EU-PWI TF meeting, Madrid, 29-31 October 2007 Progress with tritium removal and mitigation 2006-7 G....

EU-PWI TF meeting, Madrid, 29-31 October 2007 EU Plasma-Wall Interactions Task Force

Progress with tritium removal Progress with tritium removal and mitigation 2006-7and mitigation 2006-7G. Counsell1, P. Coad1, J.A. Ferreira8, M. Rubel6, F.L. Tabares8, A. Widdowson1, P. Sundelin6, V. Philipps4, G. Sergienko4, D. Tafalla8, I. Tanarro8, V. Herrero8,C. Gómez-Aleixandre, J.M. Albella8, P.Gąsior9, J. Wolowski9, J. Likonen5,C Grisolia2, A. Semerok7, C Hopf3, W Jacob3, M. Schlüter3, D Farcage7, D Hole10,T Renvall10, P-Y Thro7

1EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK2Association EURATOM-CEA, CEA/DSM/DRFC Cadarache, 13108 St.Paul lez Durance, France3Max-Planck-Institut für Plasmaphysik, EURATOM Association, D-85748 Garching, Germany4Institut für Plasmaphysik, Forschungszentrum Jülich, Association EURATOM-FZJ5Association EURATOM-TEKES, VTT Processes, PO Box 1608, 02044 VTT, Espoo, Finland6Alfvén Laboratory, Royal Institute of Technology (KTH), Association EURATOM-VR, 100 44 Stockholm, Sweden7CEA Saclay, DEN/DPC/SCP/LILM, Bat. 467,91191Gif sur Yvette, France8Association Euratom/Ciemat. Laboratorio Nacional de Fusión. 28040 Madrid, Spain9Institute of Plasma Physics and Laser Microfusion, Association EURATOM – IPPLM, Warsaw, Poland10Dept. of Engineering and Design, University of Sussex, Brighton, East Sussex, UK

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EU Plasma-Wall Interactions Task ForceOutline

Effects of Nitrogen on a-C/D erosion and deposition

Effects of Oxygen on a-C/D erosion

Photonic cleaning techniques

SEWG Work Programme

3/28

EU Plasma-Wall Interactions Task Force

Effects of Nitrogen on a-C/D Effects of Nitrogen on a-C/D erosion and depositionerosion and deposition


+ ~ 3:9x1012 cm2/s 400:1 H0:N2+

M Schlüter, C Hopf and W Jacob

NN22++/H/H00 particle beam exposure particle beam exposure

Exposure of a-C:D films in MAJESTIXYield with N2

+ chemical sputtering

Adding H0 significantly increases yield synergistic effect


Ions create broken bondsReact with H0 forming volatile CxHy species

M Schlüter, C Hopf and W Jacob

Ions create broken bondsSlow N0 at end of ion range react to produce volatile CxNy species

NN22++/H/H00 particle beam exposure particle beam exposure

2 processes needed to explain N2

+/H0 erosion:

EU Plasma-Wall Interactions Task ForceNitrogen scavengingNitrogen scavenging

a-C/D on Si(heatable)

, N2

PSI-2, Berlin

FL Tabares et al

No significant ion flux to a-C/D sample


T= 60ºC T=80 ºC

CH4

H2

N2+CH4

• N2 addition supresses deposition – net erosion

• Effect not seen with Ne

• Cumulative effect - N2 required for scavenging decreases with exposure

Nitrogen scavengingNitrogen scavenging

FL Tabares et al


#102965

LFS HFS

Nitrogen-assisted ICRF dischargesNitrogen-assisted ICRF discharges

ICRF H2/N2 plasma in TEXTOR

• 40 kW, 29 MHz• B ~ 2.3 T, Bv ~ 0.04T• 0.04 Pa• 3 - 6x1017 m-3

• N2/(N2+H2) ~ 0.0 - 0.8

V. Philipps et al

• Plasma recovery possible but with high radiation fraction

• Nitrogen retained in the wall and fuels the plasma

• Hydrogen recycling flux reduced by factor 2

EU Plasma-Wall Interactions Task ForceNitrogen-assisted ICRF dischargesNitrogen-assisted ICRF discharges

40 s Exposure of:

Pre-boronised layer on Silicon

a-C:D laboratory layer on Silicon

Uncoated Inconel

Silicon probes: no visible change in topography after exposure.

Inconel probe: carbon layer formed during exposure.

P. Sundelin, M. Rubel, V. Philipps, G. Sergienko

Analysis: SEM, X-ray spectroscopy, IBA

No evidence for enhanced erosion rate with N2


Sample Din Dex Bin Bex Cin Cex

H2-N2 plasma

+ ICRF

O2-He glow

Inconel - 1 - - - -

B on Si 13 13 36 49 83 101

a-C:D/Si 610 590 - - 792 1077

a-C:D/Si

B on Si

552

17

6

2

8

300

8

280

880

12

20

30

P. Sundelin, M. Rubel, V. Philipps, G. Sergienko

Nitrogen-assisted ICRF dischargesNitrogen-assisted ICRF discharges

Units of 1015cm-2


Deeper understanding, but ….

‘Story’ on nitrogen still seems confused or even contradictory

May offer options for:

reduction of deposition in remote areas

High a:C/D removal rates without Oxygen in some circumstances

Section summarySection summary


Effects of Oxygen on a-C/D Effects of Oxygen on a-C/D erosionerosion


C. Hopf, W. Jacob, V. Rohde

Oxidation cleaning relies on phys < chem

phys (C, Al, Fe) approach chem for a-C/H at high Eion

phys (W) always more than factor 10 lower

is lower than TRIM for O on AL, W – surface oxide effect

Selectivity in oxidationSelectivity in oxidation


• Laser interfermoetry• Cross-checked with:

- Profilometry- XPS- C balance in glow

1 fringe=/2n ..144nm n hard C …2.2

Impact of material mixingImpact of material mixing

Photodiode

He,Ar CH4O2

Oven

Turbo pump

Oven

T~600ºC

GlowDischarge Laser

(Li, Mg)

Francisco L. Tabarés, J.A. Ferreira, D. Tafalla, I. Tanarro, V. Herrero,C. Gómez-Aleixandre, J.M. Albella


BeO MgO

C (kJ/mol) -609 -601

(g/cm3) 3.01 3.58

Melting point (K) 2200 3073

Oxidation of Mg/a-C/H mixOxidation of Mg/a-C/H mix

Mg: good analogue for Be

Oxides have similar characteristics

Low electrical conductivity

high thermal conductivity

Uniformly distributed Mg in a-C/H layers produced

Etching by He/O2 glow discharge plasma:

•Constant erosion rate•O balance: Not matched•Similar rate as in pure C

Interfermeter fringes

RGA



Film

RGA

C C/Li layer C/Li mixed C/Mg mixed

O2 1.8e-6 1.1e-6 3.3e-6 1.2e-6

O2 1.06e-6 3.8e-7 2.7e-6 9.13e-7

CO 9.06e-7 1.5e-7 1.1e-6 6.08e-7

CO2 1.09e-7 2.9e-8 2.0e-7 8.64e-8

H2 3.5e-6 1.4e-7 7.0e-6 4.07e-6

Erosion rate

(nm/s)

0.18 0.06 0.23 0.19

CO+2CO2/ O2 1 0.55 0.55 0.85

• Erosion rates and products ~unaffected in homogenousa-(C+M)/H films (M=Li,Mg)

• Film structure may have significant impact

Oxidation of Mg/a-C/H mixOxidation of Mg/a-C/H mix


EU Plasma-Wall Interactions Task ForceOxidation of B/a-C/H mixOxidation of B/a-C/H mix

C. Hopf, W. Jacob, V. Rohde

• He/O2 GDC (-60Vbias) of boronated hydrocarbon layers in GDCC

• Significant fall in removal rate from pure-C to pure-B levels

Impurity accumulation

• Differences between B and metallic impurities?

EU Plasma-Wall Interactions Task ForceHe/OHe/O22 ICRF discharges ICRF discharges

CO and CO2 products (about 75%) released mostly after ICRF pulses

C removal rate O2 injection rate

Neutral pressure at the antenna box (~1x10-1 Pa) determines max O2 inj.

TEXTOR

• Re-conditioning attempted by ICRF conditioning D2/He

• Successive wall cleaning with ICRF was necessary

• Recovery procedure accompanied by tokamak disruptions (10 disruptive shots).

Further optimization necessary

V. Philipps et al


Concerns over selectivity

Some confusion over impact of non-volatile impurities – effect of film structure?

Further in-vessel testing conducted



Photonic cleaning techniquesPhotonic cleaning techniques


Scanning regime

Scan speed v (m/s)

Step size X (m)

Pitch Y (m)

Offset pitch Y (m)

Regime 1 0.2 10 100 50

Regime 2 0.2 10 100 No second pass

Regime 3 1.0 50 100 50

Regime 4 1.0 50 100 No second pass

Laser cleaning of JET divertor tilesLaser cleaning of JET divertor tiles

A Widdowson, J P Coad,D Farcage, D Hole, J Likonen,T Renvall, A Semerok, P-Y Thro

Very effective at a-C/H removal – up to 3m2/m/hr

Some issues with selectivity

CFC substrate can be damaged – optimisaton needed

EU Plasma-Wall Interactions Task ForceLaser cleaning of TEXTOR tilesLaser cleaning of TEXTOR tiles

Vacuum chamber

Laser beam

Lens

Focusing lens

Target

Diffractive optical system

CCD

Computer A&CU

Measurementsystem

IEA

Spectroscopy stage

Spectrometer

Motion stage

Vacuum chamber

Laser beam

Lens

Focusing lens

Target

Diffractive optical system

CCD

Computer A&CU

Measurementsystem

IEA

Spectroscopy stage

Spectrometer

Motion stage

J. Wolowski, M Rubel, V. Philipps, IPP ASCR (Prague, CR)

0 60 120

-0,04

0,00

after series of 50 shots

U[V

]

T [ms]

before series of shots

E/z=0.15 keVD+1

Si+1

C+1

O+1

(D+1)

C+1

(O+1)

Si+1

0 60 120

-0,04

0,00


U[V

]

T [ms]


E/z=0.15 keVD+1

Si+1

C+1

O+1

(D+1)

C+1

(O+1)

Si+1

Changeof theD+1 line

0 60 120

-0,04

0,00


U[V

]

T [ms]


E/z=0.15 keVD+1

Si+1

C+1

O+1

(D+1)

C+1

(O+1)

Si+1

0 60 120

-0,04

0,00


U[V

]

T [ms]


E/z=0.15 keVD+1

Si+1

C+1

O+1

(D+1)

C+1

(O+1)

Si+1

Changeof theD+1 line

650 655 660

0

50

100

signal in preliminary stage

approximation

Rel

ativ

e in

tens

ity [

AU

] D CII

Wavelength [nm]

648 650 652 654 656 658 660 662 664

0

20

40

60

80

100

signal after 50 shots approximation

of deuteriu peak

Rel

ativ

e in

tens

ity [

AU

]

D CII

Wavelength [nm]

650 655 660

0

50

100


approximation

Rel

ativ

e in

tens

ity [

AU

] D CII

Wavelength [nm]

648 650 652 654 656 658 660 662 664

0

20

40

60

80

100


of deuteriu peak

Rel

ativ

e in

tens

ity [

AU

]

D CII

Wavelength [nm]

650 655 660

0

50

100


approximation

Rel

ativ

e in

ten

sity

[A

U] D CII

Wavelength [nm]

648 650 652 654 656 658 660 662 664

0

20

40

60

80

100


of deuteriu peak

Rel

ativ

e in

tens

ity [

AU

]

D CII

Wavelength [nm]

Characterised with -

ion time of flightoptical spectrocopy

0 10 20 30 40 50 60

-20

-15

-10

-5

0

Inve

ntor

y le

vel

[dB

]

Number of shots

spot diameter 4.5 mm spot diameter 3.5 mm

0 10 20 30 40 50 60

-20

-15

-10

-5

0

Inve

ntor

y le

vel

[dB

]

Number of shots

spot diameter 4.5 mm spot diameter 3.5 mm


Surface profile complicates optimisation

Laser cleaning alignmentLaser cleaning alignment

Variation in focal-point to tile distance

8mm movement ½ power

A Widdowson, J P Coad,D Farcage, D Hole, J Likonen,T Renvall, A Semerok, P-Y Thro


Tile Total tritium release measured at J1A stack (GBq)

Estimated tritium release from off-gas measurements (GBq)

G4A 5BW 0.52 5.58 G3B 3IN 0.07 23.3 G3B 14IN 0.14 89.6

Products of Laser cleaningProducts of Laser cleaning

T-released to stack in each region

Only 10% (at most) of estimated inventory at treated locations

non-gaseous products?A Widdowson, J P Coad,D Farcage, D Hole, J Likonen,T Renvall, A Semerok, P-Y Thro


Video of laser cleaning

Evidence of particulates

Products of Laser cleaningProducts of Laser cleaning

Dust probably contains bulk of T released

May be unavoidable with this wavelength

Integrated dust collection necessaryA Widdowson, J P Coad,D Farcage, D Hole, J Likonen,T Renvall, A Semerok, P-Y Thro


Analysis methods: 3He+ NRA at 2 MeV and microscopy.

Graphite plates with TEXTOR co-deposits: CD = up to 1019 cm2

Dust collected from metal plate adjacent to target: CD = 3.9x1017 cm2

Dust produced by laser cleaning still contains significant fuel

P.Gąsior, P. Sundelin, M. Rubel

Dust during TEXTOR tile cleaningDust during TEXTOR tile cleaning

Important note:

Single result

Must be verified by other fully quantitative studies.


Laser cleaning effective at a-C/H removal

Selectivity is an issue – need to maintain focus and optimise speed, step size etc.

Dust produced may contain bulk of tritium released – need for collection scheme



Work Programme for the Work Programme for the SEWG on fuel removalSEWG on fuel removal


Long term objectives:Long term objectives:

Develop an integrated scenario for fuel removal in ITER

Derive a credible tritium inventory control scheme relying on developed cleaning techniques to meet ITER operational requirements.

Assess combined efficiency, removal rates and schedule needed.

Assess efficiency (if any) with hydrogenic retention in metals for developed fuel removal technologies (chemical and photonic)

Begin exploration of new fuel removal technologies, targeted at hydrogenic retention in metals (for ITER with future all-metal

divertor)

SEWG – Fuel RemovalSEWG – Fuel Removal

EU Plasma-Wall Interactions Task ForceSEWG – Fuel RemovalSEWG – Fuel Removal

Objectives for 2008:Objectives for 2008:

i. Quantify impact of metallic impurities

ii. Resolve the impact of nitrogen molecules

iii. Explore impact of repetitive oxidising plasmas (GDC/RF) on beryllium bulk

iv. Demonstrate beryllium oxide removal rates

v. Demonstrate removal of co-deposit trapped in ITER-relevant tile gaps

vi. Further advance chemical and photonic cleaning methods towards an ITER relevant system

EU-PWI TF meeting, Madrid, 29-31 October 2007 Progress with tritium removal and mitigation 2006-7 G....

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Transcript of EU-PWI TF meeting, Madrid, 29-31 October 2007 Progress with tritium removal and mitigation 2006-7 G....