Download - EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 1 Report of the Special Expert Working Group on Chemical

1Institut für PlasmaphysikAssoziation EURATOM-Forschungszentrum Jülich

EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ

SEWG Chemical ErosionS. Brezinsek

TEC

Report of the Special Expert Working Groupon Chemical Erosion

S. Brezinsek

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

SEWG members:CEA E. Gauthier, J. Hogan …CIEMAT F. Tabares …FZJ A. Pospieszczyk, A. Kirschner, A. Kreter, D. Borodin, G. Sergienko, V. Philipps … IPP W. Jacob, J. Roth, Ch. Hopf, M. Mayer, M. Schlüter, T. Schwarz-Selinger

R. Pugno, A. Kallenbach, W. Bohmeier … UKAEA M.F. Stamp …




TECStatus: ITER - tritium inventory limit

0 200 400 600 800 10000

100

200

300

400

500

600

S=0.5,moldyn

S=0,moldyn

Tri

tiu

m c

o-d

ep

oit

ion

(g

)

Number of ITER pulses

Brooks/Kirschner

present evaluation

S=1

In-vessel limit

WBC, PSI 2002

Roth/KirschnerERO, PSI 2004

600 full performance shots!




TECFlux dependence of Ychem

• In-situ calibration: mass/optical spectroscopy • Temperature normalisation to Tmax

• Ion energy normalisation to 30 eV• Flux dependence

Roth et al. EPS2003, PSI 2004

Y(E,T,)=

Description of Y as function of- Ion energy- Surface temperature- Ion flux

Ylow(E,T)

6*10211+

0.54




TECERO modelling for ITER scenarios

standard ITER operation

Roth, Kirschner et al. NF 2004

•Plasma simulation from B2 Eirene•Steady-state temperature profiles along the divertor target (Federici 2003)

But: No consideration of ELMs, no a-C:H layers,

no synergetic effects …




TECTopics to be discussed

Improvement in the data evaluation Better spectroscopic data interpretation Photon efficiencies

Higher Hydrocarbons Influence of

ELMs (e.g. AUG) & detached plasmas (e.g. DIII-D, JET) Geometry and strike-point positions (e.g. JET, AUG)

Erosion of redeposited a-C:H layers (e.g. JET) Synergetic effects

Mixed layers, Be and W (e.g. PISCES) He+, Ar+ (e.g. MAJESTIX), N2 (e.g. JET, AUG)

ERO modelling Benchmark experiments (e.g. PSI-2, TEXTOR)




TEC







Topics to be discussed




TECSpectroscopic data interpretation

Brezinsek,Pospieszczyk et al. 2004

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

CD/D g C /DII g

YChemC

YtotalC

YPhysC

500 750 1000 1250 1500

T / Ksurface

ero

sio

n y

ield

Yin

%c

D : S/XB=507 (ADAS)CD(1.5 nm): D/XB=100 (A.Pos.) CII(426.7 nm): S/XB=87 (ADAS)

gTEXTOR 89155-70

TEXTOR pre-heatable

graphite limiter

New experiments with intensity corrections:Y=3.3 % at Tmax=830 K

Previous experiments(in Roth data base)

Y=4.2 % at Tmax=830 K

Intensity correction:- Photon efficiency correction of Dg due to D2 molecules- Impurity background in the CD spectrum subtracted




TEC











TECHigher Hydrocarbons

Vignettation l-o-s

YC2H4≈ 3.0 %

GIM 10

GIM 9a

b

c

de

JET: C2 light from C2H4 injection

t / s

Higher hydrocarbons only partially treated!

Brezinsek, Stamp 2004




TEC











TECPlasma regimes – H-mode in AUG

Pugno et al. PSI 2004

There is an ion flux dependence in H-mode discharges

Data not normalised!

with ELMs

Integrated over ELMs!




TEC

Detached plasmas: still large uncertainties, big scatter of data

-> DIII-D practically no chemical erosion (Whyte et al NF 2001)

-> JET inner divertor: 15% erosion (strike point on vertical target),

less on horizontal target (Stamp 2003)

-> AUG …

-> TEXTOR test limiter: increase of C2 signal! Higher erosion

Effect of rate coefficients?

(Pospieszczyk EPS 1995)

New experiments necessary!

High flux and low energy should reduce the erosion yield!

Plasma regimes – detachment




TECGeometry and strike-point positions

1

2 3

57072 57076 57080 570840,0

5,0x1015

1,0x1016

Shot number

2C

arbo

n de

posi

tion

( C

/cm

S

)

11

1

2 2

3

3

1

2 3

1

2 3

57072 57076 57080 570840,0

5,0x1015

1,0x1016

Shot number

2C

arbo

n de

posi

tion

( C

/cm

S

)

11

1

2 2

3

3

57072 57076 57080 570840,0

5,0x1015

1,0x1016

Shot number

2C

arbo

n de

posi

tion

( C

/cm

S

)2

Car

bon

depo

sitio

n ( C

/cm

S

)C

arbo

n de

posi

tion

( C

/cm

S

)

11

1

2 2

3

3

Esser et al. PSI 2004

Strike-point position important Stepwise transport of carbon

QMB – deposition monitor




TEC





He+, Ar+ (e.g. MAJESTIX) on a-C:H layers, N2 (e.g. JET, AUG)

Mixed layers, Be and W (e.g. PISCES)ERO modelling

Benchmark experiments (e.g. PSI-2, TEXTOR)





TEC

Sweep of the strike point through the corner in L-mode

0 18time / s20222414123

16

C narrow ch2 C wide ch2

I / 10ph s

cm15

-1-2

a-C:H layers in the inner divertor of JET

Brezinsek et al. PSI 2004

• Strong C2 light emission from hydrocarbon layers => C2Dy

• Different ratio of C2 to CD light • Removal within one discharge in H-mode with strike-point fixed at the location of the layer

a-C:D layer

strike point

14.3 s14.7 s15.0 s

ch3




TEC












TEC

UHV chamber

Setup MAJESTIX

H2

CH 3

N2(CH3)2

ellipsometry, infrared

substratesubstrate

preparation chamber

rf plasma H

WienFilter

Ar + 1 keV

Ar + 20 eV

de-celeration

UHV experiment with 2 radical beam sources and one ion beam source

W. Jacob, Ch. Hopf, A. von Keudell, M. Meier, and T. Schwarz-Selinger:” Particle-beam Experiment to Study Heterogeneous Surface Reactions Relevant to Plasma-assisted Thin Film Growth and Etching”, Review of Scientific Instruments 74, 5123-5136 (2003).

Synergetic effects – Ion beam and H




TEC

10 100 1000

0,01

0,1

1

10

chem

ical

spu

tterin

g yi

eld

energy (eV)

N+

2 Ar+

Ne+

He+

H+

2

Combined interaction of ions with atomic H leads to chemical sputtering

here: ratio H/ion = 400

strongly enhanced erosion

Ch. Hopf, A. von Keudell, and W. Jacob, ”Chemical Sputtering of Hydrocarbon Films”, J. Appl. Phys. 94, 2373 (2003).Modeling results: Ch. Hopf and W. Jacob, unpublished, N2 data: M. Meier et al., unpublished

atomic H + ions

Model parameters:a = 0.4R 400

Status:TW4-TPP-ERCARIntermediate Report Jan. 2004

Synergetic effects – chemical sputtering

on hard a-C:H layer




TEC

10 100 1 000

0.1

1

10

1E12

1E13

Hopf's model: = 0.4 nm, E

bb= 5 eV

a = 0.4

eros

ion

rate

=

Y ( Ne+ ), TRIM.SP ( Ne+ ); ( H° )

Y ( Ne+ | H°)

Yie

ld (

erod

ed C

per

ion)

: Y

=

/

ION

Ne+ energy [eV]

M. Schlüter, unpublished

Chemical sputtering yield for the simultaneous interaction of H and Ne+

Good agreement with the model by Hopf et al.

Status:TW4-TPP-ERCARNew results

Synergetic effects – new results




TEC

0 20 40 60 80 1000.00

0.05

0.10

0.15

0.20

0.25

0.30

ero

sio

n r

ate

(n

m s

-1)

N2/(N

2+H

2) ratio (%)

Ion energy 30 eV 50 eV 100 eV 200 eV

Erosion was measured in low-temperature ECR plasmas in mixtures of N2 and H2 (p = 1 Pa).The ion energy was varied by applying an rf bias to the sample electrode.

Steep increase of erosion rate with increasing N2 admixture (factor 15).

Maximum for 20 to 30 % N2.

Slow decrease from 30 to 100 % N2.

Sun Chao, Ch. Hopf, T. Schwarz-Selinger, and W. Jacob, unpublished

Status:TW3-TPP-SCAVOPNew results

New results: Erosion in N2/H2 plasmas

Scavenger experiments performed by Tabares in JET, ASDEX, PISCES => see CIEMAT




TEC

• Expose C target to Be seeded D plasma, Target Bias 50V• Increase Be concentration from 0.0 to 0.15 % during exposure• Monitor Be1+ line and CD-band• Target temperature ~ 500K high chemical erosion

• Expose C target to Be seeded D plasma, Target Bias 50V• Increase Be concentration from 0.0 to 0.15 % during exposure• Monitor Be1+ line and CD-band• Target temperature ~ 500K high chemical erosion

CD-band decreases by ~80% for a Be plasma concentration of 0.15 %

Be surface coverage after exposure 87% (AES).

Indicates shielding effect through Be layer formation

Indicates shielding effect through Be layer formation

Synergetic effects – Be and C

Schmidt et al. PSI 20040.00 0.05 0.10 0.150

20

40

60

80

100

CD

-Ba

nd

inte

ns

ity

[%]

Be plasma concentration [%]

CD-Band intensity [%] Linear Fit: CD = 100.0 - 580.6 * CBe




TEC

0.0 0.1 0.2 0.3 0.40

20

40

60

80

100

Be s

urf

ace c

on

cen

trati

on

[%

]

Be plasma concentration [%]

500K 1000K 1200K 1280K

Be surface concentration increases quickly with Be plasma concentration

Expose C targets to a Be seeded D plasma at:• At target temperatures from ~500K to ~1280K• Be plasma concentrations from 0 to 0.35 %

Measure (AES) Be surface concentration after exposure

At temperatures ≥ 1200K diffusion and thermally enhanced erosion reduce Be surface coverage

Almost full surface coverage for Be plasma concentrations < 1%

Almost full surface coverage for Be plasma concentrations < 1%

Schmidt et al. PSI 2004

Synergetic effects – Be and C




TEC












TECERO modelling

- Parallelisation of ERO code

- Improvement of surface model for material mixing (TriDyn)

- Merging of various versions (limiter – divertor – linear devices)

- Including global transport for divertor devices, code coupling??

- Modelling:

• transport of injected hydrocarbons – TEXTOR, JET, AUG(D/XB, deposition efficiency, re-erosion of deposits)

• chemical erosion studies (Roth formula, JET, ITER)

• PISCES (Be-C layers, tungsten)

• formation of mixed layers (dedicated experiments at TEXTOR)




TECExample: ERO modelling for ITER

Erosion & re-deposition along outer target: Roth vs. 1% yield

Sticking = 0 for hydrocarbons, MolDyn for atoms

Gross erosion 10 times larger with fixed 1% than Roth yield. Local re-deposition significantly smaller with fixed yield.

with Roth yield:

94% re-deposition

6% loss to PFR

with fixed yield:

80% re-deposition

20% loss to PFR

-2.0x1020

6.0x1020

1.4x1021

2.2x1021 SOLPFRRoth

par

ticl

es [

1/m

2 s]

-0.2 0.0 0.2 0.4 0.6-1.5x10

22

5.0x1021

2.5x1022

fixed (1%) gross erosion re-deposition re-deposition minus gross erosion

distance along outer plate [m]




TECERO modelling – PSI-2 experiments

comparison of databases (Erhardt & Langer; Alman, Ruzic & Brooks, Janev & Reiter)

check of sticking coefficients in-situ study of erosion and deposition

Bohmeyer et al. PSI2004




TECFuture work

Improvement in the data evaluation Erosion yield for higher hydrocarbons Extension of the plasma parameter regime (detached plasmas) erosion of redeposited layers (a-C:H layer) Synergetic effects

effect of mixed layers, Be and C Chemical erosion He+, N2+ - H mixtures

ERO Modelling TEXTOR and JET methane puffs an hydrocarbon transport,

D/XB values, higher hydrocarbons, PISCES sticking coefficients, data base, PSI-2




TECOnline manual on ERO webpage

Download - EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 1 Report of the Special Expert Working Group on Chemical

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