Computer Science
Scientific paper
Sep 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.........2l&link_type=abstract
Thesis (PhD). THE OHIO STATE UNIVERSITY, Source DAI-B 65/03, p. 1365, Sep 2004, 283 pages.
Computer Science
Scientific paper
A new trans-rotational temperature diagnostic with ±50K accuracy has been developed for use in nonequilibrium, low temperature, monatomic gases seeded with carbon monoxide (CO). The scheme utilizes single- photon laser induced fluorescence (LIF) of CO under vibrationally-excited conditions in which single-photon transitions from the CO X1Σ + ground electronic state to upper electronic A1Π or D'1Σ+ states become accessible to a tunable, narrowband ArF excimer laser at 193 nm. Two vibrationally excited environments in which the chemistry is well understood were used as a testbed; an optically-pumped 3% CO/Ar plasma at 100 torr and a 4% CO/He d.c. glow discharge at 8 torr. The LIF saturation limit was experimentally investigated and diagnostic advantages of either regime discussed. For the optically-pumped CO/Ar plasma, a spatially-averaged LIF temperature of 536 ± 103 K (2σ) was obtained from rotationally resolved X 1Σ+ (v' = 20) → D '1Σ+ (v' = 2) LIF excitation spectra. Temperature measurements pumping the X 1Σ+ (v' = 7) → A 1Π (v' = 1) 4th Positive (528 ± 51 K) were also found to compare well with line-of-sight Fourier Transform-InfraRed (FT-IR) emission measurements (536 ± 10 K). Spatially averaged FT- IR spectroscopy of the CO 1st overtone was used to verify that an adequate vibrational population (˜0.1%) existed within the positive column of the CO/He d.c. glow discharge. The A-X (7,1) transition was pumped and subsequent (8,1) emission at 200.8 nm collected. The resulting rotational spectral peaks were assigned and a subset used to determine a spatially averaged rotational temperature of 432 ± 44 K on the discharge centerline. This was found to be in good agreement with FT-IR spectroscopy measurements (395 ± 10 K). As a prelude to Planar-LIF (PLIF) temperature measurements, vibrationally-resolved emission from laser excitation of various rotational lines within the A-X and D'-X bands were used to investigate spectral interferences. This information was used to determine that a simple aqueous organic filter (urea) in the A-X case, or commercial glass filter (UG-11) in the D '-X case, are adequate for rejecting elastically-scattered radiation and extraneous ro-vibrational bands during PLIF imaging. Single-shot and accumulated PLIF images were obtained for the 3% CO/Ar optically pumped plasma. Using a Two-Line ratio method, A-X band Q-branch images were used to spatially resolve the trans-rotational temperature. While the single-shot precision, determined from four trials, was ≈±200 K (2σ), the accuracy was ≈±100 K. The accuracy of PLIF results implied a systematic error which may be attributed to the ICCD camera having a slightly nonlinear response at the 50% gain setting.
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