1. 1 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Th Loarer with contributions from D Borodin, C Brosset, J Bucalossi, S Droste, G Esser, G Haas, A Herrmann, A Kirscher, A Kreter, K Krieger, J Likonen, A Litnovsky, M Mayer, V Mertens, Ph Morgan, V Philipps, G Ramos, S Richter, V Rohde, J Roth, M Rubel, A Sergienko, E Tsitrone, E Vainonen-Ahlgren, P Wienhold, EU TF on PWI and JET EFDA contributors Gas balance and Fuel retention - Overview of Gas balance and fuel retention results Tokamak experiments (JET, TS, AUG, TEXTOR) Post mortem analysis (Laboratories) - Summary and further plans Euratom

2. 2 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Introduction - Evaluation of hydrogenic retention in present tokamaks is of high priority to establish a database for ITER (400 sec ~ 7min…10-20 sec 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 mobilisable T-limit (350 g) in 35 pulses. - Retention rates of this order (~10-20%) or higher are regularly found using gas balance in C-wall tokamaks. - Retention rate ~5 times lower are obtained using post mortem analysis - Are these two methods reliable to evaluate the retention and is it possible to understand why they lead to different results ? - SEWG to clarify Gas Balance vs post mortem analysis

3. 3 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid physics: material erosion, migration & fuel retention QMB measurements Spectroscopy Gas balance measurements Deposition probes 13 C migration Post mortem tile analysis D,T Mechanisms for fuel retention Two basic mechanisms for Long term fuel retention Deep Implantation, Diffusion/Migration, Trapping C, Be C, Be, D,T In carbon wall devices codeposition dominates retention (also expected for Be wall conditions, JET ILW, ITER) Codeposition Short term retention (Adsorption: dynamic retention) Recovered by outgasing in between discharges

4. 4 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Calibrated Particle Source (Gas, NBI…) Divertor cryo-pumps Wall Retention Long & Short Term Particle balance procedure on JET Repeat sets of identical discharges (no intershot conditioning) Plasma Injection = Pumped + Short Term Ret + Long Term Ret Total recovered from cryo-regeneration: Pumped + intershot outgassing over ~800s (assumed equal to Short Term Ret ) Regenerate cryopumps before and after expt. collect total pumped gas (accuracy~1.2%)

5. 5 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Particle fluxes: H mode Type I From L mode to Type I ELM H-mode Increase of long term retention - with the recycling flux - with ELMs Energy I p =2.0MA, B T =2.4T 13MW NBI+ICRH ELM Energy~100kJ @16 sec, Ret~5.2x10 21 Ds -1 LongRet ~ ShortRet @20 sec, Ret~2.9x10 21 Ds -1 LongRet >>ShortRet Injection Pumped flux Retention Long Term Ret Th Loarer et al

6. 6 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Integrated particle fluxes HαHα CIII Type I ELMs Type III ELMs L mode Type I ELMs Type III ELMs Integrated CIII and H α horizontal light (L-mode, Type III and Type I ELMs) - Slope for Type I ELMy H-mode shows both enhanced recycling and total carbon source. Higher recycling and ELM Enhanced carbon erosion and transport leading to stronger carbon deposition and fuel codeposition

7. 7 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid ELM induced C deposition Non-linear dependence of carbon erosion on ELM energy thermal decomposition of surface layers and favourable geometry rapidly increases QMB deposition Can explains high deposition rates on water-cooled louvres during 97-98 JET DT experiments high T-retention A Kreter, G Esser et al

8. 8 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Particle Balance summary on JET - Long term retention increases from L-mode to H-mode Increased C erosion and transport due to increased recycling and effect of ELMs enhanced C erosion enhanced co-deposition and retention. - Recovery between pulses (short term retention) always constant within a factor ~2 – in the range 1-3 10 22 D Independent of discharge type, ELM energy, quantity of injected particles Pulse type Heating phase (s) Divertor phase (s) Injection (Ds -1 ) Long term retention (Ds -1 ) ret / inj L-mode81126 ~1.8 10 22 1.74 10 21 ~10% Type III221350 ~0.6 10 22 1.31 10 21 ~20% Type I3250 ~1.7 10 22 2.83 10 21 ~17%

9. 9 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Tore Supra: the DITS project Objectives : Clarify post mortem analysis vs Gas Balance Retention mechanisms (codeposition vs bulk migration) (Deuterium Inventory in Tore supra) 3 phases : dedicated experimental campaign Gas Balance dismantling of a sector of the limiter samples for post mortem analysis sample analysis (collaboration with european labs, EU PWI TF)

10. 10 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Scenario of the DITS campaign Main issue : UFOs (C + metals + D ? ) detachment disruptions scenario at lower LH power (< 1.8 MW) + slow ramp up - No evolution for C - Fe and O level increasing to values before carbo/boronisation Scenario 2 (lower power ~ 80 s) Scenario 1 (nominal – 120 s) Repetitive pulses every 20 mn (~ 40 mn of plasma each day) 5 h of plasma w/o conditionning E Tsitrone et al

11. 11 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid UFOs on CCD imaging of the TPL E Tsitrone et al

12. 12 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid 1 st scenario : P LH = 2 MW2 nd scenario : P LH = 1.6-1.8 MW No wall saturation observed after 5h00 E Tsitrone et al Injected ~ 5.8x10 24 D (19.5 g) Trapped ~3.3x10 24 D (11 g)

13. 13 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Inventory proportional to discharge duration Disch. OK Disruptions Outgassing Trapping E Tsitrone et al

14. 14 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Total exhausted = (6×10 -5 Pa) × (1.3×10 6 s) × 10 m 3 /s ~ 700 Pa.m 3 /s ~ 3.5×10 23 D atoms to be compared to WI ~ 3.3×10 24 D atoms (~ 10 %) (upper limit : D 2 concentration in pumped gas decreases rapidly) Long term recovery << wall inventory E Tsitrone et al

15. 15 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Summary DITS experimental campaign : successfully completed 13 C carbonisation / 11 B boronisation performed 5h of plasma w/o conditionning : 1 year of operation in 2 weeks Reliable operation (LH, cooling loops, PFCs) Main limit : UFOs disruptions operational limit ? 80 % of the objective reached (WI = 3.3 10 24 D or ~11g) : ok for qualitative and quantitative analysis Particle balance No wall saturation, retention proportional to discharge duration. Exhausted gas dominated by D during the shots Disruptions at low Ip, long term recovery : negligible in the balance DITS project on tracks : TPL sector dismantled, selected fingers extracted samples available for analysis ~ november 2007

16. 16 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Phases of discharges observed in C Typical discharge puff and pump steady phase reached after ~2sec V Rohde et al.

17. 17 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Full W configuration: Carbon free machine, How does it compare to C in terms of fuel retention ? In typical discharge puff and pump steady phase not reached V Rohde et al.

18. 18 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Gas balance with W wall Wall loading observed, no steady state reached V Rohde et al.

19. 19 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Gas Balance summary from AUG in W -Gas Balance is needed to verify the benefit of full tungsten wall. -Support from EU TF on PWI to investigate gas balance, but support more difficult from man power point of view. -However, experiments performed and detailed analysis to start soon. -Data set exits, but direct comparison with C is very difficult due to different plasma scenario. -Accuracy is dominated by pumping of cryo pump. - Due to the high gas puffing rate (>10 22 Ds -1 ), an accuracy of ~1% is required in AUG. Improvement of the accuracy by adding a separated volume to store all the gas (as in AGHS in JET) V Rohde et al.

20. 20 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Deuterium retention in CFC Deuterium retained in the samples (by TDS) EK98 DMS780 NB31 Comparison with PISCES-A data (J.Roth PSI 06) Retention in both CFCs slightly higher than in EK98 Good agreement with N11 exposed in PISCES-A No saturation observed for obtained fluences Fuel retention in TEXTOR is dominated by co-deposition (Contribution of in-bulk retention to total retention ~10%) Photograph of the test limiter with material stripes exposed in TEXTOR NB31 ITER DMS780 JET EK98 TEXTOR: T s = 500K A.Kreter et al.

21. 21 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Toroidal direction Poloidal direction SOL Plasma Shaped cells 10x10x12(15)mm Rectangular cells 10x10x15 mm The shape of a castellation cells can be optimized to reduce impurity and fuel transport into gaps 2 shapes of castellation studied Experimental details Shaped and rectangular cells exposed under the same plasma conditions 16 repetitive discharges: 112 sec, Te~20eV, ne~6x10 18 m -3 Fluence averaged over plasmawetted area: Rectangular cells: 2.2*10 20 D/cm 2 Shaped cells: 4.2*10 20 D/cm 2 Post-exposure analyses with SIMS, Dektak, NRA and EPMA on all sides of poloidal and toroidal gaps. Gaps 0.5 mm Exposure of W castellated limiter in the SOL of TEXTOR 20 o Toroidal gaps Poloidal gaps A. Litnovsky

22. 22 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Toroidal gaps exposed deep in plasma Fuel accumulation in toroidal gaps Shaped geometry Rectangular geometry D/C (%) N С, *10 16 at./cm 2 N D, *10 14 at./cm 2 D/C (%) N C, N D D/C (%) N С, *10 16 at./cm 2 N D, *10 15 at./cm 2 D/C (%) N C, N D Distance from the top of a gap, mm Plasma-closest edge Less fuel in gaps of shaped cells Distance from the top of a gap, mm Plasma-closest edge D Σ =1.46×10 15 at/cm 2 D Σ =3.46×10 15 at/cm 2

23. 23 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Poloidal gaps Different fuel retention in the poloidal and toroidal gaps Plasma flow open side shadowed side Plasma- Ongoing research: short summary More fuel retention in plasma-shadowed sides; 2-3 times more fuel stored in gaps of shaped cells*; Toroidal gaps At least 2 times less fuel stored in gaps of shaped cells exposed deeper in plasma; Independently on shaping, at least 2 times more fuel stored in the toroidal gaps exposed further away from plasma; Still less fuel in gaps of shaped cells exposed further away from plasma, although the difference is around 50%. A. Litnovsky et al., Phys. Scr. T 128 (2007) 45;

24. 24 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Be toroidal belt limiter Operation: 1989 – 1992 56 000 s of plasma (~16 hours) 2000 castellated blocks. Studies performed with Ion Beam Analysis on two tiles: Castellated grooves: both sides of 6 grooves; Side surface between the tiles; Top surfaces of tiles. Deposition and Fuel Inventory in Castellated Beryllium Limiters from JET Be M. Rubel et al

25. 25 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Top and Side Surfaces of Cleaved Beryllium Limiter Tiles Cleaved limiter blocks mounted in the chamber for IBA Bridging of some gaps by molten Be. Grooves are not filled with Be. M. Rubel et al.

26. 26 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Deposition in the Castellated Grooves of the Beryllium Limiter Tiles Side ASide B Surfaces in the castellated groove Freshly cleaved surface Freshly cleaved surface Messages: Deuterium deposition in the castellation is 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.

27. 27 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid 10μm 7μm7μm 72μm 44cm 3 67cm 3 99cm 3 105cm 3 233cm 3 17cm 3 464cm 3 26μm 10μm 38μm 33μm 41μm 19cm 3 24cm 3 60g on louvre 18μm300μm32μm Thicknesses: surface analyses Volumes: integration over torus 130μm 200μm22μm Deposition at divertor (MkIISRP, 2001-2004) J Likonen et al - Carbon: inner total 625 g (1.0 g/cm3) =3.1x10 25 C-atoms = 3.7x10 20 /sec, D/C from NRA 30g D Injected D: 1800g, retention fraction: 1.7% - Carbon: outer 507 g = 2.5x10 25 C= 3.1x10 20 /sec Deuterium: D/C from NRA 13 g retention fraction: 0.7% Total D retention: 43 g = 2.4 % of injected No SRP included

28. 28 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid J Likonen et al Deposition at OPL and IWGL (MkIISRP, 2001-2004)

29. 29 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid J Likonen et al Conclusion for MkIISRP, 2001-2004 - Deposition at divertor very asymmetric (70% inner divertor, 30% at the outer) - Main D retention at divertor - OPL limiters have minor contribution to D retention - IWGL have most likely a small contribution - D retention: 10% (MkIIA), 4% (MkIIGB), 3% (MkIISRP, SRP analysis under way) - Long term fuel retention: 13% (TFTR), 8% (TEXTOR), 5% (DIII- D) and 4% (AUG with C)

30. 30 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid AUG Wall areas and analysis methods inner heat shield upper divertor upper PSL lower PSL pump duct inner divertor roof baffle outer divertor ICRH limiter Analysis methods NRA D( 3 He,p) - 1000 keV: D inventory in 2 µm - 2500 keV: D inventory in 10 µm Marker stripes for RBS - Deposition of B, C (talk on 9.5.2007) SIMS Data for 2002-2003 and 2004-2005 Campaigns Carbon dominated machine

31. 31 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Deuterium retention in 2002–2003 Long-term D retention 3 – 4% of fuelling Majority on divertor tiles (50-60%), followed by remote areas (20%) RetentionFuelling from (B+C), assuming D/(B+C)=0.4 Gas balance (V Mertens 2003): 10 –20% Marginal agreement, taking error bars into account M Mayer et al, Nuc Fus 2007

32. 32 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Exposed for 2 campaigns 2003 – 2005 about 7000 plasma seconds Thin W-coating with 4 µm thickness using PVD 6A 6B 5 4 9A 9B 9C 1 low 1 up 2 3A 3B W C 10 M Mayer et al Surface temperature close to RT, with maximum of 500 K D/W = 20 – 30% at surface: trapping with C: 2–4×10 21 C/m 2 D/W = 0.01 – 0.1% in W-layer Tungsten machine Preliminary results Analysed tile for D inventory

33. 33 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Evaluation of the total amount of D retained in W D-inventory: 1.5×10 21 D/m 2 AUG wall area: 72 m 2 1×10 23 D-atoms = 0.3 g D-input in 2 campaigns: 160 g Retention with W-walls: < 0.2% of input (Retention with C-walls ~ 4% of input) M Mayer et al

34. 34 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Summary & Comparison Gas balance-Post mortem - Post mortem analysis confirm that the long term retention in the PFCs is low. AUG (~4% in C, less in W), JET (~3-4%), TEXTOR and TS (DITS) ~8% - Post mortem analysis is representative of the averaged over a campaign of a small area (difficult for extrapolation: flakes in JET during DTE ): cumulative effects of thermal release (plasma ops.), GDC, disruptions, ….. (eg JET Averaged power with MkIIGB~4MW, and averaged fuel rate ~5x10 21 Ds -1 in 2007) - Retention in PFCs, mainly in the divertor (30% Outer leg/ 70% inner leg) - Retention in gaps always associated to carbon, typical length ~4mm Gas balance: Long term retention evaluated in the range 10-20% for carbon machine. Analysis generally carried out for plasma conditions different from averaged Retention increases with recycling (gas/NBI injection) and the ELMs (Type III to Type I) eg interesting pulse~5 times the average JET ~15-20MW, and fuel rate ~2.5x10 22 Ds -1 Long term recovery between pulses is negligible in the overall balance Gas balance or Post mortem analysis: Carbon leads to high retention Further results and experiments (main) - AUG: analysis of the retention in a full W machine answer to the question of C - Tore Supra: DITS project Where is the D trapped ? In the carbon structure ? - JET: Preparation of the ILW (no carbon), reference pulses to be quantify in Carbon - Complementary experiments of post mortem analysis