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At least 757 records · Page 42

All sources NASA NTRS DOE OSTI

DOE OSTI2020

Cosmogenic activation of silicon

In the production of 3 H, 7 Be, and 22 Na by interactions of cosmic-ray particles with silicon can produce radioactive backgrounds in detectors used to search for rare events. Through controlled irradiation of silicon CCDs and wafers with a neutron beam that mimics the cosmic-ray neutron spectrum, followed by direct counting, we determined that the production rate from cosmic-ray neutrons at sea level is (112 ± 24) atoms/( kg day ) for 3 H, (8.1 ± 1.9) atoms/( kg day ) for 7 Be, and (43.0 ± 7.2) atoms/( kg day ) for 22 Na . Complementing these results with the current best estimates of activation cross sections for cosmic-ray particles other than neutrons, we obtain a total sea-level cosmic-ray production rate of (124 ± 25) atoms/(kg day) for 3 H, (9.4 ± 2.0) atoms/( kg day ) for 7 Be, and (49.6 ± 7.4) atoms/( kg day ) for 22 Na. These measurements will help constrain background estimates and determine the maximum time that silicon-based detectors can remain unshielded during detector fabrication before cosmogenic backgrounds impact the sensitivity of next-generation rare-event searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Unifying simulation and inference with normalizing flows

There have been many applications of deep neural networks to detector calibrations and a growing number of studies that propose deep generative models as automated fast detector simulators. We show that these two tasks can be unified by using maximum likelihood estimation (MLE) from conditional generative models for energy regression. Unlike direct regression techniques, the MLE approach is prior independent and non-Gaussian resolutions can be determined from the shape of the likelihood near the maximum. Using an ATLAS-like calorimeter simulation, we demonstrate this concept in the context of calorimeter energy calibration. Published by the American Physical Society 2025

Hadronic calorimiters↗

DOE OSTI2020

Benchmarking boron carbide equation of state using computation and experiment

Boron carbide ( B 4 C ) is of both fundamental scientific and practical interest due to its structural complexity and how it changes upon compression, as well as its many industrial uses and potential for use in inertial confinement fusion (ICF) and high-energy density physics experiments. Here, we report the results of a comprehensive computational study of the equation of state (EOS) of B 4 C in the liquid, warm dense matter, and plasma phases. Our calculations are cross-validated by comparisons with Hugoniot measurements up to 61 megabar from planar shock experiments performed at the National Ignition Facility (NIF). Our computational methods include path integral Monte Carlo, activity expansion, as well as all-electron Green's function Korringa-Kohn-Rostoker and molecular dynamics that are both based on density functional theory. We calculate the pressure-internal energy EOS of B 4 C over a broad range of temperatures ( ~ 6 × 10 3 – 5 × 10 8 K) and densities (0.025–50 g / cm 3 ). We assess that the largest discrepancies between theoretical predictions are ≲ 5 % near the compression maximum at 1– 2 × 10 6 K. This is the warm-dense state in which the K shell significantly ionizes and has posed grand challenges to theory and experiment. By comparing with different EOS models, we find a Purgatorio model (LEOS 2122) that agrees with our calculations. The maximum discrepancies in pressure between our first-principles predictions and LEOS 2122 are ~ 18 % and occur at temperatures between 6 × 10 3 – 2 × 10 5 K, which we believe originate from differences in the ion thermal term and the cold curve that are modeled in LEOS 2122 in comparison with our first-principles calculations. To account for potential differences in the ion thermal term, we have developed three new equation-of-state models that are consistent with theoretical calculations and experiment. We apply these new models to 1D hydrodynamic simulations of a polar direct-drive NIF implosion, demonstrating that these new models are now available for future ICF design studies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Asymmetric temperature equilibration with heat flow from cold to hot in a quantum thermodynamic system

A model computational quantum thermodynamic network is constructed with two variable temperature baths coupled by a linker system, with an asymmetry in the coupling of the linker to the two baths. It is found in computational simulations that the baths come to “thermal equilibrium” at different bath energies and temperatures. In a sense, heat is observed to flow from cold to hot. Additionally, a description is given in which a recently defined quantum entropy S univ Q for a pure state “universe” continues to increase after passing through the classical equilibrium point of equal temperatures, reaching a maximum at the asymmetric equilibrium. Thus, a second law account Δ S univ Q ≥ 0 holds for the asymmetric quantum process. In contrast, a von Neumann entropy description fails to uphold the entropy law, with a maximum near when the two temperatures are equal, then a decrease Δ S v N < 0 on the way to the asymmetric equilibrium.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Characterizing different motility-induced regimes in active matter with machine learning and noise

Here we examine motility-induced phase separation (MIPS) in two-dimensional run-and-tumble disk systems using both machine learning and noise fluctuation analysis. Our measures suggest that within the MIPS state there are several distinct regimes as a function of density and run time, so that systems with MIPS transitions exhibit an active fluid, an active crystal, and a critical regime. The different regimes can be detected by combining an order parameter extracted from principal component analysis with a cluster stability measurement. The principal component-derived order parameter is maximized in the critical regime, remains low in the active fluid, and has an intermediate value in the active crystal regime. We demonstrate that machine learning can better capture dynamical properties of the MIPS regimes compared to more standard structural measures such as the maximum cluster size. The different regimes can also be characterized via changes in the noise power of the fluctuations in the average speed. In the critical regime, the noise power passes through a maximum and has a broad spectrum with a 1/f 1.6 signature, similar to the noise observed near depinning transitions or for solids undergoing plastic deformation.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2022

Probing the Incompressibility of Nuclear Matter at Ultrahigh Density through the Prompt Collapse of Asymmetric Neutron Star Binaries

Using 250 neutron star merger simulations with microphysics, we explore for the first time the role of nuclear incompressibility in the prompt collapse threshold for binaries with different mass ratios. We demonstrate that observations of prompt collapse thresholds, either from binaries with two different mass ratios or with one mass ratio but combined with the knowledge of the maximum neutron star mass or compactness, will constrain the incompressibility at the maximum neutron star density K max to within tens of percent. This otherwise inaccessible measure of K max can potentially reveal the presence of hyperons or quarks inside neutron stars.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2026

Utilizing the deuterium-tritium fusion resonance to diagnose thermal runaway in igniting plasmas

For high-efficiency inertial confinement fusion implosions, it is predicted that a burning hot spot will successfully encompass all surrounding fuel and then transition into a thermal runaway where the internal energy increase from fusion occurs on a timescale faster than the expansion of the fuel is able to quench the fusion chain reaction after ignition occurs. Observation of this dynamic phase transition would indicate distinct burn properties and indicate an implosion's robustness. A technique for diagnosing the presence of thermal runaway from measurements of nuclear reaction history is presented. The technique is based on taking the logarithmic derivative of the nuclear reaction history, called the 𝛼 curve, and allowing a mathematical decoupling of the mass, volume, and thermal reactivity in the fusion reaction rate equation. During thermal runaway, where the thermal temperature dominates the burn dynamics, a maximum in the 𝛼 curve is found where there is a maximum in the first derivative of the thermal fusion reactivity, an effect to the deuterium-tritium (DT) fusion cross-section resonance. This provides a distinct signature related to the fundamental nature of the DT fusion nuclear resonance and signifies the transition into the fusion thermal instability. Impacts of charged particle transport on the effect are also assessed and the analytical formulas are compared and found to be in agreement with radiation hydrodynamic codes.

high-energy-density plasmas↗

DOE OSTI2026

Observing the effects of numbers of valence nucleons on 0$^{+}_{𝑔⁡𝑠}$ → 2$^{+}_{1}$ transitions in deformed nuclei by comparing proton and neutron transition matrix elements

We examined the ratios of neutron and proton transition matrix elements, 𝑀 𝑛 /𝑀 𝑝 , for the 0$^{+}_{𝑔⁡𝑠}$ → 2$^{+}_{1}$ transitions in 48 even-even stable nuclei with 𝑁 > 20 for which electromagnetic matrix elements were compiled by Pritychenko et al. and for which high-quality inelastic proton-scattering data were available. Several deformed rare-earth nuclei have (𝑀 𝑛 /𝑀 𝑝 )/(𝑁/𝑍) values significantly below 1.0, which is not consistent with a simple liquid-drop picture. However, this phenomenon can be explained using a schematic picture in which 𝑀 𝑝 reaches a maximum at proton midshell (𝑍 = 66) and 𝑀𝑛 reaches its maximum at neutron midshell (𝑁 = 104). Several midmass vibrational nuclei have 𝑀 𝑛 /𝑀 𝑝 values significantly below 𝑁/𝑍, which is not consistent with the expectation that 𝑀 𝑛 /𝑀 𝑝 = 𝑁/𝑍 in such nuclei. As a result, a shell-model investigation of these observations might yield insights about this behavior.

Collective levels↗

DOE OSTI2023

A MHz X-ray diffraction set-up for dynamic compression experiments in the diamond anvil cell

An experimental platform for dynamic diamond anvil cell (dDAC) research has been developed at the High Energy Density (HED) Instrument at the European X-ray Free Electron Laser (European XFEL). Advantage was taken of the high repetition rate of the European XFEL (up to 4.5 MHz) to collect pulse-resolved MHz X-ray diffraction data from samples as they are dynamically compressed at intermediate strain rates (≤10 3 s −1 ), where up to 352 diffraction images can be collected from a single pulse train. The set-up employs piezo-driven dDACs capable of compressing samples in ≥340 µs, compatible with the maximum length of the pulse train (550 µs). Results from rapid compression experiments on a wide range of sample systems with different X-ray scattering powers are presented. A maximum compression rate of 87 TPa s −1 was observed during the fast compression of Au, while a strain rate of ∼1100 s −1 was achieved during the rapid compression of N 2 at 23 TPa s −1 .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Design of 1500V/200kW 99.6% Efficiency Dual Active Bridge Converters Based on 1700V SiC Power MOSFET Module

High efficiency, high density and galvanically isolated power converters are attractive for medium voltage high power applications. This paper presents a 1.5kV/200kW bidirectional Dual Active Bridge (DAB) converter using a newly developed 1.7kV SiC MOSFET module. The intended application is megawatt scale solid state transformer (SST) and 1500V PV inverter application using modular architecture. One novel model to estimate the turn-off loss using snubber capacitors is proposed and experimentally verified. An optimized PCB-based busbar design is introduced to reduce the voltage overshoot across the SiC device, making the design suitable for 1.5kVdc applications. The mechanism of how the optimized PCB-based busbar can reduce the voltage overshoot is quantitatively interpreted and experimentally verified. The DAB converter achieved an efficiency of 98.85% at 200kW and a maximum of 99.53% at 60kW. The maximum efficiency for series-resonant mode is 99.6% at 85kW and 99.3% at 200kW. The power density is 26W/inch3 (1.6MW/m3) which is much higher than traditional industry products.

Xu, Wei↗

DOE OSTI2021

Novel Transformer with Variable Leakage and Magnetizing Inductances

This paper introduces the concept of a novel variable inductance transformer (VIT) whose leakage and magnetizing inductances can be varied dynamically and independently to aid the advancement of research in isolated power electronic converters. In this transformer, the leakage inductance can be varied by varying the length of overlap between the primary and secondary windings, while the magnetizing inductance can be varied by varying the air gap between the core legs. Individual controls for the two inductances ensure that one can be varied independent of the other, as needed to satisfy different power conversion objectives. In this paper, the analytical models of the variable leakage and magnetizing inductances are presented. Analytical results are compared with those obtained from Finite Element Method (FEM) and an experimental prototype of a VIT. Analytical solutions of the variable leakage inductance present an error of less than 2.35 % when compared to FEM solutions, while the analytical solutions of the variable magnetizing inductance present a maximum error of 1.82 % when compared to experimental measurements.

image method, leakage inductance, magnetizing indu↗

DOE OSTI2022

A Nonlinear Direct Power Controller for a Three-Phase Grid-Connected Inverter with Online Parameter Update for PV Application

This work proposes a nonlinear direct power controller for a three-phase grid-connected inverter for photovoltaic application. Grid-connected converters for solar applications require advanced control architectures to ensure optimal operation and extraction of maximum power from the photovoltaic arrays. Therefore, to ensure this, a nonlinear power controller architecture has been proposed to extract the maximum power from the solar arrays and to achieve the most optimal operation. To further improve the performance, a parameter update scheme has been utilized which is based on model reference adaptive system. The latter helps to accomplish not only good dynamic response but also excellent tracking performance. The overall control come estimation architecture is verified based on computer simulations via MATLAB/Simulink and PLECS domain and various important case study results are presented.

direct power control↗

DOE OSTI2024

Vertical GaN Superjunction Diode on Sapphire with Kilovolt Dynamic Breakdown Voltage

The development of superjunction structures for use in vertical wide bandgap power devices promise to break the 1-D material limits. Additionally, the possibility of utilizing heteroepitaxial GaN-on-Sapphire wafer for vertical devices can significantly trim the material and device cost. This work introduces a quasi-vertical GaN-on-Sapphire superjunction PN diode design utilizing sputtered p-NiO on the etched GaN fins for superjunction formation. DC breakdown voltage is shown to vary with superjunction charge imbalance and significantly exceed the expected 1-D planar limit of 350V given the epilayer design used. A maximum breakdown voltage of 840 V is extracted for near charge balance conditions limited by leakage current. Dynamic breakdown of the device is characterized as a function of reverse voltage slew rate. A maximum dynamic breakdown voltage of 1160 V under a reverse voltage slew rate of 2000 V/μs is found.

Porter, Matthew↗

DOE OSTI2025

A Novel Three-Phase Isolated LLC and Non-Isolated LCL-T Resonant Converter for Fuel Cell Applications

In this paper, a novel three-phase isolated LLC and non-isolated LCL−T resonant converter topologies are introduced for fuel cell applications. In order to improve the fuel cell DC/DC converter efficiency, the current amplitude should be reduced in the power stage components. Cascaded connections of fuel cell blocks through a controllable system enable using higher voltage amplitude and bring the current amplitude lower at the target power. In this way, power losses in the passive components can be reduced, and maximum energy transfer can be established, improving the DC/DC converter efficiency from the fuel cell to the load. The introduced new converter also achieves soft switching (ZVS), minimizing the switching losses in all input and output load conditions. The presented three-phase isolated LLC and non-isolated LCL−T resonant converter systems, fed by three fuel cell modules with an output range of 190380 V, deliver 580−730 V at 450 kW maximum output power. The results reveal that the proposed systems have the advantage of reducing the size, volume, and weight and increasing the overall DC/DC converter system efficiency compared to the single-phase systems.

Asa, Erdem [ORNL] (ORCID:0000000190884812)↗

DOE OSTI2020

Analytic Thermal Model of an Optical Fiber Based Gamma Thermometer and its Application in a University Research Reactor

This paper describes and validates, by comparison with numerical modeling results, an analytical model of thermal transport in an optical fiber based gamma thermometer (OFBGT) that is appropriate for use in university research reactors. The maximum temperature difference between the thermal mass and the outer sheath ( Δ T ) for the OFBGT design that we have considered is approximately 50 ∘ C , for the OFBGT in the Central Irradiation Facility of the Ohio State University Research Reactor (OSURR) with the reactor operating at full power (450 kW). The maximum value of Δ T that is predicted by the analytic model for the OFBGT design is smaller by approximately 1.1 °C than the value of Δ T which is predicted by the numerical model, for the same OFBGT design, but including all the details of the design. We have used the analytical model of thermal transport in an OFBGT to determine a normalized Modulation Transfer Function M T F ′ ( k ) ) for the OFBGT. We conclude that MTF ′ ( k OSU ) > 0.99 , where k OSU is the spatial frequency for the axial dependence of the reactor power distribution in the

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Impacts of Voltage-Based Grid Support Functions on Energy Production of PV Customers

This paper presents the impact of inverter grid- support functions (GSFs) on photovoltaic (PV) customer energy production on a real distribution feeder in Oahu, HI. These autonomous GSFs based on local voltage measurements are good alternatives to increase PV hosting capacity. However, these functions can result in PV energy curtailment to the customer, and this study addresses the concerns about the impact of inverter GSFs through detailed quasi-static time series (QSTS) simulations. It proposes four metrics: maximum and average GSF curtailment, average increased generation and average net generation change, to assess the impact of a given control on PV systems located on customer sites. It was found that curtailment of PV production is negligible for customers where peak voltage is within ANSI C84.1 range. A reliable relationship between curtailment and peak customer voltage is demonstrated, suggesting that peak voltage could be used as an indicator of customer curtailment.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2022

An Operational Resilience Metric to Evaluate Inertia and Inverter-based Generation on the Grid

In an effort to reduce carbon emissions and curtail the effects of climate change there has been considerable effort to increase the penetration of inverter-based renewable energy sources. The adoption of renewable generation over conventional inertia-based generation sources is forming considerable challenges for the operation and stability of the power system. The power system has been designed around generation units characterized by high inertia and primary frequency response (PFR), allowing them to respond to disturbances such as faults or generators tripping off line. In contrast, the modern inverter-based assets are characterized by no contribution to inertia and they typically provide stochastic generation at their maximum output, thus having no contribution to PFR during low-frequency disturbance events. Because of this, inertia in power systems is reducing, resulting in a faster rate of frequency change after a disturbance occurs. As more inverter-based generation units are added to the grid it is important to understand the stability of the system and the size of disturbance a system is capable of withstanding. This paper presents a resilience metric that evaluates the maximum size of disturbance a systems can withstand based on the system inertia and the primary frequency control of inverter and inertia-based generation. The results are shown visually and are based on the real-time operation of generation units and their characteristics such as latency, ramp rates, and energy constraints. It is demonstrated that the real-time positioning or bias of the generating units has an effect of the size of disturbance that a system can withstand, i.e. its resilience. It is expected that this type of analysis can help operators increase the resilience of power systems in the future.

13 HYDRO ENERGY↗

DOE OSTI2020

Determination of Series Resistance in CdSeTe/CdTe Solar Cells by the Jsc–Voc Method

While commonly used in Si solar cell characterization, the Suns–Voc method of determining series resistance (Rs) is rarely used for CdTe and its alloys. However, it is advantageous relative to the slope method—commonly used in the CdTe community—because it measures series resistance at the maximum power point, at which a solar cell operates. Using the self-consistent predecessor to Suns–Voc, Jsc –Voc, , we determine Rs of two different CdSeTe/CdTe solar cell structures to be 0.96 and 2.72 Ωcm2, with repeated measurements showing little deviation

13 HYDRO ENERGY↗