Effects of stochastic magnetic boundaries on divertor optimizations - - PowerPoint PPT Presentation

1

Effects of stochastic magnetic boundaries on divertor optimizations

• M. Kobayashi

National Institute for Fusion Science, Oroshi-cho 322-6, Toki-city 509-5292, Japan

1st IAEA Technical Meeting on Divertor Concepts 29 Sep. – 2 Oct. 2015, IAEA Headquarters, Vienna, Austria

2

Stochastic magnetic boundaries appear in Stellarators due to the intrinsic non-axisymmetirc magnetic configuration  zero toroidal current favourable for steady state operation Tokamaks when symmetry breaking perturbation is applied  Aiming at edge plasma control, ELM mitigation/suppression

What do we benefit from the stochastic boundary for divertor optimization?

RMP for ELMs mitigation Intrinsic edge stochastization in Stellarators Stochastic field as a tool for controlling edge plasma

Introduction

3 Summary: Effects of stochastic magnetic boundary Confinement region Ergodic region Laminar region PFC Benefit Density pump-out PL-H ↑ Enhanced radiation Impurity screening Control of radiation & detachment Strike line splitting (non-uniform power/particle load) Energy transport barrier Change of divertor density regime Cost of divertor volume (10~20% of a) Decontamination Challenge for engineering (RMP coils, 3D shape) ELM mitigation/suppression Change of Er & turbulent transport Peak power load? Pumping efficiency? Core performance? Fueling efficiency ↓ Disadvantage Issues to be assessed

4

Onset of stochastic instability by island overlapping: σChir > 1

separatrix X-point O-point “overlap”

? ?

increases

r

B ~

Stochastic trajectories Island “overlaps” With increasing , island becomes large. Field lines in overlap region share B field with neighboring island, and “forget” from which island come from.

K.H. Finken et al., “The structure of magnetic field in the TEXTOR-DED”

1 ) 1 , ( ) ( 5 . ) , (

2 1

> + ∆ + =

m m w w m n

n Chir

σ

m n /

= ι

) 1 /(

+ =

m n

ι

) 1 , (

+ ∆

m m

n

) , (

2

m n w ) 1 , (

1

+

m n w

' / ~

,

ι

n m r

B w ∝

r

B ~

5

Field line structure in stochastic magnetic boundary

Schematics of field line structure

Laminar region (edge surface layers) Short & long LC coexist Stochastic region No clear separatrix, locally ergodic, remnant islands

poloidal radial

K.H. Finken et al., PRL 98 (2007) 065001.

Perturbation coil current PFCs Perturbation field Stochastic region Laminar region (edge surface layers) Short B lines Long B lines r θ Remnant islands φ Connection length (LC) distribution in TEXTOR- DED Poloidal turns

6

Effects on divertor density regime

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. High recycling in 2D tokamaks The modest dependence in 3D configuration

101 102 1 10 probe_masuzaki_29265

Te div (eV) Te_div (eV) Tdiv (eV) 2D Tdiv (eV) 3D Tdiv (eV) 3D

nup (1019 m-3)

~nup-2

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

~nup-1 ~nup-0.3

Detach

10-1 100 1 10 probe_masuzaki_29265

ne div (10^19 m-3) ndiv (10^19 m-3) ndiv (10^19 m-3) ndiv (10^19 m-3) 2D ndiv (10^19 m-3) 3D nup^1 ndiv (10^19 m-3) 3D nup^1.5

nup (1019 m-3)

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

~nup3 ~nup1 ~nup1.5

Detach

3 up div

n n ∝

2 −

∝

up div

n T

1 ~−

∝

up div

n T

1 ~ up div

n n ∝

8 nup (m-3)

1018 1019 1020

Tu p , T d

• w

n ( e V )

Tdown Tup

10 100 1000 (b) fm0=5

nup (1020 m-3)

n d

• w

n ( 1 2 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 ⊥

• 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

Ø loss of //-Momentum

⊥

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

Pressure conservation along flux tube

Divertor plate

poloidal

+V//

(+ φ)

• V//

(- φ) radial

2 // // // m m m m

f V L D ∝ =

⊥ ⊥

λ τ τ

9

W7-AS

Y . Feng et al., Plasma Phys. Control. Fusion vol.53 (2011) 024009.

m/n=9/5

HSX

• A. Bader et al., Nucl. Fusion vol.53 (2013) 113036.

m/n=7/8

Mach probe scanning path

nV// (1023 /m2/s) 5.0

• 5.0

1.0 2.0 3.0 4.0

• 4.0
• 3.0
• 2.0
• 1.0

3.0 3.5 4.0 4.5 R (m)

• 1.0
• 0.5

0.5 1.0

Z( m )

Simulation (EMC3-EIRENE) (a) LHD

m/n=7~2/10

LHD

Mach number

TEXTOR-DED

• H. Frerichs et al., Nucl. Fusion vol.52 (2012) 023001.

m/n=6/2

Tore Supra Mach number

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

m/n=18/6

Mach number

DIII-D

m/n~10/3

10

Flow alternation is detected in experiments

Mach probe scanning path

nV// (1023 /m2/s) 5.0

• 5.0

1.0 2.0 3.0 4.0

• 4.0
• 3.0
• 2.0
• 1.0

3.0 3.5 4.0 4.5 R (m)

• 1.0
• 0.5

0.5 1.0 Z (m)

Simulation (EMC3-EIRENE)

(a)

LHD

Z (m) Simulation (EMC3-EIRENE) Experiments (b) Mach Number

Tore Supra

J.P. Gunn et al., JNM 290-293 (2001) 877.

11

In these cases, the following effects are small, due either to

1.

Large separation of counter flow (λm~2πa/m)

2.

Relatively high Te in SOL

High recycling regime can be recovered in 3D configuration for some cases

δm~8 cm nu 1019 m-3 ned 1019 m-3

EMC3-EIRENE

TEXTOR-DED (m/n=3/1) Tore Supra (m/n=18/6) W7-X (m/n=5/5) numerical simulation

• M. Lehnen et al., J. Nucl. Mater. 337-339 (2005) 171.
• B. Meslin et al., J. Nucl. Mater. 266-269 (1999)

318.

• Y. Feng et al., Nucl. Fusion 49 (2009) 095002.

m m m m

f V L D ∝ =

⊥ ⊥ 2 // // //

λ τ τ

5 . 2 2 //

) / (

e e t r e e e

T B B n q q κ χ⊥

⊥ =

4 up down

n n ∝

3 up down

n n ∝

3 up down

n n ∝

12

Multi-machine comparison for divertor density regime

ØReplacement of //-energy flux with ⊥ -flux

 reduction of //-conduction energy

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

Ø

⊥ loss of //-Momentum  //-pressure drop

div LCFS

p p >

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

collisional collisionless large Large Larg e mag netic shea r

a

La rg e m

Operation domain for high recycling regime

Can be avoided in detached phase Preferable for core performance (?)

10-4 10-3 10-2 10-1 100 101 10-2 10-1 100 101

parameters_devices_density_regime_mod4_high-recycling tau_m// / tau_m perp mid tau_m// / tau_m perp mid tau_m// / tau_m perp mid

q_perp_e / q_//_e mid

⊥ m m

τ τ

/

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

LHD (m/n~5/10, strong shear) W7-AS (m/n=9/5) HSX

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

No high recycling Tore Supra (m/n=18/6) ITER (m/n~10/3) W7-X (m/n=5/5) DIII-D (m/n≈10/3)

TEXTOR-DED (m/n=3/1) EAST (m/n~3/1) High recycling No High recycling

2 // // // m m m

V L D λ τ τ

⊥ ⊥

=

5 . 2 2 //

) / (

e e t r e e e

T B B n q q κ χ⊥

⊥ = t r B

B /

5 // 2 //

10 6 . 3

− ⊥ ⊥

× <                

e e m m

q q τ τ

e e q

q

//

/

⊥

α up down

n n ∝

3) < α ( ) 3 ( ≈ α

13

Effects on impurity screening

14

0.5 1 2 2.5 3 3.5 C-concentration_fig8b_DED C concentration (%) m/n=3/1 Icoil=2kA ne (1019 m-3)

• 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 Carbon_Tore_Supra C6+ (10^17 m-3) ne edge (1019 m-3)

0.5 1 2 4 6 8 C_all_Nebar#81896to81933_080407_375_woLID CVI/ne normalized ne (1019 m-3)

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

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

Ø

Enhanced outward particle flux due to braiding B field, density pump-out  Effective friction force  Drive impurity towards divertor

Ø

High edge density  screening of CX flux, shallow penetration of neutral impurity

15

0.1 1 10 ratio 3.60m ratio 4.00m 2 4 6 8 10

Better screening

C in core C source VI IV ∝

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.

ØThicker stochastic layer/SOL ( ) relative to neutral

impurity penetration ( )  better screening

ne (1019 m-3)

SOL st−

λ

imp

λ ↑

− imp SOL st

λ λ /

16

Impurity screening: species dependence Better screening for non-recycling impurity

• Ph. Ghendrih et al., NF 42 (2002) 1221.

Tore Supra Ratio of boundary to core impurity concentration

Better screening for O & N (non-recycling) than Ne (recycling) is due to the wall pumping (!?).

17

Impurity screening: species dependence Good screening for High Z impurity (Fe)

• Ph. Ghendrih et al., JNM 290-293 (2001) 798.

Ergodic divertor

Tore Supra LHD

• S. Morita et al., NF 53 (2013) 093017.

Low ionization potential of Fe (7.9 eV)  shallow penetration to edge stochastic layer  better screening (!?)

18

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

Ø

Thicker stochastic layer/SOL & enhanced particle transport seem to provide screening effects.

Ø

Weak dependence on outward particle flux.

Operation domain for Impurity screening

101 102 10-1 100 101

parameters_devices_impurity_mod9-1_no-screening

lambda_st / lambda_ion C0 0.05eV mid lambda_st / lambda_ion C0 0.05eV mid lambda_st / lambda_ion C0 0.05eV mid

D_st / D_perp mid

Impurity screening with 3D effects

imp SOL st

λ λ

/

− Impurity screening No impurity screening

(m/n=3/1)

TEXTOR-DED LHD ITER W7-AS Tore Supr a W7-X

(6/2)

DIII-D

(12/4)

(a)

Effects of outward particle flux

p p st ⊥

Γ Γ / 18

4 / 1

>         Γ Γ        

⊥ − p p st imp SOL st

λ λ

) / (

// t r p st

B B V n = Γ r n D

p r

∂ ∂ − ≈ Γ

⊥ ⊥ ⊥ ⊥

= Γ Γ D L V B B

t r p r p st // // 2

) / (

19

Effects on edge radiation & detachment stablity

20

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Radiation enhancement with edge stochastic layer

• Ph. Ghendrih et al., NF 42 (2002) 1221.

Tore Supra

Enhanced edge recycling in ergodic layer  high density, low Te region with extended volume (10~20% of a)  enhanced radiation Ergodic divertor

Tore Supra Multi-machine scaling (X-point divertor)

21

1 2 3 2 4 6 8 10 UP_93206_3f 11:14:25 2011/11/01 Prad(MW) Prad(MW) n_thom (1019 m-3)

Increased volume of low Te region (~10 eV) at remnant island with RMP leads to enhanced carbon radiation

Radiation collapse Without RMP With RMP Radiation Power (a.u.)

ne dependence of radiation power (bolometer)

100 101 102 103 4.4 4.6 4.8 TS_85948_ts_withPrad_t=3.500_0.035s Te(eV) Te(eV) R (m)

100 101 4.4 4.6 4.8 TS_85948_ts_withPrad_t=3.500_0.035s ne(e19m**-3) ne(e19m**-3) R (m)

Without RMP With RMP

Resonance layer

Te flattening at island Te, ne profiles at outboard midplane (Thomson scattering)

10-1 100 101 4.4 4.6 4.8 TS_85948_ts_withPrad_t=3.500_0.035s Prad (MW/m3) 1e17 Prad (MW/m3) 1e17 R (m) (Estimated with ncarbon=0.01ne neτ = 1017 m-3 s)

Carbon radiation

RD Radiation enhanced

LHD

) m (10 n

• 3

19 e

22

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

Ø

Modification of 3D edge radiation structure with RMP application  stable detachment

Ø

Separation between radiation region & confinement region is important factor for stable detachment

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

093032.

LHD

AXUV_P7.5_D1.0_3.0_C1_NUP7.0_DP1DT3_temp16_2mm_NPIN2 11:15:07 2012/10/02 AXUV (a.u.) t=3.0-3.5s Intensity(mW/m**2)

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

AXUV_P08_D1.0_3.0_C1_NUP7.0_DP1DT3_temp18_2mm_NPIN2 11:00:57 2012/10/02 AXUV (a.u.) t=4.0-6.0 s Intensity(mW/m**2)

Channel

Intensity (a.u.)

Channel

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

• Y. Feng et al., NF 45 (2005) 89.

Carbon radiation distribution by EMC3-EIRENE

X-point radiation divertor radiation

23

0.00 0.05 0.10 0.15 2 10-43 10-4 4 10-4 5 10-4 6 10-4 7 10-4 8 10-4 9 10-4 10-3 2 10-3 Rax_Lc_w_LCFS_X_162deg_20140928

a_x-a_LCFS a_x-a_LCFS Delta_LCFS-div (m)

br/B0 ave

Operation domain of stable detachment in LHD & W7-AS

Key geometric parameters: Recently the effects of RMP on detachment are being investigated in NSTX, DIII-D, AUG etc.

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

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. 0.2 1.0 2.0

Stable detachment LHD W7-AS div island LCFS

x

, −

∆

(m)

/ ~ B br

div LCFS

x

−

∆

island LCFS

x

−

∆

,

,div island LCFS

x

−

∆

div island LCFS

x

, −

∆

3

/ ~ 10 B br

−

×

24

Effects on divertor power load

25

Non-uniform plasma heat/particle deposition at divertor plates

Distribution changes also from inward to outward configuration  Global distribution has close correlation with magnetic field structure Inward shifted configuration (Rax=3.60 m) EMC3-EIRENE inboard

• utboard
• utboard

Toroidal angle (deg.) Poloidal angle (deg.) Outward shifted configuration (Rax=3.75 m) EMC3-EIRENE inboard

• utboard
• utboard

Poloidal angle (deg.) Toroidal angle (deg.)

LHD

26

Divertor foot-prints of flux tubes & power load in various configurations

Single peak : Good correlation between long flux tubes and peak power load. Multi-peak : foot-print width becomes broad, power peak does not necessarily correlate with Lc peak.

• S. Masuzaki et al., CPP 50 (2010) 629.
• S. Masuzaki et al., JNM 390-391 (2009) 286.

LHD

27

Significant change of power load profile depending on upstream plasma parameters

High temperature  Clear splitting of power flux, broader foot print Low temperature  Single peak t=1.2s t=2.4s

(d) (e)

IR camera view on divertor plates High Te Low Te

High Te Low Te

• S. Masuzaki et al., CPP 50 (2010) 629.
• S. Masuzaki et al., JNM 390-391 (2009) 286.

4 8 10 20

1 2 3 4

(b) 200 400 1 2 1 2 3 4 time (s) (c)

4 8 10 20 n

e,bar

(10

19

m

• 3

) P

NBI

(MW) (b) 200 400 1 2 1 2 3 4 T

e, LCFS

(eV) n

e, LCFS

(10

19

m

• 3

) time (s) (c)

2 4 101 102 103 104

20 40 60 80 100 120

Pdiv (MW/m2) Lc (m)

t=2.4-2.6s t=1.4-1.6s position (mm) (a)

LHD

28

Experiments & 3D modelling analysis on divertor power depositions

Ø

Single peak with lower Te is only qualitatively reproduced with EMC3-EIRENE (D ┴ =0.2, χ ┴ =0.6 m2/s)

Ø

Splitting and broadened power flux with higher Te is NOT reproduced with EMC3-EIRENE

Ø

Qualitatively, higher temperature  larger cross-field transport coefficients

Experiments 2 4 101 102 103 104

20 40 60 80 100 120

Pdiv (MW/m2) Lc (m)

Low Te High Te position (mm) (a)

EMC3-EIRENE

4 8 101 102 103 104 20 40 60 80 100 120

PRB_6I_P10_D0.2_0.6_NUP2.0_DP1DT9_L 23:57:17 2009/10/12

Energy(W/m**2) Energy(W/m**2) Energy(W/m**2) Rax360 position (mm)

D ┴ =0.2, χ ┴ =0.6 m2/s 1.0, 3.0 5.0, 15.0

• S. Masuzaki et al., CPP 50 (2010) 629.
• S. Masuzaki et al., JNM 390-391 (2009) 286.

Due to change of transport or equilibrium? LHD

29 Laminar transport & radial penetration of field lines plays a key role on power deposition

• Ph. Ghendrih et al., JNM 241-243 (1997) 517.

A WKB approximation of the energy transport in the laminar region + the radial penetration of a field line Turbulent transport with an effective diffusion of the order of 1 m2/s ~ comparable to limiter data.  the level of turbulent transport was weakly affected by the stochastic boundary despite the decrease of the largescale density fluctuations.

• Ph. Ghendrih et al., FST 56 (2009) 1432.

Tore Supra

2D contour of minimum radial penetration

• f field lines on divertor plate.

Modelling Experiments

30

DIII-D

• H. Frerichs et al., POP 21 (2014) 020702.

Experiments & 3D modelling analysis on divertor power depositions

3D simulation shows that a recycling condition affects the footprint splitting of particle & heat deposition. Heat flux pattern with high recycling condition agrees with IR camera measurements.

Particle flux (kA/m2) Heat flux (MW/m2) Low recycling High recycling Modelling Modelling & Experiments IR camera

31

Effects on particle transport

32

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Density pump-out

Combination of two effects:

• 1. An enhanced transport in the outermost stochastic region
• 2. Pumping capability of some wall components due to change in plasma-

wall interaction by RMP  No pump-out observed with He discharge.  No density pump-out with saturated wall at steady state?

• Ph. Ghendrih et al., FST 56 (2009) 1432.

Tore Supra DIII-D

T.E. Evans et al., Nat. Phys. 2 (2006) 419.

Other physics on going? e.g. Er, increased turbulent diffusion …

• M. Leconte et al., NF 54 (2014) 013004.

33

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.
• S. Masuzaki et al., JNM 313-316 (2003) 852.

Tore Supra

Density pump-out  low fueling efficiency

Time (s)

Thin & thick ergodic.

Ø

Significant low fueling efficiency with edge ergodic layer and with thicker ergodic layer.

Ø

Due both to increased wall retention & screening of neutral penetration.

LHD

34

Formation of steep Te profile at the edge

35

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.
• N. Ohyabu et al., NF 27 (1987) 2171.

T.E. Evans et al., JNM 145-147 (1987) 812.

Sharp transition of Te at the edge with ED.

TEXT

• Ph. Ghendrih et al., NF 42 (2002) 1221.

Pinch effect caused by combination of microscale transport and stochastic field lines?

• S. Feron et al., JNM 241-243 (1997) 328.

Tore Supra Numerical simulation

36

Correlation between cross-field transport (χ┴) & with LC mode structure (?)

105 104 103 102 101 100 Connection length, LC (m) Poloidal mode number of remnant islands

Outboard Inboard

Poloid al Radia l

2 3 4 5 8 7 6

100 200 2.6 2.7 2.8 2.9 4.7 4.8 4.9 5.0

tsmap@109715 17:52:31 2013/09/22 'Te' Te(eV)

R (m)

t=4.400+/-0.050 s 1.00/0.20_I30_4.00_I44_30.00

2.6 2.7 2.8 2.9 4.7 4.8 4.9 5.0 R (m) 100 200 Te (eV) χ┴ = 0.2 m2/s 4.0 4.0 30.0 30.0 The change of χ┴ radius corresponds to the change of mode number from m=4 to 5.  Boundary between edge surface layer (laminar zone) and stochastic region (long LC region).

PNBI=7 MW, nLCFS=1.9x1019 m-3

• M. Kobayashi et al., CPP 54 (2014) 383.

LHD

37

Effects on L-H transition power threshold

38

• F. Ryter et al., NF 52 (2012) 114014.

Increase in L-H transition power threshold with RMP No remarkable change in confinement (AUG)

ASDEX-Upgrade At low density: no effect on L-H transition. ~ 50% of Greenwald limit: H-mode with small ELM achieved. > 60% of Greenwald limit: Remains L mode. No remarkable change in confinement with RMP. Common confinement degradation with increasing recycling.

39

• P. Gohil et al., NF 51 (2011) 103020.

DIII-D

He Clear threshold for D plasma, δB/BT ~ 3x10-4. Increase in L-H transition power threshold with RMP

Off-resonant

No clear threshold for He plasma. Clear increase for resonant component cases. Plasma screening effect has to be assessed.

40

• M. Leconte et al., NF 54 (2014) 013004.

Increase in L-H transition power threshold with RMP: resistive drift wave turbulent simulation No RMP With RMP H-mode H-mode Input power Input power

VZF2 : zonal flow energy ε : turbulence energy

RMP damps Zonal Flow by decrease of long range correlation  Mean flow shear decrease  loss of stabilization of turbulence  delay of L-H transition

41

S.M. Kaye et al., NF 51 (2011) 113019.

With RMP Without RMP Slight increase in L-H transition power threshold with RMP

NSTX

42

Effects on edge Er & turbulent transport

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

Tendency to form positive Er due to fast escaping electrons along open field lines created by RMP.

TEXTOR-DED

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

43

44 Variety of Er formations observed depending on RMP’s phases

Conway G.D. et al 2015 Plasma Phys. Control. Fusion 57 014035.

ASDEX-Upgrade

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Reduction in density fluctuation with ED

45

Tore Supra

Reduction in fluctuation at large scale structure, k < 4 cm-1 (> 25 mm)  magnetic island scale generated by Ergodic divertor. “The large electrostatic structures which govern the anomalous transport are strongly affected by the correlation loss induced by stochasticity.”

46 Change in wavenumber spectrum broadening with RMP (TEXTOR-DED) (Destructive role of DED on turbulence cells)

• Y. Xu et al., NF 47 (2007) 1696.

TEXTOR-DED

DED on DED on

Wave number spectrum broadening Radial Poloidal The increase of the k spectrum width during the DED at all frequency component. “With DED, the coherent frequency modes are all destroyed, and turbulence eddies are reduced for all frequency.”

47

Consequences to resultant turbulent transport differs in devices

Reduction in density (pressure) fluctuation, increase in velocity (potential) fluctuation with ED.  Turbulent transport remains unchanged.

• Ph. Ghendrih et al., NF 42 (2002) 1221.
• P. Beyer et al., PPCF 44 (2002) 2167.

Tore Supra

Numerical simulation (RBM3D: flux driven resistive ballooning turbulence)

48 Reduction in blob turbulence transport with RMP (TEXTOR-DED).

TEXTOR-DED

Consequences to resultant turbulent transport differs in devices

Before DED During DED

• Y. Xu et al., NF 49 (2009) 035005.

Radial particle flux in experiments ExB flux in simulations

• D. Reiser, POP 14 (2007) 082314.

ATTEMPT: 3D flux driven (fluid drift) turbulence model with SOL effects of

• pen filed lines

49

Consequences to resultant turbulent transport differs in devices

Little change in Isat fluctuation with RMP.

Muller H.W. et al 2013 J. Nucl. Mater. 438 S64–71

ASDEX-Upgrade

50

Challenge for engineering

51

RMP coil installation

The internal ITER ELM coil set consisting of 3 toroidal rows with 9 window-frame type coils. How can this be extrapolated for DEMO under severe neutron flux environment ?

T.E. Evans et al., NF 53 (2013) 093029.

52

Helical coil Helical coil Divertor plates Dome R=3.90 m a~0.65 m 10 field periods of magnetic configuration First wall : stainless steel Divertor : carbon

Super-conducting coils in 3D shape: (an example of LHD)

53

Closed divertor in 3D shape: (an example of LHD)

Divertor plates Dome Cryogenic pump is installed under domes.

54

Unexpected heat load: (an example of LHD)

Divertor legs enters behind divertor plates First wall Carbon tiles for pipe protection Divertor legs hit diagnostic

55

Challenge in technology to integrate cryogenic system in complex 3D shape (Liquid He, Liquid N, water cooling pipes, heat shield structure …)

Further upgrade

• T. Murase et al., NIFS Annual report (2015).

Cryo-panel Pumping speed ~ 30 m3/s x 3sections

• Div. pressure ~ 0.5 Pa

~10 22 atoms/s (~fueling rate at high density operation) In-vessel Divertor plate Cryo-pump Dome Divertor leg Cryo-panel Pumping speed ~ 8 m3/s Design speed Cryo-sorption panel Improved

56 Summary: Effects of stochastic magnetic boundary Confinement region Ergodic region Laminar region PFC Benefit Density pump-out PL-H ↑ Enhanced radiation Impurity screening Control of radiation & detachment Strike line splitting (non-uniform power/particle load) Energy transport barrier Change of divertor density regime Cost of divertor volume (10~20% of a) Decontamination Challenge for engineering (RMP coils, 3D shape) ELM mitigation/suppression Change of Er & turbulent transport Peak power load? Pumping efficiency? Core performance? Fueling efficiency ↓ Disadvantage Issues to be assessed

• Ph. Ghendrih et al., JNM 266-269 (1999) 189.

57

In some cases, the high recycling regime appears: Tore Supra, TEXTOR-DED (m/n=3/1)

J.P. Gunn et al., JNM 290-293 (2001) 877. The flow alternation with ED. 58

• T. Shoji et al., JNM 196-198 (1992) 296.

Increase in L-H transition power threshold with ED. 59

• M. Leconte et al., NF 54 (2014) 013004.

Increase in L-H transition power threshold with ED. No RMP With RMP H-mode H-mode Input power Input power 60

• F. Ryter et al., NF 52 (2012) 114014.

Increase in L-H transition power threshold with RMP (AUG). 61

• P. Gohil et al., NF 51 (2011) 103020.

Increase in L-H transition power threshold with RMP (DIII-D). 62

S.M. Kaye et al., NF 51 (2011) 113019. Increase in L-H transition power threshold with RMP (NSTX). With RMP Without RMP 63

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

Change in density limit with RMP (TEXTOR-DED). 64

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Increase in particle confinement time with ED. 65

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Density pump-out with ED. 66

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Particle screening with ED. 67

Reduction in density fluctuation, increase in velocity (potential) fluctuation with ED.

• Ph. Ghendrih et al., NF 42 (2002) 1221.

68

Reduction in blob turbulence transport with RMP (TEXTOR-DED).

• Y. Xu et al., NF 49 (2009) 035005.

69

Change in correction length with RMP (TEXTOR-DED). 70

• Y. Xu et al., NF 47 (2007) 1696.

71 Change in fluctuation as a function of wavenumber with RMP (Tore Supra). Payan J. et al 1995 Nucl. Fusion 35 1357

72 Change in fluctuation as a function of wavenumber with RMP (Tore Supra).

Xu Y . et al 2011 Nucl. Fusion 51 063020

73 Change in fluctuation as a function of wavenumber with RMP (Tore Supra).

Robinson J.R. et al 2012 Plasma Phys. Control. Fusion 54 105007

Reduction in blob turbulence transport with RMP (TEXTOR-DED).

• Y. Xu et al., NF 49 (2009) 035005.

74

• M. Kobayashi et al., NF in press.

Change in turbulence transport with RMP.

• M. Kobayashi et al., NF in press.

75

Change in turbulence transport and Er with RMP. 76

Conway G.D. et al 2015 Plasma Phys. Control. Fusion 57 014035

Change in turbulence transport and Er with RMP. 77

Conway G.D. et al 2015 Plasma Phys. Control. Fusion 57 014035

Little change in Isat fluctuation with RMP (AUG). 78

Muller H.W. et al 2013 J. Nucl. Mater. 438 S64–71

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Enhancement of radiation with ED. 79

• Ph. Ghendrih et al., NF 42 (2002) 1221.

Enhancement of radiation with ED. 80

• P. Monier-Garbet et al., JNM 290-293 (2001) 925.

Enhancement of radiation with ED. 81

• R. Guirletet al., JNM 266-269 (1999) 513.

Enhancement of radiation with ED. 82

• Ph. Ghendrih et al., NF 42 (2002) 1221.

Impurity screening with ED. 83

• Ph. Ghendrih et al., JNM 290-293 (2001) 798.

Impurity screening with ED. 84

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Change in radial E-field with ED. 85

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

Sharp transition of Te at the edge with ED. 86

Sharp transition of Te at the edge with ED.

• Ph. Ghendrih et al., NF 42 (2002) 1221.

87

Sharp transition of Te at the edge with ED.

• S. Feron et al., JNM 241-243 (1997) 328.

88

Sharp transition of Te at the edge with ED.

• S. Masuzaki et al., NF 42 (2002) 750.

89

Heat flux pattern on divertor plates with ED.

• Ph. Ghendrih et al., JNM 241-243 (1997) 517.

In order to complete the analysis, a WKB approximation of the energy transport in the laminar region yields the deposited parallel energy flux in terms of the radial penetration

• f a field line over the typical parallel coherence scale. Using the computed angle

between the field line and the target plate one can check the calculation with the experimental deposited energy flux. Agreement on both the peaking and position of the patterns is obtained. This gives us confidence that present calculations will allow to determine the energy deposition on poorly imaged parts of the ergodic divertor coils.

It was found that is was governed by turbulent transport with an effective diffusion of the order of 1 m2/s, thus comparable to limiter

• data. This result confirmed that the level of turbulent transport was

weakly affected by the stochastic boundary despite the decrease of the largescale density fluctuations.

• Ph. Ghendrih et al., JNM 241-243 (1997) 517.
• Ph. Ghendrih et al., FST 56 (2009) 1432.

90

Heat flux pattern on divertor plates with ED.

• Ph. Ghendrih et al., PPCF 38 (1996) 1653.

91