Microscopic Damage of Tungsten and Molybdenum Exposed to Low-Energy Helium Ions**supported by the National Magnetic Confinement Fusion Program of China (No. 2011GB108011), National Natural Science Foundation of China (No. 11405023) and the Scientific Research Fund of Liaoning Provincial Education Department (No. L2014539) and the Fundamental Research Funds for the Central Universities of China (No. DC201502080410)

Abstract

Polycrystalline tungsten (W) and molybdenum (Mo) materials both non-annealed and annealed at temperatures of 800-1750°C have been irradiated with low-energy (220 eV), high-flux (∼1021 ions/m2 ·s) He+ at an irradiation temperature of 600°C and at a dose of 1.0×1025 ions/m2. This non-destructive conductive atomic force microscopy technique provides direct observation and comparison of surface swellings with growth of nanoscale defects in the irradiated materials. A coral-like surface structure and nanostructured defects were formed in W when irradiated at a He+ dose of 1.0×1025 ions/m2. Increasing the annealing temperature resulted in an increase in the size of nanostructured defects and serious surface damage of W. Compared to W, Mo suffered much less surface damage after being irradiated at various He+ doses.