Experimental methods to characterize surface changes of plasma facing materials exposed to ITER-like relevant fusion conditions*

Inside a tokamak fusion reactor there will inevitably be wall degradation caused by plasma interactions. Recent studies have shown growth of helium nano tendrils, often called fuzz, on the surface of tungsten plasma facing components (PFCs) under low energy ion irradiation within a high temperature environment. Fuzz structures can decrease the thermal conductivity and hardness, but more importantly can easily sputter and erode introducing impurities into the core plasma, quenching the plasma. Unique experiments performed at CMUXE are used to quantify the fuzz depth, tendril size, and erosion by using ion beams and lasers. Different fuzz depths and densities are formed on tungsten surfaces when varying He/D ion irradiation energy and exposure time. SEM analysis provides insight on tendril size and fuzz depth while Spectrograph and Faraday cup are used to characterize the surface remotely. Experiments are performed under conditions relevant to ITER like devices including simultaneous high temperature D-He irradiation combined with laser irradiation to simulate ELMs. The goal of this research is to further advance the understanding of plasma interactions with PFCs regarding conditions to minimize fuzz structures and identify better materials and plasma conditions for divertor materials.