Gamma-ray spectroscopy at MHz counting rates with a compact LaBr3 detector and silicon photomultipliers for fusion plasma applications

Abstract

Gamma-ray spectroscopy measurements at MHz counting rates have been carried out, for the first time, with a compact spectrometer based on a LaBr scintillator and silicon photomultipliers. The instrument, which is also insensitive to magnetic fields, has been developed in view of the upgrade of the gamma-ray camera diagnostic for α particle measurements in deuterium-tritium plasmas of the Joint European Torus. Spectra were measured up to 2.9 MHz with a projected energy resolution of 3%-4% in the 3-5 MeV range, of interest for fast ion physics studies in fusion plasmas. The results reported here pave the way to first time measurements of the confined α particle profile in high power plasmas of the next deuterium-tritium campaign at the Joint European Torus.

Development of a new compact gamma-ray spectrometer optimised for runaway electron measurements

“…By almost doubling the equivalent energy of the perturbation signals the relative shifts of the reference peak increases accordingly, thus confirming that this shift are indeed caused by the output currents. For a perturbation of approximately 600 keV and a rate of 500 kHz the shift of the reference peak is below 1.5 % showing a better performance than a previous detector based on coupling a SiPM with a LaBr3 crystal 16,17 . Fig.…”

“…Finally a dedicated electronic readout circuit was developed for this detector. The original design, proposed in 14 and subsequently improved in 16,17 , was implemented to achieve fast signals (see figure 1) in order to reach high counting rate capability and minimize pile-up events. The electronic board was further improved by adding active components to obtain desirable features such as signal amplification and an on-line correction of gain shifts caused by temperature fluctuations.…”

“…At high counting rates the signal current generated by the large amount of the SiPM ADP cells that are activated by gamma-ray detection can become significant. This relative large current generates a drop in the SiPM over voltage and a consequent reduction of the detector gain, which produces a shift of the spectrum towards lower energies 17 .…”

Real-time implementation with FPGA-based DAQ system of a probabilistic disruption predictor from scratch

“…By almost doubling the equivalent energy of the perturbation signals the relative shifts of the reference peak increases accordingly, thus confirming that this shift are indeed caused by the output currents. For a perturbation of approximately 600 keV and a rate of 500 kHz the shift of the reference peak is below 1.5 % showing a better performance than a previous detector based on coupling a SiPM with a LaBr3 crystal 16,17 .…”

Performance of the prototype LaBr3 spectrometer developed for the JET gamma-ray camera upgrade

“…Dedicated tests at counting rates up to few MHz were also successfully performed by using reactions emitting gamma-rays at nuclear accelerators and in a condition that closely mirrored the radiation load expected from a deuterium-tritium plasma at full power at JET. The experimental setup and results of these measurements are addressed in Nocente's article 16 . In order to investigate the behavior of the pilot spectrometer during a JET shot, a 60 seconds measurement with two LED pulses has been performed.…”