Plasma Diagnostics for High Power Microwaves
Abstract
The goal of this project is to develop state-of-the-art optical diagnostics to probe the generation of plasmas in high power microwave (HPM) systems. The proposed research aims to understand the coupling between HPMs and plasmas including how plasmas are generated in HPM sources, how their dielectric properties vary across scales of length and time, and how they can programmatically switch, steer, and waveguide HPMs in dynamic environments (i.e., in free space away from HPM sources). These research initiatives will inform strategies to either detect and mitigate the formation of unwanted plasmas in HPM sources or tailor plasma properties in free space to enable the tunable propagation of HPMs. This project shall incorporate novel diagnostic capabilities to explore these scientific challenges and enable a new class of HPM technologies that limit pulse broadening and feature shorter pulse widths, frequency agility, broadband tunability, higher peak powers, higher operational frequencies (including expansion into the X, L, Ku, and Ka bands), and more compact size. Open questions this equipment will directly probe include: 1) Can the generation of plasmas be detected locally in HPM systems using diagnostics that are independent of microwave propagation? 2) How does the presence of impurities (e.g., from desorption, dielectric ablation, etc.) and boundary effects influence the generation of plasmas in HPM systems? 3) Can plasmas be used to waveguide, steer, and programmatically control the propagation of HPMs in free space? Based on the topic of a proposed ONR YIP, several instruments are requested to design a model system to explore microwave breakdown, allow time- and spatially-resolved measurements of plasma dielectric properties with MHz repetition rates, and develop enhanced spectroscopic access to plasma-surface interactions in microwave resonators. The combined facility will be used to provide unprecedented spectroscopic insight into HPM systems, the fundamental processes that generate plasmas, and how the dielectric properties of plasmas can be tuned to enable control over HPM propagation. More broadly, the proposed facility will enhance existing DoD projects that focus on developing the next generation HPM sources and uncover strategies where plasmas can engineer precision in HPM technologies. The proposed HPM diagnostic facility will offer the following new capabilities: 1) Simultaneous amplitude and phase measurements over a frequency range spanning 100 GHz 2 THz with a time resolution of ~ 800 fs and repetition rate > 1 MHz. 2) Spatiotemporal mapping of emission and absorption spectroscopy with repetition rates > 1 MHz. 3) Modular microwave resonator that allows the probing of plasma properties and study of variable gas properties, plasma-surface interactions, and microwave interactions. With the support of DoD grants and startup funds, we have acquired a femtosecond laser and spectrometer to enable THz diagnostics and probe the coupling between neutral species and free electrons in determining the dielectric response of plasmas. This existing facility will be further enhanced by adding several components, including a streak camera, broadly tunable CW Ti:sapphire laser, and a microwave signal generator/amplifier to create plasmas in microwave resonators. These components will be used to build time- and spatially-resolved optical diagnostics to probe plasmas in model HPM systems and enable the following measurements: 1) Spatial and temporal mapping of the free electron density and dielectric properties of plasmas using chirped THz spectroscopy and Doppler-free absorption spectroscopy. 2) In-situ probing of dielectric ablation (i.e., solid) and breakdown using time-resolved emission and absorption spectroscopy. 3) Dynamic waveguiding, steering, and modulation of HPMs by engineering the dispersion characteristics of plasmas in a waveguide system
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 06, 2023
- Source ID
- N000142312282
Entities
People
- Thomas C Underwood
Organizations
- Office of Naval Research
- United States Navy
- University of Texas at Austin