Plasma and Fusion Research

Volume 15, 2402039 (2020)

Regular Articles

Radiation Resistant Camera System for Monitoring Deuterium Plasma Discharges in the Large Helical Device
Mamoru SHOJI and LHD Experiment Group
National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
(Received 28 November 2019 / Accepted 5 May 2020 / Published 8 June 2020)


Radiation resistant camera system was constructed for monitoring deuterium plasma discharges in the Large Helical Device (LHD). This system has contributed to safe operation during two experimental campaigns without serious problems due to radiation (neutrons and gamma-rays). The cameras steadily functioned even in the plasma discharge with the maximum neutron emission rate in FY 2017, though some bright specks temporarily appeared on the images. The cameras have been installed in shield boxes which consist of lead boxes covered with 10% borated polyethylene blocks in all directions. For optimizing the design of the shield box, the radiation flux distribution was calculated by MCNP-6 code, which reveals the reduction of the radiation flux and the change of the energy spectra in the shield box. Thanks to the optimization, significant extension of the lifetime of the cameras has been realized. Investigation of the influence of the radiation on the CCD image sensor shows that the number of bright specks generally increases with the radiation flux to the camera, which also indicates that some bright specks disappear by the self-annealing process on the image sensor. This phenomenon also highly contributes to the further extension of the lifetime of the radiation resistant cameras.


radiation resistant camera, neutron, gamma-ray, CCD, deuterium plasma, LHD

DOI: 10.1585/pfr.15.2402039


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