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POLAR is a compact space-borne detector designed to perform reliable measurements of the polarization for transient sources like Gamma-Ray Bursts in the energy range 50-500keV. The instrument works based on the Compton Scattering principle with the plastic scintillators as the main detection material along with the multi-anode photomultiplier tube. POLAR has been launched successfully onboard the Chinese space laboratory TG-2 on 15th September, 2016. In order to reliably reconstruct the polarization information a highly detailed understanding of the instrument is required for both data analysis and Monte Carlo studies. For this purpose a full study of the in-orbit performance was performed in order to obtain the instrument calibration parameters such as noise, pedestal, gain nonlinearity of the electronics, threshold, crosstalk and gain, as well as the effect of temperature on the above parameters. Furthermore the relationship between gain and high voltage of the multi-anode photomultiplier tube has been studied and the errors on all measurement values are presented. Finally the typical systematic error on polarization measurements of Gamma-Ray Bursts due to the measurement error of the calibration parameters are estimated using Monte Carlo simulations., Comment: 43 pages, 30 figures, 1 table; Preprint accepted by NIMA

POLAR is a new satellite-born detector aiming to measure the polarization of an unprecedented number of Gamma-Ray Bursts in the 50-500 keV energy range. The instrument, launched on-board the Tiangong-2 Chinese Space lab on the 15th of September 2016, is designed to measure the polarization of the hard X-ray flux by measuring the distribution of the azimuthal scattering angles of the incoming photons. A detailed understanding of the polarimeter and specifically of the systematic effects induced by the instrument's non-uniformity are required for this purpose. In order to study the instrument's response to polarization, POLAR underwent a beam test at the European Synchrotron Radiation Facility in France. In this paper both the beam test and the instrument performance will be described. This is followed by an overview of the Monte Carlo simulation tools developed for the instrument. Finally a comparison of the measured and simulated instrument performance will be provided and the instrument response to polarization will be presented., Preprint Accepted for Publication in Nuclear Instruments and Methods in Physics Research A

The POLAR detector is a space based Gamma Ray Burst (GRB) polarimeter with a wide field of view, which covers almost half the sky. The instrument uses Compton scattering of gamma rays on a plastic scintillator hodoscope to measure the polarization of the incoming photons. The instrument has been successfully launched on board of the Chinese space laboratory Tiangong 2 on September 15, 2016. The construction of the instrument components is described in this article. Details are provided on problems encountered during the construction phase and their solutions. Initial performance of the instrument in orbit is as expected from ground tests and Monte Carlo simulation.

The Gamma-ray Burst Polarimeter-POLAR is a highly sensitive detector which is dedicated to the measurement of GRB’s polarization with a large effective detection area and a large field of view (FOV). The optimized performance of POLAR will contribute to the capture and measurement of the transient sources like GRBs and Solar Flares. The detection energy range of POLAR is 50 keV ~ 500 keV, and mainly dominated by the Compton scattering effect. POLAR consists of 25 detector modular units (DMUs), and each DMU is composed of low Z material Plastic Scintillators (PS), multi-anode photomultipliers (MAPMT) and multi-channel ASIC Front-end Electronics (FEE). POLAR experiment is an international collaboration project involving China, Switzerland and Poland, and is expected to be launched in September in 2016 onboard the Chinese space laboratory “Tiangong-2 (TG-2)”. With the efforts from the collaborations, POLAR has experienced the Demonstration Model (DM) phase, Engineering and Qualification Model (EQM) phase, Qualification Model (QM) phase, and now a full Flight Model (FM) of POLAR has been constructed. The FM of POLAR has passed the environmental acceptance tests (thermal cycling, vibration, shock and thermal vacuum tests) and experienced the calibration tests with both radioactive sources and 100% polarized Gamma-Ray beam at ESRF after its construction. The design of POLAR, Monte-Carlo simulation analysis, as well as the performance test results will all be introduced in this paper.

The hard X-ray polarimeter POLAR aims to measure the linear polarization of the 50-500 keV photons arriving from the prompt emission of gamma-ray bursts (GRBs). The position in the sky of the detected GRBs is needed to determine their level of polarization. We present here a method by which, despite of the polarimeter incapability of taking images, GRBs can be roughly localized using POLAR alone. For this purpose scalers are attached to the output of the 25 multi-anode photomultipliers (MAPMs) that collect the light from the POLAR scintillator target. Each scaler measures how many GRB photons produce at least one energy deposition above 50 keV in the corresponding MAPM. Simulations show that the relative outputs of the 25 scalers depend on the GRB position. A database of very strong GRBs simulated at 10201 positions has been produced. When a GRB is detected, its location is calculated searching the minimum of the chi2 obtained in the comparison between the measured scaler pattern and the database. This GRB localization technique brings enough accuracy so that the error transmitted to the 100% modulation factor is kept below 10% for GRBs with fluence Ftot \geq 10^(-5) erg cm^(-2) . The POLAR localization capability will be useful for those cases where no other instruments are simultaneously observing the same field of view., Comment: 13 pages, 10 figures

Gamma-ray polarimetry is a new powerful tool to study the processes responsible for the emission from astrophysical sources and the environments in which this emission takes place. Few successful polarimetric measurements have however been performed thus far in the gamma-ray energy band due to the difficulties involved. POLAR is a dedicated polarimeter designed to perform high precision measurements of the polarization of the emission from gamma-ray burst in the 50-500 keV energy range. This new polarimeter is expected to detect approximately 50 gamma-ray bursts per year while performing high precision polarization measurements on approximately 10 bursts per year. The instrument was launched into lower earth orbit as part of the second Chinese space lab, the Tiangong-2, on September 15th 2016 and has been taking data successfully since being switched on one week after. The instrument uses a segmented scintillator array consisting of 1600 plastic scintillator bars, read out by 25 flat-panel multi-anode photomultipliers, to measure the Compton scattering angles of incoming photons. The small segmentation and relatively large uniform effective area allow the instrument to measure the polarization of a large number of transient events, such as gamma-ray bursts, with an unprecedented precision during its two year life-time. The final flight model underwent detailed calibration prior to launch as well as intensive space qualification tests, a summary of which will be presented in this paper. The instrument design will be discussed first followed by an overview of the on-ground tests, finally the in-orbit behavior as measured during the first weeks of the mission will be presented.

POLAR is a space-borne instrument designed for measurements of the polarization of the prompt hard X- and gamma-ray emission from the Gamma Ray Bursts (GRB). POLAR consists of 25 identical Detection Modules equipped with Front-End Electronics (FEE) units. This paper describes: design, strategy and verification process of the POLAR trigger mechanism.

Gamma Ray Bursts (GRBs) are the strongest explosions in the universe which might be associated with creation of black holes. Magnetic field structure and burst dynamics may influence polarization of the emitted gamma-rays. Precise polarization detection can be an ultimate tool to unveil the true GRB mechanism. POLAR is a space-borne Compton scattering detector for precise measurements of the GRB polarization. It consists of a 40$\times$40 array of plastic scintillator bars read out by 25 multi-anode PMTs (MaPMTs). It is scheduled to be launched into space in 2016 onboard of the Chinese space laboratory TG2. We present a dedicated methodology for POLAR calibration and some calibration results based on the combined use of the laboratory radioactive sources and polarized X-ray beams from the European Synchrotron Radiation Facility. They include calibration of the energy response, computation of the energy conversion factor vs. high voltage as well as determination of the threshold values, crosstalk contributions and polarization modulation factors., Comment: 2015 IEEE NSS conference proceedings

POLAR is a joint European-Chinese experiment aimed at a precise measurement of hard X-ray polarization (50-500 keV) of the prompt emission of Gamma-Ray Bursts. The main aim is a better understanding of the geometry of astrophysical sources and of the X-ray emission mechanisms. POLAR is a compact Compton polarimeter characterized by a large modulation factor, effective area, and field of view. It consists of 1600 low-Z plastic scintillator bars read out by 25 at-panel multi-anode photomultipliers. The incoming X-rays undergo Compton scattering in the bars and produce a modulation pattern; experiments with polarized synchrotron radiation and GEANT4 Monte Carlo simulations have shown that the polarization degree and angle can be retrieved from this pattern with the accuracy necessary for identifying the GRB mechanism. The flight model of POLAR is currently under construction in Geneva. The POLAR instrument will be placed onboard the Chinese spacelab TG-2, scheduled for launch in low Earth orbit in 2015. The main milestones of the space qualification campaign will be described in the paper.

POLAR is a space instrument designed for measurements of the polarization of the prompt hard X- and gamma-ray emission from the Gamma Ray Bursts (GRB).

The main performance challenge of POLAR - a novel hard X-ray polarimeter, is to achieve high statistical accuracy and large modulation factors. Both require great level of response uniformity. Though, typical sensitivity of multi-anode PMTs may vary between its channels up to the factor of two to three. Moreover, the measured signal can be further altered by light coupling quality. We investigate response equalization based on utilizing of an optical mask with light-blocking diaphragms. It is placed between scintillator bars and the PMT photo-cathode. Each PMT channel-pad is equipped with the unique diaphragm with its area related to the initial sensitivity of the corresponding channel. We present module/mask construction details, test setup and measurement results done before and after applying of the mask corrections. Applicability of the method is discussed with respect to the instrument dynamic range, low energy threshold requirements and aging effects due to the in-space utilization.

POLAR is a novel compact space-borne Compton polarimeter conceived for a precise measurement of hard X-ray polarization and optimized for the detection of Gamma-Ray Burst (GRB) photons in the energy range 50–500 keV. In December 2009 we have performed a systematic calibration of one modular unit of POLAR at four energy levels (200, 288, 356 and 511 keV) with a 100% polarized synchrotron radiation source at the beam line ID15A at ESRF. The detector was displaced several times on the beam line in order to achieve a uniform illumination, which mimics the flux from a GRB placed on the zenith of the experiment. Several rotations of the detector on the beam axis allowed us to test the response of POLAR to several polarization angles. Two different analysis methods to reconstruct the polarization angle of the beam and the modulation factor μ 100 are presented; the first relies on the existence of a unpolarized sample, produced by merging two data sets with orthogonal polarization directions, and is less dependent on systematic effects due to asymmetries in the detector; the second is independent from unpolarized measurements, and will likely be used to analyze the polarization of GRB during the flight. Both methods reconstruct the input polarization angle within 2° and produce modulation factors μ 100 between 30% and 50% depending on the beam energy. Monte Carlo simulations performed with GEANT4 confirm the experimental results.

In Summer 2005, a high brilliance, vacuum ultraviolet (lambda=13 nm) free electron laser named FLASH (free electron laser in Hamburg) commenced its routine operation at DESY in Hamburg. The FLASH is driven by a 700 MeV electron linac based on high-purity superconducting Niobium cavities developed by the TESLA Technology collaboration at DESY. The gamma radiation doses along the containment tank walls of the accelerator modules 4 and 5 of the electron linac were evaluated using radiochromic films during its routine operation. This paper highlights a genetic algorithm (GA) developed by us in order to unfold the dosimeter readings. The unfolded data were used to inverse calculate the radiation source strength at the cavities, thereby quantifying the field emission induced radiation produced by each individual cavity belonging to the accelerator module.

During a long range intercontinental commercial flight from Europe to Australia the neutron and photon dose equivalents have been evaluated using a pair of electronic pocket dosemeters ALOKA PDM-313 and ALOKA PDM-111, respectively. A temperature compensated superheated emulsion (bubble) detector and an aluminium oxide TL-Dosimeter were carried together for the purpose of in-flight calibration of the electronic dosemeters. We have evaluated the radiation doses during flights from various cities in the northern hemisphere to Sydney (Australia). The results were compared with the cosmic radiation exposure calculated using the EPCARD and CARI 6 flight dose computation codes developed by GSF (Germany) and FAA (USA), respectively. A simple method of aviation dose interpolation based on polynomial fitting has been proposed.

Electronic components during High Energy Physics experiments are exposed to high level of radiation. Radiation environment causes many problems to electronic devices. The goal of several experiments done at DESY (Deutsches Elektronen Synchrotron, Hamburg) was to investigate nature of irradiation effects, caused damages and possible techniques of mitigation. One of aspects of experiments is radiation measurements. The propositions of building radiation monitoring system, using different semiconductor components, are presented. Second aspect is radiation tolerance. Different electronic devices were tested: FPGA chips, CCD sensors, bubble dosimeters and LED diodes. Components were irradiated in TESLA Test Facility 2 tunnel and in laboratory using 241 Am/Be neutron source. The results of experiments are included and discussed.