Department of Physics

The GRAPES-3 experiment is designed to perform precision studies of gamma-ray sources in the TeV-PeV energy region. It consists of 400 plastic scintillator detectors spanning an effective area of 25000 m2 and a large area (560 m2) muon telescope which records ∼ 4 x 109 muons every day. With the recent installation of an improved triggerless data acquisition (DAQ) system, the information related to every muon is recorded with a timing resolution of 10 ns. The angular resolution and pointing accuracy of the upgraded muon telescope has been validated by characterizing the shadow of the moon among recorded muons. Here, the details of the analysis and results, as well as the simulation studies to account for the deflection of the particles in the Earth’s magnetic field will be presented.

In this article, a comparative experimental and simulations analysis has been carried out to understand the role of tapered gap region on current density and energy of pseudospark (PS)-based electron beam emission. These studies have been performed for 5-gap and 8-gap regions in a tapered multigap multiaperture-based PS electron beam source, keeping the same electron beam fill factor, and other geometrical parameters identical. The source has been operated in a self-breakdown mode. Around four-times increase in the beam current has been observed in the 8-gap case at the fixed applied gap potential ranging between 20 and 25 kV, whereas the tapered interelectrode gap angle has been reduced from 7.5° to 4.5°. The field penetration inside the hollow cathode cavity and tapered region have also been analyzed using simulations, and the obtained results are explained based on built-up space charge in these regions.

We report a dual-core gain-loss assisted optical fiber-segment to host an exceptional point between two quasi-guided hybrid-modes, and study the adiabatic mode conversion phenomenon by a stroboscopic gain-loss variation around the identified EP.

We investigated the impact of thermally expanded graphite (ExG) on thermal conductivity and charging/discharging time for pristine pentadecane (PD), a potential phase change material for low-temperature thermal energy storage applications. The expanded graphite is prepared using a high-temperature (~ 950 ℃) thermal shock on chemically treated natural graphite flakes and is vacuum impregnated in pentadecane. Four different 5, 10, 15, and 20 mass% expanded graphite and pentadecane (PD-ExG) composite samples are considered for intensive studies of their thermophysical properties using differential scanning calorimeter (DSC), temperature history (T-history), and transient plane source measurements. DSC measurements showed the reduction in latent heat of fusion of pentadecane with increased mass% of ExG, but the melting temperature remained nearly unaffected. Further, thermal conductivity of pentadecane-expanded graphite composites enhanced from ~ 0.18 W m−1 K−1 (for pristine pentadecane) to 1.1 W m−1 K−1, 2.6 W m−1 K−1, 4.7 W m−1 K−1, and 7.1 W m−1 K−1 for 5, 10, 15, and 20 mass% ExG composite samples, respectively. The discharge time for these PD-ExG composites reduced about 42.7 to 67.81% as compared to pristine PD sample. PD-ExG composite with 10% or more ExG also showed the shape stability of PD-ExG composites and thus reduced leakage of PD in liquid state. Thus, PD-ExG form stable phase change material composite with enhanced thermal conductivity and enhanced charge/discharge rate, making it a suitable PCM for low-temperature thermal energy storage system such as space cooling.

The GRAPES-3 experiment located in Ooty consists of an array of 400 plastic scintillator detectors spread over an area of 25000m2 and a large area (560 m2) muon telescope. Every day, the array records about 3 million showers induced by the interaction of primary cosmic rays in the atmosphere. One of the primary objectives of the experiment is to measure the energy spectrum and composition of the cosmic rays in the TeV-PeV energy range. However, some of the detected showers have cores outside the array. This fraction increases with energy due to the higher lateral spread of shower particles at higher energies. Identifying these events is thus crucial for accurate measurement of the cosmic ray energy spectrum. This work will describe simple cut based as well as machine learning based strategies for identifying and excluding such events and their impact on the cosmic ray energy spectrum as measured by the Bayesian unfolding technique.

The GRAPES-3 experiment located in Ooty consists of a dense array of 400 plastic scintillator detectors spread over an area of 25,000 m2 and a large area (560 m2) tracking muon telescope. Everyday, the array records about 3 million showers in the energy range of 1 TeV - 10 PeV induced by the interaction of primary cosmic rays in the atmosphere. These showers are reconstructed in order to find several shower parameters such as shower core, size, and age. High-energy showers landing far away from the array often trigger the array and are found to have their reconstructed cores within the array even though their true cores lie outside, due to reconstruction of partial information. These showers contaminate and lead to an inaccurate measurement of energy spectrum and composition. Such showers are removed by applying quality cuts on various shower parameters, manually as well as with machine learning approach. This work describes the improvements achieved in removal of such contaminated showers with the help of machine learning.

This book highlights the qualitative and quantitative sequential changes in microstructure of P22 steel under various stress and temperature conditions. The P22 alloy is an established material used under elevated temperature and stress for the components of thermal power plants. Temperature and stress levels for laboratory experimentation have been selected based on the true operating condition of a boiler. This book describes both continuous as well as interrupted tests that were performed under given parameters. Subsequently, the microstructures, bulk hardness and NDE parameters (magnetic and non-linear ultrasonic) have been evaluated. For reliable data, the microstructures have been observed at different regions of creep exposed samples by different characterization techniques. This has been further followed by drawing correlation between specific features like precipitate size variation with creep strain / creep time and so on. Given the contents, this book will be a useful reference for researchers and professionals working in the area of materials especially in thermal power plants.

Herein, density functional theory-based comparative studies on cubic CsMX3 (M-: Pb, Sn, Ge; X-: Cl, Br, I) and rhombohedral CsGeI3 perovskites are reported. The structural stability indicator analysis shows that Ge-based perovskites may exhibit small rhombohedral distortion led by lone pair (4 (Formula presented.)) electrons on off-centering Ge atom. The role of lone pair on Ge atom in rhombohedral distortion is corroborated by bond length, electronegativity, and charge density distributions. Nearly agreeable bandgap ((Formula presented.)) values are noticed for cubic CsPbX3 (X-: Cl, Br, I) and rhombohedral CsGeI3, and the corresponding values are 3.04, 2.30, 1.72, and 1.45 eV, respectively. The effect of Jishi et al. reparameteried Tran–Blaha-modified Becke–Johnson exchange-correlation (XC) potential is discussed in context of optoelectronic properties. The changes in bandgap are attributed to the lifting of electronic degeneracy either by spin-orbit coupling or symmetry lowering in rhombohedral distortion. The rhombohedral CsGeI3 is thus further emphasized to account its ferroelectricity with computed total polarization ((Formula presented.)) around 32.75 μC cm−2. The suitable (Formula presented.) (1.45 eV), high absorption (≈105 cm−1), tolerable reflectivity (19%), and carrier effective masses (0.61 and 0.27) enable rhombohedral CsGeI3 (superior 30.5% spectroscopy-limited maximum efficiency [SLME] at 1 μm thickness) to outperform conventional CsPbI3 (27.6% SLME at 1 μm) and others which may attract PV community to further address its underexplored promise.

We investigate an anti-parity-time (APT)-symmetric gain-loss assisted microcavity system based on scattering (S)-matrix formalism and report the fascinating aspects of encircled exceptional points (EPs) toward topological state-transfer applications.