Development of a retro-reflecting corner cube mirror for JSNS target container monitoring

Teshigawara, Makoto   ; Wakui, Takashi  ; Maekawa, Fujio  ; Futakawa, Masatoshi  ; Kato, Takashi; Kikuchi, Kenji; Nakamura, Koji*; Fukai, Takashi*; Yoshida, Nobutoshi*; Naoe, Takashi*   ; Yamaguchi, Yoshihito*

The spallation neutron source facility (JSNS) in J-PARC project is under construction. Highest neutron intensity, especially peak intensity, is provided to neutron beam users in JSNS. However, the pressure wave caused by the intense pulsed proton beam gives vibration related pitting damage on the target beam window, resulting in a shorter life-time. It is very important to monitor the pitting damage of the target beam window to estimate its life-time. Laser Doppler method is a useful acoustic vibration measurement technique to monitor damage caused by pitting damage. We adopted a retro-reflecting corner cube mirror to enable this measurement. We developed a retro-reflective corner cube mirror with the reflectivity of 12 %, which is made by Ni using electroforming. Finally, we could install the retro-reflective mirror on the real target container with an optimized brazing method (Ag based brazing).