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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Single-Bunch Instabilities Driven by Space Charge During Low-Energy Cooling at Injection in the EIC Hadron Storage Ring

This paper presents a simulation-based study of single-bunch dynamics at the injection energy of 23.8 GeV for protons in the EIC hadron storage ring, focusing on the impact of space-charge–driven instabilities. The analysis demonstrates that at this energy, the proton bunch experiences significant transverse space-charge forces, which can reduce the stability margin in the presence of the geometric and resistive wall impedance. Various collective effects were considered, with particular attention to the nonlinear nature of the transverse space charge. To stabilize the beam, high chromaticity and octupoles were introduced and their effects analyzed using the ELEGANT code. The results provide a quantitative assessment of the stability thresholds and offer guidance for the machine design and operational strategy at injection.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Solutions to Droop and the Green Gap by Novel Carrier Injection

Long-wavelength (green, yellow, red) visible light-emitting diodes (LEDs) have historically been inefficient compared to blue light-emitters in the III-nitrides. This is due to many factors, including poor material quality due to the low growth temperatures required for high Incomposition InGaN quantum wells (QWs), and the polar nature of the III-nitride crystal structure. Spontaneous and piezoelectric polarization in the III-nitrides causes enhanced quantum-confined Stark effect (QCSE), which spatially separates electrons and holes and reduces radiative recombination (ie: light output) from the devices. Polarization in the crystal also induces additional potential barriers that electrons and holes must cross over before entering the QWs where they can recombine to emit light. Both of these polarization effects worsen as emission wavelength increases, making blue III-nitride LEDs are the most efficient and red III-nitride LEDs the least efficient. The focus of this project has been solving the latter polarization-related issue through the implementation of V-defects in long wavelength LEDs. V-defects are morphological defects which are commonly observed in c-plane III-nitrides. They are observed as hexagonal pyramid-shaped depressions on the c-plane surface, with six semipolar sidewalls. They typically form at the apex of threading dislocations (TDs) under conditions of kinetically-limited growth and low growth-temperature. They were initially thought to be detrimental to LED performance and much early work focused on eliminating them entirely from III-nitride devices. However, over the past decade work has emerged that indicate that they can improve LED performance by allowing electrons and holes to bypass the polarization-induced barriers present in the c-plane and directly enter the QWs of an LED. This is due to the semipolar nature of the V-defect sidewall: these sidewalls are thin and lack the polarization-induced barriers which prevent carriers easily moving between layers. V-defects have since been determined to be an efficient avenue by which to inject electrons and holes into the c-plane QWs where they can recombine to emit light. Throughout this project we have explored lateral injection through a variety of methods: simulation (Task 2), epitaxial growth of V-defect and non-V-defect LEDs (Tasks 1, 3, 4, 5, 6), and advanced characterization methods (Task 7). All tasks have been completed. A description of each task completed follows from this section.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Response of Surface Ultraviolet and Visible Radiation to Stratospheric SO 2 Injections

Climate modification by stratospheric SO 2 injections, to form sulfate aerosols, may alter the spectral and angular distributions of the solar ultraviolet and visible radiation that reach the Earth’s surface, with potential consequences to environmental photobiology and photochemistry. We used modeling results from the CESM1(WACCM) stratospheric aerosol geoengineering large ensemble (GLENS) project, following the RCP8.5 emission scenario, and one geoengineering experiment with SO 2 injections in the stratosphere, designed to keep surface temperatures at 2020 levels. Zonally and monthly averaged vertical profiles of O 3 , SO 2 , and sulfate aerosols, at 30 N and 70 N, served as input into a radiative transfer model, to compute biologically active irradiances for DNA damage ( i DNA ), UV index (UVI), photosynthetically active radiation (PAR), and two key tropospheric photodissociation coefficients ( j O1D for O 3 + hν (λ < 330 nm) → O( 1 D) + O 2 ; and j NO2 for NO 2 + hν (λ < 420 nm) → O( 3 P) + NO). We show that the geoengineering scenario is accompanied by substantial reductions in UV radiation. For example, comparing March 2080 to March 2020, i DNA decreased by 25% to 29% in the subtropics (30 N) and by 26% to 33% in the polar regions (70 N); UVI decreased by 19% to 20% at 30 N and 23% to 26% at 70 N; and j O1D decreased by 22% to 24% at 30 N and 35% to 40% at 70 N, with comparable contributions from sulfate scattering and stratospheric O 3 recovery. Different responses were found for processes that depend on longer UV and visible wavelengths, as these are minimally affected by ozone; PAR and j NO2 were only slightly lower (9–12%) at 30 N, but much lower at 70 N (35–40%). Similar reductions were estimated for other months (June, September, and December). Large increases in the PAR diffuse-direct ratio occurred in agreement with previous studies. Absorption by SO 2 gas had a small (~1%) effect on j O1D , i DNA , and UVI, and no effect on j NO2 and PAR.

42 ENGINEERING↗
DOE OSTI2016

A giant Lyα nebula in the core of an x-ray cluster at z = 1.99: implications for early energy injection

We present the discovery of a giant ≳100 kpc Lyα nebula detected in the core of the X-ray emitting cluster CL J1449+0856 at z = 1.99 through Keck/LRIS narrow-band imaging. This detection extends the known relation between Lyα nebulae and overdense regions of the universe to the dense core of a 5–7 × 10{sup 13} M {sub ⊙} cluster. The most plausible candidates to power the nebula are two Chandra-detected AGN host cluster members, while cooling from the X-ray phase and cosmological cold flows are disfavored primarily because of the high Lyα to X-ray luminosity ratio (L{sub Lyα}/L{sub X}≈0.3, ≳10–1000 times higher than in local cool-core clusters) and by current modeling. Given the physical conditions of the Lyα-emitting gas and the possible interplay with the X-ray phase, we argue that the Lyα nebula would be short-lived (≲10 Myr) if not continuously replenished with cold gas at a rate of ≳1000 M {sub ⊙} yr{sup −1}. We investigate the possibility that cluster galaxies supply the required gas through outflows and we show that their total mass outflow rate matches the replenishment necessary to sustain the nebula. This scenario directly implies the extraction of energy from galaxies and its deposition in the surrounding intracluster medium (ICM), as required to explain the thermodynamic properties of local clusters. We estimate an energy injection of the order of ≈2 keV per particle in the ICM over a 2 Gyr interval. In our baseline calculation, AGNs provide up to 85% of the injected energy and two-thirds of the mass, while the rest is supplied by supernovae-driven winds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

ION INJECTION AT QUASI-PARALLEL SHOCKS SEEN BY THE CLUSTER SPACECRAFT

Collisionless shocks in space plasma are known to be capable of accelerating ions to very high energies through diffusive shock acceleration (DSA). This process requires an injection of suprathermal ions, but the mechanisms producing such a suprathermal ion seed population are still not fully understood. We study acceleration of solar wind ions resulting from reflection off short large-amplitude magnetic structures (SLAMSs) in the quasi-parallel bow shock of Earth using in situ data from the four Cluster spacecraft. Nearly specularly reflected solar wind ions are observed just upstream of a SLAMS. The reflected ions are undergoing shock drift acceleration (SDA) and obtain energies higher than the solar wind energy upstream of the SLAMS. Our test particle simulations show that solar wind ions with lower energy are more likely to be reflected off the SLAMS, while high-energy ions pass through the SLAMS, which is consistent with the observations. The process of SDA at SLAMSs can provide an effective way of accelerating solar wind ions to suprathermal energies. Therefore, this could be a mechanism of ion injection into DSA in astrophysical plasmas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The Timing of Potential Last Nucleosynthetic Injections into the Protosolar Molecular Cloud Inferred from 41 Ca– 26 Al Systematics of Bulk CAIs

Short-lived radionuclides (SLRs) provide important information about the chronology of the early solar system. Among them, 41 Ca, due to its decay to 41 K with a half-life of only 0.1 Ma, is particularly valuable in constraining the timescales and origins of both SLRs and the formation of the oldest solar system materials, the Ca–Al-rich inclusions (CAIs). The initial abundance of 41Ca in the solar system, expressed as the ( 41 Ca/ 40 Ca)I ratio, is the key to unveiling the origin of this nuclide. Here, we report a new solar system ( 41 Ca/ 40 Ca)I ratio of 2.0 × 10 −8 derived from the K isotope compositions of two CAIs. This new ratio is about four times higher than the previous value inferred from a mineral isochron. Such a high ( 41 Ca/ 40 Ca)I ratio in the CAIs exceeds that expected for the protosolar molecular cloud by ∼1000×, implying very late injection of the 41 Ca (and possibly other SLRs) into the protosolar molecular cloud. The correlated enrichments of 41 Ca and 26 Al in the bulk CAI samples hint at a common stellar origin of both SLRs. The injection time estimated from our new data depends on the stellar source—it ranges from 0.6 Ma for a Wolf–Rayet wind to 1.0 Ma for a TP-AGB star ejecta.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

On the Injection Scale of the Turbulence in the Partially Ionized Very Local Interstellar Medium

The cascade of magnetohydrodynamic (MHD) turbulence is subject to ion–neutral collisional damping and neutral viscous damping in the partially ionized interstellar medium. By examining the damping effects in the warm and partially ionized local interstellar medium, we find that the interstellar turbulence is damped by neutral viscosity at ~261 au and cannot account for the turbulent magnetic fluctuations detected by Voyager 1 and 2. The MHD turbulence measured by Voyager in the very local interstellar medium (VLISM) should be locally injected in the regime where ions are decoupled from neutrals for its cascade to survive the damping effects. With the imposed ion–neutral decoupling condition and the strong turbulence condition for the observed Kolmogorov magnetic energy spectrum, we find that the turbulence in the VLISM is sub-Alfvénic, and its largest possible injection scale is ~194 au.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Exact Calculation of Nonideal Fields Demonstrates Their Dominance of Injection in Relativistic Reconnection

Magnetic reconnection is an important source of energetic particles in systems ranging from astrophysics to the laboratory. The large separation of spatiotemporal scales involved makes it critical to determine the minimum physical model containing the necessary physics for modeling particle acceleration. Here, by resolving the energy gain from ideal and nonideal magnetohydrodynamic electric fields self-consistently in kinetic particle-in-cell simulations of reconnection, we conclusively show the dominant role of the nonideal field for the early stage of energization known as injection. The importance of the nonideal field increases with magnetization, guide field, and in three dimensions, indicating its general importance for reconnection in natural astrophysical systems. We obtain the statistical properties of the injection process from the simulations, paving the way for the development of extended MHD models capable of accurately modeling particle acceleration in large-scale systems. The novel analysis method developed in this study can be applied broadly to give new insight into a wide range of processes in plasma physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Durability Study of a High-Pressure Common Rail Fuel Injection System Using Lubricity Additive-Dosed Gasoline-Like Fuel—Improved Endurance with Upgraded Hardware

Gasoline compression ignition (GCI) is a promising combustion technology that can help the commercial transportation sector achieve operational flexibility and meet upcoming criteria pollutant regulations. However, high-pressure fuel injection systems (>1000 bar) are needed to enable GCI and fully realize its benefits compared to conventional diesel combustion. This work is a continuation of previous durability studies that identified three key technical risks after running gasoline-like fuel through a heavy-duty, common rail injection system: (i) cavitation damage to the inlet check valve of the high-pressure pump, (ii) loss of injector fueling capacity, (iii) cavitation erosion of the injector nozzle holes. Upgraded hardware solutions were tested on a consistent 400- to 800-hour NATO durability cycle with the same gasoline-like fuel as previous studies. The upgraded pump showed no signs of abnormal wear or cavitation damage to the inlet check valve. In contrast to previous studies, there were no signs of pump performance degradation observed after 400 hours of testing. Material selection and design upgrades were also made to the injector which, only showed a 6.5% loss in fueling capacity after 800 hours of durability testing compared to 49.3% previously. Finally, geometric nozzle hole features such as higher inlet radius of curvature and higher K-factor were found to correlate with reduced cavitation erosion. However, mitigation of eccentric radial needle motion (i.e., wobble) is likely needed to further suppress cavitation. In general, the results from this study indicate there are viable hardware-based solutions for improving the endurance of high-pressure systems when running with gasoline-like fuel.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2024

HSW-V v1.0: localized injections of interactive volcanic aerosols and their climate impacts in a simple general circulation model

Abstract. A new set of standalone parameterizations is presented for simulating the injection, evolution, and radiative forcing by stratospheric volcanic aerosols against an idealized Held–Suarez–Williamson (HSW) atmospheric background in the Energy Exascale Earth System Model version 2 (E3SMv2). In this model configuration (HSW with enabled volcanism, HSW-V), sulfur dioxide (SO2) and ash are injected into the atmosphere with a specified profile in the vertical, and they proceed to follow a simple exponential decay. The SO2 decay is modeled as a perfect conversion to a long-living sulfate aerosol which persists in the stratosphere. All three species are implemented as tracers in the model framework and are transported by the dynamical core's advection algorithm. The aerosols contribute simultaneously to local heating of the stratosphere and cooling of the surface by a simple plane-parallel Beer–Lambert law applied on two zonally symmetric radiation broadbands in the longwave and shortwave ranges. It is shown that the implementation parameters can be tuned to produce realistic temperature anomaly signatures of large volcanic events. In particular, results are shown for an ensemble of runs that mimic the volcanic eruption of Mt. Pinatubo in 1991. The design requires no coupling to microphysical subgrid-scale parameterizations and thus approaches the computational affordability of prescribed aerosol forcing strategies. The idealized simulations contain a single isolated volcanic event against a statistically uniform climate, where no background aerosols or other sources of externally forced variability are present. HSW-V represents a simpler-to-understand tool for the development of climate source-to-impact attribution methods.

Hollowed, Joseph P. (ORCID:0000000286581672)↗
NASA NTRS1969

Electron injection into zinc oxide.

Electron injection into ZnO from aqueous solutions of stable substances, correlating injection with oxidation potential of substance

Freund, T.↗
NASA NTRS1969

Carrier injection electroluminescence

Carrier injection luminescence properties useful for display medium applications, discussing group II-VI compounds as injection host crystal materials

Haas, R. W.↗
NASA NTRS1972

Main tank injection pressurization program

Computer program predicts performance of fluorine-hydrogen main tank injection pressurization system for full range of liquid-hydrogen-fueled space vehicles. Analytical model includes provisions for heat transfer, injectant jet penetration, and ullage gas mixing. Analysis predicts GF2 usage, ullage gas and tank wall temperatures, and LH2 evaporation.

Cady, E. C.↗
NASA NTRS1972

Exploratory study of the effects of injection configurations and inlet flow conditions on the characteristics of flow in spherical chambers

Flow visualization studies were conducted to evaluate techniques for injecting simulated-fuel and simulated-propellant gases into a spherical cavity for application to open-cycle gaseous-core nuclear rockets. Preliminary studies were conducted with six simulated-fuel injectors and eight simulated-propellant injection configurations. Additional tests were conducted with the best configuration to determine the effect of weight-flow ratio, gas density ratio, injector location, and flow distribution on the simulated-fuel containment characteristics.

Johnson, B. V.↗
NASA NTRS1972

Inviscid analysis of jet injection between two moving streams

An analytical method is developed for determining the flow interaction when a two-dimensional jet is injected between two moving streams. The jet is flowing out of channel and is turned as it enters between the external streams. The local velocity variation resulting from the flow interaction provides a static pressure variation along the jet bounding streamlines that is a priori unknown. Hense, the flow must be obtained by coupling the three flow regions (the jet and the free stream on either side) along the jet boundaries. Both external streams have the same total pressure, which is different from that in the jet. The solution is for the condition that the total pressure in the jet does not differ from the free-stream value by a large amount compared with the free-stream dynamic head. Results are given for the shape of the jet boundaries for various injection configurations.

Goldstein, M. E.↗
NASA NTRS1971

Solutions for Reacting and Nonreacting Viscous Shock Layers with Multicomponent Diffusion and Mass Injection

Numerical solutions are presented for the viscous shocklayer equations where the chemistry is treated as being either frozen, equilibrium, or nonequilibrium. Also the effects of the diffusion model, surface catalyticity, and mass injection on surface transport and flow parameters are considered. The equilibrium calculations for air species using multicomponent: diffusion provide solutions previously unavailable. The viscous shock-layer equations are solved by using an implicit finite-difference scheme. The flow is treated as a mixture of inert and thermally perfect species. Also the flow is assumed to be in vibrational equilibrium. All calculations are for a 45 deg hyperboloid. The flight conditions are those for various altitudes and velocities in the earth's atmosphere. Data are presented showing the effects of the chemical models; diffusion models; surface catalyticity; and mass injection of air, water, and ablation products on heat transfer; skin friction; shock stand-off distance; wall pressure distribution; and tangential velocity, temperature, and species profiles.

Moss, J. N.↗