v.philipps, efpw padua, dec 2005 introduction report on the european task force on plasma wall...

V.Philipps, EFPW Padua, Dec 2005

Introduction

Report on the European Task Force on Plasma Wall Interaction 2005

V. Philipps, J . Roth, A. Loarte

on behalf of the EU- PWI TF members

• Introduction: ITER, PWI & fusion

• Report on 2005 work

• Summary and outlook



scientific case for the TF

Rationale (EFDA): “to provide ITER with information concerning lifetime-expectations of the divertor target plates and tritium inventory build-up rates in the foreseen starting configuration and to suggest improvements, including material changes, which could be implemented at an appropriate stage “

and to „improve the efficiency of work by synergies which are to be executed from the expansion of the work of individual tasks to the operation of all European devices”

EU TF Plasma Wall Interaction

First EU Task Force ,formed end of 2002


PWI will become a key issue in future due to • much larger particle fluencies

• much larger power densities in transients

energy input: 1 ITER pulse about 0.5-1 JET years

divertor ion fluence: 1 ITER pulse about 4 JET years

stored energy: ITER about 100 x JET

T-retention & wall lifetime will become critical

PWI & Fusion

Most of PWI and plasma experience is with graphite wallsselection of first wall materials was determined by optimisation of plasma performance and flexibility


ITER

700m2 Be first wall

100m2 Tungsten

50 m2 Graphite CFC

Material selection determines largely

- Critical PWI topics & EU-PWI-TF work programme

ITER material selection

Rationale for ITER material choice is

to guarantee access to a broad range of plasma scenarios

to confirm predictions on

Fusion power, confinement, MHD, ELMs , ITB & current drive, disruptions, Power & particle exhaust


Working strategy

• Contact Persons in associations

• Definition of working topics, common experiments and data analysis by EU TF team and contact persons

• Special working groups (SEWG)

• SEWG meetings and general TF meetings (4)

• All reports and information on the PWI TF Web site

http://www.efda-taskforce-pwi.org


Organisation & work structure

Work plan has been defined for each association

topic

asso

ciat

ion


1

Co-ordinated experiments in associations

• Fusion devices

• linear plasma machines

• lab experiments

2

EFDA PWI technology programme

• specific tasks

• integration of work outside associations

3

Integrated wall experiments in fusion devices

Working strategy

working topics, common experiments and data analysis


Seven topics defined 1. Erosion behaviour and impurity location (SEWG) ◄report

2. Material transport and re-deposition ◄report

3. Fuel recycling, retention and removal (2 SEWG)

4. Transient heat loads (SEWG)◄report

5. Edge & erosion and deposition modelling

6. Edge and SOL physics

7. Task force relevant diagnostics

+ SEWG on high Z plasma facing materials

Organisation & work structure


1. Erosion behaviour & location

• Carbon chemical erosion under ITER conditions (SEWG)JET, AUG, TEXTOR , Tore Supra, PSI Berlin, Pisces

• Impurity production behaviour in the main chamber JET , AUG

• Influence of Be on chemical erosion of C EU-US technology task & IPP

• High temperature sputtering of W and Be EU-UU technology task, IPP Garching, FZJ , ENEA

• Characterisation of C/W/Be mixed-material formation EU-US technology task


FZJ: Erosion at test limiters in TEXTOR (high fluxes) , D/XB calibration, ERO code modelling

IPP: Synergistic erosion of Ho with inert gases Erosion mitigation due to metal doping Erosion and deposition in ASDEX UpgradeErosion and deposition in PSI-2 D/XB calib.

UKAEA: chemical erosion at JETCEA: Chemical erosion on neutraliser plate

CIEMAT: Influence of N2 on C-erosion/deposition

EU-US collaboration:PISCES-B Influence of Be seeding

collaboration through ITPA:JT60-U,DIIID Chemical erosion at divertor plates

in future we hope also for contributions from Magnum linear device

SEWG chemical erosion (S.Brezinsek/J. Roth)Main open question: chemical erosion yield of the ITER graphite target

Carbon chemical erosion


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

→ Low yields under ITER divertor conditions

→ further decrease by Be deposition

open questions: Influence of surface conditions, redeposited layers, dependence on structure ..

Chemical erosion

Chemical erosion depends in a complex manner on ion flux, energy, surface temperature and condition


AUG experiments on chemical erosion

No CD+ (420 nm) !

CH form CH4 puff

Chemical erosion under detached conditions ( Te< 2eV, Tsurf< 400K )

CH source from CH4 injection visible, D/XB values determined

> intrinsic CH signal very low, at the detection limit

low intrinsic erosion yield (details under analysis


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 fluxesSOL

sweep

#63253KS3O

0.01

0.02

0.03

0.04

0.05

0.06

0.07

PFRsweep

GG

C2H

yD

/

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

chem

KY4D

EFIT

0.4 0.8 1.2 1.60.0

JET experiments on chemical erosion

C2H4 injection in outer divertor with slow strike points sweeps attached conditions (Te>15eV)

• DX/B values from injection used for the reference discharge

• Most reliable value for Ychem is achieved withthe strike point at GIM10 injection

→Ychem from higher hydrocarbons about 2%


Time (s)

0 500 1000 1500 2000

Nor

m.

CD

Ban

d st

reng

th

(Arb

. un

its)

0.1

1

Sur

face

car

bon

conc

entr

atio

n

0.1

1

0.18 % Be0.41 % Be

0.13 % Be

1.10 % Be

0.03 % Be

Introduction

• Fast decrease of C-erosion for comparably small Be plasma concentrations (upstream)

• Critical issue: thermal stability of Be layers

EU-US collaboration (PISCES B, UCSD)

Dependence of carbon chemical erosion Be plasma concentration

1. Erosion behaviour & location


Binding energy (eV)

110115

N(E

) (

Arb

units

)

0250

500

750

1000

Be 1s

carb

idic

meta

llic

Be oxideBe, afterD2 plasma

112.2

eV

111.8

eV

Graphite,afterBe seededD2 plasma

280285

35

00

40

00

45

00 C 1s

gra

ph

ite

carb

idic

XPS data shows surface layer is largely Be2C

• Virtually all C remaining at the surface is bound as carbide

• Presence of carbide inhibits chemical erosion of C

• Carbide layer reduces sputtering yield of bound Be

• Subsequently deposited Be can more easily erode

XPS analysis of Be on C sample surface

Much better understanding of chemical erosion behaviour but still open questions to be addressed


2. Material transport and re-deposition

A main research topic of EU PWI TF

• Global and local material transport ways work in JET, AUG , TEXTOR, Tore Supra

• Quantitative erosion/deposition balances work in JET, AUG, Tore Supra, TEXTOR

• Dedicated deposition studies Quartz detectors, sticking monitors, temperature dependence

work in JET, AUG, TEXTOR, PSI-2 Berlin

• Migration to gaps and hidden areas work in JET, AUG, TEXTOR, Tore Supra


Involved Associations

1. Fusion devices:

AUG

JET

TEXTOR

Tore Supra

2. Linear PSI devices

PSI-2 Berlin

PISCES-B

future: Magnum

3. Several associations involved through post mortem surface and tile analysis

VR Stockholm

Tekes

CNR Milano

IFPILM Warsaw

Jozef Stefan Institute-Ljubljana



Erosion, deposition & material migration

Main tasks:

Global erosion/deposition material balances

(AUG, JET, TEXTOR, Tore Supra)

Growing understanding and data consistency

Fuel retention:1. From overall material deposition and associated fuel retention (T-codeposition)

2. From fuel balances

Still a lack of consistency between both methods!!Needs further work


Neutralizers : ~10 g

TPL : ~5.5 g Outboardmovablelimiter :~1.5 g

Net erosion estimate : 40 g → 20 g maximum missing

Tore Supra:Somewhat coherent carbon balance but overall carbon deposition not sufficient to explain D retention evaluated from fuel balances

Antennas +launchers : ~1 g

Erosion, deposition, example TS


• Carbon is transported stepwise

• Final C- deposition pattern determined by plasma operation scenarios

• No significant long range transport of Be

louver

Quartz monitor

C deposition

Be deposition

JET

250 300 350 400 450 500

0.01

0.1

1 C D

Rel

ativ

e A

mo

un

t [t

o C

at

RT

]

Temperature [K]

AUG

• Deposition probes beneath the divertor: strong decrease with temperature

• From re-erosion by D-atoms

Work on understanding the mechanism of migration and deposition



• On plasma wetted areas, C is effectively transported by multi-step chemical erosion, promoting significant deposition in gaps (depending on geometry)

• In shadowed areas, C deposition is governed mainly by high sticking species (line-of-sight). Deposition is determined by competition with re-erosion by atomic hydrogen , only a minor fraction migrates longer distances

• Be does not show long range transport

ITER:

C- transport down the vertical target→ trapping in gaps & migration towards the PFR (dome )

Be- deposition on the vertical target → some transport in the upper SOL & trapping in gaps



Tritium retention mitigation and detritiation needed in ITER

SEWG: fuel removal

EU PWI activities

Removal of carbon layers by oxidation: transformation of carbon in CO and CO2 which is pumped out

O2 venting, GDC and ICRH plasmas in O2

(AUG, TEXTOR) only remove C, contamination with O

N2-seeding: prevent C deposition by scavenger action

(Ciemat, AUG, JET) only remove C, effective enough? works only during deposition, N increase also C erosion

Photocleaning: ablation of codeposits (lasers, flashlamps)

UKAEA, JET, CEA, IFPILM Warsaw

difficult access, production of dust


Several technology tasks in the field of T removal

Optimisation of He-O Glow for C-H removal

Characterisation PFC Oxidation Damage,

T removal by non-O2 oxidative methods

T retention in ITER-like material mixes and Tsurf


simple and proven technique, Slow C removal rate 2.3x1019 C/s (5.2 g C in total)

GDC

GDC

Integral data from QMS

CO

CO2

HD

00:00 01:00 02:00 03:00 04:000.0

0.5

1.0

1.5

2.0

2.5

rem

ova

l, 10

23 a

tom

s

time, hh:mm

0

1

2

3

4

5

rem

ove

d C

, g

A Kreter et al

O2 GDC in TEXTOR tokamak

Depos. in H2/CH4 GDCleaning in 5%O2/He GD

After 45’ GDC, 75 % of hydrogen released

Some cleaning of gaps possible, needs further work

Cleaning of gaps by O2 GDC (Ciemat)

a-C:H coated Thermocoax 1mm


• Co-deposit from TEXTOR tiles removed at ~0.5mm/h at 185 C (prob. higher at 130C), but O3 also removes underlying graphite (EK98)

• Eroded surface becomes roughened & chemisorbtion forms stable C-O complexes (to >700C)

125C

135C130C

~ 1mm EK98

~ 4

0m

/h E

K98 • Oxidation rates of solid EK98

for 2.3% O3 in O2

• Peaks at ~50m/h at 130C

• Decreases with burn-off

• Works at lower temperature but not selective for deposit !

Oxidation with Ozone

H-K Hinssen et al

EFDA Technology task


Laser treatment 20 W, λ≈1 μm, 10kHz, 100ns pulse duration

h~50mh~50m1 scaning, 2s

TEXTOR tile

Photocleaning

• Flash-lamp assembly to clean JET lower divertor floor tile in active Be area, operated remotely

CEA UKAEA

JET horizontal divertor tile


-10

0

10

20

30

40

50

60

70

1700 1750 1800 1850 1900 1950 2000 2050 2100

Channel Number

Coun

ts

JET 8360 (reference)

JET 8374 (treated)

• ~0.5 GBq of T released in ~20ms exposure to flash-lamp from ~50cm2 of horizontal divertor tile

• surface analysis shows that D is released only form outer 0.5-1 m at the surface

• Total T content ~5GBq still present on peak regions of this tile

• Results consistent with removal rate ~0.2m/flash at 250J – lower than expected


4. Transient heat loads

Special expert working group, Chairman: Alberto Loarte

IPP Garching G. Pautasso, A. Herrmann, T. Eich

JET: V. Riccardo, J. Paley, P. Andrew

UKAEA: G. Counsell

FZJ: K.H. Finken

FTU: G. Maddaluno

ITER: G. Federici


SEWG Transient heat loads

Characteristics of transient heat loads has a major impact on target design and materials

Present specifications for disruptions in ITER

1. W th.que. ~ Wth = 350 MJ

2. Energy quench time ~ 1 ms

3. power deposition Pdisr ~ 3 P

s.s. , toroidally uniform

Best assumptions presently

• Wt.q. ~ (0.25 ± 0.12) Wth

• tt.q. ~ (2.3 ± 1.8) ms

• Pdisr ~ (7.5 ± 2.5) P

s.s.

Revision of ITER assumptions following work of EU-PWI SEWG

on Disruption


Before the thermal quench the plasma has lost a large part of its energy

Typical Wt.q. /Wmax: 0.25 ± 0.12 for JET0.40 ± 0.22 for ASDEX Upgrade

Riccardo PautassoJET AUG

JET and AUG

4. Transient heat loads


power loads on divertor : confirm large broadening at the thermal quench

Plasma energy at thermal quench: ~ 50% of that 20 ms earlier similar to JET

and ASDEX Upgrade results

G. Counsell to be published G. Counsell to be published

Recent work in Mast


Technology tasks on material damage and modelling

(EU-FZK-RF)

• Modelling of Disruptions and ELMs

• Validation of ELM Damage Modelling (EU-RF)

• ELM-Disruption exposed Target Characterisation

• W and CFC damage and plasma evolution in ITER

• Modelling of Be damage under Disruptions/ELMs, fut.EU-RF)

• W and CFC under-threshold damage studies


PWI experiences are mainly with graphite walls in short pulse devices

not enough experience on

• Long pulse operation

• T retention under ITER like material conditions

• Operation performance with full metallic walls

• Melt layer behaviour

ASDEX-U tungsten first wall experiment

JET ITER like wall experiment

Tore Supra long pulse operation

steady state plasma simulators (Magnum )

Integrated Wall material experiments


AUG: stepwise implementation of a full tungsten FW

Objectives

• Erosion, deposition migration in a W/C environment

• Behaviour under transient heat loads

• Hydrogen retention behaviour

• Impurity seeding to replace intrinsic C radiation

• Development of W diagnostics

Compatibility of W first wall with all relevant operation scenarios

Wall material experiments: AUG


W Programme at AUG

guard/ICRHlimiter

aux.limiter

hor.plate

lower PSL

roofbaffle

2006/2007(planned)

W-coating starting with campaign

2003/2004

2004/2005

2005/2006

60%

70%

85%

100%

• Transition to W-device

• W coating of lower divertor probably next year, depending on availability of technical solution (thick coating)

• C deposition on W rather small, but role of surface conditioning and recycling not yet completely clear

• Restrictions of working space identified, but remedies developed


New Focus on High-Z PFCs

Large number of EU associations involved in characterisation of W materials, development of W coatings, W bulk target concepts and

test of W as PFC

CEA Caderache W coatings, W Components, diagnosticCNR Milano Test of high-Z PFCsENEA Frascati W coatings, high-Z operation, erosion/deposition/retentionFZ Jülich W bulk PFCs, diagnostic, high-Z operation, erosion/deposition, modelingFZ Karlsruhe W materials, W components, modelingIPP Garching W coatings, diagnostic, high-Z operation, erosion/deposition/retention, modelingIPP Prague W coatingsJSI Lublijana W-H surface interactionKFKI Budapest W coatingsTEKES Helsinki W coatings, erosionVR Stockholm erosion/deposition/retention


350 MJ

20 MJ

ITER

JET

Objectives

• Demonstrate low T retention

• Study effect of Be on W erosion

• Study ELMs and disruptions on wall & divertor, melt layer behaviour

• Develop control / mitigation techniques for ELMs and disruptions

• Test de-tritiation techniques

• Operate tokamak without C - radiation

Demonstrate operation of ITER scenarios at high current and heating power with Be/W wall choice

Wall material experiments: JET


JET with ITER like material choice

Objectives

• Study influence of carbon chemistry

• Effect of Be deposition on carbon release and transport

• Study of Be/C(W) layers, their thermal stability, T-retention

• Demonstrate sufficiently low fuel retention of an ITER-like material selection to meet ITER requirements.

STRATEGY: both options prepared, decide options depending on requirements

Demonstrate operation of ITER scenarios at high current and heating power with Be/C/ W wall choice

Integrated Wall material experiments


• Many critical PWI issues have been addressed and significant progress achieved, inter-association collaboration & has been increased (but should be even more )

• EU PWI research has benefit strongly from accompanying -EFDA technology programme, including also new partners

• Special Expert Working Groups have proven effective in advancing knowledge on specific issues

• In general, PWI research has strengthen, now in the focus of tokamak research , in particular in AUG High Z and ITER-like wall experiment in JET

Concluding remarks



EFDA- STAC decided to continue the EU PWI TF to concentrate the EU PWI programme on jointly defined important experiments in EU fusion devices

Future strategy as discussed during last EU TF meeting

• strengthen the topical oriented work

• increase the objectives of existing SEWGs, new SEWG on dust

• improve cooperation with JET TF E and vice versa

• strengthen the PWI-EFDA technology programme to keep the lab work in close relation with fusion experiments

Concluding remarks


ITER PWI Strategies: aiming for a maximum flexibility

Divertor: prepare a CFC and a full tungsten divertor in parallel

Decide the ITER divertor for the Tritium phase depending on

• transient power losses

• ELM& disruption control

• melt layer behaviour

• fuel retention

in the H-phase

[ need adequate diagnostic to detect fuel retention and material deposition rates in the H- phase]

For Discussion


Strategies for ITER: aiming for a maximum flexibility

First wall material choice: strong effort needed on

• characteristics of first wall PSI (steady state, ELMS..• fuel retention & removal with the present ITER materials

choice (JET ITER like wall experiment)

• plasma behaviour with high Z walls (AUG FW W experiment)

Keep (improve) the possibility to change the first wall

For Discussion

v.philipps, efpw padua, dec 2005 introduction report on the european task force on plasma wall...

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