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

Abstract

A large volume and fast response gamma ray diagnostic based on the LaBr 3 (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 LaBr 3 (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 LaBr 3 (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 LaBr 3 (Ce) detector was performed using 60 Co and 137 Cs gamma ray sources. We surveyed a neutron effect on the LaBr 3 (Ce) detector in an electron-cyclotron-heated deuterium plasma discharge. The pulse counting rate of LaBr 3 (Ce) detector under the total neutron emission rate of 2×10 11 n/s was 110 kcps. Therefore, the LaBr 3 (Ce) detector is expected to be utilized in most of ion cyclotron resonance frequency (ICRF) discharges, where the total neutron emission rate of ∼10 11 n/s. We plan to measure the gamma ray spectrum in deuterium ICRF discharges.

Gamma ray diagnostics for high time resolution measurement in large helical device

“…Additionally, gamma ray diagnostics played an important role in knock-on tail observation [41][42][43] through the 6 Li(d, p ′ 𝛾) 8 Be reaction [44,45] and a study toward aneutronic p-11 B fusion [46]. In the commissioning of gamma ray diagnostics based on a large volume LaBr 3 :Ce detector conducted in LHD [47], the gamma ray signal suffered from prompt gamma rays induced by neutrons. In this manuscript, improvement of gamma ray diagnostics and initial results of gamma ray spectrum measurements in 6 LiF pellet injection discharge were reported.…”