arXiv subjects
Publications and source records attributed to Supratik Mukhopadhyay.
In this article, we report the simulated response of timing RPCs of different gas gaps. A 3D Montecarlo code was developed and integrated with Garfield++ to simulate the avalanche processes with space charge effects which allow actual charge and timing spectrums. The results of this study are presented with examples of timing RPCs of gas gaps 0.02 cm and 0.03 cm.
A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at the planned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC was placed in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx.
Space charge accumulation within GEM holes is one of the vital phenomena which affects many of the key working parameters of the detector. This accumulation is found to be significantly affected by the initial primary charge configurations and applied GEM voltages since they determine charge sharing and the subsequent evolution of detector response. In this work, we have studied the effects of space charge phenomena on different parameters for single GEM detectors using a hybrid numerical model.
We present a deep reinforcement learning-based framework for automatically discovering patterns available in any given initial configuration of fat robot swarms. In particular, we model the problem of collision-less gathering and mutual visibility in fat robot swarms and discover patterns for solving them using our framework. We show that by shaping reward signals based on certain constraints like mutual visibility and safe proximity, the robots can discover collision-less trajectories leading to well-formed gathering and visibility patterns.
A numerical model based on Finite Element Method (FEM) has been developed to simulate the electrical properties of RPC utilizing the law of current conservation. It has been used to systematically investigate the effect of the electrical as well as the geometrical parameters of the device components on the potential distribution and field configuration which govern the RPC performance. The numerical model has been validated by comparing the dark current and electric field with those produced by another mathematical model based on surface currents. The efficacy of the present model has been demonstrated by comparing its results to the experimental measurements performed with a glass RPC. The measured and estimated values of these observables have been found to be in good agreement.
Detecting out-of-distribution (OOD) data at inference time is crucial for many applications of machine learning. We present XOOD: a novel extreme value-based OOD detection framework for image classification that consists of two algorithms. The first, XOOD-M, is completely unsupervised, while the second XOOD-L is self-supervised. Both algorithms rely on the signals captured by the extreme values of the data in the activation layers of the neural network in order to distinguish between in-distribution and OOD instances. We show experimentally that both XOOD-M and XOOD-L outperform state-of-the-art OOD detection methods on many benchmark data sets in both efficiency and accuracy, reducing false-positive rate (FPR95) by 50%, while improving the inferencing time by an order of magnitude.
This work reports a cost-effective, multi-parameter readout and data-acquisition system for a muon scattering tomography system based on Resistive Plate Chambers (RPCs). Initial test measurements with a prototype Resistive Plate Chamber were performed using a low-cost FPGA coupled to the NINO ASIC for the event selection and handling data. The Time over-Threshold (TOT) property of NINO ASICs has been used to achieve better position information and achieve precise tracking capability. In our test setup, we try to build an imaging setup using a single RPC and lead block, which covers some areas of RPC. A glass RPC of dimension 30cm x 30cm, filled with a gas mixture of 95% Freon and 5% Isobutane, equipped with two orthogonal panels of readout strips of width 3 cm and pitch 3.2 cm, has been operated.
In this paper, a detailed investigation has been carried out to understand the physics behind GEM charging-up and its effects on gain. Experiments have been performed on both double and triple GEM with the help of 55Fe X-ray source and a comparative study of these configurations along with the single GEM results observed in our previous work has been reported. The increase in gain due to polarization of GEM foil dielectric and reduction in gain due to charge accumulation on dielectric are studied for various field configurations and different radiation intensities.
Resistive Plate Chamber (RPC) is a gaseous detector, known for its good spatial resolution and excellent time resolution. Due to its fast response and excellent time resolution, it is used for both triggering and timing purpose. But the time resolution of RPC is dependent on the detector geometry, applied voltage and the gas mixture used for detector operation. In this work, we have tried to develop a numerical model to estimate the time resolution of the detector. The model is developed using COMSOL Multiphysics, a commercially available finite element method solver. Using the primary ionization information from HEED and the electron transport properties from MAGBOLTZ, the model solves the Boltzmann equations to simulate the avalanche in the detector and finds the time to cross a previously determined threshold current, which is used to measure the time resolution of the detector.
The working of a resistive plate chamber depends on the electric field applied inside the gas gap. The strength of this electric field inside the gas gap depends on parameters like electrode thickness, permittivity, gas gap, among others. The applied electric field can get significantly modified by space charge effect. This can be a major concern while working in high rate particle physics experiments. Accumulation of space charge generated due to consecutive avalanches can distort the applied field. During this investigation, we have observed that the strength of this perturbation in electric field is a function of the amount of charge, electrode thickness, permittivity, and gas gap. In this paper, we have studied the dependence of the applied field on parameters linked to RPC fabrication, mentioned above. In addition, we have used the method of image to calculate the additional polarisation field due to space charge for a basic five layers of the geometry of an RPC. The variation of the perturbation in electric field with the same three parameters electrode thickness, permittivity, gas gap has also been discussed.
Discharge probability in GEM-based gaseous detectors has been numerically estimated using an axisymmetric hydrodynamic model. Initial primary charge configurations in the drift region, obtained using Heed and Geant4, are found to have significant effect on the subsequent evolution of detector response. Simulation of energy resolution has been performed to establish the capability of the hydrodynamic model to capture statistical nature of the experimental situation. Finally, single and triple GEM configurations exposed to alpha sources have been simulated to estimate discharge probability which have been compared with available experimental data. Despite the simplifying and drastic assumptions in the numerical model, the comparisons are encouraging.
Numerical qualification of an eco-friendly alternative gas mixture for avalanche mode operation of Resistive Plate Chambers is the soul of this work. To identify the gas mixture, a numerical model developed elsewhere by the authors has been first established by comparing the simulated figure of merits (efficiency and streamer probability) with the experimental data for the gas mixture used in INO-ICAL. Then it has been used to simulate the same properties of a gas mixture based on argon, carbon di-oxide and nitrogen, identified as potential replacement by studying its different properties. Efficacy of this eco-friendly gas mixture has been studied by comparing the simulated result with the standard gas mixture used in INO-ICAL as well as with experimental data of other eco-friendly hydrofluorocarbon (HFO1234ze) based potential replacements. To increase the efficacy of the proposed gas mixture, studies of the traditional way (addition of a little amount of SF$_6$) and an alternative approach (exploring the option of high-end electronics) were carried out.
Among numerous applications of muon tomography, deployment in civil structures has caught attraction of many recently. In this work, the appropriateness of muon scattering tomography to detect defects in concrete structures has been studied numerically. A few basic concrete structures that are frequently used in civil construction, have been considered as test cases. A simulation has been performed on Geant4 platform where an imaging setup built with several gaseous ionization detectors, having a specific spatial resolution for tracking the muons, have been modeled. The images of the test cases with and without the defect have been simulated for a month-long exposure of cosmic muons on the basis of their scattering from the composite concrete structures. The images have been compared using t-test to evaluate the performance of the imaging setup in identifying the defects. Further processing of the images has been done with a pattern recognition method proposed in our earlier work to improve defect identification. The efficacy of the said method has been evaluated in terms of the PRM-score devised in this work. The limitation and advantages of the present application of the muon scattering tomography encompassing the imaging and image processing technique in non-destructive evaluation of concrete structures have been discussed.
A fast, hydrodynamic numerical model has been developed on the COMSOL Multi-physics platform to simulate the evolution and dynamics of charged particles in gaseous ionization detectors based on the Gaseous Electron Multipliers (GEM). Effects of using two-dimensional (2D), 2D axisymmetric and three-dimensional(3D) models of the detectors have been analyzed to choose the optimum configuration. The chosen model has been used to follow the entire operating regime of single, double and triple GEM detectors, including avalanche and streamer mode operations. The accumulation of space charge, its contribution towards the distortion of the applied electric field and production of streamers have been investigated in fair detail using the optimized model.
Mechanisms of charging-up and charging-down of Gas Electron Multiplier (GEM) have been studied. Experimental investigations have been carried out on both dielectric polarization and radiation charging of GEMs. Environmental parameters, such as pressure and temperature have been monitored to normalize their effects on the charging-up and charging-down measurements. Variation in gain due to the combined, as well as individual, effects of the mentioned parameters has been illustrated.
This work has been carried out to simulate a Resistive Plate Chamber and corroborate it with experimental measurements in order to develop a numerical tool for studying the performance of the device for any gas mixture. This will allow us to explore the feasibility of operating these chambers in their avalanche mode within the Iron Calorimeter setup at India-based Neutrino Observatory with any eco-friendly substitute. The simulation has considered a hydrodynamic model of charge transport to emulate the electronic and ionic growths in the device as a function of the applied voltage which determines its working mode as either of the avalanche or streamer. In order to validate, the simulation result has been compared with compatible experimental data available in the literature.
Resistive plate chamber (RPC) is one of the state-of-the-art particle detection technology for the High Energy Physics (HEP) experiments. The basic operating mechanism of an RPC involves ionization of gas due to the passage of charged particles followed by electron transport , avalanche, and subsequent electromagnetic induction on readout strips due to the movement of the electrons and ions. Especially during streamer mode of operation, the electric field applied to the RPC can get significantly modified due to the presence of large number of electrons and ions. In this study, we have worked on dominant issues related to the estimation of electric field due to the space charge arising out of the presence of electrons, ions within an RPC. For this purpose we have considered two approaches: representation of the space charge cloud as (a) a collection of ring charges, and (b) as a collection of line charges. The results from these different methods have been compared with results available in the literature.
This work reports a cost-effective, simple front-end readout and DAQ of a RPC-based muon scattering tomography system under construction. The Time-over-threshold property of NINO ASICs has been exploited to achieve precise tracking by extraction of position information. The use of a low-cost FPGA for event selection and TOT measurement has been demonstrated for a prototype RPC which has been triggered by a cosmic ray hodoscope of three plastic scintillators. The relation between input pulse width and TOT has been established by analyzing the waveforms of the RPC signals. The TOT profile at different working voltages has been obtained by the FPGA and it has been fitted with the Gaussian distribution. Its standard deviation represents an estimate of the tracking precision.