Exposure of reduced activation ferritic steel F82H to TEXTOR plasma

Reduced activation ferritic steel, which is a leading structural material candidate for a fusion demonstration reactor, has been installed in TEXTOR and exposed to neutral beam heated plasma. When the heat load was lower than 5 MW/m2, the insertion of the test limiter did not influence the plasma parameters. Visible spectroscopy near the surface showed that the emission related to constituent element such as iron and chromium is comparable to that from the stainless steel. It means that the sputtering from the ferritic steel is comparable to that from the stainless steel even for plasma exposure in high heat flux condition. When the heat load was ∼10 MW/m2, the limiter was melted slightly. The strange motion of melted layer was observed by 2D camera. It slowly moved (∼0.5 cm/s) in a spiral motion, forming a small droplet ∼1 mm in diameter which was then released. The released droplet turned toward the limiter and hit the surface. The mechanism of this motion is discussed.