[en] Multi-pixel photon counter (MPPC) is one of devices called silicon photomultiplier (SiPM). It is characterized by a fast response time, high gain coefficient, high photon detection efficiency resulting in good energy resolution, low voltage operation, resistance to mechanical shocks, compactness and immunity to a magnetic field. A MPPC gain is temperature dependent, so it is necessary to use a device that allows a constant value of a MPPC gain. In this paper we report on a detector designed at the National Centre for Nuclear Research (NCBJ). This detector is equipped with MTCD-NCBJ, a MPPC temperature compensation device. We have studied the performance of a Hamamatsu MPPC as a function of both temperature and bias voltage. A climate chamber was used to control detector temperature. Our special interest was in measurements at high count rates and for this purpose CeBr₃ scintillators were used with a decay time of about 20 ns. Since in such experiments a short output signal scintillators were needed, we used a trans-impedance amplifier (TIA) to obtain signals as short as 110 ns. In addition, TIA minimizes the gain shift, by stabilizing detector parameters, defining both static and dynamic working points, when a detected event count rate rapidly changes in time. Measurements were done with a fast change from a background event count rate to a high count rate obtained with a 400 MBq ¹³⁷Cs source emitting a gamma line with an energy of 662 KeV. To study the dependence of main detector setup parameters on gamma-ray energy, we used PuBe and PuC sources which allowed for measurements up to 4.4 and 6.1 MeV, respectively. We also tested a multi-channel setup prepared at NCBJ for the upgraded gamma camera at the Joint European Torus (JET). Obtained results prove a correct and effective operation of a detector consisting of MPPC, MTCD-NCBJ and a scintillator in measurements at count rate up to approx 1 MHz. (authors)

[en] In forthcoming deuterium-tritium (DT) experiments on JET a significant population of alpha-particles will be produced. For operating alpha-particle diagnostics at high DT neutron fluxes, specific improvements have to be made. Proposed new detectors for gamma-ray measurements will be based on CeBr₃ and LaBr₃:Ce scintillators. They are characterized by a good energy resolution, a relatively high detection efficiency for a few MeV gamma-rays and a fast response time. An overview of scintillator parameters is presented. A description of the properties of photodetectors is given to indicate optimal setups. Results of measurements, using gamma-ray sources with energies up to a few MeV, are discussed with relation to the DT campaign requirements. (paper)

[en] Gamma-ray spectroscopy measurements at MHz counting rates have been carried out, for the first time, with a compact spectrometer based on a LaBr_3 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.

[en] In this work, we describe the solution developed by the gamma ray camera upgrade enhancement project to improve the spectroscopic properties of the existing JET γ-ray camera. Aim of the project is to enable gamma-ray spectroscopy in JET deuterium-tritium plasmas. A dedicated pilot spectrometer based on a LaBr_3 crystal coupled to a silicon photo-multiplier has been developed. A proper pole zero cancellation network able to shorten the output signal to a length of 120 ns has been implemented allowing for spectroscopy at MHz count rates. The system has been characterized in the laboratory and shows an energy resolution of 5.5% at E_γ = 0.662 MeV, which extrapolates favorably in the energy range of interest for gamma-ray emission from fast ions in fusion plasmas.

[en] The Joint European Torus (JET), the largest magnetic confinement plasma physics experiment in operation, has a large amount of key diagnostics for physics exploration and machine operation, which include several Gamma-Ray Diagnostics. The Gamma-Ray Spectrometer (GRS), Gamma Camera (GC) and Gamma-Ray Spectrometer Upgrade (GSU) diagnostics have similar Control and Data Acquisition Systems (CDAQ) based on the Advanced Telecommunication Computing Architecture standard, featuring Field Programmable Gate Arrays for data processing and management. During past JET-EP2 enhancements, the GRS and GC diagnostics were successfully installed and commissioned. However, the installed CDAQ software that interfaces these diagnostics to JET Control and Data Acquisition System is different, requiring higher maintenance costs. Benefiting from the Gamma Camera Upgrade (GCU) and new GSU installation and commissioning, the upgrading of the software and controller hardware used in the GRS and GC was evaluated, aiming at software standardization between all three diagnostics for easier maintenance. This paper describes the software standardization process between the diagnostics towards the usage of the same CDAQ software as well as the same Operating System (OS) for the controllers, which allows the operator to minimize the maintenance time, avoiding the need for system specific expertise. The rationale behind the choice of MARTe framework as CDAQ software and Scientific Linux as OS will also be presented.

[en] Highlights: • The GCU project aims at insztalling 19 new scintillators in JET Gamma-Camera. • FPGA codes need to be rebuilt to cope with the new signals. • Dedicated codes were designed fitted to the new signal shape. • Code tested during installation of the 19 detectors in Camera. • Results obtained with algorithms at FPGA are presented. - Abstract: The Gamma-Ray Camera Upgrade (GCU) project aims at installing a new set of 19 scintillators with multi-pixel photon counter (MPPC) embedded, capable to meet the high fluxes expected during deuterium-tritium plasmas while improving the diagnostic spectroscopic capabilities. GCU will benefit from the Advanced Telecommunications Computing Architecture (ATCA)-based Data Acquisition System (DAQ), successfully installed and commissioned during the JET-EP2 enhancement. However, to cope with the new GCU detector signals, the DAQ Field Programmable Gate Array (FPGA) codes need to be rebuilt. This work presents the FPGA code upgrade for Gamma Camera (GC) DAQ, capable to sustain the expected fast response of new detectors, while exploiting the full capabilities of the DAQ. Dedicated codes were designed, capable to acquire the new signals at full rate, and simultaneously processing them in real-time through suitable algorithms, fitted to the new signals shape. First results of real-time processing codes applied to data from detector prototypes are presented.