Physical Sciences

The auto differentiable simulation is a type of simulation that outputs of the simulation include not only the simulation result itself, but also their derivatives with respect to various input parameters. It provides an efficient method to study sensitivity of the simulation results with respect to the input parameters. Furthermore, it can be used in gradient based optimization methods for rapidly optimizing design parameters. In this paper, we present the development of a fast and transparent auto-differentiation module/class designed for easy integration into numerous simulation codes. As an application, this auto-differentiation module is integrated into a parallel particle-in-cell code with message passing interface (MPI) on distributed memory computers.

Conventional Rutherford cables are typically made from solid round wire. While multistage cables have been made elsewhere, the purpose was usually to achieve a higher strand count and therefore a higher current carrying capability. In this work, we attempt to use two-stage roped strands made from ultrafine wires to fabricate Rutherford cables. The ultimate goal of this work is to obtain a very flexible cable that can wind accelerator magnet coils with a very tight bend radius in both the easy way (along the broad face of the cable) and the hard way (along the edge of the cable) in the wind-and-react manner, or wind coils with a radius typically used today but in the react-and-wind manner with a much reduced degradation in critical current. We report our experience fabricating such Rutherford cables at the Lawrence Berkeley National Laboratory, and the initial findings from the analysis of the experimental cables made. We will discuss how the conventional wisdom and some rules of thumb for making Rutherford cables are no longer applicable or relevant, and the new thinking required in designing these cables.

Abstract REBCO coated conductors are of significant interest for high-field superconducting applications owing to their exceptional critical current retention under high magnetic fields. However, depending on the fabrication route, microstructural inhomogeneities such as porosity, Cu x O precipitates, and a-axis oriented grains can emerge at various length scales, disrupting current transport and limiting the critical current density. This study investigates and characterizes such defects in commercial REBCO conductors of varying specifications. Top-view SEM images of the REBCO layer were acquired following chemical etching of Cu and Ag layers to expose the microstructure for analysis. Conventional image analysis and segmentation techniques prove insufficient for reliably quantifying these defects, while manual identification remains prohibitively labor-intensive. To overcome these limitations, a machine learning approach is explored to enable rapid, automated, and accurate defect detection. Specifically, an open-source computer vision model, Mask R-CNN, is fine-tuned on domain-specific SEM image data. The fine-tuned model achieved a validation mean average precision of 45.23% and enabled quantitative defect analysis across 63 tapes. Partial correlation analysis, controlling for confounding between defect types, revealed independent associations with critical current density that varied in strength and sign across defect types and measurement conditions. These findings motivate further targeted characterization to establish the microstructural origins of these relationships and inform conductor optimization.

In this note, we develop in closed form the dynamical $SO(3)$ spin map determined by the Thomas-BMT equation for a charged particle with general gyromagnetic ratio in a uniform longitudinal magnetic and electric field. This field configuration provides an idealized model of uniform particle acceleration with transverse (solenoidal) confinement. The spin map is expressed in a factorized Lie-algebraic (axis-angle) form, making it straightforward to determine the corresponding $SU(2)$ or quaternion representation. To facilitate numerical implementation, the Lie generators are expressed as functions of the six phase space variables commonly used for charged particle transport in $s$-based tracking codes. The dynamical evolution of these phase space variables is also described. This allows exact transport of both phase space and spin variables over long distances in such a field region, without the need for numerical integration.

Superconducting magnets enable energy-frontier accelerators by generating strong magnetic fields to steer and focus the particles. Although high-temperature superconductors such as (, RE = rare earth) hold a strong potential for generating a higher magnetic field than Nb-Ti and , the associated magnet and conductor technology for accelerator applications is still in its infancy. The U.S. Magnet Development Program is developing magnet technology in collaboration with industry. Here we report an experiment of making a dipole magnet called C3 using commercial high-temperature superconducting wires. The magnet, following a canted design, generated a dipole field of 5.99 T at 4.2 K in its clear aperture of 65 mm at 6.795 kA when a resistive voltage of appeared across one of the coils in the magnet. The stored energy was 53 kJ at the peak field. The magnet showed no degradation in the current-carrying capability at 4.2 K after the thermal cycle. We report on the detailed design, fabrication, and performance of the C3 magnet that can be of interest to potential users of this emerging technology. We also discuss issues and research needs to inform future magnet development. The experiment represented another step to addressing if the high-temperature superconducting accelerator magnet technology can increase the discovery capability of future particle accelerators.

Active neutron interrogation techniques that integrate Gamma-Ray and Neutron Spectroscopy (GRNS) with Associated Particle Imaging (API) offer a highly promising approach for achieving three-dimensional (3D) bulk geochemical analysis of planetary shallow surfaces. While API-GRNS using prompt γ -rays has been explored previously, the complementary use of backscattered fast neutrons within the API framework remains comparatively underexplored. Most prior fast neutron API demonstrations are based on forward scattering measurements in a transmission geometry, whereas planetary surface deployments require a backscatter geometry in which neutrons are measured after being scattered from the target. This study presents a proof-of-concept laboratory demonstration of API-based backscattered fast neutron imaging for material discrimination, with emphasis on distinguishing hydrogen-rich from hydrogen-deficient targets relevant to planetary exploration. Experiments were conducted using a D–T neutron generator-based API system at Lawrence Berkeley National Laboratory (LBNL), employing 6Li-activated CLYC (Cs2LiYCl6:Ce) and EJ-309 scintillators for coincident detection of alpha particles and fast neutrons. The system successfully imaged contrasting materials with high and low mass number 〈 A 〉 based on their neutron scattering characteristics, investigating the feasibility of backscattered fast neutron imaging as a complementary diagnostic to API-based γ -ray spectroscopy and as a method to distinguish hydrogen-bearing materials. Monte Carlo simulations using GEANT4 provide insight into the observed image contrast, highlighting the roles of elastic and inelastic scattering kinematics, macroscopic cross sections, and detector timing resolution. While quantitative hydrogen retrieval and depth sensitivity analyses are beyond the present scope, this work establishes a foundation for future studies aimed at extending API-based fast neutron imaging toward hydrated minerals and water, depth profiling, and integration with other GRNS sensors for planetary shallow subsurface exploration.

Automatic differentiation provides an efficient means of computing derivatives of complex functions with machine precision, thereby enabling differentiable simulation. In this work, we propose the use of the norm of the tangent map, obtained from differentiable tracking of particle trajectories, as a computationally efficient indicator of chaotic behavior in phase space. In many cases, a one-turn or few-turn tangent map is sufficient for this purpose, significantly reducing the computational cost associated with dynamic aperture optimization. As an illustrative application, the proposed indicator is employed in the dynamic aperture optimization of an ALS-U lattice design.

This article was originally published online on 16 June 2026 with an error in Eq. (25) and Ref. 48. Equation (25) and Ref. 48 appear correctlybelow. All online and printed versions of the article were corrected on 22 June 2026. AIP Publishing apologizes for this error. (Formula presented)

The published article has been revised. The name of the author Pramod Sharma was previously incorrect and appeared as Pramond Sharma. The original article has been corrected.

The structural biology method of X-ray footprinting mass spectrometry (XFMS) is available at two national synchrotron beamlines in the USA: one at the Advanced Light Source (ALS) on the West Coast and the other at the National Synchrotron Light Source II on the East Coast. XFMS is a solution-state technique that utilizes oxidative modifications of proteins at micromolar concentrations in aqueous buffer to extract structural information. X-rays are employed to generate hydroxyl radicals in situ, which covalently modify specific protein side chains. These modifications are subsequently quantified using liquid chromatography and mass spectrometry. Ratiometric changes in modification levels between two protein states (e.g. with and without ligand) generate a relative solvent accessibility map of the protein pairs, which serves to reveal structural features. Up until recently, the XFMS capability was available as part of a shared program at the ALS without a dedicated beamline. In this article, we describe the commissioning of ALS beamline 3.3.1, dedicated to XFMS, including the installation of a new focusing mirror, the design and construction of a new endstation with automated sample handling and exposure capabilities, and the use of accurate empirical dose calculations using Gafchromic film. Finally, we showcase the new beamline capabilities using two protein systems.