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At least 1,765 records · Page 98

Actuators Using Piezoelectric Stacks and Displacement Enhancers

Actuators are used to drive all active mechanisms including machines, robots, and manipulators to name a few. The actuators are responsible for moving, manipulating, displacing, pushing and executing any action that is needed by the mechanism. There are many types and principles of actuation that are responsible for these movements ranging from electromagnetic, electroactive, thermo-mechanic, piezoelectric, electrostrictive etc. Actuators are readily available from commercial producers but there is a great need for reducing their size, increasing their efficiency and reducing their weight. Studies at JPL’s Non Destructive Evaluation and Advanced Actuators (NDEAA) Laboratory have been focused on the use of piezoelectric stacks and novel designs taking advantage of piezoelectric’s potential to provide high torque/force density actuation and high electromechanical conversion efficiency. The actuators/motors that have been developed and reviewed in this paper are operated by various horn configurations as well as the use of pre-stress flexures that make them thermally stable and increases their coupling efficiency. The use of monolithic designs that pre-stress the piezoelectric stack eliminates the use of compression stress bolt. These designs enable the embedding of developed solid-state motors/actuators in any structure with the only macroscopically moving parts are the rotor or the linear translator. Finite element modeling and design tools were used to determine the requirements and operation parameters and the results were used to simulate, design and fabricate novel actuators/motors. The developed actuators and performance will be described and discussed in this paper.

rotary devices↗

GCAP 2.0: A Global 3-D Chemical-Transport Model Framework for Past, Present, and Future Climate Scenarios

This manuscript describes version 2.0 of the Global Change and Air Pollution (GCAP 2.0) model framework, a one-way offline coupling between version of the NASA Goddard Institute for Space Studies (GISS) general circulation model (GCM) and the GEOS-Chem global 3-D chemical-transport model (CTM). Meteorology for driving GEOS-Chem has been archived from the E2.1 contributions to Phase 6 of the Coupled Model Intercomparison Project (CMIP6) for the preindustrial and recent past. In addition, meteorology is available for the near future and end-of-the century for seven future scenarios ranging from extreme mitigation to extreme warming. Emissions and boundary conditions have been prepared for input to GEOS-Chem that are consistent with the CMIP6 experimental design. The model meteorology, emissions, transport and chemistry are evaluated in the recent past and found to be largely consistent with GEOS-Chem driven by the Modern-Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) product and with observational constraints.

Global Change and Air Pollution (GCAP 2.0) model↗

Constraining the Surface Exposure Age of Asteroid Bennu Using Cosmogenic Radionuclides in an OSIRIS-REx Aggregate Sample and Individual Particles

Observations by NASA’s OSIRIS-REx spacecraft of asteroid Bennu revealed evidence that this small rubble-pile asteroid experiences several active surface processes that likely control its recent surface exposure history. In October 2020, the spacecraft collected a surface sample from a relatively young ~20 m diameter crater (Hokioi) on asteroid Bennu, and the sample was successfully delivered to Earth on September 24, 2023. Based on the population of craters >50 m diameter, Bennu’s surface is 0.1–1 Ga old, but the old surface is affected by recent processes including smaller meteoroid impacts, mass movement, and particle ejections. The sampling location within Hokioi crater was selected based on its relatively flat surface devoid of large boulders, but the crater floor is also believed to be one of the youngest surfaces on asteroid Bennu, with an age of <100 kyr. As the crater is ~2 m deep, the samples that were collected by OSIRIS-REx may have been relatively shielded from cosmic rays during most of its recent history. This scenario is different from the samples that were collected by Hayabusa2 from asteroid Ryugu, where cosmogenic noble gas and radionuclides indicate cosmic-ray exposure (CRE) ages of ~5 Myr near the surface. Our goal is to understand the recent exposure history of surface samples of asteroid Bennu utilizing radionuclides ( 10 Be, 26 Al, 36 Cl, 41 Ca) produced by both galactic (GCR) and solar (SCR) cosmic rays. With half- lives ranging from 0.1 to 1.36 million years (Myr), the concentrations of these cosmogenic nuclides provide information on the duration and exposure conditions (irradiation depth) of these samples on a timescale of a few Myr. This work will test one of the OSIRIS-REx mission’s driving hypotheses about asteroid Bennu’s recent evolution: that Hokioi crater is part of a population of small (25 m) spectrally red craters on Bennu that are less than 0.1 Myr old.

K. C. Welten↗

Major Achievements of the Springfields Decommissioning Program - 16512

Since the 1940's, Springfields has manufactured fuel products for the UK's nuclear power stations and for international customers. The early operations were in support of the atomic weapons program, closely followed by fuel manufacture for electricity generation via the Magnox power stations commencing in the late 1950's. In 2005, responsibility for the assets and liabilities of Springfields was transferred to the Nuclear Decommissioning Authority (NDA). A new company, Springfields Fuels Limited, was created to run the site, which was managed and operated by Westinghouse Electric UK Ltd on the NDA's behalf. On April 1, 2010, Westinghouse entered into an agreement with the NDA for a long-term lease of the Springfields site, which transferred responsibility for the commercial fuel manufacturing business and Springfields Fuels Limited to Westinghouse. Today, the main Springfields activities include: - Oxide fuels for Advanced Gas-cooled and Light Water Reactors, as well as intermediate fuel products, such as powders, granules and pellets, - Manufacture of Uranium Hexafluoride (now in Care and Maintenance), - Processing and recovery of Uranium residues, - Decommissioning and demolition of redundant plants and buildings. Some 120 plant buildings and support facilities have been successfully decommissioned and demolished in the period 1996 to date. These range from 1940's buildings, subsequently converted for nuclear fuel manufacture, together with some of the formerly sealed chemical agent manufacture and storage facilities. Decommissioning of the now redundant Magnox manufacturing facilities is ongoing at Springfields without compromising the other site operations. Westinghouse is managing all activities related to the whole lifecycle, planning, design, safety case, radiation protection, Post Operational Clean Out (POCO), service diversions, characterization, decommissioning all phases through to ground remediation, waste disposal and agreed end states. Decommissioning of process plants starts with the removal of the majority of radiological activity or hazard contained within the plant. This is known as Post Operational Clean Out. Once this is complete, the plant may be dismantled. Work is scoped and defined within packages (at plant or cell level) to aid control and commercial monitoring as the decommissioning is progressed. This package approach also enables clean or lightly contaminated items to be removed separately to aid potential re-cycling and minimize decontamination and waste disposal costs. Westinghouse is further optimising work package delivery by planning parallel POCO and Decommissioning work phases within plant at a cell level to systematically remove redundant plant and reduce hazard earlier, whilst optimising use of both internal and external resources to reduce total project cost. Waste and Residues from all phases are disposed of via authorized disposal routes and in accordance with our environmental authorizations. On completion of decommissioning and removal of plant and equipment the building is re-assessed radiologically, categorized and appropriate remediation work progressed to render it safe for conventional demolition. The major elements of the success achieved to date can be attributed to the following elements: - Overall programme management with extensive experience of planning, cost, and risk management. Integration of the programme within a major commercial site without compromising safety or operations. - Complete site EHS management working within a complex regulatory framework including the Nuclear Site Licenses, Environmental Authorisations and Security requirements. - Avoiding safety complacency by use of rigorous and systematic process to emphasise safety over competing goals. Including structured use of Human Performance and Corrective Action and Learning processes. - Unique safety experiences attained through complex hazard reduction across a broad range of uranium manufacturing and chemical hazard/agent facilities. - Project leadership and excellence utilizing a core site team to deploy repeatable processes and safe practices to deliver complex scope within budget and schedule. - Optimised use of internal and external resources, with extensive use of Operating Experience to drive continuous improvement and problem resolution. - Management of Contractors from initial selection, pre-qualification, tender assessment and Performance using varied contract forms across delivery phases. - Use of Westinghouse expertise for safety case, waste management, uranium recovery, health physics and design. - Implementation of a work package to ensure gated discreet manageable packages. Underpinned by package specific method statements, with appropriate hold points to maintain management and control of the works. - Continuous local safety focus via safety planning, induction, plant specific training, proactive risk assessment, and a defined approach to decoupling operating plant safety cases enabling focussed and usable documentation. This paper will provide an overview of the latest decommissioning activities achieved on the Springfields site and will focus on best practices that allowed Westinghouse to maintain the program on time and on budget. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

High Performance Heat Pipe Power Transient Testing at SPHERE Facility

Microreactors are being researched, designed, and built at Idaho National Laboratory (INL). Microreactors are small reactors defined at less than 20MW of power. These reactor concepts are also being looked at throughout industry for various applications. An important aspect of these reactor designs is economic feasibility i.e. lower overnight capital cost. The driving factors for implementing microreactors are quick setup and takedown, minimal operators, and the ability to manufacture them readily and to fit in mid-sized containers for transport. A specific area of research to aid in successful integration of these factors within the designs is passive heat removal of the core’s thermal power. Interest in heat pipes to achieve this passive heat removal has been shown across multiple industry partners. Because of this interest, INL has developed a test facility to facilitate experimental tests for sodium filled heat pipes. INL has developed the Single Primary Heat Extraction and Removal Emulator (SPHERE) facility to run experiments on high performance, sodium filled heat pipes. As mentioned above, heat pipes are passive heat transfer devices. Radially, heat pipes are broken up into an outer wall, a small annular gap, a wick structure, and a centerline gap. They function by utilizing latent heat transfer. Heat pipes are traditionally separated into three regions, an evaporator (heat input), an adiabatic region, and finally a condenser region (heat removal). As heat is being applied to the evaporator, the working fluid undergoes a phase change to a vapor. This phase change causes a differential pressure across the axial length of the pipe driving flow down the center gap of the heat pipe. The vapor flows down past the adiabatic region to the condenser where the heat is removed. This heat removal forces the working fluid to phase change back to a liquid. The wick structure is then utilized to drive the flow back towards the evaporator by capillary forces. This backflow is aided by the annular gap. Because this heat transfer mechanism functions with latent heat transfer, the heat pipe is close to isothermal down the axial length. Heat pipes can operate under a wide range of working fluids. Considerations for these working fluids are primarily driven by operating temperatures amongst other important factors based around overall performance. Sodium filled heat pipes operate from 450°C up to 900°C. This temperature range works well for the current microreactor designs. In conjunction with this experimental capability, INL has developed a modeling software to simulate heat pipe physics within reactor cores. This modeling software is called Sockeye and functions under the established INL Multiphysics Object Oriented Simulation Environment (MOOSE). SPHERE also supports Sockeye development by providing the modeling team with experimental data on an array of setups and operating parameters to support validation efforts. A power transient experiment was performed utilizing the SPHERE facility to continue to aid with Sockeye development. The testing followed a proposed test plan to ramp up and down the temperature of the heat pipe. Sockeye models steady state heat pipe operation with high accuracy, the data provided by the power transient testing aims to assist with the validation efforts and further enhance transient modeling capability of the tool [2].

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

Development of an Offshore Direct-Drive Wind Turbine Model by Using a Flexible Multibody Simulation (Poster)

Modern wind turbines are complex, highly-coupled systems. The dynamic interaction between various components is especially pronounced for multi-megawatt wind turbines. As a result, design process is generally split in several phases. First step consists of creating a global aero-elastic model that includes essential dynamics of structural components using the minimum-possible number of degrees of freedom (d.o.f.). The most important simplifications concern drivetrain and rotor-nacelle assembly (RNA). This approach has been shown valid for several wind turbine configurations. Nevertheless, with increasing size of wind turbines, any simplified design approach must be validated. The present work deals with the comparison and validation of the two modeling approaches for directdrive offshore wind turbines. ARNA/drivetrain model idealized as collection of lumped masses and springs is compared to a detailed Finite Element Method (FEM) based model. The comparison between models focuses on dynamic loads concerning drivetrain system. The comparison is performed in several operational conditions in order to explore the range of validity of the simplified model. Finally, the paper proposes a numerical-based workflow to assess the validity of simplified models of RNA/drivetrain in an aero-elastic global WT model.

17 WIND ENERGY↗

Earthquake response of head-mounted equipment in advanced nuclear reactors

The seismic response of safety-related equipment mounted on the head of an advanced reactor, including pumps, control rod drive mechanisms, and reactor monitoring devices, will affect the design and layout of many advanced reactors. High earthquake-induced accelerations in such equipment may challenge their seismic qualification and trigger the need for additional support framing on the reactor head. Base isolation is a design solution that can drastically reduce seismic demands on equipment. This article describes a set of earthquake-simulator experiments conducted on a scale-model of a base-isolated reactor vessel including four representations of head-mounted equipment, with frequencies spanning from 4.5 to 27 Hz. Dynamic responses of the head-mounted equipment, including displacements, accelerations, and strains, were measured in the experiments for three support conditions: conventional, and seismically isolated using single concave Friction Pendulum (SFP) bearings and triple Friction Pendulum (TFP) bearings. Seismic isolation was effective at reducing equipment responses (accelerations, displacements, and strains) with respect to those in the conventionally supported vessel across a range of seismic inputs. Companion numerical studies highlight the accuracy to be expected in the calculation of different response quantities for lightly damped equipment. The importance of characterizing damping in head-mounted, safety-related equipment through physical experiments to support design and risk assessment is made clear through the numerical simulations.

Engineering↗

Driving towards cost-competitive biofuels through catalytic fast pyrolysis by rethinking catalyst selection and reactor configuration

Catalytic fast pyrolysis (CFP) has emerged as an attractive process for the conversion of lignocellulosic biomass into renewable fuels and products. Considerable research and development has focused on using circulating-bed reactors with zeolite catalysts (e.g., HZSM-5) for CFP because of their propensity to form gasoline-range aromatic hydrocarbons. However, the high selectivity for aromatics comes at the expense of low carbon yield, a key economic driver for this process. In this contribution, we evaluate non-zeolite catalysts in a fixed-bed reactor configuration for an integrated CFP process to produce fuel blendstocks from lignocellulosic biomass. These experimental efforts are coupled with technoeconomic analysis (TEA) to benchmark the process and guide research and development activities to minimize costs. The results indicate that CFP bio-oil can be produced from pine with improved yield by using a bifunctional metal-acid 2 wt% Pt/TiO 2 catalyst in a fixed-bed reactor operated with co-fed H 2 at near atmospheric pressure, as compared to H-ZSM5 in a circulating-bed reactor. The Pt/TiO 2 catalyst exhibited good stability over 13 reaction-regeneration cycles with no evidence of irreversible deactivation. The CFP bio-oil was continuously hydrotreated for 140 h time-on-stream using a single-stage system with 84 wt% of the hydrotreated product having a boiling point in the gasoline and distillate range. This integrated biomass-to-blendstock process was determined to exhibit an energy efficiency of 50% and a carbon efficiency of 38%, based on the experimental results and process modelling. TEA of the integrated process revealed a modelled minimum fuel selling price (MFSP) of $4.34 per gasoline gallon equivalent (GGE), which represents a cost reduction of $0.85 GGE -1 compared to values reported for CFP with a zeolite catalyst. TEA also indicated that catalyst cost was a significant factor influencing the MFSP, which informed additional CFP experiments in which lower-cost Mo2C and high-dispersion 0.5 wt% Pt/TiO 2 catalysts were synthesized and evaluated. These materials demonstrated CFP carbon yield and oil oxygen content similar to those of the 2 wt% Pt/TiO 2 catalyst, offering proof-of-concept that the lower-cost catalysts can be effective for CFP and providing a route to reduce the modelled MFSP to $3.86–3.91 GGE -1 . This report links foundational science and applied engineering to demonstrate the potential of fixed-bed CFP and highlights the impact of coupled TEA to guide research activities towards cost reductions.

09 BIOMASS FUELS↗

Vehicle Systems Integration Laboratory Accelerates Powertrain Development

ORNL's Vehicle Systems Integration (VSI) Laboratory accelerates the pace of powertrain development by performing prototype research and characterization of advanced systems and hardware components. The VSI Lab is capable of accommodating a range of platforms from advanced light-duty vehicles to hybridized Class 8 powertrains with the goals of improving overall system efficiency and reducing emissions.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

Reducing Coercive-Field Scaling in Ferroelectric Thin Films via Orientation Control

The desire for low-power/voltage operation of devices is driving renewed interest in understanding scaling effects in ferroelectric thin films. As the dimensions of ferroelectrics are reduced, the properties can vary dramatically, including the robust scaling relationship between coercive field ( E c ) and thickness ( d ), also referred to as the Janovec-Kay-Dunn (JKD) law, wherein E c ∝ d -2/3 . Here, we report that whereas (001)-oriented heterostructures follow JKD scaling across the thicknesses range of 20-330 nm, (111)-oriented heterostructures of the canonical tetragonal ferroelectric PbZr 0.2 Ti 0.8 O 3 exhibit a deviation from JKD scaling wherein a smaller scaling exponent for the evolution of E c is observed in films of thickness ≤ 165 nm. X-ray diffraction reveals that whereas (001)-oriented heterostructures remain tetragonal for all thicknesses, (111)-oriented heterostructures exhibit a transition from tetragonal-to-monoclinic symmetry in films of thickness ≤ 165 nm as a result of the compressive strain. First-principles calculations suggest that this symmetry change contributes to the deviation from the expected scaling, as the monoclinic phase has a lower energy barrier for switching. This structural evolution also gives rise to changes in the c/a lattice parameter ratio, wherein this ratio increases and decreases in (001)- and (111)-oriented heterostructures, respectively, as the films are made thinner. In (111)-oriented heterostructures, this reduced tetragonality drives a reduction of the remanent polarization and, therefore, a reduction of the domain-wall energy and overall energy barrier to switching, which further exacerbates the deviation from the expected scaling. Altogether, this work demonstrates a route toward reducing coercive fields in ferroelectric thin films and provides a possible mechanism to understand the deviation from JKD scaling.

36 MATERIALS SCIENCE↗

Characterization of the onset of ion cyclotron parametric decay instability of lower hybrid waves in a diverted tokamak

The goal of the lower hybrid current drive (LHCD) program on Alcator C-Mod is to develop and optimize reactor-relevant steady-state plasmas by controlling current density profile. However, current drive efficiency precipitously decreases as the line averaged density (n{sup ¯}{sub e}) increases above ∼1 × 10{sup 20} m{sup −3}. Previous simulations show that the observed loss of current drive efficiency in high density plasmas stems from the interactions of LH waves with edge/scrape-off layer plasmas [Wallace et al., Phys. Plasmas 19, 062505 (2012)]. A recent observation [Baek et al., Plasma Phys. Controlled Fusion 55, 052001 (2013)] shows that the configuration dependent ion cyclotron parametric decay instability (PDI) is excited in the density range where the discrepancy between the experiments and simulations remains. Comparing the observed spectra with the homogeneous growth rate spectra indicates that the observed ion cyclotron PDI can be excited not only at the low-field-side but also at the high-field-side (HFS) edge of the tokamak. The model analysis shows that a relevant PDI process to Alcator C-Mod LHCD experiments is decay into ion cyclotron quasi-mode driven by parallel coupling. The underlying cause of the observed onset of ion cyclotron PDI is likely due to the weaker radial penetration of the LH wave in high density plasmas, which can lead to enhanced convective growth. Configuration-dependent PDIs are found to be correlated with different edge density profiles in different magnetic configurations. While the HFS edge of the tokamak can be potentially susceptible to PDI, as evidenced by experimental observations and ray-tracing analyses, enhancing single-pass absorption is expected to help recover the LHCD efficiency at reactor-relevant densities because it could suppress several parasitic loss mechanisms that are exacerbated in multi-pass regimes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Differences in cluster and internal wake effects from mesoscale and large-eddy simulations off the US East Coast

Mesoscale simulations are increasingly used to estimate wake effects within and between large wind farms, despite limited validation for large-scale wake effects. This study evaluates the capabilities and limitations of mesoscale simulations in capturing wake-induced impacts on wind turbine power production through a direct comparison with large-domain large-eddy simulations (LESs) for three planned offshore wind farms under realistic atmospheric conditions and a range of atmospheric stabilities. We assess mesoscale performance in replicating wake characteristics behind single and multiple turbine clusters and quantify the resulting variability in mean turbine power. Results show that mesoscale Weather Research and Forecasting simulations with the Fitch wind farm parameterization capture key features of the velocity deficit downstream of both single and multiple wind farms, with mean root-mean-square errors near 5 % and good agreement with stability-driven wake behavior. However, in these simulations, the mesoscale Fitch parameterization underestimates power losses from internal wake effects, particularly when turbines align with the prevailing wind direction or under stable stratification. In these conditions, individual wakes persist and dominate downstream power deficits. The coarse resolution of the mesoscale simulations limits their ability to resolve individual wind turbine wakes that drive power fluctuations within wind farms. Nonetheless, mesoscale simulations can yield accurate estimates of combined wake losses from internal and cluster effects across some wind direction sectors, where errors in wake representation may cancel each other out. These findings underscore the strengths of mesoscale simulations for capturing broader wake patterns while highlighting their limitations for modeling turbine-level power losses. Future work should explore hybrid modeling approaches to capture both long-range cluster wake propagation and localized internal wake dynamics.

17 WIND ENERGY↗

Observation of multiple metastable states induced by electric pulses in the hysteresis temperature range of 1 T - TaS 2

The electric pulses induced responses of 1T - TaS 2 in the commensurate charge-density-wave phase in the hysteresis temperature region (160 ~ 210 K) have been investigated. We observed an abrupt jump of the resistance excited by pulse, followed by a slow relaxation process in a time scale of ~ 100 s. At a fixed temperature, the various electric pulses can drive the system to multi metastable states. Here, we propose that the spontaneous evolution or slow relaxation of the system by pulse excitations corresponds to the rearrangements of the textures of CCDW domains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Overview of interpretive modelling of fusion performance in JET DTE2 discharges with TRANSP

In the paper we present an overview of interpretive modelling of a database of JET-ILW 2021 D-T discharges using the TRANSP code. The main aim is to assess our capability of computationally reproducing the fusion performance of various D-T plasma scenarios using different external heating and D-T mixtures, and to understand the performance driving mechanisms. We find that interpretive simulations confirm a general power-law relationship between increasing external heating power and fusion output, which is supported by absolutely calibrated neutron yield measurements. A comparison of measured and computed D-T neutron rates shows that the calculations' discrepancy depends on the absolute neutron yield. The calculations are found to agree well with measurements for higher performing discharges with external heating power above ~20 MW, while low-neutron shots display an average discrepancy of around +40% compared to measured neutron yields. A similar trend is found for the ratio between thermal and beam-target fusion, where larger discrepancies are seen in shots with dominant beam-driven performance. We compare the observations to studies of JET-ILW D discharges, to find that on average the fusion performance is well modelled over a range of heating power, although an increased unsystematic deviation for lower-performing shots is observed. The ratio between thermal and beam-induced D-T fusion is found to be increasing weakly with growing external heating power, with a maximum value of ≳1 achieved in a baseline scenario experiment. An evaluation of the fusion power computational uncertainty shows a strong dependence on the plasma scenario type and fusion drive characteristics, varying between ±25% and 35%. D-T fusion alpha simulations show that the ratio between volume-integrated electron and ion heating from alphas is ≲10 for the majority of analysed discharges. Alphas are computed to contribute between ~15% and 40% to the total electron heating in the core of highest performing D-T discharges. An alternative workflow to TRANSP was employed to model JET D-T plasmas with the highest fusion yield and dominant non-thermal fusion component because of the use of fundamental radio-frequency heating of a large minority in the scenario, which is calculated to have provided ~10% to the total fusion power.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Controlled nanopatterning of a polymerized ionic liquid in a strong electric field

Nanolithography has become a driving force in advancements of the modern day's electronics, allowing for miniaturization of devices and a steady increase of the calculation, power, and storage densities. Among various nanofabrication approaches, scanning probe techniques, including atomic force microscopy (AFM), are versatile tools for creating nanoscale patterns utilizing a range of physical stimuli such as force, heat, or electric field confined to the nanoscale. In this study, the potential of using the electric field localized at the apex of an AFM tip to induce and control changes in the mechanical properties of an ion containing polymer—a polymerized ionic liquid (PolyIL)—on a very localized scale is explored. In particular, it is demonstrated that by means of AFM, one can form topographical features on the surface of PolyIL-based thin films with a significantly lower electric potential and power consumption as compared to nonconductive polymer materials. Lastly,, by tuning the applied voltage and ambient air humidity, control over dimensions of the formed structures is reproducibly achieved.

36 MATERIALS SCIENCE↗

Heterogeneous Two-Phase Pillars in Epitaxial NiFe 2 O 4 -LaFeO 3 Nanocomposites

Self-assembled epitaxial oxide nanocomposites have been explored for a wide range of applications, including multiferroic and magnetoelectric properties, plasmonics, and catalysis. These so-called “vertically aligned nanocomposites” form spontaneously during the deposition process when segregation into two phases is energetically favorable as compared to a solid solution. However, there has been surprisingly little work understanding the driving forces that govern the synthesis of these materials, which can include point defect energetics, surface diffusion, and interfacial energies. To explore these factors, La-Ni-Fe-O films have been synthesized by molecular beam epitaxy and it is shown that these phase segregate into spinel-perovskite nanocomposites. Using complementary scanning transmission electron microscopy and atom-probe tomography, the elemental composition of each phase is examined and found that Ni ions are exclusively found in the spinel phase. From correlative analysis, a model for the relative favorability of the Ni2+ and Ni3+ valences under the growth conditions is developed. It is shown that multidimensional characterization techniques provide previously unobserved insight into the growth process and complex driving forces for phase segregation.

36 MATERIALS SCIENCE↗

Nanoscale Magnetic Domains in Polycrystalline Mn 3 Sn Films Imaged by a Scanning Single-Spin Magnetometer

Noncollinear antiferromagnets with novel magnetic orders, vanishingly small net magnetization, and exotic spin related properties hold enormous promise for developing next-generation, transformative spintronic applications. A major ongoing research focus of this community is to explore, control, and harness unconventional magnetic phases of this emergent material system to deliver state-of-the-art functionalities for modern microelectronics. Here we report direct imaging of magnetic domains of polycrystalline Mn 3 Sn films, a prototypical noncollinear antiferromagnet, using nitrogen-vacancy-based single-spin scanning microscopy. Nanoscale evolution of local stray field patterns of Mn 3 Sn samples are systematically investigated in response to external driving forces, revealing the characteristic “heterogeneous” magnetic switching behaviors in polycrystalline textured Mn 3 Sn films. Furthermore, our results contribute to a comprehensive understanding of inhomogeneous magnetic orders of noncollinear antiferromagnets, highlighting the potential of nitrogen-vacancy centers to study microscopic spin properties of a broad range of emergent condensed matter systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Ion and Electron Acoustic Bursts during Anti-Parallel Reconnection Driven by Lasers

Magnetic reconnection converts magnetic energy into thermal and kinetic energy in plasma. Among the numerous candidate mechanisms, ion acoustic instabilities driven by the relative drift between ions and electrons (or equivalently, electric current) have been suggested to play a critical role in dissipating magnetic energy in collisionless plasmas. However, their existence and effectiveness during reconnection have not been well understood due to ion Landau damping and difficulties in resolving the Debye length scale in the laboratory. We report a sudden onset of ion acoustic bursts measured by collective Thomson scattering in the exhaust of anti-parallel magnetically driven reconnection using high-power lasers. The ion acoustic bursts are followed by electron acoustic bursts with electron heating and bulk acceleration. We reproduce these observations with one- and two-dimensional particle-in-cell simulations in which an electron outflow jet drives ion acoustic instabilities, forming double layers. These layers induce electron two-stream instabilities that generate electron acoustic bursts and energize electrons. Our results demonstrate the importance of ion and electron acoustic dynamics during reconnection when ion Landau damping is ineffective, a condition applicable to a range of astrophysical plasmas including near-Earth space, stellar flares and black hole accretion engines.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗