Characterization of dusts and impurities from the interaction between the first wall materials and energetic laser beams

Abstract

Study and control the formation mechanisms of dusts and impurities from the interaction between the edge plasma and the first wall materials are critical issues to achieve high performance in advanced tokamak (such as ITER). In this study, two major investigations have been carried out. Firstly, we have characterized the morphology and size of the dust particles formed from the interaction between the first wall materials and energetic laser beams. By choosing different laser powers we investigated the number and average size of dust particles as a function of deposited laser energy densities. The results indicate that the number and size of dust particles for tungsten and graphite targets both increase with laser power, but there are some differences in details between tungsten and graphite targets. This implies there are different mechanisms of dust generation for these two materials. Secondly, a high sensitivity molecular beam Time-of-Flight mass spectrometer (TOF-MS) has been developed to directly measure intermediate impurities from the interactions. This enables many intermediate impurities including transient clusters and ions are observed. The observed impurity ions are C n +, n = 4–32. The intensity distribution of the measured C n + indicates that larger carbon impurities are formed by complicated ways: probably including both syntheses by step growth and fragmentation from nano/micro flakes.