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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Toward a long-lifetime polarized photoelectron gun for the Ce+BAF positron source

The addition of spin-polarized, continuous-wave (c.w.) positron beams to the 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) would provide a significant capability to the experimental nuclear physics program at Jefferson Lab. Based on bremsstrahlung and pair-production in a high-Z target, the positron source requires a 120 MeV spin-polarized c.w. electron beam of several milliamperes. While the beam dynamics of the high-current electron beam are tenable, sustaining this current for weeks of user operations requires an unprecedented charge lifetime from a high-polarization GaAs-based photocathode. A promising approach to exceed the kilocoulomb charge lifetime barrier is reducing the ion back-bombardment fluence at the photocathode. By increasing the laser size and managing the emittance growth with an adequate cathode/anode design, significantly enhanced charge lifetime may be achieved. Based upon a new simulation model that qualitatively explains the lifetime data previously measured at different spot sizes, we describe the practical implications on the parameter space available for a kilocoulomb-lifetime polarized photogun design.

Bruker, M.↗
DOE OSTI2026

Track Matching in the DUNE Near Detectors

The Deep Underground Neutrino Experiment (DUNE) is an international particle physics experiment looking answer some of the largest unanswered questions in neutrino physics. DUNE uses a high power neutrino beam produced at Fermi National Accelerator Laboratory (Fermilab), and consists of a near detector (ND) also located at Fermilab and a far detector (FD) 1300 km away at the Sanford Underground Research Facility (SURF) in South Dakota. In the first phase of the experiment, the ND complex will contain a modular liquid argon TPC (ND-LAr) and a solid scintillator-based muon spectrometer (TMS), in addition to a beam monitoring detector (SAND) and systems for moving ND-LAr and TMS away from the neutrino beam axis (PRISM). A prototype of ND-LAr, the 2x2 demonstrator, alongside a solid scintillator muon tagger provided by repurposed MINERvA planes, has been built and taken data at Fermilab. For analyses with the ND, connecting particle tracks (such as muons) that exit the liquid argon active volume into the solid scintillator muon detector can improve particle identification and energy reconstruction, and alleviate pileup due to the intense beam. To match tracks between detectors during reconstruction, we have explored using Graph Neural Networks (GNNs) to connect tracks segments between the liquid argon detector region and the solid scintillator detector planes. We have trained a GNN on reconstructed simulated data from the 2×2 demonstrator and repurposed MINERvA planes. We will evaluate its performance and then train a similar network on reconstructed ND-LAr and TMS simulations.

Xing, Daniel [U. Colorado, Boulder]↗
DOE OSTI2021

Towards High-Repetition-Rate Fast Neutron Sources Using Novel Enabling Technologies

High-flux, high-repetition-rate neutron sources are of interest in studying neutron-induced damage processes in materials relevant to fusion, ultimately guiding designs for future fusion reactors. Existing and upcoming petawatt laser systems show great potential to fulfill this need. Here, we present a platform for producing laser-driven neutron beams based on a high-repetition-rate cryogenic liquid jet target and an adaptable stacked lithium and beryllium converter. Selected ion and neutron diagnostics enable monitoring of the key parameters of both beams. A first single-shot proof-of-principle experiment successfully implemented the presented platform at the Texas Petawatt Laser facility, achieving efficient generation of a forward-directed neutron beam. This work lays the foundation for future high-repetition-rate experiments towards pulsed, high-flux, fast neutron sources for radiation-induced effect studies relevant for fusion science and applications that require neutron beams with short pulse duration.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

FAST Low-Energy Beamline Studies: Toward High-Peak 5D Brightness Beams for FAST-GREENS

The FAST beamline is the injector for the planned Gamma-Ray Electron ENhanced Source (GREENS) program, which aims to achieve the demonstration and first application of a high-efficiency, high-average-power free-electron laser at 515 nm. FAST-GREENS requires high 5D peak brightness; transverse normalized projected emittances of 3 mm-mrad and a peak current of 600 A are the minimum beam requirements for the FEL to reach the 10% efficiency goal. In this work, studies of the low-energy section of the FAST beamline are presented toward these ends, including preliminary measurements of beam compression and beam emittance. An effort toward developing a high-fidelity simulation model that could be later optimized for FAST-GREENS is presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Electron Energy Partition across Interplanetary Shocks. III. Analysis

An analysis of model fit results of 15,210 electron velocity distribution functions (VDFs), observed within ±2 hr of 52 interplanetary (IP) shocks by the Wind spacecraft near 1 au, is presented as the third and final part on electron VDFs near IP shocks. The core electrons and protons dominate in the magnitude and change in the partialto-total thermal pressure ratio, with the core electrons often gaining as much or more than the protons. Only a moderate positive correlation is observed between the electron temperature and the kinetic energy change across the shock, while weaker, if any, correlations were found with any other macroscopic shock parameter. No VDF parameter correlated with the shock normal angle. The electron VDF evolves from a narrowly peaked core with flaring suprathermal tails in the upstream to either a slightly hotter core with steeper tails or much hotter flattop core with even steeper tails downstream of the weaker and strongest shocks, respectively. Both quasi-static and fluctuating fields are examined as possible mechanisms modifying the VDF, but neither is sufficient alone. For instance, flattop VDFs can be generated by nonlinear ion acoustic wave stochastic acceleration (i.e., inelastic collisions), while other work suggested they result from the combination of quasi-static and fluctuating fields. This three-part study shows that not only are these systems not thermodynamic in nature; even kinetic models may require modification to include things like inelastic collision operators to properly model electron VDF evolution across shocks or in the solar wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Electron Energy Partition across Interplanetary Shocks. II. Statistics

Abstract A statistical analysis of 15,210 electron velocity distribution function (VDF) fits, observed within ±2 hr of 52 interplanetary (IP) shocks by the Wind spacecraft near 1 au, is presented. This is the second in a three-part series on electron VDFs near IP shocks. The electron velocity moment statistics for the dense, low-energy core, tenuous, hot halo, and field-aligned beam/strahl are a statistically significant list of values illustrated with both histograms and tabular lists for reference and baselines in future work. Given the large statistics in this investigation, the beam/strahl fit results in the upstream are now the most comprehensive attempt to parameterize the beam/strahl electron velocity moments in the ambient solar wind. The median density, temperature, beta, and temperature anisotropy values for the core(halo)[beam/strahl] components, with subscripts ec(eh)[eb], of all fit results, respectively, are , , , and . This work will also serve as a 1 au baseline and reference for missions like Parker Solar Probe and Solar Orbiter .

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Measurement of neutrino oscillations using neutrino and antineutrino beams in the NOvA experiment

NOvA is a long-baseline accelerator neutrino oscillation experiment using the NuMIneutrino beam from Fermilab. Its main physics goals are to probe the 3-flavour oscillationparameters: neutrino mass hierarchy, CP-violating phase dcp and octant of .23 mixingangle by observing electron neutrino appearance and muon neutrino disappearance. Twofunctionally identical detectors are placed off-axis from the centre of the NuMI beam.The near detector at Fermilab is 100 m underground, and the far detector is locatedon the surface at Ash River, 810 km away from the beam source. The initial neutrinobeam spectra are measured using the near detector data and the oscillation parametersare extracted by fitting the observed data to the predicted neutrino spectrum in the fardetector.This thesis is centered around how to improve the sensitivity of |.m232| and .23 measurementsin the muon neutrino disappearance analysis. NOvA will take data for about12 years. The operation of the NOvA experiment for each year costs tens of millions ofdollars, thus it is valuable to maximise the sensitivity of the analysis. Three samples ofmuon neutrino events are studied in this thesis to improve the analysis sensitivities. First,higher energy muon neutrinos are investigated by extending the energy range in NOvA’scurrent standard analysis. Second, for the sample of events used in NOvA’s existing analysis,a new energy estimator which has been developed to improve the neutrino energy resolution is considered. Furthermore, in addition to binning the events as function ofenergy and hadronic energy fraction, three particle identifiers are introduced to separateneutrino events by signal purity to reduce the effects from backgrounds. Third, an additionallower purity sample of muon neutrino charged current (CC) events that look similarto neutral current events and have not been included in NOvA’s existing analyses havebeen studied.This thesis reanalyses NOvA’s data used in the 2020 analysis, corresponding to anexposure of 13.60×1020 protons on target (POT) in the neutrino beam mode recordedfrom February 6, 2014 to March 20, 2020, and 12.50×1020 protons on target in theantineutrino beam mode recorded between June 29, 2016 to February 26, 2019. Thisthesis has implemented a fit to Asimov fake data, generated where sin2 .23 = 0.59 and.m232 = 2.5 × 10-3 eV2. These sensitivity studies show that the uncertainty range of|.m232| at 1 s in the new analysis is reduced by 5.5% and the significance of maximaldisappearance rejection improves by 7.7%, compared to the standard analysis. This isequivalent to adding 11-16% more data. The best fit values of the oscillation parametersfrom fitting to the far detector (FD) data with the new analysis are found to besin2 .23 = 0.568+0.025-0.043 (sin2 .23 = 0.454+0.046-0.026) and .m232 = 2.399+0.055-0.070 × 10-3 eV2 (.m232= -2.427+0.055-0.067 × 10-3 eV2) for the normal (inverted) hierarchy. The difference in thebest fit for sin2 .23 (.m232) between the new analysis and NOvA’s 2020 analysis is around2% (1.4%). The uncertainty range at 1 s for .m232 decrease by 8% (4%) for the normalhierarchy (inverted hierarchy) compared to the standard analysis. The uncertainty rangefor sin2 .23 is close to the standard analysis. This thesis also implements the fit from combiningelectron neutrino appearance and muon neutrino disappearance. The combinedanalysis shows that the best fit values are very close to the standard analysis. However,the uncertainty range of .m232 at 1 s is reduced by 3.7% using the new analysis. The maximaldisappearance significance is not improved in the new analysis, but the new analysisslightly improves the rejection of the disfavoured octant.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Proton transparency and neutrino physics: New methods and modeling

Extracting accurate results from neutrino oscillation and cross section experiments requires accurate simulation of the neutrino-nucleus interaction. The rescattering of outgoing hadrons (final state interactions) by the rest of the nucleus is an important component of these interactions. We present a new measurement of proton transparency (defined as the fraction of outgoing protons that emerge without significant rescattering) using electron-nucleus scattering data recorded by the CLAS detector at Jefferson Laboratory on helium, carbon, and iron targets. This analysis uses a new data-driven method to extract the transparency. It defines transparency as the ratio of electron-scattering events with a detected proton to quasi-elastic electron-scattering events where a proton should have been knocked out. Our results are consistent with previous measurements that determined the transparency from the ratio of measured events to theoretically predicted events. We find that the GENIE event generator, which is widely used by oscillation experiments to simulate neutrino-nucleus interactions, needs to better describe both the nuclear ground state and proton rescattering in order to reproduce our measured transparency ratios, especially at lower proton momenta.

direct reactions↗
DOE OSTI2023

Particle Acceleration by Magnetic Reconnection in Geospace

Particles are accelerated to very high, non-thermal energies during explosive energy-release phenomena in space, solar, and astrophysical plasma environments. While it has been established that magnetic reconnection plays an important role in the dynamics of Earth’s magnetosphere, it remains unclear how magnetic reconnection can further explain particle acceleration to non-thermal energies. Here we review recent progress in our understanding of particle acceleration by magnetic reconnection in Earth’s magnetosphere. With improved resolutions, recent spacecraft missions have enabled detailed studies of particle acceleration at various structures such as the diffusion region, separatrix, jets, magnetic islands (flux ropes), and dipolarization front. With the guiding-center approximation of particle motion, many studies have discussed the relative importance of the parallel electric field as well as the Fermi and betatron effects. However, in order to fully understand the particle acceleration mechanism and further compare with particle acceleration in solar and astrophysical plasma environments, there is a need for further investigation of, for example, energy partition and the precise role of turbulence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Physics Basis, Optimization, and Control for Integrated 3D Edge Long-pulse Tokamak Scenarios

The aim of this project with international collaborations (PI: J.-K. Park of Princeton Plasma Physics Laboratory) is to develop a unified physics basis and predictive capability for the control of edge-localized modes (ELMs) with optimized non-axisymmetric (3D) fields, by leveraging the unique research capabilities of international KSTAR tokamak in Korea. At the University of California, Irvine, we use a fusion simulation code GTC to study the effects of the 3D magnetic fields (including both magnetic islands and stochastic magnetic field lines) on microturbulence. We focus on the effects of 3D equilibrium on turbulent and neoclassical transport that leads to ELM suppression. During the project period, the UCI team of this collaboration has made significant progress in understanding turbulent transport in 3D geometry including both tokamaks with RMP and stellarators. Four UCI postdoctoral researchers, Drs. Javier Nicolau, Gyungjin Choi, Pengfei Liu, and Xishuo Wei were partially supported by this project and collaborating with the entire project team. We have published 4 journal papers and gave several invited talks. This project advance physics understand of 3D effects on microturbulence, specially effects of magnetic islands. It will contribute to the DOE SciDAC ISEP project in the area of GTC development for general 3D geometry capability, rigorous verification and validation, and readiness for the emerging exascale computing. Through collaborations with computational scientists, the project helps to advance high performance computing in the area of GPU acceleration, linear solver, and data management.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Whitepaper submitted to Snowmass21: Advanced accelerator linear collider demonstration facility at intermediate energy

It is widely accepted that the next lepton collider beyond a Higgs factory would require center-of-mass energy of the order of up to 15 TeV. Since, given reasonable space and cost restrictions, conventional accelerator technology reaches its limits near this energy, high-gradient advanced acceleration concepts are attractive. Advanced and novel accelerators (ANAs) are leading candidates due to their ability to produce acceleration gradients on the order of 1--100~GV/m, leading to compact acceleration structures. Over the last 10-15 years significant progress has been achieved in accelerating electron beams by ANAs. For example, the demonstration of several-GeV electron beams from laser-powered capillary discharge waveguides, as well as the proof-of-principle coupling of two accelerating structures powered by different laser pulses, has increased interest in ANAs as a viable technology to be considered for a compact, TeV-class, lepton linear collider. However, intermediate facilities are required to test the technology and demonstrate key subsystems. A 20-100 GeV center-of-mass energy ANA-based lepton collider can be a possible candidate for an intermediate facility. Apart from being a test beam facility for accelerator and detector studies, this collider will provide opportunities to study muon and proton beam acceleration, investigate charged particle interactions with extreme electromagnetic fields (relevant for beam delivery system designs and to study the physics at the interaction point), as well as precision Quantum Chromodynamics and Beyond the Standard Model physics measurements. Possible applications of this collider include the studies of $\gamma\gamma$ and $e$-ion collider designs.

43 PARTICLE ACCELERATORS↗