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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 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Seeding Coherent Radiation Sources with Sawtooth Modulation

Seed radiation sources have the ability to increase longitudinal coherence, decrease saturation lengths, and improve performance of tapering, polarization control and other FEL features. Typically, seeding schemes start with a simple sinusoidal modulation, which is manipulated to provide bunching at a high harmonic of the original wavelength. In this paper, we consider seeding from sawtooth modulations. The sawtooth creates a clean phase space structure, providing a maximal bunching factor without the need for an FEL interaction. While a pure sawtooth modulation is a theoretical construct, it is possible to approach the waveform by combining two or more of the composite wavelengths. We give examples of sawtooth seeding for HGHG, EEHG and other schemes, and note that the sawtooth modulation may aid in suppression of the microbunching instability.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Modeling Photovoltaic Module-Level Power Electronics in the System Advisor Model; NREL (National Renewable Energy Laboratory)

Module-level power electronics, such as DC power optimizers, microinverters, and those found in AC modules, are increasing in popularity in smaller-scale photovoltaic (PV) systems as their prices continue to decline. Therefore, it is important to provide PV modelers with guidelines about how to model these distributed power electronics appropriately in PV modeling software. This paper extends the work completed at NREL that provided recommendations to model the performance of distributed power electronics in NREL’s popular PVWatts calculator [1], to provide similar guidelines for modeling these technologies in NREL's more complex System Advisor Model (SAM). Module-level power electronics - such as DC power optimizers, microinverters, and those found in AC modules-- are increasing in popularity in smaller-scale photovoltaic (PV) systems as their prices continue to decline. Therefore, it is important to provide PV modelers with guidelines about how to model these distributed power electronics appropriately in PV modeling software.

14 SOLAR ENERGY↗
DOE OSTI2012

PV Cell and Module Calibrations at NREL

NREL has equipment to measure any conceivable cell or module technology. The lack of standards for low concentration modules complicates matters. Spectrally adjustable simulators are critical for more than three junctions. NREL's 10-channel fiber optic simulator has shown that the light can be set for each junction within 1% of what it would be under the reference spectrum for up to a five-junction cell. Uncertainty in module simulators dominated by spatial nonuniformity for calibration labs. Manufacturers can mitigate this error by using matched reference modules instead of cells.

14 SOLAR ENERGY↗
DOE OSTI2017

A Practical Irradiance Model for Bifacial PV Modules: Preprint

A model, suitable for a row or multiple rows of photovoltaic (PV) modules, is presented for estimating the backside irradiance for bifacial PV modules. The model, which includes the effects of shading by the PV rows, is based on the use of configuration factors (CFs) to determine the fraction of a source of irradiance that is received by the backside of the PV module. Backside irradiances are modeled along the sloped height of the PV module, but assumed not to vary along the length of the PV row. The backside irradiances are corrected for angle-of-incidence losses and may be added to the front side irradiance to determine the total irradiance resource for the PV cell. Model results are compared with the measured backside irradiances for NREL and Sandia PV systems, and with results when using the RADIANCE ray tracing program.

14 SOLAR ENERGY↗
DOE OSTI2017

A Practical Irradiance Model for Bifacial PV Modules

A model, suitable for a row or multiple rows of photovoltaic (PV) modules, is presented for estimating the backside irradiance for bifacial PV modules. The model, which includes the effects of shading by the PV rows, is based on the use of configuration factors to determine the fraction of a source of irradiance that is received by the backside of the PV module. Backside irradiances are modeled along the sloped height of the PV module, but assumed not to vary along the length of the PV row. The backside irradiances are corrected for angle-of-incidence losses and may be added to the front side irradiance to determine the total irradiance resource for the PV cell. Model results are compared with the measured backside irradiances for NREL and Sandia PV systems, and with results when using ray tracing software.

14 SOLAR ENERGY↗
DOE OSTI2024

Power Module Precursors and Prognostics

This project focuses on finding and utilizing electrical properties (precursors) of power electronic devices and modules whose changes have strong correlations with different modes and levels of degradations in order to realize online and lightweight state of health evaluation and fault diagnosis. Results from this project will contribute to higher safety, reliability, and power density of power electronic components. The approaches mainly include reviewing academic literature and industry practices for state of the art precursor identification and extraction, accelerated life cycles (ALC) of various power modules to create different degradations in-house, and developing techniques for gate-driver-integratable precursor detection circuit. In FY24, the results includes two sets of definitively detected aging precursors (on-state resistance and gate threshold voltage) for two sets of power modules respectively, controlled accelerated lifetime cycling of multiple silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) modules, and the development and validation of a gate voltage detection system.

ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2025

Design and Commission of Solid State Switch Driver in SLAC Subbooster Modulator

The LINAC sub-booster modulator is a pulsed power supply to provide a 30kV pulse to drive a klystron in SLAC LINAC. It has utilized vacuum tetrode as pulse switch for more than 60 years. With the vacuum tetrode availability becoming less and its cost surging, a natural choice is to use solid state switch in this pulsed power modulator. To commission solid state switch in LINAC sub-booster modulator, a driver board is designed to drive a BEHLKE HTS-LC2 series MOSFET based switches. The design concept and some concerns in design will be presented. The driver board is universal for all HTS-LC2 series switches because they share the same driver signals and connections. After the driver is commissioned, two AI systems are introduced to design one core part of the driver, the results are presented here. During the commission of the driver board in the LINAC sub-booster modulators, some problems happened and were addressed.

AI Circuit Design↗
DOE OSTI2011

Tree Image Growth Analysis Using the Instantaneous Phase and Frequency Modulation

We propose the use of Amplitude-Modulation Frequency-Modulation (AM-FM) methods for tree growth analysis. Tree growth is modeled using phase modulation. For adapting AM-FM methods to different images, we introduce the use of fast filterbank filter coefficient computation based on piecewise linear polynomials and radial frequency magnitude estimation using integer-based Savitzky-Golay filters for derivative estimation. For a wide range of images, a simple filterbank design with only 4 channel filters is used. Filterbank specification is based on two different methods. For each input image, the FM image is estimated using dominant component analysis. A tree growthmodel is developed to characterize and depict quarterly and half-seasonal growth of trees using instantaneous phase. Qualitative evaluation of inter- and intraring reconstruction is performed on 20 aspen images and a mixture of 12 tree images of various types. Qualitative scores indicate that the results were mostly of good to excellent quality (4.4/5.0 and 4.0/5.0 for the two databases, resp.).

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Flicker: A review of temporal light modulation stimulus, responses, and measures

Flicker has been an important lighting system consideration for over a century. More precise terms are temporal light modulation (TLM) as the stimulus, and responses to TLM as the unwanted visual, cognitive, or physiological consequences. As lighting technology evolved, different forms of TLM emerged, and so did responses to them. Today, some LED systems – encompassing the LED, driver, and control – can result in TLM causing severe unwanted effects, while other LED systems produce no unwanted effects at all. LED systems can deliver a much wider range of luminous waveforms than conventional lighting systems, some exhibiting very high modulation depths. More than any light source before, they can elicit perceptions of the phantom array. Direct flicker effects at modulation frequencies less than about 80 Hz and the stroboscopic effect at frequencies greater than 80 Hz are fairly well understood, but the phantom array effect needs more exploration and characterisation. This review focuses on the technology and research history that led to current metrics for quantifying TLM and human responses to TLM. Notably, visually impaired individuals may exhibit alterations in their response to TLM, but such a discussion is beyond the intent of this review. Thus, the focus is on individuals with normal visual function.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

The production of Multiple Small Peptaibol Families by Single 14-Module Peptide Synthetases in Trichoderma/Hypocrea

The most common peptaibibiotic structures are 11-residue peptaibols found widely distributed in the genus Trichoderma/Hypocrea. Frequently associated are 14-residue peptaibols sharing partial sequence identity. Genome sequencing projects of 3 Trichoderma strains of the major clades reveal the presence of up to 3 types of nonribosomal peptide synthetases with 7, 14, or 18-20 amino acid adding modules. We here provide evidence that the 14-module NRPS type found in T. virens, T. reesei (teleomorph Hypocrea jecorina) and T. atroviride produces both 11- and 14- residue peptaibols based on the disruption of the respective NRPS gene of T. reesei, and bioinformatic analysis of their amino acid activating domains and modules. The structures of these peptides may be predicted from the gene structures and have been confirmed by analysis of families of 11- and 14-residue peptaibols from the strain 618, termed hypojecorins A (23 sequences determined, 4 new) and B (3 new sequences), and the recently established trichovirins A from T. virens. The distribution of 11- and 14-residue products is strain-specific and depends on growth conditions as well. Possible mechanisms of module skipping are discussed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Modulating Transition Metal Reactivity with Force

The reactivity and selectivity of a transition metal catalyst is intimately related to its ligand-sphere geometry, and, in many cases, the ideal ligand geometry for one step of a catalytic cycle is poorly matched to the ideal ligand geometry for another. For this reason, methods for reversibly modulating ligand geometry on the time scale of catalytic turnover or monomer enchainment are highly desirable. Mechanical force represents a heretofore untapped approach to modulate catalyst geometry and/or reactivity, with the potential to do so on the timescale of catalytic turnover or monomer enchainment. Macroscopic mechanical forces are large, directional and localized to an extent that differentiates them from other forms of energy input such as heat or light. Here, in this Concept, we describe our efforts to address the fundamental challenges associated with force-modulated transition metal catalysis by employing molecular force probe ligands comprising a stiff stilbene photoswitch tethered to rotationally flexible biaryl bisphosphine ligand. Our efforts to date include the modulation of catalytic activity through force-mediated ligand perturbations, quantification of the force-coupled ligand effects on the energetics of elementary organometallic transformations, and evaluation of the mechanisms of force transduction in these systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Simulation of the impact of particle recycling on the plasma in MPS-LD device based on the BOUT++ LPD module

A linear plasma device (LPD) module has been developed under the BOUT++ framework to simulate plasma transport in the MPS-LD. However, previously, the LPD module used a simplistic neutral particle model that only includes particle density and velocity, which prevents the full understanding of the plasma-neutrals interactions. In this work, we further optimize the neutral model by using a more complete neutral fluid model containing the continuity equation, momentum equation, and energy equation. The reactions such as charge exchange, excitation, and radiation collisions are included. Since the neutral particle source is mainly provided by particle recycling from the target, a particle recycling model is employed, which includes both fast reflection and slow thermal release. The upgraded LPD module is applied to simulate the argon (Ar) discharge experiment of MPS-LD, and the benchmark against experiment measurement and SOLPS-ITER simulation results are presented. Good agreements are obtained, showing the validation of the upgraded module. After that, the impact of particle recycling on Ar plasma is investigated. It is found that a higher recycling coefficient (R) promotes the achievement of high-density plasma at the target. In conclusion, the recycled Ar atoms change target plasma pressure as well as plasma-neutral collisions, which both contribute to plasma momentum loss, thus promoting the rollover of ion flux to the target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Flexible‐rate optoelectronic wireless transmission system at 101 GHz using multiband CAP‐PAM modulation and envelope detection

Abstract In this paper, we have experimentally demonstrated the first flexible‐rate optoelectronic terahertz wireless transmission system at 101 GHz based on multiband CAP‐PAM modulation and cost‐efficient envelope detection. Instead of traditional M‐QAM mapping, PAM‐N mapping is used in CAP modulation with low‐computational complexity. The system performances and optimal capacity in both single‐band case and multiband case are intensively investigated. The results show that the highest data rate for single‐band system is 13.35 Gbit/s with CAP‐PAM‐5 modulation, while the optimum aggregate transmission line rate of 8.49 Gbit/s can be obtained with 4‐sub‐bands CAP‐PAM‐{5,3,2,2} modulation under 7% FEC limit of 3.8 × 10 −3 for four‐user access.

Zhang, Jiao↗
DOE OSTI2018

Investigating PID shunting in polycrystalline silicon modules via multiscale, multitechnique characterization

We investigated the potential-induced degradation (PID) shunting mechanism in multicrystalline-silicon photovoltaic modules by using a multiscale, multitechnique characterization approach. Both field-stressed modules and laboratory-stressed mini modules were studied. We used photoluminescence, electroluminescence, and dark lock-in thermography imaging to identify degraded areas at the module scale. Small samples were then removed from degraded areas, laser marked, and imaged by scanning electron microscopy. We used simultaneous electron-beam induced current imaging and focused ion beam milling to mark around PID shunts for chemical analysis by time-of-flight secondary-ion mass spectrometry or to isolate individual shunt defects for transmission electron microscopy and atom-probe tomography analysis. By spanning a range of 10 orders of magnitude in size, this approach enabled us to investigate the root-cause mechanisms for PID shunting. We observed a direct correlation between recombination active shunts and sodium content. The sodium content in shunted areas peaks at the SiNX/Si interface and is consistently observed at a concentration of 0.1% to 2% in shunted areas. Analysis of samples subjected to PID recovery, either activated by electron beam or thermal effects only, reveals that recovery of isolated shunts correlates with diffusion of sodium out of the structural defects to the silicon surface. We observed the role of oxygen and chlorine in PID shunting and found that those species - although sometimes present in structural defects where PID shunting was observed - do not play a consistent role in PID shunting.

14 SOLAR ENERGY↗
DOE OSTI2020

Linear viscoelastic characterization of electrically conductive adhesives used as interconnect in photovoltaic modules

Electrically conductive adhesives (ECAs) are incorporated into recent designs of photovoltaic (PV) modules and replace the traditional metallic solders as interconnects. This transition depicts a significant material change, and a proper understanding of the interconnects' mechanical response has not yet been established. However, such an understanding is necessary to (a) identify the driving forces for module degradation and failure, (b) allow for module design optimization, and (c) enable accurate lifetime predictions. This study summarizes the framework for the mechanical materials characterization and modeling of ECAs for PV applications. Only high-fidelity material models are able to capture the rate and temperature dependency of the ECA interconnect and allow for accurate modeling of the materials response. Furthermore, a linear viscoelastic representation is found to describe the mechanical response of the ECAs sufficiently well. The effects of curing conditions and environmental exposure are investigated, and material models for a variety of ECAs are reported and prepared for the use in numerical simulations. Overall, a finite element simulation of a generic submodel of a shingled cell module is used to highlight the need for high-fidelity material models and demonstrates the error made in the predicted stress states by using less sophisticated models.

14 SOLAR ENERGY↗
DOE OSTI2021

Influence of the Bulk Resistivity on Silicon Heterojunction Solar Cells and Module Reliability

Recent developments in industry on surface passivation open the possibility of using less doped substrates in silicon solar cells. In this report we investigate how the bulk resistivity affects the performance of silicon cells and the reliability of modules. Herein, n- and p-type silicon heterojunction cells with bulk resistivities between 3 and 15 000 Ωcm are studied. We measure the current–voltage characteristics of n-type cells across the resistivity range, and we find comparable responses to illumination intensities between 0.1 and 1 suns. The cells with bulk resistivities over 1000 Ωcm show breakdown voltages larger than -1000 V, almost two orders of magnitude higher than in typical commercial cells. Although modules have bypass-diodes to prevent cells from going into breakdown, higher breakdown voltages can improve the reliability of modules in case of bypass-diode failure and reduce the module cost by easing the number of bypass-diodes required. Finally, the cells have been submitted to light soaking. The float-zone p-type cells with bulk resistivities over 10 000 Ωcm are less sensitive to light-induced degradation than cells with bulk resistivities below 10 Ωcm. The former show to recover few hours after light soaking, while the latter recover only after dark annealing.

14 SOLAR ENERGY↗
DOE OSTI2025

Earth-scattering induced modulation in low-threshold dark matter experiments

Dark matter particles with sufficiently large interactions with ordinary matter can scatter in the Earth before reaching and scattering in a detector. This induces a modulation in the signal rate with a period of one sidereal day. We calculate this modulation for sub-GeV dark matter particles that interact either with a heavy or an ultralight dark-photon mediator and investigate the resulting signal in low-threshold detectors consisting of silicon, xenon, or argon targets. The scattering in the Earth is dominated by dark matter scatters off nuclei, while the signal in the detector is easiest to observe from dark matter scattering off electrons. We investigate the properties of the modulation signal and provide projections of the sensitivity of future experiments. We find that a search for a modulation signal can probe new regions of parameter space near the energy thresholds of current experiments, where the data are typically dominated by backgrounds.

Models for Dark Matter↗
DOE OSTI2018

Tritium Module for Calculating the Behavior of Tritium in a Loop of a Reactor Installation with Sodium Coolant

A description of the models and the results of tests of the Tritium module, which is intended for modeling the transport of tritium in the loops of fast reactors, are presented. The characteristics features of the module are alienability, functional relation with other modules of the code, and calculation of model coefficients as a function of the temperature of the coolant and surface of the loops. The module makes it possible to perform calculations of the behavior of tritium, including transport along loops, penetrability through the channel walls, run-off in a cold trap, and flow through leaks in the reactor installation.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗