  Various neutron diagnostic tools are used in fusion reactors to evaluate
different aspects of plasma performance, such as fusion power, power density,
ion temperature, fast ion energy, and their spatial distributions. The stilbene
scintillator has been proposed for use as a neutron diagnostic system to
measure the characteristics of neutrons from the Korea Superconducting Tokamak
Advanced Research (KSTAR) fusion reactor. Specially designed electronics are
necessary to measure fast neutron spectra with high radiation from a gamma-ray
background. The signals from neutrons and gamma-rays are discriminated by the
digital charge pulse shape discrimination (PSD) method, which uses total to
partial charge ratio analysis. The signals are digitized by a flash
analog-to-digital convertor (FADC). To evaluate the performance of the
fabricated stilbene neutron diagnostic system, the efficiency of 10 mm
soft-iron magnetic shielding and the detection efficiency of fast neutrons were
tested experimentally using a 252Cf neutron source. In the results, the
designed and fabricated stilbene neutron diagnostic system performed well in
discriminating neutrons from gamma-rays under the high magnetic field
conditions during KSTAR operation. Fast neutrons of 2.45 MeV were effectively
measured and evaluated during the 2011 KSTAR campaign.
