arXiv subjects
Publications and source records attributed to A. Vasiljev.
The performance of triple-GEM detectors in He+N2 gas mixtures is studied in the range of 1-10 atm. The results obtained are relevant in the field of minimization of ionic space-charge effect in the TPC and neutron detection.
We study the performance of the triple GEM (Gas Electron Multiplier) detector in pure noble gases He and Kr at high pressures, varying from 1 to 15 atm. The operation in these gases is compared to that recently studied in Ne, Ar and Xe. It turned out that light noble gases, He and Ne, have superior performance: the highest gain, approaching 10^5, and an unusual gain dependence on pressure. In particular, the maximum gain in He and Ne does not decrease with pressure, in contrast to Ar, Kr and Xe. These results are of high relevance for understanding basic mechanisms of electron avalanching in noble gases and for applications in cryogenic particle detectors, X-ray imaging and neutron detectors.
We study the feedback of positive ions in triple and quadruple Gas Electron Multiplier (GEM) detectors. The effects of GEM hole diameter, detector gain, applied voltages, number of GEMs and other parameters on ion feedback are investigated in detail. In particular, it was found that the ion feedback is independent of the gas mixture and the pressure. In the optimized multi-GEM structure, the ion feedback current can be suppressed down to 0.5% of the anode current, at a drift field of 0.1 kV/cm and gain of 10^4. A simple model of ion feedback in multi-GEM structures is suggested. The results obtained are relevant to the performance of time projection chambers and gas photomultipliers.
Multiple-GEM detectors are considered to be good candidates for tracking devices in experiments with high hadronic background. We present the results of the triple-GEM detectors beam test in a high intensity pion beam. The detectors had an optimized two-dimensional readout with minimized strip capacitance. Such optimization permitted the starting point of the efficiency plateau down to a gain of 5000. The probability of GEM discharges induced by heavily ionizing particles has been measured as a function of gain: at a gain of 20000 it amounts to 10^(-11) per incident particle. Such a value will ensure safe operation of the detector in the conditions of forward region of the LHC experiments.
ATLAS is a general purpose experiment approved for the LHC collider at CERN. An important component of the detector is the central hadronic calorimeter; for its construction more than 600,000 Wave Length Shifting (WLS) fibres (corresponding to a total length of 1,120 Km) have been used. We have built and put into operation a dedicated instrument for the measurement of light yield and attenuation length over groups of 20 fibres at a time. The overall accuracy achieved in the measurement of light yield (attenuation length) is 1.5% (3%). We also report the results obtained using this method in the quality control of a large sample of fibres.