KSTAR 핵융합 중성자 진단장치 설계 및 특성평가

Abstract

The Korea Superconducting Tokamak Advanced Research (KSTAR) project was started in December 1995, and its construction was completed in August 2007. On June 13, 2008, the KSTAR reactor successfully produced its first plasma, and the diagnostic systems played an important role in achieving the first successful plasma operation. In fact, various diagnostic systems are required to protect reactor devices, to control plasma, and to evaluate the plasma's performance in fusion reactors. One of the most essential tools for control of the burning plasma in fusion reactors is the neutron diagnostic system to prove the presence of the plasma by measuring the neutrons from fusion reactions directly. The stilbene scintillator has been proposed as one of the best candidates for a neutron diagnostic system for the KSTAR reactor because the stilbene scintillator, which has good pulse shape discrimination (PSD) capability, a fast response (= 10 ㎱) and it can also evaluate neutron energy using an unfolding method, is well-known to be an excellent material for detection of fast neutrons in a high gamma-ray background environment. If fast-neuron spectra are to be measured amid a high gamma-ray background, especially-designed electronics are necessary. For instance, a digital charge pulse shape discrimination method, utilizing a total-to-partial-charge-ratio analysis, discriminates neutron from gamma-ray signals. In addition, a flash analog-to-digital convertor (FADC) with a field-programmable gate array (FPGA) increases the data-transfer rate for real-time evaluation of plasma performance. In the present study, measurements and simulations were performed in order to confirm the neutron diagnostic system's response to D-D fusion reaction neutrons. Performance evaluation of stilbene was conducted in a KSTAR campaign and it provided satisfactory results measuring real-time neutron flux with temporal resolution of 1 ㎳, and it operated well under high magnetic field conditions.