Neutron Shielding Design of Infrared Imaging Video Bolometer for LHD Deuterium Experiment

InfraRed imaging video bolometer (IRVB) is a powerful diagnostic for the plasma radiation measurement. Study on plasma radiation phenomena, e.g., plasma detachment, is one of the crucial issues to realize a fusion reactor. In order to apply the IRVB to such a study, a shielding is required to protect an IR camera from neutron irradiation. In the large helical device (LHD), deuterium experiment has started in 2017. Then, the shielding was designed using MCNP6 code with the 3-D modeling of LHD. The guideline of the neutron flux for the design was determined by the operational experience in JT-60U tokamak and by the result of the irradiation in OKTAVIAN. The strong neutron flux due to the location close to the vacuum vessel and the influx through the lens hole were reduced sufficiently. The designed shielding was applied to the LHD deuterium experiments and the IRVB with the shielding could be operated successfully without any dead pixels in the neutron emission rate up to 3.3×10
¹⁵
n·s
^-1
, which is the maximum rate in the first experimental campaign and in the total neutron emission of 3.6×10
¹⁸
n. These correspond to the neutron emission rate of 2.9×10
⁷
n·s
^-1
and the total neutron emission of 3.2 × 10
¹⁰
n at around the IR camera.