1. 1 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Th Loarer with special thanks to N Bekris, S Brezinsek, C Brosset, J Bucalossi, P Coad, G Esser, W Fundamenski, E Gauthier, A Kreter, J Likonen, B Lipschultz, M Mayer, P Monier-Garbet, Ph Morgan, R Neu, B Pégourié, V Philipps, R Pitts, V Rohde, J Roth, M Rubel, C Skinner, J Strachan, E Tsitrone. And also EU TF on PWI and JET EFDA contributors Fuel retention in tokamaks

2. 2 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom OUTLINE - Introduction - Evaluation of fuel retention in tokamaks - Gas Balance - Post mortem analysis - Extrapolation to ITER - Summary

3. 3 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Introduction - Evaluation of hydrogenic retention in present tokamaks is of high priority to establish a database and a reference for ITER (400 s…usually 10-20 s today). - T retention constitutes an outstanding problem for ITER operation particularly for the choice of the materials (carbon ?) - A retention rate of 10% of the T injected in ITER would lead to the in-vessel T- limit (350/700g) in ~35/70 pulses. - Retention rates of this order or higher (~20%) are regularly found using gas balance. - Retention rate often lower (3-4%) are obtained using post mortem analysis

4. 4 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom D,T Wall Mechanisms for fuel retention Two basic mechanisms for Long term fuel retention Deep Implantation, Diffusion/Migration, Trapping C, Be C, Be, D,T Codeposition Short term retention (Adsorption: dynamic retention) ~ Recovered by outgassing In tokamaks today  Two complementary methods Gas balance  How much ? During the pulse / integrated pulse/days. Post mortem  Where and how? Integrated over experimental campaign

5. 5 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Gas balance Divertor cryo-pumps Plasma Calibrated Particle Source (Gas, NBI, pellets) Exhaust by NBI boxes, Diag… Retention Short & Long Term 1 - Function of time - Measurement of the Injected and pumped fluxes (Pressure gauges and pumping speed) 2 - Integral of Pumped flux + intershot outgassing (~ Short Term Ret ) (Collected in a calibrated volume).  Separate Short and long term retention Gas Balance  Retention = Injection - Pumped + Plasma

6. 6 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Retention: Short and long term Short term retention - Depends on plasma scenario, wall conditioning and Material (Be, C)… -“Limited” to “fast” reservoir and recovered in between pulses (outgassing) Actively cooled device  Steady state operation-->Long term retention Long term retention - Co-deposition  Correlated to C production - Implantation  Edge plasma, material structure… Dynamic retention: ≈ 5 x10 21 D JET ≈ 2.5 10 22 D ~ wall area ratio

7. 7 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Plasma scenario: C prodution - Long term retention - Drop by ~60% when moving from L-mode to Type III H-mode. - Increases by ~60% when moving from L-mode to Type I H-mode.  Retention correlated to increase of C erosion T Loarer et al., EPS 2007 Pulse typeDivertor phase (s) Injection (Ds -1 ) Long term retention (Ds -1 ) L-mode 2 MW 126 ~1.8  10 22 1.34  10 21 Type III 6 MW - <5-10 kJ 350 ~0.6  10 22 0.8  10 21 Type I 13 MW – 100 kJ 50 ~1.7  10 22 2.08  10 21 Series of repetitive and consecutive discharges (~no history effect)

8. 8 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Carbon production and scenario - DTE on JET and TFTR (at high NBI power more T retention by co-deposition) C Skinner et al. JNM 1997, 1999 J Strachan et al. Nuc. Fus. 2003 L mode (3-4MW) Type I H mode 10-15MW - Increase of carbon source depends on scenario (ELMs, recycling flux…)  enhanced retention by co-deposition - Increase by a factor of ~2 of carbon source from L to type I ELMy H-Mode

9. 9 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Implantation and “wall” saturation - As T surf increases  Strong outgassing of D, C x D y from target plates (eventually lost of n e control) - Outgassing  signature that implantation is saturated for overheated PFCs - Also observed on long discharges in TRIAM-1M, Tore Supra. (Sakamoto et al. IAEA 2006, JNM 2007 Grisolia, JNM 1999, ). Nakano et al. IAEA 2004, Nuc Fus 2006 But, with gas balance analysis this strong outgassing “hides” co-deposition. And since carbon source increases this enhances retention by co-deposition.

10. 10 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Inventory proportional to duration B Pégourié I-21 - Recent exp. campaign of 10 days on TS repeating the same long pulse (2min – 2MW) - Total of 5 h of plasma w/o conditioning Sugiyama et al. Pys. Scrip 2004, Skinner et al, EPS 2001 - Steady state retention and wall inventory proportional to plasma duration - Weak recovery by outgassing and also by disruptions, independently of the amount retained. DDC in TFTR after DTE (Skinner JNM 1997, 1999) and JET V Philipps P1-63

11. 11 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Retention in carbon devices Retention by co-deposition dominates Limit/cancel co-deposition ?  High Z Skinner et al. JNM 1997, 1999T Nakano et al. JNM 2007 V Mertens et al. EPS 2003 Lasser et al. FED 1999 Long term retention  Cumulative, proportional to pulse duration and linked to Carbon source (recycling, ELMs…)  JET, JT-60U, AUG, TEXTOR, TS…  DT exp on JET and TFTR Continuous increase of T inventory as the T operations are going on and dominated by co-deposition  TFTR P Andrew et al. FED 1999

12. 12 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom High Z – Alcator C-Mod D Whyte et al., IAEA 2006 ~4x10 21 D D Whyte et al. IAEA 2006, B Lipschultz et al., PSI 2008 - 16 repeated pulses (w/o disrp) in cleaned Mo walls - Retained D fluence remains linear with incident D ion  ~3.5x10 20 Ds -1 - Net D wall recovery with planned disruptions B Lipschultz I-14 - Mo  retention proportional pulse duration  Implantation? Co-deposition with B? - Effective D recovery by disruption with Mo as PFC G Wright I-19

13. 13 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom High Z - W in ASDEX Upgrade AUG from “all C” to “all W” (Carbon free) - With 70% of W the retention was still around 10-20% (C dominated) - 100% W significant drop of retention below 1% ~45% W ~70% W V Mertens et al., EPS 2003, V Rohde et al. EPS 2007 dom. ICRH 2004 100% W w/o Boronisation V Rohde P1-61 R Dux I-06

14. 14 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Where is the fuel retained?  Post mortem analysis

15. 15 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom MethodPrincipleQuantity measured SIMS Secondary Ion Mass Spectroscopy Incident ion flux (Cs+, Ar+, O+) with an angle ~20-30° with respect to the surface -Analysis of “sputtered” ions + CH 3, + CH 4 … and/or ionised fragments -Depth ~  m RBS Rutherford Back Scattering He+ incident beam (protons) @~1-3MeV) Measurement of the energy of the reflected beam Analysis of the elemental surface. From nm to mm TDS Thermodesorption Temperature ramp up (room up to 1600K) of a sample. Under vacuum or inert atmosphere (Mostly Ar or He) w or w/o H2 Total quantity of H, D, O, C x D y …trapped in the material, coupled to Mass Spectrometer Activation Energy NRA Nuclear Reaction Analysis Nuclear reaction triggered above an energy threshold of the incident 3 He beam~1-3MeV 2 D( 3 He,p) 4 He Target 2 D, particle analysed: p, “product” 4 He 10 Be( 3 He,p) 12 B -- 12 C( 3 He,p) 14 N -- 13 C( 3 He,p) 15 N Ratio D/C, Be/C Depth profile 1Mev  ~1.5  m 2.5MeV  ~7.5  m PIGE Proton Induced Gamma Emission 13 C(p,  ) N 14 Use the narrow resonance for protons at 1.748MeV giving a 9.17MeV gamma (  ) Concentration of 13 C vs depth Smaller depth resolution, but detection limit ~10 times better than NRA) NMR Nuclear Magnetic Resonance Resonance frequency proportional to the distance C—H of the element “connected” to H(D) Used for liquids, in organic chemistry Post Mortem Analysis Wide range of methods for different objectives  Surface analysis, Structure, Depth profile, Composition…

16. 16 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Where and how ? Implantation in CFC D retained in the samples (by TDS) EK98 DMS780 NB31 Comparison with PISCES-A data No saturation observed for these fluences and   0.5 Test limiter with material stripes exposed in TEXTOR TEXTOR: NB31 ITER DMS780 JET EK98 T s = 500K A.Kreter et al. 2007 J Roth et al. PSI 2006. Test limiter for dedicated experiments since removed at the end of the experiment; also the case of marker exp ( 13 C)

17. 17 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Where and how ?: co-deposition with C  Dedicated 13 C experiment to localize deposition and associated retention Different Carbon erosion-transport and eventually co-deposition with plasma scenario L and H mode Also 13 C experiments in TEXTOR: P WIenhold et al. JNM 2001, JET: J Likonen et al. FED 2003, AUG: M Mayer et al. JNM 2005, JET: P Coad et al. Nuc. Fus. 2006. DIII-D: Wamplers et al., JNM 2005, 2007 H-mode NRA L-mode NRA L-mode PIGE 3 He,p NRA

18. 18 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom C-erosion/deposition: JET 2001-2004 Carbon deposition on PFCs Louvre: 60g (from QMB) 17g 44g 67g Negligible 19g 24g Erosion No clear erosion or deposition 105g 233g 99g 464g From deposit thickness (  = 1.0 gcm -3 - 1.8 for the substrate) -Total C deposition Inner: 625 g Outer: 507 g J Likonen P1-70

19. 19 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom D/C ratios: JET 2001-2004 0.910.25 0.15 0.11 0.42 0.02 0.120.08 0.14 0.17 0.79 D/C ratio and retention Injected : 1800g (5.381x10 26 D) In the divertor area  Total D: 66 g = 3.7 % of  inj (2.2x10 20 Ds -1 ) Retention 70% Inner + 30% Outer J Likonen P1-70

20. 20 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Retention at First wall (JET – MkII-SRP, 2001-2004) - Total D retention: 0.3g (0.02%) - Outer poloidal limiters have a minor contribution to D retention 19μm 0.96 cm 3 D/C=0.09 10μm 0.5 cm 3 D/C=0.02 0.9μm 0.04cm 3 D/C=0.13 3μm 0.2cm 3 D/C=0.13 J Likonen P1-70 M Mayer et al., PSI 2000, C Brosset et al, PSI 2004, 2006 JET: First wall~200°C Divertor structure ~50°C TEXTOR ~8-10% (300°C) Tore Supra ~10-15% (120°C) ~3.8% - Gap inventory always connected with C co-deposition (large in gaps, small in narrow castellated grooves) M Rubel et al, JNM 2007

21. 21 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Temperature effect - JT-60U Masaki IAEA 2006, Hayashi PSI 2006, Sugiyama PSI 2006, Hirohata PSI 2006 T wall = 300°C 6 years – 8h20 of NBI - Higher T wall  lower D/C ratio on PFCs - No drop of co-deposition in remote area T wall =150°C 3 years – 2h10 of NBI Long discharges JT-60U “Normalised” to NBI time (8h20) - Carbon: inner + dome ~550 g  1.0x10 21 /sec (2.7 times higher than in JET: 3.7x10 20 s -1 ) - Carbon: outer erosion ~340 g  210 g comes from the main chamber PFC  D/C~ 0.01-0.15 Remote  D/C~ 0.75 Same as JET 50 ° C Retention ~ 1.3x10 20 Ds -1 (~8%)

22. 22 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom 2002 – 2003 4940 s 6A 4 AUG – From all C to all W  D inventory W C C C C-dominated campaign 2002/2003 Normalised to 3000 s - D on divertor tiles 0.9 – 1.3 g - D below roof baffle 0.4 g  1.3-1.7g Total D-inventory dominated by inner divertor and remote areas  Long term inventory ~ 3 – 4% M Mayer et al, Nuc Fus 2007

23. 23 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom 2007 2620 s 6A 4 AUG – all W: Analysed tile D inventory From C-dominated to all W D inventory reduced ~5-10  Retention<1% W W W W M Mayer I-13 Full W camp 2007 – No Boronisation Norm. to in 3000 s - D on divertor tiles 0.15 – 0.23 g - D below roof baffle 0.03 g  0.18-0.26g (drop ~7-10)  D retention in inner divertor still dominated by C-codeposition: drop ~10-15  D retention in outer divertor dominated by trapping in W – Drop ~5-10

24. 24 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Gas balance – Post mortem  Extrapolation to ITER Post mortem analysis - Accuracy of NRA, SIMS… ~ 10% - But cannot include all the PFCs, and effect of oxygen when removed from the vessel… When analysing the “ same plasma ”  Gas Balance and Post mortem lead to similar evaluation - Accuracy ~10% for D (H) (Better: He or T) - But C x D y cont., long term outgassing... Gas Balance “Global measurement” for “specific” plasma conf. with “minimum” of power/gas P in ~15-20MW –  inj ~2-3x10 22 Ds -1 “Local measurement” integrated over an exp. camp. Reflects the averaged discharge P in ~4MW,  inj ~4x10 21 Ds -1 Long term Ret (10-20%)  4-8x10 20 Ds -1 Retention in the divertor area (MKII-SRP) + Subdivertor (as in JT 60U) Long term Ret  4x10 20 Ds -1

25. 25 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom All C reaches tritium limit (700g) in less than 30-40 discharges All-W reduces tritium problem, but n-effects need to be considered Fuel inventory estimates for ITER - More R&D required for evaluation of n-effects: - Need to improve modeling in retention by co-deposition/trapping (fluence…) Evaluations based on ion + CX fluxes to the wall and resulting - Implantation - PFC erosion and associated co-deposition J Roth R-1 Roth PPCF 2008

26. 26 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Summary Gas balance: Long term retention for C machine depends on Plasma scenario  As far as C source exists  co-deposition dominates, increases with C production recycling, ELMs (AUG, JET, JT-60U, TFTR, TS) and  to pulse duration.  Retention by implantation saturates for overheated PFCs (JT-60U)  Long term recovery (outgassing and disruption) is weak (TFTR, JET and TS)  Mo exhibits retention  to plasma duration, but D recovery from disruption.  Full W shows a significant drop of the retention ~1%. Extrapolation to ITER - A full C machine would reach the limit in “few” discharges of 400s - A high Z device would limit the co-deposition and strongly reduce retention Post Mortem analysis  Confirms long term retention in PFCs is low but high in remote areas  In carbon  AUG-JET (3-4%), JT-60U~8%, TEXTOR & TS ~10-15%  Significant drop of the retention below 1% in AUG with full W configuration Complementary and reliable methods  retention in full metal wall (ILW)

27. 27 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom END…

28. 28 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Short term: plasma scenario n e ~0.7n GW P TOT (MW) NBI+ICRH~13MW D   (in) D  (out) Time (s) #69260 I p = 2.0 MA, B  = 2.4 T - Short term retention : “limited” to “fast” reservoir and recovered in between pulses (outgasing) - Long term retention : Co-deposition and implantation : Slow process compared to short term over 5-10 sec.  W ELM ~100 kJ ~ 60 Hz T. Loarer et al., EPS 2007 Heating phase Injection Exhausted Retention

29. 29 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Retention in gaps 2 decay lengths in TFTR  1 ~2mm  hydrogen rich deposition ((D+T)/C~0.2  prompt redeposition of C 2 D x (1,3,5)... with high sticking coefficient  2 ~6-12mm influenced by the gap width (up to 30mm with large gaps)  migration of neutral hydrocarbon with low sticking coefficient T Tanabe et al. Fus Sci and Tech 2005 0 3 6 9 12 15 18 03691215 Distance from Plasma [mm] D and C [e17/cm2]] D, Side A D, Side B C, Side A C, Side B JET Be Limiter Tiles - D deposition in the castellation always associated with Carbon. - Short decay length of deposition in the castellation: = 1.5 mm. -D content in the castellated groove does not exceed 8 x 10 17 cm -2. - No deuterium detected in bulk beryllium. M. Rubel et al. TFTR

30. 30 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Retention in gaps M Rubel et al, JNM 2007 Be limiter tiles of Mk-I divertor Distribution of D on side surface in the gaps between the Mk-I CFC tiles.

31. 31 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Gas Balance: Accuracy DT experiments in JET…over the first week the most difficult part to evaluate is the outgassing. In actual tokamak discharges. Loarer JNM 2005  65% of retention during the pulses (~10sec)  40% of retention over the campaign  17% after intensive cleaning (~6 months) T particle balances from Gas balance analysis  Good agreement between gas balance and cryopump reg. (green points)

32. 32 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom JET DTE Campaign 1997-1998 T Vessel inventory End of DTE1 campaign Injected-Exhausted (35g – 23.5g) 11.5 g Clean up phase (D, H, He, Disrp, GDC…)  Remove 5.3g 6.2 g Venting  Remove 2.5g 3.7 g Flakes  Remove 0.5g 3.2 g Inner and Outer wall  Remove 0.1g 3.1 g 480 Tiles of Divertor  Remove 0.1g 3.0 g still remaining (flakes) After the campaign and intense cleaning campaign (pulses, conditioning, venting, the T inventory in the PFCs is “negligible” (~0.2 g). Trapped tritium in flakes. Bekris et al. JNM 2005

33. 33 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom JETand TFTR DTE Campaign Skinner et al. EPS 2001 4.2g 2.06g Drop by a factor of ~2 in 1 1/2 year

34. 34 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom High Z material: Alcator C-Mod Wampler, IEEE 1999, PSI 1998 - OSP (net erosion): low D retention  consistent with results from Mo erosion and B deposition. -ISP Boron coverage is very small whilst D content is also very small - Boron surface layers from boronisation was found at all locations except near the OSP Dominant impurity: Boron and “some” amount of Mo

35. 35 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Gas balance: AUG - All W V Rohde et al. this conf. P1-61 Gas balance divided in 3 phases - Limiter - Ramp up - Steady State  Long term  Carbon PFC  W Main Chber  All W

36. 36 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom DTE: TFTR and JET C Skinner et al. 2002 Effect of oxygen on samples removed from device

37. 37 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom DTE: TFTR C Skinner et al. 2002

38. 38 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Location of TFTR tritium inventory C Skinner et al. 2002

39. 39 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom Co-deposition and Carbon production - Increase of carbon source (ELMs, recycling flux…)  enhanced retention by co-deposition Non-linear carbon deposition on ELM energy  Thermal decomposition of surface layers A Kreter, G Esser et al sub PRL A Kreter I-03

40. 40 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom High Z exp in Alcator C-Mod B Liptschultz I-14 - Although cleaning process allows to remove the boron layers, there is still a non negligible amount of boron at the surface - If experiments are carried out in AUG with full W and boronisation, this could clarify the possible effect of boron in the retention behaviour observed in Alcator C-Mod

41. 41 Th LoarerFuel retention in tokamaks – PSI Conference 26-30 May - Toledo Euratom One possible explanation are plasma impurities, largely B (~1 %), that are present in the C-Mod plasma and in the first 500 nm Mo tiles. Overall, in both high-Z devices the campaign integrated retention on D is small, much smaller than for carbon or boron co-deposition. Alcator C-Mod and ASDEX Upgrade Alcator C-mod, MoASDEX Upgrade, W Gas balanceVariation between net outgassing and up to 50% retention, linear with number of discharges ~1% retention, Post- mortem ≤ 1 %< 0.2 % retention (to be confirmed) Modelling1-2 % retention, linear with number of discharges Roth R-1