Bando T, Ohdachi S, Zhou R J, Zhong G Q, Yuan Y, Hu L Q, Ling B L
SOKENDAI (The Graduate University for Advanced Studies), 322-6 Oroshi-cho, Toki, Japan.
National Institute for Fusion Science, National Institutes of Natural Sciences, 322-6 Oroshi-cho, Toki, Japan.
Rev Sci Instrum. 2019 Jan;90(1):013507. doi: 10.1063/1.5054325.
Scintillators, which are more tolerant of neutrons or γ-rays than semiconductors, are a promising candidate for soft X-ray (SX) diagnostics in high neutron flux environments such as JT-60SA or ITER. Although scintillators are tolerant of radiations, neutrons and γ-rays can cause scintillation light and become noise on SX signals. Therefore, a method to estimate the temporal effect by the radiations on SX signals and an appropriate design of the radiation shield based on the estimation are required. In previous studies, it has been proposed for estimating the effect by the radiations to calculate the absorption powers due to SXs, neutrons, and γ-rays in scintillators assuming that amplitudes of scintillation light are proportional to the absorption powers. In this study, an experimental examination of this proposal is conducted in the Experimental Advanced Superconducting Tokamak (EAST). It is shown that the proposal may be valid in the examination of EAST. In addition to results in EAST, initial results of a multi-channel scintillator-based SX diagnostic in the Large Helical Device (LHD) are introduced. Although a scintillator-based SX diagnostic in LHD observes oscillations of SXs by magnetohydrodynamic (MHD) phenomena successfully, the observed temporal effect on SX signals by neutrons or γ-rays is more significant than the expected effect, which is estimated by calculating the absorption powers. One of the possible reasons for the contradiction between the results in EAST and LHD is unexpected γ-rays around the scintillators in LHD. Although the temporal effect by the radiations is significant in the current system of LHD, the degradation of amplitudes of SX signals after the deuterium plasma experiments is not observed with the current level of the fluence. The scintillator-based SX diagnostic in LHD may work as a diagnostic to research MHD instabilities in deuterium plasma experiments without additional maintenance during an experimental campaign by making the pinhole larger or setting an additional radiation shield.
闪烁体比半导体对中子或γ射线具有更高的耐受性，是在诸如JT - 60SA或ITER等高中子通量环境中进行软X射线（SX）诊断的有前途的候选材料。尽管闪烁体对辐射具有耐受性，但中子和γ射线会产生闪烁光并成为SX信号上的噪声。因此，需要一种方法来估计辐射对SX信号的时间效应，并基于该估计进行适当的辐射屏蔽设计。在先前的研究中，已经提出通过假设闪烁光的幅度与吸收功率成正比，计算闪烁体中由于SX、中子和γ射线引起的吸收功率来估计辐射的影响。在本研究中，在实验先进超导托卡马克（EAST）中对该提议进行了实验检验。结果表明，该提议在EAST的检验中可能是有效的。除了EAST的结果外，还介绍了大型螺旋装置（LHD）中基于多通道闪烁体的SX诊断的初步结果。尽管LHD中基于闪烁体的SX诊断成功地通过磁流体动力学（MHD）现象观测到了SX的振荡，但观测到的中子或γ射线对SX信号的时间效应比通过计算吸收功率估计的预期效应更为显著。EAST和LHD结果之间矛盾的一个可能原因是LHD中闪烁体周围存在意外的γ射线。尽管在LHD的当前系统中辐射引起的时间效应很显著，但在当前通量水平下，未观察到氘等离子体实验后SX信号幅度的下降。通过增大针孔或设置额外的辐射屏蔽，LHD中基于闪烁体的SX诊断在氘等离子体实验期间可能无需额外维护即可作为研究MHD不稳定性的诊断工具。
