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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 145 records · Page 8
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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 OSTI2024

Collisionless cooling of perpendicular electron temperature in the thermal quench of a magnetized plasma

Thermal quench of a nearly collisionless plasma against an isolated cooling boundary or region is an undesirable off-normal event in magnetic fusion experiments, but an ubiquitous process of cosmological importance in astrophysical plasmas. Parallel transport theory of ambipolar-constrained tail electron loss is known to predict rapid cooling of the parallel electron temperature $T_{e\Vert}$ although $T_{e\Vert}$ is difficult to diagnose in actual experiments. Instead direct experimental measurements can readily track the perpendicular electron temperature $T_{e\bot}$ via electron cyclotron emission. The physics underlying the observed fast drop in $T_{e\bot}$ requires a resolution. Here two collisionless mechanisms, dilutional cooling by infalling cold electrons and wave-particle interaction by two families of whistler instabilities, are shown to enable fast $T_{e\bot}$ cooling that closely tracks the mostly collisionless crash of $T_{e\Vert}$. These findings motivate both experimental validation and reexamination of a broad class of plasma cooling problems in laboratory, space, and astrophysical settings.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Puzzles of Exotic Decay Processes

The growing interest in the physics of unstable nuclei, along with their manifestations in laboratory experiments and astrophysical observations, highlights the existence of features in decay processes within complex quantum systems that are not yet fully understood. Furthermore, this paper considers examples of such phenomena, including two-step decay processes, resonance effects, threshold peculiarities, and the interactions between bound and continuum states, as well as the related dynamics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Exact and locally implicit source term solvers for multifluid-Maxwell systems

Recently, a family of models that couple multifluid systems to the full Maxwell equations have been used in laboratory, space, and astrophysical plasma modeling. These models are more complete descriptions of the plasma than reduced models like magnetohydrodynamic (MHD) since they are derived more closely from the full kinetic Vlasov-Maxwell system, without assumptions like quasi-neutrality, negligible electron mass, etc. Thus these models naturally retain non-ideal MHD effects like electron inertia, Hall term, pressure anisotropy/nongyrotropy, displacement current, among others. One obstacle to broader application of these model is that an explicit treatment of their source terms leads to the need to resolve rapid processes like plasma oscillation and electron cyclotron motion, even when these are not important. In this paper, we suggest two ways to address this issue. First, we derive the analytic solutions to the source update equations, which can be implemented as a practical, but less generic solver. We then develop a time-centered, locally implicit algorithm to update the source terms, allowing stepping over the fast kinetic time-scales. For a plasma with S species, the locally implicit algorithm involves inverting a local (3 S + 3) × (3 S + 3) matrix only, thus is very efficient. The performance can be further increased by using the direct update formulas to skip null calculations. In this paper, we present benchmarks illustrating the exact energy-conservation of the locally implicit solver, as well as its efficiency and robustness for both small-scale, idealized problems and largescale, complex systems. The locally implicit algorithm can be also easily extended to include other local sources, like collisions and ionization, which are difficult to solve analytically.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

A cancellation problem in hybrid particle-in-cell schemes due to finite particle size

The quasi-neutral hybrid particle-in-cell algorithm with kinetic ions and fluid electrons is a popular model to study multi-scale problems in laboratory, space, and astrophysical plasmas. Here, it is shown that the different spatial discretizations of ions as finite-spatial-size particles and electrons as a grid-based fluid can lead to significant numerical wave dispersion errors in the long wavelength limit (kd i «1, where k is the wavenumber and di is the ion skin-depth). The problem occurs when high-order particle-grid interpolations, or grid-based smoothing, spreads the electric field experienced by the ions across multiple spatial cells and leads to inexact cancellation of electric field terms in the total (ion + electron) momentum equation. Practical requirements on the mesh spacing Δx/d i are suggested to bound these errors from above. The accuracy impact of not respecting these resolution constraints is shown for a non-linear shock problem.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Effects of Coulomb coupling on friction in strongly magnetized plasmas

The friction force on a test particle traveling through a plasma that is both strongly coupled and strongly magnetized is studied using molecular dynamics simulations. In addition to the usual stopping power component aligned antiparallel to the velocity, a transverse component that is perpendicular to both the velocity and Lorentz force is observed. This component, which was recently discovered in weakly coupled plasmas, is found to increase in both absolute and relative magnitude in the strongly coupled regime. Strong coupling is also observed to induce a third component of the friction force in the direction of the Lorentz force. These first-principles simulations reveal novel physics associated with collisions in strongly coupled, strongly magnetized, plasmas that are not predicted by existing kinetic theories. The effect is expected to influence macroscopic transport in a number of laboratory experiments and astrophysical plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Insights from binary pulsars and laboratories into baryon number violation: Implications for GeV dark matter

Rare processes in laboratory and within astrophysical environments can be highly sensitive probes of baryon-number-violating interactions at the TeV scale. We demonstrate the power of neutron stars to constrain baryon-number violation by considering a minimal extension of the standard model involving a TeV-mass scalar mediator and a GeV scale Majorana fermion ψ . We find that a Δ B = 2 mass-loss process in binary pulsar systems via n → γ ψ and the subsequent scattering ψ n → π − K + places stringent constraints on the model parameter space. These limits will become much stronger, due to the possibility of Λ → γ ψ decays at the tree level, if the neutron star equation of state is hyperonic. We compare these constraints with ongoing and future collider experiments, n − n ¯ oscillations, and dinucleon decay searches at future large-scale neutrino experiments, finding that the binary pulsars bounds on couplings are significantly tighter for specific flavor combinations. Published by the American Physical Society 2024

baryons↗
DOE OSTI2023

Cooling flow regime of a plasma thermal quench

A large class of Laboratory, Space, and Astrophysical plasmas is nearly collisionless. When a localized energy or particle sink, for example, in the form of a radiative cooling spot or a black hole, is introduced into such a plasma, it can trigger a plasma thermal collapse, also known as a thermal quench in tokamak fusion. Here we show that the electron thermal conduction in such a nearly collisionless plasma follows the convective energy transport scaling in itself or in its spatial gradient, due to the constraint of ambipolar transport. As a result, a robust cooling flow aggregates mass toward the cooling spot and the thermal collapse of the surrounding plasma takes the form of four propagating fronts that originate from the radiative cooling spot, along the magnetic field line in a magnetized plasma. The slowest one, which is responsible for deep cooling, is a shock front.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Capturing a New State of Matter: Relativistic Electron-Positron Plasma (LDRD Final Report)

Relativistic electron-positron (pair) plasmas were a main component of the universe shortly after the Big Bang and are produced around many astrophysical objects, but laboratory pair plasmas have remained elusive. High-intensity lasers can drive dense relativistic positron jets; over the last ten years, we have optimized high-energy ultra-short-pulse laser-matter interaction experiments to make a large number (10 10 – 10 12 ) of positrons in a small volume (< 3 mm 3 ). However, these jets are transient (10 ps), making observations of collective effects difficult. The goal of 20-LW-021 was to trap laser-driven electron-positron jets using pulsed-power-driven high-magnetic-field solenoids, allowing longer confinement times and ultimately an observable laboratory relativistic pair plasma. The project has been remarkably successful: we have found that pulsed-power magnetic fields can effectively trap laser-driven charged particles and produce charge-neutral pair beams. The project thus far has resulted in six published journal articles. The success of these components has put a laboratory pair plasma almost within reach.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Conference Support for 2024 MagNetUS Meeting

The 4th annual MagNetUS meeting was held from April 14-18, 2024 in Los Angeles, California at the UCLA Lake Arrowhead Conference Center. The goal of the meeting was to continue the successful template of a mix of invited talks, contributed talks, posters, and discussion sessions established by the first three MagNetUS meetings, in order to 1) communicate physics advances relevant for basic magnetized plasma research which can be performed at small and mid-size experimental facilities; 2) allow collaborator facilities to connect and interact with existing users and potential new users; and 3) grow the community of potential users of collaborator facilities, as well as scientists who focus on theory/modeling and spacecraft observations. The meeting was attended by 77 participants (71 in person) from 23 unique institutions and included 14 invited talks, 19 contributed talks, 22 posters, and six discussion sessions. Topics covered by the meeting included fusion research, space and astrophysical systems (including laboratory analogs), magnetic reconnection, plasma thrusters, turbulence, waves, dusty plasmas, laser plasmas, plasma vortices, plasma sources, and software ecosystems. Discussion sessions included discussions on science communication, with NSF and DOE program managers, on the MagNetUS application process for new users, on experimental facility capabilities, and as a tie-in to the Solar Wind Machine meeting.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

The APOGEE Data Release 16 Spectral Line List

The updated H-band spectral-line list (from λ15000–17000) adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) for the SDSS-IV Data Release 16 (DR16) is presented in this work. The APOGEE line list is a combination of atomic and molecular lines, with data drawn from laboratory, theoretical, and astrophysical sources. Oscillator strengths and damping constants are adjusted using high signal-to-noise, high-resolution spectra of the Sun, and α Boo (Arcturus), as “standard stars.” Updates to the DR16 line list, as compared to the previous DR14 version, include the addition of molecular H{sub 2}O and FeH lines, as well as a much larger (by a factor of ∼4) atomic line list, including a significantly greater number of transitions with hyperfine splitting. More recent references and line lists for the crucial molecules, CO and OH, as well as for C{sub 2} and SiH, are also included. In contrast to DR14, DR16 contains measurable lines from the heavy neutron-capture elements cerium (as Ce ii), neodymium (as Nd ii), and ytterbium (as Yb ii), as well as one line from rubidium (as Rb i), which may be detectable in a small fraction of APOGEE red giants.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Magnetic Energy Conversion in Magnetohydrodynamics: Curvature Relaxation and Perpendicular Expansion of Magnetic Fields

Abstract The mechanisms and pathways of magnetic energy conversion are an important subject for many laboratory, space, and astrophysical systems. Here, we present a perspective on magnetic energy conversion in magnetohydrodynamics through magnetic field curvature relaxation (CR) and perpendicular expansion (PE) due to magnetic pressure gradients, and quantify their relative importance in two representative cases, namely 3D magnetic reconnection and 3D kink-driven instability in an astrophysical jet. We find that the CR and PE processes have different temporal and spatial evolutions in these systems. The relative importance of the two processes tends to reverse as the system enters the nonlinear stage from the instability growth stage. Overall, the two processes make comparable contributions to magnetic energy conversion, with the PE process somewhat stronger than the CR process. We further explore how these energy conversion terms can be related to particle energization in these systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Oscillation-independent probes of nonstandard neutrino interactions from supernovae

Extreme astrophysical environments provide unique laboratories for testing fundamental neutrino interactions. We present the first oscillation-independent astrophysical probe of nonstandard neutrino interactions (NSI), using coincident neutral-current signals across diverse detectors to break degeneracies that have long limited sensitivity reach. Using self-consistent NSI supernova simulations and flavor-independent neutral-current scattering we show that anticorrelated signatures between JUNO liquid scintillator and dark matter detectors such as DARWIN/XLZD, ARGO, or RES-NOVA enable clear discrimination between NSI and flavor-conversion effects. For a Galactic supernova at Betelgeuse distance our approach enables an independent probe of neutrino-quark NSI couplings in parameter space that can reach and extend beyond current terrestrial limits. This multidetector approach enables breaking degeneracies in terrestrial searches and is broadly applicable to a wide range of upcoming experiments, establishing a new principle for testing fundamental interactions with astrophysical data.

Beatty, Angela R. [San Francisco State U.; LBL, Be↗
DOE OSTI2026

Fiducial-cosmology-dependent systematics for the DESI 2024 full-shape analysis

We assess the impact of the fiducial cosmology choice on cosmological inference from full-shape (FS) fits of the galaxy power spectrum in the DESI 2024 Data Release 1 (DR1). Using a suite of AbacusSummit DR1 mock catalogues based on the Planck 2018 best-fit cosmology, we quantify potential systematic shifts introduced by analysing the data under five secondary cosmologies — featuring variations in matter density, thawing dark energy, higher effective number of neutrino species, reduced clustering amplitude, and the DESI DR1 BAO best-fit w 0 w a CDM cosmology — relative to DESI's baseline Planck 2018 cosmology. We investigate two complementary FS analysis approaches: full-modelling (FM) and ShapeFit (SF), each with distinct sensitivities to the assumed fiducial model. Across all tracers, we find for FM that systematic shifts induced by fiducial cosmology mismatches remain well below the DESI DR1 statistical uncertainties, with maximum deviations of 0.22σ DR1 in ΛCDM scenarios and 0.12σ DR1+SN when including SN Ia mock data in extended w 0 w a CDM fits. For SF, the shifts in the compressed parameters remain below 0.45σ DR1 for all tracers and cosmologies.

dark energy experiments↗
DOE OSTI2022

Plasma image classification using cosine similarity constrained convolutional neural network

Plasma jets are widely investigated both in the laboratory and in nature. Astrophysical objects such as black holes, active galactic nuclei and young stellar objects commonly emit plasma jets in various forms. With the availability of data from plasma jet experiments resembling astrophysical plasma jets, classification of such data would potentially aid in not only investigating the underlying physics of the experiments but also the study of astrophysical jets. In this work we use deep learning to process all of the laboratory plasma images from the Caltech Spheromak Experiment spanning two decades. We found that cosine similarity can aid in feature selection, classify images through comparison of feature vector direction and be used as a loss function for the training of AlexNet for plasma image classification. We also develop a simple vector direction comparison algorithm for binary and multi-class classification. Using our algorithm we demonstrate 93 % accurate binary classification to distinguish unstable columns from stable columns and 92 % accurate five-way classification of a small, labelled data set which includes three classes corresponding to varying levels of kink instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Electron acceleration in laboratory-produced turbulent collisionless shocks

Astrophysical collisionless shocks are among the most powerful particle accelerators in the Universe. Generated by violent interactions of supersonic plasma flows with the interstellar medium, supernova remnant shocks are observed to amplify magnetic fields and accelerate electrons and protons to highly relativistic speeds. In the well-established model of diffusive shock acceleration, relativistic particles are accelerated by repeated shock crossings. However, this requires a separate mechanism that pre-accelerates particles to enable shock crossing. This is known as the ‘injection problem’, which is particularly relevant for electrons, and remains one of the most important puzzles in shock acceleration. In most astrophysical shocks, the details of the shock structure cannot be directly resolved, making it challenging to identify the injection mechanism. In this letter we report results from laser-driven plasma flow experiments, and related simulations, that probe the formation of turbulent collisionless shocks in conditions relevant to young supernova remnants. We show that electrons can be effectively accelerated in a first-order Fermi process by small-scale turbulence produced within the shock transition to relativistic non-thermal energies, helping overcome the injection problem. Our observations provide new insight into electron injection at shocks and open the way for controlled laboratory studies of the physics underlying cosmic accelerators.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

EMPDF : inferring the Milky Way mass with data-driven distribution function in phase space

We introduce the emPDF (empirical distribution function), a novel dynamical modelling method that infers the gravitational potential from kinematic tracers with optimal statistical efficiency under the minimal assumption of steady state. emPDF determines the best-fitting potential by maximizing the similarity between instantaneous kinematics and the time-averaged phase-space distribution function (DF), which is empirically constructed from observation upon the theoretical foundation of oPDF (Han et al. 2016). This approach eliminates the need for presumed functional forms of DFs or orbit libraries required by conventional DF- or orbit-based methods. emPDF stands out for its flexibility, efficiency, and capability in handling observational effects, making it preferable to the popular Jeans equation or other minimal assumption methods, especially for the Milky Way (MW) outer halo where tracers often have limited sample size and poor data quality. We apply emPDF to infer the MW mass profile using Gaia DR3 data of satellite galaxies and globular clusters, obtaining enclosed masses of M (,r) = 26±8, 46±8, 90±13⁠, and 149±40 x 10 10 M ⊙ at r = 30, 50, 100⁠, and 200 kpc, respectively. These are consistent with the updated constraints from simulation-informed DF fitting (Li et al. 2020). While the simulation-informed DF offers superior precision owing to the additional information extracted from simulations, emPDF is independent of such supplementary knowledge and applicable to general tracer populations. emPDF is currently implemented for tracers with complete 6D kinematics within spherical potentials, but it can potentially be extended to address more general problems.

Astrophysics of Galaxies (astro-ph.GA)↗
DOE OSTI2021

Ion Acceleration in Driven Magnetic Reconnection during High-energy–Density Plasma Interaction

Strongly driven magnetic reconnection occurs in astrophysical events and also in laboratory experiments with laser-produced plasma. We have performed 2.5D particle-in-cell simulations of collisions of two high-energy–density plasmas resulting in strongly driven magnetic reconnection that demonstrates significant non-thermal ion acceleration. Such acceleration is significant only when the plasma beta is sufficiently low that the Alfvén speed at the reconnection inflow exceeds the thermal speed. Under these conditions, the most energetic ions are primarily accelerated by the Hall electric field in the reconnection outflow, especially at the trailing edge of an emerging plasmoid in the outflow. Here, laboratory experiments in the near future should be able to confirm these predictions and their applicability to astrophysical situations.

79 ASTRONOMY AND ASTROPHYSICS↗