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At least 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Advanced Diagnostic and Prognostic Testbed (ADAPT) Testability Analysis Report

As system designs become more complex, determining the best locations to add sensors and test points for the purpose of testing and monitoring these designs becomes more difficult. Not only must the designer take into consideration all real and potential faults of the system, he or she must also find efficient ways of detecting and isolating those faults. Because sensors and cabling take up valuable space and weight on a system, and given constraints on bandwidth and power, it is even more difficult to add sensors into these complex designs after the design has been completed. As a result, a number of software tools have been developed to assist the system designer in proper placement of these sensors during the system design phase of a project. One of the key functions provided by many of these software programs is a testability analysis of the system essentially an evaluation of how observable the system behavior is using available tests. During the design phase, testability metrics can help guide the designer in improving the inherent testability of the design. This may include adding, removing, or modifying tests; breaking up feedback loops, or changing the system to reduce fault propagation. Given a set of test requirements, the analysis can also help to verify that the system will meet those requirements. Of course, a testability analysis requires that a software model of the physical system is available. For the analysis to be most effective in guiding system design, this model should ideally be constructed in parallel with these efforts. The purpose of this paper is to present the final testability results of the Advanced Diagnostic and Prognostic Testbed (ADAPT) after the system model was completed. The tool chosen to build the model and to perform the testability analysis with is the Testability Engineering and Maintenance System Designer (TEAMS-Designer). The TEAMS toolset is intended to be a solution to span all phases of the system, from design and development through health management and maintenance. TEAMS-Designer is the model-building and testability analysis software in that suite.

Ossenfort, John↗
DOE OSTI2021

A Bimodal Diagnostic Cloud Fraction Parameterization. Part II: Evaluation and Resolution Sensitivity

A wide range of approaches exists to account for subgrid cloud variability in regional simulations of the atmosphere. This paper addresses the following questions: 1) Is there still benefit in representing subgrid variability of cloud in convection-permitting simulations? 2) What is the sensitivity to the cloud fraction parameterization complexity? 3) Are current cloud fraction parameterizations scale-aware across convection-permitting resolutions? These questions are addressed for regional simulations of a 6-week observation campaign in the U.S. southern Great Plains. Particular attention is given to a new diagnostic cloud fraction scheme with a bimodal subgrid saturation-departure PDF, described in Part I. The model evaluation is performed using ground-based remote sensing synergies, satellite-based retrievals, and surface observations. It is shown that not using a cloud fraction parameterization results in underestimated cloud frequency and water content, even for stratocumulus. The use of a cloud fraction parameterization does not guarantee improved cloud property simulations, however. Diagnostic and prognostic cloud schemes with a symmetric subgrid saturation-departure PDF underestimate cloud fraction and cloud optical thickness, and hence overestimate surface shortwave radiation. These schemes require empirical bias-correction techniques to improve the cloud cover. The new cloud fraction parameterization, introduced in Part I, improves cloud cover, liquid water content, cloud-base height, optical thickness, and surface radiation compared to schemes reliant on a symmetric PDF. Furthermore, cloud parameterizations using turbulence-based, rather than prescribed constant subgrid variances, are shown to be more scale-aware across convection-permitting resolutions.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2020

Wind Tunnel Investigation of the Supersonic Stage Separation Aerodynamics of a Generic 0.0175-Scale Bimese Two-Stage-to-Orbit Reusable Launch Vehicle Configuration

A wind tunnel investigation was conducted of the supersonic stage separation aerodynamics of a generic two-stage-to-orbit bimese wingbody configuration in the NASA Langley Research Center Unitary Plan Wind Tunnel. Proximity and isolated model testing was conducted at Mach numbers of 2.3, 3.0, and 4.5 and a unit Reynolds number of 2.0 million per foot using 0.0175-scale models of the Langley Glide-Back Booster concept designated as the orbiter and booster in belly-to-belly and back-to-belly configurations. Longitudinal forces and moments were obtained on both models and surface static pressure measurements were obtained on the orbiter model at 328 relative proximity locations and at relative angles of attack of 0 degrees and 5 degrees. The test results supported a larger effort to develop and validate experimental and computational tools applicable to the design and simulation of stage separation and abort procedures for reusable launch vehicles composed of multiple bodies, including winged bodies. An initial proof-of-concept experiment featuring low-cost uninstrumented models was conducted to verify an emerging automated model control system and new support system hardware, and to identify potential model and support system blockage and unsteady aerodynamics/model dynamics prior to committing to higher-fidelity instrumented models. This investigation led to upgrades in the facility stage separation hardware, calibration and testing techniques and capabilities, and data analysis and documentation methodologies that have been extended to the more recent NASA Constellation and Space Launch System crew and cargo launch vehicle programs. A virtual diagnostics interface methodology was used to facilitate the design of the stage separation support hardware, to position the models in the test section, and to define the experimental test space. Advances in the facility automated model positioning system established a foundation for the development of a continuous-sweep data acquisition technique that is responsible for significant productivity improvements to the current NASA Space Launch System test program. The automated model positioning capability was leveraged to conduct a companion statistically-designed stage separation experiment requiring randomization of the relative proximity positions of the orbiter and booster models. The respective zones of influence and interference effects of the orbiter and booster were identified from three-dimensional scatter plots, contour and influence maps, and two-dimensional plotting methods. The highly-nonlinear, shock-dominated aerodynamic characteristics of the orbiter and booster in the Unitary Plan Wind Tunnel exhibited good agreement with independent test data obtained in a NASA Marshall Space Flight Center wind tunnel and with computational fluid dynamics predictions using a compressible, three-dimensional flow solver and an inviscid, unstructured Cartesian method.

Erickson, Gary E.↗
DOE OSTI2013

Energy levels, wavelengths, and transition rates of multipole transitions (E1, E2, M1, M2) in Au{sup 67+} and Au{sup 66+} ions

The fully relativistic configuration interaction method of the FAC code is used to calculate atomic data for multipole transitions in Mg-like Au (Au{sup 67+}) and Al-like Au (Au{sup 66+}) ions. Generated atomic data are important in the modeling of M-shell spectra for heavy Au ions and Au plasma diagnostics. Energy levels, oscillator strengths and transition rates are calculated for electric-dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2) for transitions between excited and ground states 3l−nl{sup ′}, such that n=4,5,6,7. The local central potential is derived using the Dirac–Fock–Slater method. Correlation effects to all orders are considered by the configuration interaction expansion. All relativistic effects are included in the calculations. Calculated energy levels are compared against published values that were calculated using the multi-reference many body perturbation theory, which includes higher order QED effects. Favorable agreement was observed, with less than 0.15% difference.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

Propagation speed of rotation signals for field lines undergoing magnetic reconnection

Reconnection is associated with two bending of the magnetic field lines. Considering the usual plane of a 2D reconnection simulation, the first bending is in-plane and produces the needed topological changes by bringing oppositely directed filed lines in proximity. The second is typical of fast reconnection and is out of plane, leading to the formation of the Hall magnetic field. This second rotation has recently been observed to proceed at superAlfvénic speeds and to carry substantial energy fluxes (Shay et al., Phys. Rev. Lett. 107, 065001 (2011)). We revisit these rotations with a new diagnostics based on dispersing a multitude of virtual probes into a kinetic simulation, akin the approach of multi spacecraft missions. The results of the new diagnostics are compared with the theory of characteristics applied to the two fluid model. The comparison of virtual probes and the method of characteristics confirm the findings relative to the out of plane rotation and uncover the existence of two families of characteristics. Both are observed in the simulation. The early stage of reconnection develops on the slower compressional branch and the later faster phase develops on the faster torsional branch. The superAlfvénic signal is only relevant in the second phase.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Improving dynamic collision frequencies: Impacts on dynamic structure factors and stopping powers in warm dense matter

Simulations and diagnostics of high-energy-density plasmas and warm dense matter rely on models of material response properties, both static and dynamic (frequency-dependent). Here, in this work, we systematically investigate variations in dynamic electron–ion collision frequencies ν(ω) in warm dense matter using data from a self-consistent-field average-atom model. We show that including the full quantum density of states, strong collisions, and inelastic collisions lead to significant changes in ν(ω). These changes result in red shifts and broadening of the plasmon peak in the dynamic structure factor, an effect observable in x-ray Thomson scattering spectra, and modify stopping powers around the Bragg peak. These changes improve the agreement of computationally efficient average-atom models with first-principles time-dependent density functional theory in warm dense aluminum, carbon, and deuterium.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Electron-impact excitation of Fe{sup 2+}: A comparison of intermediate coupling frame transformation, Breit-Pauli and Dirac R-matrix calculations

Modeling the spectral emission of low-charge iron group ions enables the diagnostic determination of the local physical conditions of many cool plasma environments such as those found in H II regions, planetary nebulae, active galactic nuclei, etc. Electron-impact excitation drives the population of the emitting levels and, hence, their emissivities. By carrying-out Breit-Pauli and intermediate coupling frame transformation (ICFT) R-matrix calculations for the electron-impact excitation of Fe{sup 2+}, which both use the exact same atomic structure and the same close-coupling expansion, we demonstrate the validity of the application of the powerful ICFT method to low-charge iron group ions. This is in contradiction to the finding of Bautista et al., who carried-out ICFT and Dirac R-matrix calculations for the same ion. We discuss possible reasons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Upper boundaries of active galactic nucleus regions in optical diagnostic diagrams

The distribution of galaxies in optical diagnostic diagrams can provide information about their physical parameters when compared with ionization models under proper assumptions. By using a sample of central emitting regions from the Mapping Nearby Galaxies at Apache Point Observatory survey (MaNGA), we find evidence of the existence of upper boundaries for narrow-line regions (NLRs) of active galactic nuclei (AGNs) in optical Baldwin, Phillips & Terlevich (BPT) diagrams, especially in diagrams involving [Sii]λλ6716, 6731/Hα. Photoionization models can reproduce the boundaries well, as a consequence of the decrease of [Sii]λλ6716, 6731/Hα and [Oiii]λ5007/Hβ ratios at very high metallicity. Whilst the exact location of the upper boundary in the [Sii] BPT diagram depends only weakly on the electron density of the ionized cloud and the secondary nitrogen prescription, its dependence on the shapes of the input spectral energy distributions (SEDs) is much stronger. This allows us to constrain the power-law index of the AGN SED between 1 Ryd and ~100 Ryd to be less than or equal to -1.40 ± 0.05. The coverage of photoionization models in the [Nii] BPT diagram has a stronger dependence on the electron density and the secondary nitrogen prescription. With the density constrained by the [Sii] doublet ratio and the input SED constrained by the [Sii] BPT diagram, we find that the extent of the data in the [Nii] BPT diagram favours those prescriptions with high N/O ratios. Furthermore, although shock-ionized clouds can produce line ratios similar to those from photoionization, the resulting shapes of the upper boundaries, if they exist, would likely be different from those of photoionizing origin.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Opportunities for gas-phase science at short-wavelength free-electron lasers with undulator-based polarization control

Free-electron lasers (FELs) are the world's most brilliant light sources with rapidly evolving technological capabilities in terms of ultrabright and ultrashort pulses over a large range of photon energies. Their revolutionary and innovative developments have opened new fields of science regarding nonlinear light-matter interaction, the investigation of ultrafast processes from specific observer sites, and approaches to imaging matter with atomic resolution. A core aspect of FEL science is the study of isolated and prototypical systems in the gas phase with the possibility of addressing well-defined electronic transitions or particular atomic sites in molecules. Notably for polarization-controlled short-wavelength FELs, the gas phase offers new avenues for investigations of nonlinear and ultrafast phenomena in spin-orientated systems, for decoding the function of the chiral building blocks of life as well as steering reactions and particle emission dynamics in otherwise inaccessible ways. This roadmap comprises descriptions of technological capabilities of facilities worldwide, innovative diagnostics and instrumentation, as well as recent scientific highlights, novel methodology, and mathematical modeling. The experimental and theoretical landscape of using polarization controllable FELs for dichroic light-matter interaction in the gas phase will be discussed and comprehensively outlined to stimulate and strengthen global collaborative efforts of all disciplines. Published by the American Physical Society 2025

Ilchen, Markus↗
DOE OSTI2017

Pulsed high-voltage discharge in air with a pressure gradient

Results of experiments on high-voltage discharges in air with a pressure gradient are presented. The experiments were carried out at the setup developed at the Institute of Applied Physics, Russian Academy of Sciences. The goal of the experiments was laboratory modeling of high-altitude atmospheric discharges―sprites and jets. The setup and diagnostic techniques are described. The experimental results include the distribution of the gas pressure in the vacuum chamber formed by means of pulsed air puffing, photographs of discharges in air with a pressure gradient, and the dependences of the discharge current and optical emission intensity on the initial conditions.

42 ENGINEERING↗
DOE OSTI2018

Experimental Demonstration of Ion Beam Cooling with Pulsed Electron Beam

Cooling ion beams at high energy is presently considered for several ion colliders, in order to achieve high luminosities by enabling a significant reduction of emittance of hadron beams. Electron beam at cooling channel in a few to tens MeV can be accelerated by a RF/SRF linac, and thus using bunched electrons to cool bunched ions. To study such cooling process, the DC electron gun of EC35 cooler at the storage ring CSRm, IMP was modified by pulsing the grid voltage. A 0.07-3.5 micro-second pulse length with a repetition frequency of less than 250 kHz and synchronized with the ion revolution frequency was obtained. The first experimental demonstration of cooling of a coasting and bunched ion beam by a pulsed electron beam was carried out. Data analysis indicates the bunch length shrinkage and the momentum spread reduction of bunched 12C+6 ion beam as evidence of cooling. A longitudinal grouping effect of the coasting ion beam by the electron pulses has also been observed*. In this paper, we will present experimental results and comparison to the simulation modelling, particularly on the bunched electron cooling data after carefully analyzing the beam diagnostic signals.

Zhang, Yuhong↗
DOE OSTI2016

Enhancing Fundamental Understanding of Magnetic Confinement in the Presence of Flows, Non-Conservative Forces, Dynamics, Collisions, Relaxation and Kinetic Effects

Pulsed high-power technology is used to create MHD-governed, dynamically-evolving, plasma-filled magnetic flux tubes. Advanced diagnostics measure the dynamical evolution and the measurements are then related to theoretical models. The dynamics are relevant to solar coronal plasma loops, astrophysical jets, and other situations where magnetic field lines intercept a boundary and current flows from the boundary into the plasma along the field lines. The morphology is time-dependent and determined by complex physics involving magnetic forces, hydrodynamic forces, and boundary conditions. Unlike magnetic fusion plasma experiments which are in approximate MHD equilibrium, fast accelerated plasma flows are a dominant feature. Typical parameters are: electric current 50-150 kA, applied voltage 3-6 kV, magnetic field 0.3 to 3 kG, experiment duration 10 μs, jet velocity 10’s of km/s, flux tube dimensions a few cm in radius and 10’s of cm in length. A scheme for measuring the wavelength of a quasi-neutral magnetic plasma wave using a single point of measurement was demonstrated both by an actual spacecraft (MMS) and in the lab. The experimental work is supported by a strong theoretical component. Theoretical activities included proposing a model for driving astrophysical jets (model motivated by lab experiments), and providing new insights into fast collisionless magnetic reconnection by demonstration of a new, more fundamental parameter than previously used.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

GMC Collisions as Triggers of Star Formation. II. 3D Turbulent, Magnetized Simulations

We investigate giant molecular cloud collisions and their ability to induce gravitational instability and thus star formation. This mechanism may be a major driver of star formation activity in galactic disks. We carry out a series of 3D, magnetohydrodynamics (MHD), adaptive mesh refinement simulations to study how cloud collisions trigger formation of dense filaments and clumps. Heating and cooling functions are implemented based on photo-dissociation region models that span the atomic-to-molecular transition and can return detailed diagnostic information. The clouds are initialized with supersonic turbulence and a range of magnetic field strengths and orientations. Collisions at various velocities and impact parameters are investigated. Comparing and contrasting colliding and non-colliding cases, we characterize morphologies of dense gas, magnetic field structure, cloud kinematic signatures, and cloud dynamics. We present key observational diagnostics of cloud collisions, especially: relative orientations between magnetic fields and density structures, like filaments; {sup 13}CO( J = 2-1), {sup 13}CO( J = 3-2), and {sup 12}CO( J = 8-7) integrated intensity maps and spectra; and cloud virial parameters. We compare these results to observed Galactic clouds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Interaction of Hemispherical Blast Waves with Inhomogeneous Spheres: Probing the Collision of a Supernova Ejecta with a Nearby Companion Star in the Laboratory

Past laboratory experiments at high energy density have provided insights into the physics of supernovae, supernova remnants, and the destruction of interstellar clouds. In a typical experimental setting, a laser-driven planar blast wave interacts with a compositionally homogeneous spherical or cylindrical target. In this work we propose a new laboratory platform that accounts for curvature of the impacting shock and density stratification of the target. Both characteristics reflect the conditions expected to exist shortly after a supernova explosion in a close binary system. We provide details of a proposed experimental design (laser drive, target configuration, diagnostic system), optimized to capture the key properties of recent ejecta–companion interaction models. Good qualitative agreement found between our experimental models and their astrophysical counterparts highlights the strong potential of the proposed design to probe details of the ejecta–companion interaction for broad classes of objects by means of laboratory experiments at high energy density.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Uncovering turbulent plasma dynamics via deep learning from partial observations

One of the most intensely studied aspects of magnetic confinement fusion is edge plasma turbulence which is critical to reactor performance and operation. Drift-reduced Braginskii two-fluid theory has for decades been widely applied to model boundary plasmas with varying success. Towards better understanding edge turbulence in both theory and experiment, we demonstrate that a novel multi-network physics-informed deep learning framework constrained by partial differential equations can accurately learn turbulent fields consistent with the two-fluid theory from partial observations of electron pressure which is not otherwise possible using conventional equilibrium models. This technique presents a novel paradigm for the advanced design of plasma diagnostics and validation of magnetized plasma turbulence theories in challenging thermonuclear environments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1975

The NATA code; theory and analysis. Volume 2: User's manual

The NATA code is a computer program for calculating quasi-one-dimensional gas flow in axisymmetric nozzles and rectangular channels, primarily to describe conditions in electric archeated wind tunnels. The program provides solutions based on frozen chemistry, chemical equilibrium, and nonequilibrium flow with finite reaction rates. The shear and heat flux on the nozzle wall are calculated and boundary layer displacement effects on the inviscid flow are taken into account. The program contains compiled-in thermochemical, chemical kinetic and transport cross section data for high-temperature air, CO2-N2-Ar mixtures, helium, and argon. It calculates stagnation conditions on axisymmetric or two-dimensional models and conditions on the flat surface of a blunt wedge. Included in the report are: definitions of the inputs and outputs; precoded data on gas models, reactions, thermodynamic and transport properties of species, and nozzle geometries; explanations of diagnostic outputs and code abort conditions; test problems; and a user's manual for an auxiliary program (NOZFIT) used to set up analytical curvefits to nozzle profiles.

Bade, W. L.↗
NASA NTRS1984

Ageostrophic motions in the stratosphere from satellite observations

The diagnostic approach used by Palmer (1981) to compare the predictions of the theoretical model of sudden warming in the winter polar stratosphere of Dunkerton et al. (1981) with Tiros-N Stratospheric Sounding Unit data on the event of February 13-17, 1979, is applied to data from the Nimbus-7 Limb IR Monitor of the Stratosphere for the same event. The data are presented as height-latitude cross sections of the zonally averaged zonal wind, the Coriolis terms, and the wave-flux terms and discussed. Some encroachment of easterlies from the equatorial regions into the midlatitudes is observed on February 13, in agreement with the early phase of the model and in contrast to the lack of encroachment seen in the narrower-coverage Tiros-N data, but the further evolution deviates significantly from the model predictions.

Elson, L. S.↗
NASA NTRS1985

Spectrum and chemical composition of the remarkable planetary nebula NGC 6537

The planetary nebula NGC 6537 appears to be an irregular bipolar object. Conventional procedures have been employed to observe the spectrum of NGC 6537 with the image dissector scanner at the Lick 3-m telescope. Both red- and green-sensitive tubes were employed in order to cover the spectrum from the practical UV limit near lambda 3300 A to the near-infrared limit near lambda 8600 A. The instrumental response function was determined on the basis of the observation of suitable comparison stars. On Oct. 23, 1984, observations with the International Ultraviolet Explorer (IUE) were obtained. A table containing the optical region spectrum of NGC 6537 is presented along with a table providing the UV fluxes, a table listing the ionic concentrations, and a table with data describing the chemical composition of NGC 6537. Attention is given to theoretical models and the determination of the nebular chemical composition, and aspects of plasma diagnostics.

Feibelman, W.↗