Hyperthermal atomic oxygen source for near-space simulation experiments
- Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, Massachusetts 01731 (United States)
- Propulsion Directorate, Air Force Research Laboratory, Edwards AFB, California 93524 (United States)
- Spectral Sciences, Inc., 4 Fourth Ave., Burlington, Massachusetts 01803 (United States)
A hyperthermal atomic oxygen (AO) beam facility has been developed to investigate the collisions of high-velocity AO atoms with vapor-phase counterflow. Application of 4.5 kW, 2.4 GHz microwave power in the source chamber creates a continuous discharge in flowing O{sub 2} gas. The O{sub 2} feedstock is introduced into the source chamber in a vortex flow to constrain the plasma to the center region, with the chamber geometry promoting resonant excitation of the TM{sub 011} mode to localize the energy deposition in the vicinity of the aluminum nitride (AlN) expansion nozzle. The approximately 3500 K environment serves to dissociate the O{sub 2}, resulting in an effluent consisting of 40% AO by number density. Downstream of the nozzle, a silicon carbide (SiC) skimmer selects the center portion of the discharge effluent, prior to the expansion reaching the first shock front and rethermalizing, creating a beam with a derived 2.5 km s{sup -1} velocity. Differential pumping of the skimmer chamber, an optional intermediate chamber and reaction chamber maintains a reaction chamber pressure in the mid-10{sup -6} to mid-10{sup -5} Torr range. The beam has been characterized with regard to total AO beam flux, O{sub 2} dissociation fraction, and AO spatial profile using time-of-flight mass spectrometric and Kapton-H erosion measurements. A series of reactions AO+C{sub n}H{sub 2n} (n=2-4) has been studied under single-collision conditions using mass spectrometric product detection, and at higher background pressure detecting dispersed IR emissions from primary and secondary products using a step-scan Michelson interferometer. In a more recent AO crossed-beam experiment, number densities and predicted IR emission intensities have been modeled using the direct simulation Monte Carlo technique. The results have been used to guide the experimental conditions. IR emission intensity predictions are compared to detected signal levels to estimate absolute reaction cross sections.
- OSTI ID:
- 22051032
- Journal Information:
- Review of Scientific Instruments, Vol. 80, Issue 9; Other Information: (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ALUMINIUM NITRIDES
ATOMIC BEAMS
ATOM-MOLECULE COLLISIONS
COLLIDING BEAMS
CROSS SECTIONS
DENSITY
EXCITATION
INFRARED SPECTRA
MASS SPECTROSCOPY
MICHELSON INTERFEROMETER
MICROWAVE RADIATION
MONTE CARLO METHOD
NOZZLES
OXYGEN
PLASMA
SIGNALS
SILICON CARBIDES
TIME-OF-FLIGHT METHOD
VAPORS
VORTEX FLOW