Transient heat load tests with Nd:YAG laserMain results of

EFDA TW3-TPP/ERCARPWI Task Force meeting – CEA Cadarache

17-19 October 2005

Douglas d’Hulst, Jaap G. van der Laan and Friso Schmalz

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.

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.

100

1000

10000

0,1 1 10 100

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

disruptions10 MJm-2

safe operation regime

ELMs 1 MJm-2

Effusivity 0.5 MJm-2

Repetitive heat load2.5 MJm-2

Test facilitiesNd: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

Effusivity measurements

ASDEX Upgrade samples

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

Effusivity measurements

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Deposition 1 Deposition 2 Erosion 1 Erosion 2 Reference Laser Power

Effusivity measurements

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Deposition 1 Deposition 2 Erosion 1 Erosion 2 Reference Laser Power

Repetitive heat loads

Repetitive heat loads

* 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

Repetitive heat loads

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

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

Graphite Applications

* 3-D distribution of porosity

* Can analyse data set to give spatially-resolved density distribution

Pore distribution in UCAR CPaul Mummery, Manchester Materials Science Centre

Cracking in UCAR C

1mm

Paul Mummery, Manchester Materials Science Centre

Fibre composite pore structure

Paul Mummery, Manchester Materials Science Centre

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

Additional remarkNRG 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