Two new vertical neutron cameras characterized by high detection efficiency were developed on the Large Helical Device in order to observe poloidal structures of helically trapped beam ions created by the perpendicularly injected positive-ion based neutral beam (P-NB) and are newly operated since 2018. In this work, the neutron fields at the vertical neutron cameras are investigated using the Monte Carlo N-particle transport code to evaluate the performance of its collimators. The results indicate that neutrons are attenuated by the heavy concrete and are well collimated through the collimator to detectors. Neutron spectra at the detector position show over 99% of uncollided 2.45 MeV neutrons. Time evolution of neutron emission profiles during the short pulse of P-NB injection is measured by the vertical neutron cameras. Peaks on the neutron emission profiles corresponding to the helically trapped beam ion are successfully obtained, as designed. The decrease in line integrated neutron flux at the peak positions after the P-NB stops is consistent with the behavior of the total neutron emission rate measured by the neutron flux monitor.

中文翻译：

---

新安装的垂直中子相机在大型螺旋装置中低中子产率放电的性能

在大型螺旋装置上开发了两个具有高检测效率的新型垂直中子相机，以观察由垂直注入的正离子基中性束 (P-NB) 产生的螺旋俘获束离子的极向结构，并于 2018 年新投入使用在这项工作中，使用蒙特卡罗 N 粒子传输代码研究垂直中子相机的中子场，以评估其准直器的性能。结果表明，中子被重混凝土衰减，并通过准直器准直到探测器。探测器位置的中子谱显示超过 99% 的未碰撞的 2.45 MeV 中子。垂直中子相机测量 P-NB 注入短脉冲期间中子发射剖面的时间演变。按照设计，成功获得了对应于螺旋俘获束离子的中子发射剖面上的峰值。P-NB 停止后峰值位置的线积分中子通量的减少与中子通量监测器测量的总中子发射率的行为一致。