Speaker
Description
The ICAL (Iron CALorimeter) set-up at India-based Neutrino Observatory (INO) [1] will use a large number of Resistive Plate Chambers (RPC) as the active detector element which will be stacked one above the other with alternate iron layers. The timing and spatial information from the RPCs will help determining the track of a muon produced from the interaction of atmospheric neutrino with the iron for obtaining its energy, charge and directional information. The presence of the inherent geometrical components like button and edge spacers, corners may affect the efficiency (already observed experimentally [2]) as well as timing properties of the RPC since the electric fields in the close vicinity of these regions have been found to differ from the otherwise uniform value inside the chamber [3]. In the present study, the effect of spacers and corners on the time resolution of RPC have been calculated numerically treating the resistive plates as perfect dielectrics with zero conductivity and the medium resistive coating as perfect conductor. Garfield [4] framework has been used for the study which uses neBEM [5], a field solver based on boundary element method, to generate the field map, MagBoltz to calculate the electron transport properties in a gaseous medium and HEED to calculate the primary ionization due to passage of a charged particle. The field map has also been calculated using COMSOL [6], which uses finite element method and the results have been compared with that from neBEM. Thousand muons, each of energy 2 GeV, have been passed through a bakelite RPC at an angle 14.5∘ with the axis of the chamber and the time taken by the electrons, produced in the gas ionization to reach the RPC plate has been filled in a histogram. The standard deviation of the histogram gives the time resolution of the RPC. A gas mixture of R134-A, Isobutane and SF6 has been used for this study in a ratio 95.0 : 4.5 : 0.5. The time resolution has been found to be about 0.32 ns, which is fairly close to the value found in experiments (1 - 2 ns). The same will be evaluated at the critical regions to study the effect of different geometrical components like corners and spacers. It is also planned to include the spatial and energy distributions of the passing muons in the calculation. The relevant results will be reported in the workshop. References : [1] ICAL collaboration, arXiv:1505.07380, 27/05/2015. [2] M. Bhuyan et al., Nucl. Instrum. Meth. A 661 (2012) S68. [3] A. jash et al., Springer Proceedings in Physics, ISBN 978-3-319-25619-1 (accepted). [4] Garfield - simulation of gaseous detectors, http://garfield.web.cern.ch/garfield [5] N. Majumdar and S. Mukhopadhyay, 2007 JINST 2 P09006. [6] COMSOL : a multiphysics simulation tool, http://www.comsol.co.in
