Formation and mitigation of fiberform nanostructured tungsten by helium and sub-ms laser pulse irradiations

Abstract

Fiberform nanostructured tungsten is formed on tungsten surface by helium plasma irradiation under a specific condition. It is revealed that the optical reflectivity of tungsten is significantly decreased by the formation of the nanostructure. We present the experimentally obtained necessary condition to form the structure in the linear plasma device NAGDIS-II. We investigate the effects of laser irradiation to the helium-irradiated surface on the optical reflectivity. It is revealed that the sub-ms laser pulse irradiation alleviates the surface roughness and recovers the optical reflectivity. However, when the structure is finer, the recovery rate becomes low, typically less than half; moreover, it decreases with the number of pulses.

Keywords:

• helium irradiation
• laser irradiation
• in-vessel mirror material
• optical reflectivity
• tungsten

Acknowledgements

The authors are grateful to Prof. S. Takamura at Aichi Institute of Technology for fruitful discussion. This work was supported in part by a Grant-in-Aid for Young Scientists (Start-up) (19860096) from JSPS. This work was also supported in part by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (B), 19360413, 2008.