Time resolved neutron yield detector for SPIDER

Two scintillator neutron yield detectors have been tested and characterized for installation on the SPIDER beam test facility in Padova, Italy. SPIDER is a part of the facility designed to create a full scale 1 MV neutral beam injector prototype for direct application to ITER. SPIDER will produce 2.45 MeV neutrons via D-D reactions of the D- beam impinging on the deuterium already embedded in the beam dump. The scintillator detectors will be used to provide an independent measurement of the global neutron yield produced. These detectors are comprised of a new plastic scintillator EJ276, capable of discriminating between neutron and gamma radiation, coupled with a photomultiplier tube. Tests to determine the stability, functionality, and accuracy of the device, as well as energy scale calibration and diagnostic firmware validation were performed in a laboratory setting using two gamma sources (Co60 and Cs137) and an LED. The detectors were found to have acceptable reproducibility and energy resolution, and the firmware has been validated. During 2019 it has been discovered that there may be some intrinsic long term instability in the signal gain of both detectors, which will be continuously monitored. Experiments have been performed at the ISIS Neutron and Muon Source facility in Didcot and at the Frascati neutron generator, which confirm the neutron/gamma pulse shape discrimination capabilities of the detector. The system has been installed in SPIDER and is operational, with the addition of the LED pulser and SPIDER data acquisition system integration remaining to be completed.