Surface degeneration of tungsten wires irradiated with low-energy (12–220 eV) helium ions

In order to investigate the evolutionary process of deformed tungsten on first wall and divertor plate, polycrystalline tungsten (W) wires are utilized as irradiation samples exposed to the low-energy, high-flux (∼1022 ions/m2·s) helium (He) ions. The irradiation experiments are performed by using a high-density plasma source system. The energy of He+ changes from 12 to 220 eV with an ion fluence of 1.0 × 1025/m2. Surface degeneration of these samples is observed by using a scanning electron microscopy. Results show that surface microstructures of irradiated W wires are strongly dependent on the energy of He+. Increasing the energy of He+ from 30 to 220 eV leads to an increase in the sputtering yield of W wires from 1.40 × 10−3 to 4.72 × 10−2 W/He+. As a result of He+ irradiation, loose structures and holes are formed in the surface layer of the W wires. The He+ -induced surface degenerations of W wires are discussed based on the experimental observation. As the He+ energy increases, the sputtering yield rapidly increases, and serious surface etching occurs.