, impurity injection energy, source location, drift, E field, turbulent transport Thicker stochastic layer Higher density Larger particle outflux Thermal force suppression

101 102 103 10-1 100 101

D_st / D_perp mid (min 50%)

(12/4)

DIII-D LHD W7-AS Tore Supra W7-X ITER

(6/2) (m/n=3/1)

imp SOL st

  /

D Dst /

TEXTOR-DED Impurity screening No impurity screening

(Operation domain of upper half of density range) 3 2

10                 

 

D Dst

imp SOL st

 

  • Thicker stochastic layer/SOL & enhanced particle

transport seem to provide screening effects.

  • No clear boundary identified in the

parameterization with thermal force suppression.

Operation domain for Impurity screening

(12/4)

DIII-D LHD W7-AS Tore Supra W7-X ITER

(6/2) (m/n=3/1)

i i q

q

//

/

 imp SOL st

  /

 Impurity screening No impurity screening TEXTOR-DED

(Operation domain of upper half of density range)

101 102 103 10-1 100 101 102 103

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

15

Impact on detachment control

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Detachment stabilization with RMP application (LHD, W7-AS)

  • Modification of 3D edge radiation structure with RMP application  stable detachment
  • Separation between radiation region & confinement region is important factor for stable detachment
  • M. Kobayashi et al., Nucl. Fusion 53 (2013) 093032.

16

LHD

Channel

Experiments Simulation

Intensity (mW/m2)

Channel Carbon radiation distribution by EMC3-EIRENE

Without RMP Inboard side

LOS of measurements Ch1 Ch16

Unstable detachment With RMP X-point of island

Channel

Intensity (a.u.)

Channel

Stable detachment Radiation condensation at X-point (MARFE like behavior) W7-AS Large DxLCFS-div Small DxLCFS-div Unstable detach. Stable detach.

  • Y. Feng et al., NF 45 (2005) 89.

Carbon radiation distribution by EMC3-EIRENE

X-point radiation divertor radiation EX/P6-26 N. Ohno et al. (Thursday)

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

0.00 0.05 0.10 0.15

  • 4
  • 4
  • 4
  • 4
  • 4 -4 -4 -4
  • 3

17

Operation domain of stable detachment in LHD & W7-AS

Key geometric parameters:

/ ~ B br

Recently the effects of RMP on detachment are being investigated in NSTX, DIII-D, too.

LHD

div LCFS

x

D

W7-AS Divertor plate Baffle Remnant island of m/n=1/1 LCFS Confinement region

island LCFS

x

D

X-point

,

,div island LCFS

x

D

Conditions for stable detachment 1) RMP field must be strong enough (intrinsic ones insufficient, additional MP needed). 2) the geometric SOL width ( ) must be sufficiently large.

div island LCFS

x

, 

D

0.2 1.0 2.0

Stable detachment LHD W7-AS div island LCFS

x

, 

D

(m)

3

/ ~ 10 B br

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SLIDE 18

25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

10-6 10-5 10-4 102 103 104 x

18

               

 

D Dst

imp SOL st 2

 

               

 

 

High recycling + Impurity screening High recycling + Impurity screening High recycling + Impurity screening High recycling + Impurity screening

Thicker SOL enhanced particle flux

               

  e e m m

q q

// 2 //

 

Enhanced ⊥ transport of momentum & energy

Optimization possibility for a future reactor

Optimization Absence of high recycling regime:

  • If pumping efficiency is sufficient

with proper baffle/divertor design

  • Detached phase

 physical sputtering is suppressed Candidate for optimization (?!)

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

Summary

  • The 3D effects : competition between transports parallel (//) and perpendicular (⊥) to magnetic field, in
  • pen stochastic field lines or magnetic islands.
  • The competition process affects energy, particle and momentum transport in divertor/SOL region

♦ Density regime  absence of high recycling regime Momentum loss via ⊥-transport, enhanced ⊥-energy transport, //-convection energy flux ♦ Impurity screening Friction force enhancement, ion thermal force suppression, thicker SOL with stochastization & ID Need further study on quantification of screening efficiency, source characteristics, E-field, turbulence ♦ Detachment stability Radiation modification by RMP, sufficiently large , separation between radiation region & confinement region  Detachment stabilization

19 6 // 2 //

10 4

  

                 

e e m m

q q   Operation domain for high recycling:

3 2

10                 

 

D Dst

imp SOL st

 

Operation domain for impurity screening:

/ ~ B br

div island LCFS

x

, 

D

Further study: Edge E-field/turbulence, plasma response to MP, Divertor heat load (strike-line splitting), ELM mitigation/suppression, control of high-Z impurity Systematic understandings of the impact of 3D divertor configurations will open new perspective on divertor

  • ptimization for future reactors.
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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

20

W7-AS

  • Y. Feng et al., PPCF 44 (2002) 611.

LHD

  • S. Masuzaki et al., JNM 313-316 (2003) 852.

Absence of high recycling regime prior to detachment in the 3D configurations

TEXTOR-DED (m/n=6/2)

  • M. Clever et al., Nucl. Fusion 52 (2012) 054005.

In helical devices as well as tokamaks with RMP, the modest density dependence is often observed.

3 up div

n n 

2 

up div

n T

High recycling in 2D tokamaks 1 ~

up div

n T

1 ~ up div

n n 

The modest dependence in 3D configuration

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

21

  • Y. Corre et al., Nucl. Fusion 47 (2007) 119.

Tore Supra

Impurity screening has been observed in many devices with edge stochastic layer

Experiments with density scan shows better screening at high density (low Te)

Higher n

10-1 100 2 4 6 8 CIV/ne CV/ne Experiments

CIII/ne CIV/ne CV/ne

2 4 6 8

ne (1019 m-3)

LHD

  • M. Kobayashi et al., Nucl. Fusion 53 (2013) 033011.

C emission from core C emission from source C6+ density (1017 m-3)

  • M. Lehnen et al., PPCF 47 (2005) B237.

TEXTOR-DED

C concentration (%) ne (1019 m-3)

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

  • 6
  • 5
  • 4

102 103 104

22

High recycling + Impurity screening High recycling + Impurity screening High recycling + Impurity screening High recycling + Impurity screening

Thicker SOL, enhanced particle transport Enhanced ⊥ transport of momentum & energy

Which direction to go for 3D divertor optimization of a future reactor?

Absence of high recycling regime: Trade-off between pumping efficiency and controllability of detachment & impurity transport with 3D B field. Optimization 3D effects 3D effects

Larger Br/B0, higher density Larger magnetic shear, larger pol. mode, collisional

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

23

Magnetic field structure (stochastic or island) can be investigated with heat propagation experiments

  • K. Ida et al., New Journal of Physics 15 (2013) 013061.

The time delay of heat propagation changes depending on the magnetic topology: Magnetic island  time delay at O-point Stochastic field  no time delay OV/2-3 K.Ida et al. (Monday) EX/1-3 T. Evans et al. (Tuesday)

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

10-6 10-5 10-4 102 103 104 x

24

               

 

D Dst

imp SOL st 2

 

               

 

 

High recycling + Impurity screening High recycling + Impurity screening High recycling + Impurity screening High recycling + Impurity screening

Thicker SOL, enhanced particle transport

               

  e e m m

q q

// 2 //

 

Enhanced ⊥ transport of momentum & energy

Indication for 3D divertor optimization of a future reactor

Absence of high recycling regime: This might not be drawback 1. After detached phase is achieved. 2. Since relatively high nup can be achieved due to slow Tdiv decrease  better impurity screening via thermal force suppression  better core plasma performance A divertor should be optimized considering balance with pumping efficiency. Optimization

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

div LCFS

x

D

(cm) LC (m)

Possibility of 3D edge radiation structure control and radiation stabilization

W7-AS Large DxLCFS-div Small DxLCFS-div

Large and short LC  Radiation region moves to inboard side  Hot island  Better neutral screening  Stable detachment

[22] P. Grigull et al. JNM 313-316 (2003) 1287. [23] Y. Feng et al., NF 45 (2005) 89. 25

Decoupling between core and recycling region in terms of neutral fueling plays a key role.

Unstable detach. Stable detach.

div LCFS

x

D

W7-AS Divertor plate Baffle

div LCFS

x

D

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25th IAEA Fusion Energy Conference (FEC 2014) St. Petersburg, Russia, 13-18 October 2014 OV/4-4

26

Impact of RMP on edge electric field

TEXT In many devices, the change of edge electric field (potential profile) has been observed  Effects on edge turbulence, drift ….  impurity transport TEXTOR-DED

These results suggest that the stochastic layer induced by RMP application can impact on edge turbulence transport, and hence on plasma-wall interaction, impurity transport and also plasma confinement.

TEXTOR-DED

  • O. Schmitz et al., JNM 390-391 (2009) 330.