High energy-intensity atomic oxygen beam source for low earth orbit materials degradation studies
Abstract
A high intensity (10 to the 19th O-atoms/s-sr) high energy (5 eV) source of oxygen atoms has been developed that produces a total fluence of 10 to the 22d O-atoms/sq cm in less than 100 hours of continuous operation at a distance of 15 cm from the source. The source employs a CW CO2 laser sustained discharge to form a high temperature (15,000 K) plasma in the throat of a 0.3-mm diameter nozzle using 3 to 8 atmospheres of rare gas/O2 mixtures. Visible and infrared photon flux levels of 1 watt/sq cm have been measured 15 cm downstream of the source while vacuum UV (VUV) fluxes are comparable to that measured in low earth orbit. The reactions of atomic oxygen with kapton, Teflon, silver, and various coatings have been studied. The oxidation of kapton (reaction efficiency = 3x10 to the -24 cm + or - 50 percent) has an activation energy of 0.8 Kcal/mole over the temperature range of 25 to 100 C at a beam energy of 1.5 eV and produces low molecular weight gas phase reaction products (H2O, NO, CO2). Teflon reacts with approx 0.1 to 0.2 efficiency to that of kapton at 25 C and both surfaces show a ruglike texture after exposure to the O-atom beam. Angular scattering distribution measurements of O-atoms show a near cosine distribution from reactive surfaces indicating complete accommodation of the translational energy with the surface while a nonreactive surface (nickel oxide) shows specular-like scattering with 50 percent accommodation of the translational energy with the surface. A technique for simple on orbit chemical experiments using resistance measurements of coated silver strips is described.
- Publication:
-
Presented at the 16th International Symposium on Rarefied Gas Dynamics
- Pub Date:
- 1988
- Bibcode:
- 1988rgd..symp.....C
- Keywords:
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- Degradation;
- Earth Orbital Environments;
- Oxygen Atoms;
- Particle Beams;
- Reentry Vehicles;
- Carbon Dioxide Lasers;
- Energy Transfer;
- Silver;
- Nuclear and High-Energy Physics