1. Transient heat load tests with Nd:YAG laser Main results of EFDA TW3-TPP/ERCAR PWI Task Force meeting – CEA Cadarache 17-19 October 2005 Douglas dHulst, Jaap G. van der Laan and Friso Schmalz

2. Objectives Study of power handling characteristics of CFC tiles exposed to plasmas for high fluences and repetitive power fluxes. The goal is to understand if plasma erosion changes the thermal properties of the tile surface for power loads typical of ~ 10 MW/m², that is, far away from any material ablation limit. Secondly the effect of repetitive power fluxes on the material micro-structure is to be examined.

3. Experiments 1.Determining the effusivity of samples from AUG exposed CFC tiles (< 0.5 MJ/m²). 2.Investigate the influence of repetitive heat loads on NB-31 (± 2.5 MJ/m²), special emphasis on fibre-matrix debonding.

4. 100 1000 10000 0,1110100 big particles small and medium particles no particle emission 2 3 4 5 absorbed peak power density (MW/m²) pulse duration (ms) Brittle destruction analysis, J. Linke (Feb. 04) VDEs 60 MJm -2 disruptions 10 MJm -2 safe operation regime ELMs 1 MJm -2 Effusivity 0.5 MJm -2 Repetitive heat load 2.5 MJm -2

5. Test facilities Nd:YAG laser & HV chamber – t = 0.2-20 ms – E = 2 – 70 J (– 25 J for 5 ms) Specimen holder with HF heating Fast IR-pyrometer

6. Effusivity measurements

7. ASDEX Upgrade samples

8. Effusivity measurements *Pulse energy 12 – 18 J *Pulse length 3 – 6 ms *Spot size 30 – 40 mm² *Sample temperature 530°C *Absorbed energy density ± 0.5 MJ/m² *Absorbed power density ± 100 MW/m²

9. Effusivity measurements

11. Repetitive heat loads

12. *Pulse length 5 ms *Pulse energy 22 J *Spot size 7.5 mm² *Pulse frequency 3 Hz *Amount of pulses 1000 *Sample temperature 300°C ( - 750°C) *Absorbed energy density 2.5 MJ/m² *Absorbed power density 0.5 GW/m²

13. Repetitive heat loads

14. Effects of repetitive heat loads difficult to detect *No effects on surface detected with SEM *No effects visible on cross section with optical microscopy *No effects visible on thermal diffusivity measurements *No effects visible on effusivity measurements

15. Advantages of Tomography *3-D data set *Ability to visualise internal features non-destructively *Characterise structures –Virtual metallography *Study deformation processes Paul Mummery, Manchester Materials Science Centre

16. Graphite Applications *3-D distribution of porosity *Can analyse data set to give spatially-resolved density distribution Pore distribution in UCAR C Paul Mummery, Manchester Materials Science Centre

17. Cracking in UCAR C 1mm Paul Mummery, Manchester Materials Science Centre

18. Fibre composite pore structure Paul Mummery, Manchester Materials Science Centre

19. Conclusions *No influence of erosion on power handling characteristics of CFC *Deposited layers show a low thermal contact with the original sample surface *No effects detected of repetitive heat loads *Recommendation to try to detect effects with X-ray tomography

20. Additional remark NRG is involved in an EFDA-task with TNO on explosively bonded structures of solid W on Cu or W. low temperature joint of 0.2- 0.3 mm plate, on possibly curved surfaces; promise for thick and dense W on heat sinks