Effect of Transient Heat Loads on Neutron Irradiated Tungsten and Carbon Based Materials

For the design and construction of ITER, the determination of effects of short transient events like edge localized modes (ELMs) has become an important issue, especially in combination with the expected deterioration of material properties caused by neutron irradiation. Hence this study deals with the evaluation of the influence of radiation effects on the thermal shock resistance of potential plasma facing materials like pure tungsten, W-Re or W-La₂O₃ as well as graphite and carbon fiber composites (CFCs) which were exposed to a neutron dose of ~1 dpa (in carbon) at T=200degC. In situ observations at room temperature during single and multiple shot loadings (les100 pulses) were done on macroscopic erosion (particle release), surface temperature and absorbed current. In combination of microscopic investigations of the surface morphology of the loaded area (4times4 mm²) and weight loss measurements a drastic quantitative increase of particle release after neutron irradiation was found for carbon based materials, in particular under disruption like conditions (Deltat=5 ms, P=0.8 GW/m²). For tungsten, the onset of crack formation and severe cracking was observed already for ELM like conditions (Deltat=1 ms, P=0.2 to 1.3 GW/m²), which are expected to occur with a frequency of 1 Hz during the operation of ITER.