Large Volume and Fast Response Gamma Ray Diagnostic in the Large Helical Device*)

A large volume and fast response gamma ray diagnostic based on the LaBr3(Ce) scintillator was installed to obtain the gamma ray spectrum in the Large Helical Device (LHD) for understanding energetic ion confinement. The advantages of the LaBr3(Ce) scintillator are relatively sensitive to gamma rays due to its relatively heavy weight density of 5.3 g/cc, high counting operation because of a relatively short pulse width of 100 ns, and relatively better energy resolution of 3%. The gamma ray diagnostic was installed at the outboard side of LHD. The radiation shielding for the LaBr3(Ce) detector was designed to avoid unwanted signals due to stray neutrons and gamma rays using the three-dimensional radiation transport calculation MCNP6. In-situ energy calibration of the LaBr3(Ce) detector was performed using 60Co and 137Cs gamma ray sources. We surveyed a neutron effect on the LaBr3(Ce) detector in an electron-cyclotron-heated deuterium plasma discharge. The pulse counting rate of LaBr3(Ce) detector under the total neutron emission rate of 2x1011 n/s was 110 kcps. Therefore, the LaBr3(Ce) detector is expected to be utilized in most of ion cyclotron resonance frequency (ICRF) discharges, where the total neutron emission rate of 1011 n/s. We plan to measure the gamma ray spectrum in deuterium ICRF discharges.(c) 2023 The Japan Society of Plasma Science and Nuclear Fusion Research