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DOE OSTI2025

Unified differentiable digital twin for the IOTA/FAST facility

As the design complexity of modern accelerators grows, there is more interest in using advanced simulations that have fast execution time or produce insights about accelerator state. One notable example of additional information are gradients of physical observables with respect to design parameters produced by differentiable simulations. The IOTA/FAST facility has recently begun a program to implement and experimentally validate a unified start-to-end differentiable digital twin to serve as a virtual accelerator test stand, allowing for rapid prototyping of new software and experiments with minimal beam time costs. In this contribution we will discuss our plans and progress. Specifically, we will cover the selection and benchmarking of both physics and ML codes, the development of generic interfaces between device models and surrogate or physics-based sections, and the export of the parameters through either a deterministic event loop or a fully asynchronous EPICS soft input/output controller. We will also discuss challenges in model calibration and uncertainty quantification, as well as future plans to support larger proton accelerators like PIPII and Booster.

Kuklev, Nikita [Fermilab]↗

DOE OSTI2017

Achieving algorithmic resilience for temporal integration through spectral deferred corrections

Spectral deferred corrections (SDC) is an iterative approach for constructing higher-order-accurate numerical approximations of ordinary differential equations. SDC starts with an initial approximation of the solution defined at a set of Gaussian or spectral collocation nodes over a time interval and uses an iterative application of lower-order time discretizations applied to a correction equation to improve the solution at these nodes. Each deferred correction sweep increases the formal order of accuracy of the method up to the limit inherent in the accuracy defined by the collocation points. In this paper, we demonstrate that SDC is well suited to recovering from soft (transient) hardware faults in the data. A strategy where extra correction iterations are used to recover from soft errors and provide algorithmic resilience is proposed. Specifically, in this approach the iteration is continued until the residual (a measure of the error in the approximation) is small relative to the residual of the first correction iteration and changes slowly between successive iterations. Here, we demonstrate the effectiveness of this strategy for both canonical test problems and a comprehensive situation involving a mature scientific application code that solves the reacting Navier-Stokes equations for combustion research.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2014

Micromechanical Behavior of Solid-Solution-Strengthened Mg-1wt.%Al Alloy Investigated by In-Situ Neutron Diffraction

In-situ neutron-diffraction experiments were employed to investigate the micromechanical behavior of solid-solution-strengthened Mg-1wt.%Al alloy. Two starting textures were used: 1) as-extruded then solutionized texture, T1, in which the basal poles of most grains are tilted around 70~85 from the extrusion axis, and 2) a reoriented texture, T2, in which the basal poles of most grains are tilted around 10~20 from the extrusion axis. Lattice strains and diffraction peak intensity variations were measured in situ during loading-unloading cycles in uniaxial tension. Twinning activities and stress states for various grain orientations were revealed. The results show that the soft grain orientations, favorably oriented for either extension twinning or basal slip, exhibit the stress relaxation, resulting in the compressive residual strain after unloading. On the other hand, the hard grain orientations, unfavorably oriented for both extension twinning and basal slip, carry more applied load, leading to much higher lattice strains during loading followed by tensile residual strains upon unloading.

Lee, Sooyeol↗

NASA NTRS2004

Combining Hard with Soft Materials in Nanoscale Under High-Pressure High-Temperature Conditions

Nano-composites with a primary nanocrystalline ceramic matrix and a secondary nanocrystalline material (metal or semiconductor) were synthesized by infiltration of an appropriate liquid into ceramic compacts under pressures of up to 8 GPa and temperatures of up to 2000 K. The purpose of our work is to obtain nanocomposites which constitute homoger?ous mixtures of two phases, both forming nano- grains of about 10 nm in size. The high pressure is used to bring the porosity of the compacted powders down to the nano-scale and force a given liquid into the nano-sized pores. The advantage of the infiltration technique is that, in a single, continuous process, we start with a nanocrystalline powder, compress it to form the matrix of the composite, and crystallize and/or synthesize a second nanomaterial in the matrix pores. The key limitation of this technology is, that the pores in the matrix need to stay open during the entire process of infiltration. Thus the initial powder should form a rigid skeleton, otherwise the so-called self-stop process can limit cr block a further flow of the liquid phase and hinder the process of the composite formation. Therefore powders of only very hard ceramic materials like diamond, Sic, or Alz03, which can withstand a substantial external load without undesired deformation, can be used as the primary phase. With this technique, using diamond and S i c ceramic powders infiltrated by liquid metals (AI, Zn, Sn, Ag, Au) and semiconductors (Si, Ge, GaAs, CdTe), we obtained nano-composites with the grain size in the range of 10 - 30 nm. Our work addresses the key problem in manufacturing bulk nanocrystalline materials, i.e. preservation of nano-scale during the fabrication process. In this paper we discuss basic technical and methodological problems associated with nano-infiltration based on the results obtained for Zn-Sic composites.

Palosz, B.↗

DOE OSTI2014

An investigation of the liquid to glass transition using integral equations for the pair structure of coupled replicae

Extensive numerical solutions of the hypernetted-chain (HNC) and Rogers-Young (RY) integral equations are presented for the pair structure of a system of two coupled replicae (1 and 2) of a “soft-sphere” fluid of atoms interacting via an inverse-12 pair potential. In the limit of vanishing inter-replica coupling ε{sub 12}, both integral equations predict the existence of three branches of solutions: (1) A high temperature liquid branch (L), which extends to a supercooled regime upon cooling when the two replicae are kept at ε{sub 12} = 0 throughout; upon separating the configurational and vibrational contributions to the free energy and entropy of the L branch, the Kauzmann temperature is located where the configurational entropy vanishes. (2) Starting with an initial finite coupling ε{sub 12}, two “glass” branches G{sub 1} and G{sub 2} are found below some critical temperature, which are characterized by a strong remnant spatial inter-replica correlation upon taking the limit ε{sub 12} → 0. Branch G{sub 2} is characterized by an increasing overlap order parameter upon cooling, and may hence be identified with the hypothetical “ideal glass” phase. Branch G{sub 1} exhibits the opposite trend of increasing order parameter upon heating; its free energy lies consistently below that of the L branch and above that of the G{sub 2} branch. The free energies of the L and G{sub 2} branches are found to intersect at an alleged “random first-order transition” (RFOT) characterized by weak discontinuities of the volume and entropy. The Kauzmann and RFOT temperatures predicted by RY differ significantly from their HNC counterparts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Neutron spectroscopic study of crystal field excitations in Tb 2 Ti 2 O 7 and Tb 2 Sn 2 O 7

We present time-of-flight inelastic neutron scattering measurements at low temperature on powder samples of the magnetic pyrochlore oxides Tb 2 Ti 2 O 7 and Tb 2 Sn 2 O 7 . These two materials possess related, but different ground states, with Tb 2 Sn 2 O 7 displaying "soft" spin ice order below T N approx 0.87 K, while Tb 2 Ti 2 O 7 enters a hybrid, glassy-spin ice state below T g approx 0.2 K. Our neutron measurements, performed at T = 1.5 K and 30 K, probe the crystal field states associated with the J = 6 states of Tb 3+ within the appropriate Fd3-barm pyrochlore environment. These crystal field states determine the size and anisotropy of the Tb 3+ magnetic moment in each material's ground state, information that is an essential starting point for any description of the low temperature phase behavior and spin dynamics in Tb 2 Ti 2 O 7 and Tb 2 Sn 2 O 7 . While these two materials have much in common, the cubic stanate lattice is expanded compared to the cubic titanate lattice. As our measurements show, this translates into a factor of approx 2 increase in the crystal field bandwidth of the 2J +1 = 13 states in Tb 2 Ti 2 O 7 compared with Tb 2 Sn 2 O 7 . Our results are consistent with previous measurements on crystal field states in Tb 2 Sn 2 O 7 , wherein the ground state doublet corresponds primarily to mJ = {vert_bar}+-5> and the first excited state doublet to mJ = {vert_bar}+-4>. In contrast, our results on Tb 2 Ti 2 O 7 differ markedly from earlier studies, showing that the ground state doublet corresponds to a significant mixture of mJ = {vert_bar}+-5>, mJ = {vert_bar}+-4> and mJ = {vert_bar}+-2>, while the first excited state doublet corresponds to a mixture of mJ = {vert_bar}+-4>, mJ = {vert_bar}+-5> and mJ = {vert_bar}+-1>. We discuss these results in the context of proposed mechanisms for the failure of Tb 2 Ti 2 O 7 to develop conventional long range order down to 50 mK.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Experimental demonstration of enhanced self-amplified spontaneous emission by photocathode temporal shaping and self-compression in a magnetic wiggler

In this paper we demonstrate experimentally the generation of attosecond soft X-ray free-electron laser (XFEL) pulses based on a novel approach to enhanced self-amplfied spontaneous emission. Instead of utilizing an external laser, we shape the electron beam at the cathode by laser pulse stacking. We enhance the high-current spike in the beam profile through a self-compression process which uses short-range coherent synchrotron radiation in a wiggler and a downstream magnetic chicane. The undulator taper is then matched with the energy chirp along the beam for attosecond XFEL generation. Start-to-end simulations are performed to demonstrate the proposed method. The measured spectra suggest that a ~250 as pulse duration is achieved at ~940 eV in the experiment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS2003

The Discovery of an Evolving Dust Scattered X-ray Halo Around GRB 031203

We report the first detection of a time-dependent, dust-scattered X-ray halo around a gamma-ray burst. GRB3 031203 was observed by XMM-Newton starting six hours after the burst. The halo appeared as concentric ring-like structures centered on the GRB location. The radii of these structures increased with time as t(sup 1/2), consistent with small-angle X-ray scattering caused by a large column of dust along the line of sight to a cosmologically distant GRB. The rings are due to dust concentrated in two distinct slabs in the Galaxy located at distances of 880 and 1390 pc, consistent with known Galactic features. The halo brightness implies an initial soft X-ray pulse consistent with the observed GRB.

Vaughan, S.↗

NASA NTRS2011

Robonaut 2 - Initial Activities On-Board the ISS

Robonaut 2, or R2, arrived on the International Space Station in February 2011 and is currently undergoing testing in preparation for it to become, initially, an Intra-Vehicular Activity (IVA) tool and then evolve into a system that can perform Extra-Vehicular Activities (EVA). After the completion of a series of system level checks to ensure that the robot traveled well on-board the Space Shuttle Atlantis, ground control personnel will remotely control the robot to perform free space tasks that will help characterize the differences between earth and zero-g control. For approximately one year, the fixed base R2 will perform a variety of experiments using a reconfigurable task board that was launched with the robot. While working side-by-side with human astronauts, Robonaut 2 will actuate switches, use standard tools, and manipulate Space Station interfaces, soft goods and cables. The results of these experiments will demonstrate the wide range of tasks a dexterous humanoid can perform in space and they will help refine the methodologies used to control dexterous robots both in space and here on earth. After the trial period that will evaluate R2 while on a fixed stanchion in the US Laboratory module, NASA plans to launch climbing legs that when attached to the current on-orbit R2 upper body will give the robot the ability to traverse through the Space Station and start assisting crew with general IVA maintenance activities. Multiple control modes will be evaluated in this extra-ordinary ISS test environment to prepare the robot for use during EVAs. Ground Controllers will remotely supervise the robot as it executes semi-autonomous scripts for climbing through the Space Station and interacting with IVA interfaces. IVA crew will locally supervise the robot using the same scripts and also teleoperate the robot to simulate scenarios with the robot working alone or as an assistant during space walks.

Diftler, M. A.↗

NASA NTRS2015

Large Solar Energetic Particle Events Associated With Filament Eruptions Outside Active Regions

We report on four large filament eruptions (FEs) from solar cycles 23 and 24 that were associated with large solar energetic particle (SEP) events and interplanetary type II radio bursts. The post-eruption arcades corresponded mostly to C-class soft X-ray enhancements, but an M1.0 flare was associated with one event. However, the associated coronal mass ejections (CMEs) were fast (speeds approx. 1000 km/s) and appeared as halo CMEs in the coronagraph field of view. The interplanetary type II radio bursts occurred over a wide wavelength range, indicating the existence of strong shocks throughout the inner heliosphere. No metric type II bursts were present in three events, indicating that the shocks formed beyond 2-3 Rs. In one case, there was a metric type II burst with low starting frequency, indicating a shock formation height of approx.2 Rs. The FE-associated SEP events did have softer spectra (spectral index >4) in the 10-100 MeV range, but there were other low-intensity SEP events with spectral indices ⩾4. Some of these events are likely FE-SEP events, but were not classified as such in the literature because they occurred close to active regions. Some were definitely associated with large active region flares, but the shock formation height was large. We definitely find a diminished role for flares and complex type III burst durations in these large SEP events. Fast CMEs and shock formation at larger distances from the Sun seem to be the primary characteristics of the FE-associated SEP events.

filaments↗

DOE OSTI2022

Designing, synthesizing, and modeling active fluids

We review recent advances in the design, synthesis, and modeling of active fluids. Active fluids have been at the center of many technological innovations and theoretical advances over the past two decades. Research on this new class of fluids has been inspired by the fascinating and remarkably efficient strategies that biological systems employ, leading to the development of biomimetic nano- and micro-machines and swimmers. The review encompasses active fluids on both the nano- and micro-scale. We start with examples of biological active systems before we discuss how experimentalists leverage novel propulsion mechanisms to power nano- and micro-machines. Furthermore, we then examine how the study of these far-from-equilibrium systems has prompted the development of new simulation methods and theoretical models in nonequilibrium physics to account for their mechanical, thermodynamic, and emergent properties. Recent advances in the field have paved the way for the design, synthesis, and modeling of autonomous systems at the nano- and micro-scale and opened the door to the development of soft matter robotics.

36 MATERIALS SCIENCE↗

NASA NTRS2011

Enhanced Fuel-Optimal Trajectory-Generation Algorithm for Planetary Pinpoint Landing

An enhanced algorithm is developed that builds on a previous innovation of fuel-optimal powered-descent guidance (PDG) for planetary pinpoint landing. The PDG problem is to compute constrained, fuel-optimal trajectories to land a craft at a prescribed target on a planetary surface, starting from a parachute cut-off point and using a throttleable descent engine. The previous innovation showed the minimal-fuel PDG problem can be posed as a convex optimization problem, in particular, as a Second-Order Cone Program, which can be solved to global optimality with deterministic convergence properties, and hence is a candidate for onboard implementation. To increase the speed and robustness of this convex PDG algorithm for possible onboard implementation, the following enhancements are incorporated: 1) Fast detection of infeasibility (i.e., control authority is not sufficient for soft-landing) for subsequent fault response. 2) The use of a piecewise-linear control parameterization, providing smooth solution trajectories and increasing computational efficiency. 3) An enhanced line-search algorithm for optimal time-of-flight, providing quicker convergence and bounding the number of path-planning iterations needed. 4) An additional constraint that analytically guarantees inter-sample satisfaction of glide-slope and non-sub-surface flight constraints, allowing larger discretizations and, hence, faster optimization. 5) Explicit incorporation of Mars rotation rate into the trajectory computation for improved targeting accuracy. These enhancements allow faster convergence to the fuel-optimal solution and, more importantly, remove the need for a "human-in-the-loop," as constraints will be satisfied over the entire path-planning interval independent of step-size (as opposed to just at the discrete time points) and infeasible initial conditions are immediately detected. Finally, while the PDG stage is typically only a few minutes, ignoring the rotation rate of Mars can introduce 10s of meters of error. By incorporating it, the enhanced PDG algorithm becomes capable of pinpoint targeting.

Acikmese, Behcet↗

DOE OSTI2017

New Evidence for a Coronal Mass Ejection-driven High Frequency Type II Burst near the Sun

We report observations of the high frequency type II radio burst (≈430–30 MHz) that occurred in the solar corona on 2015 November 4. The drift rate of the burst, estimated close to the start frequency of its fundamental component (≈215 MHz), is unusually high (≈2 MHz s{sup −1}). Our analysis shows that the estimated speed of the magnetohydrodynamic shock driver of the burst varies with time. The peak speed and acceleration are very large, ≈2450 km s{sup −1} and ≈17 km s{sup −2}, respectively. There is spatio-temporal correlation between the type II burst and the associated coronal mass ejection (CME) in the whitelight and extreme-ultraviolet images. The time profile of the shock speed and the light curve of the associated soft X-ray flare correlate well. These results indicate that in the present case, (i) the magnetohydrodynamic shock responsible for the high frequency coronal type II burst is driven by the CME and (ii) the time profile of the type II burst shock speed represents the near-Sun kinematics of the CME.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1994

A Yohkoh search for `black-light flares'

Calculations which predict that a phenomenon analogous to stellar negative pre-flares could also exist on the Sun were published by Henoux et al. (1990), and Aboudarham et al., (1990), who showed at the beginning of a solar white-light flare (WLF) event an electron beam can cause a transient darkening before the WLF emission starts, under certain conditions. They named this event a `black light flare' (BLF). Such a BLF event should appear as diffuse dark patches lasting for about 20 seconds preceding the WLF emission, which would coincide with intense and impulsive hard X-ray bursts. The BLF location would be at (or in the vicinity of ) the forthcoming bright patches. Their predicted contrast depends on the position of the flare on the solar disk and on the wavelength band of the observation. The Yohkoh satellite provided white-light data from the aspect camera of the Soft X-ray Telescope (SXT) instrument (Tsuneta et al., 1991), at 431 nm and with a typical image interval of 10 - 12 s. We have studied nine white-light flares observed with this instrument, with X-ray class larger than M6. We have found a few interesting episodes, but no unambiguous example of the predicted BLF event. This study, although the best survey to date, was not ideal from the observational point of view. We therefore encourage further searches. Successful observations of this phenomenon on the Sun would greatly strengthen our knowledge of the lower solar atmosphere and its effects on solar luminosity variations.

Van Driel-Gesztelyi, Lidia↗

NASA NTRS2011

GRB 081029: A Gamma-Ray Burst with a Multi-Component Afterglow

We present an analysis of the unusual optical light curve of the gamma-ray burst GRB 081029, a long-soft burst with a redshift of z = 3.8479. We combine X-ray and optical observations from the Swift X-Ray Telescope and the Swift UltraViolet Optical Telescope with ground-based optical and infrared data obtained using the REM and ROTSE telescopes to construct a detailed data set extending from 86 s to approx. 100000 s after the BAT trigger. Our data cover a wide energy range, from 10 keV to 0.77 eV (1.24 A to 16000 A). The X-ray afterglow shows a shallow initial decay followed by a rapid decay starting at about 18000 s. The optical and infrared afterglow, however, shows an uncharacteristic rise at about 5000 s that does not correspond to any feature in the X-ray light curve. Our data are not consistent with synchrotron radiation from a jet interacting with an external medium, a two-component jet, or continuous energy injection from the central engine. We find that the the optical light curves can be broadly explained by a collision between two ejecta shells within a two-component jet. A growing number of gamma-ray burst afterglows are consistent with complex jets, which suggests that some (or all) gamma-ray burst jets are complex and will require detailed modelling to fully understand them.

Holland, Stephen T.↗

NASA NTRS2021

THE 450DAYS X-RAY MONITORING OF THE CHANGING-LOOK AGN 1ES 1927+654

1ES 1927+654 is a nearby active galactic nucleus (AGN) which underwent a changing-look event in early 2018, developing prominent broad Balmer lines which were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in May 2018, and that includes 265 NICER (for a total of 678 ks) and 14 Swift/XRT (26 ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169 ks) exposures. In the X-rays, 1ES 1927+654 shows a behaviour unlike any previously known AGN. The source is extremely variable both in spectral shape and flux, and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from kT ∼ 80 eV (for a 0.3–2 keV luminosity of L(0.3−2) ∼ 10^(41.5) erg/s) to ∼ 200 eV (for L(0.3−2) ∼ 10^(44) erg/s). The spectra show evidence of ionized outflows, and of a prominent feature at ∼ 1 keV, which can be reproduced by a broad emission line. The unique characteristics of 1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties.

C. Ricci↗

NASA NTRS2021

The 450 Day X-Ray Monitoring of the Changing-look AGN 1ES 1927+654

1ES 1927+654 is a nearby active galactic nucleus (AGN) that underwent a changing-look event in early 2018, developing prominent broad Balmer lines that were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in 2018 May and that includes 265 NICER (for a total of 678 ks) and 14 Swift/XRT (26 ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169 ks) exposures. In the X-rays, 1ES 1927+654 shows a behavior unlike any previously known AGN. The source is extremely variable both in spectral shape and flux and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst, the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from kT∼80 eV (for a 0.3–2 keV luminosity ofL0.3−2∼1041.5erg s−1) to∼200 eV (forL0.3−2∼1044erg s−1). The spectra show evidence of ionized outflows and of a prominent feature at ∼1 keV, which can be reproduced by a broad emission line. The unique characteristics of1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties.

Astrophysical black holes↗

DOE OSTI2025

Circles and triangles, the NLSM and Tr(Φ 3 )

A surprising connection has recently been made between the amplitudes for Tr(Φ 3 ) theory and the non-linear sigma model (NLSM). A simple shift of kinematic variables naturally suggested by the associahedron/stringy representation of Tr(Φ 3 ) theory yields pion amplitudes at all loops. In this note we provide an elementary motivation and proof for this link going in the opposite direction, starting from the non-linear sigma model and discovering its formulation as a sum over triangulations of surfaces with simple numerator factors. This uses an ancient connection between “circles” and “triangles”, interpreting the equation y = $\sqrt{1 – x^2}$ both as parametrizing points a circle as well as generating the number of triangulations of polygons. A further simplification of the numerator factors exposes them as arising from the kinematically shifted Tr(Φ3) theory, and gives rise to novel tropical representations of NLSM amplitudes. The connection to Tr(Φ 3 ) theory defines a natural notion of “surface-soft limit” intrinsic to curves on surfaces. Remarkably, with this definition, the soft limit of pion amplitudes vanishes directly at the level of the integrand, via obvious pairwise cancellations. We also give simple, explicit expressions for the multi-soft factors for tree and loop-level integrands in the limit as any number of pions are taken “surface-soft”.

Scattering Amplitudes↗