Simulation Studies for Electromagnetic Design of INO ICAL Magnet and Its Response to Muons

The iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) will be used to measure neutrino mass hierarchy. The magnet in the ICAL detector will be used to distinguish the μ^- and μ⁺ events induced by ν_μ and anti-ν_μ, respectively. Due to the importance of the magnet in ICAL, an electromagnetic simulation has been carried out to study the B-field distribution in iron using various designs. The simulation shows better uniformity in the portion of the iron layer between the coils, which is bounded by regions that have lesser field strength as we move to the periphery of the iron layer. The ICAL magnet was configured to have a tiling structure that gave the minimum reluctance path, while keeping a reasonably uniform field pattern. This translates into less ampere-turns needed for generation of the required magnetic field. At low ampere-turns, a larger fractional area with |B| ≥ 1 T can be obtained using a soft magnetic material. A study of the effect of the magnetic field on muon trajectories has been carried out using GEANT4. For muons up to 20 GeV, the energy resolution improves as the magnetic field increases from 1.1 to 1.8 T. The charge identification efficiency for muons was found to be >90% except for large zenith angles.