Nitrogen Vibrational Population Measurements in the Plenum of a Hypersonic Wind Tunnel

Montello, Aaron; Nishihara, Munetake; Rich, John Martin; Adamovich, Igor V.; Lempert, Walter R.

doi:10.2514/1.j051514

Cited by 27 publications

(19 citation statements)

References 29 publications

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“…The Nd:YAG laser (Ekspla SL-333) outputs pulses of approximately 150 psec duration, with a maximum energy of ~120 mJ/pulse at the 532 nm 2 nd harmonic wavelength. A portion of this beam is used to pump the modeless dye laser used in our previous work (Montello 2012). The remaining green light is split with a 50:50 nonpolarized beam splitter, forming the pump and probe beams.…”

Section: B Picosecond Cars Diagnostic Systemmentioning

confidence: 99%

Picosecond CARS Measurements of Nitrogen Vibrational Loading and Rotational/Translational Temperature in Nonequilibrium Discharges

Montello

Yin

Burnette

et al. 2012

43rd AIAA Plasmadynamics and Lasers Conference

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Picosecond Coherent Anti-Stokes Raman Spectroscopy is used to study vibrational energy loading and relaxation kinetics in nitrogen and air nsec pulsed non-equilibrium plasmas, in both plane-to-plane and pin-to-pin geometries. In 10 kHz repetitively pulsed plane-to-plane plasmas, up to ~50% of coupled discharge power is found to load vibrations, in good agreement with a master equation kinetic model. In the pin-to-pin geometry, ~33% of total discharge energy in a single pulse in air at 100 torr is found to couple directly to nitrogen vibrations by electron impact, also in good agreement with model predictions. Post-discharge, the total quanta in vibrational levels v=0-9 is found to increase by a factor of ~2 in air and by a factor of ~4 in nitrogen, respectively, a result in direct contrast to modeling results which predict the total number of quanta to be essentially constant until ultimately decaying by V-T relaxation and mass diffusion. More detailed comparison between experiment and model show that the vibrational distribution function (VDF) predicted by the model during, and directly after, the discharge pulse is in good agreement with that determined experimentally. However, for time delays exceeding ~10 μsec, the experimental VDF shows populations of vibrational levels v≥2 greatly exceeding modeling predictions, which predicts their monotonic decay due to net downward V-V transfer and corresponding increase in v=1 population. This is at variance with the experimental results, which show an increase in the populations of levels v=2 and v=3, reaching a maximum at t~50-100 μsec after the discharge pulse, and relatively steady v=4-9 populations at t~10-100 μsec. It is concluded that a collisional process is feeding high vibrational levels at a rate which is comparable to the rate at which population of the high levels is lost due to net downward V-V energy transfer. A likely candidate for the source of additional vibrational quanta is quenching of metastable electronic states of nitrogen to highly excited vibrational levels of the ground electronic state.

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Section: B Picosecond Cars Diagnostic Systemmentioning

confidence: 99%

Picosecond CARS Measurements of Nitrogen Vibrational Loading and Rotational/Translational Temperature in Nonequilibrium Discharges

Montello

Yin

Burnette

et al. 2012

43rd AIAA Plasmadynamics and Lasers Conference

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“…This approach has been previously used in electrically excited gasdynamic lasers, such as CO laser [70] and oxygen-iodine laser [71,72]. Recently, broadband psec vibrational CARS diagnostics has been used to measure vibrational and rotational temperatures of molecular gas mixtures excited in a plenum of a Mach 5 plasma wind tunnel by two fully overlapped electric discharges, a repetitive nanosecond pulse discharge (to sustain ionization) and transverse dc discharge (to load energy into the plasma) [73][74][75]. The 'pulser-sustainer' discharge configuration consists of orthogonal plane-to-plane electrode pairs, one of which is excited with a ~30 kV, 100 kHz repetitively pulsed 5 ns pulsed power supply, and the other with a 4.5 kV dc power supply.…”

Section: Vibrational Cars: Vibrational and Rotational Temperatures Inmentioning

confidence: 99%

“…In these experiments, the degree of vibrational nonequilibrium was controlled by injecting various 'relaxer' species, such as N 2 , O 2 , NO, H 2 , and CO 2 , into a nitrogen flow excited in the 'pulser-sustainer' discharge in the nozzle plenum. CARS measurements have been done in the plenum, free stream, and behind a bow shock in a Mach 5 plasma wind tunnel [74,75]. Figure 21 shows v = 0 and v = 1 N 2 Q-branch CARS spectra obtained in 300 Torr N 2 discharges.…”

Section: Vibrational Cars: Vibrational and Rotational Temperatures Inmentioning

confidence: 99%

Coherent anti-Stokes Raman scattering and spontaneous Raman scattering diagnostics of nonequilibrium plasmas and flows

Lempert

Adamovich

2014

J. Phys. D: Appl. Phys.

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The paper provides an overview of the use of coherent anti-Stokes Raman scattering (CARS) and spontaneous Raman scattering for diagnostics of low-temperature nonequilibrium plasmas and nonequilibrium high-enthalpy flows. A brief review of the theoretical background of CARS, four-wave mixing and Raman scattering, as well as a discussion of experimental techniques and data reduction, are included. The experimental results reviewed include measurements of vibrational level populations, rotational/translational temperature, electric fields in a quasi-steady-state and transient molecular plasmas and afterglow, in nonequilibrium expansion flows, and behind strong shock waves. Insight into the kinetics of vibrational energy transfer, energy thermalization mechanisms and dynamics of the pulse discharge development, provided by these experiments, is discussed. Availability of short pulse duration, high peak power lasers, as well as broadband dye lasers, makes possible the use of these diagnostics at relatively low pressures, potentially with a sub-nanosecond time resolution, as well as obtaining single laser shot, high signal-to-noise spectra at higher pressures. Possibilities for the development of single-shot 2D CARS imaging and spectroscopy, using picosecond and femtosecond lasers, as well as novel phase matching and detection techniques, are discussed. 45 I 2

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“…For this work, mixtures of Rhodamine 640 (R640) and Kiton Red 620 (KR620) were used. The dye laser output is centered near 604 nm, with a full width at half maximum (FWHM) of approximately 5-6 nm [20].…”

Section: Picosecond Cars Diagnostic Systemmentioning

confidence: 99%

Energy conversion in high enthalpy flows and non-equilibrium plasmas

Frederickson

Leonov

Nishihara

et al. 2015

Progress in Aerospace Sciences

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Nitrogen Vibrational Population Measurements in the Plenum of a Hypersonic Wind Tunnel

Cited by 27 publications

References 29 publications

Picosecond CARS Measurements of Nitrogen Vibrational Loading and Rotational/Translational Temperature in Nonequilibrium Discharges

Picosecond CARS Measurements of Nitrogen Vibrational Loading and Rotational/Translational Temperature in Nonequilibrium Discharges

Coherent anti-Stokes Raman scattering and spontaneous Raman scattering diagnostics of nonequilibrium plasmas and flows

Energy conversion in high enthalpy flows and non-equilibrium plasmas

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