Elucidating Plasma Formation Near Dielectric Interfaces in High Power Microwave Systems (23-000003500)
Abstract
This proposal seeks to probe the mechanism that leads to microwave breakdown in high power microwave (HPM) systems. Unlike conventional studies that focus on bulk ionization and microwave attenuation on a system level, we focus on exploring how dielectric interfaces influence the initiation and threshold for plasma production on a component level. These efforts aim to develop predictive insight into the conditions that lead to plasma production in HPM systems well before microwave attenuation can be measured. This includes understanding the coupling between dielectric surfaces (e.g., charge distributions, etc.), gas dynamics (e.g., outgassing, etc.), and electromagnetic fields that leads to microwave breakdown.The approach of this proposal focuses on developing insight into where,why, and how plasmas forms in HPM systems. We develop a modular resonant cavity that uses microwave resonance near dielectric interfaces to induce field strengths that are representative of HPM systems across a range of frequencies. A modular design enables variation in dielectric materials and diagnostic access to probe dynamic plasma-solid interfaces during microwave pulses. Optical access enables operando characterization of plasma breakdown using a suite of novel diagnostics including single-shot THz time-domain spectroscopy, emission spectroscopy, absorption spectroscopy, and laser polarimetry to quantify the plasma, gaseous (i.e., outgassing, ablation), and interfacial dielectric properties respectively. These diagnostics, and the novel resonator geometry, will inform how interfaces can be designed in HPM systems to limit the formation of unwanted plasma and broaden the operating regime of HPM sources. This has the potential to improve the predictability of HPM systems and enable technologies with:#Higher pulse energies by identifying, understanding, and mechanistically limiting unwanted plasma formation in HPM sources.#Higher frequencies by controlling plasma formation near dielectric boundaries using tunable interfacial chemistry and surface roughness.#Improved predictability by testing andvalidating design strategies to limit unwanted plasma production.#Improved performance probing by developing diagnostic tools to detect localized plasma formation before microwave attenuation occurs.The proposed work makes use of synergistic equipment and state-of-the-art diagnostics that were awarded through a recent ONR DURIP, #Plasma Diagnostics for High Power Microwaves#. Insights and diagnostic capabilities outlined in this proposal can be applied to broader programmatic interests including:#Dielectric Breakdown: Mechanistic insight into dielectric breakdown and surface flashover (i.e., measuring surface charging, ablation, plasma production) within pulsed power systems (in collaboration with Prof. David Wetz, see letter of support). #Microwave Breakdown: Quantify the threshold for microwave breakdown and plasma properties in operational HPM sources. Validate mechanistic simulations using experimental measurement of interfacial properties (i.e., surface charging, rate of outgassing, etc.) during microwave breakdown (in collaboration with Dr. Salvador Portillo and Prof. Ravindra Joshi, see letters of support). Approved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 12, 2023
- Source ID
- N000142312306
Entities
People
- Thomas C Underwood
Organizations
- Office of Naval Research
- United States Navy
- University of Texas at Austin