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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Switchable rocker arm

A rocker arm includes an outer arm and an inner arm which selectively pivots relative to the outer arm. The rocker arm also includes a lock pin which is displaced along a lock pin axis between a coupled position and a decoupled position. The rocker arm also includes a linkage and a linkage guide which guides the linkage along a linkage axis. One surface of the linkage engages an actuator while another surface of the linkage engages the lock pin such that the linkage translates motion from the actuator to motion of the lock pin.

42 ENGINEERING↗
DOE OSTI2023

Adaptive pinscreen transport case for classified articles

An article transport case comprising an outer shell including opposing sections, first and second pinscreen assemblies, and first and second securement mechanisms. The pinscreen assemblies each include a frame, a securement plate, and a number of pins. The first and second securement mechanisms are configured to be in a secured configuration to retain the first and second sections in a closed configuration and keep the securement plates in a secured position thereby restraining the pins against the article in an article conforming arrangement. The securement plates are in an unsecured position so that the pins are free to translate longitudinally when the securement mechanisms are in an unsecured configuration such that the pins are not restrained in the article conforming arrangement when the shell is open.

Busenitz, Clark Andrew↗
DOE OSTI2024

Electrical connectors including glass seals and methods of fabrication

An electrical connector comprises an outer shell, at least one pin, and an insulating seal. The outer shell includes at least one side wall defining a cavity and having an inner surface. The outer shell is formed from electrically conductive material. The pin is positioned within the cavity and is also formed from electrically conductive material. The insulating seal is configured to provide electrical isolation of the pin and fills the cavity between the inner surface of the side wall and the pin. The insulating seal is formed from glass doped with a transition metal oxide.

Eichorst, Dennis J.↗
DOE OSTI2024

ANS Winter 2024 Summary: Optimizing the ATF-2Ramp Power Profile

When the Halden Boiling Water Reactor closed down in 2018, a need to restore the capability for in-reactor power ramp testing arose. Such testing is valuable for studying pellet-clad interaction phenomena in nuclear fuels. The data from these studies is of great interest to a number of research programs, including the accident-tolerant fuel (ATF) program at Idaho National Laboratory (INL). In 2022, Woolstenhulme et al. proposed several power ramp testing ideas using facilities at INL, including irradiation in the Transient Reactor Test Facility (better known as TREAT) and the Advanced Test Reactor (ATR) [1]. Worrall et al. [2] and Labossiere-Hickman et al. [3] subsequently performed feasibility studies for the ATR testing options in 2023. This summary further investigates the three-pin trefoil design (Fig. 1) for the proposed ATF-2Ramp Experiment discussed in Labossiere-Hickman et al. [3]. ATF-2Ramp is designed to operate in the center flux trap (CFT) of the ATR during a powered axial locator mechanism (PALM) cycle: a short, variable-powered cycle with an asymmetric power distribution. Previously, it was shown that tailoring the thickness of the hafnium (Hf) neutron shields (“mini-shrouds”) surrounding each pin offered a degree of control sufficient to achieve the programmatic linear heat generation rate (LHGR) targets for ATF-2Ramp during the high-power period of a PALM cycle. New work involves shortening the experiment test train for consistency with the fuel pins in ATF-2D [4] and then shaping the axial power profile of the three test pins.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Stationary Oxygen Vacancy Construction toward a Superior-Performance Ultrahigh Nickel Single-Crystal Cathode

Oxygen vacancies exert a complex and profound influence on the layered cathodes, especially those with ultrahigh nickel content. They can facilitate lithium-ion transport and enhance electronic conductivity, while aggressive oxygen vacancy formation causes structural degradation and electrolyte decomposition. Herein, taking ultrahigh nickel single-crystal LiNi 0.92 Co 0.06 Mn 0.02 O 2 (SC-Ni92) as a model material, we propose a pinning strategy to harness the benefits of oxygen vacancies while mitigating their detrimental effects. Through a carefully controlled thermal process, both oxygen vacancies and pinning atoms are successfully introduced into the surface region. The resulting anchored oxygen vacancies, capitalizing on their inherent advantages, improve conductivity and lithium-ion diffusion. Simultaneously, the neighboring pinning atoms effectively increase the migration barrier and suppress the adverse effects of these vacancies, including electrolyte decomposition and structural degradation during long-term electrochemical cycling. Consequently, oxygen vacancy-anchored single-crystal LiNi 0.92 Co 0.06 Mn 0.02 O 2 (SC-Ni92-OV) demonstrates significantly improved high-voltage electrochemical performance, with 86.16% capacity retention after 200 cycles at 4.6 V and 1 C in a half-cell and 90.71% after 300 cycles at 4.5 V and 1 C in a full cell. Furthermore, this study not only provides valuable insights into the chemistry of oxygen vacancy but also introduces a viable strategy for leveraging oxygen vacancies to achieve stable high-voltage performance in ultrahigh nickel single-crystal cathodes.

defects in solids↗
DOE OSTI2021

Intrinsic doping limitations in inorganic lead halide perovskites

Inorganic halide perovskites (HP's) of the CsPbX 3 (X = I, Br, Cl) type have reached prominence in photovoltaic solar cell efficiencies, leading to the expectation that they are a new class of semiconductors relative to the traditional ones. Peculiarly, they have shown an asymmetry in their ability to be doped by holes vs. electrons. Indeed, both structural defect-induced doping as well as extrinsic impurity-induced doping strangely often result in HP's in a unipolar doping (dominantly p-type) with low free carriers’ concentration. This raises the question whether such doping limitations presents just a temporary setback due to insufficient optimization of the doping process, or perhaps this represents an intrinsic, physically-mandated bottleneck. Here we study three fundamental Design Principles (DP's) for ideal doping, applying them via density functional doping theory to these HP's, thus identifying the violated DP that explains the doping limitations and asymmetry in these HP's. Here, the target DP are: (i) requires that the thermodynamic transition level between different charge states induced by the dopants must ideally be energetically shallow both for donors (n-type) or acceptors (p-type); DP-(ii) requires that the ‘Fermi level pinning energies’ for electrons E (n) pin and holes E (p) pin (being the limiting value of the Fermi level before a structural defect that compensate the doping forms spontaneously) should ideally be located inside the conduction band for n-type doping and inside the valence band for p-type doping. DP-(iii) requires that the doping-induced shift in equilibrium Fermi energy ΔE (n) F towards the conduction band for n-type doping (shift of ΔE (p) F towards the valence band, for p-type doping) to be sufficiently large. We find that, even though in HP's based on Br and Cl there are numerous shallow level dopants that satisfy DP-(i), in contrast DP-(ii) is satisfied only for holes and DP-(iii) fails for both holes and electrons, being the ultimate bottleneck for the n-type doping in Iodide HP's. This suggests an intrinsic mechanism for doping limitations in this class of semiconductors in terms of recognized physical mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Significant reduction in the low-field magnetization of Nb 3 Sn superconducting strands using the internal oxidation APC approach

Nb 3 Sn superconductors are promising for building accelerator magnets for future energy-frontier circular colliders. A critical factor for this application is the low-field persistent-current magnetization because it leads to several critical issues: e.g. low-field instability (including flux jumps), hysteresis loss, and field errors in magnet bores. Suppression of low-field magnetization requires reduction of low-field critical current density (J c ) or effective subelement size (d eff ). However, reduction of deff of state-of-the-art Nb 3 Sn conductors—the restacked-rod-process (RRP ® ) type—below 40–50 μm without a pronounced decrease in high-field J c is difficult. On the other hand, the internal oxidation method which forms artificial pinning centers (APC) in Nb 3 Sn offers an alternative approach to reducing the low-field magnetization. Compared with a conventional Nb 3 Sn conductor whose flux pinning force versus field (F p –B) curve peaks at ~20% of its irreversibility field (B irr ), the F p –B curve peaks of APC conductors shift to higher fields due to the point pinning effect, leading to flattening of the J c –B curves. The goal of this paper is to quantitatively study how much the APC approach can reduce the low-field magnetization. Here we measured the J c –B curves of an RRP ® conductor and two APC conductors (reacted at 700 °C) from zero field to B irr using a high-field vibrating sample magnetometer. Here the results showed that the APC conductors have higher non-Cu J c at high fields (e.g. 32%–41% higher at 16 T) and simultaneously lower non-Cu Jc at low fields (e.g. 28%–34% lower at 1 T) compared with the RRP ® . This effect is due to a competition between their Nb3Sn layer fraction ratios and layer F p ratios. Suppose they reach the same 16 T non-Cu J c , then the 1 T non-Cu J c and magnetization of the APC conductors are only half or even less compared with the RRP ® conductor.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Vortex phase diagram of the kagome superconductor CsV 3 ⁢Sb 5

The screening response of the kagome superconductor CsV 3 ⁢Sb 5 was obtained from high-resolution ac mutual inductance measurements. At zero applied magnetic field and low temperatures, we observe no evidence for gapless quasiparticles, while near T c we find evidence for enhanced fluctuations. A rich vortex state appears above H c⁢1 ≈30 Oe, exhibiting successive emergence of vortex phases. For a fixed magnetic field, lowering the temperature below T c⁡ (H) leads to a wide range of vortex liquid state in a landscape of weak pinning potential, which gives rise to an irreversibility line. Further lowering the temperature, we identify the vortex melting line followed by the peak effect manifested in enhanced vortex pinning strength and critical current. Finally, we suggest that such an unusual behavior, where the peak effect region is fully contained within the vortex lattice state below the irreversibility line, is a consequence of the strong anisotropy and weak bulk pinning in CsV 3 ⁢Sb 5 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Investigation of constituent redistribution in U-Pu-Zr fuels and its dependence on varying Zr content

This contribution investigates fuel constituent segregation and fuel-cladding chemical interactions (FCCI) in three U-Pu-Zr fuel pins irradiated to ~11% burnup in Experimental Breeder Reactor-II as part of the X441 DP-1 experiment. In examined pins, Zr content ranged from 6 to 10 and 14 wt.%, while Pu concentration was constant at 19 wt.% Pu. The primary goal of the investigation was to determine the role Zr content plays in fuel performance and this manuscript provides assessment of both constituent redistribution and FCCI as a function of axial position. FCCI was observed in all pins, though no cladding failure was noted. Optical and scanning electron microscopy (SEM) results show that variation in Zr content alters the number and relative size of constituent redistribution zones in the fuel. For example, larger Zr-rich central regions and smaller U-rich intermediate regions were observed in 14 wt.% Zr fuels. More importantly, all examined fuels have four or more discrete constituent redistribution regions, where each region has dissimilar morphological features. The existence of four to six distinctive regions deviates from traditionally accepted three region redistribution model, highlights complexity of constituent redistribution in this metal fuel, and identifies the need to conduct additional studies using state-of-the-art instrumentation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Experimental validation of simplified radionuclide transport bubble scrubbing code in sodium coolant pool

Solid radionuclides released following fuel pin failure may become entrained in gaseous fission products and be rapidly transported through the coolant pool to the cover gas region. Sensitivity studies on radionuclide transport have identified this potential pathway as one of both high concern and high uncertainty. The simplified radionuclide transport scrubbing code utilizes classical aerosol scrubbing mechanisms to model this phenomenon and predict aerosol masses reaching the cover gas region. This paper serves to validate this code in a sodium environment while conducting a parametric study to analyze the effects of aerosol size, bubble size, pool temperature, pool depth, aerosol density, and aerosol concentration. Through a series of experimental tests, it was determined that aerosol sizes ranging from 0.001 to 1.0 µm are of primary concern as aerosols in this range have a ratio of aerosol mass entering the sodium pool from the fuel pin to aerosol mass exiting the sodium pool to the cover gas region of less than 10. Further, the experimental results were found to match the trends found in the scrubbing model closely, but significantly more scrubbing was seen experimentally. Decreasing bubble size and increasing pool depth and aerosol density were all found to increase scrubbing both experimentally and theoretically. Pool temperature was found to have a negligible effect on scrubbing amounts; however, this was largely due to a subsequent increase in bubble size corresponding to increasing temperatures which offset the increase in scrubbing due to increased temperature. Varying aerosol concentration was found to have no effect on scrubbing ratios. A final series of tests was conducted for a more prototypic fuel pin failure with a heterogenous bubble swarm. From these tests, it was found that the experimental scrubbing quantities were larger than for the single bubble case. Overall, it was found that the simplified bubble transport scrubbing code accurately models the trends of the bubble scrubbing but provides a conservative estimate of scrubbing quantities. Model limitations fail to model the complex phenomena present for fission product scrubbing via bubble transport, but match trends seen experimentally.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Preliminary conceptual design of fast neutron spectrum nuclear thermal rocket cores using monolithic uranium nitride fuel

This paper presents a few nuclear thermal rocket (NTR) reactor core preliminary conceptual designs based on the use of monolithic uranium nitride (UN) fuel plates or pins clad with tungsten (W), alloyed or unalloyed as needed. High-assay low-enriched uranium (HALEU) as well as high-enriched uranium (HEU) are considered. Nominal core thermal powers are between 300 and 1100 MW corresponding to thrusts between 66 kN and 240 kN. The estimated thrust-to-reactor-weight ratios (T/WRx) achievable with the HEU plate and pin configurations are between 3.8 and 10.9. The T/WRx achievable with the HALEU plate and pin configurations are lower, 1.9–4.0, than those achievable with HEU. It is noteworthy that even a relatively modest increase in fuel enrichment above the HALEU limit enables a significant increase in T/WRx. It must be emphasized that these results do not yet account for uncertainties and that the appropriateness of the assumed fuel thermal design limits for normal operation (i.e., peak centerline temperature of 3100 K) will need to be confirmed. Finally, just like for the other UN-based fuels currently considered for NTR applications (i.e., CERMET and CERCER), the proposed UN fuel systems need significant testing in prototypic conditions to confirm the appropriate performance for safe NTR applications. However, the monolithic fuel systems may have, overall, a higher technology readiness level (TRL), and, consequently, shorter fuel development and validation time may result.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Advanced Characterization of Fuel-cladding Chemical Interaction between U-10Zr Fuel and HT9 Cladding Tested in Fast Flux Test Facility

Fuel cladding chemical interaction (FCCI) can greatly accelerate the cladding failure. However, due to the limited space in a fuel cladding assembly, it is historically challenging to gain an mechanistical understanding of the formation mechanism of FCCI and its influence on fuel and cladding performance. With the imminent need to qualify U-10Zr based metallic fuel cladded by HT-9 for advanced reactors demonstration project, it is of vital importance to use advanced characterization method to study FCCI in a unprecedent detailed manner and gain better mechanism understanding of FCCI. Mechanistic Fuel Failure (MFF) series of prototypic fuel elements irradiated in FFTF [1, 2] provides the best samples to study FCCI since the MFF-series assemblies had an axial fuel height the same as proposed length by industry partners. Jason et al. [3] has performed preliminary post-irradiation examination on a MFF fuel pin sample, which was extracted from the HT9 cladded U-10at.%Zr MFF-3 pin MFF-3 pin (#193045) at an axial location of X/L = 0.98. This sample has a peak burnup of 5.7 at.% and peak inner cladding temperature (PICT) of around 615 °C during in-core testing. Scanning electron microscope examination has identified visible FCCI region on more than half of the HT9 circumference [3]. The most striking feature are grain boundary attacking by apparently lanthanides (Lns) rich phase. However, SEM cannot provide accurate assessment of phase and concentration of grain boundary phases and prevented a better understanding of the formation mechanism of such attach. This study, by pairing transmission electron microscope (TEM) characterization and atom probe tomography (APT) techniques with in-situ micro-tensile testing in scanning electron microscope (SEM), aims at gaining in-depth understanding on the formed FCCI region. The identified FCCI region roughly consists of multilayers as illustrated in Figure 1 (c). The main findings are: (1) layer-B shows observable lanthanides (Lns) infiltration along grain boundaries and mechanical softening due to FCCI- and irradiation-induced microstructural and microchemistry changes, particularly the recovery of martensitic lath structure and dissolution of pre-existing M23C6 together with the formation of coarsened Laves phases, (Fe, Cr)2(Mo, W); (2) layer-C is Fe depleted but Lns significantly enriched, becoming very brittle; (3) layer-D is mainly composed of UFe2 and Lns; (4) three FCCI-induced intermetallic U-Fe-Zr phases, ? (Fe0.5Zr0.32U0.18), e (Fe0.3Zr0.4U0.3), ? (Fe0.06Zr0.23U0.71), were identified near layer-E; (5) the ? (Fe0.5Zr0.32U0.18) phase was characterized to be a face centered cubic (FCC) crystal structure. These results will help to better understanding the governing mechanism of FCCI and facilitating the development of theoretical model for assessing the performance of metallic fuel and cladding integrity.

36 MATERIALS SCIENCE↗
DOE OSTI2023

MOOSE Reactor Module: An Open-Source Capability for Meshing Nuclear Reactor Geometries

The U.S. Department of Energy (DOE) Nuclear Energy Advanced Modeling and Simulation (NEAMS) program has developed numerous physics solvers utilizing the open-source Multiphysics Object-Oriented Simulation Environment (MOOSE) framework for multiphysics reactor analysis. These solvers require input finite element meshes representing the discretized spatial domain. Typically, reactor analysts turn to licensed tools for the creation of reactor geometry meshes. Recently, open-source functionality has been added to the MOOSE framework to mesh common reactor geometries and improve MOOSE-based nuclear reactor application user workflows. The new functionality is primarily contained in the new Reactor module of MOOSE and includes support for hexagonal pins, assemblies, and cores, extended Cartesian geometry support, options for modeling static and rotating control drums within a hexagonal assembly, core periphery triangulation, and automatic tagging of pin, assembly, plane, and depletion regions for easier post processing of physics results. A set of reactor geometry mesh builder objects further streamlines the construction of hexagonal and Cartesian cores and allows mapping of materials to regions during mesh generation. The meshes produced with the MOOSE Reactor module may be used directly within MOOSE-based applications or exported as Exodus II files for use in other finite element solvers. The tools have been demonstrated and verified using a variety of NEAMS physics solvers on a range of reactor applications, including a sodium-cooled fast reactor core analysis using Griffin, a fast reactor assembly thermal deformation analysis using MOOSE Tensor Mechanics, and a heat pipe–cooled microreactor coupled analysis using Griffin, Bison, and Sockeye. MOOSE’s Reactor module provides significant advantages compared to the use of external meshing tools when analyzing Cartesian and hexagonal reactor lattices using MOOSE-based applications: immediate accessibility (open-source) to the end user, low barrier to entry for new users, speed of mesh generation, volume preservation of meshed fuel pins, and simplification of analysis workflow when used in conjunction with MOOSE-based applications.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2026

PWR Core Analysis for Cycle Extension and Uprates with LEU+ Accident Tolerant Fuel and 80 GWd/Tonne Burnup Limit

The U.S. Nuclear Regulatory Commission has recently drafted a rule enabling fuel burnup increase in light water reactors up to 80 GWd/t. In conjunction with use of fuel enrichment up to 10%, and accident tolerant fuel (ATF), this is anticipated to facilitate 24-month cycles in PWRs, along with further power uprates. In this paper, PWR core analysis is performed for 20% increased PWR power output along with cycle extension up to 24 months, in combination with use of chromia-doped fuel and chromium-coated clad, considered to be the most near-term ATF concepts. In combination, these lead to challenging conditions with a core average discharge burnup of up to ~74 GWd/t, challenging even the 80 GWd/t burnup limit. Analysis is performed using the 2-step method with POLARIS (within SCALE) used for the lattice calculations and PARCS for the core calculations. Core designs are first baselined for current operating conditions (LEU, 62 GWd/t discharge burnup limit) and then derived that meet cycle constraints on power distribution and the updated lead pin discharge burnup limit while maintaining at least two batches of fuel in the core. Gadolina loadings in fuel pins of up to 8% are used, with enrichment zoning both within the core and, to a limited extent, within assemblies. Here, doped fuel with coated cladding can utilize the same core designs as the reference UOX cores, exhibiting slightly lower burnup due to higher fuel density, which also offsets the slight reactivity penalty from the doping and coating. For the analysis performed here, doped fuel enabled a core with 24-month cycle and 20% uprate to stay within the 80 GWd/t lead pin discharge burnup limit.

LEU+↗
DOE OSTI2021

Substantial reduction of the anisotropy in the critical current densities J c of Ni-doped CaKFe 4 As 4 single crystals by chemical and irradiation-induced disorder

Here, we demonstrate that the anisotropy in the critical current densities, J c , of CaK(Fe 1–x Ni x ) 4 As 4 (x = 0, 0.015, 0.025, and 0.030) single crystals reduces with increasing chemical and irradiation-induced disorder. The magnetic field dependences of J c are analyzed by performing magnetization measurements with H applied parallel and perpendicular to the crystallographic c-axis. The results show that undoped crystals display large anisotropies in Jc due to an enhancement of the vortex pinning with H applied parallel to the crystallographic ab-planes. This anisotropy reduces substantially as Ni addition increases. Moreover, we found that random disorder introduced by proton irradiation enhances mainly the vortex pinning for H parallel to the c-axis. Consequently, using adequate fluencies, the vortex pinning at low temperatures in both undoped and doped samples becomes close to isotropic. These results make the CaKFe 4 As 4 system promising for applications that require isotropic J c under magnetic fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Evidence of Kramer extrapolation inaccuracy for predicting high field Nb 3 Sn properties

Future applications requiring high magnetic fields, such as the proposed Future Circular Collider, demand a substantially higher critical current density, J c , at fields ≥16 T than is presently available in any commercial strand, so there is a strong effort to develop new routes to higher J c Nb 3 Sn. As a consequence, evaluating the irreversibility field (H irr ) of any new conductor to ensure reliable performance at these higher magnetic fields becomes essential. To predict the irreversibility field for Nb 3 Sn wires, critical current measurements, I c , are commonly performed in the 12-15 T range and the Kramer extrapolation is used to predict higher field properties. Here, the Kramer extrapolation typically models the contribution only for sparse grain boundary pinning, yet Nb 3 Sn wires rely on a high density of grain boundaries to provide the flux pinning that enables their high critical current density. However, whole-field range VSM measurements up to 30 T recently showed for Nb 3 Sn RRP® wires that the field dependence of the pinning force curve significantly deviates from the typical grain boundary shape, leading to a 1-2 T overestimation of Hirr when extrapolated from the typical mid-field data taken only up to about 15 T. In this work we characterized a variety of both RRP® and PIT Nb 3 Sn wires by transport measurements up to 29 T at the Laboratoire National des Champs Magnétiques Intenses (LNCMI), part of the European Magnetic Field Laboratory in Grenoble, to verify whether or not such overestimation is related to the measurement technique and whether or not it is a common feature across different designs. Indeed we also found that when measured in transport the 12-15 T Kramer extrapolation overestimates the actual H irr in both types of conductor with an inaccuracy of up to 1.6 T, confirming that high field characterization is a necessary tool to evaluate the actual high field performance of each Nb 3 Sn wire.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Asymmetric crossing of the attractive and repulsive magnetic potential by Abrikosov vortices

Here, we present studies of Abrikosov vortex motion across the magnetically charged edges of long thin ferromagnetic stripes placed above or under a thin superconducting film. The magnetic charges at the stripe edges form attractive or repulsive potential wells for vortices. Using a relatively small in-plane magnetic field to polarize the stripe edges and normal-to-plane magnetic field to induce up or down polarized vortices, we tune the attractive or repulsive stripe-vortex interactions. Imaging of the vortex dynamics reveals that the repulsive magnetic potential U m + acts as a robust vortex pinning barrier, while the attractive U m - has practically no effect on the vortex motion irrespective of the position of the stripes located above or underneath the superconducting film. We analyze the observed asymmetry using equations of the overdamped vortex motion. The formal analytical solution yields an asymmetry, but the numerical modeling with and without noise terms does not confirm it. Instead, we find that the asymmetry is caused by the creation of spontaneous vortices at the maxima of U m , which depends on the edge polarity and suppress U m - . Furthermore, our experiment and time-dependent Ginzburg-Landau simulations demonstrate that magnetic pinning dominates over vortex pinning due to corrugations of the superconducting layer deposited on top of the ferromagnetic stripes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Reversible ratchet effects in a narrow superconducting ring

We study the ratchet effect in a narrow pinning-free superconductive ring based on time-dependent GinzburgLandau (TDGL) equations. Voltage responses to external dc and ac currents at various magnetic fields are studied. Due to asymmetric barriers for flux penetration and flux exit in the ring-shaped superconductor, the critical current above which the flux-flow state is reached, as well as the critical current for the transition to the normal state, are different for the two directions of applied current. Furthermore, these effects cooperatively cause ratchet signal reversal at high magnetic fields, which has not been reported to date in a pinning-free system. The ratchet signal found here is larger than those induced by asymmetric pinning potentials. Our results also demonstrate the feasibility of using mesoscopic superconductors to employ a superconducting diode effect in versatile superconducting devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗