Characterization of silicon photomultipliers for new high-energy space telescopes

International audiencePhoton detection is a major issue of high-energy astronomy instrumentation. One classical setup that has proven successful in space missions is the combination of photomultiplier tubes (PMTs) with scintillators, converting incoming high-energy photons into visible light, which is converted in an electrical impulse. Although being extremely sensitive and rapid, PMTs have the drawback of being bulky, fragile, and requiring a high-voltage power supply of thousands volts. The silicon photomultipliers (SiPM) appear to be a promising alternative to PMTs in many applications such as small satellites. We have started a R&D program to assess the possibility of using SiPMs for space-based applications in the high-energy astronomy domain. We present here the results of our characterization of SiPMs coming from several manufacturers. Each detector has been tested at low temperature and pressure to study its performance in a representative space environment. For this, we developed a dedicated vacuum chamber with a specific mechanical and thermal controlled system. Once dark current, dark count rate and PDE were measured, we made irradiation tests on two selected detectors to understand the susceptibility of SiPM to radiation damage. Finally, we aim to perform thermal cycling and mechanical tests on detectors and study their coupling to scintillators, in parallel with their space qualification

Spectral performance of ECLAIRs flight detectors on SVOM mission

International audienceThe hard X-ray imager of the Sino-French SVOM mission, called ECLAIRs, is dedicated to the detection and near real time localization of cosmic transients in the 4−150  keV energy range. ECLAIRs is a wide-field camera using a detection plane consisting of 6400 Schottky CdTe detectors, which makes images of the hard X-ray sky thanks to a coded mask. The detection plane is highly modular, being made of 200 hybrid modules of 4 x 8 pixels (called “XRDPIX”). Based on both an extremely low noise design and the use of innovative technologies, the ECLAIRs instrument will achieve the unprecedented low-energy threshold of 4 keV over the entire detection plane.The CdTe semiconductor detectors of 4  ×  4 mm 2  size and 1 mm thickness are biased with a high voltage going to −450V, and regulated at −20∘ C to minimize the leakage current and maximize the polarization time due to Schottky barrier lowering. The low-energy threshold required for the space mission is achieved thanks to an extensive characterization of the elements constituting the XRDPIX modules.In this paper, we introduce the astrophysical context that led to the design of the mission, with an emphasis on the study of GRBs with ECLAIRs. We provide a detailed description of the XRDPIX hybrid modules, and we explain the experimental setup used for testing and qualifying 45 flight models. We present the results of the measurements performed to validate the module performance with a radioactive source of Americium 241. We study the spectral resolution, the low energy threshold, the gain of the detectors, and their counting performance. We also present two side studies concerning the impact of low temperatures and the stability of the performance over time. To conclude, we propose optimal settings for two key configuration parameters: the high voltage bias and the peaking time, that permit obtaining the challenging 4 keV energy threshold required for the SVOM mission

Characterizing the dead time of the ECLAIRs camera on board the mission SVOM

International audienceFrench (CNES) and Chinese (CNSA) space agencies collaborate to build the SVOM (Space-based multi-band Variable Object Monitor) mission due to be launched in 2021 to study gamma-ray bursts and high-energy transients. The SVOM prime instrument, ECLAIRs, will detect and localize GRBs autonomously as well as provide a spectral and temporal characterization of the GRB prompt emission. ECLAIRs is expected to detect around 200 GRBs during the 3 year nominal lifetime of the mission. ECLAIRs is a wide-field (∼ 2 {sr}) coded mask camera with a detection plane made of 8 independent sectors of 800 Schottky CdTe detectors working in the 4-150 keV energy range. Each sector is connected to independent readout electronics. In this paper, we focus on the study of the temporal performance and we estimate how dead time will affect bright transient lightcurves. We discuss the analytical model based on simulations over a large range of source count rates on a dedicated test bench. We show that dead time will not significantly affect ECLAIRs data, even for the brightest GRBs (3.7% of lost counts for a count rate of 105 counts.s- 1 over the detection plane in the energy range 4-150 keV) and our model can nicely correct the parts of the lightcurves which are the most affected by dead time effects for very bright GRBs