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Inertial fusion targets are of two basics types: direct drive and indirect drive. The french Laser MegaJoule (LMJ) will preferentially use indirect drive experiments. However, to contribute to the determination of the best target for inertial fusion energy, both direct and indirect drive will be considered on LMJ-facility. That is why studies on materials for use as first-wall LMJ target chamber and for different applications are of significant interest. In direct drive, targets will be directly heated and imploded by intense 351-nm wavelength laser light and part of this UV energy will be back-scattered off the target surface and consequently deposited onto the target chamber first wall. Such a deposited fluence should average 0.3-J/cm2. The aim of this study was to determine both the fluence level at which physical damage occurs on some considered protective materials and the associated damage mechanisms. Investigations have been carried out on boron carbide and carbon-based materials. Basically, experiments consisted of illuminating samples with a 355-nm gaussian pulse of roughly 3-ns duration generated by frequency conversion through KDP- crystals of a YAG-laser light. In our investigations, characterization of ejected species and transient hemispherical directional reflectivity measurement of the illuminated materials were conducted. All these experiments have shown that boron carbide was a better candidate than carbon-based materials as first-wall LMJ target chamber use. Analyzing the defect type, size and density and the composition and physical-state of the considered materials has allowed predicting the impact of induced-ablation of the first-wall on LMJ target chamber use and lifetime. Composition analysis were addressed using micro-Raman spectroscopy. Preliminary experiments have revealed significant changes in damage mechanism versus laser fluence.
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