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Title: Electron density and gas density measurements in a millimeter-wave discharge

Journal Article · · Physics of Plasmas
DOI:https://doi.org/10.1063/1.4959171· OSTI ID:1467854

Here, electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3 μs long at 110 GHz and 2.2 μs long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density, where the collisional plasma frequency is equal to the microwave frequency, over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial structure and temporal dynamics of gas heating at atmospheric pressure were found to agree well with published numerical simulations.

Research Organization:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Fusion Energy Sciences (FES); US Air Force Office of Scientific Research (AFOSR)
Grant/Contract Number:
FC02-93ER54186; FA9550-15-1-0058
OSTI ID:
1467854
Alternate ID(s):
OSTI ID: 1287753
Journal Information:
Physics of Plasmas, Vol. 23, Issue 8; ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 33 works
Citation information provided by
Web of Science

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Cited By (7)

Plasma fluid modeling of microwave streamers: Approximations and accuracy journal November 2017
Effects of pressure and incident field on visible light intensity from microwave nitrogen breakdown journal February 2018
Numerical analysis of plasma structure observed in atmospheric millimeter-wave discharge at under-critical intensity journal July 2018
Electron density measurement of a lightning stepped leader by oxygen spectral lines journal August 2018
Discharge from a high-intensity millimeter wave beam and its application to propulsion journal January 2018
Physics and application of gas discharge in millimeter wave beams journal October 2018
Space and time evolution of light emitted from microwave nitrogen breakdown journal August 2019