arXiv subjects

Harishankar Ramachandran

Publications and source records attributed to Harishankar Ramachandran.

5 recordsLinked to original sources

arXiv2026

Numerical Study of Alfven Wave-Energetic Particle Interaction in the Inner Van Allen Belt and predictions of Seismic-Related Energetic Proton Bursts for the IITMSAT Mission

The IIT Madras nano-satellite aims to investigate the science of energetic particle precipitation from the inner Van Allen radiation belt into the upper ionosphere as a potential precursor to earthquakes. Precursors in the form of low frequency electromagnetic waves can appear several hours before an earthquake. These waves, captured near the ionosphere magnetosphere transition region, propagate along geomagnetic field lines as Alfven waves and interact resonantly with trapped energetic particles in the radiation belt, causing their precipitation. Such precipitation can be observed by satellites as energetic particle bursts occurring a few hours prior to the earthquake. A numerical study of Alfven wave energetic proton interactions in the inner Van Allen belt is presented here to investigate the energetic proton precipitation and make predictions to support the scientific objective of the IITM satellite mission. A kinetic model of the energetic trapped proton population in the inner belt is developed, yielding a steady-state distribution that reproduces the observed density profile. The Finite Difference Time Domain method is employed to simulate both narrowband seismic event specific emissions and broadband background noise representing magnetohydrodynamic Alfven wave activity in the inner radiation belt. The studies of interactions of narrow-band Alfven wave packets with the energetic protons in the belt reveals that a sharp cyclotron resonance condition arises at a low Alfven frequency 10 Hz, causing substantial precipitation of high energy protons 125 MeV from their stable mirror orbits. This precipitation can be clearly distinguished from background noisy interactions. Based on these results, we predict the optimal satellite orbital altitude for detecting such energetic proton bursts.

physics.space-ph↗

arXiv2023

A 3D Kinetic Distribution that Yields Observed Plasma Density in the Inner Van Allen Belt

A steady-state distribution is obtained that approximately yields the observed plasma density profile of the inner Van Allen radiation belt. The model assumes a collisionless, magnetized plasma with zero electric field present. The inner Van Allen belt consists of a plasma comprising high-energy protons and relativistic electrons. The particle trajectories are obtained from the collisionless Lorentz Force equation for different initial distributions. The resulting steady-state distributions obtained after particles lost to the loss cone are eliminated and are used to generate the density profile. The distribution's dependence on energy and magnetic moment is adjusted to make the density profile agree with observations. For a distribution that is a function of energy times a function of magnetic moment, the calculation leads to the desired type of density profile. The kinetic distribution and the type of density profile obtained are presented.

physics.plasm-ph↗

arXiv2017

IITMSAT Communications System : A LeanSat Design Approach

IITMSAT is a student-built nano satellite mission of Indian Institute of Technology Madras, Chennai, India. The objective is to study the precipitation of high energy electrons and protons from Van-Allen radiation belts to lower altitude of 600-900 km due to resonance interaction with low frequency EM waves. The unique communications system design of IITMSAT evolves from the challenging downlink data requirement of 1 MB per day in the UHF band posed by the mission and the satellite's payload, SPEED (Space based Proton and Electron Energy Detector). To ensure continuous downlink data stream in the short Low earth Orbit passes, a robust physical layer protocol was designed to counter time-varying aspects of a Space-Earth telecom link. For the on-board communications system, two types of design alternatives exist for each module. The first option is a custom design wherein a module is developed from scratch using discrete components.The other option is an integrated design wherein an electronics COTS module can be directly plugged into the subsystem. This module is evaluated by carrying out vibration and thermal tests. If an integrated module is low-cost and meets the design requirements, it is preferred over a custom design. In order to carry out performance tests under simulated link conditions, an RF attenuation test setup was designed that can work at extreme temperatures. Burn-In tests for 72 hours at ambient and extreme temperatures were carried out. Integrated tests indicate all IITMSAT design requirements have been met. Hence a robust communications system has been validated. The time taken for development of on-board telecom and GS was less than a year and was achieved at a low cost which agrees to a LeanSat approach.

astro-ph.IM↗

arXiv2014

A Nano-satellite Mission to Study Charged Particle Precipitation from the Van Allen Radiation Belts caused due to Seismo-Electromagnetic Emissions

In the past decade, several attempts have been made to study the effects of seismo-electromagnetic emissions - an earthquake precursor, on the ionosphere and the radiation belts. The IIT Madras nano-satellite (IITMSAT) mission is designed to make sensitive measurements of charged particle fluxes in a Low Earth Orbit to study the nature of charged particle precipitation from the Van Allen radiation belts caused due to such emissions. With the Space-based Proton Electron Energy Detector on-board a single nano-satellite, the mission will attempt to gather statistically significant data to verify possible correlations with seismo-electromagnetic emissions before major earthquakes.

astro-ph.IM↗

arXiv2010

The sinusoid and the phasor

Mathieu equation is widely used to study several natural phenomenon. In this paper, we show that replacing the sinusoid in the Mathieu equation with a phasor can lead to solutions that behave in a totally different way. Solutions of Mathieu equation are either bounded or grow unboundedly at an exponential rate. Solutions of this new equation are always unbounded and grow linearly with time.

physics.plasm-ph↗