TEC Trilateral Euregio Cluster 1 S. Brezinsek Spectroscopic determination of carbon erosion yields...

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TEC

Trilateral Euregio Cluster

S. Brezinsek

Institut für PlasmaphysikAssoziation EURATOM-Forschungszentrum Jülich

Spectroscopic determination of carbon erosion yields and the composition of chemically eroded

molecular carbon species

S. Brezinsek

Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Jülich, Germany

Thanks to: A. Pospieszczyk, M. Stamp, G. Sergienko, A. Kirschner, P.T. Greenland, P. Wienhold I. Möller, U. Fantz, the TEXTOR-group and JET-EFDA contributors

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Outline

Motivation Methods Absorption spectroscopy on hydrocarbon molecules Emission spectroscopy on hydrocarbon molecules

CD emission spectroscopy C2 emission spectroscopy

C3 emission spectroscopy

Importance of C2 - intrinsic hydrocarbon source at JET

Conclusion

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Motivation

Carbon is the plasma-facing material for the first divertor of ITER good thermo-mechanical properties chemical erosion

Mass spectroscopy:Mix of CDx, C2Dy, C3Dz

TEXTOR, Philipps 1989ASDEX-U, Kallenbach 1994

Emission spectroscopy Mix of CDx, C2Dy observed

JET, Stamp 2001

Identification: species, location, a:C-D film characteristic Quantification: individual contribution, total amount Minimisation: optimum plasma and surface parameters Spectroscopy as an in-situ tool

D, D +

graph ite

a:C-D

CD x C D2 y C D3 z

x 4y 6z 8

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Spectroscopic methods

Dissociation chain of hydrocarbon molecules is important

CD4+

CD4

CD3+

CD3 CD2 CD C

CD2+ CD+ C+ C2+

D2

D2

A part of the dissociation chain of CD4:

Emission spectroscopy: CD, CD+, C, D, D2 can be measured

Absorption spectroscopy: CD2, CD3, CD4 can be measured

Interpretation: calibration experiments erosion-deposition modelling (ERO code)

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Absorption spectroscopy

Not yet tested in a tokamak – only in laboratory experiments

Absorption experiment

in TEXTOR in preparation

Database extended for CD3 and CD4

Detection of CD3 (4.8 µm) and CD4 (4.2 µm) in front of the inner limiter (graphite)

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Emission spectroscopy - CD

Calibration: CD4 injection through a gas inlet (stainless steel)

390 400 410 420 430 440

0

5

10

15

20

25

30

35

40

CD A-X transitionCD B-X transition

CD+ A-X transition

CD

CDCD+

CD4 puff - gas inlet

DD

CD+

CD

CD

CII

inte

nsi

ty /

arb

. un

its

/ nmTEXTOR # 93694

DHigh resolution survey spectrometer

simplified chain

CD4

CD3

CD2

CD

C D

gas inlet

LCFS

SOL

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Determination of the chemical erosion yield

- accessible photon flux

CD: A-X band

- inverse photon efficiencies

D CD CD4

A-X band

Chydrocarbon flux chem

Y =chem

C

D

chem

t

T =T =3500 Krot vib

(2-2) band

420.0 424.0 428.0 432.0 436.0

inte

ns

ity

/ ar

b. u

nit

s

/ nm

0.0

0.8

1.4

0.2

0.6

1.0

1.2

PR

Q

(1-1) band

0.4

(0-0) band

1.6Assumption: only CD4

- total photon flux

A-X spectrum simulation

XB

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Interaction with the surface (i)

450 460 470 480 490 500 510 520

0

5

10

15

C2 v=1)

C2 d-a transition

CD+ A-X transition

CD+

CD4 puff - gas inlet

D

C2 v=0)

CIII

inte

nsi

ty /

arb

. un

its

/ nmTEXTOR # 93694

CIIHigh resolution survey spectrometer

Calibration: CD4 injection through a gas inlet (stainless steel)

ion side CD 4a-C :Dlayer

After several shots: C2 appeared in the spectrum!a-C:D layer is built up

on the protection shield

Additional parameters:- surface layer growth- geometry- temperature

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Interaction with the surface (ii)

Calibration: CD4 injection through a test limiter (graphite)

C2 always detectable in the spectrum (in correlation with the injection)

500 510 520 530 540 550 560

0

500

1000

1500

2000

C2

C2

inte

nsity

/ a

rb. u

nits

/ nm

390 400 410 420 430 440

0

1000

2000

3000

4000

5000

6000

CD

inte

nsity

/ a

rb. u

nits

/ nm

TEXTOR #93732

CD

TEXTOR gas inlet

LCFS

SOL

TEXTOR limiter

LCFS

SOL

Interpretation: release of CD4 from the secondary source (film) intrinsic background conversion factors? yield determination?

More data has to be analysed!

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Emission spectroscopy – C2 (i)

Indirect measurement of C2Dy via C2 radicals

Dissocation of C2Dy can lead to CD radicals

C2D6

CDC2dissociation

chain

H H D D H e H e

0.5

1.0

1.5

0

C H (C D )

A 2" - X 2!

A S D E X U p g rad e

gas puff

m a in gas

C 2H 6C 2H 6CD 4 CD 4 CH 4CH 4

pho

ton

flux

CH

(CD

) [1

017 s

-1]

H H D D H e He

0 .5

1 .0

1 .5

0

C 2 / C H

A S D E X U p gra de

gas puff

m a in gas

C 2H 6C 2H 6CD 4 CD 4 CH 4CH 4

pho

ton

flux

ratio

C2/C

H

ASDEX-U (outer divertor, L-mode) U. Fantz 2003

C2 can be used to determine the contribution of C2Dy

significant amount of C2Dy ends up as CD

Absorption spectroscopy:

direct measurement ofC2Dy with y=1,2,4,5,6

CD C2

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Emission spectroscopy – C2 (ii)

Additional information about the initial species might be accessible via the rovibrational analysis of the spectrum

500 502 504 506 508 510 512 514 516 518

0,0

0,2

0,4

0,6

0,8

1,0

modelling: T

rot=4000 K

n(v=1)

:n(v=2)

:n(v=3)

=1:0.3:0.1

inte

nsi

ty /

arb

. un

its

/ nm

C2 Swan system (d-a transition: band head v=0)

JET # 61379 H-mode

CII multiplet

v'=v''=1

v'=v''=0

v'=v''=3v'=v''=2

inner divertor

0,0

0,2

0,4

0,6

0,8

1,0

inte

nsi

ty /

arb

. un

its

different dissoc. paths different dissoc. energies different rovibrational population

spectra simulation is not yet precise enough molecular constants resolution: ~500 K

U. Fantz

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Emission spectroscopy – C2 (iii)

Sublimation of carbon can lead to the release of carbon clusters Emission of atomic C, C2 and C3 molecules

Energy of C I reflects the surface temperature

Cluster formation observed in electron-beam experiments and laser ablation experiments

on graphite targets

T. Hirai 2003

Rovibrational temperature of C2 molecules should reflect the surface temperature! Should be lower than 3000 K Sublimation experiments at DIII-D performed (Isler 2001)

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Emission spectroscopy – C3

C3 molecules have been observed in laser ablation experiments

Emission of C3 has not yet been observed in tokamaks

S. Arepalli 1999

C3

C2

Overlap of C3 lines with lines of CD and CD+

C3 emission at high temperatures (2000 K)

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JET divertor

Strong C2 emission observed at different locations in the JET divertor

here: corner region of the inner divertor

Normal spectrum Strong C2 emission spectrum

425 450 475 500 525 550 575 600

0,0

2,0x104

4,0x104

6,0x104

8,0x104

1,0x105

1,2x105

1,4x105

1,6x105

d-av=-1

d-av=-2

d-av=-1

D

CII

CII

CII

C2

C2

C2

CIII

CII

D

inte

nsity

/ ar

b. u

nits

/ nm

JET # 56975 KS3A ch4 t=54.7 sinner divertor

CD

C2

d-av=0

425 450 475 500 525 550 575 600

0,0

2,0x104

4,0x104

6,0x104

8,0x104

1,0x105

1,2x105

1,4x105

1,6x105

inte

nsi

ty /

arb

. un

its

/ nm

JET # 56975 KS3A ch4 t=62.5 sinner divertor

CII

D

CIII

CDCII D

CII

C2

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JET divertor

Strong C2 emission observed at different locations in the JET divertor

Always: on the shoulder of the inner divertor

Near to the strike point: L-mode: corner region of the inner divertor H-mode: horizontal plate inner and outer divertor

C2

C2

C2

P. Coad 2003

radius / m

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Conclusion

Emission spectroscopy can provide information about a-C:D layers Observation of different molecular species is necessary: CD, C2 ...

Interpretation is challenging owing to the indirect measurement In-situ calibration of photon fluxes is important

Main release of CD4 and C2Dy from a-C:D layers likely (no C3)

Contribution of C2Dy to the formation of CD has to be considered for

total hydrocarbon flux determination erosion yield determination

Rovibrational analysis has to be improved (molecular data) to give

information about the initial hydrocarbon species

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Total hydrocarbon flux determination

CDCD CD4

A-X

C 2

C D C2 y 2

A-X

higher hydrocarbons also contribute to C :chem

only methane family

CD correction for ethane family

add ethane family

C 2

C D C2 y 2

A-XC D CD2 y

A-X

CD CD4

A-X

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TEC Trilateral Euregio Cluster 1 S. Brezinsek Spectroscopic determination of carbon erosion yields...

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