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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

On the motion of compact objects in relativistic viscous fluids

We present a world-line effective field theory of compact objects moving relativistically through a viscous fluid. The theory is valid when velocity gradients are small compared to the inverse size of the object. Working within the EFT eliminates the need to solve a boundary value problem by turning all interactions between the fluid and the object into a source term in the action. We use the EFT to derive the relativistic equations of motion for a compact object immersed in a viscous fluid in a curved background, when the relative velocity of the object and the fluid is small compared to the speed of light.

astrophysical black holes↗
DOE OSTI2024

Overview of recent results from the ST40 compact high-field spherical tokamak

ST40 is a compact, high-field ($B_{\mathrm{T0}}\unicode{x2A7D} 2.1\,\,\,\textrm{T}$) spherical tokamak (ST) with a mission to expand the physics and technology basis for the ST route to commercial fusion. The ST40 research programme covers confinement and stability; solenoid-free start-up; high-performance operating scenarios; and plasma exhaust. In 2022, ST40 obtained central deuterium ion temperatures of $9.6 \pm 0.4\ \textrm{keV}$, demonstrating for the first time that pilot plant relevant ion temperatures can be reached in a compact, high-field ST. Analysis of these high-ion temperature plasmas is presented, including a summary of confinement, transport and microstability characteristics, and energetic particle instabilities. Recent scenario development activities have focused on establishing diverted H-mode plasmas across a range of toroidal fields and plasma currents, along with scenarios with high non-inductive current fractions. In future operations, beginning in 2025, a 1 MW dual frequency (104/137 GHz) electron cyclotron (EC) system will be installed to enable the study of EC and electron Bernstein wave plasma start-up and current drive. Predictive modelling of the potential performance of these systems is presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Innovative compact braze-free accelerating cavity

We report that high energy physics experiments using particle accelerators as well as industrial and medical applications are continuously seeking more compact, robust and cheaper accelerating structures. As of today, stable operating gradients, exceeding 100 MV/m, have been demonstrated by the SLAC group in the X-Band (11.424 GHz). These experiments show that hard structures, fabricated without high-temperature processes, achieve a better high gradient performance in terms of accelerating gradients. Therefore, we present an innovative and compact type of accelerating cavity that avoids any high-temperature processes like brazing or diffusion bonding. All cells are joined together by means of specifically designed and proprietary screws which ensure good vacuum and RF contacts. Two three-cell standing-wave accelerating structures, designed to operate in the pi-mode at 11.424 GHz, have been successfully built and cold tested. In order to guarantee a vacuum envelope and mechanically robust assembly, we used the Electron Beam Welding (EBW) and the Tungsten Inert Gas (TIG) processes. Lastly, this work has been carried out in the framework of a funded project by the Vth Committee of the INFN for the Laboratori Nazionali di Frascati (LNF), within a large international collaboration between LNF, SLAC and KEK for the development of X-Band accelerating cavities using "hard structure" technology.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

DIVERSITY OF SHORT GAMMA-RAY BURST AFTERGLOWS FROM COMPACT BINARY MERGERS HOSTING PULSARS

Short-duration gamma-ray bursts (sGRBs) are widely believed to result from the mergers of compact binaries. This model predicts an afterglow that bears the characteristic signatures of a constant, low-density medium, including a smooth prompt-afterglow transition, and a simple temporal evolution. However, these expectations are in conflict with observations for a non-negligible fraction of sGRB afterglows. In particular, the onset of the afterglow phase for some of these events appears to be delayed and, in addition, a few of them exhibit late-time rapid fading in their light curves. We show that these peculiar observations can be explained independently of ongoing central engine activity if some sGRB progenitors are compact binaries hosting at least one pulsar. The Poynting flux emanating from the pulsar companion can excavate a bow-shock cavity surrounding the binary. If this cavity is larger than the shock deceleration length scale in the undisturbed interstellar medium, then the onset of the afterglow will be delayed. Should the deceleration occur entirely within the swept-up thin shell, a rapid fade in the light curve will ensue. We identify two types of pulsar that can achieve the conditions necessary for altering the afterglow: low-field, long-lived pulsars, and high-field pulsars. We find that a sizable fraction (≈20%-50%) of low-field pulsars are likely to reside in neutron star binaries based on observations, while their high-field counterparts are not. Hydrodynamical calculations motivated by this model are shown to be in good agreement with observations of sGRB afterglow light curves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Observations of compact sources in galaxy clusters using MUSTANG2

Compact sources can cause scatter in the scaling relationships between the amplitude of the thermal Sunyaev–Zel’dovich Effect (tSZE) in galaxy clusters and cluster mass. Estimates of the importance of this scatter vary – largely due to limited data on sources in clusters at the frequencies at which tSZE cluster surveys operate. In this paper, we present 90 GHz compact source measurements from a sample of 30 clusters observed using the MUSTANG2 instrument on the Green Bank Telescope. We present simulations of how a source’s flux density, spectral index, and angular separation from the cluster’s centre affect the measured tSZE in clusters detected by the Atacama Cosmology Telescope (ACT). By comparing the MUSTANG2 measurements with these simulations we calibrate an empirical relationship between 1.4 GHz flux densities from radio surveys and source contamination in ACT tSZE measurements. We find 3 per cent of the ACT clusters have more than a 20 per cent decrease in Compton-y but another 3 per cent have a 10 per cent increase in the Compton-y due to the matched filters used to find clusters. As sources affect the measured tSZE signal and hence the likelihood that a cluster will be detected, testing the level of source contamination in the tSZE signal using a tSZE-selected catalogue is inherently biased. We confirm this by comparing the ACT tSZE catalogue with optically and X-ray-selected cluster catalogues. Furthermore, there is a strong case for a large, high-resolution survey of clusters to better characterize their source population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Magnetic frame-dragging correction to the electromagnetic solution of a compact neutron star

ABSTRACT Neutron stars are usually modelled as spherical, rotating perfect conductors with a predominant intrinsic dipolar magnetic field anchored to their stellar crust. Due to their compactness, General Relativity corrections must be accounted for in Maxwell’s equations, leading to modified interior and exterior electromagnetic solutions. We present analytical solutions for slowly rotating magnetized neutron stars, taking into account the magnetic frame-dragging correction. For typical compactness values, i.e. Rs ∼ 0.5 [R*], we show that the new terms lead to a per cent order correction in the magnetic field orientation and strength compared to the case, with no magnetic frame-dragging correction. Also, we obtain a self-consistent redistribution of the surface azimuthal current. We verify the validity of the derived solution through two-dimensional particle-in-cell simulations of an isolated neutron star. Defining the azimuthal electric and magnetic field amplitudes during the transient phase as observables, we prove that the magnetic frame-dragging correction reduces the transient wave amplitude, as expected from the analytical solution. We show that simulations are more accurate and stable, when we include all first-order terms. The increased accuracy at lower spatiotemporal resolutions translates into a reduction in simulation runtimes.

Torres, R. (ORCID:0000000291820228)↗
DOE OSTI2016

Digging deeper into the Southern skies: A compact Milky Way companion discovered in first-year Dark Energy Survey data

Here, the Dark Energy Survey (DES) is a 5000 sq. degree survey in the southern hemisphere, which is rapidly reducing the existing north-south asymmetry in the census of MW satellites and other stellar substructure. We use the first-year DES data down to previously unprobed photometric depths to search for stellar systems in the Galactic halo, therefore complementing the previous analysis of the same data carried out by our group earlier this year. Our search is based on a matched filter algorithm that produces stellar density maps consistent with stellar population models of various ages, metallicities, and distances over the survey area. The most conspicuous density peaks in these maps have been identified automatically and ranked according to their significance and recurrence for different input models. We report the discovery of one additional stellar system besides those previously found by several authors using the same first-year DES data. The object is compact, and consistent with being dominated by an old and metal-poor population. DES J0034-4902 is found at high significance and appears in the DES images as a compact concentration of faint blue point sources at ~ 87 {kpc}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Compact steady-state tokamak performance dependence on magnet and core physics limits

Compact tokamak fusion reactors using advanced high-temperature superconducting magnets for the toroidal field coils have received considerable recent attention due to the promise of more compact devices and more economical fusion energy development. Facilities with combined fusion nuclear science and Pilot Plant missions to provide both the nuclear environment needed to develop fusion materials and components while also potentially achieving sufficient fusion performance to generate modest net electrical power are considered. The performance of the tokamak fusion system is assessed using a range of core physics and toroidal field magnet performance constraints to better understand which parameters most strongly influence the achievable fusion performance. This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Unraveling trace anomaly of supradense matter via neutron star compactness scaling

The trace anomaly Δ ≡ 1/3 −𝑃/𝜖 =1/3 −𝜙 quantifies the possibly broken conformal symmetry in supradense matter under pressure 𝑃 at energy density 𝜖. Perturbative QCD (pQCD) predicts a vanishing Δ at extremely high energy or baryon densities when the conformal symmetry is realized but its behavior at intermediate densities reachable in neutron stars (NSs) is still very uncertain. The extraction of Δ from NS observations strongly depends on the employed model for nuclear equation of state (EOS). Using the IPAD-TOV method based on an intrinsic and perturbative analysis of the dimensionless (IPAD) Tolman-Oppenheimer-Volkoff (TOV) equations that are further verified numerically by using 10 5 EOSs generated randomly with a metamodel in a very broad EOS parameter space constrained by terrestrial nuclear experiments and astrophysical observations, here we first show that the compactness 𝜉 ≡ 𝐺⁡𝑀 NS /𝑅⁢𝑐 2 ≡ 𝑀 NS /𝑅 of a NS with mass 𝑀 NS and radius 𝑅 scales very accurately with $\bar{Π}$ c ≡ $Π$ c · (1 +18⁢X/25) ≡ X/(1 +3⁢X 2 +4⁢X) · (1 +18⁢X/25) where X ≡ 𝜙 c = 𝑃 c /𝜖 c is the ratio of pressure over energy density at NS centers. The scaling of NS compactness thus enables one to readily read off the central trace anomaly Δ c = 1/3 −X directly from the observational data of either the mass-radius or red-shift measurements. Finally, we then demonstrate indeed that the available NS data themselves from recent X-ray and gravitational wave observations can determine model insensitively the trace anomaly as a function of energy density in NS cores, providing a stringent test of existing NS models and a clear guidance in a new direction for further understanding the nature and EOS of supradense matter.

nuclear astrophysics↗
DOE OSTI2025

Modeling and design of compact, permanent-magnet transport systems for highly divergent, broad energy spread laser-driven proton beams

Laser-driven (LD) ion acceleration has been explored in a newly constructed short focal length laser beamline at the BELLA petawatt facility (interaction point 2, iP2). For applications utilizing such LD ion beams, a beam transport system is required, which for reasons of compactness be ideally contained within 3 m. While they are generated from a micron-scale source, large divergence and energy spread of LD ion beams present a unique challenge to transporting them compared to beams from conventional accelerators. This study gives an overview of proposed compact transport designs using permanent magnets satisfying different requirements depending on the application for the iP2 laser beamline such as radiation biology, material science, and high-energy density science. These designs are optimized for different parameters such as energy spread and peak proton density according to the application’s need. The various designs consist solely of permanent magnet elements, which can provide high magnetic field gradients on a small footprint. While the field strengths are fixed, we have shown that the beam size is able to be tuned effectively by varying the placement of the magnets. The performance of each design was evaluated based on high-order particle tracking simulations of typical LD proton beams. We also examine the ability of certain configurations to tune and select beam energies, critical for specific applications. A more detailed investigation was carried out for a design to deliver 10 MeV LD accelerated ions for radiation biology applications. With these transport system designs, the iP2 laser beamline is ready to house various application experiments.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Neutron-Resonance Transmission Analysis with a Compact Deuterium-Tritium Neutron Generator

Neutron Resonance Transmission Analysis (NRTA) is a spectroscopic technique which uses the resonant absorption of neutrons in the epithermal range to infer the isotopic composition of an object. This spectroscopic technique has relevance in many traditional fields of science and nuclear security. NRTA in the past made use of large, expensive accelerator facilities to achieve precise neutron beams, significantly limiting its applicability. Here, we describe a series of NRTA experiments where we use a compact, low-cost deuterium-tritium (DT) neutron generator to produce short neutron beams (2.6 m) along with a 6 Li-glass neutron detector. The time-of-flight spectral data from five elements – silver, cadmium, tungsten, indium, and 238 U – clearly show the corresponding absorption lines in the 1-30 eV range. The experiments show the applicability of NRTA in this simplified configuration, and prove the feasibility of this compact and low-cost approach. This could significantly broaden the applicability of NRTA, and make it practical and applicable in many fields, such as material science, nuclear engineering, and arms control.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

(2+1)-dimensional compact Lifshitz theory, tensor gauge theory, and fractons

The (2+1)-dimensional continuum Lifshitz theory of a free compact scalar field plays a prominent role in a variety of quantum systems in condensed matter physics and high energy physics. It is known that in compact space, it has an infinite ground-state degeneracy. In order to understand this theory better, we consider two candidate lattice regularizations of it using the modified Villain formalism. We show that these two lattice theories have significantly different global symmetries (including a dipole global symmetry), anomalies, ground-state degeneracies, and dualities. In particular, one of them is self-dual. Given these theories and their global symmetries, we can couple them to corresponding gauge theories. Here, these are two different U(1) tensor gauge theories. The resulting models have excitations with restricted mobility, i.e., fractons. Finally, we give an exact lattice realization of the fracton and lineon-elasticity dualities for the Lifshitz theory, and scalar and vector charge gauge theories.

2-dimensional systems↗
DOE OSTI2023

Nuclear and hybrid equations of state in light of the low-mass compact star in HESS J1731-347

Here, we sample over 500 relativistic mean-field theories constrained by chiral effective-field theory and properties of isospin-symmetric nuclear matter and test them against known stellar structure constraints. This includes a recent mass and radius measurement of a compact object in supernova remnant HESS J1731-347, with an unusually low mass of M = 0.77$^{+0.20}_{–0.17}$M ⊙ and a compact radius of R = 10.4$^{+0.86}_{–0.78}$ km. We show that none of the sampled nuclear models meet all constraints at the 68% credibility level, but that hybrid equations of state with a quark-matter inner core and nuclear outer core easily can. This indicates a tension between astrophysical constraints and low-energy nuclear theory.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Gravitational wave emission from collisions of compact scalar solitons

We numerically investigate the gravitational waves generated by the head-on collision of equal-mass, self-gravitating, real scalar field solitons (oscillatons) as a function of their compactness $C$. We show that there exist three different possible outcomes for such collisions: (1) an excited stable oscillaton for low $C$, (2) a merger and formation of a black-hole for intermediate $C$, and (3) a pre-merger collapse of both oscillatons into individual black-holes for large $C$. For (1), the excited, aspherical oscillaton continues to emit gravitational waves. For (2), the total energy in gravitational waves emitted increases with compactness, and possesses a maximum which is greater than that from the merger of a pair of equivalent mass black-holes. The initial amplitudes of the quasi-normal modes in the post-merger ring-down in this case are larger than that of corresponding mass black-holes -- potentially a key observable to distinguish black-hole mergers with their scalar mimics. For (3), the gravitational wave output is indistinguishable from a similar mass, black-hole--black-hole merger. Based on these results, LIGO may be sensitive to oscillaton collisions from light scalars of mass 10 -12 eV $\lesssim$ m $\lesssim$ 10 -10 eV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Versatile compact heater design for in situ nano-tomography by transmission X-ray microscopy

A versatile, compact heater designed at National Synchrotron Light Source-II for in situ X-ray nano-imaging in a full-field transmission X-ray microscope is presented. Heater design for nano-imaging is challenging, combining tight spatial constraints with stringent design requirements for the temperature range and stability. Finite-element modeling and analytical calculations were used to determine the heater design parameters. Performance tests demonstrated reliable and stable performance, including maintaining the exterior casing close to room temperature while the heater is operating at above 1100°C, a homogenous heating zone and small temperature fluctuations. Two scientific experiments are presented to demonstrate the heater capabilities: (i) in situ 3D nano-tomography including a study of metal dealloying in a liquid molten salt extreme environment, and (ii) a study of pore formation in icosahedral quasicrystals. The progression of structural changes in both studies were clearly resolved in 3D, showing that the new heater enables powerful capabilities to directly visualize and quantify 3D morphological evolution of materials under real conditions by X-ray nano-imaging at elevated temperature during synthesis, fabrication and operation processes. This heater design concept can be applied to other applications where a precise, compact heater design is required.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Additive Manufactured Compact Microwave Absorbers

A high-performance, compact microwave absorber was created using Fused Deposition Modeling (FDM) 3D printing. Both a narrowband and a broadband absorber were created. The narrowband absorber was designed at 4.9 GHz, mid-band in WR-187 waveguide. The broadband absorber tried to achieve the best attenuation across the entire 3.95 to 5.85 GHz band. Two types of carbon loaded polylactic acid (PLA) plastic and one type of unloaded PLA were 3D printed with variable percentages of air to achieve different values of effective dielectric constant and loss tangent. The absorber comprised five or six rectangular pieces of these plastic materials. The thickness and fill factor values for each piece were optimized to minimize reflection through fast analytic modeling in MATLAB®. The results were then verified by HFSS® simulation as well. The stack progressed from the lowest loss and lowest dielectric constant to the highest at the shorting end. The final narrowband load had simulated return loss of 87 dB at 4.9 GHz with an analytic solution in MATLAB. The measured return loss of the 3D printed attenuator was 73 dB at 4.929 GHz. The total length of the absorber was 2.44 inches. A commercial absorber for WR-187 with return loss of 40 dB has length of 13 inches. The experiment proves that an effective and compact microwave absorber can be created using 3D printing.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Modeling, Design, and Experimental Verification of a WPT Level-3 Wireless Charger with Compact Secondary Coupler

This study introduces a wireless power transfer (WPT) Level-3 rated charger with >11 kW nominal output. The proposed system is interoperable for WPT Level-1, 2, and 3 charger applications of which power levels and airgap separations are defined in SAE J2954. The system designed for this study is capable of operating at Z 1 (100-150 mm), Z 2 (140-210 mm) and Z 3 (170-250 mm) vehicle assembly ground clearance range classes with a very compact vehicle-side (secondary) coupler. The couplers are characterized for the maximum output power (P out ) and the coupling coefficient (k) with different airgaps. System frequency response and the sensitivity analysis are presented. Experimental results are shown for 190.5 mm and 216 mm airgap separations. These results demonstrate that the proposed system with a very compact secondary can be operated at these ground clearance classes with high efficiency at WPT level-3 charging levels.

Onar, Omer↗
DOE OSTI2014

Design and development of a portable flash X-ray source driven by battery powered compact Marx generator

The design, construction and operational characteristics of a portable flash X-ray source driven by battery-powered compact Marx is reported. The novel configuration of compact Marx utilizes hollow capacitors in successive stages to enhance the erection reliability. The characteristic impedance of this system is ∼ 200 Ω. At discharge of ∼ 22 kV, >200 kV output pulse of 60 ns duration (FWHM) with rise time of <5 ns (10% - 90%) is produced. The pulser requires Nitrogen gas pressurization up to 3 atm for operation at maximum rating. The Marx generator assembly is fitted in to a stainless steel tube of 10 cm diameter and 1.2 m length. While using a demountable sealed X-ray tube of matched impedance, this device produces an X-ray pulse of approximately ∼ 30 ns duration and has maximum energy of ∼ 200 keV. This true tabletop device is able to produce dose up to 100 mR per shot, measured at the distance of 30 cm from output window. The focal spot size has been passively confirmed to be in the sub-millimeter (<1 mm) range. (author)

43 PARTICLE ACCELERATORS↗