1. TFE Th Loarer – SEWG – 12 September 2007 1 Euratom Th Loarer V Philipps 2, J Bucalossi 1, D Brennan 3, J Brzozowski 4, N Balshaw 3, R Clarke 3, G Esser 2, M Freisinger 2, S Grünhagen 5, J Hobirk 6, S Knipe 3, A Kreter 2, Ph Morgan 3, R Stagg 3, L Worth 3 and JET EFDA contributors* Fuel retention in L and H-mode experiments in JET 1 - Association EURATOM-CEA, DSM-DRFC, CEA Cadarache, 13108 St Paul lez Durance, France. 2 - IPP, Forschungszentrum Juelich, D-52425 Juelich, Germany 3 - Euratom-UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA, UK. 4 - EURATOM/VR Association - Fusion Plasma Physics, EES, KTH, Stockholm, Sweden 5 - FZ Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany 6 - Max-Planck IPP-EURATOM Association, Garching, Germany *See Appendix of M.L.Watkins et al., Fusion Energy Conference 2006 (Proc. 21st Int. Conf. Chengdu) IAEA, (2006) Outline Introduction Evaluation of fuel retention at JET Short and long term retention; associated particle fluxes Recycling flux and ELMs Recovery between discharges Summary

2. TFE Th Loarer – SEWG – 12 September 2007 2 Euratom 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). - A retention of 10% of the T injected would lead to the limit of 350g (working guideline for initial operation) in only 35 pulses. - Fuel retention experiments in JET studied in a series of repetitive and identical discharges to minimise the contribution from previous experiments (history), achieve a high accuracy (~1.2%) - Reference database under C-wall conditions completed before Be/W Evaluation of Long term fuel retention with different materials

3. TFE Th Loarer – SEWG – 12 September 2007 3 Euratom 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 JET (and other 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. TFE Th Loarer – SEWG – 12 September 2007 4 Euratom Calibrated Particle Source (Gas, NBI…) Divertor cryo-pumps Retention (wall) Long & Short Term Procedure on JET Regeneration of the cryopump before and after the session (1.2%) Repeat the same discharge (~10) w/o conditioning between pulses Plasma Injection = Pumped + Short Term Ret + Long Term Ret Total Recovered from Cryo regeneration: Pumped + outgassing in between pulses ~800s (Short Term Ret)

5. TFE Th Loarer – SEWG – 12 September 2007 5 Euratom Gas Balance From cryo-pump regeneration (~1%) and calibrated gas injection Evaluation of the pumped flux - During the plasma - Between pulses t (s) 0 10 100 1000 Plasma During plasma inj > pump Retention>0 Short & Long term Between pulses inj =0 pump = Outgasing Retention<0 Short term retention only (dynamic retention) Evaluation of Short and Long term retention Injection = Long Term Ret + Short Term Ret + Pumped flux

6. TFE Th Loarer – SEWG – 12 September 2007 6 Euratom Type III ELMs # 68619 I p /B T =2.0MA/2.4T, 6.0MW ICRH only 13 repetitive pulses Also in L mode and Type I ELMy H-mode Reproducible plasma conditions in all shots Type III ELMs 53-70 s P TOT ~ 6.0MW Density Fueling 5.8 10 21 Ds -1 D (in & out) Div Pressure Vessel pressure

7. TFE Th Loarer – SEWG – 12 September 2007 7 Euratom L-mode Total Injected: 1.349 10 24 D (4.511g) Total Recovered (Pumped flux and outgassing in between pulses): 1.208 10 24 D (3.946g) Long Term Retention: 0.141 10 24 D (0.472g) Heating Phase (81 s) Injection Long Term Ret ~1.8x10 22 Ds -1 1.74x10 21 Ds -1 ~10% L-mode, Type I & III ELMy H-mode Evaluation of Short and Long term retention during the pulse Heating Phase Injection Long Term Ret Type III 221s ~0.6x10 22 Ds -1 1.31x10 21 Ds -1 ~20% Type I 32 s ~1.7x10 22 Ds -1 2.83x10 21 Ds -1 ~17%

8. TFE Th Loarer – SEWG – 12 September 2007 8 Euratom Particle fluxes: L mode Drop of retention not only due to decrease of inj I p =2.0MA, B T =2.4T 1.2MW ICRH only @15 sec, Ret~6.5x10 21 Ds -1 LongRet=1.74x10 21 Ds -1 (25%) ShortRet=4.8x10 21 Ds -1 (75%) @25 sec, Ret~4.65x10 21 Ds -1 LongRet=1.74x10 21 Ds -1 (35%) ShortRet=2.91x10 21 Ds -1 (65%) Injection Pumped flux Retention Long term Ret

9. TFE Th Loarer – SEWG – 12 September 2007 9 Euratom During the pulse: H mode Type III I p =2.0MA, B T =2.4T ~5MW ICRH only ITER_like conf. @16 sec, Ret=53% Ret~6.3x10 21 Ds -1 LongRet=1.3x10 21 Ds -1 (33%) ShortRet=2.0x10 21 Ds -1 (66%) @28 sec, Ret=43% Ret~2.35x10 21 Ds -1 LongRet=1.3x10 21 Ds -1 (55%) ShortRet=1.05x10 21 Ds -1 (45%) Injection Pumped flux Retention Long term Ret Lower gas rate (1/3) but codeposition becomes dominant

10. TFE Th Loarer – SEWG – 12 September 2007 10 Euratom 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~150kJ @16 sec, Ret~5.2x10 21 Ds -1 LongRet=2.8x10 21 Ds -1 (54%) ShortRet=2.4x10 21 Ds -1 (46%) @20 sec, Ret~2.9x10 21 Ds -1 LongRet=2.8x10 21 Ds -1 (97%) ShortRet=0.1x10 21 Ds -1 (3%) Injection Pumped flux Retention Long Term Ret

11. TFE Th Loarer – SEWG – 12 September 2007 11 Euratom Strong increase of the recycling flux in Type I ELMy H-mode Same behavior observed with CIII Recycling flux: D signals D Inner leg D Outer leg D Horizontal view Type I Type III L mode - L mode and Type III Similar recycling (D ) In, Out and Horizontal. - No significant variation on the Outer leg region (small ELMs~150kJ). -Strong increase of recycling flux (D ) when moving to Type I ELMy H- mode - Same behavior on the Horizontal view as on the inner leg. Type I Type III L mode CIII Horizontal view CIII Inner leg CIII Outer leg Higher recycling and ELM Enhanced carbon erosion and transport leading to stronger carbon deposition and fuel codeposition

12. TFE Th Loarer – SEWG – 12 September 2007 12 Euratom Integrated Hα and CIII horizontal light (L-mode, Type III and Type I ELMs) The slope for Type I ELMy H-mode show enhanced recycling and total carbon source. Integrated particle fluxes H α CIII Type I ELMs Type III ELMs L mode

13. TFE Th Loarer – SEWG – 12 September 2007 13 Euratom Recovery in between pulses Small fraction recovered > plasma content ~ 0.5x10 22 D (70m 3, ~5-6 10 19 m -3 ) Except for disruptions, this amount is ~constant and independent of I p, B T, n e, P in, inj, Wdia (plasma scenario) Independent of inventory accumulated during the pulse and previous pulses Within a factor of ~2 the recovery is constant in the range 1-3x10 22 D No major contribution on the overall retention Short term retention

14. TFE Th Loarer – SEWG – 12 September 2007 14 Euratom Summary - Repetitive pulses on JET for fuel retention analysis (accuracy ~1.2%) Evaluation of both short and long term retention Confirm the strong concerns about fuel retention in C tokamak ITER with mixed material (C, Be, W) Burning Phase Injection Long Term Ret 400s ~ 5x10 22 Ts -1 ? - In all the cases, the recovery in between pulses corresponds to a weak contribution in the overall fuel retention (short term retention) Heating Phase Injection Long Term Ret L mode 81s ~1.8x10 22 Ds-1 1.74x10 21 Ds -1 ~10% Type III 221s ~0.6x10 22 Ds -1 1.31x10 21 Ds -1 ~20% Type I 32 s ~1.7x10 22 Ds -1 2.83x10 21 Ds -1 ~17% - Increase of long term retention - with the recycling flux - with ELMs Energy

15. TFE Th Loarer – SEWG – 12 September 2007 15 Euratom Slides in reserve

16. TFE Th Loarer – SEWG – 12 September 2007 16 Euratom ELM induced C deposition QMB1 (inner): Deposition per ELM vs. ELM energy - Increased deposition due to thermal decomposition of co-deposited layers - Enhanced carbon erosion (Recycling and ELM energy) and transport leading to stronger carbon deposition and fuel codeposition Fit formula: y = 10 12 * x * exp(x/165) "Area" term "Thermal" term B field configuration A.Kreter, H.G.Esser

17. TFE Th Loarer – SEWG – 12 September 2007 17 Euratom Injection (integral:1.8 x 10 23 D-atoms) Divertor pumping Wall pumping Long term retention (codeposition) 2 x 10 21 D/s Dynamic wall retention (decrease in 10 sec by about 50%) 3.9 x 10 21 2.2 x 10 21 Integrated wall pumping 3 x 10 22 Measured long term outgassing (800s) 2.85 x 10 22 Example: particle balance in 70534 during steady state phase Long and short term retention V Philipps

18. TFE Th Loarer – SEWG – 12 September 2007 18 Euratom 1. Campaign averaged retention about 5 times smaller due to effects of long term outgassing, thermal release from subsequent plasma operation, GDC, disruptions (reasonable) Codeposition D C C, D Local C-erosion and redeposition does not contribute much to retention (similar D content of eroded and deposited layers) Needed: long range transport from net erosion to deposition areas main chamber to divertor outer strike zone to PFR, inner divertor,.. freshly deposited C-layers are D-rich (analysis after about 2h) Further reduction by long term outgassing (reduction by about a factor of 2 between 2h and 24h ) and subsequent plasma operation Discussion