eu-pwi tf meeting, madrid, 29-31 october 2007 progress with tritium removal and mitigation 2006-7 g....
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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
EU Plasma-Wall Interactions Task Force
+ ~ 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
EU Plasma-Wall Interactions Task Force
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
EU Plasma-Wall Interactions Task Force
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
EU Plasma-Wall Interactions Task Force
#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
EU Plasma-Wall Interactions Task Force
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
EU Plasma-Wall Interactions Task Force
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
EU Plasma-Wall Interactions Task Force
Effects of Oxygen on a-C/D Effects of Oxygen on a-C/D erosionerosion
EU Plasma-Wall Interactions Task Force
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
EU Plasma-Wall Interactions Task Force
• 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
EU Plasma-Wall Interactions Task Force
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
Francisco L. Tabarés, J.A. Ferreira, D. Tafalla, I. Tanarro, V. Herrero,C. Gómez-Aleixandre, J.M. Albella
EU Plasma-Wall Interactions Task Force
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
Francisco L. Tabarés, J.A. Ferreira, D. Tafalla, I. Tanarro, V. Herrero,C. Gómez-Aleixandre, J.M. Albella
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
EU Plasma-Wall Interactions Task Force
Concerns over selectivity
Some confusion over impact of non-volatile impurities – effect of film structure?
Further in-vessel testing conducted
Section summarySection summary
EU Plasma-Wall Interactions Task Force
Photonic cleaning techniquesPhotonic cleaning techniques
EU Plasma-Wall Interactions Task Force
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
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
Changeof theD+1 line
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
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
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
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
signal in preliminary stage
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
signal after 50 shots approximation
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
EU Plasma-Wall Interactions Task Force
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
EU Plasma-Wall Interactions Task Force
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
EU Plasma-Wall Interactions Task Force
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
EU Plasma-Wall Interactions Task Force
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.
EU Plasma-Wall Interactions Task Force
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
Section summarySection summary
EU Plasma-Wall Interactions Task Force
Work Programme for the Work Programme for the SEWG on fuel removalSEWG on fuel removal
EU Plasma-Wall Interactions Task Force
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