outer divertor target heat fluxes during resonant magnetic ... · 201711 iaea tm on divertor...

Outer divertor target heat fluxes during resonant magnetic perturbation induced ELM suppressed regimes in KSTAR

H. H. Leea, Y. Ina, Y. M. Jeona, A. Loarteb, R. A. Pittsb, K. M. Kima, H. Frerichsc,

O. Schmitzc, B. Caoa, G. Y. Parka, J. -K. Parkd, J. W. Ahne, S. H. Honga and J. G. Baka aNational Fusion Research Institute, Daejeon, Korea bITER Organization, France cUniversity of Wisconsin-Madison, USA dPrinceton Plasma Physics Laboratory, USA eOak Ridge National Laboratory, USA

e-mail contact: [email protected]

201711 IAEA TM on Divertor Concept (China)

mailto:[email protected]

Contents

• Introduction to divertor IRTV measurement on KSTAR

• 3D structure of the heat flux profile in RMP-ELM suppression regime on KSTAR

• Dynamics of the heat flux profile during RMPs

• Summary

IR CameraVacuum cassette

Optics

Divertor tiles

18°

Model FLIR SC6101

Detector type InSb

(Indium Antimonide)

Spectral Range 3.0 ~ 5.0 𝛍𝐦

Resolution 640 × 512

Detector Pitch 25 μm

Integration time 10 μsec to 687 sec

Max Frame Rate (@ Min Window)

35.112 kHz (64 × 4) 9.009 kHz (640x4)

Full frame rate 125 Hz

Temperature range up to 1500 °C

Infrared Camera

• KSTAR divertor IRTV consists of the vacuum cassette + optics (periscope) + IR camera • Sapphire viewport / ZnSe and CaF2 lenses are used • Standard optics provides the 18o solid angle and 1.2 mm/pixel resolution

Introduction to div. IRTV measurement

Since 2015 campaign, add-on 3X zoom lens has been applied for the divertor IRTV, providing 3 times higher spatial resolution of ~ 0.4 mm/pixel than standard lens

Sample image taken with standard lens Spatial resolution ~ 1.2 mm/pixel along the tile

Sample image taken with 3X zoom lens Spatial resolution ~ 0.4 mm/pixel along the tile

Central Div. tile

Inner Div. tile

Outer Div. tile

view of 3X zoom

lens

BT, Ip


KSTAR #13127

Heat flux reconstruction code (NANTHELOT*) has been developed

𝜕

𝜕𝑥𝜅𝜕𝑇

𝜕𝑥+

𝜕

𝜕𝑦𝜅𝜕𝑇

𝜕𝑦+

𝜕

𝜕𝑧𝜅𝜕𝑇

𝜕𝑧= 𝜌𝐶𝑝

𝜕𝑇

𝜕𝑡, 𝑞⊥ = −𝜅

𝜕𝑇

𝜕𝑥 at surface

• Finite Volume Method is applied to solve the heat diffusion equation • 1D ~ 3D solutions can be chosen • Both explicit and implicit are available • Temperature-dependent thermal properties are considered • Surface layer effect can be compensated • Benchmarked against THEODORE [Herrmann PPCF 37 17 (1995)]

measured by div. IRTV


*C. S. Kang RSI 87 083508 (2016)

For the study of the outer heat flux profile, the striking point is actively controlled to be located on the central divertor target tile


The measurement of the ELM heat load has been achieved with fast IR camera acquisition frequency of ~ 9 kHz (integration time of 100 μs) on KSTAR

KSTAR #16237 ( Ip = 600 kA, BT = 2.3 T, PNBI = 4.0 MW)

3.5 4 4.5 5 5.50

1

2

3

4

5

D

[a.

u.]

& W

dia

[x1

00

kJ]

Time [sec]

3.5 4 4.5 5 5.50

20

40

60

max

(q

) [M

W/m

2]

Time [sec]

Wdia

D


4.277 4.2775 4.278 4.2785 4.279 4.2795 4.280

20

40

60

ma

x(q)

[MW

/m2]

Time [sec]

1.42 1.44 1.46 1.48 1.5 1.52 1.54 1.56 1.58 1.60

20

40

60

Rsep,EFIT Outer

R [m]

q [M

W/m

2]

𝜏𝐼𝑅 ~ 440 𝜇𝑠 †

𝜏|| ~ 220 𝜇𝑠 *

* 𝜏|| ≡ 2𝜋𝑞95𝑅/ 𝑇𝑖 + 𝑇𝑒 /𝑚𝑖 : ion parallel connection time † 𝜏𝐼𝑅 : ELM rising time measured by IRTV

The measurement of the ELM heat load has been achieved with fast IR camera acquisition frequency of ~ 9 kHz (integration time of 100 μs) on KSTAR


n=1 +BR

-BR

+BR

-BR

n=2

3D heat flux profile during RMP-ELM suppression regime

B

𝝓 𝑰𝒑, 𝑩𝑻

𝜽

in (𝑟, 𝜃, 𝜙) coordinates

n = 1, +90 phasing


In 2017, the longest sustainment of RMP-ELM suppression regime of 34 secs was achieved on KSTAR

0.2

0.4

0.6KSTAR #18726

q95

D [a.u.]

IRMP,T

[A]

PNBI

/10 [MW]

Ip [MA]

1

2

3

1000

2000

3000

0 5 10 15 20 25 30 35 404.0

4.5

5.0

5.5

6.0

N

Time [sec]

0

1

2

3

34 secs

n=1, +90 phasing RMPs

0

0.5

1

q/max(q

) [a.u.]

0

0.5

1

0

0.5

1

0

0.5

1

1.44 1.46 1.48 1.5 1.520

0.5

1

R [m]

Φ=45 (t=7.00 s)

Φ=117 (t=7.20 s)

Φ=189 (t=7.40 s)

Φ=261 (t=7.60 s)

Φ=333 (t=7.80 s)

The heat flux profile measurement result represents the effects of 3D RMPs on the divertor heat load

The striation pattern observed on the target tile is different according to the phase of RMPs (rotating RMPs)


-4

-2

0

2

4

I rmp [kA

]

KSTAR #19211 (Ip = 530 kA, P

NBI =3.1 MW)

Irmp,top

Irmp,mid

Irmp,bot

Time [sec]

R [m

]

6.6 6.8 7 7.2 7.4 7.6 7.8 81.44

1.46

1.48

1.5

1.52

0 200 400 600 800 1000 1200

q

[kW/m2]

The main 3D structure feature follows the field line tracing calculation† although details of the calculation can be slightly different according to plasma response models

† K. Kim PoP 24 052506 (2017)

Time [sec]

R [m

]

6.8 7 7.2 7.4 7.6 7.8 81.44

1.46

1.48

1.5

1.52The measurement time can be regarded as the toroidal angle

Vacuum

Ideal plasma response


n=2 RMPs

Dynamics of the heat flux profile during RMPs

Sometimes, it was observed that the striking point splitting is much clearer during the ELM suppression regime while the heat flux profile becomes very sharp with larger peak heat load

n=2 RMPs

A B

KSTAR Div. IRTV #15656 (tm

= 7.36 sec, Tsurf

[o C])

100 200 300 400 500 600

20

40

60

80

100

120

140

160

180

200 100

120

140

160

180

200

220

240

260

6.9 7 7.1 7.2 7.3 7.4 7.50

2

4

6

8

Time [sec]

D [a

.u.]

KSTAR #15656 (tm

= 7.36 sec)

0 20 40 60 80 100 120 1400

0.2

0.4

0.6

0.8

1

A B

Distance [mm]

q [M

W/m

2]



6.9 7 7.1 7.2 7.3 7.4 7.50

2

4

6

8

Time [sec]

D [a

.u.]

KSTAR #15656

-40 -30 -20 -10 0 10 20 30 40 500

0.2

0.4

0.6

0.8

1

Ltile

-Lsep

[mm]

q [M

W/m

2]

w/o ELM suppression

w/ ELM suppression

n=2 RMPs




0.0

0.2

0.4

0.6

0.8

-4

-2

0

2

0

2

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

100

200

300

IIVCC

[kA]

D [a.u.]

Wtot

[kJ]

max(qperp

) [MW/m2]

KSTAR #19032

Time [sec]

Ip [kA]

Φ=+45 Φ=+90 Φ=+135 Φ=+180


5 6 7 8 9 10 11 12 13 14 150.25

0.26

0.27

0.28

0.29

0.3

0.31

Time [sec]

We

tte

d A

rea

[m

2]

Broadening ∝Awet

𝐴𝑤𝑒𝑡 = 𝑞⊥𝑑𝑆𝑑𝑖𝑣

max 𝑞⊥ − 𝑞𝐵𝐺

-20 -10 0 10 20 30 40 50 60 700

2

4

6

8

10

12x 10

5

L-Lsep

[mm]

q [

W/m

2]

KSTAR #19032 div. heat flux

w/o RMP @ 5.63 s

Mitigation @ 6.60 s

Suppression ( = +45) @ 7.90 s

Suppression ( = +90) @ 10.13 s

Suppression ( = +135) @ 12.20 s

Suppression ( = +180) @ 14.20 s

The recent measurement result implies that higher peak heat flux in ELM-supp. regime than those in the w/o RMP and ELM-mitigation regimes is a global phenomenon. But, the physical mechanism for this phenomenon is still under investigation

Summary

• The divertor IRTV has been applied to investigate the non-axisymmetric outer divertor target heat flux profile in the presence of the external resonant magnetic perturbations in KSTAR

• It has been realized that the non-axisymmetric outer divertor tearget heat flux pattern during RMP-ELM suppression regime agrees well with the expectation of field line tracing calculation although there are some differences in details, which are under investigation

• In KSTAR, it was sometimes observed that peak heat flux in ELM-supp. regime becomes higher than those in the w/o RMP and ELM-mitigation regimes regardless of the toroidal phase of RMPs.

• But, how this observation relates with plasma operation scenario or machine circumstances should be investigated comprehensively considering plasma transport, plasma response to external RMPs as well as SOL power balance.

outer divertor target heat fluxes during resonant magnetic ... · 201711 iaea tm on divertor...

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