1. 1 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Th Loarer with contributions from C. Brosset 1, J. Bucalossi 1, P Coad 2, G Esser 3, J. Hogan 4, J Likonen 5, M Mayer 6, Ph Morgan 2, V Philipps 3, V. Rohde 6, J Roth 6, M Rubel 7, E Tsitrone 1, A Widdowson 2, EU TF on PWI and JET EFDA contributors Gas balance and Fuel retention 1) Association EURATOM-CEA, CEA-Cadarache,13108 St Paul lez Durance, France. 2) Culham Science Centre, EURATOM-UKAEA Fusion Association, OX14 3DB, UK 3) Institute of Plasma Physics, Association EURATOM-FZJ, 52425 Jülich, Germany 4) Oak Ridge National Laboratory, Fusion Energy Division, TN37831-8072, USA 5) Association EURATOM-TEKES, VTT Processes, PO Box 1608, 02044 VTT Espoo, Finland. 6) Max-Planck IPP-EURATOM Association, Garching, Germany 7) Alfven Laboratory, Royal Institute of Technology, Association EURATOM-VR, Stockholm, Sweeden Outline: Gas balance and fuel retention During a pulse, after/between pulses Integrated over a day, a week and a full campaign Fuel retention mechanisms Summary and further plans TEC Euratom

2. 2 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 - Evaluation of the hydrogenic retention in present tokamaks is of crucial importance for the long discharges foreseen in ITER (400 sec ~ 7min). - A retention of 5% of the T injected would lead to the limit of 350g (working guideline for initial operation) in 70 pulses (1% ~1g). - In the EU TF on PWI, SWEG to study gas balance and fuel retention, to assess the processes of the fuel retention and to extrapolate to ITER. - SWEG meeting on gas balance and fuel retention at JET 11 and 12 July 2006 INTRODUCTION Results from different test beds and tokamaks Limiter and Divertor devices in EU: ASDEX Upgrade, JET, TEXTOR, Tore Supra, but also from Alcator-C, JT-60U, Triam

3. 3 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Retention during pulse Significant retention unless : Low fuelling rate (Long L mode in JET) No influence of W observed between 2003 and 2005 in AUG (45 to 80% of W coverage) No influence of ELMs observed so far (W and/or C) Phase 2 : ~ constant retention rate Always a significant fraction of the injected flux (20-50%), but small fraction of the recycling flux (1-5%) Phase 2 Low fuelling AUG Common features on all devices : Phase 1 : decreasing retention rate ~ 1 to 50-100 s Machine (Limiter/Divertor), Scenario Conditioning and Material (Be - C – W)… Phase 1 TS

4. 4 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Also observed on JT-60U… n e ~0.65 n GW Low fueling (low n e ) ~ no retention High fueling (high n e ) significant retention Kubo et al., IAEA 2006

5. 5 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Strong retention in Alcator C-mod - Pulse duration of ~ 2 sec, but very high plasma density. -16 repeated discharges (~ 30 s plasma exposure w/o disruptions) - Retained D fluence remains linear with incident D ion to the wall at an average rate of 0.75% D Whyte et al., IAEA 2006 Metallic device (Mo, room temperature) Co-deposition ?

6. 6 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Recovery after/between pulses Retention Short pulse ~ 10-30% Long pulse/Strong injection ~ 50% Small fraction recovered after shot, but > plasma content (C, C-W and Be) Independent of inventory cumulated during the pulse (TS, JET, AUG) Except for disruptions, this amount is independent of I p, B T, density, input power, fuelling method. [V. Mertens et al., EPS 2003] AUG JET t wall Recovery ~ retention in phase 1 Transient mechanism

7. 7 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 D Whyte et al., IAEA 2006 Strong retention…and recovery in Alcator C-mod Net depletion of D fuel from the wall is observed Cummulative effect of planned disruption H/D recovery over a C-Mod run day.

8. 8 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Integrated balance - Day --- Total Injected --- Total exhausted --- Outgased between pulses TS Short discharges Recovery between pulses is significant Cumulated inventory can be ~ recovered by conditionning (GDC…): Overall balance ~0 Long discharges Same recovery between pulses but negligible compared to the overall balance Significant inventory built up proportional to discharge duration (at least in limiter machine) Phase 1 Phase 2

9. 9 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Steady state retention – Saturation ? - Wall saturation is a local de-saturation of overheated PFCs. - BUT does not prevent and/or cancel retention in other areas (layers, gaps, below divertor…) - No wall saturation in the sense of no retention observed. - Uncontrolled outgassing is no more observed in fully actively cooled devices (TS); the source is constant. - Retention rate is also constant and for the same plasma, no history effect is observed. TS before before upgrade, only 80% actively cooled and no pumping Time (s) Central Line Density (10 19 m -2 ) 26776 4.5MW 19249 2.5-3MW 19621 1.8MW 19622 1.8MW 19980 2.4MW 19976 2.4MW - Result of overheated PFCs and as T surf increases outgassing Eventually, Outgassing > Exhaust loss of density control (also observed on JET w/o pumping and JT-60U w div. pumping) C Grisolia et al., PSI 1999 TS T Nakano et al., IAEA 2004

10. 10 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Integrated gas balance – Day - Week Integration over a campaign : long term retention Retention = N inj – N recovery - N disruptions - N cleaning Gas balance accuracy limited by the requirement to substract pairs of large numbers. For integrated balance of the order of week the accuracy strongly depends on - the time for the integration ( pulse~10 sec, day~10 5 sec), - evaluation of the outgassing flux, D and C x H y released (disruptions) Gas balance is an upper limit of the retention Fuel retention over period ~ day/week complementary method required: Post-mortem analysis of samples from limiters, main chamber, deposition in gaps in between tiles, below the limiter/divertor… But this analysis cannot include all PFCs and air (H 2 0) exposure during transfert. Post mortem analysis is a lower limit of the retention Recovery Disruption Cleaning …

11. 11 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 0 1000 2000 3000 4000 5000 6000 648006500065200654006560065800 JET pulse # ISP at horizontal tile integral erosion ISP at vertical tile integral deposition ISP at hori- zontal tile integral erosion ISP at hori- zontal tile integral erosion ISP at vertical tile integral deposition Quartz Micro Balance Integral deposition when inner strike point at vertical tile 3 Integral erosion when inner strike point at horizontal tile 4 QMB4 (LBSRP) integral behaviour for restart / commissioning phase frequency [Hz] G Esser et al.,

12. 12 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 D/C 0.12 0.090.05 0.32 0.31 0.28 0.13 10.050.30.38 Fuel retention in JET (MKII GB) (NRA: D/C ratio, SIMS: layer thicknesses) Only plasma facing surfaces at divertor included (not tile gaps, inner limiters...) MkIIGB Divertor time: 57500 sec (16 hours) D injection: 766g Inner ion flux: 1.3x10 27 C deposition: 400g Rate: 3.4x10 20 Cs -1 Inner Divertor: D/C~0.2 J Likonen, P Coad et al., -D retention in the divertor: 3% (Mk-IIGB)

13. 13 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 38 g 73 g 55g 63g 300g 5g Total inner: 603 gTotal outer 380g Fuel retention in JET (MKII-SRP) - D retention in the divertor: 2.4% (MKII-SRP), 3% (Mk-IIGB), consistent with DTE1 results ~2% (Mk IIA, 0.2 g in tiles 0.5 g in 150 g flakes). - Lower limit: analysis does not include all PFCs (SRP, main chamber…) - Flakes in subdivertor after DTE1 ~1 kg : seen but not quantified ~ 3g MkII-SRP D injection: 1800g C dep: inner (outer): 603g (380g) C dep rate: 3.7 10 20 s -1 (2.2 10 20 s -1 ) Inner (outer) divertor D/C~0.3 (0.2) D retention inner: 1.6% (30g) D retention outer: 0.8% (12.6g) Total D retention 2.4% (42g), no SRP, no main chamber P Coad, A Windowson et al.,

14. 14 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 W-coverage in ASDEX-Upgrade 2002/2003 2004/2005 Increasing coverage with W Regular boronizations about 8 per discharge period Mainly effective in main chamber 6370 s 75.4 g D 3864 s 43.9 g D B-concentration in main chamber deposits 200280% 200574 – 98% M Mayer

15. 15 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 2002/2003 campaign: Mainly carbon machine (45% W) Retention governed by trapping on inner tile surface (70% inner divertor tiles, 20% in remote ares (below roof baffle,...) Total retention ~4% of input (10-20% from gas balance) 2004/2005 campaign: Full W machine except the divertor (Carbon) No significant difference in retention between 2002/2003 and 2004/2005 AUG: 2002/2003: Deposition of D and C M Mayer et al., PSI 2004

16. 16 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Hydrogen retention and carbon deposition in JT-60U K Masaki et al., IAEA 2006 Highest (D+H) retention ~16x10 22 m -2 on layer on outer dome wing and highest concentration (D+H)/C ~13% In plasma-shadowed area underneath the dome, ~2 m layers found (8x10 19 Cs -1 ) and a very high concentration (D+H)/C ~80%

17. 17 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Retention mechanism Adsorption : phase 1 AUG, JET, TEXTOR, TS Implantation (saturates, sensitive to T surf ) : TS, JET and JT60U Bulk diffusion (long pulse / high flux, high Te) Suspected to play a dominant role in long pulse in TS Codeposition (low Te, cold shadowed areas in direct line of sight of C source) : supposed to be the dominant process (AUG and JET) Density control Detritiation (depth in C) Detritiation (remote areas) ITER Limited (released after shot) Limited (reservoir >> plasma) (fluence) 0.5 for CFC (Lab exp) (not for graphite) (fluence) Fuel retention mechanisms (in C) Main open issue : Dominant retention mechanism with mixed materials (C/Be/W) ? Courtesy E Tsitrone

18. 18 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 M Sakamoto al., IAEA 2006 Real time measurement of Co deposition in TRIAM - In situ and real time measurement of erosion/deposition based on interference of a thin semi-transparent layer. - Located 7.5cm from the LCFS and viewing a poloidal limiter Growing rate ~2.3x10 -4 nm s -1 (~1.5x10 16 Mo m -2 s -1 ) Retention ~ 4 10 17 Hs -1 (8x10 21 H after 5h25 of plasma) Similar to Alcator-C (11x10 21 D in 30 sec) …lower flux but longer duration! Constant increase of wall inventory and growth of deposited layer of Mo

19. 19 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 In these samples the D is trapped in the 3.7 m deposited layer (~40%) - D located in depth (up to 10 m) >> the ion implantation (few nm) CFC samples (Sepcarb® N11) exposed in the SOL of TS 3.7 m No saturation observed with fluence

20. 20 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Open porosity at the matrix/fibre interface significant role in D migration ? Analysis of these CFC samples (Sepcarb® N11) No modification of the C hybridization in both the CFC matrix and the fibers observed with Electron Energy Loss Spectroscopy (EELS). No C-D chemical bonding Transport mechanism and D migration in the bulk (8 m) to be investigated

21. 21 Th LoarerGas balance and fuel retention – EU TF on PWI – 13 November 2006 Summary Gas balance and fuel retention: Large data base with carbon showing common features for the retention (AUG, JET, TEXTOR, Tore Supra, but also JT-60U, LHD) - During pulse: significant retention unless low fuelling - Long term: ~0 for short pulse, significant for long discharges (TS) - No wall saturation (sense of no retention) is observed for actively cooled devices - Recovery after pulse independent of the cumulated inventory Retention in carbon dominated devices: ~10-20% (Gas balance: upper limit) ~ 3-4% (Post-mortem: lower limit) Still no influence of W (AUG: 80%) on the retention (ELMs ? AUG &JET) Co-deposition dominant process (AUG and JET) New results w/o C as PFC: Full W (AUG) and W-Be (JET) (Alcator-C, Triam) Co-deposition cancelled with full metallic machine and therefore should significantly reduce the retention compare to Mo ! Future exp in AUG (series of experiments on gas balance proposed), JET (2 gas balance experiments late 2006 and early 2007) and TS (Sector of TPL removed for analysis) ITER: 200 Pam 3 s -1, D-T 50% (5 10 22 Ts -1 for 400sec), assuming retention similar to carbon devices ~70 (5%) before reaching 350g detritiation