D. Rigamonti

High performance detectors for upgraded gamma ray diagnostics for JET DT campaigns

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.

First neutron spectroscopy measurements with a pixelated diamond detector at JET

A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET) in 2013 along an oblique line of sight and demonstrated the possibility to carry out neutron spectroscopy measurements with good energy resolution and detector stability in discharges heated by neutral beam injection and radio-frequency waves. Starting from these positive results, within the Vertical Neutron Spectrometer project of the Joint European Torus, we have developed a pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude. In this paper we describe the main features of the DVNS, including the detector design, energy resolution, and data acquisition system for on-line processing. Preliminary spectroscopy measurements of 2.5 MeV neutrons from the present deuterium plasma at JET are finally presented.

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

Gamma-ray spectroscopy measurements at MHz counting rates have been carried out, for the first time, with a compact spectrometer based on a LaBr3 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.

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

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 LaBr3 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 Eγ = 0.662 MeV, which extrapolates favorably in the energy range of interest for gamma-ray emission from fast ions in fusion plasmas.

Response function of single crystal synthetic diamond detectors to 1-4 MeV neutrons for spectroscopy of D plasmas

A Single-crystal Diamond (SD) detector prototype was installed at Joint European Torus (JET) in 2013 and the achieved results have shown its spectroscopic capability of measuring 2.5 MeV neutrons from deuterium plasmas. This paper presents measurements of the SD response function to monoenergetic neutrons, which is a key point for the development of a neutron spectrometer based on SDs and compares them with Monte Carlo simulations. The analysis procedure allows for a good reconstruction of the experimental results. The good pulse height energy resolution (equivalent FWHM of 80 keV at 2.5 MeV), gain stability, insensitivity to magnetic field, and compact size make SDs attractive as compact neutron spectrometers of high flux deuterium plasmas, such as for instance those needed for the ITER neutron camera.

The upgraded JET gamma-ray cameras based on high resolution/high count rate compact spectrometers

The JET gamma-ray cameras have been recently upgraded within the gamma-ray camera upgrade project in support of development of JET high performance deuterium plasma scenarios and in preparation of deuterium-tritium experiments. New, dedicated detectors based on a LaBr3 crystal and silicon photo-multipliers have been developed and replaced pre-existing CsI detectors in all 19 channels. The new instrument gives opportunity of making two-dimensional gamma-ray measurements with a counting rate capability exceeding 1 MCounts/s (MCps) and energy resolution better than 5% at 1.1 MeV. The upgrade is of relevance for fast ion and runaway electron physics studies in high performance deuterium discharges and also in plasmas with tritium at neutron yields in the range up to about 5 × 1017 n/s.

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

A new compact gamma-ray spectrometer was developed in order to optimise the measurement of bremsstrahlung radiation emitted from runaway electrons in the MeV range. The detector is based on a cerium doped lutetium-yttrium oxyorthosilicate (LYSO:Ce) scintillator coupled to a silicon photomultiplier and is insensitive to magnetic fields. A dedicated electronic board was developed to optimise the signal readout as well as for online control of the device. The detector combines a dynamic range up to 10 MeV with moderate energy non-linearity, counting rate capabilities in excess of 1 MHz, and an energy resolution that extrapolates to a few % in the MeV range, thus meeting the requirements for its application to runaway electron studies by bremsstrahlung measurements in the gamma-ray energy range.

Characterization of a compact LaBr3(Ce) detector with Silicon photomultipliers at high 14 MeV neutron fluxes

A new compact gamma-ray spectrometer based on a Silicon Photo-Multiplier (SiPM) coupled to a LaBr3(Ce) crystal has been developed for the upgrade of the Gamma Camera (GC) of JET, where it must oper ...