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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

High energy protons generation by two sequential laser pulses

The sequential proton acceleration by two laser pulses of relativistic intensity is proposed to produce high energy protons. In the scheme, a relativistic super-Gaussian (SG) laser pulse followed by a Laguerre-Gaussian (LG) pulse irradiates dense plasma attached by underdense plasma. A proton beam is produced from the target and accelerated in the radiation pressure regime by the short SG pulse and then trapped and re-accelerated in a special bubble driven by the LG pulse in the underdense plasma. The advantages of radiation pressure acceleration and LG transverse structure are combined to achieve the effective trapping and acceleration of protons. In a two-dimensional particle-in-cell simulation, protons of 6.7 GeV are obtained from a 2 × 10{sup 22 }W/cm{sup 2} SG laser pulse and a LG pulse at a lower peak intensity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

High-yield and high-angular-fluence neutron generation from deuterons accelerated by laser-driven collisionless shock

Since a bright collimated neutron source is an essential tool for global security missions and fundamental scientific research. In this paper, we study a compact high-yield and high-angular-fluence neutron source particularly suitable for high-energy neutron applications utilizing the breakup reaction of laser-driven deuterons in a 9 Be converter. The neutron generation scaling from such a reaction is used to guide the choice and optimization of the acceleration process for bulk ions in a low density CD 2 foam. In particular, the collisionless shock acceleration mechanism is exploited with proper choice in the laser and target parameter space to accelerate these ions toward energies above the temperature of the distribution. Particle-in-cell and Monte Carlo simulations are coupled here to investigate this concept and possible adverse effects as well as the contribution from the surface ions accelerated and the optimal converter design. The simulation results indicated that our design can be a practical approach to increase both the neutron yield and angular fluence of laser-driven neutron sources, reaching >10 11 neutron/pulse (or >10 8 neutron/J) and >10 11 neutron/sr (or >10 8 neutron/sr/J) with present-day kJ-class high-power lasers. Such developments will advance fundamental neutron science, high precision radiography, and other global security applications with laser-driven sources.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Coronal electron confinement by double layers

In observations of flare-heated electrons in the solar corona, a longstanding problem is the unexplained prolonged lifetime of the electrons compared to their transit time across the source. This suggests confinement. Recent particle-in-cell (PIC) simulations, which explored the transport of pre-accelerated hot electrons through ambient cold plasma, showed that the formation of a highly localized electrostatic potential drop, in the form of a double layer (DL), significantly inhibited the transport of hot electrons. The effectiveness of confinement by a DL is linked to the strength of the DL as defined by its potential drop. In this work, we investigate the scaling of the DL strength with the hot electron temperature by PIC simulations and find a linear scaling. We demonstrate that the strength is limited by the formation of parallel shocks. Based on this, we analytically determine the maximum DL strength, and also find a linear scaling with the hot electron temperature. The DL strength obtained from the analytic calculation is comparable to that from the simulations. At the maximum strength, the DL is capable of confining a significant fraction of hot electrons in the source.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Grid Modernization Laboratory Consortium - Testing and Verification

This paper highlights some of the unique testing capabilities and projects being performed at several national laboratories as part of the U. S. Department of Energy Grid Modernization Laboratory Consortium. As part of this effort, the Grid Modernization Laboratory Consortium Testing Network isbeing developed to accelerate grid modernization by enablingaccess to a comprehensive testing infrastructure and creating a repository of validated models and simulation tools that will be publicly available. This work is key to accelerating thedevelopment, validation, standardization, adoption, and deployment of new grid technologies to help meet U. S. energy goals.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Modeling a Thermionic Electron Source Using a Physics-Informed Neural Network

We explore the application of Physics-Informed Neural Networks (PINNs) for simulation of thermionic electron sources. This is motivated by the need for quick surrogate models used to simulate such sources within a digital twin of a complete particle accelerator. Here, a PINN was developed on a simplified model of the thermionic source: the planar diode. This model very accurately simulated the system, and performed significantly better than a traditional neural network while also using less training data. We hope to apply this proof-of-concept in motivating the development of a PINN model for a full thermionic electron source at the University of Chicago.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Improvement of dose distribution in breast radiotherapy using a reversible transverse magnetic field Linac-MR unit

Purpose: To investigate the improvement in dose distribution in tangential breast radiotherapy using a reversible transverse magnetic field that maintains the same direction of Lorentz force between two fields. The investigation has a potential application in future Linac-MR units. Methods: Computed tomography images of four patients and magnetic fields of 0.25–1.5 Tesla (T) were used for Monte Carlo simulation. Two patients had intact breast while the other two had mastectomy. Simulations of planning and chest wall irradiation were similar to the actual clinical process. The direction of superior-inferior magnetic field for the medial treatment beam was reversed for the lateral beam. Results: For the ipsilateral lung and heart mean doses were reduced by a mean (range) of 45.8% (27.6%–58.6%) and 26.0% (20.2%–38.9%), respectively, depending on various treatment plan setups. The mean V{sub 20} for ipsilateral lung was reduced by 55.0% (43.6%–77.3%). In addition acceptable results were shown after simulation of 0.25 T magnetic field demonstrated in dose-volume reductions of the heart, ipsilateral lung, and noninvolved skin. Conclusions: Applying a reversible magnetic field during breast radiotherapy, not only reduces the dose to the lung and heart but also produces a sharp drop dose volume histogram for planning target volume, because of bending of the path of secondary charged particles toward the chest wall by the Lorentz force. The simulations have shown that use of the magnetic field at 1.5 T is not feasible for clinical applications due to the increase of ipsilateral chest wall skin dose in comparison to the conventional planning while 0.25 T is suitable for all patients due to dose reduction to the chest wall skin.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Plasmoid statistics in relativistic magnetic reconnection

Plasmoids, overdense blobs of plasma containing magnetic fields and high-energy particles, are a self-consistent outcome of the reconnection process in the relativistic regime. Recent two-dimensional particle-in-cell (PIC) simulations have shown that plasmoids can sustain a variety of processes (e.g. mergers, bulk acceleration, growth, and advection) within the reconnection layer. We developed a Monte Carlo code, benchmarked with the recent PIC simulations, to examine the effects of these processes on the steady-state size and momentum distributions of the plasmoid chain. The differential plasmoid size distribution is shown to be a power law, ranging from a few plasma skin depths to ~0.1 of the reconnection layer’s length. The power-law slope is shown to be linearly dependent upon the ratio of the plasmoid acceleration and growth rates, which slightly decreases with increasing plasma magnetization. We perform a detailed comparison of our results with those of recent PIC simulations and briefly discuss the astrophysical implications of our findings through the representative case of flaring events from blazar jets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Shock wave acceleration of protons in inhomogeneous plasma interacting with ultrashort intense laser pulses

The acceleration of protons, triggered by solitary waves in expanded solid targets is investigated using particle-in-cell simulations. The near-critical density plasma is irradiated by ultrashort high power laser pulses, which generate the solitary wave. The transformation of this soliton into a shock wave during propagation in plasma with exponentially decreasing density profile is described analytically, which allows to obtain a scaling law for the proton energy. The high quality proton bunch with small energy spread is produced by reflection from the shock-front. According to the 2D simulations, the mechanism is stable only if the laser pulse duration is shorter than the characteristic development time of the parasitic Weibel instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tension force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Nonideal Fields Solve the Injection Problem in Relativistic Reconnection

Magnetic reconnection in relativistic plasmas is well established as a fast and efficient particle accelerator, capable of explaining the most dramatic astrophysical flares. With particle-in-cell simulations, we demonstrate the importance of nonideal fields for the early stages (“injection”) of particle acceleration. Most of the particles ending up with high energies (near or above the mean magnetic energy per particle) must have passed through nonideal regions where the assumptions of ideal magnetohydrodynamics are broken (i.e., regions with E > B or nonzero E ∥ = E ∙ B/B), whereas most of the particles that do not experience nonideal fields end up with Lorentz factors of order unity. So, injection by nonideal fields is a necessary prerequisite for further acceleration. Our results have important implications for the origin of nonthermal particles in high-energy astrophysical sources.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Analysis of Fire-Induced Circulations during the FireFlux2 Experiment

Despite recent advances in both coupled fire modeling and measurement techniques to sample the fire environment, the fire–atmosphere coupling mechanisms that lead to fast propagating wildfires remain poorly understood. This knowledge gap adversely affects fire management when wildland fires propagate unexpectedly rapidly and shift direction due to the fire impacts on local wind conditions. In this work, we utilized observational data from the FireFlux2 prescribed burn and numerical simulations performed with a coupled fire–atmosphere model WRF-SFIRE to assess the small-scale impacts of fire on local micrometeorology under moderate wind conditions (10–12 m/s). The FireFlux2 prescribed burn provided a comprehensive observational dataset with in situ meteorological observations as well as IR measurements of fire progression. To directly quantify the effects of fire–atmosphere interactions, two WRF-SFIRE simulations were executed. One simulation was run in a two-way coupled mode in which the heat and moisture fluxes emitted from the fire were injected into the atmosphere, and the other simulation was performed in a one-way coupled mode for which the atmosphere was not affected by the fire. The difference between these two simulations was used to analyze and quantify the fire impacts on the atmospheric circulation at different sections of the fire front. The fire-released heat fluxes resulted in vertical velocities as high as 10.8 m/s at the highest measurement level (20 m above ground level) gradually diminishing with height and dropping to 7.9 m/s at 5.77 m. The fire-induced horizontal winds indicated the strongest fire-induced flow at the lowest measurement levels (as high as 3.3 m/s) gradually decreasing to less than 1 m/s at 20 m above ground level. The analysis of the simulated flow indicates significant differences between the fire-induced circulation at the fire head and on the flanks. The fire-induced circulation was much stronger near the fire head than at the flanks, where the fire did not produce particularly strong cross-fire flow and did not significantly change the lateral fire progression. However, at the head of the fire the fire-induced winds blowing across the front were the strongest and significantly accelerated fire progression. The two-way coupled simulation including the fire-induced winds produced 36.2% faster fire propagation than the one-way coupled run, and more realistically represented the fire progression.

Benik, Jeremy T.↗
DOE OSTI2021

Electro-optic sampling beam position monitor for relativistic electron beams

Here, an electro-optic sampling beam position monitor for installation at the SLAC National Accelerator Laboratory FACET-II facility is described. Simulations of the detector signal were performed using realistic electron beam current profiles, demonstrating that this single-shot, non-destructive, compact detector is capable of resolving the relative transverse offset and longitudinal separation of an ultra-relativistic, two-bunch electron beam to order 1 μm and 10 fs, respectively. A design study was performed to optimize the detector’s response to the ultra-relativistic two-bunch electron beam utilized in plasma wakefield accelerator experiments. In addition, the expected sensitivity to beam tilt is studied for typical electron beams used in free electron lasers.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Multiphase flow simulations of a moving fluidized bed regenerator in a carbon capture unit

To accelerate the commercialization and deployment of carbon capture technologies, computational fluid dynamics (CFD)-based tools may be used to model and analyze the performance of carbon capture devices. This work presents multiphase CFD-based flow simulations for the regeneration device responsible for extracting CO 2 from CO 2 -loaded sorbent particles before the particles are recycled. The use of solid particle sorbents in this design is a departure from previously reported systems, where aqueous sorbents are employed. Another new feature is the inclusion of a series of perforated plates along the regenerator height. The influence of these plates on sorbent distribution is examined for varying sorbent holdup, fluidizing gas velocity, and particle size. The residence time distribution of sorbents is also measured to classify the low regime as plug flow or well-mixed flow. The purpose of this work is to better understand the sorbent flow characteristics before reaction kinetics of CO 2 desorption can be implemented.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2016

DYNAMICS OF CORONAL RAIN AND DESCENDING PLASMA BLOBS IN SOLAR PROMINENCES. II. PARTIALLY IONIZED CASE

Coronal rain clumps and prominence knots are dense condensations with chromospheric to transition region temperatures that fall down in the much hotter corona. Their typical speeds are in the range 30–150 km s{sup −1} and of the order of 10–30 km s{sup −1}, respectively, i.e., they are considerably smaller than free-fall velocities. These cold blobs contain a mixture of ionized and neutral material that must be dynamically coupled in order to fall together, as observed. We investigate this coupling by means of hydrodynamic simulations in which the coupling arises from the friction between ions and neutrals. The numerical simulations presented here are an extension of those of Oliver et al. to the partially ionized case. We find that, although the relative drift speed between the two species is smaller than 1 m s{sup −1} at the blob center, it is sufficient to produce the forces required to strongly couple charged particles and neutrals. The ionization degree has no discernible effect on the main results of our previous work for a fully ionized plasma: the condensation has an initial acceleration phase followed by a period with roughly constant velocity, and, in addition, the maximum descending speed is clearly correlated with the ratio of initial blob to environment density.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Simulation of Statistical Fluctuations in the Spin Precession Measurements at RHIC

Measurements of the driven spin coherent precession S x (t)=S x (0) - S x (1) sin(ωt+φ 0 ) were initiated in RHIC Run13. The expected value of the precession amplitude S x (1) ~ 2 x 10 -4 is about the statistical error in a single measurement and data fit gives a biased estimate of the S x (1) . For a proper statistical interpretation of the results of the several measurements, statistical fluctuations were studied using Monte-Carlo simulation. Preliminary results of the spin precession measurements in RHIC Run13 are presented.

43 PARTICLE ACCELERATORS↗