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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Thermal Flux Maximization from a DD Neutron Generator

The University of Sharjah recently acquired a model DD-109.4M neutron generator from Adelphi Technology. The generator is moderated and has three neutron ports which are capable of providing fast and thermal neutrons. The neutron ports are plugged with polyethylene layers of different thickness in order to control the neutron flux at different regions in the port. Neutron Activation Analysis (NAA) is an important analysis technique to determine the amounts of isotopes in a sample at different concentrations. For many isotopes the ability to precisely determine their concentrations is enhanced by utilizing thermal neutrons in the activation process; where the capture cross section is greatest. It is thus important to subject the sample to the maximum thermal flux in order to minimize the time required to activate the sample and consequently extend the lifetime of the neutron generator. A detailed MCNP model of the neutron generator has been developed for the purpose of determining the moderator thickness required to maximize the thermal neutron flux in the neutron port. The maximization of the neutron flux must therefore take into account both the forward and backscattered neutrons reaching the sample. Also provided in this work is a mapping of the thermal flux at different moderator thicknesses in order to study the variation of the flux over the area of the sample. The developed model will be used as the basis for optimizing experiments and predicting their results. A study was performed to determine the moderator thickness needed to maximize the thermal neutron flux that can be obtained from a DD neutron generator. This has a significant role in the efficient utilization of the neutron generator. The maximum thermal neutron flux was found at approximately a 3.2 cm moderator thickness. The thermal neutron flux is resulting from both the directly moderated neutrons and the backscattered neutrons from the surrounding polyethylene. The results obtained in this work will be verified experimentally by irradiating samples at different moderator thickness and performing a neutron activation analysis for these samples. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

Flux Estimation of a PuBe source using Delayed Gamma Neutron Activation Analysis

For handling and storage of a highly radioactive source, it is necessary to have an accurate knowledge of the radioactive source as well as the neutron flux. Recently, due to radiation safety requirements, a PuBe alpha-neutron source at an activation facility at IIT-Kanpur had to be taken out of its original damaged howitzer and placed inside a new shielded container. While, this effort was successful in reducing the radiation dose, and making the setup safe for laboratory measurements, the new source moderator configuration left the new Pu-Be source spectrum unknown. Therefore, in this work we have used delayed gamma neutron activation analysis (DGNAA) of aluminum, copper, iron, manganese (found in iron), and silver for thermal neutron flux estimation of the Pu-Be neutron source. A series of DGNAA measurements with different samples were carried out to find the value of the average thermal neutron flux of a Pu-Be neutron source at Indian Institute of Technology-Kanpur. The order of the thermal neutron flux is found to be nearly 1.64 x 10{sup 5} excluding aluminum. Upon including aluminum, the value of thermal neutron flux decreases to 1.57x10{sup 5}. We have used common metals (like aluminum, silver, copper and iron) to calculate the thermal neutron flux. The calculated value of the thermal neutron flux is consistent for all the metals except for iron. Iron is giving a value almost four times larger than the average calculated value of the thermal neutron flux using other six samples. The reason is currently being investigated. The DGNAA technique came out to be a very useful technique. Now that we know the thermal neutron flux of the Pu-Be source, our future work will include improving the safety and shielding calculations for our activation facility at IIT-Kanpur. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

Prediction of MeV electron fluxes throughout the outer radiation belt using multivariate autoregressive models

The Van Allen radiation belts surrounding the Earth are filled with MeV-energy electrons. This region poses ionizing radiation risks for spacecraft that operate within it, including those in geostationary orbit (GEO) and medium Earth orbit. In order to provide alerts of electron flux enhancements, 16 prediction models of the electron log-flux variation throughout the equatorial outer radiation belt as a function of the McIlwain L parameter were developed using the multivariate autoregressive model and Kalman filter. Measurements of omnidirectional 2.3 MeV electron flux from the Van Allen Probes mission as well as >2 MeV electrons from the GOES 15 spacecraft were used as the predictors. Furthermore, we selected model explanatory parameters from solar wind parameters, the electron log-flux at GEO, and geomagnetic indices. For the innermost region of the outer radiation belt, the electron flux is best predicted by using the Dst index as the sole input parameter. For the central to outermost regions, at L≥4.8 and L ≥5.6, the electron flux is predicted most accurately by including also the solar wind velocity and then the dynamic pressure, respectively. The Dst index is the best overall single parameter for predicting at 3 ≤ L ≤ 6, while for the GEO flux prediction, the K P index is better than Dst. Finally, a test calculation demonstrates that the model successfully predicts the timing and location of the flux maximum as much as 2 days in advance and that the electron flux decreases faster with time at higher L values, both model features consistent with the actually observed behavior.

58 GEOSCIENCES↗
DOE OSTI2022

Estimation of the Surface Fluxes for Heat and Momentum in Unstable Conditions with Machine Learning and Similarity Approaches for the LAFE Data Set

Abstract Measurements of three flux towers operated during the land atmosphere feedback experiment (LAFE) are used to investigate relationships between surface fluxes and variables of the land–atmosphere system. We study these relations by means of two machine learning (ML) techniques: multilayer perceptrons (MLP) and extreme gradient boosting (XGB). We compare their flux derivation performance with Monin–Obukhov similarity theory (MOST) and a similarity relationship using the bulk Richardson number (BRN). The ML approaches outperform MOST and BRN. Best agreement with the observations is achieved for the friction velocity. For the sensible heat flux and even more so for the latent heat flux, MOST and BRN deviate from the observations while MLP and XGB yield more accurate predictions. Using MOST and BRN for latent heat flux, the root mean square errors (RMSE) are 107 Wm $$^{-2}$$ - 2 and 121 Wm $$^{-2}$$ - 2 , respectively, as well as the intercepts of the regression lines are $$\approx 110$$ ≈ 110 Wm $$^{-2}$$ - 2 . For the ML methods, the RMSEs reduce to 31 Wm $$^{-2}$$ - 2 for MLP and 33 Wm $$^{-2}$$ - 2 for XGB as well as the intercepts to just 4 Wm $$^{-2}$$ - 2 for MLP and $$-1$$ - 1 Wm $$^{-2}$$ - 2 for XGB with slopes of the regression lines close to 1, respectively. These results indicate significant deficiencies of MOST and BRN, particularly for the derivation of the latent heat flux. In fact, in contrast to the established theories, feature importance weighting demonstrates that the ML methods base their improved derivations on net radiation, the incoming and outgoing shortwave radiations, the air temperature gradient, and the available water contents, but not on the water vapor gradient. The results imply that further studies of surface fluxes and other turbulent variables with ML techniques provide great promise for deriving advanced flux parameterizations and their implementation in land–atmosphere system models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Effects of Fluorine on Solidification, Viscosity, Structure, and Heat Transfer of CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes

To mitigate the chemical reaction between mold fluxes and high-Al steel, CaO-Al{sub 2}O{sub 3}-based mold fluxes were proposed to replace the conventional CaO-SiO{sub 2}-based mold fluxes. However, the high viscosity of CaO-Al{sub 2}O{sub 3}-based mold fluxes is harmful to the lubrication to the strand. In this article, the effects of fluorine on solidification, viscosity, structure, and heat transfer of CaO-Al{sub 2}O{sub 3}-based mold fluxes were evaluated. The addition of fluorine increased the break temperature and decreased the heat transfer rate of mold fluxes. It also reduced the flux viscosity at 1673 K (1400 °C) when fluorine content increased from 4.0 to 6.9 mass pct; but a further increase of fluorine to 12.5 mass pct did not notably change the flux viscosity. This phenomenon was correlated to the synergic effects of the dissociation of flux network and the increased potential of nucleation at high temperature with the fluorine addition.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Al{sub 2}O{sub 3}/(B{sub 2}O{sub 3 }+ Na{sub 2}O) Ratio on CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes: Melting Property, Viscosity, Heat Transfer, and Structure

CaO-Al{sub 2}O{sub 3}-based mold fluxes, which are under development for the continuous casting of high-Al steel, contain fluxing compounds, such as Na{sub 2}O and B{sub 2}O{sub 3}. The reaction between [Al] and the fluxing agents in mold fluxes leads to an increase in Al{sub 2}O{sub 3} and a decrease in B{sub 2}O{sub 3} and Na{sub 2}O concentrations, changing the properties of mold fluxes. The effect of the Al{sub 2}O{sub 3}/(B{sub 2}O{sub 3 }+ Na{sub 2}O) ratio on the melting properties, viscosity, heat transfer, and structure of the CaO-Al{sub 2}O{sub 3}-based mold fluxes is presented in this work. The increase of the Al{sub 2}O{sub 3}/(B{sub 2}O{sub 3 }+ Na{sub 2}O) ratio in the fluxes raised the melting temperature and high-temperature viscosity of mold fluxes but decreased the heat transfer rate across the flux disks. It also enhanced the degree of polymerization by promoting the formation of 3-D aluminate structure, which accounted for the change of the viscous behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Deep Vadose Zone Contaminant Flux Evaluation at the Hanford BY-Cribs Site using Forward and Imposed Concentration Modeling Approaches

For sites with vadose zone contamination, the nature and extent of groundwater contaminant plumes are related to the flux into groundwater. In thick vadose zones at arid sites, transport is likely relative slow, complicating direct measurement of contaminant flux. A predictive numerical analysis was applied to estimate contaminant flux to groundwater at the Hanford BY Cribs site. The site received large amounts of waste water in the 1950’s, containing contaminants such as technicium-99 and nitrate. Recently, large increases in groundwater concentrations have been observed in site groundwater wells and, for potential remediation purposes, the assumption that the changes are the result of increased vadose zone fluxes into groundwater needed to be evaluated. The analysis approach uses forward simulations, tracking contaminants during and after disposal, and imposed concentration (IC) simulations, where concentrations, derived from electrical conductivity data obtained in 2007, are imposed on the flow field. A total of three IC methods, relating electrical conductivity to nitrate concentrations, are developed and tested. The numerical analysis shows that the forward simulations predict high fluxes during and directly after disposal, with decreasing trends starting not later than 1970. Although the IC simulations show differences in the nitrate vadose zone mass imposed in 2007 compared to forward simulations, the IC simulations also show declining nitrate fluxes over time. The predicted fluxes of the forward and IC simulations after 2007 are in reasonable agreement. Given the declining nature of the contaminant fluxes, it can be concluded that the observed concentration increases in the groundwater below the BY Cribs site cannot be explained as resulting from an increase in contaminant flux from the vadose zone. An alternative explanation, based on the observed decrease in aquifer thickness below the site, is presented.

Oostrom, Martinus↗
DOE OSTI2015

Effects of increased upward flux of dissolved salts caused by CO2 storage or other factors

Injection of CO2 in deep saline aquifers is being considered to reduce greenhouse gases in the atmosphere, and this process is expected to increase the pressure in these deep aquifers. One potential consequence of pressurization is an increase in the upward flux of saline water. Saline groundwater occurs naturally at shallow depths in many sedimentary basins, so an upward flux of solutes could degrade the quality of freshwater aquifers and threaten aquatic ecosystems. One problem could occur where saline water flowed upward along preferential paths, like faults or improperly abandoned wells. Diffuse upward flow through the natural stratigraphy could also occur in response to basin pressurization. This process would be slower, but diffuse upward flow could affect larger areas than flow through preferential paths, and this motivated us to evaluate this process. We analyzed idealized 2D and 3D geometries representing the essential details of a shallow, freshwater aquifer underlain by saline ground water in a sedimentary basin. The analysis was conducted in two stages, one that simulated the development of a freshwater aquifer by flushing out saline water, and another that simulated the effect of a pulse-like increase in the upward flux from the basin. The results showed that increasing the upward flux from a basin increased the salt concentration and mass loading of salt to streams, and decrease the depth to the fresh/salt transition. The magnitude of these effects varied widely, however, from a small, slow process that would be challenging to detect, to a large, rapid response that could be an environmental catastrophe. The magnitude of the increased flux, and the initial depth to the fresh/salt transition in groundwater controlled the severity of the response. We identified risk categories for salt concentration, mass loading, and freshwater aquifer thickness, and we used these categories to characterize the severity of the response. This showed that risks would likely be minor if the upward flux was smaller than a few tenths of the magnitude of recharge, according to the 2D analyses. The 3D analyses also show that upward flux could occur without a significant increase in the risk categories. The major contribution of this work is that it shows how a large increase in diffuse upward flux from a basin could cause significant problems, but a small increase in upward flux may occur without significantly affecting risks to the shallow freshwater flow system. This heightens the importance of understanding interactions between shallow and deep hydrologic systems when characterizing CO2 storage projects.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

The charge transfer transition phenomenon and microstructure of Eu{sup 3+}-doped NaCaPO{sub 4} phosphors sintered with NH{sub 4}Cl flux via solid-state reaction

Graphical abstract: This paper describes: The charge transfer transition phenomenon and microstructure of Eu{sup 3+}-doped NaCaPO{sub 4} phosphors sintered with NH{sub 4}Cl flux via solid-state reaction. The emission intensity of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux is enhanced as the sintering temperature was increased from 800 °C to 1000 °C and reveals the maximum value at 1000 °C. Photoluminescence emission spectra of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux sintered at various sintering temperature for 3 h via solid state reaction method (λ{sub ex} = 270 nm). Highlights: ► NH{sub 4}Cl flux is helpful for enhancing the crystallization degree and decreasing surface defects. ► A single phase of NaCaPO{sub 4}:Eu{sup 3+} phosphor was observed as the sintering temperature was increased from 800 °C to 1000 °C. ► The intensity of the excitation peaks displays a maximum value at 1000 °C. ► The NaCaPO{sub 4} host added with NH{sub 4}Cl flux and sintered at the different temperature can affect the morphology. ► The NaCaPO{sub 4} host added with NH{sub 4}Cl flux and sintered at the different temperature can affect fluorescent properties. - Abstract: NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux sintered at various sintering temperature (800, 900, 1000, 1100 °C) for 3 h under air atmosphere were synthesized successfully via solid state reaction method. It is found that the addition of NH{sub 4}Cl flux and different sintering temperatures can affect the morphology and fluorescent properties of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphor. The X-ray diffractions show a single phase and the microstructure observations show uniform morphologies for NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors sintered at the range from 900 °C to 1000 °C, indicating that addition of 2 wt.% NH{sub 4}Cl flux is helpful for enhancing the crystallization, thus improving the luminescence intensity of the charge transfer transition. The intensity of the excitation peaks displayed a maximum value at 1000 °C. The chromaticity (x, y) is in the orange-red region (0.54, 0.39) and the lifetime value is about 2.1 ms, suitable for the remote phosphor packages.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Changes in inundation drive carbon dioxide and methane fluxes in a temperate wetland

Wetlands cycle carbon by being net sinks for carbon dioxide (CO 2 ) and net sources of methane (CH 4 ). Daily and seasonal temporal patterns, dissolved oxygen (DO) availability, inundation status (flooded or dry/partially flooded), water depth, and vegetation can affect the magnitude of carbon uptake or emissions, but the extent and interactive effects of these variables on carbon gas fluxes are poorly understood. We characterized the linkages between carbon fluxes and these environmental and temporal drivers at the Old Woman Creek National Estuarine Research Reserve (OWC), OH. We measured diurnal gas flux patterns in an upstream side channel (called the cove) using chamber measurements at six sites (three vegetated and three non-vegetated). We sampled hourly from 7 AM to 7 PM and monthly from July to October 2022. DO concentrations and water levels were measured monthly. Water inundation status had the most influential effect on carbon fluxes with flooded conditions supporting higher CH 4 fluxes (0.39 μmol CH 4 m –2 s –1 ; –1.23 μmol CO 2 m –2 s –1 ) and drier conditions supporting higher CO 2 fluxes (0.03 μmol CH 4 m –2 s –1 ; 0.86 μmol CO 2 m –2 s –1 ). When flooded, the wetland was a net CO 2 sink; however, it became a source for both CH 4 and CO 2 when water levels were low. We compared chamber-based gas fluxes from the cove in flooded (July) and dry (August) months to fluxes measured with an eddy covariance tower whose footprint covers flooded portions of the wetland. The diurnal pattern of carbon fluxes at the tower did not vary with changing water levels but remained a CO 2 sink and a CH 4 source even when the cove where we performed the chamber measurements dried out. Furthermore, these results emphasize the role of inundation status on wetland carbon cycling and highlight the importance of fluctuating hydrologic patterns, especially hydrologic drawdowns, under changing climatic conditions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Monitoring autophagic flux using p62/SQSTM1 based luciferase reporters in glioma cells

Highlights: • A luciferase based autophagic flux detection system, Luc2p-p62 vs. Luc2p-p62ΔU, was developed. • This system can be used to detect TMZ-induced autophagic flux changes in U87MG cells. • This system can assay the effect of autophagy modulators in different types of tumor cells. Autophagy is a highly dynamic process characterized with the term of autophagic flux. In the present study, we developed a quantifiable luciferase reporter system to measure the capacity as well as the dynamics of autophagic flux. Briefly, a luciferase variant of Luc2p was fused with p62/SQSTM1 or its UBA domain deletion mutant (p62ΔU) and transfected into cells. The expressed Luc2p-p62 fusion protein was primarily degraded via autophagy, while Luc2p-p62ΔU was employed as a normalization control due to its resistance to autophagic degradation. The luciferase activity of the lysates from two parallel populations of glioma cells expressing either Luc2p-p62 or Luc2p-p62ΔU was determined and the ratio of Luc2p-p62ΔU/Luc2p-p62 was used to assay the autophagic flux. By this approach, the induction of autophagy was manifested as an increased Luc2p-p62ΔU/Luc2p-p62 ratio, which could be neutralized by autophagy inhibitors or knockdown of ATG5. The performance of our autophagic flux detection system was comparable to a recently reported GFP-LC3-RFP-LC3ΔG probe. We tested the system in TMZ treated glioma cells, and found that coadministration of chloroquine to attenuate cellular autophagic flux significantly improved the TMZ efficacy by triggering more early apoptosis. Collectively, our luciferase-based autophagic flux assay may serve as a useful alternative yet sensitive method for autophagic flux detection in tumor cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Large Eddies Regulate Turbulent Flux Gradients in Coupled Stable Boundary Layers

Due to strong mean wind shear, the stable boundary layer (SBL) becomes vertically coupled. In a coupled SBL, large turbulent eddies enhance cross-layer mixing and vertically mix turbulent kinetic energy. However, large gradients in momentum and heat fluxes are frequently observed, degrading the performance of Monin-Obukhov similarity theory. It is shown that increased vertical gradients of mean variables (i.e., wind speed and potential temperature) can cause flux gradients. This process is operated upon by downward penetrating large eddies with altered phase difference, contributing unevenly to fluxes and thus causing flux gradients. In the coupled SBL with small gradients in mean variables, large eddies are vertically synchronized, contributing evenly to fluxes across layers and thus causing small flux gradients. As turbulent production becomes weak and the cross-layer difference in turbulent flux transport increases, large eddies become less vertically synchronized, contributing unevenly to fluxes across layers and thus causing large flux gradients.

58 GEOSCIENCES↗
DOE OSTI2021

Joint CO 2 Mole Fraction and Flux Analysis Confirms Missing Processes in CASA Terrestrial Carbon Uptake Over North America

Terrestrial biosphere models (TBMs) play a key role in the detection and attribution of carbon cycle processes at local to global scales and in projections of the coupled carbon-climate system. TBM evaluation commonly involves direct comparison to eddy-covariance flux measurements. This study uses atmospheric CO 2 mole fraction ([CO 2 ]) measured in situ from aircraft and tower, in addition to flux-measurements from summer 2016 to evaluate the CASA TBM. WRF-Chem is used to simulate [CO 2 ] using biogenic CO 2 fluxes from a CASA parameter-based ensemble and CarbonTracker version 2017 (CT2017) in addition to transport and CO 2 boundary condition ensembles. The resulting “super ensemble” of modeled [CO 2 ] demonstrates that the biosphere introduces the majority of uncertainty to the simulations. Both aircraft and tower [CO 2 ] data show that the CASA ensemble net ecosystem exchange (NEE) of CO 2 is biased high (NEE too positive) and identify the maximum light use efficiency E max a key parameter that drives the spread of the CASA ensemble in summer 2016. These findings are verified with flux-measurements. The direct comparison of the CASA flux ensemble with flux-measurements confirms missing sink processes in CASA. Separating the daytime and nighttime flux, we discover that the underestimated net uptake results from missing sink processes that result in overestimation of respiration. NEE biases are smaller in the CT2017 posterior biogenic fluxes, which assimilates observed [CO 2 ]. Flux tower analyses, however, reveal an unrealistic overestimation of nighttime respiration in CT2017 due to the limitation of inversion strategy.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

New two-dimensional space-resolving flux detection technique for measurement of hohlraum inner radiation in Shenguang-III prototype

The space-resolving measurement of X-ray flux from a specific area (laser spot, re-emitting wall, or capsule) inside the hohlraum is an ongoing and critical problem in indirectly driven inertial-confinement fusion experiments. In this work, we developed a new two-dimensional space-resolving flux detection technique to measure the X-ray flux from specific areas inside the hohlraum by using the time- and space-resolving flux detector (SRFD). In two typical hohlraum experiments conducted at the Shenguang-III prototype laser facility, the X-ray flux and radiation temperature from an area 0.2 mm in diameter inside the hohlraum were measured through the laser entrance hole (LEH). The different flux intensities and radiation temperatures detected using the SRFD from the inner area of the LEH were compared with the result measured using the flat-response X-ray detector from the entire LEH. This comparison was also analyzed theoretically. The inner area detected using the SRFD was found to be the re-emitting wall area alone. This important improvement in space-resolving X-ray flux measurement will enhance the current X-ray flux space characterization techniques, thereby furthering the quantitative understanding of X-ray flux space behavior in the hohlraum.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

MAGNETIC HELICITY FLUX IN THE PRESENCE OF SHEAR

Magnetic helicity has risen to be a major player in dynamo theory, with the helicity of the small-scale field being linked to the dynamo saturation process for the large-scale field. It is a nearly conserved quantity, which allows its evolution equation to be written in terms of production and flux terms. The flux term can be decomposed in a variety of fashions. One particular contribution that has been expected to play a significant role in dynamos in the presence of mean shear was isolated by Vishniac and Cho. Magnetic helicity fluxes are explicitly gauge dependent however, and the correlations that have come to be called the Vishniac-Cho flux were determined in the Coulomb gauge, which turns out to be fraught with complications in shearing systems. While the fluxes of small-scale helicity are explicitly gauge dependent, their divergences can be gauge independent. We use this property to investigate magnetic helicity fluxes of the small-scale field through direct numerical simulations in a shearing-box system and find that in a numerically usable gauge the divergence of the small-scale helicity flux vanishes, while the divergence of the Vishniac-Cho flux remains finite. We attribute this seeming contradiction to the existence of horizontal fluxes of small-scale magnetic helicity with finite divergences.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

SEPARATION OF THE INTERSTELLAR BOUNDARY EXPLORER RIBBON FROM GLOBALLY DISTRIBUTED ENERGETIC NEUTRAL ATOM FLUX

The Interstellar Boundary Explorer (IBEX) observes a remarkable feature, the IBEX ribbon, which has energetic neutral atom (ENA) flux over a narrow region {approx}20{sup 0} wide, a factor of 2-3 higher than the more globally distributed ENA flux. Here, we separate ENA emissions in the ribbon from the distributed flux by applying a transparency mask over the ribbon and regions of high emissions, and then solve for the distributed flux using an interpolation scheme. Our analysis shows that the energy spectrum and spatial distribution of the ribbon are distinct from the surrounding globally distributed flux. The ribbon energy spectrum shows a knee between {approx}1 and 4 keV, and the angular distribution is approximately independent of energy. In contrast, the distributed flux does not show a clear knee and more closely conforms to a power law over much of the sky. Consistent with previous analyses, the slope of the power law steepens from the nose to tail, suggesting a weaker termination shock toward the tail as compared to the nose. The knee in the energy spectrum of the ribbon suggests that its source plasma population is generated via a distinct physical process. Both the slope in the energy distribution of the distributed flux and the knee in the energy distribution of the ribbon are ordered by latitude. The heliotail may be identified in maps of globally distributed flux as a broad region of low flux centered {approx}44{sup 0}W of the interstellar downwind direction, suggesting heliotail deflection by the interstellar magnetic field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

VARIATIONS OF SOLAR ELECTRON AND PROTON FLUX IN MAGNETIC CLOUD BOUNDARY LAYERS AND COMPARISONS WITH THOSE ACROSS THE SHOCKS AND IN THE RECONNECTION EXHAUSTS

The magnetic cloud boundary layer (BL) is a dynamic region formed by the interaction of the magnetic cloud (MC) and the ambient solar wind. In the present study, we comparatively investigate the proton and electron mean flux variations in the BL, in the interplanetary reconnection exhaust (RE), and across the MC-driven shock by using the Wind data from 1995 to 2006. In general, the proton flux has higher increments at lower energy bands compared with the ambient solar wind. Inside the BL, the core electron flux increases quasi-isotropically and the increments decrease monotonously with energy from {approx}30% (at 18 eV) to {approx}10% (at 70 eV); the suprathermal electron flux usually increases in either parallel or antiparallel direction; the correlation coefficient of electron flux variations in parallel and antiparallel directions changes sharply from {approx}0.8 below 70 eV to {approx}0 above 70 eV. Similar results are also found for RE. However, different phenomena are found across the shock where the electron flux variations first increase and then decrease with a peak increment (>200%) near 100 eV. The correlation coefficient of electron flux variations in parallel and antiparallel directions is always around 0.8. The similar behavior of flux variations in BL and RE suggests that reconnection may commonly occur in BL. Our work also implies that the strong energy dependence and direction selectivity of electron flux variations, which were previously thought to have not enough relevance to magnetic reconnection, could be considered as an important signature of solar wind reconnection in the statistical point of view.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Formation of a compound flux rope by the merging of two filament channels, the associated dynamics, and its stability

We present observations of compound flux rope formation, which occurred on 2014 January 1, via merging of two nearby filament channels, the associated dynamics, and its stability using multiwavelength data. We also discuss the dynamics of cool and hot plasma moving along the newly formed compound flux rope. The merging started after the interaction between the southern leg of the northward filament and the northern leg of the southward filament at ≈01:21 UT and continued until a compound flux rope formed at ≈01:33 UT. During the merging, the cool filament plasma heated up and started to move along both sides of the compound flux rope, i.e., toward the north (≈265 km s{sup –1}) and south (≈118 km s{sup –1}) from the point of merging. After traveling a distance of ≈150 Mm toward the north, the plasma cooled down and started to return back to the south (≈14 km s{sup –1}) after ≈02:00 UT. The observations provide a clear example of compound flux rope formation via merging of two different flux ropes and the occurrence of a flare through tether cutting reconnection. However, the compound flux rope remained stable in the corona and had a confined eruption. The coronal magnetic field decay index measurements revealed that both the filaments and the compound flux rope axis lie within the stability domain (decay index <1.5), which may be the possible cause for their stability. The present study also deals with the relationship between the filament's chirality (sinistral) and the helicity (positive) of the surrounding flux rope.

79 ASTRONOMY AND ASTROPHYSICS↗