EU Plasma-Wall Interaction TF – Meeting 13.-15.11.05 – SFA Ljublijana SEWG Chemical Erosion S....

Institut für PlasmaphysikAssoziation EURATOM-Forschungszentrum Jülich

EU Plasma-Wall Interaction TF – Meeting13.-15.11.05 – SFA Ljublijana

SEWG Chemical ErosionS. Brezinsek




Report of the Special Expert Working Groupon Chemical Erosion

S. Brezinsek

TF-E

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

SEWG members:CEA E. Tsitrone, E. DelchambreFZJ A. Pospieszczyk, A. Kirschner, A.Kreter, D. Borodin, V. Philipps … IPP W. Jacob, J. Roth, Ch. Hopf, T. Schwarz-Selinger

R. Pugno, A. Kallenbach, W. Bohmeyer, M. Baudach … UKAEA M.F. Stamp CIEMAT F. Tabares, D. Tafalla, J.A. FerreiraFOM G. vanRooij, J. Westerhout and TFE members







Motivation - ITER

Beryllium

Tungsten

ITER

Lifetime issues Erosion, transport, and deposition of divertor material (CFC) Erosion, transport, and deposition of first wall material (Be) => mixed material systems (Be, C, W) Control of transient heat loads (ELMs and disruptions)

Safety issues Retention of tritium via co-deposition Methods to release the trapped tritium Dust formation (Be and T)

Research goal: minimisation of risksand optimisation of ITER availability!

Issues reflect the principle structure of the special expert working groups! All topics are related to each other!

Graphite







ITER – Divertor Plasma Parameter Range

Standard operation scenario Semi-detached and recombining divertor plasma (Te<1.5eV) High ion and atom flux (>3*1024 m-3) High surface temperature (up to1600 K)

-0.2 0.0 0.2 0.4 0.61E17

1E19

1E21

1E23

1E25

ion flux atom flux electron density electron temperature

flu

x [1

/m2 s]

, den

sity

[1/

m3 ]

distance along outer plate [m]

0

5

10

15

20

tem

per

atu

re [

eV]

B2-Eirene simulation for the ITER outer divertor

(A.S. Kukushkin)

Result from AUG with W main chamber and C divertor (Kallenbach et al. 2006) :Outer Divertor is the remaining source of carbon => Chemical erosion main process







Chemical Erosion Yield - Present Description

Erosion yield Y as function of Surface temperature Incident ion energy Incident particle flux

Roth et al. PSI 2004

ITERrange

1019

1020

1021

1022

1023

1024

10-3

10-2

10-1

Che

mic

al E

rosi

on Y

ield

(at

/ion)

Ion Flux (m-2

s-1)

Ion Beams IPP PSI1 JT-60U outer div ToreS 2001 ToreS 2002 TEXTOR PISCES JET 2001

1025

But in ITER: Detached plasma operation Comparable atom and ion flux Low energy of incident particles Hot target surface

Y =chem

C

D

chem

Fuel outflux:

Hydrocarbon influx:

C

chem

D

Erosion yield:







Motivation - Tasks

Which species are eroded from the PFC? Methane-, ethane-, propane family ….

Where are the species eroded from? How much is eroded? Spatial distribution of the erosion yield along the target ….

What does the plasma do with the eroded hydrocarbons? Hydrocarbon catabolism and transport….

Where are the break-up products deposited?Inner divertor ….

Amount of deposited particles? Which hydrocarbon films are produced?Hard layers, soft layers….

Which species is re-eroded?Higher hydrocarbons preferred ….

We have to understand:

We should (try to) influence (control) these processes to ensure a safe operation.

Erosion

Migration

Deposition

Re-erosion







ITER predictions / SEWG

Predictions for

ITER

Data base & Codes: HYDKIN

ADAS, TRIM…

Code and data base validation: benchmark experiments TEXTOR, AUG, TJ-II …

Plasma backgroundB2-Eirene

or EDGE2D

Tokamak experiments JET, AUG, TEXTOR…

ERO modellingLaboratory experimentsMAJESTIX …

Linear experimentspilot-MAGNUM, PSI-II







Outline

Recent experimental results from: TEXTOR TJ-II ASDEX Upgrade JET Pilot-MAGNUM PSI-II Laboratory Experiments (IPP) ERO – ITER predictions







TEXTOR Photon efficiency calibration: benchmark for HYDKIN and ERO Hydrocarbon catabolism 13CH4 experiments Long term deposition and erosion pattern ….







Spectroscopic approach

C 2

C D C2 y 2

A-XC D CD2 y

A-X

CD CD4

A-X

~

Photon flux proportional to particle flux (in ionising plasmas)

C2CD C2y2

A-X

CD CD CD4

A-X

Effective inverse photon efficiencies (D/XB-values) include dissociation chain D/XB-values depend on geometry, surface conditions etc.

=B

D

X

: - particle flux

X X - e citation rate coefficient B B - ranching ratio

f t- photon lux [el. ransition] t

D - ecay rate [ionisation, dissociation ...]D

Chemical erosion yield is given by a corrected methane erosion yield







Comparison with HYDKIN and ERO

calculations:

D/XB values without contamination from deposited and re-eroded hydrocarbons

Simple and highly reproducible plasmas

D/XBExp. =36D/XBHYDKIN=46D/XBERO=32

CD A-X band(CD from CD4)

TEXTOR: Photon Efficiencies for Methane

plasma

gas inletCD A-X430.7+/-1.0nm

CD A-X430.7+/-1.0nm

gas inlet

BB

top view side view

# 98032# 98031 TEXTOR TEXTOR

high field side

ERO modelling CD A-X light







CxHy in D plasmas: Te=35 eV, ne=2.2*1018m-3 at the emission locationCxDy in H plasmas: Te=45 eV, ne=1.8*1018m-3 at the emission location

CH A-X band (Gerö band) C2 d-a band (Swan band)

Brezinsek et al. PSI 2006

TEXTOR: Effective Photon Efficiencies for CxHy , CxDy







HYDKIN: Photon Efficiencies for Methane

Comparison of measured effective photon efficiencies with HYDKIN (Reaction kinetic analysis - Reiter 2006) for CH from CH4

(const. plasma, no deposition, no transport)

Janev-Reiter database is reliable in the range between 5 eV and 100 eV Influence of other surface parameter and geometry: loss of photons Data base is used as input for the ERO code!

Brezinsek et al.PSI 2006







TEXTOR: CD+ Observed in Hot Edge Plasmas

TEXTOR benchmark experiment with CD4: 20 % of theoretically expected

CI 909.5 nm per C observed 50 % of theoretically expected

CII at 426.7 nm per C+ observed 20 % of theoretically expected

D per D observed

l / nm

0.0

0.2

0.4

0.8

420.0 425.0415.0 430.0 435.0inte

nsity

/ ar

b. u

nits

T 3500 Krot»

TEXTOR #93964

CD A-X bandmodelling

CD

=> CD+ identified in TEXTOR plasmas=> break-up via molecular ions important







Part of the dissociation chain (CH4):

CH4+

CH4

CH3+

CH3 CH2 CH C

CH2+ CH+ C+ C2+

Reaction kinetic analysis with HYDKIN (Reiter 2006) for CH4

Te=45 eV

CH+

CH

Te=5 eV

CH

CH+

Hot limiter plasma (TEXTOR, TJII)Cold divertor plasma (AUG, JET)

HYDKIN: CH+ vs. CH in the CxHy Catabolism







TJ-II Hydrocarbon injection experiments a-C:H film production and destruction due to hydrocarbon puffing Nitrogen scavenger experiments ….







TJ-II: Hydrocarbon Injection Experiments

Stellarator – current free device; Strong ripple; ECRH heated plasmas Injection of CH4, C2H4 and H2 through a mobile instrumented graphite limiter

Gas pulses of 12-15 ms (4 – 8x1018 particles) Much lower fuelling efficiency for C2H4 than for H2. Hα photon yield 15% per H atom

that of H2 (Garcia-Cortes et al. JNM 2005)

Photon flux ratio CH/Hα 3 times higher for C2H4 than for CH4 (Te=3eV ne=2x1018 m-3) deposition of carbon films with high H content

#12940 (H2 puff)

12940.Densidad2_

H wallTi (0)(a.u.)CV (a.u.)

1000 1050 1100 1150 1200 1250

ne (1012

) (cm-3

)H limiter

0

0.4

0.8

Time (ms)

1000 1050 1100 1150 1200 1250

#12937 (C2H

4 puff)

Time(ms)

0.8

0.4

0

H

CH

Tabares et al.PSI2006

C2H4







AUG Photon efficiencies, hydrocarbon particle fluxes and erosion yield in detached and attached plasmas Long term erosion deposition pattern Carbon source determination 13CH4 injection experiments ….







z /

m

1.0 1.5 2.0R / m

OSP sweep

injectionintrinsic

-1.25

-0.75

-0.50

S4=1.594 m

T4

S3

NP

S4

S2=0.541 mS3=1.038 m

S1=0.000 m

S1

T1LP9

ISP sweep

injection intrinsic

-1.00

T3=1.170 mT4=1.242 m

valve

S2

T3

LP1NP: Neutral Pressure GaugeLP: Langmuir Probe

VOL

T1=0.395 m

VOLT3

ROV18

ROV16

ROV15 (blind)

ROV14

ROV13

ROV12

ROV11

T4

ROV17

AUG: Hydrocarbon Injection in Detached Plasmas

L-mode discharges with outer divertor detachment Injection of CH4 and C2H4 in the SOL, Separatrix and PFR

in the volume: Te=1.2 eV, ne=3*1020m-3 at the target (separatrix): Te=2.3 eV, ne=4*1018m-3







Brezinsek et al. PFCM 2006

AUG: Photon Efficiencies in Detached Plasmas

Intrinsic CD A-X spectrum --- attached plasma ---

Intrinsic CD A-X spectrumwith strong BD contamination

--- detached plasma ---

CH A-X spectrum from injection and CD A-X intrinsic background

--- detached plasma ---

CH A-X spectrum from injection and CD A-X intrinsic background

--- attached plasma ---







Brezinsek et al. PFCM 2006

AUG: Photon Efficiencies in Detached Plasmas

Intrinsic C2 d-a spectrum --- attached plasma ---

Intrinsic C2 d-a spectrum --- detached plasma ---

C2 d-a spectrum from injection --- detached plasma ---

C2 d-a spectrum from injection --- attached plasma ---

Below the detection limit!







AUG: Erosion Yields in Detached Plasmas

Decrease of CH and C2 light much stronger than increase of D/XB

=> Significant decrease of the hydrocarbon flux in detachment

D/XB for CH from CH4: 18 +/-7D/XB for CH from C2H4: 47 +/-19

Measured D/XB values are slightly higher than in attached plasmas and higherthan predictions with HYDKIN!

Ychem=3.2*10-2 (ion flux only)

Ychem=2.9*10-3 (atom and ion flux)

Erosion yield at the separatrix for detached conditions:

Reduced influx is largely compensated by lower plasma ion outflux=> atom outflux important

Roth-formula: Ychem=2.5*10-3 (atom and ion flux)

only ions

ions & atoms

detachment (at separatrix)

Roth et al. NF 2004







JET Hydrocarbon injection experiments a-C:H film production and destruction as function of the strike-point Nitrogen scavenger experiments 13CH4 tracer experiment….







2.20 2.40 2.60 2.80 3.00 3.202.20 2.40

7

6

53

1

2

4

#63253

t2

t3

t1

KS3I KS3O

1.80

1.70

1.60

1.50

1.40

1.30

1.80

1.70

1.60

1.50

1.40

1.30

he

ight

[m

]

major radius [m]

GIM 10OSP sweep

#63250

KS3 - integrated photon fluxes

loc

al T [e

V]

e

time [s]22 23 24 25

021

4

5

12

20

loc

al n

[1

0 m

]e

19-3

n mapped on GIM10 location

e

T mapped on GIM10 location

e

1

0

4

8

PFREFIT

#63250

KY4D #63253

2

3

16

24

SOL

Circumferential injectioninto the attached outer divertor:i) Discharge with C2H4 injectionii) Discharge with H2 injection

Nearly identical local plasma conditions

Assumption: symmetric and homogenous injection

JET: CxHy Contribution to the Erosion Yield







Most reliable value for Ychem is achieved when the strike point is at GIM10

Toroidal inhomogeneity of gas injection module included (=> information from 13CH4 tracer experiments)

Bypass in the outer divertor considered!

Photon efficiencies and erosion yield lowered in comparison to first analysis (Brezinsek et al. EPS 2005)

D/XB for C2 Swan band from C2H4 about 75 Ychem associated to higher hydrocarbons about 0.6%

SOL

sweep

#63253KS3O

0.25

0.50

0.75

1.00

1.25

1.50

1.75

PFRsweep

YC

2Hy [

%]

impinging ion flux (at GIM10) [10 ions s m ]23 -1 -2

chem

KY4D

EFIT

0.4 0.8 1.2 1.60.0

Brezinsek et al. PSI 2006

JET: CxHy Contribution to the Erosion Yield







JET: Preferred Release of Hydrogen-rich Hydrocarbons

K S 3 A

# 5 6 9 7 6

500 550 600 l / nm

# 5 6 9 7 6

0.0 0.5 1.0 1.5 2.0 2.5

intensity /

10ph sc

m15

-1-2 14.7 s

450 C I I

C I I I D

D

C D

v = 0 v = - 1

v = - 2

C2

C I I

v = 1

500 550 600

D

C D

l / nm

C2

v = 0

v = 1

v = - 1

v = - 2

K S 3 A

0.0 0.5 1.0 1.5 2.0 2.5

intensity /

10ph sc

m15

-1-2 14.7 s

450

15.0 s

C I I

# 5 6 9 7 6

C I I

C I I I D

a-C:D layer

14.3 s14.7 s15.0 s

ch3

Spectroscopy detects: strong C2 light emission Deposition monitor: strong material deposition

Soft layer detected and“(re)moved/cleaned”.

Brezinsek et al JNM2005

Ratio of C2/CH line emission indicate hydrogen-rich layer near to louvre Strike-point utilised to “clean up” deposited areas Thermal decomposition of deposited layers most probable







JET: History Effect

0

20

40

60

80

100

120

140

68

13

3

68

13

4

68

13

5

68

13

6

68

13

7

68

13

8

68

13

9

68

14

0

68

14

1

68

14

2

68

14

3

68

14

4

68

14

5

68

14

6

68

14

7

68

14

8JET pulse #

no

rma

lize

d

[

Hz/

s]

H mode cleaningsweep

L modereference sweep

H modehorizontal target

H mode verticaltarget

Identical discharges!

doubleNBI

Material deposition on the QMB depends on the strike-point position of previous discharges! Identical plasma discharges lead to different net deposition on QMB Strike-point configuration as well as ELM type influence deposition







Pilot-MAGNUM Erosion yield at ITER-relevant fluxes….







Pilot-MAGNUM: Plasma Parameter Range

Arc

Coils

ThomsonScattering

Target

Spectroscopy

0.55 m

Parameter variation:Source current & flowVessel pressureMagnetic fieldTarget potential

5

4

3

2

1

0

Ele

ctro

n T

empe

ratu

re (

eV)

1019

2 3 4 5 6

1020

2 3 4 5 6

1021

2 3 4 5 6

1022

Electron Density (m-3

)

>1023 H+/m2s >1024 H+/m2s >1025 H+/m2s

Ion fluxes and plasma parameters at the target are comparable to predicted ITER divertor conditions!

v. Rooij et al.ITPA Toronto 2006







Pilot-Magnum: First Results on Erosion Yields

Ionising hydrogen plasma (Te=3.5 eV)in front of the fine grain graphite target.

Preliminary work basedon CH A-X band analysis: gas injection for calibration in preparation uncertainties in the surface temperature

New experiments planed!

Experimental data in-line with the Roth-formula!







PSI-II Re-erosion of hydrocarbons at elevated wall temperatures Hydrocarbon spectroscopy….







TMPQMS analyses the

exhaust ~1 m upstream

forepump

Large collector probe

duct

Langmuir probe

100 sccm H2

discharge regiontarget chamber

0.1 Pa

TM pumps

20 cm

floating W disk

CH4 +100 sccm H2

~200C~ 150C

0.8 Pa

PSI-II: CxHy Erosion from Deposited a-C:H Layers

Bohmeyer et al. PFCM 2006

• Injection of methane into a PSI-II hydrogen plasmas• a-C:H layers build up on the “heatable” wall• Erosion by neutral hydrogen• Detection of the eroded species with the aid of QMS and collector probes in the pump duct

Collectorprobes for

in situ analysis

heated







4000 5000 6000 7000 8000tim e (sec)

0E+0

2E-12

4E-12

6E-12

8E-12

inte

nsity

(A

)

2 6

1 5

2 7

2 9

plasm aO N

2 sccm C H 4

Increasing wall temperature

Wall temperature fixed at 180° C

Dominant erosionproduct from

the hot wall (180°C)is acetylen (m=26)!

PSI-II: CxHy Erosion from a-C:H Layers at Walls

QMS in the pump duct:







PSI-II: Deposition/Erosion in the PSI-II Pump Duct

0 50 100 150 200 250 300 350 400 450 500tim e (m in)

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

6 5

prob

e th

ickn

ess

(nm

)

0.10 nm /m in

0.14 nm /m in

P lasm aO N

Plasm aO FF

probe tem perature 400 K

2 sccm C H 40.06 nm /m in

Unheated duct: deposition ( 0.01…0.05 nm/min) along the duct (2 sccm CH4)

Heated collector probe: erosion (2 sccm CH4 )

Erosion by atomic hydrogen

Reduced erosion during CH4 injection

Surface temperature is the key parameter for the erosion/deposition “switch”

Bohmeyer et al.







Laboratory experiments (IPP Garching) Nitrogen/hydrogen mixtures Re-deposition of soft a-C:H films after thermal decomposition….







Redeposition of Soft a-C:H Films after Thermal Decomposition

movable tubular oven Tmax = 1300 K

sample position

sample positionfor MBMS

Jacob et al.2005

TESS: Setup







TESS: Thermal effusion spectra

4 amu : D2 32 amu : C2D4 & C2D6

18 amu : CD3 & H2O 34 amu : C3D8

20 amu : CD4 46 amu : C3D6 & C4D8

28 amu : C2D2 & CO2 50 amu : C4D10 & C5D12

Hard a-C:D Soft a-C:D

Tramp = 15 K/min

- Large contributions from long chain hydrocarbons-High redeposition (~5ß%)

500 600 700 800 900 1000 11001

10

100

1000

10000

100000

dN

/dt (

cps)

Temperature (K)

4 amu 18 amu 20 amu 28 amu 32 amu 34 amu 46 amu 50 amu 66 amu

875 K

Jacob et al.2005







QMS

0 10000 20000

1E-9

1E-8

Pre

ssu

re (

mb

ar)

Time (s)

soft a-C:D hard a-C:D

Shift of oven causes desorption of material which wasredeposited on the walls of the glass tube.Redeposition fraction from integration » 41%

TESS: Redepositon







ITER Predictive modelling for ITER with ERO (here: only C)







Chemical erosion yield (D+ graphite) along outer target

Erosion yield YRoth: - min(YRoth) ~ 0.04% around strike point (high flux)

- max(YRoth) ~ 0.6% @ Tsurf = 670°C

1E20

1E21

1E22

1E23

1E24

1E25

Roth

Y = 1%

ion flux [1/m2s]

ion energy [eV] surface temperature [°C] Roth yield [%]

ion

flu

x

distance along outer plate [m]

-0.2 0.0 0.2 0.4 0.61x10

-2

1x10-1

1x100

1x101

1x102

1x103

Ein, T

surf, Y

Rot

h

ITER: Chemical Erosion Yield at the Outer Target







ITER predictions / ERO

no lifetime problem (1mm in 500 ITER discharges) T co-deposition critical for D phase (30 ITER discharges) => not an issue for H phase

Influence of Be C erosion reduced by a factor of 2.5 T co-deposition problem remains SEWG ITER-material mix / T retention

Present status (Kirschner et al. 2006):

Still large uncertainties!Improvements possible!

Implementation of new results will help to increase the levelof confidence!







Summary

Predictions for

ITER

Data base & Codes: HYDKIN

ADAS, TRIM…

Code and data base validation: benchmark experiments TEXTOR, AUG, TJ-II …

Plasma backgroundB2-Eirene

or EDGE2D

Tokamak experiments JET, AUG, TEXTOR…

ERO modellingLaboratory experimentsMAJESTIX …

Linear experimentspilot-MAGNUM, PSI-II

SEWG meetingin MARCH 2007at JET!

EU Plasma-Wall Interaction TF – Meeting 13.-15.11.05 – SFA Ljublijana SEWG Chemical Erosion S....

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