THERMAL-SHOCK BEHAVIOR OF VARIOUS FIRST-WALL MATERIALS UNDER SIMULATION LOAD TESTS BY LASER-BEAM IRRADIATION

For materials selection of plasma-facing components in nuclear fusion devices it is necessary to determine threshold values of materials dam age under short-time high heat fluxes in laboratory experiments. Plasm a disruption loads were simulated with different nonmetallic candidate materials using Nd-YAG high power solid state lasers. The impinging e nergy density was varied between 0.2 and 20 MJ/m(2) with pulse lengths t(p) ranging from 0.1 to 10 ms. Special experiments were carried out in situ in a scanning electron microscope coupled with a pulsed Nd-YAG laser and various analytical equipments. Thermal shock crack formatio n and propagation response, erosion behaviour and distribution of elem ents after successive thermal shock loading can be studied in situ wit h high lateral resolution inside a SEM. The dependence of damage initi ation and propagation on the laser beam parameters such as pulse energ y and number, spot size and pulse length was studied for fine grain gr aphites, nitride and carbide ceramics, CFC compound and coated materia ls. The threshold values for these structural damages were quantified using a heat flux parameter phi(abs)root t(p). Detected damage paramet ers are 3D-erosion profiles, length and orientation distribution of cr acks, redeposition rate, etc. Threshold values received by electron be am loads and by numerical calculations under comparable conditions are in approximate agreement with the laser load experimental results. It can be concluded that laser beam simulation represents a simple metho d for thermal shock testing.