institute for plasma physics rijnhuizen heat load asymmetries in mast g. de temmerman a,b, a. kirk...

Institute for Plasma Physics Rijnhuizen

Heat load asymmetries in MASTHeat load asymmetries in MASTG. De Temmermana,b, A. Kirka, E, Nardona, P. Tamaina, A. Thorntona

aPresent address: FOM Institute for Plasma Physics Rijnhuizen, Ass. EURATOM FOM, Nieuwegein, NL

dEURATOM/UKAEA Fusion association, Culham Science Centre, Abingdon, OX14 3DB

G. De Temmerman Annual meeting of the SEWG on transient heat loads

MWIR camera (SBFP, USA):

320 x 256 pixel @ 300Hz up to 10kHz for 128 x 8 pixel window

Range of lenses (5-50mm), 5mm typical resolution

2.5-5 µm

LWIR camera (Thermosensorik, D):

256 x 256 pixel @ 880Hz up to 20kHz for 128 x 8 pixel window (up to 25 kHz)

2 lenses (15-25mm), 7mm typical resolution

7.6-9 µm

2

Hardware


2 types of views mainly available (with standard lenses):

LWIR camera view 4, 15 mm lens

MWIR camera view 4, 13mm lens

MWIRLWIR

Spatial resolution: 7mm for LWIR, 5mm for MWIR

Used for dust transport studies

Zoomed views possible

MWIR camera view 4, 50mm lens, 1.3mm resolution

MWIR camera view 4, 50mm lens, 1.3mm resolution

Available for upper and lower divertor

3

Available views (1/3)


LWIR MWIR

2 types of views mainly available (with standard lenses):

LWIR camera view 1, 15 mm lens

MWIR camera view 1, 13mm lens

Spatial resolution: 7mm for LWIR, 5mm for MWIR

4 strike points observed simultaneously

14.5kHz max for LWIR

6kHz max for MWIR

4



Wide angle view (7mm lens, midplane)

Views around 70% of the vessel

Ideal for disruption studies

E. Delchambre et al,Images taken during a disruption (1 frame every 3.2ms)



Outline

LWIR/MWIR imaging and heat flux calculations

Status of the MAST DMV

Heat flux profiles during ELM control experiments

Heat load asymmetries during L-mode discharges

Heat load asymmetries during H-mode discharges


Combined LWIR/MWIR imagingOver-estimation of temperature at 5m compared to 8m: 30-40% Attempt of modelling the effect of hot

spots on temperature measurements (E. Delchambre, PFMC12 conference):

bulk substrate

covered with dust in radiative equilibrium (given coverage)

2 temperature distribution

7

MAST case can be reproduced using different assumptions on dust coverage and size (at least for the lower divertor)

Difference between upper and lower divertor (under investigation)

Future work:

LWIR/MWIR measurements on carbon and tungsten at different base temperatures

0 100 200 300 4000

100

200

300

400 Lower divertor Upper divertor

91%

TL

WIR

(C

)

TMWIR

(C)

56%


Heat flux calculations

3-5 µm• toroïdal symmetry• Use of temperature profile along a tile (see red line)• 2D hypothesis• linear calculation• Thermal quadrupoles approach [JL. Gardarein, International Journal of Thermal Sciences, 48 (2009) 1-13]

What has been done : code development and preliminary tests with experimental data.

[ J.L. Gardarein]

Future works: - test with numerical data (inverse calcul. should give input exp. data)- C++ development

SWEEPING OF THE STRIKE POINT


MAST DMV: design and status

Disruptions can be mitigated via the injection of large quantities (~ 1021 particles) of impurity gas

Mitigation decreases heat loads by radiating away stored energy prior to thermal quench

Fast acting valve used to inject gas

Noble gases used for impurity species

Disruption mitigation valve on MAST- Supplied by FZJ- To be operational by the end of September- Located on HM12, centre left port- Gas injected along a pipe to deliver impurities to 30 cm from the plasma edge- Installed on the machine, final commissioning in next few weeks

BOLOMETER VIEWS

Valve

To vessel


DMV: plans for end 2009

Experimental proposals Physics studies only initially – no active mitigation of disruptions via prediction

Disruption mitigation experiments for M7c and continuing to M8 Study the effect of mitigation on target heat loads using upper and lower divertor IR cameras

Observe the evolution and penetration of the injected impurities using fast cameras

Coverage of DMV from two opposite sectors with high speed cameras

Assess the effect of an edge transport barrier on disruption mitigation

Dependence of mitigation timescales on q=2 surface location

Mitigation of plasmas at high beta


φ

R

Deepest radius reached by FL: (Ψpol1/2)min

φ

R (m)

Heat flux during ELM control experiments

Strike point splitting observed by IR in outer divertor

Vacuum modelling predicts splitting

Spiralling structure exists despite stochasticity

Good match between heat flux profile and calculated field lines radial penetration


LWIR

MWIR

Camera views for routine observation of all 4 strike-points– high-speed region-of-interest imaging (vertical)– building database for studying heat load asymmetries (in/out and up/down) for a wide range of plasma scenarios

Power balance in L-mode discharges

15

In L-mode, all the energy coming to the SOL goes in the divertors (no close fitting wall in MAST)

0 50 100 150 200 250 3000

50

100

150

200

250

300Forward B

DND SND

Reversed BDND

En

erg

y to

th

e S

OL

(kJ

)

Energy to the targets (kJ)

15

Heat load asymmetries in L-mode


-6 -4 -2 0 2 4

-1.0

-0.5

0.0

0.5

1.0 Forward B Reversed B

(Ed

ow

n-E

up)/

(to

tal)

rsep

(cm)

LOWERSINGLE NULL

UPPERSINGLE NULL

FRACTION OF UP/DOWN ENERGYVERSUS SEPARATION BETWEEN PRIMARY ANDSECONDARY SEPARATRICES

FRACTION OF IN/OUT ENERGY VERSUS SEPARATION BETWEEN PRIMARY ANDSECONDARY SEPARATRICES

-6 -4 -2 0 2 4

0.4

0.6

0.8

1.0 Forward B Reversed B

(Eo

ut-E

in)/

(to

tal)

rsep

(cm)

L-mode:

Asymmetries depend on magnetic configuration

Non-symmetric behavior of in/out asymmetries



0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

1

2 rsep

=6.4x10-2cm

rsep

=-1.5cm

rsep

=-3.7cm

rsep

=1.5cm

rsep

=2.6cm

Hea

t fl

ux

(MW

/m-2)

R (m)

Lower divertor

-6 -4 -2 0 2 4

0

5

10

15

20

25

30

35

Upper divertor Lower divertor

q (

cm)

rsep

(cm)


Evolution of q with magnetic geometry

Change of heat flux profile with magnetic geometry

Up/down asymmetry: qupper > q

lower

q decreases in SND with input power


-6 -4 -2 0 2 4

0

5

10

15

20

25

30

35

Upper divertor Lower divertor

q (

cm)

rsep

(cm)

-4 -2 0 2 4

0.02

0.04

0.06

0.08

1

Isat 5

Isat

2

Isat 6

Isat

3

Isat 7

Isat

4

Isat 8

Isat

<i

Isat>

Exp

on

enti

al d

ecay

len

gth

(m

)

rsep

(m)

Comparison IR data at target and probe measurements at midplane

Gundestrop probe


q asymmetric behaviour also observed at midplane

Large scatter for different pins in DND configuration, not clear why ?


0.00 0.05 0.100.00

0.05

0.10

04.0167.03.003.195

09.05.062.1)(

SOLeq Pqncm

q scaling in L-mode: 1st attempt

Dataset: 70 DND L-mode discharges

NBI power: 0 to 3.5MW

04.0167.03.003.195

09.05.062.1)( SOLeq Pqncm

Previous scaling (Ahn et al) gave similar power dependence


500 Hz70us integration time

Heat flux profiles during ELMs

Experimental setup:

LWIR camera:

13.5kHz, upper divertor

MWIR camera:

5.6kHz, lower divertor

DND discharges

Up/down, in/out asymetries

Heat flux profiles

Power balance


1.25 1.30 1.35 1.40 1.45 1.50-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

t t+72s t+144s t+216s t+288s t+360s t+432s t+504s

Hea

t fl

ux

(MW

.m-2)

z (m)

1.0 1.1 1.2 1.3 1.4

1

2

3

4

5

6

7

8

9

Hea

t fl

ux

(MW

.m-2)

R (m)

t t+72us t+144us t+216us t+288us t+360us t+432us t+576us

Heat flux profiles during ELMs

Evolution of heat flux profiles during an ELM (1 frame every 72 s):

Inner divertor Outer divertor

Filamentary structure clearly observed in outer divertor

Heat flux profile in inner divertor only slightly modified during an ELM


Energy balance during ELMs

0 1 2 3 4 5 6 7 8 90

2

4

6

8

EIR

(kJ

)

W (kJ)

Comparison between ELM energy from EFIT and IR

Within uncertainties, power balance seems achieved during ELMs


0 5 10 15 20 251.0

1.5

2.0

2.5

3.0

Eu

pp

er/E

low

er

Eelm

(kJ)

averaged over 5 ELMs

Ratio of energy to upper and lower divertors

0 5 10 15 20 25

10

20

30

40

50

60

Eo

ute

r/Ein

ner

Eelm

(kJ)

averaged over 5 ELMs

Heat load asymmetries during ELMs

Ratio of energy to outer and inner divertors

Eouter is between 15 and 40 times higher than E inner

Eupper is between 1.5 and 2.5 times higher than Elower


Future plans

LWIR/MWIR measurements on tungsten and carbon at elevated temperatures

Heat load asymmetry study during SND shots

Use both IR cameras for maximum time resolution (10 and 20kHz)

Study of surface layer effect on inner and outer divertor

Effect of ELM coils on heat fluxes during H-mode (hopefully)

Heat load studies during DMV experiments

institute for plasma physics rijnhuizen heat load asymmetries in mast g. de temmerman a,b, a. kirk...

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