Neutron-gamma measurements at the Madison Symmetric Torus

The detection of high energy particles is widely considered as a crucial task for fusion reactors physics. A particular role, in this context, is owned by neutrons and photons which, being not charged, can leave the fusion machine and provide useful information about the plasma. In this contribution, the energy calibration and the first experimental measurements of a new diagnostic for the neutron-gamma detection are presented. The experimental system is composed of 6 scintillator cells coupled with flat photomultiplier tubes (PMTs) through silicon rubber interfaces. The output anode signals are fed into a CAEN DT5725 14 bit 250 MS/s Digitizer, equipped with algorithms for real-time analysis of each individual scintillation event. The PMTs are operated at relatively low voltage (~1kV), in order to avoid saturation effects, by means of a CAEN DT5533E HV power supply module. One detector cell is based on NaI(Tl) crystal scintillator, the remaining ones use EJ-309 organic liquid scintillators. While the former, sensible only to high energy photons, is used for gamma-ray spectra analysis, the latter are used for fast neutron detection, thanks to their capability to separate neutrons from the gamma-ray component of the radiation field, by means of the Pulse Shape Discrimination (PSD) technique [1]. ...