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DOE OSTI2021

Impact of Coherent Beam-Beam Interaction on the Collisionless Damping of the Transverse Coupled-Bunch Instability

In the EIC design, at high average-current operation, the transverse coupled-bunch instability (TCBI) induced by the long-range transverse resistive-wall wakefield in the electron storage ring (eSR) has a fast growth rate and requires efficient mitigation. A natural mitigation mechanism is provided by the beam-beam interaction at the interaction point (IP), which gives a strong Landau damping for the TCBI in the eSR. In this study, using a simplified simulation model, we investigate how this Landau damping from the beam-beam interaction behaves when the coherent beam-beam interaction at IP is considered. Our method and results will be presented in this paper.

Li, R.↗

DOE OSTI2021

Investigation of HTS Twisted Stacked-Tape Cable (TSTC) Conductor for High-Field, High-Current Fusion Magnets

The critical currents of a twisted single-tape were measured at 4.2 K in fields up to 17 T. It was confirmed that the critical current of a twisted-tape was similar to that of a flat tape in c-axis fields. Based on the single-tape critical-currents, a 40-tape (4-mm width) twisted stacked-tape cable (TSTC) conductor was experimentally evaluated at fields up to 17 T at 4.2 K. It was found that the Lorentz load degradation of the TSTC conductor was negligible at the end of a cyclic test. The TSTC cabling method has been considered to be suitable for developing a high-field high-current REBCO conductor for magnet applications as well as power transmission cables. A method to fabricate the inner legs of a D-shape toroidal field coil using a TSTC conductor has been discussed. This method allows the conductor to properly resist the transverse Lorentz load and mitigate ac loss issues by adopting a parallel-HTS-tape flat cable configuration where necessary.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2026

Unveiling field-transverse spin anisotropy in the spin liquid candidate α-RuCl3 via spin Hall magnetoresistance

α-RuCl3 has emerged as a possible candidate for a quantum spin liquid (QSL) that promises exotic quasiparticles relevant for fault-tolerant quantum computation. Here, we report spin-sensitive transport measurements using a proximal spin Hall metal, platinum (Pt), to probe magnetic moments in the insulator α-RuCl3. We observe spin Hall magnetoresistance (SMR), where both the transverse and longitudinal resistivities exhibit angular oscillations between the in-plane magnetic field and the current, driven by the interplay between the spin Hall effect in Pt and local magnetic moments in α-RuCl3. These oscillations occur from 1.5 to 18 T, covering the zigzag antiferromagnetic, putative QSL, and supposedly partially field-polarized phases. The phase of the SMR oscillations suggests that the local moments, whether static or fluctuating, develop spin anisotropy with a quantization axis in-plane and largely transverse to the magnetic field across all fields from 1.5 to 18 T. Temperature dependence indicates that the spin anisotropy operates at an energy scale similar to that of the reported QSL signatures in α-RuCl3.

Idzuchi, Hiroshi [Tohoku University, Japan]↗

DOE OSTI2024

Intrinsic magnetism in KTaO3 heterostructures

There has been intense recent interest in the two-dimensional electron gases (2DEGs) that form at the surfaces and interfaces of KTaO3 (KTO), with the discovery of superconductivity at temperatures significantly higher than those of similar 2DEGs based on SrTiO3 (STO). Like STO heterostructures, these KTO 2DEGs are formed by depositing an overlayer on top of appropriately prepared KTO surfaces. Some of these overlayers are magnetic, and the resulting 2DEGs show signatures of this magnetism, including hysteresis in the magnetoresistance (MR). Here, we show that KTO 2DEGs fabricated by depositing AlOx on top of KTO also show hysteretic MR, indicative of long-range magnetic order, even though the samples nominally contain no intrinsic magnetic elements. The hysteresis appears in both the transverse and longitudinal resistance in magnetic fields both perpendicular to and in the plane of the 2DEG. The hysteretic MR has different characteristic fields and shapes for surfaces of different crystal orientations and vanishes above a few Kelvin. Density functional theory (DFT) calculations indicate that the magnetism likely arises from Ta4+ local moments created in the presence of oxygen vacancies.

Physics↗

DOE OSTI2025

Unconventional magnetotransport and antiferromagnetic order in Eu 2 ⁢InTe 5

Here, we report on the structural characterization and physical properties of Eu 2 ⁢InTe 5 , a distorted square-net motif antiferromagnetic semiconductor. Single crystal x-ray diffraction measurements reveal a distortion of the Te square-net layers such that an orthorhombic supercell is necessary to accurately describe the structure. Magnetization, resistivity, and specific heat measurements confirm antiferromagnetic ordering at 𝑇 𝑁 = 7.3K. Anisotropy in magnetization data suggests the magnetic moments are oriented parallel to the 𝑐 axis. We observe an unconventional transverse magnetoresistance and Hall resistivity in the paramagnetic state (𝑇 ≤ 80K), indicating strong coupling between localized Eu 2+ magnetic moments and conduction electrons. Resistivity and Hall measurements indicate the material is a heavily doped semiconductor, with impurity states related to disorder. Our findings highlight a relatively unexplored Eu-based antiferromagnetic semiconductor with unconventional magnetotransport behavior.

Cook, Matthew S. [Oak Ridge National Laboratory (O↗

DOE OSTI2021

Giant anomalous Nernst signal in the antiferromagnet YbMnBi 2

A large anomalous Nernst effect (ANE) is crucial for thermoelectric energy conversion applications because the associated unique transverse geometry facilitates module fabrication. Topological ferromagnets with large Berry curvatures show large ANEs; however, they face drawbacks such as strong magnetic disturbances and low mobility due to high magnetization. Herein, we demonstrate that YbMnBi 2 , a canted antiferromagnet, has a large ANE conductivity of ~10 A m –1 K –1 that surpasses large values observed in other ferromagnets (3–5 A m –1 K –1 ). The canted spin structure of Mn guarantees a non-zero Berry curvature, but generates only a weak magnetization three orders of magnitude lower than that of general ferromagnets. The heavy Bi with a large spin–orbit coupling enables a large ANE and low thermal conductivity, whereas its highly dispersive p x/y orbitals ensure low resistivity. The high anomalous transverse thermoelectric performance and extremely small magnetization make YbMnBi 2 an excellent candidate for transverse thermoelectrics.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2025

Analytical estimates of beam intensity limitations in the EIC Beam Accumulator Ring

This report summarizes analytical estimates of beam intensity limitations in the Beam Accumulator Ring (BAR), a part of the Electron-Ion Collider injector complex under development at Brookhaven National Laboratory. The BAR is designed to accumulate a polarized electron beam with a single-bunch charge up to 28 nC for subsequent acceleration in the Rapid Cycling Synchrotron and then injection into the Electron Storage Ring. Analytical models of longitudinal and transverse collective effects are developed using a broadband impedance model calibrated with the beam-based measurement results from NSLS VUV. The study evaluates the impact of resistive-wall and geometric impedances, assessing microwave and transverse mode coupling instabilities, bunch lengthening, and beam-induced heating.

43 PARTICLE ACCELERATORS↗

DOE OSTI2025

Single-Bunch Instabilities at the Fermilab Recycler Ring

Understanding and characterizing collective instabilities is critical for high-intensity operation at the Fermilab Recycler Ring. This work presents an application of the the Nested Head-Tail (NHT) formalism for modeling single-bunch transverse instabilities, incorporating analytical solutions to the resistive wall impedances in the absence of space charge. Predicted growth rates and mode structures are benchmarked against PyHEADTAIL simulations and ongoing experimental measurements. The experimental program includes studies of bare-machine instabilities at different machine parameters. These results support the understanding of naturally-occurring instabilities in the Recycler and contribute to the development of predictive tools for beam stability in future high-intensity configurations.

Gonzalez-Ortiz, C. [Fermilab]↗

DOE OSTI2025

Single-Bunch Instabilities at the Fermilab Recycler Ring

Gonzalez-Ortiz, Cristhian [Fermilab]↗

DOE OSTI2026

Extreme Transverse Magnetoresistance in TiZn 16

Extreme magnetoresistance (XMR) is a phenomenon characterized by an increase in resistance by factors of 10 4 –10 7 % when a magnetic field is applied. This phenomenon is found in a number of semimetals such as WTe 2 , PtSn 4 , Cd 3 As 2 , and LaSb. The origin of XMR is still hotly debated, possibly with different materials having different (or multiple) explanations. Extreme transverse magnetoresistance of up to 8000% at 14 T and 1.8 K is measured in TiZn 16 , a semimetal with a multitude of bands crossing the Fermi energy, akin to PtSn 4 . The magnetoresistance is suppressed when the magnetic field is rotated to be parallel to the applied current, similar to PtSn 4 and PdSn 4 . The resistance of TiZn 16 follows Kohler's rule, but displays different behavior under an applied transverse field and under a longitudinal magnetic field, suggesting distinct electrical phases. Also present are Shubnikov-de Haas and de Haas-van Alphen oscillations with a transverse magnetic field up to 43 T, showing that despite an insulator-like temperature-resistance curve, charge carriers are still present. This positions TiZn 16 as an interesting addition to the investigation of XMR materials as a multi-band metal with complex Fermi surface geometries.

extreme magnetoresistance↗

DOE OSTI2021

Transverse barrier formation by electrical triggering of a metal-to-insulator transition

Application of an electric stimulus to a material with a metal-insulator transition can trigger a large resistance change. Resistive switching from an insulating into a metallic phase, which typically occurs by the formation of a conducting filament parallel to the current flow, is a highly active research topic. Using the magneto-optical Kerr imaging, we found that the opposite type of resistive switching, from a metal into an insulator, occurs in a reciprocal characteristic spatial pattern: the formation of an insulating barrier perpendicular to the driving current. This barrier formation leads to an unusual N-type negative differential resistance in the current-voltage characteristics. We further demonstrate that electrically inducing a transverse barrier enables a unique approach to voltage-controlled magnetism. By triggering the metal-to-insulator resistive switching in a magnetic material, local on/off control of ferromagnetism is achieved using a global voltage bias applied to the whole device.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Computational general relativistic force-free electrodynamics: II. Characterization of numerical diffusivity

Scientific codes are an indispensable link between theory and experiment; in (astro-)plasma physics, such numerical tools are one window into the universe’s most extreme flows of energy. The discretization of Maxwell’s equations – needed to make highly magnetized (astro)physical plasma amenable to its numerical modeling – introduces numerical diffusion. It acts as a source of dissipation independent of the system’s physical constituents. Understanding the numerical diffusion of scientific codes is the key to classifying their reliability. It gives specific limits in which the results of numerical experiments are physical. We aim at quantifying and characterizing the numerical diffusion properties of our recently developed numerical tool for the simulation of general relativistic force-free electrodynamics by calibrating and comparing it with other strategies found in the literature. Our code correctly models smooth waves of highly magnetized plasma. We evaluate the limits of general relativistic force-free electrodynamics in the context of current sheets and tearing mode instabilities. We identify that the current parallel to the magnetic field (j ∥ ), in combination with the breakdown of general relativistic force-free electrodynamics across current sheets, impairs the physical modeling of resistive instabilities. We find that at least eight numerical cells per characteristic size of interest (e.g., the wavelength in plasma waves or the transverse width of a current sheet) are needed to find consistency between resistivity of numerical and of physical origins. High-order discretization of the force-free current allows us to provide almost ideal orders of convergence for (smooth) plasma wave dynamics. The physical modeling of resistive layers requires suitable current prescriptions or a sub-grid modeling for the evolution of j ∥ .

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

Single-Bunch Instabilities Driven by Space Charge During Low-Energy Cooling at Injection in the EIC Hadron Storage Ring

This paper presents a simulation-based study of single-bunch dynamics at the injection energy of 23.8 GeV for protons in the EIC hadron storage ring, focusing on the impact of space-charge–driven instabilities. The analysis demonstrates that at this energy, the proton bunch experiences significant transverse space-charge forces, which can reduce the stability margin in the presence of the geometric and resistive wall impedance. Various collective effects were considered, with particular attention to the nonlinear nature of the transverse space charge. To stabilize the beam, high chromaticity and octupoles were introduced and their effects analyzed using the ELEGANT code. The results provide a quantitative assessment of the stability thresholds and offer guidance for the machine design and operational strategy at injection.

43 PARTICLE ACCELERATORS↗

DOE OSTI2022

Directional ballistic transport in the two-dimensional metal PdCoO2

Abstract In an idealized infinite crystal, the material properties are constrained by the symmetries of the unit cell. The point-group symmetry is broken by the sample shape of any finite crystal, but this is commonly unobservable in macroscopic metals. To sense the shape-induced symmetry lowering in such metals, long-lived bulk states originating from an anisotropic Fermi surface are needed. Here we show how a strongly facetted Fermi surface and the long quasiparticle mean free path present in microstructures of PdCoO 2 yield an in-plane resistivity anisotropy that is forbidden by symmetry on an infinite hexagonal lattice. We fabricate bar-shaped transport devices narrower than the mean free path from single crystals using focused ion beam milling, such that the ballistic charge carriers at low temperatures frequently collide with both of the side walls that define the channel. Two symmetry-forbidden transport signatures appear: the in-plane resistivity anisotropy exceeds a factor of 2, and a transverse voltage appears in zero magnetic field. Using ballistic Monte Carlo simulations and a numerical solution of the Boltzmann equation, we identify the orientation of the narrow channel as the source of symmetry breaking.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Performance of the ATLAS RPC detector and Level-1 muon barrel trigger at √(s)=13 TeV

The ATLAS experiment at the Large Hadron Collider (LHC) employs a trigger system consisting of a first-level hardware trigger (L1) and a software-based high-level trigger. The L1 muon trigger system selects muon candidates, assigns them to the correct LHC bunch crossing and classifies them into one of six transverse-momentum threshold classes. The L1 muon trigger system uses resistive-plate chambers (RPCs) to generate the muon-induced trigger signals in the central (barrel) region of the ATLAS detector. The ATLAS RPCs are arranged in six concentric layers and operate in a toroidal magnetic field with a bending power of 1.5 to 5.5 Tm. The RPC detector consists of about 3700 gas volumes with a total surface area of more than 4000 m2. This paper reports on the performance of the RPC detector and L1 muon barrel trigger using 60.8 fb-1 of proton-proton collision data recorded by the ATLAS experiment in 2018 at a centre-of-mass energy of 13 TeV. Detector and trigger performance are studied using Z boson decays into a muon pair. Measurements of the RPC detector response, efficiency, and time resolution are reported. Measurements of the L1 muon barrel trigger efficiencies and rates are presented, along with measurements of the properties of the selected sample of muon candidates. Measurements of the RPC currents, counting rates and mean avalanche charge are performed using zero-bias collisions. Finally, RPC detector response and efficiency are studied at different high voltage and front-end discriminator threshold settings in order to extrapolate detector response to the higher luminosity expected for the High Luminosity LHC.

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Magnetotransport properties of the topological nodal-line semimetal CaCdSn

Topological nodal-line semimetals support protected band crossings, which form nodal lines or nodal loops between the valence and conduction bands and exhibit novel transport phenomena. Here we address the topological state of the nodal-line semimetal candidate material CaCdSn, and report magnetotransport properties of its single crystals grown by the self-flux method. In this work, our first-principles calculations show that the electronic structure of CaCdSn harbors a single nodal loop around the Γ point in the absence of spin-orbit coupling effects. The nodal crossings in CaCdSn are found to lie above the Fermi level and yield a Fermi surface that consists of both electron and hole pockets. CaCdSn exhibits high mobility (μ ≈ 3.44 × 10 4 cm 2 V –1 s –1 ) and displays a field-induced metal-semiconductor-like crossover with a plateau in resistivity at low temperature. We observe an extremely large and quasilinear nonsaturating transverse as well as longitudinal magnetoresistance (MR) at low temperatures (≈ 7.44 × 10 3 % and ≈ 1.71 × 10 3 %, respectively, at 4 K). We also briefly discuss possible reasons behind such a large quasilinear magnetoresistance and its connection with the nontrivial band structure of CaCdSn.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Some observations concerning "laminarization" in heated vertical tubes

For low "turbulent" Reynolds numbers in strongly-heated vertical gas flow, fundamental results of existing direct numerical simulation (DNS) databases have been examined to deduce differences between cases which "revert" to turbulent and those that yield integral parameters which correspond to laminar flow (henceforth laminarizing or laminarized). The objectives of this paper are (1) to examine the streamwise evolution of near-wall flow structures and (2) to determine which, if any, proposed laminarization parameters could be used to discriminate between turbulent and laminarizing flows resulting. Views of streamlines in r-θ cross sections showed evidence of a ring of irregular-shaped streamwise vortices near the wall at all locations. The transverse advection of these vortices is hypothesized to provide a path of least resistance to the transport of streamwise momentum in the wall-normal direction. It is demonstrated that a steady streamwise laminar vortex can provide apparent turbulent momentum transport (as a consequence of the Reynolds decomposition) such that a reasonable mean velocity profile is predicted near the wall. For the present cases, the values of the non-dimensional radius (y c,w + = Re τ,w ) and of the modified wall Reynolds number did discriminate whether turbulent or laminarizing flow resulted.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2021

Tamper-resistant fastener

A tamper-resistant threaded fastener including a circular head having a slot formed in the head transverse to the longitudinal axis, the slot having an enlarged region intermediate an apex and a base of the slot. A cap member includes a head having a drive feature formed therein, the head extending to a first shank portion, extending to an enlarged second shank portion, extending to a foot. The cap member is insertable in the slot only from a direction transverse to the longitudinal axis. During rotational installation of the fastener and cap member in a threaded counterbored opening for securing a barrier for protecting an asset, the foot shears inside the slot at a predetermined rotational drive force, the cap member being rotatable in the opening and protectively covering the fastener head.

Neidigk, Stephen↗