Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session UF23: Basic Plasma Physics Phenomena in Low- temperature Plasmas III |
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Chair: Stuart Loch, Auburn University Room: Virtual GEC platform |
Friday, October 8, 2021 10:15AM - 10:30AM |
UF23.00001: Computational modeling of a nonlinearly coupled light and particle beam propagation Prabhat Kumar, Andres Castillo, Alexandros Gerakis, Kentaro Hara Interaction of light and gas particles plays an important role in laser diagnostics, optical tweezers, cold plasmas, and space propulsion. While a collimated light beam naturally diffracts without any guiding media and particles diffuse due to their thermal motion in vacuum, precisely tailoring the coupling of the two can lead to mutually self-guided beams. A self-consistent computational model for co-propagation of light and particle beams has been developed and validated against experimental results from relevant literature. While the previous studies have focused on the trapping of particles due to optical forces, we investigate and quantify the mutual guiding (i.e., particle trapping and light guiding) effects using our computational model. We further employ our model to gain insight into the opportunities and limitations of employing a coupled light-particle beam as a space propulsion system. The influence of several relevant parameters such as particle density, temperature, laser beam waist, and power on effective particle trapping and waveguiding is explored. |
Friday, October 8, 2021 10:30AM - 10:45AM |
UF23.00002: Dynamic Mode Splitting and Plasma-Induced Transparency in Microplasma Photonic Crystals Xinhang Song Microplasma-based photonic crystals having a 3D structure, a lattice constant of 1 mm, and operating in the 110-170 GHz spectral region have been designed and realized at the University of Illinois. These 3D periodic structures allow for the integration of complex metallic structures with plasma microcolumns, thereby creating versatile platforms to study plasma-resonator interactions and active tuning of electromagnetic modes. By exploiting the frequency dependence of the dielectric permittivity of low temperature plasma, the strength of cavity-waveguide coupling can be tuned by the electron density. |
Friday, October 8, 2021 10:45AM - 11:00AM |
UF23.00003: Theoretical Linkage of Electron Emission and Gas Breakdown Mechanisms Amanda M Loveless, Adam M Darr, Haoxuan Wang, James C Welch III, Allen L Garner Characterizing electron emission and gas breakdown behavior from nanoscale to microscale is important for micro- and nano-electromechanical systems, directed energy, and microplasmas. Theoretical studies often investigate emission mechanism transitions piecemeal given the complexity in linking them over a broad parameter space. This study reports various approaches for linking these mechanisms. The first reports the development of a common nondimensionalization scheme to link quantum space-charge-limited emission, classical space-charge-limited emission, space-charge-limited emission with collisions, field emission (FE), field emission driven microscale gas breakdown, and Paschen’s law (PL)1. Since common microplasmas use a series resistor as a current limiter, we also incorporate a series resistor into a microscale gas breakdown theory2 and compare to particle-in-cell (PIC) simulations. The implications of these results on ongoing nanoscale and microscale gas breakdown experiments will be discussed. |
Friday, October 8, 2021 11:00AM - 11:15AM |
UF23.00004: Experimental Studies of Gas Breakdown and Electron Emission for Nanoscale Gaps Haoxuan Wang, Amanda M Loveless, Adam M Darr, Allen L Garner Traditionally, gas breakdown is driven by Paschen’s law. Reducing gap distance to microscale creates high electric fields that strip electrons by field emission (FE), which adds space-charge that theoretically causes breakdown voltage (Vbd) to decrease linearly with decreasing gap distance d1. With reducing d, electron emission ultimately transits from FE to space-charge limited emission2, which may change breakdown behavior. This study reports experimental measurements for current as a function of voltage for d from 20 nm to 800 nm with various protrusion widths a to characterize field enhancement. At atmospheric pressure, Vbd decreases linearly with d down to ~200 nm for various a. For d < 200 nm, the slope of Vbd changes, possibly due to space-charge altering field emission prior to breakdown or due to reduced collisions because the electron mean free path exceeds d. At atmospheric pressure, Vbd ~ 5 V for d = 20 nm; Vbd ~ 300 V for d = 800 nm. We will also report the dependence of emission and breakdown on gap distance and pressure, and the implications on device design. |
Friday, October 8, 2021 11:15AM - 11:30AM |
UF23.00005: Asymptotic Analysis of AC Microscale Gas Breakdown Shivani Mahajan, Amanda M Loveless, Abbas Semnani, Allen L Garner Characterizing radiofrequency (RF), microwave (MW), and direct current (DC) breakdown in microscale gaps is critical for multiple applications, such as cold-plasma based limiters and protection shields, which offer an enhanced solution for protecting electronics against high power electromagnetic radiation due to their self-sustainability and reconfigurability. While prior studies considered transitions between RF and MW at macroscale1 and DC at microscale2, a full asymptotic theory linking RF, MW, and DC breakdown at microscales remains elusive. This study considers microscale MW breakdown due to field emission (FE) and avalanche using matched asymptotic analyses considering small (FE) and large (Townsend avalanche (TA)) ionization for DC and low (RF) and high (MW) frequencies to derive relevant scalings at microscale. We study the impact of gas, pressure, and frequency on the breakdown voltage parametrically, and quantify FE and TA contributions. Furthermore, we compare to preliminary results from particle-in-cell simulations and discuss relevance to device design. |
Friday, October 8, 2021 11:30AM - 11:45AM |
UF23.00006: Features of emissive cathode microturbulence Sedina Tsikata, Kentaro Hara, Thibault Dubois Cathode emitters, used to sustain plasma thruster ionization and neutralization, have been the subject of modeling and optimization studies for several decades. Though apparently simple in operation, they exhibit poorly-understood mode transitions and features such as ion acoustic turbulence [1, 2], implicated in the production of high-energy ions that lead to erosion. Gaining insight into the nature of these and other unstable modes present in both thrusters and cathodes can advance predictive discharge modeling capabilities. In recent coherent Thomson scattering studies of cathode emitters, we have identified and characterized a millimeter-scale unstable mode present in the plume of a cathode operated with a Hall thruster. The mode propagation within the region connecting cathode and thruster plumes is found to exhibit a directivity influenced by the thruster magnetic field. Spatial localization of this mode is also determined. Results from these investigations provide new information on the coupling dynamics of the cathode and thruster plumes. |
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