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Thomson Scattering Density Calibration by Rayleigh and Rotational Raman Scattering on NSTX

Description: The multi-point Thomson scattering (MPTS) diagnostic measures the profiles of the electron temperature Te(R) and density ne(R) on the horizontal midplane of NSTX. Normal operation makes use of Rayleigh scattering in nitrogen or argon to derive the density profile. While the Rayleigh scattering ne(R) calibration has been validated by comparison with other density measurements and through its correlation with plasma phenomena, it does require dedicated detectors at the laser wavelength in this filter polychromator based diagnostic. The presence of dust and/or stray laser light precludes routine use of these dedicated spectral channels for Thomson scattering measurement. Hence it is of interest to investigate the use of Raman scattering in nitrogen for the purpose of density calibration, since it could free up detection equipment, which could then be used for the instrumentation of additional radial channels. In this paper the viewing optics "geometrical factor" profiles obtained from Rayleigh and Raman scattering are compared. While both techniques agree nominally, residual effects on the order of 10% remain and will be discussed.
Date: July 16, 2008
Creator: LeBlanc, B.P.
Partner: UNT Libraries Government Documents Department

Dynamics of the flame flowfields in a low-swirl burner

Description: The concept of using low swirl to stabilize lean premixed turbulent flame was introduced in 1992. Since then, the low-swirl burner (LSB) has become a useful laboratory tool for the study of detailed flame structures as well as turbulent burning speeds. Its main attribute is that the flame is freely propagating and is locally normal to the turbulent approach flow (Figure 1). Therefore, the turbulent flame brush is not influence by physical boundaries. The capability of LSB to support very lean flames and very turbulent flames [1, 2] was further exploited in recent studies to test the validity of the flame regime concept. Using 2D imaging diagnostics (e.g. planar laser induced fluorescence, PLIF, and planar laser induced Rayleigh scattering) our analysis showed that the wrinkled flame regime to be valid at a turbulence intensity level much higher than previously thought [3-5]. This provided experimental verification of a new 'thin reaction zone' regime for the Kalovitz number range of 1 < Ka < 10 (Ka = (u{prime}/s{sub L}){sup 3/2} (l{sub x}/d{sub L}){sup 1/2}) proposed by Peters. Due to its freely propagating nature, modeling and simulations of LSB flames are non-trivial. The flame position cannot be specified a priori because it is coupled to the turbulent flowfield and the turbulent flame speed may be required as input. This has not been a significant issue when treating the LSB flame as a close approximation to a 1D premixed turbulent flame. However, to support the development of more robust 3D simulation methods, accurate information on the flowfield dynamics in particular those at the burner exit and the interactions between the core and swirl air flows becomes important. In the past, velocity measurements in LSB have concentrated on collecting information along the centerline. The objective of this investigation is to conduct a detailed study using ...
Date: July 1, 2003
Creator: Cheng, Robert; Johnson, Matthew R. & Cheng, Robert K.
Partner: UNT Libraries Government Documents Department

"Quadrupoled" materials for second-order nonlinear optics

Description: We describe a new approach to second-order nonlinear optical materials, namely quadrupoling. This approach is valid in the regime of Kleinman (full permutation) symmetry breaking, and thus requires a two- or three dimensional microscopic nonlinearity at wavelengths away from material resonances. This {open_quotes}quadrupolar{close_quotes} nonlinearity arises from the second rank pseudotensor of the rotationally invariant representation of the second-order nonlinear optical tensor. We have experimentally investigated candidate molecules comprised of chiral camphorquinone derivatives by measuring the scalar invariant associated with the rank two pseudotensor using hyper-Rayleigh scattering. We have found sizable scalar figures of merit for several compounds using light for which the second harmonic wavelengths are greater than 100 nm longer than the absorption peak location. At these wavelengths, the quadrupolar scalar is as large as the polar (EFISH) scalar of p-nitroaniline. Prospects for applications are discussed.
Date: October 1, 1997
Creator: Hubbard, S.F.; Petschek, R.G. & Singer, K.D.
Partner: UNT Libraries Government Documents Department

The Development of Cavity Ringdown Spectroscopy as a Sensitive Continuous Emission Monitor for Metals

Description: The aim of this study is to evaluate cavity ringdown spectroscopy (CRDS) as an ultra-sensitive technique for trace analysis of metals. Potential applications of CRDS meeting the Department of Energy needs include: Mercury Continuous Emission Monitor Multi-Metal Emissions Monitor Radionuclide Detector and Monitor CRDS is based upon the measurement of the rate of light absorption in a closed optical cavity. A laser pulse is injected into a stable optical cavity through one of the cavity mirrors. This light pulse is trapped between the mirror surfaces and decays exponentially over time at a rate determined by the round trip losses within the cavity. When used for trace analysis, the primary loss mechanisms governing the decay time are mirror reflectivity losses, atomic absorption from the sample, and Rayleigh scattering from air in the cavity. The decay time is given by t= d c 1- R ( )+ als + bd [ ] (1) where d is the cavity length, R is the reflectivity of the cavity mirrors, a is the familiar Beer's Law absorption coefficient of a sample in the cavity, ls is the length of the optical path through the sample (i.e., approximately the graphite furnace length), b is the wavelength-dependent Rayleigh scattering attenuation coefficient, and c is the speed of light. Thus, variations in a caused by changes in the sample concentration are reflected in the ringdown time. As the sample concentration increases (i.e., a increases), the ringdown time decreases yielding an absolute measurement for a. With the use of suitable mirrors, it is possible to achieve thousands of passes through the sample resulting in a significant increase in sensitivity. An additional benefit is that it is not subject to collisional quenching, the branching of fluorescence emission into multiple transitions, and the ability to detect only a fraction of the ...
Date: June 1, 1999
Creator: Miller, George P.
Partner: UNT Libraries Government Documents Department

Upgraded Calibrations of the Thomson System at DIII-D

Description: The DIII-D Thomson system measures electron density and temperature with eight pulsed ND:YAG lasers along three paths through the plasma vessel. The components of the Thomson system are absolutely calibrated so the measurements can be combined into a single profile from a normalized plasma radius ({rho}) of about 0.1 to the edge of the plasma. A monochromator calibration and opto-electronic calibration measure the detectors' absolute sensitivity to background and pulsed light. A Rayleigh scattering calibration and transmission calibrations measure the transmission of light to the detectors. The calibration systems are being upgraded to reduce the effect of systematic errors on the temperature and density measurements. The systematic errors can be checked by a comparison of overlapping channels and estimated from fits to the profiles. The contributions of the systematic uncertainties relative to the statistical uncertainties of the measurement are discussed through simulations and experimental data.
Date: August 1, 2000
Creator: Bray, B.; Hsieh, C.; Carlstrom, T.N. & Makariou, C.C.
Partner: UNT Libraries Government Documents Department

Implementation of a Rayleigh scattering optical depth parameterization

Description: A new procedure for calculating Rayleigh scattering cross sections and optical depths has been developed for use in the solar radiation transfer model of the LLNL Chemistry-Radiation-Transport Models. This procedure replaces the previous method for determining the optical depths in which the parameterization of Hansen and Travis (1974) was used to generate a table of optical depths for wavelengths ranging from 0.135 {mu}m to 0.729 {mu}m; the table was then placed directly in the shortwave package. Hansen and Travis calculate Rayleigh scattering optical depths, {tau}, using {tau} = 0.08569{lambda}{sup {minus}4} (1 + 0.0113{lambda}{sup {minus}2} + 0.00013{lambda}{sup {minus}4}) where {lambda} is wavelength in {mu}m and the standard surface pressure is 1013 mB. The new scheme uses instead the parameterization of Nicolet (1984) to find the Rayleigh scattering cross sections for an arbitrary set of wavelength bins, and from these cross sections, determines the optical depths. The Nicolet parameterization was recommended by the WMO (1986), and calculates Rayleigh scattering cross sections using O{sub RS} = 4.02 {times} 10{sup {minus}28}/{lambda}{sup {minus}}(4 + x) where x=0.389{lambda} + 0.09426/{lambda}-0.3328 for {lambda} < 0.55 {mu}m and x=0.04 for {lambda} > 0.55 {mu}m.
Date: October 1, 1994
Creator: Kemball-Cook, S.R. & Grant, K.E.
Partner: UNT Libraries Government Documents Department

Multiscalar measurements of turbulence-chemistry interactions in nonpremixed flames

Description: Selected results from experiments conducted over the past several years involving simultaneous multiscalar point measurements in turbulent nonpremixed flames are reviewed in this paper. In these experiments, spontaneous Raman scattering and Rayleigh scattering measurements of the major species and temperature were combined with laser-induced fluorescence measurements of minor species. The most important feature of these experiments is that they provide detailed data on the instantaneous relationships among species concentration, temperature, and derived scalar quantities that reflect the state of mixing or the progress of reaction. The data allow quantitative comparisons of the thermochemical states in turbulent flames with those in idealized representations, such as steady strained laminar flames, perfectly stirred reactors, or adiabatic equilibrium. The data may also be compared with results (measured or calculated) from unsteady laminar flames and from direct numerical simulations (DNS) of turbulent reacting flows. such comparisons provide insights into the fundamental nature of turbulence-chemistry interactions, and they allow one to examine the validity of some of the basic assumptions that turbulent combustion models are built upon. Furthermore, these data allow quantitative evaluations of the predictive accuracy, strengths, and limitations of a wide variety of combustions models.
Date: December 1, 1995
Creator: Barlow, R.S.
Partner: UNT Libraries Government Documents Department

Precise tests of x-ray scattering theories in the Compton regime.

Description: The authors report two experiments intended to test the accuracy of state-of-the-art theoretical predictions for x-ray scattering from low-Z atoms. The first one deals with the differential x-ray scattering cross sections in Ne and He from 11-22 keV and the Ne Compton-to-Rayleigh scattering ratio in this energy range. It was found that, in order to be consistent with the experimental results, an accurate description at low Z must include nonlocal exchange, electron correlation, and dynamic effects. The second experiment concerns the ratio of helium double-to-single ionization for Compton scattering in the 8-28 keV energy range where published experimental and theoretical results so far fail to give a consistent picture. The progress of the experiment and the data analysis is reported.
Date: January 15, 1999
Creator: Dunford, R. W.; Gemmell, D. S.; Kanter, E. P.; Krassig, B.; Southworth, S. H. & Young, L.
Partner: UNT Libraries Government Documents Department

The Development of Cavity Ringdown Spectroscopy as a Sensitive Continuous Emission Monitor for Metals

Description: The aim of this study is to evaluate cavity ringdown spectroscopy (CRDS) as an ultrasensitive technique for trace analysis of metals. Potential applications of CRDS to meet stated Department of Energy needs include: Mercury Continuous Emission Monitor Multi-Metal Emissions Monitor Radionuclide Detector and Monitor A full description of the technique can be found in Ref. 1. Briefly, CRDS is based upon the measurement of the rate of light absorption in a closed optical cavity. PMT Cavity Mirror Sample Cavity Mirror Laser Pulse A laser pulse is injected into a stable optical cavity through one of the cavity mirrors. This light pulse is trapped between the mirror surfaces and decays exponentially over time at a rate determined by the round trip losses within the cavity. When used for trace analysis, the primary loss mechanisms governing the decay time are mirror reflectivity losses, atomic absorption from the sample, and Rayleigh scattering from air in the cavity. The decay time is given by t = d c 1- R ( ) +als + bd [ ] (1) where d is the cavity length, R is the reflectivity of the cavity mirrors, a is the familiar Beer's Law absorption coefficient of a sample in the cavity, ls is the length of the optical path through the sample (i.e., approximately the graphite furnace length), b is the wavelength-dependent Rayleigh scattering attenuation coefficient, and c is the speed of light. Thus, variations in a caused by changes in the sample concentration are reflected in the ringdown time. As the sample concentration increases (i.e., a increases), the ringdown time decreases yielding an absolute measurement for a. With the use of suitable mirrors, it is possible to achieve thousands of passes through the sample. This results in an effective path length reaching into the kilometers and a corresponding ...
Date: June 1, 2000
Creator: Miller, George P.
Partner: UNT Libraries Government Documents Department

Filtered Rayleigh scattering diagnostic for multi-parameter thermal-fluids measurements : LDRD final report.

Description: Simulation-based life-cycle-engineering and the ASCI program have resulted in models of unprecedented size and fidelity. The validation of these models requires high-resolution, multi-parameter diagnostics. Within the thermal-fluids disciplines, the need for detailed, high-fidelity measurements exceeds the limits of current engineering sciences capabilities and severely tests the state of the art. The focus of this LDRD is the development and application of filtered Rayleigh scattering (FRS) for high-resolution, nonintrusive measurement of gas-phase velocity and temperature. With FRS, the flow is laser-illuminated and Rayleigh scattering from naturally occurring sources is detected through a molecular filter. The filtered transmission may be interpreted to yield point or planar measurements of three-component velocities and/or thermodynamic state. Different experimental configurations may be employed to obtain compromises between spatial resolution, time resolution, and the quantity of simultaneously measured flow variables. In this report, we present the results of a three-year LDRD-funded effort to develop FRS combustion thermometry and Aerosciences velocity measurement systems. The working principles and details of our FRS opto-electronic system are presented in detail. For combustion thermometry we present 2-D, spatially correlated FRS results from nonsooting premixed and diffusion flames and from a sooting premixed flame. The FRS-measured temperatures are accurate to within {+-}50 K (3%) in a premixed CH4-air flame and within {+-}100 K for a vortex-strained diluted CH4-air diffusion flame where the FRS technique is severely tested by large variation in scattering cross section. In the diffusion flame work, FRS has been combined with Raman imaging of the CH4 fuel molecule to correct for the local light scattering properties of the combustion gases. To our knowledge, this is the first extension of FRS to nonpremixed combustion and the first use of joint FRS-Raman imaging. FRS has been applied to a sooting C2H4-air flame and combined with LII to assess the upper sooting limit ...
Date: January 1, 2004
Creator: Beresh, Steven Jay; Grasser, Thomas W.; Kearney, Sean Patrick & Schefer, Robert W.
Partner: UNT Libraries Government Documents Department

Techniques of the FLASH Thin Target Experiment

Description: The fluorescence yield in air is reported for wavelength and pressure ranges of interest to ultra-high energy cosmic ray detectors. A 28.5 GeV electron beam was used to excite the fluorescence. Central to the approach was the system calibration, using Rayleigh scattering of a nitrogen laser beam. In atmospheric pressure dry air, at 304 K the yield is 20.8 {+-} 1.6 photons per MeV.
Date: October 30, 2007
Creator: Abbasi, R.; Abu-Zayyad, T.; Belov, K.; Belz, J.; U., /Utah; Bergman, D.R. et al.
Partner: UNT Libraries Government Documents Department

Application of advanced laser diagnostics to hypersonic wind tunnels and combustion systems.

Description: This LDRD was a Sandia Fellowship that supported Andrea Hsu's PhD research at Texas A&amp;M University and her work as a visitor at Sandia's Combustion Research Facility. The research project at Texas A&amp;M University is concerned with the experimental characterization of hypersonic (Mach&gt;5) flowfields using experimental diagnostics. This effort is part of a Multidisciplinary University Research Initiative (MURI) and is a collaboration between the Chemistry and Aerospace Engineering departments. Hypersonic flight conditions often lead to a non-thermochemical equilibrium (NTE) state of air, where the timescale of reaching a single (equilibrium) Boltzmann temperature is much longer than the timescale of the flow. Certain molecular modes, such as vibrational modes, may be much more excited than the translational or rotational modes of the molecule, leading to thermal-nonequilibrium. A nontrivial amount of energy is therefore contained within the vibrational mode, and this energy cascades into the flow as thermal energy, affecting flow properties through vibrational-vibrational (V-V) and vibrational-translational (V-T) energy exchanges between the flow species. The research is a fundamental experimental study of these NTE systems and involves the application of advanced laser and optical diagnostics towards hypersonic flowfields. The research is broken down into two main categories: the application and adaptation of existing laser and optical techniques towards characterization of NTE, and the development of new molecular tagging velocimetry techniques which have been demonstrated in an underexpanded jet flowfield, but may be extended towards a variety of flowfields. In addition, Andrea's work at Sandia National Labs involved the application of advanced laser diagnostics to flames and turbulent non-reacting jets. These studies included quench-free planar laser-induced fluorescence measurements of nitric oxide (NO) and mixture fraction measurements via Rayleigh scattering.
Date: September 1, 2009
Creator: North, Simon W. (Texas A&M University, College Station, TX); Hsu, Andrea G. (Texas A&M University, College Station, TX) & Frank, Jonathan H.
Partner: UNT Libraries Government Documents Department

Rayleigh scattering and nonlinear inversion of elastic waves

Description: Rayleigh scattering of elastic waves by an inclusion is investigated and the limitations determined. In the near field of the inhomogeneity, the scattered waves are up to a factor of 300 stronger than in the far field, excluding the application of the far field Rayleigh approximation for this range. The investigation of the relative error as a function of parameter perturbation shows a range of applicability broader than previously assumed, with errors of 37% and 17% for perturbations of {minus}100% and +100%, respectively. The validity range for the Rayleigh limit is controlled by large inequalities, and therefore, the exact limit is determined as a function of various parameter configurations, resulting in surprisingly high values of up to k{sub p}R = 0.9. The nonlinear scattering problem can be solved by inverting for equivalent source terms (moments) of the scatterer, before the elastic parameters are determined. The nonlinear dependence between the moments and the elastic parameters reveals a strong asymmetry around the origin, which will produce different results for weak scattering approximations depending on the sign of the anomaly. Numerical modeling of cross hole situations shows that near field terms are important to yield correct estimates of the inhomogeneities in the vicinity of the receivers, while a few well positioned sources and receivers considerably increase the angular coverage, and thus the model resolution of the inversion parameters. The pattern of scattered energy by an inhomogeneity is complicated and varies depending on the object, the wavelength of the incident wave, and the elastic parameters involved. Therefore, it is necessary to investigate the direction of scattered amplitudes to determine the best survey geometry.
Date: December 1, 1995
Creator: Gritto, R.
Partner: UNT Libraries Government Documents Department

Horizontal Thomson Scattering Systems for DIII-D and SSPX

Description: DIII-D--Three of the seven existing core Thomson scattering laser beams were redirected to probe the previously unmeasured central region of the DIII-D plasma. Modifications to the existing collection optics system and support tower were made to inject the lasers and collect scattered light in this new extended region. Stray light levels were reduced to acceptable levels to permit Rayleigh scattering calibration on five of the six new channels, indicating that the new in-vessel dump operates well. Measurements of the plasma temperature and density from the plasma edge to the center are now possible. Peaked density profiles are now observed in this new measurement region. SSPX--We have completed the design and installation of a 10-spatial channel Thomson scattering system to measure the plasma temperature and density profile on SSPX. A single-pulsed YAG laser operating at 0.7 J and 8 ns is used to scatter photons into a 7-element collection optic that provides a spatial resolution of 1.5 cm at the outer plasma edge and 7.5 cm at the inner edge of a .5 m radius spheromak plasma. The collected light is then analyzed by a 4-channel interference filtered polychromator which has been optimized to measure temperatures between 2 eV and 2 keV and densities as low as 1 x 10{sup 12} cm{sup 3}. We use an in-vessel beam dump and a series of entrance and exit baffles to reduce the stray laser light and provide for an absolute density calibration by Rayleigh scattering in argon gas.
Date: August 1, 1999
Creator: Nilson, D.G.; Hill, D.N.; Wood, R.D.; McClean, H.; Moeller, J.M.; Labik, G. et al.
Partner: UNT Libraries Government Documents Department

A Raman Fiber Optic Probe Assembly for use in Hostile Environments

Description: This invention provides a device for Raman spectroscopic measurement of composition and concentrations in a hostile environment by the use of a first fiber optic as a means of directing high intensity monochromatic light from a laser to the hostile environment and a second fiber optic to receive the lower intensity scattered light for transmittal to a monochromator for analysis. To avoid damage to the fiber optics, they are protected from the hostile environment. A preferred embodiment of the Raman fiber optic probe is able to obtain Raman spectra of corrosive gases and solutions at temperatures to 600 F and pressures up to 2000 psi. The incident exciting fiber optic cable makes an angle of substantially 90{degree} with the collecting fiber optic cable. This 90{degree} geometry minimizes the Rayleigh scattering signal picked up by the collecting fiber, because the intensity of Rayleigh scattering is lowest in the direction perpendicular to the beam path of the exciting light and therefore a 90{degree} scattering geometry optimizes the signal to noise ratio.
Date: September 21, 1998
Creator: Schmucker, John E.; Falk, Jon C.; Archer, William B. & Blasi, Raymond J.
Partner: UNT Libraries Government Documents Department

Crack identification and characterization in long wavelength elastic wave scattering

Description: We discuss apparent characteristic features of Rayleigh scattering of elastic waves from cracks. Interpreting these features, a procedure is suggested that in some experimental situations may be useful to distinguish generally-shaped cracks from volume defects and to determine from elliptically-shaped cracks the orientation, shape and size.
Date: January 1, 1978
Creator: Gubernatis, J.E. & Domany, E.
Partner: UNT Libraries Government Documents Department

The Effect of the Earth's Atmosphere on LSST Photometry

Description: The Large Synoptic Survey Telescope (LSST), a ground-based telescope currently under development, will allow a thorough study of dark energy by measuring, more completely and accurately than previously, the rate of expansion of the universe and the large-scale structure of the matter in it. The telescope utilizes a broadband photometric system of six wavelength bands to measure the redshifts of distant objects. The earth's atmosphere makes it difficult to acquire accurate data, since some of the light passing through the atmosphere is scattered or absorbed due to Rayleigh scattering, molecular absorption, and aerosol scattering. Changes in the atmospheric extinction distribution due to each of these three processes were simulated by altering the parameters of a sample atmospheric distribution. Spectral energy distributions of standard stars were used to simulate data acquired by the telescope. The effects of changes in the atmospheric parameters on the photon flux measurements through each wavelength band were observed in order to determine which atmospheric conditions must be monitored most closely to achieve the desired 1% uncertainty on flux values. It was found that changes in the Rayleigh scattering parameter produced the most significant variations in the data; therefore, the molecular volume density (pressure) must be measured with at most 8% uncertainty. The molecular absorption parameters produced less significant variations and could be measured with at most 62% uncertainty. The aerosol scattering parameters produced almost negligible variations in the data and could be measured with &gt; 100% uncertainty. These atmospheric effects were found to be almost independent of the redshift of the light source. The results of this study will aid the design of the atmospheric monitoring systems for the LSST.
Date: August 30, 2006
Creator: Rahlin, Alexandra S. & /SLAC, /MIT
Partner: UNT Libraries Government Documents Department

Rayleigh/Raman/LIF measurements in a turbulent lean premixed combustor

Description: Much of the industrial electrical generation capability being added worldwide is gas-turbine engine based and is fueled by natural gas. These gas-turbine engines use lean premixed (LP) combustion to meet the strict NO{sub x} emission standards, while maintaining acceptable levels of CO. In conventional, diffusion flame gas turbine combustors, large amount of NO{sub x} forms in the hot stoichiometric zones via the Zeldovich (thermal) mechanism. Hence, lean premixed combustors are rapidly becoming the norm, since they are specifically designed to avoid these hot stoichiometric zones and the associated thermal NO{sub x}. However, considerable research and development are still required to reduce the NO{sub x} levels (25-40 ppmvd adjusted to 15% O{sub 2} with the current technology), to the projected goal of under 10 ppmvd by the turn of the century. Achieving this objective would require extensive experiments in LP natural gas (or CH{sub 4}) flames for understanding the combustion phenomena underlying the formation of the exhaust pollutants. Although LP combustion is an effective way to control NO{sub x}, the downside is that it increases the CO emissions. The formation and destruction of the pollutants (NO{sub x} and CO) are strongly affected by the fluid mechanics, the finite-rate chemistry, and their (turbulence-chemistry) interactions. Hence, a thorough understanding of these interactions is vital for controlling and reducing the pollutant emissions. The present research is contributing to this goal by providing a detailed nonintrusive laser based data set with good spatial and temporal resolutions of the pollutants (NO and CO) along with the major species, temperature, and OH. The measurements reported in this work, along with the existing velocity data on a turbulent LP combustor burning CH{sub 4}, would provide insight into the turbulence-chemistry interactions and their effect on pollutant formation.
Date: December 31, 1995
Creator: Nandula, S.P.; Pitz, R.W.; Barlow, R.S. & Fiechtner, G.J.
Partner: UNT Libraries Government Documents Department

Rayleigh temperature profiles in a hydrogen diffusion flame

Description: Rayleigh scattering from a hydrogen-air laminar jet diffusion flame in combination with a numerical model of the flame has been used to determine temperature profiles. The model predictions of species concentration are used to calculate a mean Rayleigh cross-section which is used to relate the Rayleigh scattered intensity to temperature. Using an argon ion laser producing 7.5 watts at 488 nm and an optical multichannel analyzer (OMA), the scattered light was imaged into a spectrometer. The OMA was rotated 90 degrees to its normal orientation, allowing scans to be taken along the spectrometer exit slit. This resulted in a spatially resolved Rayleigh signal along the laser beam through the entire flame. Spatial resolution of 0.18 mm on each of the 500 detector elements with good signal-to-noise ratios was achieved even with integration times of only 0.03 second. Since the entire profile is made simultaneously, particulate perturbed profiles are easily recognized and discarded. Transverse profiles are presented to show flame structure. Axial profiles are compared to radiation corrected thermocouple measurements.
Date: September 1, 1978
Creator: Smith, J.R.
Partner: UNT Libraries Government Documents Department

Measurement of the stimulated thermal Rayleigh scattering instability

Description: Growth of perturbations due to stimulated thermal Rayleigh scattering was observed on a laser beam propagating in a 1 meter cell of CC14. Initial sinusoidal irradiance perturbations were seeded onto the laser leam, and their amplification in the cell was recorded by a near field camera. The perturbation growth rate is in agreement with analytical predictions of linearized propagation theory.
Date: April 1, 1989
Creator: Karr, T.J.; Rushford, M.C.; Murray, J.R. & Morris, J.R.
Partner: UNT Libraries Government Documents Department

Experimental study of unsteady laminar and turbulent flame propagation in an enclosure by Rayleigh scattering

Description: The Rayleigh scattering technique has been used to investigate the flame structure of unsteady propane/air flames propagating under quiescent and turbulent conditions initiated by three ignition methods: (1) conventional spark plug (2) pulse jet combustion (PJC) and (3) Pre-Chamber ignition (PCI). The Rayleigh signal obtained for the laminar cases are all characterized by a sharp transition associated with the large density change which occurs as leading flame front of the expanding flame kernel crosses the measurement point. This indicates that the local flame structures are independent of the ignition source and may be characterized as flamelets. The maximum burning rates deduced from the pressure records show that PJC and PCI increases the burning rate from two to three times above that of conventional spark ignition. The Rayleigh scattering signal obtained for the turbulent cases are also characterized by sharp transition. The wrinkled laminar flamelet model, therefore, provides a valid description of the flame structures for all these unsteady flames. For a given equivalence ratio, the maximum turbulent burning rate deduced for the three turbulent cases with different ignition sources are similar. This suggests that while PJC and PCI enhances burning rate when conditions in the chamber are quiescent, the enhancement is not significant when turbulence fluctuations are present. The PJC and PCI, however, are capable of igniting leaner conditions than the spark plug. This may be due to the injection process which initially disperses ignition sites to a larger volume at a faster rate.
Date: September 1, 1992
Creator: Tamai, R. (Consiglio Nazionale della Ricerche, Naples (Italy). Ist. Motori); Shepherd, I.G. & Cheng, R.K. (Lawrence Berkeley Lab., CA (United States))
Partner: UNT Libraries Government Documents Department

Nuclear Resonance Fluorescence for Safeguards Applications

Description: In nuclear resonance fluorescence (NRF) measurements, resonances are excited by an external photon beam leading to the emission of {gamma} rays with specific energies that are characteristic of the emitting isotope. The promise of NRF as a non-destructive analysis technique (NDA) in safeguards applications lies in its potential to directly quantify a specific isotope in an assay target without the need for unfolding the combined responses of several fissile isotopes as often required by other NDA methods. The use of NRF for detection of sensitive nuclear materials and other contraband has been researched in the past. In the safeguards applications considered here one has to go beyond mere detection and precisely quantify the isotopic content, a challenge that is discussed throughout this report. Basic NRF measurement methods, instrumentation, and the analytical calculation of NRF signal strengths are described in Section 2. Well understood modeling and simulation tools are needed for assessing the potential of NRF for safeguards and for designing measurement systems. All our simulations were performed with the radiation transport code MCNPX, a code that is widely used in the safeguards community. Our initial studies showed that MCNPX grossly underestimated the elastically scattered background at backwards angles due to an incorrect treatment of Rayleigh scattering. While new, corrected calculations based on ENDF form factors showed much better agreement with experimental data for the elastic scattering of photons on an uranium target, the elastic backscatter is still not rigorously treated. Photonuclear scattering processes (nuclear Thomson, Delbruck and Giant Dipole Resonance scattering), which are expected to play an important role at higher energies, are not yet included. These missing elastic scattering contributions were studied and their importance evaluated evaluated against data found in the literature as discussed in Section 3. A transmission experiment was performed in September 2009 to test and ...
Date: February 4, 2011
Creator: Ludewigt, Bernhard A; Quiter, Brian J & Ambers, Scott D
Partner: UNT Libraries Government Documents Department

Aromatics oxidation and soot formation in flames

Description: Work during this contract period has been concerned with the mechanisms through which aromatics are formed and destroyed in flames, and the processes responsible for soot formation. Recent progress has been primarily in two areas: experiments and modeling of the soot nucleation process in low pressure benzene flames and preparation for experiments on the destruction mechanisms of benzene. In addition, we have incorporated weak collision'' formalisms into a fall-off computer code.
Date: January 1, 1989
Creator: Howard, J. B.
Partner: UNT Libraries Government Documents Department

Application of modern diagnostic methods to environmental improvement. Annual progress report, October 1994--September 1995

Description: The Diagnostic Instrumentation and Analysis Laboratory (DIAL), an interdisciplinary research department in the College of Engineering at Mississippi State University (MSU), is under contract with the US Department of Energy (DOE) to develop and apply advanced diagnostic instrumentation and analysis techniques to aid in solving DOE`s nuclear waste problem. The program is a comprehensive effort which includes five focus areas: advanced diagnostic systems; development/application; torch operation and test facilities; process development; on-site field measurement and analysis; technology transfer/commercialization. As part of this program, diagnostic methods will be developed and evaluated for characterization, monitoring and process control. Also, the measured parameters, will be employed to improve, optimize and control the operation of the plasma torch and the overall plasma treatment process. Moreover, on-site field measurements at various DOE facilities are carried out to aid in the rapid demonstration and implementation of modern fieldable diagnostic methods. Such efforts also provide a basis for technology transfer.
Date: December 1, 1995
Creator: Shepard, W.S.
Partner: UNT Libraries Government Documents Department