Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al.,...

Forschungszentrum Jülich

in der Helmholtz-Gemeinschaft

Institut für Energieforschung - Plasmaphysik

EURATOM Assoziation – FZJ

TEC A. Litnovsky et al., Meeting of the EU TF PWI

SEWG on mixed materials, JET, Culham, July 9, 2007

Slide 1 of 13

Formation of mixed W/C and Mo/C layers in TEXTOR

A. Litnovsky,

V. Philipps, P. Wienhold, S. Richter, K. Krieger,

G. Sergienko, A. Kirscher, A. Kreter, S. Droste, D. Borodin

and TEXTOR Team







Slide 2 of 13

Mixed layers in TEXTOR

“Naturally” formed during the PWI experiments

Can be observed after exposure of high-Z limiters

in the SOL plasmas using Limiter Lock systems

Example: twin limiters, castellated limiters







Slide 3 of 13

Exposure of twin W/C limiter in the SOL plasmas of TEXTOR*

W content in the deposit is

the largest neat tangency

point

W found deposited locally on

the carbon part of the limiter

*M. Rubel, V. Philipps, A. Huber and T. Tanabe, Phys. Scr. T81 (1999) 61

Deuterium retention only in

carbon deposition area

W deposited in gaps of C

rough surface despite of C

net erosion area







Slide 4 of 13

Exposures of castellated limiters: general parameters

Experiment Experiment 1 (Mo castellated limiter II)

Experiment 2(W castellated limiter III)

No. of discharges 39 16

Duration of exposure 219 s. 112 s.

Local Te, eV. ~25 eV ~ 20 eV

Local Ne, cm-3 2.5*1012 6*1012

Averaged fluence 2.0×1020 D/cm2 2.2×1020 D/cm2

Bulk temperature of the limiter 220-260oC 200-250oC

Temperature excursions Local heating of plasma closest edge up to 1600oC

Local heating of plasma closest edge up to 1500oC

Diagnostics used: He beam, fast probe, pyrometers, thermocouples,

video observation system, spectroscopy (D, Mo, W)







Slide 5 of 13

0 2000 4000 6000 8000 100000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

Ato

m d

istr

ibu

tio

n 1

017 a

t./c

m2

Distance, micron

A B

EPMAEPMA

0 100 200 300 400 500 600100

101

102

103

104

105

Thickness, nm

MoCDB

MoCDB

SIMS/DEKTAKSIMS/DEKTAKIntensity, a.u.

~ 75 nm

Investigations of deposited layers: Experiment 1

Plasma flow

AB

A: Plasma facing side of the gap

SIMS (calibrated

with Dektak)

EPMAscan

~ 1.7 mm

~ 1.5 mm

Measured spot (~ 30 nm)

Measured spot (~ 30 nm)







Slide 6 of 13

Investigations of deposited layers:Experiment 1: EPMA signals modeling

0 10 20 30 40 50 60 700

50

100

150

200

250D

ep

os

it t

hic

kn

es

s,

nm

Molybdenum share in the deposit at. %

calculated for Carbon

~ SIMS value

At least ~50 at % Mo in the deposit are needed to suit with SIMS results for this location







Slide 7 of 13

0 2 4 6 8 10 12 145.0x1016

1.0x1017

1.5x1017

2.0x1017

2.5x1017

3.0x1017

3.5x1017

Distance along the gap, mm

C, at/cm2


Plasma flow

AB

A: Plasma facing side of the gap

SIMS (calibrated

with Dektak)

EPMAscan

~ 1 mmEPMA value

(without W mixing)~ 25 nm

EPMA value (without W mixing)

~ 25 nm

NRA value~ 42 nm

NRA value~ 42 nm

SIMS/DEKTAK value

~ 50 nm

SIMS/DEKTAK value

~ 50 nm

EPMA modeled value (41 at. % W

in the deposit)

EPMA modeled value (41 at. % W

in the deposit)

EPMA, NRA, SIMS/DEKTAK

W castellated limiter

NRAscan







Slide 8 of 13


W castellated limiter: W mixing quantification

43,7%

69,6%

2,3%

36%

2,5%

41,6%

3,0%

27,3%

3,5% Observations:

Strong W intermixing on the plasma-closest edges of gaps

(>40 at. % of W);

W-share decreases with the depth of the gap

Looks like more W in plasma-shadowed gaps;

More analyses to follow.

open gap shadowed gapPlasma-







Slide 9 of 13

Comparison of the experiments 1 and 2What are these mixed deposits?

Mo/C W/CNMo/NC (gap edge)~ 50 at % Mo NW/NC (gap edge) ~ 40-70 at % W

D/C < 0.1 D/C <<0.1

Less than 0.1% of impinging D

flux trapped in gaps

Less than 0.1% of impinging D

flux trapped in gaps

The properties of W/C and Mo/C mixed deposits are very similar







Slide 10 of 13

Comparison of the experiments 1 and 2Similarity of W/C and Mo/C layers: why so?

Same geometry of studied samples

No much difference between Mo and W for EPMA simulation: CKα absorption is similar

Exposure in similar plasma conditions

Y, cm2/mg

Mo W C

19.2 17 6







Slide 11 of 13

Comparison of the experiments 1 and 2Similarity of W/C and Mo/C layers: why so? Part II

General feature: metal intermixing decreases with the gap depth

Cn+, D+

C0 , D0

Mo

MoC0, D0

65 at.% Mo* 50 at.% Mo

Very low D content: are W/C layers actually an issue for ITER?

*A. Litnovsky et al, Proc. of 32nd EPS, ECA Vol. 29C, P-

1.015 (2005);A. Litnovsky et al.,J. Nucl. Mater. in

press







Slide 12 of 13

Summary

Mixed W/C and Mo/C deposits observed during investigations of twin

W/C limiters and in the experiments with castellated limiters in TEXTOR

Large share of metal (up to 70 at. %) in the intermixed layers

W/C and Mo/C layers formed in gaps of castellated limiters are similar

Metal share in the deposit decreases with distance

from the metal source

Generally low D-retention in studied mixed layers







Slide 13 of 13

Thank you







Additional slide

NRA spot size







Additional slide

W mixing: detailed results

10000 11000 12000 13000 14000 15000

0

10

20

30

40

50

60

70

80

10000 11000 12000 13000 14000 15000

0

10

20

30

40

50

60

70

80 W mixing in the deposit, at. %

plasma open gap er1b

Distance along the gap, micron

plasma shadowed gap er2b







Additional slide

SIMS measurement locations







Additional slide

Encapsulated deposits*

0 100 200 300 4001x102

1x103

1x104

1x105

Thickness, nm

Intensity, a.u.

SubstrateDepositW-layer D

C

W13C

SIMS spectra show an a:C-D deposit with a

thickness of ~120 nm, covered with a ~ 100 nm thick

layer of pure tungsten

*A. Litnovsky et al., Phys. Scr. T128 (2007) 45;

Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al.,...

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