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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 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effect of the Enhanced Breakdown Strength in Plasma-Filled Optical System of Electron Beam Formation

The article presents recent results of the dramatically enhanced electric breakdown strength observed in the accelerating gap of a plasma-filled optical system for the formation and focusing of a wide-aperture pulsed electron beams with currents up to 80 A and energies up to 35 keV. This system is a plasma-optical diode type device in which the acceleration and formation of the electron beam occurs in the double layer between the emissive surface of the plasma cathode (electron emitter) stabilized by a fine mesh grid and the open surface of the anode plasma. The anode plasma is created by the toroidal plasma generator of original design based on the ion source with closed drift of electrons with an anode layer.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

A spin light emitting diode incorporating ability of electrical helicity switching

Fabrication and optical characteristics of a spin light-emitting-diode (spin-LED) having dual spin-injection electrodes with anti-parallel magnetization configuration are reported. Alternating a current between the two electrodes using a computer-driven current source has led us to the observation of helicity switching of circular polarization at the frequency of 1 kHz. Neither external magnetic fields nor optical delay modulators were used. Sending dc-currents to both electrodes with appropriate ratio has resulted in continuous variation of circular polarization between the two opposite helicity, including the null polarization. These results suggest that the tested spin-LED has the feasibility of a monolithic light source whose circular polarization can be switched or continuously tuned all electrically.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Ground state study of the thin ferromagnetic nano-islands for artificial spin ice arrays

In this work, we used numerical simulations to study the magnetic ground state of the thin elongated (elliptical) ferromagnetic nano-islands made of Permalloy. In these systems, the effects of demagnetization of dipolar source generate a strong magnetic anisotropy due to particle shape, defining two fundamental magnetic ground state configurations—vortex or type C. To describe the system, we considered a model Hamiltonian in which the magnetic moments interact through exchange and dipolar potentials. We studied the competition between the vortex states and aligned states—type C—as a function of the shape of each elliptical nano-islands and constructed a phase diagram vortex—type C state. Our results show that it is possible to obtain the elongated nano-islands in the C-state with aspect ratios less than 2, which is interesting from the technological point of view because it will be possible to use smaller islands in spin ice arrays. Generally, the experimental spin ice arrangements are made with quite elongated particles with aspect ratio approximately 3 to ensure the C-state.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Compact spherical neutron polarimeter using high-T{sub c} YBCO films

We describe a simple, compact device for spherical neutron polarimetry measurements at small neutron scattering angles. The device consists of a sample chamber with very low (<0.01 G) magnetic field flanked by regions within which the neutron polarization can be manipulated in a controlled manner. This allows any selected initial and final polarization direction of the neutrons to be obtained. We have constructed a prototype device using high-T{sub c} superconducting films and mu-metal to isolate regions with different magnetic fields and tested device performance in transmission geometry. Finite-element methods were used to simulate the device’s field profile and these have been verified by experiment using a small solenoid as a test sample. Measurements are reported using both monochromatic and polychromatic neutron sources. The results show that the device is capable of extracting sample information and distinguishing small angular variations of the sample magnetic field. As a more realistic test, we present results on the characterization of a 10 μm thick Permalloy film in zero magnetic field, as well as its response to an external magnetic field.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Advances in plasma–wall interaction control for H-mode operation over 100 s with ITER-like tungsten divertor on EAST

A total power injection up to 0.3 GJ has been achieved in EAST long pulse H-mode operation of 101.2 s with an ITER-like water-cooled tungsten (W) mono-block divertor, which has steady-state power exhaust capability of 10 MWm –2 . The peak temperature of W target saturated at 12 s to the value T ~ 500 °C with a heat flux ~3.3 MW m –2 being maintained during the discharge. By tailoring the 3D divertor plasma footprint through edge magnetic topology change, the heat load was broadly dispersed and thus peak heat flux and W sputtering were well controlled. Active feedback control of H-mode detachment with D 2 fuelling or divertor impurity seeding has been achieved successfully, with excellent compatibility with the core plasma performance. Active feedback control of radiative power utilizing neon seeding was achieved with f rad = 18%–41% in H-mode operation, exhibiting potential for heat flux reduction with divertor and edge radiation. This has been further demonstrated in DIII-D high β P H-mode scenario within the joint DIII-D/EAST experiment using impurity seeding from the divertor volume. Steady-state particle control and impurity exhaust has been achieved for long pulse H-mode operation over 100 s with the W divertor by leveraging the effect of drifts and optimized divertor configuration, coupled with strong pumping and extensive wall conditioning. Methods toward the reduction of divertor W sourcing, which is of crucial importance for a metal-wall tokamak, are also explored. These advances provide vital experimental information on favourable core-edge integration for high power, long-pulse H-mode operation in EAST, ITER and CFETR.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Figure-of-Merit for a Cold Coupled Moderator at the SNS Second Target Station suited for Direct Geometry Inelastic Spectrometers

The suite of moderators for the Second Target Station (STS) at the Spallation Neutron Source (SNS) in Oak Ridge is currently undergoing the planning stage at which various options and configurations are being considered. The current plans for the instrument suite include two direct geometry inelastic spectrometers, CHESS and HERTZ, which will receive beam from cold moderators and work mostly in the 1-20 meV incident energy range. CHESS will be a relatively short (wide bandwidth) instrument that is dedicated to studying small samples (∼mm3) with coarse energy resolution (2.5 – 5% of Ei). HERTZ on the other hand will be designed to achieve very good energy resolution, 1 – 3% of Ei, using a long secondary flightpath with a ∼ 4 × 4 cm2 beam on sample. In this contribution, we will discuss the implications of these design requirements for the optimal moderator pulse width, and for the repetition rate that would be best suited for the spectrometers.

Ehlers, Georg↗
DOE OSTI2020

A Plug-and-Play Design Suite of Converters for the Electric Grid

Power electronic (PE) systems are increasingly being integrated into the electric grid in a distributed fashion. As the number of installations increases, the challenge of integration of these systems into the grid is also growing. Advanced control features of these systems are often overlooked or neglected due to the complex nature and novelty of these systems. This is also complicated from the vendor point of view as different converter topology integration is usually composed of single system designs with tight coupling and configurations. The presented work discusses a novel architecture for the integration of PE systems with other sources and loads to create a coordinated controllable resource for the grid. The presented work also describes a system level controller to coordinate these systems. 1 Testing results on a hardware in the loop (HIL) platform are provided to show the validity of the proposed architecture and framework.

Starke, Michael↗
DOE OSTI2021

Improved Localization Precision and Angular Resolution of a Cylindrical, Time-Encoded Imaging System From Adaptive Detector Movements

To the first order, the localization precision and angular resolution of a cylindrical, time-encoded imaging (c-TEI) system is governed by the geometry of the system. Improving either measure requires increasing the mask radius or decreasing the detector diameter, both of which are undesirable. Here, we propose an alternative option of repositioning the detector within the mask to increase the detector-to-mask distance in the direction of a source, thereby improving the localization precision and angular resolution in that direction. Since the detector-to-mask distance only increases for a small portion of the field of view (FOV), we propose implementing adaptive imaging where one leverages data collected during the measurement to optimize the system configuration. This article utilizes both simulations and experiments to set upper bounds on the potential gain from adaptive detector movements for one and two sources in the FOV. When only one source is present, adaptive detector movements can improve the localization precision and angular resolution by 20% for a source at 90 cm and by 32% for a far-field source. When two sources are present, adaptive detector movements can improve localization precision and angular resolution by up to 50% for sources that are ~10° apart (90 cm from the system). We experimentally verify these results through maximum likelihood estimation of the source position(s) and image reconstruction of point sources that are close together. As a demonstration of an adaptive imaging algorithm, we image a complex arrangement of special nuclear material at the Zero Power Physics Reactor facility at Idaho National Laboratory.

46 - INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AN↗
DOE OSTI2014

SU-E-T-631: Commissioning and Comprehensive Evaluation of the ArcCHECK Cylindrical Diode Array for VMAT QA

Purpose: Commissioning and comprehensive evaluation of ArcCHECK phantom for dosimetry of VMAT QA, using 6MV photon beam with and without the flattening filter. Methods: ArcCHECK was evaluated for response dependency on linac dose rate, instantaneous dose rate, radiation field size, beam angle and couch insertion. Scatter dose characterization, consistency and symmetry of response, dosimetric accuracy of fixed aperture arcs and clinical VMAT plans were investigated. Measurements were done using TrueBeam™ STx accelerator (Console version 1.6) with a 6 MV beam with and without flattening filter. Reference dose-grids were calculated using Eclipse TPS Analytical Anisotropic Algorithm (AAA version 10.0.39). Planned doses were calculated using symmetric 2mm 3D dose grids with 4 degree angular resolution defaulted to each control point. Gamma evaluations were performed in absolute dose mode, with default normalization to maximum dose in the curved plane and a low dose threshold of 10% to restrict the analysis to clinically relevant areas. Global and local gamma indices at 3mm/3% and 2mm/2% level were computed using SNC software (version 6.0). Results: Results of gamma analysis demonstrated an overall agreement between ArcCHECK measured and TPS calculated reference doses. Field size dependency was within 0.5% of the reference. Dose-rate based dependency was well within 1% of the TPS reference and the angular dependency was ±3% of the reference, as tested for BEV angles. At the level of 3%/3mm, narrow and wide open arcs as well as clinical VMAT cases demonstrated high level of dosimetry accuracy in global gamma passing rates for both 6X and 6F beams. At the level of 2%/2mm two VMAT cases involving the narrow heavily modulated arcs demonstrated lower passing rates. Conclusion: ArcCHECK phantom with latest software and hardware upgrades is suitable for VMAT QA. For higher sensitivity of 2%/2mm gamma analysis, we intend to use it as one of the VMAT QA evaluation metrics.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2020

Computation of graph hitting time moments; Chapel code implementation.

The project that developed this is unclassified, with the mandate to produce open source code. This code computes the hitting time moments of a graph using a linear algebra configuration. The goal of this work is to explore the performance capabilities of the Chapel programming language. Toward that end, we generate random adjacency matrices which represent a random graph. The code can also read in an adjacency matrix from a file. The main computation is the Conjugate Gradient method.SAND2020-12651 M. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Barrett, Richard↗
DOE OSTI2019

Ongoing solution reproducibility of earth system models as they progress toward exascale computing

We present a methodology for solution reproducibility for the Energy Exascale Earth System Model during its ongoing software infrastructure development to prepare for exascale computers. The nonlinear chaotic nature of climate system simulations precludes traditional model verification approaches since machine precision differences—resulting from code refactoring, changes in software environment, and so on—grow exponentially to a different weather state. Here, we leverage the nature of climate as a statistical description of the atmosphere in order to establish model reproducibility. We evaluate the degree to which two-sample equality of distribution tests can confidently detect the change in climate from minor tuning parameter changes on model output variables in order to establish the level of difference that indicates a new climate. To apply this (baselined test), we target a section of the model’s development cycle wherein no intentional science changes have been applied to its source code. We compare an ensemble of short simulations that were conducted using a verified model configuration against a new ensemble with the same configuration but with the latest software infrastructure (Common Infrastructure for Modeling the Earth, CIME5.0), compiler versions, and software libraries. We also compare these against ensemble simulations conducted using the original version of the software infrastructure (CIME4.0) of the earlier model configuration, but with the latest compilers and software libraries, to test the impact of new compilers and libraries in isolation from additional software infrastructure. The two-sample equality of distribution tests indicates that these ensembles indeed represent the same climate.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Performance Optimization of the IOTA Duoplasmatron Proton Source

We present results from online optimization studies of a duoplasmatron ion source designed to produce 50~keV protons for acceleration to 2.5~MeV and subsequent injection into the Integrable Optics Test Accelerator (IOTA) at Fermilab. Using a Bayesian exploration technique, we developed multi-parameter models of the source s proton current and employed these models to optimize its performance. Depending on the spectrometer configuration used to isolate the proton beam and the chosen optimization objective, we identified three candidate operating points, achieving normalized 50~\% emittances between 0.57 and 1.3~\textmu m and a maximum proton current of $14.5 \pm 0.6$~mA.

Banerjee, Nilanjan [Fermilab] (ORCID:0000000344660↗
DOE OSTI2022

Characterization of Low Gain Avalanche Detector Prototypes’ Response to Gamma Radiation

Motivated by the need for fast timing detectors to withstand up to 2 MGy of ionizing dose at the High Luminosity Large Hadron Collider, prototype low gain avalanche detectors (LGADs) have been fabricated in a single pad configuration, 2 × 2 arrays, and related p-i-n diodes, and exposed to Co-60 sources for study. Devices were fabricated with a range of dopant layer concentrations, and for the arrays, a variety of inter-pad distances and distances from the active area to the edge. Measurements of capacitance versus voltage and leakage current versus voltage have been made to compare pre- and post-irradiation characteristics in gain layer depletion voltage, full bulk depletion voltage, and breakdown voltage. Conclusions are drawn regarding the effects of the gammas on both surface and interface states and on their contribution to acceptor removal through non-ionizing energy loss from Compton electrons or photoelectrons. Comparison of the performances of members of the set of devices can be used to optimize gain layer parameters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1971

Precision calibration and reference voltage source for data acquisition systems

Hybrid integrated circuit operational amplifiers, which have inherent characteristics of low quiescent power dissipation and extended operational lifetime with high reliability, are source for digital systems. Amplifiers are coupled to Zener reference diode in current control and buffer configuration.

Source record↗
NASA NTRS1979

Jupiter's rings

Voyager 2 observations of the jovian ring system discovered by Voyager 1 are presented. The rings were observed both above and below the jovian equatorial plane and at extremely low and high phase angles. This ring system seems to represent a steady state configuration for small particles that are slowly moving in toward Jupiter. It must be resupplied from sources well outside Roche's limit.

Owen, T.↗
NASA NTRS1980

The Build System - Integration and management of large software avionic systems

The Build System comprises the software tools and procedures creating the flight memory load for the Space Shuttle Backup Flight System. The system has six functions: (1) configuration management, which insures that the memory load contains the proper modules, all clearly marked; (2) source translation, which translates the source code into a relocatable machine code; (3) module integration, which combines and assigns memory locations to all the object modules produced in source translation; (4) static code analysis, which verifies the integration process; (5) deliverables generation, which yields release documentation and deliverable items; and (6) release maintenance, which controls all system patches subsequent to release. Further developments will include more automation in the producing of patches from source-code updates and system requirements for tracking.

Mayer, J. T. B.↗
NASA NTRS1986

Pulse Code Modulation (PCM) data storage and analysis using a microcomputer

The current widespread use of microcomputers has led to the creation of some very low-cost instrumentation. A Pulse Code Modulation (PCM) storage device/data analyzer -- a peripheral plug-in board especially constructed to enable a personal computer to store and analyze data from a PCM source -- was designed and built for use on the NASA Sounding Rocket Program for PMC encoder configuration and testing. This board and custom-written software turns a computer into a snapshot PCM decommutator which will accept and store many hundreds or thousands of PCM telemetry data frames, then sift through them repeatedly. These data can be converted to any number base and displayed, examined for any bit dropouts or changes (in particular, words or frames), graphically plotted, or statistically analyzed.

Massey, D. E.↗