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

Abstract

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 pressuremore » were found to agree well with published numerical simulations.« less

Authors:
ORCiD logo [1];  [1];  [1];  [1]; ORCiD logo [1]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); US Air Force Office of Scientific Research (AFOSR)
OSTI Identifier:
1467854
Alternate Identifier(s):
OSTI ID: 1287753
Grant/Contract Number:  
FC02-93ER54186; FA9550-15-1-0058
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 8; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; microwave breakdown; gas discharges; radiofrequency discharges; plasma diagnostics; microwave sources; visible light; microwave spectroscopy; electric fields; density measurement

Citation Formats

Schaub, S. C., Hummelt, J. S., Guss, W. C., Shapiro, M. A., and Temkin, R. J.. Electron density and gas density measurements in a millimeter-wave discharge. United States: N. p., 2016. Web. doi:10.1063/1.4959171.
Schaub, S. C., Hummelt, J. S., Guss, W. C., Shapiro, M. A., & Temkin, R. J.. Electron density and gas density measurements in a millimeter-wave discharge. United States. doi:10.1063/1.4959171.
Schaub, S. C., Hummelt, J. S., Guss, W. C., Shapiro, M. A., and Temkin, R. J.. Tue . "Electron density and gas density measurements in a millimeter-wave discharge". United States. doi:10.1063/1.4959171. https://www.osti.gov/servlets/purl/1467854.
@article{osti_1467854,
title = {Electron density and gas density measurements in a millimeter-wave discharge},
author = {Schaub, S. C. and Hummelt, J. S. and Guss, W. C. and Shapiro, M. A. and Temkin, R. J.},
abstractNote = {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.},
doi = {10.1063/1.4959171},
journal = {Physics of Plasmas},
number = 8,
volume = 23,
place = {United States},
year = {Tue Aug 09 00:00:00 EDT 2016},
month = {Tue Aug 09 00:00:00 EDT 2016}
}

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Cited by: 3 works
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