04/15/2021
By Yifan Huang
The Kennedy College of Sciences, Department of Physics & Applied Physics, invites you to attend a doctoral dissertation defense by Yifan Huang on “Effects of Heavy Elements in the Near-Earth Space Environment.”
Ph.D. Candidate: Yifan Huang
Defense Date: Wednesday, April 21, 2021
Time: 11 a.m. to noon
Location: This will be a virtual defense via Zoom. Those interested in attending should contact the student yifan_huang@student.uml.edu at least 24 hours prior to the defense to request access to the meeting.
Committee Chair (Advisor): Paul Song, Ph.D., Professor, Department of Physics & Applied Physics, UMass Lowell
Committee Members:
- Ofer Cohen, Ph.D., Assistant Professor, Department of Physics & Applied Physics, UMass Lowell
- James Egan, Ph.D., Professor Emeritus, Department of Physics & Applied Physics, UMass Lowell
- Jiannan Tu, Ph.D., Research Professor, Department of Physics & Applied Physics, UMass Lowell
Abstract:
The space weather phenomena are various processes that take place in the terrestrial magnetosphere and ionosphere taking energy, mass and momentum from the sun. these phenomena may affect and damage the space-borne technologies and health of humans in space. One of the major links in these processes is the coupling between the magnetosphere and ionosphere which is one of the most poorly understood problem in space physics. The two regions are coupled with charged particles of various origins and electromagnetic field. Most of previous theoretical treatments of the coupling have been based on single fluid theory. This study extends it to multi-fluid and focusing on the effects of heavy ions mostly of earth origin.
We first investigate the coupling analytically with waves propagating along the magnetic field from the magnetosphere. In the presence of heavy ions, such as O+, because of differences in mass and density, each ion species responds to and hence affects the perturbations of electromagnetic fields differently. Collisions among all the species further complicate the process. With a linear analysis, the dispersion relation of parallel propagation covering a large range of frequencies, from magnetohydrodynamics (MHD) waves to light waves, with arbitrary combination of multiple positively charged species, negatively charged species, and neutral species is derived based on a multi-fluid treatment, in combination with Faraday’s law and Ampere’s law including the displacement current. In a collisional plasma, when the collision frequency is lower than the gyrofrequencies of charged species, the resonances are at the gyrofrequencies of each charged species and the cutoff frequencies are related to the densities of the charged species. Stopbands in which waves propagate with extremely high phase velocity but are strongly damped form between some of these characteristic frequencies. In the MHD wave frequency range, the coupling with neutral species slow the propagation speed comparing with the Alfven speed. The collisions between plasma and neutrons efficiently contribute to the wave damping, which is significantly reduced when the neutral species are completely driven with plasma by collisions. When the collisions become stronger, the resonances and cutoffs become weaker and may disappear. The species could couple tightly and act as a single fluid if the collisions among them are strong enough.
In the numerical model development, we have developed a global 3-D hybrid particle simulation model to simulate O+, H+, and He+ ion transport in the topside ionosphere and inner magnetosphere, covering the altitude range from topside ionosphere (~600km) to a flexible altitude in the magnetosphere up to 5 Earth’s radii. The electrons are treated as a background fluid to maintain quasi-charge neutrality, and the electron momentum equation with electron inertial ignored is used to calculate electric field. The Faraday’s law is solved to obtain perturbation magnetic field, and Ampere’s law is used to calculate electron velocity. A number of cutting-edge numerical techniques are adapted or developed to implement the code for this new next-generation model. Advanced spherical geodesic grid system is applied to generate meshes for the simulation domain. An innovative bit coding technique is developed to very efficiently locate particles in the simulation domain and to allocate particle’s contribution to moments (density, bulk velocity, temperature) on the grid points around the particle. This model for the first time fills the gap between the global ionospheric models and global magnetosphere models, and of great potential in studying magnetosphere-ionosphere coupling, in terms of mass, energy, and momentum exchange. Some privilege results are provided.
All interested students and faculty members are invited to attend the online defense via remote access.