Post on 10-Dec-2015
EU-PWI TF meeting, Caderache, 17-19 October 2005
Progress with T-recovery Progress with T-recovery techniques 2004-5techniques 2004-5P Coad1, GF Counsell1, G. Dinescu6, H. G. Esser4, JA Ferreira2, MJ Forrest1, M. Freisinger4, K Gibson1, C Grisolia3, A Grosman3, H-K Hinssen4, C. Hopf5, W. Jacob5, A Kreter4, K Kuhn4, W Jacob5, A. Lyssoivan4, R Moormann4, J-M. Noterdaeme5, V Philipps4, H. Reimer4, V. Rohde5, U. Samm4, A. Semerok3, G. Sergienko4, and M. Schluter5, FL Tabarés2, E Tristrone3
1 UKAEA2 CIEMAT3 CEA4 IPP-Juelich5 IPP-Garching6 Romanian Ass.
EU-PWI TF meeting, Caderache, 17-19 October 2005
Both retention mitigation and in situ detritiation will likely be needed in ITER
• ITER with planned PFC mix will need
– a factor 30-200 reduction in tritium retention
or
– a factor 10,000 increase in tritium removal rates
compared to model predictions and extrapolations
• Almost certainly a combination of both will be required
– even if inventory limit takes 8 months to reach, removal rates would still need to be a factor 50 improved to clean vessel in 4 month shut-down
EU-PWI TF meeting, Caderache, 17-19 October 2005
• Many techniques and technologies under consideration (though world-wide effort is still small)
• Several issues -
– intra-shot, inter-shot, overnight, weekly
– Collateral damage to in-vessel components (inc. PFC’s)
– Compatibility with plant (pumps, heating systems)
– Degree of intervention (vessel let-up?, fields energised?, vessel entry?)
– Access (i.e. to all regions of retention)
• Existence of a Be Wall (in particular) impacts on many of these issues
Be Wall in ITER may help reduce retention but also complicates other approaches
EU-PWI TF meeting, Caderache, 17-19 October 2005
RF assisted O2 GDC in TEXTOR
Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum JülichInstitut für Plasmaphysik
Total ion flux: 6 A
Wall area: 35 m2
1·1014 O+/cm2 s
Wall(-)
Removal rate:neutral pressure pumping speed
RF 13.2 MHz250 W
DC 6A (feedback controlled),400-600V
Electrode (+)
Sheath potential 280-400 V (O+ impact energy)
O2 + He
10-3 mbar
O+,O
CO
C
O+
CO, CO2, O2, He
Differentially pumped
quadrupole mass
spectrometer (QMS)
• CO weakly dependent on O2
• CO2 rises with O2
• CO/CO2 independent of He
A Kreter et al
~150C
EU-PWI TF meeting, Caderache, 17-19 October 2005
• HD molecules about 7% of removed C
H+D atoms about 28% of C (assuming H:D = 1:1), in agreement with previous observations
• C removal rate 2.3x1019 C/s (5.2 g C in total)
Removal rates by RFA-O2 GDC
Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum JülichInstitut für Plasmaphysik
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
EU-PWI TF meeting, Caderache, 17-19 October 2005
ICRF conditioning in O2 in TEXTOR
• All injected O2 converted into CO, CO2
• Only 15% of C removal during ICRF low duty cycle
• CO+CO2 outgassing until 140 sec: ~4·1020 O-atoms
about half of O amount absorbed by wall, wall not saturated
Typical shot:
• Bt = 2.3 T
• ICRF 29 MHz 50 kW (absorbed) 1-6 s
• Continuous He flow
• Fast O2 injection 2.1·1020 O/s 1.1-5.1 s (8.5x1020 in total)
Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum JülichInstitut für Plasmaphysik
0 50 100 1500.0
0.1
0.2
0.3
time, s
par
tial
pre
ssu
re, 1
0-3 m
bar
mass 44 mass 28 mass 32 mass 4 mass 3
CO2
He+D2
CO
O2
#97084IC
RF
HD
A Kreter et al
C removal rate 1.8x1019 C/s
EU-PWI TF meeting, Caderache, 17-19 October 2005
Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum JülichInstitut für Plasmaphysik
TechniqueC removal rate
Advantages DrawbacksPossible
improvements
Oxygen venting
2.5·1018 C/s for 0.3mbar, Twall=620K
•simplicity•access to all wall areas•selective removal of redeposited layers
•low removal rates•Twall > 600K needed
•higher O pressure
Glow discharge conditioning
2-3·1019 C/s•higher removal rates •applicable for low Twall
•incompatible with steady state B•non-selective carbon removal (?)•limited wall area access
•higher GD current•higher pumping rate
ICRF conditioning
1.8·1019 C/s for 1:10 duty cycle for pump out
•higher removal rates•applicable for low Twall
•compatible with steady state magnetic field
•O injection limited by pressure limit at antenna box•non-selective carbon removal (?)•limited wall area access
•higher pumping rate (also for steady state ICRF)
Summary of oxygen cleaning in TEXTORIntegral TEXTOR carbon redeposition rate ~ 2.7·1020 C/s
A Kreter et al
EU-PWI TF meeting, Caderache, 17-19 October 2005
O2 GDC in AUG
Use of He/O2 mixture plasmas in AUG• Stability of glow discharge• Less sputtering compared to pure O2 discharge or heavier noble gas admixtures• Oxidation of W in O2 plasma saturates and is reversible in an H2 discharge• No erosion in shielded places: tile gaps, behind first wall, and in deep in the divertor
Exposure time (min)Ch. Hopf et al
EU-PWI TF meeting, Caderache, 17-19 October 2005
Thermal Desorption spectra of H2 and CH4 from gaps
a-C:H coated Thermocoax 1mm
Al mask: 4mmDepos. in H2/CH4 GDCleaning in 5%O2/He GD
As deposited After 45’ GD
J.A. Ferreira and F.L. Tabarés, CIEMAT
EU-PWI TF meeting, Caderache, 17-19 October 2005
• Co-deposit removed at ~0.5m/h at 185 C (prob. higher at 130 C)20m co-deposit removed in 2d also removes 0.7mm EK98 (ass. surface oxidation)
• Eroded surface becomes roughened & chemisorbtion forms stable C-O complexes (to >700C)
125C
135C130C
~ 1mm EK98
~ 4
0m
/h E
K98 • Oxidation rates of TEXTOR
EK98 for 2.3% O3 in O2
• Peaks at ~50m/h at 130C
• Decreases with burn-off
Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum JülichInstitut für Plasmaphysik
Oxidation with Ozone
H-K Hinssen et al
EFDA/04-1174
EU-PWI TF meeting, Caderache, 17-19 October 2005
N2 seeding – impact of N ions on a-C:H
• N2+ beam irradiation of a-C:H films in
MAJESTIX
• Chemical sputtering dominates a-C:H erosion by N2
+ at low energies
• Erosion yields remarkably high: ~1 above ~50eV
W Jacob et al
EU-PWI TF meeting, Caderache, 17-19 October 2005
• Flash-lamp assembly used for in-vessel trials transferred to BeHF
• Operated remotely – PSU and water cooling outside BeHF
• OPL and G4 tiles exposed to ~80x250J pulses at range of locations
• Tritium off-gas measured
Flash-lamp trials in JET BeHF
EU-PWI TF meeting, Caderache, 17-19 October 2005
• Flash-lamp footprint covers ~30cm2
• Surface temperature rises to ~1200K during 250J flash on plasma-damaged tile
• Pulse half-width is short - less than 150 s is typical
• Peak power density ~180MW/m2 at target for 250J flash
Flash-lamp trials in JET BeHF
EU-PWI TF meeting, Caderache, 17-19 October 2005
Treated areas
Untreated areas
Heavily treated area with initially thick powdery deposit
• Clearly visible changes to co-deposit in treated areas
Flash-lamp trials in JET BeHF
EU-PWI TF meeting, Caderache, 17-19 October 2005
-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 G4 tile
• No observed T release from OPL
• NRA spectrum for D, shows that D is absent from the outer 0.5-1 m at the surface – but at least 7m codeposit remaining
• No C13 on exposed regions compared to unexposed control
• T analysis at FZK shows difference between exposed and unexposed regions within statistical variation
• Total T content ~5GBq on peak regions of G4 tile
• Results consistent with removal rate ~0.2m/flash at 250J – lower than expected
• Flash-lamp focus less sharp than predicted, energy density ~3J/cm2 at 250J.
• Trials will be repeated in November at 500J, now available.
Flash-lamp trials in JET BeHF
EU-PWI TF meeting, Caderache, 17-19 October 2005
(0.4-0.5) J/cm2 for co-deposited layer
(2.5±0.5) J/cm2 for graphite
First trials with high 100 ns repetition rate 250W mean power Nd-YAG laser :
Laser treatment TORE SUPRA
EU-PWI TF meeting, Caderache, 17-19 October 2005
20 W, λ≈1 μm, 10kHz, 100ns pulse duration
h~50m
h~0m10 scanings
h~50m1 scaning, 2s
TEXTOR tile
• Ablation at 50 cm• Field depth of some centimetres• 100 W laser power 1 m2/h of 50 μm co-deposit
Laser treatment TORE SUPRA
EU-PWI TF meeting, Caderache, 17-19 October 2005
YAG V1 IPG Fiberlaser
Wavelength (nm) 1064 1064Power (W) 200 20Repetition rate (kHz) 10 20Energy (J) 20 1Pulse length (ns) 70 120Divergence M2 35 1,6Beam diameter (mm) 1 0,25Depth of focus (mm) ±2 ±30Fluence (J/cm2) 2.5 2
TORE SUPRA
Trials of scanning Fibrelaser planned for JET in vessel or BeHF
Laser treatment
EU-PWI TF meeting, Caderache, 17-19 October 2005
Ar torch cleaning
•Plume: ~ 2mm; length ~ 10mm •Optimal distance to surface ~ 10mm•RF power: 10 to 100 W•Water cooling system needed•Pressure: 10-1100 mbar (argon)
Detritiation assessment by exposure to a small plasma torch planned for 2005-2006 WP:
•Surface scanning•Torch diameter reduced to 20 mm•RF power increased to 200 W•Test on codeposited material•Test in magnetic Field
G Dinescu et al
TORE SUPRA
EU-PWI TF meeting, Caderache, 17-19 October 2005
Selected other activities World-wide:
• ICRH on LHD
PICRH~8-149kW, 38.47MHz, 3 loop antennas, He 0.01-0.1 Pa, 3s on:2s offDischarge stable even at low pressure but H removal ~5-10 x higher with 20-40kW GDC at 5Pa He
• O-ventilation, O-ICR, 4:1He/O-ICR and O-GDC + O-removal explored on HT-7
Fastest removal with 1.5Pa O-GDC (~5.1x1014 C/cm2s). Factor 3-4 lower in 0.1Pa O-ICR and 6-10 lower in 4:1He/O-ICRWall temp only 400-450CHe/O-ICR reduces oxygen retention – 5.8x1012 O/cm2sHe-ICR or He-GDC both effective to remove oxygen (10-50% in 0.5-1h)
• Mitigated disruption removal: ITPA-led Proposal submitted (P Stangeby leading) throught JET TFE for trials using newly fitted fast, high throughput valve
EU-PWI TF meeting, Caderache, 17-19 October 2005
Be (and its alloys) may act at significant trap –
O2 from leak:15mg/shotIntrinsic O in Be 1.5 - 5mg/shot - convective erosion50mg/shot - ELMs (no melt loss) 0.1% O impurity0.5g/shot - Unmitigated disruptionsTarget CFC erosion0.15g/shot (reduces from 2-5g/shot)
Conclusions - - Purity of Be a critically important issue (how would O2 de-tritiation schemes affect this?)
- Melt loss during Type I ELM interaction with limiter Be could result in large T retention
- Be might substantially reduce aC:H T retention - but still significant due to ELM erosion
Need to explore T-removal techniques for Be trapping?
aC:H is not the only T-trap