Development of multi channel neutron spectrometer at GEKKO XII laser fusion facility

A high efficiency time‐of‐flight neutron spectrometer is under construction at the GEKKO XII laser fusion facility. Neutron spectra measured with this system is used for diagnosing fuel areal density and ion temperature of inertial‐confinement‐fusion targets. This system consists of 960 plastic scintillation detectors and a data acquisition electronics. Fuel areal density is deduced from DT neutron spectra produced in initially pure deuterium fuel. Ion temperature is also deduced from primary DD neutron energy spread. The spectrometer was designed to measure relatively rare secondary neutrons from neutron yield as low as 7×10⁵ (100 detector hits). It is also capable to measure 2.45 MeV neutron spectra in lower neutron yield experiment as low as 5×10⁵ neutron. We have constructed a 1/10 module for testing performance of the system, established calibration technique and used it in implosion experiment at the GEKKO XII laser fusion facility to demonstrate ion temperature measurement.