Projects
Title: Linear Dispersion Characteristics of Electrostatic Waves in Ordinary and Dusty Plasma.
Feb 01 - Mar 30, 2017; Indian Institute of Geomagnetism (IIG), Navi-Mumbai, India
Supervisor: Dr. Amar Kakad
Abstract
One of the most obvious features of the plasma state is the wide variety of wave motions that plasmas can support. The presence of various types of electrostatic modes in an unmagnetized electron-ion plasma as well as in dusty plasma (electrons, ions, dust grains) is studied by many researchers. In this project, we have reviewed some of the work related to the ion-acoustic waves in electron-ion and dusty plasma. The analysis of these waves is done by using fluid models. We studied electrostatic acoustic type modes in dusty plasma, mainly dust acoustic waves (DAW) and dust ion acoustic waves (DIAW). In the case of DAW, we have found that the nature of dispersion is nonlinear for both hot dust acoustic waves (HDAW) and cold dust acoustic waves (CDAW). In the case of HDAW, the nature of dispersion is first linear; then, it saturates due to resonance and dissipates its energy to the particles. Afterward, it becomes linear again after gaining energy from the system. It implies that though it is an acoustic mode, the dispersion is nonlinear, so hot dust affects the acoustic wave properties. In the case of cold dust in plasma, the dispersion is the same as in the case of ion-acoustic waves in plasma without plasma approximation. Similarly, in the case of DIAW, the nature of dispersion is the same as that of ion-acoustic waves in plasma and CDAW in dusty plasma. Nevertheless, in the limit of large wavelength and oscillation frequency of ions much greater than that of dust, the nature of dispersion will be the same as ion acoustic waves with plasma approximation (linear relation). So, no information will be lost by the wave in the system, i.e., no dissipation take place in the system. Further investigation proposes that hot and cold dust particles will modify the acoustic wave further. It is observed that the nature of dispersion is linear. Therefore, dust modifies the waves present in plasma and generates additional wave modes in the system. Therefore, it is essential to understand different plasma processes in dusty plasma.
MSc. Project: Study of ICME-Induced Cosmic Ray Variations i.e., Forbush Decrease Phenomena.
Apr 2015 - May 2016; University Department of Physics, University of Mumbai, Mumbai, India
Supervisor: Dr. Anil N. Raghav
Abstract
Researchers worldwide studied different aspects of the Forbush Decrease (FD) phenomena in the last few decades. The investigation advances the understanding of the physical mechanism behind the FD after the satellite era. We understand that the ICME is the real contributor to the non-recurrent FD. The literature suggests that the first step, FD decrease, is due to shock sheath, and the second decrease is due to the magnetic cloud of ICME. However, there are a few questions that still need to be answered. In this project report, we have investigated 18 FD events from the catalogs on the NMDB website. We aim to find out answers to the following open question; 1. Is a complete shock or MC contributing to CR decrease? or part of it? Or Is there any internal structure associated with the ICMEs shock/MC which precisely contributes to the decrease? This work investigates the internal structure of ICME shock and MC, which affect the FD main phase decrease. We found ICME can cause complex FD profiles along with the classical single or two-step FD profile. Moreover, we also noted a local decrease/increase in cosmic ray flux during the transit of ICME sub-structures. Our investigation also suggests the presence of local small-scale magnetic structures within the ICME sub-structures, which can contribute to local increase/decrease in cosmic rays.
Summer Project: Study of Soft X-ray Emission from Planetary Bodies.
Jun 6 - Jul 16, 2016; Manipal Center for Natural Sciences, Udupi, India
Supervisor: Dr. Subramnia Athirey
Abstract
Sun emits X-ray radiation continuously in all directions. This X-ray interacts with the planet's atmosphere, planet surfaces, comets, satellites, etc., and either gets absorbed or scattered back to outer space. X-ray's energy band < 5 keV is very important for the remote sensing of the planetary bodies because all the planetary bodies emit radiation in this band of the energy scale. Studying X-ray emissions from different planetary bodies helps understand the atmospheric dynamics and surface geological processes. It is the best tool to study the interaction of high energy radiation from the Sun with the planets and investigation the corresponding response of planetary bodies to the incident radiation and particles from the Sun. X-ray is one of the probes for terrestrial planets to understand the interaction of magnetized plasma and the nature of the interaction. Soft x-ray emissions from the comets and their configuration open a new way to understand the x-ray emission mechanism called Solar Wind Charge Exchange(SWCX). The dominant planetary process of X-ray emission is due to solar X-ray and the interaction of charged particles with atmospheric neutrals of the planets. Also, it is believed that SWCX is the dominant process responsible for the loss of planetary atmosphere.
The mechanism responsible for the emission of soft X-rays from these planetary objects is found to be as follows: 1] Elastic Scattering, 2] Fluorescence emission, and 3] Solar Wind Charge Exchange(SWCX). As discussed above, the dominant physical process is responsible for the emission of soft X-rays. However, we have an idea of the interplay between the planet's seasonal variations with the solar activity seasonal variations. Hence emission of X-rays will vary depending on the solar activity. As these X-rays' emissions lie in soft band X-rays, detecting them from an instrumental point of view is very challenging. Today we don't have any dedicated soft X-ray detector for studying soft X-ray emissions from these Planetary bodies. To make such a highly sensitive instrument, we should know the instrument's signal-to-noise ratio. Here in this project, we attempt to estimate the emission of soft X-rays due to these three emission mechanisms from different planetary bodies. We considered: Venus and Mars as a case study. We also attempt to develop an algorithm for the estimates of X-ray emission due to these processes for Venus and Mars. Today we don't have any dedicated instrument to detect the emission of soft X-rays from these planets. This project was very helpful in the development of an X-ray instrument for dedicated soft X-ray studies of the planets.