Megan Seeley

Electron Beam Produced Atmospheric Pressure Air Plasma: Measurements of Electron Density and Optical Observations

‡An apparatus to investigate the generation of atmospheric pressure plasma by means of an energetic electron-beam source has been constructed. Initial data on the time history of the electron and ozone concentrations for a pulsed electron-beam source over a limited pressure range are presented. An RF diagnostic system is described that infers the electron density from an absorption and phase shift measurement at X-band. Ozone concentration is measured using an ozone absorption line at 254 nm and a multi-pass White cell. An optical emission spectrum from electron-beam excited air is presented. The instrumentation used in these measurements is described in detail. Results are compared to theoretical predictions based on an air-chemistry simulation code.

Application of Tunable Diode Laser Spectroscopy for Time Resolved Measurements in Electron-Beam Produced Plasma

Summary form only given. Tunable diode laser absorption spectroscopy was used for the investigation of the temporal evolution of neutral species concentrations in air plasma, which is produced by a 100 keV electron beam at pressures from 760 Torr down to 1 Torr. The spectrometer applied is based on a set of fiber-coupled distributed feedback lasers. Absorption spectra of species (H2O, OH, CO2, CO, NO and N2O) in near infrared (1.3 -1.8 nm) were recorded with resolution ~ 1 ms. Temperatures and absolute values for the concentrations were found over a broad dynamic range. Possibilities for increasing the signal-to-noise ratio are outlined.

Chemical Composition of Electron Beam Produced Air Plasma by Means of Tunable Diode Laser Spectroscopy and Numerical Simulation

Summary form only given. The temporal evolution of neutral species concentrations of H2O, OH, CO2, CO, NO and N2O were investigated in air plasma produced by a 100 keV electron beam from atmospheric pressure down to ~ 1 mTorr. The investigation involves both experimental methods and the output of an air-chemistry simulation program. Tunable diode laser absorption spectroscopy was used to provide information on the temperatures and absolute values for the concentrations over a broad dynamic range. The spectrometer utilizes a set of fiber-coupled distributed feedback lasers, operating in the near-infrared. Absorption spectra were obtained with the temporal resolution of 1 ms or better.

Electron-Beam Generated Air Plasma: Sensors to Quantify Beam Current and Electron Density

Summary form only given. Sensors to measure the electron beam flux generated by an electron source operating at 100 keV are described. Electrons propagate into an air-plasma test cell through a transmission-window foil. A model for current stopped by the foil is discussed and compared to measurements with sensors within the test cell that is filled with air at a pressure between 1 mtorr and 760 torr. Optical emissions at 337.1 nm originate as a byproduct of electron-beam impact ionization provide an additional sensor. The N2(C3Piu-B3Pig) emission detected by an optical fiber is calibrated to the current propagating through the transmission window. The calibrated fiber can then be moved within the test cell to quantify energy deposition. An air chemistry program is used to relate energy deposition to the rate of electron-ion pair production per cm3. The methodology to process data and reduce energy deposition to electron density concentration is detailed.

Electron-Beam Generated Air Plasma: Beam Current and Electron Density Distributions

Summary form only given. Plasma generated by means of electron impact ionization of air with a 100-keV electron source involves porting the electron beam from vacuum to an air-plasma test cell filled with air at pressures between 1 mTorr and 760 Torr. Energetic electrons propagate through a thin foil transmission window that separates the vacuum in the electron source from air in the test cell. Current stopped in the transmission-window foil is used to quantify the beam flux incident on the foil and additional calibrations of current measurements within the test cell quantify electron-beam flux at various points in the test cell. Use of an air chemistry program allows the estimation of the rate of electron-ion pair production per cm3 from energy deposition measurements. From this rate the electron density is derived. General results for several pressures will be presented. Data related to using 337.1 nm emissions from the nitrogen second positive band N2(C3Piu -B3Pig) suggests an alternative optical means of estimating electron density in air.

Electron-beam produced air plasma: rf and optical diagnostics

Summary form only given. Diagnostics and results for experiments with a 100-keV electron beam used to ionize air are presented. Measurements were conducted with air at pressures in the range of 1 mtorr to 760 torr. A 1-mill aluminum transmission window separates the vacuum of the electron source from the air test cell. RF diagnostics comprise a system for simultaneous amplitude and phase measurement at 10 GHz during a 1-ms electron-beam pulse. Optical diagnostics utilized a Whites cell for ozone detection and a spectrometer to monitor N2 + and N4 + emissions. These emissions help to quantify the electron flux that emerges from the transmission window and at other locations in the test cell

Electron-beam produced air plasma: optical and electrical observations

Summary form only given. A 100 keV electron beam source is used to generate plasma in air at pressures from 760 torr to 1 mtorr. Air with normal atmospheric constituents is used as a target gas. RF diagnostics are used to measure electron density with microsecond resolution during a 1-ms electron-beam pulse. Simultaneous phase and amplitude measurements provide a means of measuring electron concentration, electron momentum-transfer collision rate and inferring an electron temperature. Optical measurements of ozone production via a Whites cell absorption technique are discussed as well as N2 + and N4 + optical emissions. The N2 + and N4 + emissions provide a means of monitoring volumetric ionization and are included in the overall calibration of beam current passing through an aluminum transmission window that separates the vacuum of the electron source from the air-plasma test cell. RF techniques and current results will be discussed