1. EU-PWI TF meeting, Madrid, 29-31 October 2007 Progress with tritium removal and mitigation 2006-7 G. Counsell 1, P. Coad 1, J.A. Ferreira 8, M. Rubel 6, F.L. Tabares 8, A. Widdowson 1, P. Sundelin 6, V. Philipps 4, G. Sergienko 4, D. Tafalla 8, I. Tanarro 8, V. Herrero 8, C. Gómez-Aleixandre, J.M. Albella 8, P.Gąsior 9, J. Wolowski 9, J. Likonen 5, C Grisolia 2, A. Semerok 7, C Hopf 3, W Jacob 3, M. Schlüter 3, D Farcage 7, D Hole 10, T Renvall 10, P-Y Thro 7 1 EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK 2 Association EURATOM-CEA, CEA/DSM/DRFC Cadarache, 13108 St.Paul lez Durance, France 3 Max-Planck-Institut für Plasmaphysik, EURATOM Association, D-85748 Garching, Germany 4 Institut für Plasmaphysik, Forschungszentrum Jülich, Association EURATOM-FZJ 5 Association EURATOM-TEKES, VTT Processes, PO Box 1608, 02044 VTT, Espoo, Finland 6 Alfvén Laboratory, Royal Institute of Technology (KTH), Association EURATOM-VR, 100 44 Stockholm, Sweden 7 CEA Saclay, DEN/DPC/SCP/LILM, Bat. 467,91191Gif sur Yvette, France 8 Association Euratom/Ciemat. Laboratorio Nacional de Fusión. 28040 Madrid, Spain 9 Institute of Plasma Physics and Laser Microfusion, Association EURATOM – IPPLM, Warsaw, Poland 10 Dept. of Engineering and Design, University of Sussex, Brighton, East Sussex, UK

2. 2/28 Outline 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. 3/28 Effects of Nitrogen on a-C/D erosion and deposition

4. + ~ 3:9x10 12 cm 2 /s 400:1 H 0 :N 2 + M Schlüter, C Hopf and W Jacob N 2 + /H 0 particle beam exposure Exposure of a-C:D films in MAJESTIX Yield with N 2 + chemical sputtering Adding H 0 significantly increases yield synergistic effect

5. Ions create broken bonds React with H 0 forming volatile C x H y species M Schlüter, C Hopf and W Jacob Ions create broken bonds Slow N 0 at end of ion range react to produce volatile C x N y species N 2 + /H 0 particle beam exposure 2 processes needed to explain N 2 + /H 0 erosion:

6. Nitrogen scavenging a-C/D on Si (heatable), N 2 PSI-2, Berlin FL Tabares et al No significant ion flux to a-C/D sample

7. T= 60ºC T=80 ºC CH 4 H2H2 N 2 +CH 4 N 2 addition supresses deposition – net erosion Effect not seen with Ne Cumulative effect - N 2 required for scavenging decreases with exposure Nitrogen scavenging FL Tabares et al

8. #102965 LFS HFS Nitrogen-assisted ICRF discharges ICRF H 2 /N 2 plasma in TEXTOR 40 kW, 29 MHz B ~ 2.3 T, B v ~ 0.04T 0.04 Pa 3 - 6x10 17 m -3 N 2 /(N 2 +H 2 ) ~ 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

9. Nitrogen-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 N 2

10. SampleD in D ex B in B ex C in C ex H 2 -N 2 plasma + ICRF O 2 -He glow Inconel-1---- B on Si13 364983101 a-C:D/Si610590--7921077 a-C:D/Si B on Si 552 17 6262 8 300 8 280 880 12 20 30 P. Sundelin, M. Rubel, V. Philipps, G. Sergienko Nitrogen-assisted ICRF discharges Units of 10 15 cm -2

11. 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 summary

12. Effects of Oxygen on a-C/D erosion

13. C. Hopf, W. Jacob, V. Rohde Oxidation cleaning relies on phys < chem phys (C, Al, Fe) approach chem for a-C/H at high E ion phys (W) always more than factor 10 lower is lower than TRIM for O on AL, W – surface oxide effect Selectivity in oxidation

14. Laser interfermoetry Cross-checked with: - Profilometry - XPS - C balance in glow 1 fringe= /2n..144nm n hard C …2.2 Impact of material mixing Photodiode He,Ar CH 4 O 2 Oven Turbo pump Oven T~600ºC Glow Discharge Laser (Li, Mg) Francisco L. Tabarés, J.A. Ferreira, D. Tafalla, I. Tanarro, V. Herrero, C. Gómez-Aleixandre, J.M. Albella

15. BeOMgO C (kJ/mol)-609-601 (g/cm 3 ) 3.013.58 Melting point (K)22003073 Oxidation 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/O 2 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

16. Film RGA CC/Li layerC/Li mixedC/Mg mixed O2O2 1.8e-61.1e-63.3e-61.2e-6 O 2 1.06e-63.8e-72.7e-69.13e-7 CO9.06e-71.5e-71.1e-66.08e-7 CO 2 1.09e-72.9e-82.0e-78.64e-8 H2H2 3.5e-61.4e-77.0e-64.07e-6 Erosion rate (nm/s) 0.180.060.230.19 CO+2CO 2 / O 2 10.55 0.85 Erosion rates and products ~unaffected in homogenous a-(C+M)/H films (M=Li,Mg) Film structure may have significant impact Oxidation of Mg/a-C/H mix Francisco L. Tabarés, J.A. Ferreira, D. Tafalla, I. Tanarro, V. Herrero, C. Gómez-Aleixandre, J.M. Albella

17. Oxidation of B/a-C/H mix C. Hopf, W. Jacob, V. Rohde He/O 2 GDC (-60V bias ) 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?

18. He/O 2 ICRF discharges CO and CO 2 products (about 75%) released mostly after ICRF pulses C removal rate O 2 injection rate Neutral pressure at the antenna box (~1x10 -1 Pa) determines max O 2 inj. TEXTOR Re-conditioning attempted by ICRF conditioning D 2 /He Successive wall cleaning with ICRF was necessary Recovery procedure accompanied by tokamak disruptions (10 disruptive shots). Further optimization necessary V. Philipps et al

19. Concerns over selectivity Some confusion over impact of non-volatile impurities – effect of film structure? Further in-vessel testing conducted Section summary

20. Photonic cleaning techniques

21. Laser 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 3m 2 / m/hr Some issues with selectivity CFC substrate can be damaged – optimisaton needed

22. Laser cleaning of TEXTOR tiles J. Wolowski, M Rubel, V. Philipps, IPP ASCR (Prague, CR) Characterised with - ion time of flight optical spectrocopy

23. Surface profile complicates optimisation Laser 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

24. Products 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

25. Video of laser cleaning Evidence of particulates Products of Laser cleaning Dust probably contains bulk of T released May be unavoidable with this wavelength Integrated dust collection necessary A Widdowson, J P Coad, D Farcage, D Hole, J Likonen, T Renvall, A Semerok, P-Y Thro

26. Analysis methods: 3 He + NRA at 2 MeV and microscopy. Graphite plates with TEXTOR co-deposits: C D = up to 10 19 cm 2 Dust collected from metal plate adjacent to target: C D = 3.9x10 17 cm 2 Dust produced by laser cleaning still contains significant fuel P.Gąsior, P. Sundelin, M. Rubel Dust during TEXTOR tile cleaning Important note: Single result Must be verified by other fully quantitative studies.

27. 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 summary

28. Work Programme for the SEWG on fuel removal

29. 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 Removal

30. 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