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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Photo-induced non-collinear interlayer RKKY coupling in bulk Rashba semiconductors

Abstract The interplay between light-matter, spin-orbit, and magnetic interactions allows the investigation of light-induced magnetic phenomena that are otherwise absent without irradiation. We present our analysis of light-driven effects on the interlayer exchange coupling mediated by a bulk Rashba semiconductor in a magnetic multilayer. The collinear magnetic exchange coupling mediated by the photon-dressed spin-orbit coupled electrons of BiTeI develops light-induced oscillation periods and displays new decay power laws, both of which are enhanced with an increasing light-matter coupling. For magnetic layers with non-collinear magnetization, we find a non-collinear magnetic exchange coupling uniquely generated by light-driving of the multilayer. As the non-collinear magnetic exchange coupling mediated by the photon-dressed electrons of BiTeI is unique to the irradiated system and it is enhanced with increasing light-matter coupling, this effect offers a promising platform of investigation of light-driven effects on magnetic phenomena in spin-orbit coupled systems. In this platform, light properties, such as its intensity, can serve as external knobs for inducing non-collinear couplings of the interlayer exchange and for modulating the collinear couplings. Both of these effects signify the photo-generated modification in the spin textures of spin-orbit coupled electrons in BiTeI.

Physics↗
DOE OSTI2022

Numerical studies on saturated kink and sawtooth induced fast ion transport in JET ITER-like plasmas

Here, this presentation examines the energetic particle transport induced by saturated kink modes and sawtooth crashes in JET deuterium plasmas. It is known that kink mode-resonant transport and phase-space redistribution from sawtooth crashes can drive strong fast ion transport with dependencies on particle pitch and energy. Measurements with JET's Faraday cup fast ion loss detector array have shown that the internal kink growth phase preceding sawtooth crashes produces substantial fast ion losses. This report will numerically investigate the dominant energetic particle transport mechanism with a detailed examination of the fast ion phase-space dependencies, resonances, orbit topology changes, induced losses, and redistribution associated with the long-lived, resonant, kink mode and non-resonant sawtooth crash. The ORBIT-kick model forms the basis of the transport studies with realistic fast ion distributions produced from TRANSP. A recently created reduced model for sawtooth induced transport is used while the saturated kink modes are modeled with ideal MHD codes. The simulations were further validated against experiment with a newly developed synthetic Faraday cup fast ion loss detector in addition to scintillator probe and neutron measurements.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

The role of RF-induced E×B flows in the mitigation of scrape-off-layer convective transport during ion cyclotron resonance heating

Abstract While multiple experiments have reported a decrease in intermittent fluctuations in the far Scrape-Off-Layer (SOL) during ion cyclotron resonance heating (Antar et al 2010 Phys. Rev. Lett. 105 165001, Li et al 2022 Nucl. Eng. Technol. 54 207–19, Antar et al 2012 Nucl. Fusion 52 103005), the physical mechanism behind this observation has not been fully established yet. In this work, we demonstrate, for the first time, a direct correlation between the amplitude of RF-induced E×B flows and turbulence suppression in the far SOL. Using the Gas Puff Imaging (GPI) diagnostic on Alcator C-Mod, we show again that Ion Cyclotron Range of Frequencies can significantly alter the flow in the SOL and introduce a shear layer in regions magnetically connected close to the antenna (Cziegler et al 2012 Plasma Phys. Control. Fusion 54 105019). With the 4-strap field-aligned antenna operated in dipole phasing, the ratio of the power coupled by the central two straps to the power coupled by the outer two straps was varied. The resulting RF-induced radial electric field magnitude thus varied, and we show that the impact on the far SOL turbulence correlates with the modified E×B velocity. We then apply a newly-developed blob tracking algorithm (Han et al 2022 Sci. Rep. 12 18142) to higher-resolution GPI videos in order to directly observe the process of blob shearing by RF-induced E×B flows. We show that the radially sheared poloidal flows act as a transport barrier by stretching, stopping, and destroying filaments, which is consistent with the observed difference in turbulence statistics.

Diab, R. (ORCID:0000000342065868)↗
DOE OSTI2022

Inference of molecular divertor density from filtered camera analysis of molecularly induced Balmer line emission during detachment in JET L-mode plasmas

Here a previously presented Monte Carlo method for estimating local plasma conditions in 2D based on intensity ratios of deuterium Balmer D α , D γ and D ε lines was amended to consider also the D α and D γ emission contributions arising from molecular processes. The obtained estimates were used to infer the molecular divertor density with the help of the molecular databases of EIRENE. The method was benchmarked against EDGE2D-EIRENE simulations and observed to reproduce the molecularly induced emission fractions and the molecular divertor densities primarily within 25% of the references. Experimental analysis of a JET L-mode density scan suggested molecularly induced D α and D γ contributions of up to 60–70% and 20%, respectively, during the process of detachment. The independent estimates of the molecular divertor density inferred from the obtained molecularly induced D α and D γ intensities agree within uncertainties with each other. Both estimates show the molecular density increasing up to approximately 1.0–2.0 x 10 20 m -3 at the outer strike point in deep detachment with its ratio to the local electron density agreeing with EDGE2D-EIRENE predictions within the scatter of the experimental data.

interferometry↗
DOE OSTI2022

Kicks and induced spins of neutron stars at birth

ABSTRACT Using simulations of non-rotating supernova progenitors, we explore the kicks imparted to and the spins induced in the compact objects birthed in core collapse. We find that the recoil due to neutrino emissions can be a factor affecting core recoil, comparable to and at times larger than the corresponding kick due to matter recoil. This result would necessitate a revision of the general model of the origin of pulsar proper motions. In addition, we find that the sign of the net neutrino momentum can be opposite to the sign of the corresponding matter recoil. As a result, at times the pulsar recoil and ejecta can be in the same direction. Moreover, our results suggest that the duration of the dipole in the neutrino emissions can be shorter than the duration of the radiation of the neutron-star binding energy. This allows a larger dipole asymmetry to arise, but for a shorter time, resulting in kicks in the observed pulsar range. Furthermore, we find that the spin induced by the aspherical accretion of matter can leave the residues of collapse with spin periods comparable to those inferred for radio pulsars and that there seems to be a slight anticorrelation between the direction of the induced spin and the net kick direction. This could explain such a correlation among observed radio pulsars. Finally, we find that the kicks imparted to black holes are due to the neutrino recoil alone, resulting in birth kicks ≤100 km s−1 most of the time.

Astronomy & Astrophysics↗
DOE OSTI2022

Living with high potassium: Balance between nutrient acquisition and K-induced salt stress signaling

High potassium (K) in the growth medium induces salinity stress in plants. However, the molecular mechanisms underlying plant responses to K-induced salt stress are virtually unknown. We examined Arabidopsis (Arabidopsis thaliana) and its extremophyte relative Schrenkiella parvula using a comparative multiomics approach to identify cellular processes affected by excess K and understand which deterministic regulatory pathways are active to avoid tissue damages while sustaining growth. Arabidopsis showed limited capacity to curb excess K accumulation and prevent nutrient depletion, contrasting to S. parvula which could limit excess K accumulation without restricting nutrient uptake. A targeted transcriptomic response in S. parvula promoted nitrogen uptake along with other key nutrients followed by uninterrupted N assimilation into primary metabolites during excess K-stress. This resulted in larger antioxidant and osmolyte pools and corresponded with sustained growth in S. parvula. Antithetically, Arabidopsis showed increased reactive oxygen species levels, reduced photosynthesis, and transcriptional responses indicative of a poor balance between stress signaling, subsequently leading to growth limitations. Furthermore, our results indicate that the ability to regulate independent nutrient uptake and a coordinated transcriptomic response to avoid nonspecific stress signaling are two main deterministic steps toward building stress resilience to excess K + -induced salt stress.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Eliminating beam-induced depolarizing effects in the hydrogen jet target for high-precision proton beam polarimetry at the electron-ion collider

We analyze beam-induced depolarizing effects in the hydrogen jet target (HJET) at the relativistic heavy ion collider (RHIC), which has been used for absolute hadron beam polarimetry and shall be employed at the electron-ion collider (EIC). The EIC’s higher bunch repetition frequencies and shorter bunch durations shift beam harmonics to frequencies that can resonantly drive hyperfine transitions in hydrogen, threatening to depolarize the target atoms. Using frequency-domain analysis of beam harmonics and hyperfine transition frequencies, we establish a photon emission threshold above which beam-induced fields are too weak to cause significant depolarization. For EIC injection (23.5 GeV) and flattop (275 GeV), beam-induced depolarization through the bunch structure renders operation at the current RHIC magnetic guide field at the target (𝐵 0 =120⁢ mT) untenable. Increasing the magnetic guide field at the target to 𝐵 0 ≈ 400⁢ mT moves all hyperfine transition frequencies to at least 3 times the cutoff frequency, ensuring reliable absolute beam polarimetry with the required 1% precision at the EIC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Magnetic field induced modification of a first-order ferromagnetic transition in Eu 2 ⁢In

Here, we present a comprehensive study of the temperature-and magnetic-field-dependent magnetization, specific heat, and local crystal structure across the first-order ferromagnetic–paramagnetic transition in Eu 2 ⁢In. Anomalies in the magnetocaloric response are observed near 𝐻 ≈ 25 kOe, including changes in field scaling of magnetic entropy, local entropy exponent, and universal master curve, which suggest an apparent weakening of the first-order character of the transition. However, quantitative analysis of the magnetocaloric parameters together with modified Arrott plots demonstrates that the transition remains first order up to at least 70 kOe. Specific-heat measurements reveal a field-induced splitting of the sharp zero-field anomaly into a doublet, providing a natural explanation for the change in the magnetocaloric response. Magnetic-field-dependent extended x-ray absorption fine structure (EXAFS) measurements show no detectable field-induced changes in the local coordination environment of Eu. We therefore attribute these observations to a magnetic-field-induced two-step transition process in Eu 2 ⁢In.

Kumar, Ajay [Ames Laboratory (AMES), Ames, IA (Uni↗
DOE OSTI2026

Noncollinear spin order, field-induced transitions, and short-range correlations in Cu 4 ⁢SO 4 ⁢(OH) 6

We report a comprehensive study of spin-$\frac{1}{2}$ quantum magnet brochantite, Cu 4 ⁢SO 4 ⁢(OH) 6 , combining high-field thermodynamic measurements, polarized neutron diffraction, inelastic neutron scattering, and nuclear magnetic resonance spectroscopy. Using bulk magnetization and specific heat measurements we construct the magnetic 𝐻−𝑇 phase diagram for magnetic fields applied along main crystallographic directions up to 24.1 T. Polarized neutron diffraction reveals a noncollinear magnetic ground state confined to the 𝑎⁢𝑏 plane. A field-induced transition is observed for magnetic fields in the 𝑎⁢𝑏 plane whose critical field and character evolve continuously with field direction in the 𝑎⁢𝑏 plane. While the transition for 𝐻 ∥ 𝑏 might be a spin-flop-like transition, the one for 𝐻 ∥ 𝑎 resembles the short-range correlated state above 𝑇 N , suggesting a magnetic configuration related to the quasi-two-dimensional correlations in the 𝑏⁢𝑐 planes. The experimental results demonstrate that the ground-state and field-induced phases cannot be explained by a simple XXZ model with a single dominant exchange interaction and that weaker interchain and anisotropic interactions have to be taken into account. Our work establishes brochantite as a low-symmetry Cu-based quantum magnet with noncollinear order and complex field-induced behavior.

Prokhnenko, Oleksandr [Helmholtz-Zentrum Berlin (H↗
DOE OSTI2024

Simulation and measurement of beam-induced heating of ceramic vacuum chambers

In this article, we summarize recent theoretical and experimental studies of the impedance and beam-induced heating of titanium-coated ceramic vacuum chambers used in the NSLS-II injection kickers. The impedance was calculated using the field matching theory assuming planar approximation and compared with the mpedanceake2 code. For the coating thickness of a few microns, we demonstrated that the beam-induced power is dissipated in the titanium coating and that the longitudinally averaged two-dimensional power density is approximated by an analytical expression, thus allowing the use of a simplified model of the power density as input for the code to simulate the temperature distribution with realistic nonuniform thickness of the Ti coating. For a few values of the NSLS-II beam current, we measured the beam-induced heating of two ceramic chambers using thermal sensors installed along the chamber and compared the measurement results with the simulations. Published by the American Physical Society 2024

36 MATERIALS SCIENCE↗
DOE OSTI2022

Temperature-Assisted Piezoresponse Force Microscopy: Probing Local Temperature-Induced Phase Transitions in Ferroics

The combination of local heating and biasing at the tip-surface junction in temperature-assisted piezoresponse force microscopy (TPFM) opens a pathway for probing local temperature-induced phase transitions in ferroics, exploring the temperature dependence of polarization dynamics in ferroelectrics and potentially discovering coupled phenomena driven by strong temperature and electric field gradients. In this study we analyze the signal-formation mechanism in TPFM and explore the interplay between thermal- and bias-induced switching in model ferroelectric materials. Furthermore, we explore the contributions of the flexoelectric and thermopolarization effects to the local electromechanical response and demonstrate that the latter can be significant for “soft” ferroelectrics. These results establish a framework for the quantitative interpretation of TPFM observations, predict the emergence of nontrivial switching and relaxation phenomena driven by nonlocal thermal-gradient-induced polarization switching, and open a pathway for exploring the physics of thermopolarization effects in various noncentrosymmetric and centrosymmetric materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Quantum Emitter Formation Dynamics and Probing of Radiation-Induced Atomic Disorder in Silicon

Near-infrared color centers in silicon are emerging candidates for on-chip integrated quantum emitters, optical-access quantum memories, and sensing. We access ensemble G-color-center formation dynamics and radiation-induced atomic disorder in silicon for a series of megaelectronvolt proton-flux conditions. The photoluminescence results reveal that the G centers are formed more efficiently by pulsed-proton irradiation than by continuous-wave proton irradiation. The enhanced transient excitations and dynamic annealing within nanoseconds allows optimization of the ratio of G-center formation to nonradiative defect accumulation. The G centers preserve narrow line widths of about 0.1 nm when they are generated by moderate pulsed-proton fluences, while the line width broadens significantly as the pulsed-proton fluence increases. This implies vacancy or interstitial clustering by overlapping collision cascades. The tracking of G-center properties for a series of irradiation conditions enables sensitive probing of atomic disorder, serving as a complementary analytical method for sensing damage accumulation. Aided by ab initio electronic structure calculations, we provide insight into the atomic disorder induced inhomogeneous broadening by introducing vacancies, silicon interstitials, and oriented strain fields in the vicinity of a G center. A vacancy leads to a tensile strain and can result in either a red shift or a blue shift of the G-center emission, depending on its position relative to the G center. Meanwhile, Si interstitials lead to compressive strain, which results in a monotonic red shift. In conclusion, high-flux and tunable ion pulses enable the exploration of the fundamental dynamics of radiation-induced defects as well as methods for the optimization of G-center formation and qubit synthesis for quantum information processing.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Light-induced microwave noise in superconducting microwave-optical transducers

Microwave-to-optical transducers are integral to the future of superconducting quantum computing, as they would enable scaling and long-distance communication of superconducting quantum processors through optical-fiber links. However, optically induced microwave noise poses a significant challenge in achieving quantum transduction between microwave and optical frequencies. In this work, we study light-induced microwave noise in an integrated electro-optical transducer harnessing the Pockels effect of thin-film lithium niobate. We reveal three sources of added noise with distinctive time constants ranging from sub-100 ns to milliseconds. Furthermore, our results provide insights into the mechanisms and corresponding mitigation strategies for light-induced microwave noise in superconducting microwave-optical transducers and pave the way toward realizing the ultimate goal of quantum transduction.

42 ENGINEERING↗
DOE OSTI2020

Indications for Lifshitz transitions in the nodal-line semimetal ZrSiTe induced by interlayer interaction

The layered material ZrSiTe is currently extensively investigated as a nodal-line semimetal with Dirac-like band crossings protected by nonsymmorphic symmetry close to the Fermi energy. A recent infrared spectroscopy study on ZrSiTe under external pressure found anomalies in the optical response, providing hints for pressure-induced phase transitions at ≈4.1 and ≈ 6.5GPa. By pressure-dependent Raman spectroscopy and x-ray diffraction measurements combined with electronic band structure calculations we find indications for two pressure-induced Lifshitz transitions with major changes in the Fermi surface topology in the absence of lattice symmetry changes. These electronic phase transitions can be attributed to the enhanced interlayer interaction induced by external pressure. Overall, our findings demonstrate the crucial role of the interlayer distance for the electronic properties of layered van der Waals topological materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Expansive open Fermi arcs and connectivity changes induced by infrared phonons in ZrTe 5

Expansive open Fermi arcs covering most of the surface Brillouin zone (SBZ) are desirable for detection and control of many topological phenomena, but they have generally been reported for Kramers-Weyl points, or unconventional chiral fermions, pinned at time-reversal invariant momentum in chiral materials. Here using first-principles band structure calculations, we show that for conventional Weyl points in ZrTe 5 with the chirality of +1/–1 near the BZ center at general momentum induced by one of the infrared phonons—the second lowest $B_{1u}$ mode for breaking inversion symmetry—they can also form expansive open Fermi arcs across the SBZ boundary to occupy most of the SBZ when projected on the (001) surface. In this work, we reveal that such expansive open Fermi arcs are evolved from the topological surface states that connect multiple surface Dirac points on the (001) surface of the topological insulator phases without lattice distortion in ZrTe 5 . Furthermore, we find that the connectivity of the induced open Fermi arcs can be changed by the magnitude of the lattice distortion of this infrared phonon mode. Thus, we propose that using coherent optical phonons to modulate lattice parameters can offer ways to induce unique topological features including expansive open Fermi arcs and to dynamically control Fermi arc connectivity in ZrTe 5 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

Impacts of irradiation-induced nanostructure on phonon linewidths and thermal conductivity in U-Zr alloy

Ion irradiation can significantly change material properties. Thermal conductivity degradation of reactor fuel is detrimental to safety and efficiency—driving research on how irradiation impacts heat-carrying phonons. Here, we report the measurements of phonon dispersion and lifetimes (inverse linewidths) in freestanding irradiated crystals and reveal the relationship between thermal conductivity and proton irradiation induced nanostructures in UZr 2.6 using inelastic x-ray scattering, electron microscopy, modulated thermoreflectance, and first-principles calculations. Irradiation results in more significant increases in phonon linewidths and decreased thermal conductivity in the basal plane than that along the c axis, decreasing thermal conductivity anisotropy. Furthermore, microscopy reveals that this results from irradiation induced nanoprecipitates and metastable phase separation. Surprisingly, irradiation leads to smaller phonon linewidths near some zone boundaries, which we attribute to irradiation induced short-range order.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Laser-induced quenching of metastability at the Mott insulator to metal transition

There is growing interest in strongly correlated insulator thin films because the intricate interplay of their intrinsic and extrinsic state variables causes memristive behavior that might be used for biomimetic devices in the emerging field of neuromorphic computing. Here, in this study, we find that laser irradiation tends to drive V 2 ⁢O 3 from supercooled/superheated metastable states toward thermodynamic equilibrium, most likely in a nonthermal way. We study thin films of the prototypical Mott-insulator V2⁢O3, which show spontaneous phase separation into metal-insulator herringbone domains during the Mott transition. Here, we use low-temperature microscopy to investigate how these metal-insulator domains can be modified by scanning a focused laser beam across the thin film surface. We find that the response depends on the thermal history: When the thin film is heated from below the Mott transition temperature, the laser beam predominantly induces metallic domains. On the contrary, when the thin film is cooled from a temperature above the transition, the laser beam predominantly induces insulating domains. Very likely, the V 2 ⁢O 3 thin film is in a superheated or supercooled state, respectively, during the first-order phase transition, and the perturbation by a laser beam drives these metastable states into stable ones. This way, the thermal history is locally erased. Our findings are supported by a phenomenological model with a laser-induced lowering of the energy barrier between the metastable and equilibrium states.

Materials Science↗
DOE OSTI2025

Light-induced anomalous Hall conductivity in the massive three-dimensional Dirac semimetal Co 3 ⁢Sn 2 ⁢S 2

Weyl semimetals can emerge from Dirac semimetals when the time-reversal or spatial-inversion symmetries are broken. Recently, it has been proposed based on Floquet theory that Dirac semimetals can be converted into Weyl semimetals even by shining circularly polarized light (CPL). Here we have investigated the possibility of such a Dirac-Weyl conversion by measuring the CPL-induced anomalous Hall conductivity (AHC) in a massive 3D Dirac semimetal Co 3 ⁢Sn 2 ⁢S 2 in the paramagnetic phase using ultrafast midinfrared pump-terahertz Faraday rotation probe spectroscopy. We find that the field-strength and driving frequency dependence of the observed AHC is well accounted for by CPL-induced nonzero Berry curvature associated with the splitting of the Dirac bands as predicted by the Floquet theory. As a result, the estimated splitting of the Dirac bands reaches about 60% of the mass gap and the calculated CPL-induced AHC quantitatively reproduces the experimental observation, demonstrating a promising route toward the realization of Floquet-Weyl states from massive Dirac semimetals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗