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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Microstructurally resolved electrochemical evolution of mechanical- and irradiation-induced damage in nuclear alloys

Abstract There is a need for high-throughput, scale-relevant, and direct electrochemical analysis to understand the corrosion behavior and sensitivity of nuclear materials that are exposed to extreme (high pressure, temperature, and radiation exposure) environments. We demonstrate the multi-scale, multi-modal application of scanning electrochemical cell microscopy (SECCM) to electrochemically profile corrosion alterations in nuclear alloys in a microstructurally resolved manner. Particularly, we identify that both mechanically deformed and irradiated microstructures show reduced charge-transfer resistance that leads to accelerated oxidation. We highlight that the effects of mechanical deformation and irradiation are synergistic, and may in fact, superimpose each other, with implications including general-, galvanic-, and/or irradiation-activated stress-corrosion cracking. Taken together, we highlight the ability of non-destructive, electrochemical interrogations to ascertain how microstructural alterations result in changes in the corrosion tendency of a nuclear alloy: knowledge which has implications to rank, qualify and examine alloys for use in nuclear construction applications.

Chen, Xin↗
NASA NTRS1998

A Viewing Angle-Kinetic Luminosity Scheme for BL Lacertae Objects

We propose a unified classification for BL Lacertae objects (BLs), focusing on the synchrotron peak frequency of the spectral energy distribution. The unification scheme is based on the angle theta that describes the orientation of the relativistic jet and on the electron kinetic luminosity Lamba(sub kin) of the jet. We assume that Lamba(sub kin) scales with the size of the jet (r) in a self-similar fashion (Lamba(sub kin) is proportional to r(exp 2)), as supported by observational data. The jets are self-similar in geometry and have the same pressure and median magnetic field at the inlet, independent of size. The self-similarity is broken for the highest energy electrons, which radiate mainly at high frequencies, since for large sources they suffer more severe radiative energy losses over a given fraction of the jet length. We calculate the optically thin synchrotron spectrum using an accelerating inner jet model based on simple relativistic gas dynamics and show that it can fit the observed infrared-to-X-ray spectrum of PKS 2155-304. We couple the accelerating jet model to the unification scheme and compare the results to complete samples of BLs. The negative apparent evolution of X-ray-selected BLs is explained as a result of positive evolution of the jet electron kinetic luminosity Lamba(sub kin). We review observational arguments in favor of the existence of scaled-down accretion disks and broad emission-line regions in BLs. The proposed unification scheme can explain the lack of observed broad emission lines in X-ray-selected BLs as well as the existence of those lines preferentially in luminous radio-selected BLs. Finally, we review observational arguments that suggest the extension of this unification scheme to all blazars.

Georganopoulos, Markos↗
NASA NTRSDate not supplied

High-fidelity Modeling and Visualizing of Solar Radiation Pressure A Framework for High-fidelity Analysis

Solar Radiation Pressure (SRP) is the force produced by the impact of sunlight photons on the surface of the spacecraft. This extra force, despite being small,plays an important role on trajectory design and orbit determination. In this pa-per we present an open-source tool that enables the user to compute high-fidelity approximations of SRP accelerations for a given spacecraft using ray-tracing techniques. The tool also allows the user to compare between different fidelity levels and different models like the N-plate or the cannonball finding a trade-off on the SRP accuracy between computation time and accuracy.

Leandro Zardain↗
DOE OSTI2022

Design and Testing of a Prototype Eddy Current Actuated Valve for the ITER Shattered Pellet Injection System

Reliably mitigating disruptions is essential for ITER to meet its long-term operational research plan without damage to the in-vessel components. Currently, the shattered pellet injection (SPI) technique is the most effective radiator of thermal energy and has been chosen for the baseline disruption mitigation system (DMS) for ITER. The SPI process uses cryogenic temperatures to desublimate material into the barrel of a pipe gun forming a solid cylindrical pellet. Pellets for ITER will initially be hydrogen and hydrogen-neon mixtures. Once formed, pellets are dislodged and accelerated using high-pressure gas (40-60 bar) delivered by a fast-opening valve. The solenoid valves currently used for SPI experiments will not operate in an ITER environment due to the large background magnetic field. An ITER prototype fast-opening valve, called a flyer plate valve (FPV), has been designed and has undergone a wide range of testing. The FPV operates by pulsing current through a pancake coil that is closely coupled with a ``flyer plate.'' The flyer plate is an aluminum plate in which eddy currents are generated creating a repulsive force from the pancake coil. The force generated in the flyer plate rapidly lifts the valve tip off the seat and delivers a pulse of gas to the rear of the pellet, breaking it free from the barrel and accelerating the pellet downstream to its intended target. The design of the valve has been iterated on over the lifetime of this project, as the DMS for ITER shifted from massive gas injection (MGI) to SPI. The most recent design has been tested, and operational ranges have been mapped. The valve must survive 3000+ cycles in an ITER-like magnetic field. The principal functional requirement of this valve is to reliably dislodge and accelerate hydrogen (or H-Ne mixture) pellets into ITER. The valve was mated with an ITER SPI test stand and has been shown to be capable of launching pellets reliably. The valve and power supply design will be discussed in this article, along with the various testing setups used to determine the feasibility of this valve for use on ITER.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2005

Texturing Blood-Glucose-Monitoring Optics Using Oxygen Beams

A method has been invented for utilizing directed, hyperthermal oxygen atoms and ions for texturing tips of polymeric optical fibers or other polymeric optical components for use in optical measurement of concentration of glucose in blood. The required texture of the sensory surface of such a component amounts to a landscape of microscopic hills having high aspect ratios (hills taller than they are wide), with an average distance between hills of no more than about 5 m. This limit on the average distance between hills is chosen so that blood cells (which are wider) cannot enter the valleys between the hills, where they could obstruct optical sensing of glucose in the blood plasma. On the other hand, the plasma is required to enter the valleys, and a high aspect ratio is intended to maximize the hillside and valley surface area in contact with the plasma, thereby making it possible to obtain a given level of optical glucose- measurement sensitivity with a relatively small volume of blood. The present method of texturing by use of directed, hyperthermal (particle energy >1 eV) oxygen atoms and ions stands in contrast to a prior method of texturing by use of thermal monatomic oxygen characterized by a temperature of the order of 0.5 eV. The prior method yields low-aspect- ratio (approximately hemispherical) craters that are tens of microns wide . too wide to exclude blood cells. The figure schematically depicts parts of a typical apparatus for texturing according to the present method. One or more polymeric optical components to be textured (e.g., multiple optical fibers bundled together for simultaneous processing) are mounted in a vacuum chamber facing a suitable ion- or atom-accelerating device capable of generating a beam of oxygen atoms and/or ions having kinetic energies >1 eV. Typically, such a device includes a heated cathode, in which case it is desirable to interpose a water-cooled thermal-radiation shield to prevent melting of the polymeric component(s) to be textured. In operation, the chamber is evacuated to a pressure .10.5 torr (less than or equal to approximately 1.3 mPa), then the beam is turned on. The resulting texture is characterized by approximately conical hills having aspect ratios greater than 1. In experiments, it was demonstrated that separations between adjacent hills can be made .1 m and that the separations and heights of the hills can be varied by varying the fluence of monatomic oxygen and/or oxygen ions.

Banks, Bruce↗
DOE OSTI2023

Irradiation of ultrasonic sensors and adhesive couplants for application in light water reactor primary loop piping and components

The Electric Power Research Institute (EPRI) Nuclear Sector and US Department of Energy Light Water Reactor Sustainability Program are committed to engaging in research and development endeavors to address materials aging issues specific to long term operation of light water power reactors. To this effect, EPRI launched an industry initiative to develop nondestructive evaluation systems for online monitoring of existing cracks in light water reactor primary coolant loop piping and components. One of the goals of this initiative is to develop a sensor system (or systems) that can determine nondestructively if cracks are growing or arrested and, in the case of the former, to characterize their growth rates. A missing component of this initiative is an experimental assessment of how sensors and adhesive couplants will perform in service when exposed to chronic energetic neutron radiation, particularly at the primary coolant loop hot and cold leg dissimilar metal welds, which join the primary loop piping to the reactor pressure vessel and reside in the vicinity of the reactor core. The objective of this experimental study was to determine how ultrasonic transducers and adhesive couplants perform when exposed to irradiation in a test reactor to simulate and accelerate in-service exposure. Further, to achieve this objective, the signal stability of piezoelectric transducers and performance of adhesive couplants as a function of accumulated fast neutron fluence were characterized by collecting ultrasonic data in-situ during irradiation. Of particular interest were the ultrasonic signal quality and time decay of the amplitude of acoustic reflections as a function of fast neutron fluence. The results of the study showed that, of the 8 transducer/substrate sample assemblies tested, only 3 generated usable ultrasonic signals through the conclusion of the irradiation campaign. It was found that high temperature epoxy tends to ultrasonically couple the sensors to the substrates better than three types of refractory ceramic cements studied, as is supported by post irradiation examination. The results obtained through this experimental study will be utilized in the achievement of the overall goal of development of a sensor system to perform online monitoring of primary loop components.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2020

Shatter Thresholds and Fragment Size Distributions of Deuterium–Neon Mixture Cryogenic Pellets for Tokamak Thermal Mitigation

Reliable mitigation is necessary to eliminate the detrimental effects of a disruption event in large high-current tokamaks such as ITER. To avoid serious damage to plasma-facing components during the thermal quench phase of a disruption, material is injected to radiate the plasma energy over the inner surface of the machine. The most promising method of material injection is a process known as shattered pellet injection (SPI). SPI utilizes cryogenic cooling to desublimate gas into the barrel of a pipe gun to form a solid pellet. High-pressure gas or a mechanical punch is used to dislodge the pellet and accelerate it into a bent tube to intentionally fracture it. Pellets made of a mixture of deuterium and neon are likely candidates for thermal mitigation. The survivability of these pellets throughout their flight path, before striking the shatter tube, is essential for reliable SPI operation. Experiments were conducted to determine intact speed limits for various mixtures. In this paper, we outline the details of brittle fracture theory and compare a theory-based model to experimental results from various mixtures of deuterium and neon pellets.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1981

Radiative-photochemical response of the mesosphere to dynamical forcing

Combination of the chemical continuity equation for odd oxygen with the second law of thermodynamics yields analytic solutions which describe the coupled behavior of temperature and ozone perturbations in response to an externally specified forcing. The results appear in a form which allows easy physical interpretation of the coupling between radiative and photochemical processes. When the forcing is chosen to mimic a planetary scale wave, the theory shows that photochemical acceleration of radiative damping reduces the amplitude of the temperature perturbation by an amount which increases with the wave period. Although ozone fluctuations are anti-correlated with those in temperature, minima in ozone do not coincide exactly in longitude with temperature maxima. The percentage variation in ozone increases upward and is always larger than that in temperature at the same pressure. This demonstrates that variations in ozone on constant pressure surfaces may serve as a sensitive indicator of wave activity in the mesosphere.

Frederick, J. E.↗
NASA NTRS1986

Equilibrium shapes of acoustically levitated drops

The quantitative determination of the shape of liquid drops levitated in an ultrasonic standing wave has provided experimental data on the radiation pressure-induced deformations of freely suspended liquids. Within the limits of small deviations from the spherical shape and small drop diameter relative to the acoustic wavelength, an existing approximate theory yields a good agreement with experimental evidence. The data were obtained for millimeter and submillimeter drops levitated in air under 1 g, where g is the sea level gravitational acceleration.

Trinh, E. H.↗
NASA NTRS2006

Oceanic Low Blows Hitting Ice Sheets Where It Hurts

The recent acceleration, thinning and retreat of large outlet glaciers in both Antarctica and Greenland is altering the mass balance of these two large ice sheets and increasing their contribution to rising sea level. In this short Perspective solicited by Science for a special March 24th issue on sea level change, I argue that the cause of these bihemispheric changes is that warmer water has gained access to the undersides of these glaciers where they come afloat from the continent. This process is particularly effective at accelerating glaciers because the beds of the large outlet glaciers are well below sea level (1000 meters or more) but "guarded" downstream by a shallow moraine formed when the glacier was more advanced. Once warmer water can breach this moraine, it sinks in the colder, fresh water behind the moraine and reaches the submarine front of the glacier. The pressure melting effect lowers the melting point of this deep ice allowing the warmer water to melt ice at rates of many tens of meters per year. This melting reduces . the frictional hold of the bed on the ice, allowing the ice to accelerate in agreement with the observations, Hansen has discussed the likelihood that approximately half of the Earth's radiation imbalance is manifesting in warmer ocean waters and Levitus et al. have seen warming in ocean temperature measurements at mid and low latitudes. The behavior of these outlet glaciers indicates this ocean warmth is reaching polar waters. The prognosis is for a continuation of this process, more negative ice sheet mass balances and increased rates of sea level rise.

Bindschadler, Robert↗
NASA NTRS2005

Two-Step Laser Ranging for Precise Tracking of a Spacecraft

A document proposes a two-step laser ranging technique for precise tracking of a coasting interplanetary spacecraft to determine the degree to which leakage of fuel, solar wind, and/or solar-radiation pressure causes it to deviate from a purely gravitational trajectory. Such a determination could contribute to the precision of a test of a theory of gravitation. In the technique, a proof mass would be released from the spacecraft. By use of laser ranging equipment on the spacecraft and retroreflectors attached to the proof mass, the relative position of the spacecraft and proof mass would be determined. Meanwhile, the position of the spacecraft relative to the Earth would be determined by ranging by use of a laser transponder. The vector sum of the two sets of ranging measurements would be the position of the proof mass relative to the Earth. Unlike the acceleration of the spacecraft, the acceleration of the proof mass should not include a residual component attributable to leakage of fuel. In addition, the effects of solar radiation and solar wind on the proof mass could be minimized by releasing the proof mass into the shadow of the spacecraft.

Chui, Talso↗
NASA NTRS1999

Paramagnetic Liquid Bridge in a Gravity-Compensating Magnetic Field

Magnetic levitation was used to stabilize cylindrical columns of a paramagnetic liquid in air between two solid supports. The maximum achievable length to diameter ratio R(sub max) was approx. (3.10 +/- 0.07), very close to the Rayleigh-Plateau limit of pi. For smaller R, the stability of the column was measured as a function of the Bond number, which could be continuously varied by adjusting the strength of the magnetic field. Liquid bridges supported by two solid surfaces have been attracting scientific attention since the time of Rayleigh and Plateau. For a cylindrical bridge of length L and diameter d, it was shown theoretically that in zero gravity the maximum slenderness ratio R (identically = L/d) is pi. The stability and ultimate collapse of such bridges is of interest because of their importance in a number of industrial processes and their potential for low gravity applications. In the presence of gravity, however, the cylindrical shape of an axisymmetric bridge tends to deform, limiting its stability and decreasing the maximum achievable value of R. Theoretical studies have discussed the stability and possible shapes of axisymmetric bridges. Experiments typically are performed in either a Plateau tank, in which the bridge is surrounded by a density-matched immiscible fluid, or in a space-borne microgravity environment. It has been shown, for example, that the stability limit R can be pushed beyond pi by using flow stabilization, by acoustic radiation pressure, or by forming columns in the presence of an axial electric field. In this work, magnetic levitation was used to simulate a low gravity environment and create quasi-cylindrical liquid columns in air. Use of a magnetic field permits us to continuously vary the Bond number B identically equal to (g)(rho)d(exp 2)/4(sigma), where g is the gravitational acceleration, rho is the density of the liquid, and sigma is the surface tension of the liquid in air. The dimensionless Bond number represents the relative importance of external forces acting on the liquid column to those due to surface tension. Our central result is that in a large magnetic field gradient we could create and stabilize columns of mixtures of water and paramagnetic manganese chloride tetrahydrate (MnCl2.4H2O), achieving a length to diameter ratio very close to pi.

Mahajan, Milind P.↗
NASA NTRS1995

Nonequilibrium, large-amplitude MHD fluctuations in the solar wind

Compressible MHD simulations in one dimension with three-dimensional vectors are used to investigate a number of processes relevant to problems in interplanetary physics. The simulations indicate that a large-amplitude nonequilibrium (e.g., linearly polarized) Alfvenic wave, which always starts with small relative fluctuations in the magnitude B of the magnetic field, typically evolves to flatten the magnetic profile in most regions. Under a wide variety of conditions B and the density rho become anticorrelated on average. If the mean magnetic field is allowed to decrease in time, the point where the transverse magnetic fluctuation amplitude delta B(sub T) is greater than the mean field B(sub 0) is not special, and large values of delta B(sub T)/B(sub 0) do not cause the compressive thermal energy to increase remarkably or the wave energy to dissipate at an unusually high rate. Nor does the 'backscatter' of the waves that occurs when the sound speed is less than the Alfven speed result, in itself, in substantial energy dissipation, but rather primarily in a phase change between the magnetic and velocity fields. For isolated wave packets the backscatter does not occur for any of the parameters examined; an initial radiation of acoustic waves away from the packet establishes a stable traveling structure. Thus these simulations, although greatly idealized compared to reality, suggest a picture in which the interplanetary fluctuations should have small deltaB and increasingly quasi-pressure balanced compressive fluctuations, as observed, and in which the dissipation and 'saturation' at delta B(sub T)/B(sub 0) approximately = 1 required by some theories of wave acceleration of the solar wind do not occur. The simulations also provide simple ways to understand the processes of nonlinear steepening and backscattering of Alfven waves and demonstrate the existence of previously unreported types of quasi-steady MHD states.

Roberts, D. Aaron↗
DOE OSTI2022

Impact of specimen preparation method on photovoltaic backsheet degradation during accelerated aging test

In this study, we highlight some important factors in the specimen preparation methods for evaluating photovoltaic backsheet properties after accelerated aging. Two different sequences are considered: Method (I) cut-then-age: cut into 1-cm wide strips and then expose to stress, and Method (II) age-then-cut: expose a larger sheet to stress and then cut into 1-cm widths for mechanical property measurements. We also compare the effect of three cutting methods, (a) tensile specimen punch, (b) paper cutter, and (c) fresh razor blade. Several commercial backsheets were evaluated, with stress exposures including (a) pressure cooker test (PCT), (b) dry ultraviolet (UV) radiation exposure, and (c) UV combined damp heat tests. Fourier transform infrared spectrometer (FTIR) and intrinsic viscosity (IV) were used to analyze the materials on unstressed materials and samples exposed to PCT. The results show that both the cutting method and the time of cutting have an impact on the backsheet mechanical properties. Additionally, under UV exposure, Method II, age-then-cut, generally resulted in a higher average value, with more variation than Method I; however, if the side strips from Method II were excluded, the variation dropped to the same level. This is because the specimens at the sides of the sheet get additional damage from UV light from the exposed sides of the sample. In contrast to UV exposure, PCT specimens prepared by Method II result in lower average values and higher variability. This is attributed to embrittlement through the bulk of the sample where the cutting of embrittled specimens appears to result in more edge defects which can then initiate a break at smaller strains. The data suggest that for UV exposures, the specimens should be cut after aging and the exposed side specimens discarded, and that for PCT exposures, the specimens should be cut before the exposure.

14 SOLAR ENERGY↗
DOE OSTI2025

Study of ponderomotive instability in the FRIB beta=0.53 half-wave resonator

Superconducting radio-frequency niobium cavities are susceptible to deformations caused by external or internal forces, leading to shifts in the cavity resonant frequency. One source of deformation comes from the radiation pressure of the cavity fields, producing the so-called Lorentz force detuning effect. This effect can couple to the cavity mechanical modes in generator driven mode, leading to ponderomotive instability. In the FRIB 322 MHz, β=0.53 Half-wave Resonators (HWR), the instability appeared when the cavity was detuned, with thresholds depending on low-level RF control parameters, such as closed loop gain, as well as accelerating gradient. Using a measured Lorentz Transfer Function, Simulink simulations were conducted to predict the instability thresholds, which were then compared with the experimental results. We will discuss how these thresholds can be broadened to enable stable operation at higher gradients.

Accelerator Physics↗
DOE OSTI2023

Exposure to multiple ion beams, broadly representative of galactic cosmic rays, causes perivascular cardiac fibrosis in mature male rats

Long-duration space exploratory missions to the Earth’s moon and the planet Mars are actively being planned. Such missions will require humans to live for prolonged periods beyond low earth orbit where astronauts will be continuously exposed to high energy galactic cosmic rays (GCRs). A major unknown is the potential impact of GCRs on the risks of developing degenerative cardiovascular disease, which is a concern to NASA. A ground-based rat model has been used to provide a detailed characterization of the risk of long-term cardiovascular disease from components of GCRs at radiation doses relevant to future human missions beyond low earth orbit. Six month old male WAG/RijCmcr rats were irradiated at a ground-based charged particle accelerator facility with high energy ion beams broadly representative of GCRs: protons, silicon and iron. Irradiation was given either as a single ion beam or as a combination of three ion beams. For the doses used, the single ion beam studies did not show any significant changes in the known cardiac risk factors and no evidence of cardiovascular disease could be demonstrated. In the three ion beam study, the total cholesterol levels in the circulation increased modestly over the 270 day follow up period, and inflammatory cytokines were also increased, transiently, 30 days after irradiation. Perivascular cardiac collagen content, systolic blood pressure and the number of macrophages found in the kidney and in the heart were each increased 270 days after irradiation with 1.5 Gy of the three ion beam grouping. These findings provide evidence for a cardiac vascular pathology and indicate a possible threshold dose for perivascular cardiac fibrosis and increased systemic systolic blood pressure for complex radiation fields during the 9 month follow up period. The development of perivascular cardiac fibrosis and increased systemic systolic blood pressure occurred at a physical dose of the three ion beam grouping (1.5 Gy) that was much lower than that required to show similar outcomes in earlier studies with the same rat strain exposed to photons. Further studies with longer follow up periods may help determine whether humans exposed to lower, mission-relevant doses of GCRs will develop radiation-induced heart disease.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Ultrafast multi-cycle terahertz measurements of the electrical conductivity in strongly excited solids

Key insights in materials at extreme temperatures and pressures can be gained by accurate measurements that determine the electrical conductivity. Free-electron laser pulses can ionize and excite matter out of equilibrium on femtosecond time scales, modifying the electronic and ionic structures and enhancing electronic scattering properties. The transient evolution of the conductivity manifests the energy coupling from high temperature electrons to low temperature ions. Here we combine accelerator-based, high-brightness multi-cycle terahertz radiation with a single-shot electro-optic sampling technique to probe the evolution of DC electrical conductivity using terahertz transmission measurements on sub-picosecond time scales with a multi-undulator free electron laser. Our results allow the direct determination of the electron-electron and electron-ion scattering frequencies that are the major contributors of the electrical resistivity.

36 MATERIALS SCIENCE↗