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

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 8; Related Information: CHORUS Timestamp: 2016-12-26 03:07:01; Journal ID: ISSN 1070-664X
American Institute of Physics
Country of Publication:
United States

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. 2016. "Electron density and gas density measurements in a millimeter-wave discharge". United States. doi:10.1063/1.4959171.
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 = {},
doi = {10.1063/1.4959171},
journal = {Physics of Plasmas},
number = 8,
volume = 23,
place = {United States},
year = 2016,
month = 8

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4959171

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Cited by: 2works
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  • 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 tomore » 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.« less
  • A millimeter-wave reflectometry system for electron density profile and fluctuation measurements is being developed and installed on the National Spherical Torus Experiment. The initial frequency coverage will be in the bands 12--18, 20--32, and 33--50 GHz, provided by frequency-tunable solid-state sources. These frequencies correspond to O-mode cutoff densities ranging from 1.8x10{sup 12} to 3.1x10{sup 13}cm{sup -3}, which will span both the plasma core ({rho}=r/a<0.8) and edge ({rho}>0.8) regions. Operated as a broadband swept-frequency (frequency-modulated continuous-wave) reflectometer, the diagnostic is expected to provide routine (shot-to-shot) time- ({<=}50 {mu}s) and spatially resolved ({approx}1 cm) density profiles. The previous hardware can be easilymore » reconfigured as a fixed-frequency reflectometer for density fluctuation measurements. The combination of measurements would be valuable for studying phenomena such as possible L- to H-mode transitions and edge-localized modes.« less
  • We present experimental results on measuring the emittance of short-pulsed (≤100 μs) high-current (80–100 mA) ion beams of heavy gases (Nitrogen, Argon) formed from a dense plasma of an ECR source of multiply charged ions (MCI) with quasi-gas-dynamic mode of plasma confinement in a magnetic trap of simple mirror configuration. The discharge was created by a high-power (90 kW) pulsed radiation of a 37.5-GHz gyrotron. The normalized emittance of generated ion beams of 100 mA current was (1.2–1.3) π mm mrad (70% of ions in the beams). Comparing these results with those obtained using a cusp magnetic trap, it was concluded thatmore » the structure of the trap magnetic field lines does not exert a decisive influence on the emittance of ion beams in the gas-dynamic ECR source of MCI.« less
  • Modified FM--CW radar techniques using swept millimeter--wave oscillators are useful for determining when a particular density has been reached in a plasma. Narrowband measurements on the Princeton Large Torus (PLT) demonstrate the suitability of these techniques for controlling high-power auxiliary plasma heating systems. Broadband measurements using these same techniques are proposed, by which the density profile could be determined.
  • A simple, low-cost millimeter-wave interferometer has been developed to measure the electron density of laboratory-type plasmas with densities nless than or equal to2 x 10/sup 12/ cm/sup -3/ . Two 38.0-GHz Gunn oscillators, whose oscillation frequencies are offset by 40 MHz, are used in a heterodyne configuration. The high intermediate frequency allows the use of inexpensive, free-running mechanically tuned Gunn oscillators and permits this system to be utilized in the study of density fluctuations. A quadrature phase comparator is used to give simultaneously both the sine and cosine components of the plasma interference signal. The phase noise of the systemmore » is found to be <0.1/sup 0/, with a settling time <100 ns. The system is to be used on a laboratory plasma to look at both the integrated electron density and the level of density fluctuations.« less