Optimization of the ITER vertical neutron camera detectors and collimators

Abstract ITER vertical neutron camera (VNC) is intended to measure time- and space-resolved neutron emission profile in the poloidal plasma section. It is composed of two fan-shaped collimating structures: lower (5 collimators) and upper (6 collimators). Every collimator contains 2 fission chambers and 2 diamond detectors. Upper VNC (UVNC) is located within upper port #18 and contains 6 lines of sight. However, upper port plug has very limited space for UVNC placement, so it is hard to manufacture sufficiently long collimators to suppress background neutrons and provide good collimation efficiency. In this work we analyzed ways of UVNC design optimization and suggested several solutions to decrease fraction of background neutrons measured by neutron detectors. All optimizations allow us to reduce fraction of background neutrons registered by fission chambers from 75% to 20%.