Carbon balance and deuterium inventory from a carbon dominated to a full tungsten ASDEX Upgrade

1. Carbon balance and deuterium inventory from a carbon dominated to a full tungsten ASDEX Upgrade M. Mayera, V. Rohdea, K. Sugiyamaa, J.L. Chena, X. Gonga, C. Hopfa, J. Likonenb, S. Lindiga, R. Neua, G. Ramosc, E. Vainonen-Ahlgrenb, A. Wiltnera, and ASDEX Upgrade Team a Max-Planck-Institut für Plasmaphysik, EURATOM Association, Garching, Germany b Association EURATOM-TEKES, VTT Processes, Espoo, Finland c CICATA-Qro, Instituto Politécnico Nacional, Querétaro, México • Evolution of B, C deposition in the divertor • Evolution of D inventory in the divertor • Comparison between plasma-sprayed and bulk W • Plasma-related aspects of all-W machine were covered by R. Dux, I-6

2. Motivation Tritium inventory in ITER dominated by codepositionwith carbon (if carbon is present) But large uncertainties: Carbon sources and carbon transport poorly understood  Stepwise replacement of C by W in AUG offers unique possibility to study C sources Be W C A. Kirschner et al., JNM 363-365 (2007) 91

3. Motivation (2) Much lower T inventory in all-W machineis predicted All-W predictions based solely onlaboratory data  Confirmation in existing tokamaks required All-W is probably the only option fora future DEMO reactor  Data from existing tokamaks required J. Roth, this conference, R-1

4. W coverage in AUG 2002 – 2007 • Step by step replacement of C tiles • by W coated tiles • 3 – 4 µm W-PVD on most tiles • 200 µm plasma-sprayed W at outer strike point

5. AUG inner divertor: Deposition of B + C 2002 – 2003 4940 s 6A Inner divertor deposition in 3000 s C 14.6 g B 2.8 g 4

6. AUG inner divertor: Deposition of B + C 2004 – 2005 3150 s 6A Inner divertor deposition in3000 s C 13.8 g B 4.7 g 4

7. AUG inner divertor: Deposition of B + C 2005 – 2006 2950 s 6A Inner divertor deposition in3000 s C 2.2 g B 2.3 g 4

8. AUG inner divertor: Deposition of B + C 2007 2620 s 6A Inner divertor deposition in3000 s C 1.0 g B  0 g (below detection limit) 4

9. AUG divertor: Evolution of B, C deposition Reduction of C deposition byfactor ~15 from C-dominatedto all-W machine  Largest decrease after coating of ICRH protection limiters with W Decrease in C plasma concentrationby factor 2–3 R. Pugno, EPS 2008  Available C source at walls > 1000 times C plasma inventory even in all-W machine

10. AUG divertor: Evolution of B, C deposition Reduction of C deposition byfactor ~15 from C-dominatedto all-W machine  Largest decrease after coating of ICRH protection limiters with W 5-6 boronizations/campaign from 2002-2006 B-deposition almost constant No boronization in 2007, extensive cleaning B-deposition below detection limit of 0.1 g

11. 11 g 80% 14 g 3 g 20% • Small influx of residual carbon in main chamber • Identical outer divertor erosion in both campaigns, M. Mayer et al., PS T128 (2007) 106 Assumptions: Carbon transport in AUG 2004 – 2005 2005 – 2006 2 g 3 g 100% Spectroscopy: 1 g A. Kallenbach et al., JNM 363-365 (2007) 60

12. 100 µm Carbon sources in all-W machine SE • Residual C deposition in all-W machine:1 g in 3000 s • Electrical arc’s can remove W coating and release C from tile 0.05 g C from inner baffle A. Herrmann, this conference, O-5 • Erosion in not fully coated tile gaps and back sides of tiles • Residual carbon layers from previous campaigns (probably small due to extensive cleaning) • C impurities in W coatings • Photo-desorption of CO, CO2 from walls V. Philipps et al., J. Nucl. Mater. 200 (1993) 355 BSE

13. 6A 3A 9B 4 1A Deuterium inventory 4940 s C-dominated campaign 2002/2003 D on divertor tiles 0.9 – 1.3 g D below roof baffle 0.4 g in 3000 s 2620 s Full W campaign 2007 D on divertor tiles 0.15 – 0.23 g D below roof baffle 0.03 g in 3000 s

14. 6A 4 Deuterium inventory in inner divertor of all-W machine Correlation between distributionsof C and D  D inventory in inner divertor still dominated by C-codeposition

15. 3B 1 Deuterium inventory in outer divertor of all-W machine D inventory in outer divertor dominated by trapping in W  Deep diffusion (> 3 µm) observed for VPS layers at outer strike point

16. AUG divertor: Evolution of D inventory • Carbon dominated machine • Total D-inventory dominated by inner divertor and remote areas • All-W machine • Boronizations result in high D-inventory, co-deposition with B (2005/2006 campaign) • D-inventory dominated by trapping in VPS-layers at outer strike point • Decrease of total D-inventory by factor 5 – 10 from C-dominated to all-W

17. VPS-W Bulk W Langmuir probes 20 mm VPS-W versus polycrystalline W in outer divertor • VPS-W and bulk W trap about the same total amount of D • Bulk W shows deep diffusion (~ mm) at low D concentrations (< 100 ppm) Background level K. Sugiyama et al., Hydrogen Workshop Salamanca

18. Extrapolation to higher fluences / longer discharge times D-inventory in AUG divertor • Good agreement between laboratory measurements and AUG data • Slower increase of D-inventory in W than in C for longer discharge times •  W even more beneficial for long pulse machines VPS-W: A.V. Golubeva et al., AIP Conf. Proc. 837 (2006) 12 poly-W: O. Ogorodnikova et al., J. Appl.Phys. 103 (2008) 034902

19. Conclusions • Decrease of divertor C deposition by factor ~15 from C-dominated to all-W machine, normalized to 3000 s • Decrease of trapped D in divertor by factor 5 – 10 from C-dominated to all-W machine • Boronizations result in high D-inventory due to co-deposition with B  Decrease of D-inventory only visible in unboronized machine • D-inventory in C-dominated machine determined by co-deposition in inner divertor + remote areas • D-inventory in all-W machine determined by deep diffusion into W at outer strike point