EU-PWI TF meeting, Caderache, October 2005 Progress with T-recovery techniques P Coad 1, GF Counsell 1, G. Dinescu 6, H. G. Esser 4, JA Ferreira 2, MJ Forrest 1, M. Freisinger 4, K Gibson 1, C Grisolia 3, A Grosman 3, H-K Hinssen 4, C. Hopf 5, W. Jacob 5, A Kreter 4, K Kuhn 4, W Jacob 5, A. Lyssoivan 4, R Moormann 4, J-M. Noterdaeme 5, V Philipps 4, H. Reimer 4, V. Rohde 5, U. Samm 4, A. Semerok 3, G. Sergienko 4, and M. Schluter 5, FL Tabarés 2, E Tristrone 3 1 UKAEA 2 CIEMAT 3 CEA 4 IPP-Juelich 5 IPP-Garching 6 Romanian Ass.

EU-PWI TF meeting, Caderache, October 2005 Both retention mitigation and in situ detritiation will likely be needed in ITER ITER with planned PFC mix will need – a factor 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, 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. PFCs) – 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, October 2005 RF assisted O 2 GDC in TEXTOR Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum Jülich Institut für Plasmaphysik Total ion flux: 6 A Wall area: 35 m 2 1·10 14 O + /cm 2 s Wall(-) Removal rate: neutral pressure pumping speed RF 13.2 MHz 250 W DC 6A (feedback controlled), V Electrode (+) Sheath potential V (O + impact energy) O 2 + He mbar O +,O CO C O+O+ CO, CO 2, O 2, He Differentially pumped quadrupole mass spectrometer (QMS) CO weakly dependent on O 2 CO 2 rises with O 2 CO/CO2 independent of He A Kreter et al ~150 C

EU-PWI TF meeting, Caderache, 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 2.3x10 19 C/s (5.2 g C in total) Removal rates by RFA-O 2 GDC Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum Jülich Institut für Plasmaphysik GDC Integral data from QMS CO CO 2 HD A Kreter et al

EU-PWI TF meeting, Caderache, October 2005 ICRF conditioning in O 2 in TEXTOR All injected O 2 converted into CO, CO 2 Only 15% of C removal during ICRF low duty cycle CO+CO 2 outgassing until 140 sec: ~4·10 20 O-atoms about half of O amount absorbed by wall, wall not saturated Typical shot: B t = 2.3 T ICRF 29 MHz 50 kW (absorbed) 1-6 s Continuous He flow Fast O 2 injection 2.1·10 20 O/s s (8.5x10 20 in total) Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum Jülich Institut für Plasmaphysik CO 2 He+D 2 CO O2O2 #97084 ICRF HD A Kreter et al C removal rate 1.8x10 19 C/s

EU-PWI TF meeting, Caderache, October 2005 Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum Jülich Institut für Plasmaphysik Technique C removal rate AdvantagesDrawbacks Possible improvements Oxygen venting 2.5·10 18 C/s for 0.3mbar, T wall =620K simplicity access to all wall areas selective removal of redeposited layers low removal rates T wall > 600K needed higher O pressure Glow discharge conditioning 2-3·10 19 C/s higher removal rates applicable for low T wall incompatible with steady state B non-selective carbon removal (?) limited wall area access higher GD current higher pumping rate ICRF conditioning 1.8·10 19 C/s for 1:10 duty cycle for pump out higher removal rates applicable for low T wall 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 TEXTOR Integral TEXTOR carbon redeposition rate ~ 2.7·10 20 C/s A Kreter et al

EU-PWI TF meeting, Caderache, October 2005 O 2 GDC in AUG Use of He/O 2 mixture plasmas in AUG Stability of glow discharge Less sputtering compared to pure O 2 discharge or heavier noble gas admixtures Oxidation of W in O 2 plasma saturates and is reversible in an H 2 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, October 2005 Thermal Desorption spectra of H 2 and CH 4 from gaps a-C:H coated Thermocoax 1mm Al mask: 4mm Depos. in H 2 /CH 4 GD Cleaning in 5%O 2 /He GD As deposited After 45 GD J.A. Ferreira and F.L. Tabarés, CIEMAT

EU-PWI TF meeting, Caderache, October 2005 Co-deposit removed at ~0.5 m/h at 185 C (prob. higher at 130 C) 20 m co-deposit removed in 2d also removes 0.7mm EK98 (ass. surface oxidation) Eroded surface becomes roughened & chemisorbtion forms stable C-O complexes (to >700 C) 125 C 135 C 130 C ~ 1mm EK98 ~ 40 m/h EK98 Oxidation rates of TEXTOR EK98 for 2.3% O 3 in O 2 Peaks at ~50 m/h at 130 C Decreases with burn-off Trilateral Euregio Cluster Assoziation EURATOM-Forschungszentrum Jülich Institut für Plasmaphysik Oxidation with Ozone H-K Hinssen et al EFDA/

EU-PWI TF meeting, Caderache, October 2005 N 2 seeding – impact of N ions on a-C:H N 2 + beam irradiation of a-C:H films in MAJESTIX Chemical sputtering dominates a-C:H erosion by N 2 + at low energies Erosion yields remarkably high: ~1 above ~50eV W Jacob et al

EU-PWI TF meeting, Caderache, 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, October 2005 Flash-lamp footprint covers ~30cm 2 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/m 2 at target for 250J flash Flash-lamp trials in JET BeHF

EU-PWI TF meeting, Caderache, 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, October 2005 ~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 m at the surface – but at least 7 m 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 ~0.2 m/flash at 250J – lower than expected Flash-lamp focus less sharp than predicted, energy density ~3J/cm 2 at 250J. Trials will be repeated in November at 500J, now available. Flash-lamp trials in JET BeHF

EU-PWI TF meeting, Caderache, October 2005 ( ) J/cm 2 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, October W, λ1 μm, 10kHz, 100ns pulse duration h~50 m h~0 m 10 scanings h~50 m 1 scaning, 2s TEXTOR tile Ablation at 50 cm Field depth of some centimetres 100 W laser power 1 m 2 /h of 50 μm co-deposit Laser treatment TORE SUPRA

EU-PWI TF meeting, Caderache, October 2005 YAG V1IPG Fiberlaser Wavelength (nm) Power (W)20020 Repetition rate (kHz)1020 Energy (J)201 Pulse length (ns)70120 Divergence M2351,6 Beam diameter (mm)10,25 Depth of focus (mm)±2±30 Fluence (J/cm 2 )2.52 TORE SUPRA Trials of scanning Fibrelaser planned for JET in vessel or BeHF Laser treatment

EU-PWI TF meeting, Caderache, 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: mbar (argon) Detritiation assessment by exposure to a small plasma torch planned for 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, October 2005 Selected other activities World-wide: ICRH on LHD P ICRH ~8-149kW, 38.47MHz, 3 loop antennas, He Pa, 3s on:2s off Discharge 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 (~5.1x10 14 C/cm 2 s). Factor 3-4 lower in 0.1Pa O-ICR and 6-10 lower in 4:1He/O-ICR Wall temp only C He/O-ICR reduces oxygen retention – 5.8x10 12 O/cm 2 s He-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, October 2005 Be (and its alloys) may act at significant trap – O 2 from leak: 15mg/shot Intrinsic O in Be mg/shot - convective erosion 50mg/shot - ELMs (no melt loss)0.1% O impurity 0.5g/shot - Unmitigated disruptions Target CFC erosion 0.15g/shot (reduces from 2-5g/shot) Conclusions--Purity of Be a critically important issue (how would O 2 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