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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.

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).

POLAR, a joint European-Chinese experiment, is a novel compact space-borne Compton polarimeter conceived and optimized for detection of the prompt emission of Gamma-Ray Bursts (GRB) and precise measurements of polarization in the hard X-ray energy range 50-500 keV. The complete instrument consists of two parts: internal one, placed inside spacelab and the detector itself, placed outside spacelab, called respectively IBOX and OBOX. The OBOX constitutes of 25 frontend electronic modules (FEE), high voltage and low voltage power supplies and the Central Task Processing Unit. The main functions of Central Task Processing Unit system are defined as follows: communication and transfer of data to IBOX, communication with all frontends, analysis of trigger signals and generation of global trigger signals, data acquisition, synchronizing of all frontends and control of power supplies. The functional requirements are fulfilled by three individual FPGA chips named respectively to their functions: Concentrator, Trigger and CPU. This article presents description of the Central Task Processing Unit hardware design and brief introduction to main components of the firmware developed for this device. Ongoing integration activities of the device with the complete POLAR instrument proved that all basic functions are working correctly. The qualification model of the instrument has been constructed and currently undergoes verification and validation tests in view of planned flight onboard the Chinese spacelab TG-2 scheduled for 2015.

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.

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.