Development of Directional Neutron Detector for Fusion Neutron Emission Profile Measurement

本研究旨在开发一种基于小型定向中子探测器阵列的紧凑型快中子相机，用于磁约束聚变(DT和/或DD)等离子体实验中先进的中子发射剖面测量。探测器的概念是由He(或H2)-Xe气体闪烁体制成的对数望远镜，通过与入射中子的弹性碰撞，选择性地探测沿正向散射的反冲氦(或质子)。为了实验验证探测器的基本性能，我们对探测器样机进行了优化设计和试制，并给出了紧凑型聚变中子相机系统在现有聚变装置上实际应用的设计考虑。(1)通过优化气体净化和气体混合比，实验研究了He-Xe气体闪烁体在α(反冲He)探测中的光输出特性。(2)开发了探测器对任意能量中子响应的蒙特卡罗模拟程序，分别对基于He-Xe和H_2-Xe气体闪烁体的定向中子探测器进行了优化设计。(3)用加速器DT中子源验证了试制的探测器系统的基本性能。针对LHD DD等离子体实验，提出了基于定向中子探测器阵列的中子相机的设计方案。实践证明，与传统的多通道中子准直器相比，本系统的体积最大可缩小1/20，性能基本保持不变。

The present study is aiming to develop a compact fast neutron camera based on an array of a small size of directional neutron detectors toward advanced neutron emission profile measurement for magnetic confinement fusion (DT and/or DD) plasma experiment. The detector concept is a counter telescope made of He(or H_2)-Xe gas scintillator to selectively detect recoil heliums (or protons) scattered in the forward direction through elastic collision with incident neutrons. We have made an optimal design and trial construction of a prototype detector to verify the basic performance experimentally, and also given a design consideration of the compact fusion neutron camera system for practical use in an existent fusion device.The main results are summarized as follows ;(1) The light output characteristics of He-Xe gas scintillator has been experimentally made clear on α (recoil He) detection through optimization of gas purification and gas mixture ratio.(2) The Monte Carlo simulation program for the detector response to neutron with an arbitrary energy has been developed, which has given an optimal design of the directional neutron detectors based on He-Xe and H_2-Xe gas scintillators for DT and DD neutron detection, respectively.(3) The basic performance on a trial manufactured prototype detector system has been verified with an accelerator DT neutron source, including some proposals for further improvement toward practical application.(4) The design consideration of a neutron camera based on an array of directional neutron detectors has been made for DD plasma experiment at LHD (in NIFS). It has been demonstrated that the present neutron camera system can largely reduce its volume up to 1/20 less than that of a conventional one with a multichannel neutron collimator, keeping almost the same performance.