Laser irradiation experiments to the tungsten surface having helium bubbles and holes

Kajita, Shin; Ono, Noriyasu*; Takamura, Shuichi*

The effects of a transient heat load on damaged tungsten due to helium plasma irradiation have been investigated using a ruby laser with long pulse duration in the divertor simulator NAGDIS-II. Helium holes/bubbles, which were formed in the surface region of powder metallurgy tungsten due to the exposure to the helium plasma, disappeared after the laser pulse irradiation to the tungsten surface with sufficient pulse energy. When a tungsten coated graphite was exposed to the helium plasma, the surface was covered with arborescent nanostructured tungsten containing many helium bubbles inside the structure. Melting traces were found on the surface after the laser pulses irradiated the surface even though the pulse energy was sufficiently lower than that for melting bulk tungsten.