FPGA-Based Pulse-Oriented Digital Acquisition System For Nuclear Detectors

Neutron/gamma-ray pulse shape discrimination (PSD) is a common technique applied to detectors (liquid organic scintillators) employed in neutron diagnostics for fusion plasmas. For example, NE213 scintillators, coupled with analogue PSD modules are in operation at JET (Joint European Torus) in the radial and vertical neutron camera and also in a compact neutron spectrometer system. However, these analogue systems present several drawbacks, such as limited count rate (typically ~0.2 MHz) and no reprocessing capability. ENEA-Frascati has therefore started to develop digital solutions to offer increased performances, both using commercial digital boards and developing in-house new digital architectures. This article illustrates the capabilities of the new digital architecture with high acquisition speed (200 Msamples/s) and high dynamic range (14 bit). The novel DWDA (Dynamic Window Data Acquisition) technique will be shown: the incoming signal is acquired only when the signal trespasses a threshold and the duration of the acquisition is variable so that every pulse in the current time window is sampled and acquired. Some experimental results will be presented.