arXiv subjects

Junying Chai

Publications and source records attributed to Junying Chai.

3 recordsLinked to original sources

arXiv2019

Design and performance of the TIGER front-end ASIC for the BESIII Cylindrical Gas Electron Multiplier detector

We present the design and characterization of TIGER (Turin Integrated Gem Electronics for Readout), a 64-channel ASIC developed for the readout of the CGEM (Cylindrical Gas Electron Multiplier) detector, the proposed inner tracker for the 2018 upgrade of the BESIII experiment, carried out at BEPCII in Beijing. Each ASIC channel features a charge sensitive amplifier coupled to a dual-branch shaper stage, optimized for timing and charge measurement, followed by a mixed-mode back-end that extracts and digitizes the timestamp and charge of the input signals. The time-of-arrival is provided by a set of low-power TDCs, based on analogue interpolation techniques, while the charge measurement is obtained either from the Time-over-Threshold information or with a sample-and-hold circuit. The ASIC has been fabricated in a 110 nm CMOS technology and designed to operate with a 1.2 V power supply, an input capacitance of about 100 pF, an input dynamic range between 3 and 50 fC, a power consumption of about 12 mW/channel and a sustained event rate of 60 kHz/channel. The design and test results of TIGER first prototype are presented showing its full functionality.

physics.ins-det↗

arXiv2018

In-flight energy calibration of the space-borne Compton polarimeter POLAR

POLAR is a compact wide-field space-borne detector for precise measurements of the linear polarisation of hard X-rays emitted by transient sources in the energy range from 50 keV to 500 keV. It consists of a 40$\times$40 array of plastic scintillator bars used as a detection material. The bars are grouped in 25 detector modules. The energy range sensitivity of POLAR is optimized to match with the prompt emission photons from the gamma-ray bursts (GRBs). Polarization measurements of the prompt emission would probe source geometries, emission mechanisms and magnetic structures in GRB jets. The instrument can also detect hard X-rays from solar flares and be used for precise measurement of their polarisation. POLAR was launched into a low Earth orbit on-board the Chinese space-lab TG-2 on September 15th, 2016. To achieve high accuracies in polarisation measurements it is essential to assure both before and during the flight a precise energy calibration. Such calibrations are performed with four low activity $^{22}$Na radioactive sources placed inside the instrument. Energy conversion factors are related to Compton edge positions from the collinear annihilation photons from the sources. This paper presents main principles of the in-flight calibration, describes studies of the method based on Monte Carlo simulations and its laboratory verification and finally provides some observation results based on the in-flight data analysis.

physics.ins-det↗

arXiv2016

A crosstalk and non-uniformity correction method for the Compact Space-borne Compton Polarimeter POLAR

In spite of extensive observations and numerous theoretical studies in the past decades several key questions related with Gamma-Ray Bursts (GRB) emission mechanisms are still to be answered. Precise detection of the GRB polarization carried out by dedicated instruments can provide new data and be an ultimate tool to unveil their real nature. A novel space-borne Compton polarimeter POLAR onboard the Chinese space station TG2 is designed to measure linear polarization of gamma-rays arriving from GRB prompt emissions. POLAR uses plastics scintillator bars (PS) as gamma-ray detectors and multi-anode photomultipliers (MAPMTs) for readout of the scintillation light. Inherent properties of such detection systems are crosstalk and non-uniformity. The crosstalk smears recorded energy over multiple channels making both non-uniformity corrections and energy calibration more difficult. Rigorous extraction of polarization observable requires to take such effects properly into account. We studied influence of the crosstalk on energy depositions during laboratory measurements with X-ray beams. A relation between genuine and recorded energy was deduced using an introduced model of data analysis. It postulates that both the crosstalk and non-uniformities can be described with a single matrix obtained in calibrations with mono-energetic X- and gamma-rays. Necessary corrections are introduced using matrix based equations allowing for proper evaluation of the measured GRB spectra. Validity of the method was established during dedicated experimental tests. The same approach can be also applied in space utilizing POLAR internal calibration sources. The introduced model is general and with some adjustments well suitable for data analysis from other MAPMT-based instruments.

physics.ins-det↗