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DOE OSTI2015

Status of efforts on fundamental and applied studies with tritium at RFNC-VNIIEF

This paper gives an overview of the efforts in the field of fundamental and applied physics with tritium carried out with the participation of RFNC-VNIIEF in 2007-2013. New physical results in the study of muon-catalyzed fusion and neutron-excess nuclei are presented; a project of a new experiment on searching for a magnetic moment of the neutrino using a tritium source and helium detector is discussed. The description of a tritium support test-bed for a plasma focus-type neutron source with intensity of 10{sup 13} s{sup -1} is given. Results of studies in the area of interaction of hydrogen isotopes with structural materials such as nickel, stainless steels, high-strength austenitic alloys and alumina-based ceramics are summarized. (authors)

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2025

Fundamental mode excitation via Joule–Thomson light expansion in nonlinear optical lattices

Under linear conditions, power injected from a single waveguide into a multi-core fiber array results in multimode propagation, progressively diminishing the spatial coherence of light. In this work, we introduce a comprehensive approach to mitigate this coherence loss by means of a nonlinear thermodynamic Joule–Thomson expansion. By leveraging the tools of optical thermodynamics, we demonstrate that as light undergoes a sudden transition from a small to a larger nonlinear optical array, it can abruptly drop its optical temperature to near-zero values. During this cooling process, light irreversibly flows into the system's fundamental mode with very high efficiency, synchronizing all elements of the lattice with the input port. We show that this nonlinear effect is highly predictable even in systems of arbitrary geometry and shape and can be controlled precisely by the initial conditions at the input of the array. In particular, for a single injection point, the reduction in optical temperature can be directly determined by the total power, irrespective of the input location.

Pyrialakos, Georgios G. (ORCID:0000000286129694)↗

DOE OSTI2024

Photonic time crystals: from fundamental insights to novel applications: opinion

In this opinion article, we briefly outline some historical highlights and the most recent developments in the novel and exciting field of photonic time-crystals and present the challenges, disruptive opportunities and potential impact on both the fundamental science of light and on photonic technologies.

Boltasseva, A. (ORCID:0000000189052605)↗

DOE OSTI2024

Fundamental bandwidth limits and shaping of frequency-modulated combs

Frequency-modulated (FM) combs based on active cavities like quantum cascade lasers have recently emerged as promising light sources in many spectral regions. Unlike passive modelocking, which generates amplitude modulation using the field’s amplitude, FM comb formation relies on the generation of phase modulation from the field’s phase. They can therefore be regarded as a phase-domain version of passive modelocking. However, while the ultimate scaling laws of passive modelocking have long been known—Haus showed in 1975 that pulses modelocked by a fast saturable absorber have a bandwidth proportional to effective gain bandwidth—the limits of FM combs have been much less clear. Here, we show that FM combs based on fast gain media are governed by the same fundamental limits, producing combs whose bandwidths are linear in the effective gain bandwidth. Not only do we show theoretically that the diffusive effect of gain curvature limits comb bandwidth, but we also show experimentally how this limit can be increased. By adding carefully designed resonant-loss structures that are evanescently coupled to the cavity of a terahertz laser, we reduce the curvature and increase the effective gain bandwidth of the laser, demonstrating bandwidth enhancement. Our results can better enable the creation of active chip-scale combs and be applied to a wide array of cavity geometries.

47 OTHER INSTRUMENTATION↗

DOE OSTI2017

Radiative sky cooling: fundamental physics, materials, structures, and applications

Radiative sky cooling reduces the temperature of a system by promoting heat exchange with the sky; its key advantage is that no input energy is required. We will review the origins of radiative sky cooling from ancient times to the modern day, and illustrate how the fundamental physics of radiative cooling calls for a combination of properties that may not occur in bulk materials. A detailed comparison with recent modeling and experiments on nanophotonic structures will then illustrate the advantages of this recently emerging approach. Potential applications of these radiative cooling materials to a variety of temperature-sensitive optoelectronic devices, such as photovoltaics, thermophotovoltaics, rectennas, and infrared detectors, will then be discussed. This review will conclude by forecasting the prospects for the field as a whole in both terrestrial and space-based systems.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Disorder effects in nitride semiconductors: impact on fundamental and device properties

Abstract Semiconductor structures used for fundamental or device applications most often incorporate alloy materials. In “usual” or “common” III–V alloys, based on the InGaAsP or InGaAlAs material systems, the effects of compositional disorder on the electronic properties can be treated in a perturbative approach. This is not the case in the more recent nitride-based GaInAlN alloys, where the potential changes associated with the various atoms induce strong localization effects, which cannot be described perturbatively. Since the early studies of these materials and devices, disorder effects have indeed been identified to play a major role in their properties. Although many studies have been performed on the structural characterization of materials, on intrinsic electronic localization properties, and on the impact of disorder on device operation, there are still many open questions on all these topics. Taking disorder into account also leads to unmanageable problems in simulations. As a prerequisite to address material and device simulations, a critical examination of experiments must be considered to ensure that one measures intrinsic parameters as these materials are difficult to grow with low defect densities. A specific property of nitride semiconductors that can obscure intrinsic properties is the strong spontaneous and piezoelectric fields. We outline in this review the remaining challenges faced when attempting to fully describe nitride-based material systems, taking the examples of LEDs. The objectives of a better understanding of disorder phenomena are to explain the hidden phenomena often forcing one to use ad hoc parameters, or additional poorly defined concepts, to make simulations agree with experiments. Finally, we describe a novel simulation tool based on a mathematical breakthrough to solve the Schrödinger equation in disordered potentials that facilitates 3D simulations that include alloy disorder.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

Fundamentals of ultrafast laser–material interaction

Short pulse laser irradiation has the ability to bring a material into a state of strong electronic, thermal, phase, and mechanical nonequilibrium and trigger a sequence of structural transformations leading to the generation of complex multiscale surface morphologies, unusual metastable phases, and microstructures that cannot be produced by any other means. In this article, we provide an overview of recent advancements and existing challenges in the understanding of the fundamental mechanisms of short pulse laser interaction with materials, including the material response to strong electronic excitation, ultrafast redistribution and partitioning of the deposited laser energy, the peculiarities of phase transformations occurring under conditions of strong superheating/undercooling, as well as laser-induced generation of crystal defects and modification of surface microstructure.

Materials Science↗

DOE OSTI2017

Fundamentals of Condensed Matter Physics Marvin L. Cohen and Steven G. Louie

This graduate level textbook on Condensed Matter Physics is written lucidly by two leading luminaries in this field. The volume draws its material from the graduate course in condensed matter physics that has been offered by the authors for several decades at the University of California, Berkeley. Cohen and Louie have done an admirable job of guiding the reader gradually from elementary concepts to advanced topics. The book is divided into four main parts that have four chapters each. Chapter 1 presents models of solids in terms of interacting atoms, which is appropriate for the ground state, and excitations to describe collective effects. Chapter 2 deals with the properties of electrons in crystalline materials. The authors introduce the Born-Oppenheimer approximation and then proceed to the periodic potential approximation. Chapter 3 discusses energy bands in materials and covers concepts from the free electron model to the tight binding model and periodic boundary conditions. Chapter 4 starts with fixed atomic cores and introduces lattice vibrations, phonons, and the concept of density of states. By the end of this part, the student should have a basic understanding of electrons and phonons in materials. Part II presents electron dynamics and the response of materials to external probes. Chapter 5 covers the effective Hamiltonian approximation and the motion of the electron under a perturbation, such as an external field. The discussion moves to many-electron interactions and the exchange-correlation energy in Chapter 6, the widely-used Density Functional Theory (DFT) in chapter 7, and the dielectric response function in Chapter 8. The next two parts of the book cover advanced topics. Part III begins with a discussion of the response of materials to photons in Chapter 9. Chapter 10 goes into the details of electron-phonon interactions in different materials and introduces the polaron. Chapter 11 presents electron dynamics in a magnetic field and Chapter 12 discusses electrical and thermal transport in materials. Part IV takes the reader further into many body effects, superconductivity, and nanoscale materials. The authors introduce Feynman diagrams and many-body perturbation theory in Chapter 13, theories of superconductivity in Chapter 14, magnetism in Chapter 15, and low dimensional systems in Chapter 16. The first two parts are required reading for the beginner planning to perform DFT calculations. The advanced student interested in conducting research in condensed matter physics will benefit from continuing on to the last two parts. There is a set of problems at the end of each part. The narrative is aided by equations and detailed figures. References at the end of the book direct the reader to relevant books and review articles for each chapter. The inside covers include a periodic table and a useful list of fundamental physical constants. The authors present the underlying mathematics elegantly, which makes the textbook quite readable for those with a good mathematical background. Students lacking a firm footing in math will find the terrain rough after Chapter 1. This field has seen many good undergraduate textbooks including those by Kittel and by Ashcroft and Mermin. This volume fills the need for a rigorous graduate level textbook, and is a required addition to the bookshelf of every condensed matter physicist. Cohen and Louie have brought refreshing clarity to a challenging subject and made it eminently accessible to the motivated student.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Copper plating qualification process for the fundamental power coupler waveguides for CEBAF cryomodules

To provide sufficient energy for CEBAF operation, cryomodules and components are being refurbished yearly as necessary. Copper plated fundamental power coupler waveguides are important components of the cryomodules. The integrity and quality of copper plating is critical to reduce the heat load from the waveguides into the He bath at 2.07 K. A search of copper plating resources is underway for plating or re-plating CEBAF-style waveguides. This effort ensures a continuous capability of copper plating on cryomodule components, especially on waveguides. To qualify plating vendors, the waveguide copper plating specifications were revisited, and a thorough plating evaluation process is being developed. The evaluation process ranges from coupon testing to sample waveguide qualification. Recent results are summarized and future work is planned.

Zhao, Liang↗

DOE OSTI2011

Fundamental Processes of Coupled Radiation Damage and Mechanical Behavior in Nuclear Fuel Materials for High Temperature Reactors

The objective of this work has been to elucidate the relationship among microstructure, radiation damage and mechanical properties for nuclear fuel materials. As representative nuclear materials, we have taken an hcp metal (Mg as a generic metal, and Ti alloys for fast reactors) and UO2 (representing fuel). The degradation of the thermo-mechanical behavior of nuclear fuels under irradiation, both the fissionable material itself and its cladding, is a longstanding issue of critical importance to the nuclear industry. There are experimental indications that nanocrystalline metals and ceramics may be more resistant to radiation damage than their coarse-grained counterparts. The objective of this project look at the effect of microstructure on radiation damage and mechanical behavior in these materials. The approach to be taken was state-of-the-art, large-scale atomic-level simulation. This systematic simulation program of the effects of irradiation on the structure and mechanical properties of polycrystalline Ti and UO2 identified radiation damage mechanisms. Moreover, it will provided important insights into behavior that can be expected in nanocrystalline microstructures and, by extension, nanocomposites. The fundamental insights from this work can be expected to help in the design microstructures that are less susceptible to radiation damage and thermomechanical degradation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2012

Fundamental Studies of Charge Migration and Delocalization Relevant to Solar Energy Conversion

This program aimed to understand the molecular-level principles by which complex chemical systems carry out photochemical charge separation, transport, and storage, and how these insights could impact the design of practical solar energy conversion and storage devices. Towards these goals, this program focused on: (1) carrying out fundamental mechanistic and transient dynamical studies of proton-coupled electron-transfer (PCET) reactions; (2) characterizing and interrogating via electron paramagnetic resonance (EPR) spectroscopic methods novel conjugated materials that feature large charge delocalization lengths; and (3) exploring excitation delocalization and migration, as well as polaron transport properties of meso-scale assemblies that are capable of segregating light-harvesting antennae, nanoscale wire-like conduction elements, and distinct oxidizing and reducing environments.

14 SOLAR ENERGY↗

DOE OSTI2012

Supersymmetry and Unification of Fundamental Interactions - SUSY2009

SUSY2009 brought together researchers from a very broad area of fundamental physics including elementary particle theory, astrophysics and cosmology and string theory with a focus on supersymmetry. Thus the topic covered at the SUSY2009 conference included the following: Search for the Higgs boson, search for supersymmetry, supersymmetry phenomenology, theories of dark matter and direct and indirect detection, neutrino physics, accelerator experiments, electroweak physics, supersymmetry phenomenology, string theory, string phenomenology, extra Dimensions as well as other recent theoretical and experimental developments. The conference was successful in fostering interdisciplinary interactions between theorists and experimentalists.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Fundamental Physics with Cold Neutrons (Final Scientific and Technical Report)

The breadth of experiments performed using slow neutrons continues to increase worldwide. The accomplishments are a result of strong collaborations among national laboratories and university-based scientists and their students. There have been a growing number of notable results in fundamental neutron physics over the course of the last three-year grant period. A number of these experiments have been carried out on the beamlines at NIST or with the participation of NIST researchers. The list below gives a brief summary of some of these results as well as some of the cooperative endeavors during the last grant period.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Fundamental Studies and Development of III-N Visible LEDs for High-Power Solid-State Lighting Applications

The goal of this program is to understand in a fundamental way the impact of strain, defects, polarization, and Stokes loss in relation to unique device structures upon the internal quantum efficiency (IQE) and efficiency droop (ED) of III-nitride (III-N) light-emitting diodes (LEDs) and to employ this understanding in the design and growth of high-efficiency LEDs capable of highly-reliable, high-current, high-power operation. This knowledge will be the basis for our advanced device epitaxial designs that lead to improved device performance. The primary approach we will employ is to exploit new scientific and engineering knowledge generated through the application of a set of unique advanced growth and characterization tools to develop new concepts in strain-, polarization-, and carrier dynamics-engineered and low-defect materials and device designs having reduced dislocations and improved carrier collection followed by efficient photon generation. We studied the effects of crystalline defect, polarizations, hole transport, electron-spillover, electron blocking layer, underlying layer below the multiplequantum- well active region, and developed high-efficiency and efficiency-droop-mitigated blue LEDs with a new LED epitaxial structure. We believe new LEDs developed in this program will make a breakthrough in the development of high-efficiency high-power visible III-N LEDs from violet to green spectral region.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2013

Interface Induced Carbonate Mineralization: A Fundamental Geochemical Process Relevant to Carbon Sequestration

We have approached the long-standing geochemical question why anhydrous high-Mg carbonate minerals (i.e., magnesite and dolomite) cannot be formed at ambient conditions from a new perspective by exploring the formation of MgCO 3 and Mg x Ca{sub (1-x)}CO 3 in non-aqueous solutions. Data collected from our experiments in this funding period suggest that a fundamental barrier, other than cation hydration, exists that prevents Mg 2+ and CO 3 2- ions from forming long-range ordered structures. We propose that this barrier mainly stems from the lattice limitation on the spatial configuration of CO 3 groups in magnesite crystals. On the other hand, the measured higher distribution coefficients of Mg between magnesian calcites formed in the absence and presence of water give us a first direct proof to support and quantify the cation hydration effect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2013

A Fundamental Investigation on the Structural Dynamics of Model Siloxane Networks under Extreme Pressure

Poly(dimethylsiloxane) elastomers are ubiquitous in their application as key components in a range of (often extreme) environments. and as such, they often experience pressures in a region where we do not understand their physical response and therefore can offer no predictive estimate of lifetime of failure . We are proposing a fundamental scientific investigation of the pressure induced morphological changes in model PDMS networks. Both NMR and BDS spectroscopies will be used to interrogate pressure induced changes and meaningful phase relations will be sought. The addition of filler to the networks will be used as an attempt to engineer the network to be more resistant to pressure changes. We have the equipment, model networks and expertise to start this project immediately; funding is sought as an investment in our time allocation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2013

Fundamental Interactions in Nuclei (Final Report)

The funding awarded during the grant period provided summer salary and travel support for the PI; support (partial or full) support for six post-doctoral researchers, and partial support for seven Ph.D students. The research covered the following topics: electroweak baryogenesis; electroweak symmetry-breaking and its implications for dark matter; fundamental symmetry tests; applications of perturbative QCD and effective field theories to nuclear physics symmetry tests and precise QCD studies. The research resulted in approximately 50 publications and numerous invited talks at major conferences and workshops.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2014

Understanding Fundamental Material Degradation Processes in High Temperature Aggressive Chemomechanical Environments

The objective of this project is to develop a fundamental understanding of the mechanisms that limit materials durability for very high-temperature applications. Current design limitations are based on material strength and corrosion resistance. This project will characterize the interactions of high-temperature creep, fatigue, and environmental attack in structural metallic alloys of interest for the very high-temperature gas-cooled reactor (VHTR) or Next–Generation Nuclear Plant (NGNP) and for the associated thermo-chemical processing systems for hydrogen generation. Each of these degradation processes presents a major materials design challenge on its own, but in combination, they can act synergistically to rapidly degrade materials and limit component lives. This research and development effort will provide experimental results to characterize creep-fatigue-environment interactions and develop predictive models to define operation limits for high-temperature structural material applications. Researchers will study individually and in combination creep-fatigue-environmental attack processes in Alloys 617, 230, and 800H, as well as in an advanced Ni-Cr oxide dispersion strengthened steel (ODS) system. For comparison, the study will also examine basic degradation processes in nichrome (Ni-20Cr), which is a basis for most high-temperature structural materials, as well as many of the superalloys. These materials are selected to represent primary candidate alloys, one advanced developmental alloy that may have superior high-temperature durability, and one model system on which basic performance and modeling efforts can be based. The research program is presented in four parts, which all complement each other. The first three are primarily experimental in nature, and the last will tie the work together in a coordinated modeling effort. The sections are (1) dynamic creep-fatigue-environment process, (2) subcritical crack processes, (3) dynamic corrosion – crack initiation processes, and (4) modeling.

36 MATERIALS SCIENCE↗