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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

An algorithm to calculate a collapsed arc dose matrix in volumetric modulated arc therapy

Purpose: The delivery of volumetric modulated arc therapy (VMAT) is more complex than other conformal radiotherapy techniques. In this work, the authors present the feasibility of performing routine verification of VMAT delivery using a dose matrix measured by a gantry mounted 2D ion chamber array and corresponding dose matrix calculated by an inhouse developed algorithm.Methods: Pinnacle, v9.0, treatment planning system (TPS) was used in this study to generate VMAT plans for a 6 MV photon beam from an Elekta-Synergy linear accelerator. An algorithm was developed and implemented with inhouse computer code to calculate the dose matrix resulting from a VMAT arc in a plane perpendicular to the beam at isocenter. The algorithm was validated using measurement of standard patterns and clinical VMAT plans with a 2D ion chamber array. The clinical VMAT plans were also validated using ArcCHECK measurements. The measured and calculated dose matrices were compared using gamma ({gamma}) analysis with 3%/3 mm criteria and {gamma} tolerance of 1.Results: The dose matrix comparison of standard patterns has shown excellent agreement with the mean {gamma} pass rate 97.7 ({sigma}= 0.4)%. The validation of clinical VMAT plans using the dose matrix predicted by the algorithm and the corresponding measured dose matrices also showed good agreement with the mean {gamma} pass rate of 97.6 ({sigma}= 1.6)%. The validation of clinical VMAT plans using ArcCHECK measurements showed a mean pass rate of 95.6 ({sigma}= 1.8)%.Conclusions: The developed algorithm was shown to accurately predict the dose matrix, in a plane perpendicular to the beam, by considering all possible leaf trajectories in a VMAT delivery. This enables the verification of VMAT delivery using a 2D array detector mounted on a treatment head.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2019

Novel design and diagnostics improvements for increased production capacity and improved reliability at the Los Alamos Isotope Production Facility

The Isotope Production Facility (IPF) at Los Alamos National Laboratory (LANL) is used to produce an array of isotopes for medical, global security, and research applications with an intense beam of protons supplied by the linear accelerator at the Los Alamos Neutron Science Center (LANSCE). An Accelerator Improvement Project (AIP) was recently conducted at IPF to improve facility reliability and reduce programmatic risk while increasing general isotope production capacity and flexibility. This was accomplished through the installation of an improved beam window assembly, more robust beam diagnostics, an active and adjustable collimator, and a new beam rastering system. This paper will highlight the four exciting innovations and how they were designed, validated, and installed in parallel as well as the significant operational advantages they provide to IPF. Key experiments and the increased currents achieved in routine production runs demonstrating the enhanced capability from the AIP will be presented. As a result, the most notable capability enhancements include irradiations with beam currents ranging from 100 nA experimental runs up to 300 μA on routine production targets and utilization of a range of cylindrical target diameters.

100 MeV protons↗
NASA NTRS1979

Electromagnetic multipole fields of neutron stars

A formalism is developed for treating general multipole electromagnetic fields of neutron stars. The electric multipoles induced in a neutron star by its rotation with an arbitrary magnetic multipole at its center are presented. It is shown how to express a family of off-centered multipoles having the same l weight as an infinite array of centered multipoles of increasing l weight referred to the rotational axis. General expressions are given for the linear momentum present in the superposition of arbitrary multipole fields, and the results are combined to compute the radiation rate of linear momentum by an off-centered dipole to zeroth order in the parameter Omega x R/c. The general Deutsch (1955) solution is then rederived in a clear consistent manner, and some minor additions and corrections are provided.

Roberts, W. J.↗
NASA NTRS2004

Spitzer Instrument Pointing Frame (IPF) Kalman Filter Algorithm

This paper discusses the Spitzer Instrument Pointing Frame (IPF) Kalman Filter algorithm. The IPF Kalman filter is a high-order square-root iterated linearized Kalman filter, which is parametrized for calibrating the Spitzer Space Telescope focal plane and aligning the science instrument arrays with respect to the telescope boresight. The most stringent calibration requirement specifies knowledge of certain instrument pointing frames to an accuracy of 0.1 arcseconds, per-axis, 1-sigma relative to the Telescope Pointing Frame. In order to achieve this level of accuracy, the filter carries 37 states to estimate desired parameters while also correcting for expected systematic errors due to: (1) optical distortions, (2) scanning mirror scale-factor and misalignment, (3) frame alignment variations due to thermomechanical distortion, and (4) gyro bias and bias-drift in all axes. The resulting estimated pointing frames and calibration parameters are essential for supporting on-board precision pointing capability, in addition to end-to-end 'pixels on the sky' ground pointing reconstruction efforts.

calibration↗
NASA NTRS2015

Linear Mode HgCdTe Avalanche Photodiodes for Photon Counting Applications

An overview of recent improvements in the understanding and maturity of linear mode photon counting with HgCdTe electron-initiated avalanche photodiodes is presented. The first HgCdTe LMPC 2x8 format array fabricated in 2011 with 64 micron pitch was a remarkable success in terms of demonstrating a high single photon signal to noise ratio of 13.7 with an excess noise factor of 1.3-1.4, a 7 ns minimum time between events, and a broad spectral response extending from 0.4 micron to 4.2 micron. The main limitations were a greater than 10x higher false event rate than expected of greater than 1 MHz, a 5-7x lower than expected APD gain, and a photon detection efficiency of only 50% when greater than 60% was expected. This paper discusses the reasons behind these limitations and the implementation of their mitigations with new results.

HgCdTe↗
DOE OSTI2014

SU-E-T-135: Dosimetric Properties of the OCTAVIUS Detector 1500

Purpose: In this study the dosimetric properties of the Octavius Detector 1500 array (PTW-Freiburg-Germany) are investigated. Methods: The chambers of the array, each with an entrance window of 4.4 × 4.4 cm{sup 2}, are arranged in a checkerboard pattern in a measurement area of 27 × 27 cm{sup 2} with a sampling frequency of 0.1 mm{sup −1} along each row which can be doubled by merging two measurements shifted by 5 mm. Linearity, stability and output factors were measured with either a Semiflex 31013 or 31010 as a reference detector. Output factors were additionally measured with a Diode 60012. The effective point of measurement was determined by comparing TPR curves of the array with Roos chamber 34001 measurements. The lateral dose response function of a single chamber was determined by comparison with a high resolution diode. An IMRT field verification was carried out with a merged OD1500 measurement. Results: The OD1500 was stable within ±0.15 %. Deviations in linearity did not exceed 1% from 5 to 1000 MU. The effective point of measurement was 8.2 mm below the surface. Deviations in output factors were below 0.77 % from 5 × 5 to 27 × 27 cm{sup 2}. As expected for the smallest field of 1 × 1 cm{sup 2}, the deviation from the diode was significant. The widths of the lateral dose response functions were σ{sup 6} = (2.07 ± 0.03) mm and σ{sup 15} = (2.09 ± 0.03) mm. Gamma Index passing rates for typical IMRT and VMAT plans were above 90 % compared to film and TPS calculations for a local 3 mm / 3 % criterion. Conclusion: The first measurements with the OD1500 array show the excellent applicability of the array for clinical dosimetry. The response of the array to the mean photon energy and dose per pulse are under investigation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Characterization and calibration of compact array spectrometers in the ultraviolet spectral region

Array-based spectrometers, with their compact size, low weight, low cost, and fast measurement time, are now frequently used in place of both conventional single-channel scanning monochromators, and broadband meters. Their rapid measurement capability makes them an attractive option for routine solar UV spectral measurements, where shortterm variability in signal is a challenge. However, compactness, portability, low cost and high speed are achieved at the expense of the spectrometer's optical and electronic performance. Thus such spectrometers are more prone to measurement error from environmental changes, and more prone to other intrinsic sources of error such as stray light and detector non-linearity, which significantly affect solar UV measurements, than a scanning monochromator. The effects of stray light and non-linearity can be reduced either by improved optical and detector design or by a detailed spectrometer characterization. We present in this paper our investigation of the performance of three different commercial array spectrometers: two mini-spectrometers, and a more elaborate array spectrometer with an on-board image amplifier device. These were tested for a subset of performance parameters: their wavelength accuracy and stability, electronic linearity, responsivity linearity, stray light sensitivity, and mechanical stability and repeatability. With all three spectrometers we found that these parameters, particularly but not limited to stray light, had a significant impact on the measurement of the incoming optical radiation. This meant that, without characterization, the instruments would be unable to accurately measure the UV component of any source with significant visible radiation. We discuss various simple and low-cost solutions for improving the performance of these instruments, and providing a rigorous calibration using a straightforward set-up including optical filters and the quasi-monochromatic light from a double monochromator.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1990

Parallel asynchronous hardware implementation of image processing algorithms

Research is being carried out on hardware for a new approach to focal plane processing. The hardware involves silicon injection mode devices. These devices provide a natural basis for parallel asynchronous focal plane image preprocessing. The simplicity and novel properties of the devices would permit an independent analog processing channel to be dedicated to every pixel. A laminar architecture built from arrays of the devices would form a two-dimensional (2-D) array processor with a 2-D array of inputs located directly behind a focal plane detector array. A 2-D image data stream would propagate in neuron-like asynchronous pulse-coded form through the laminar processor. No multiplexing, digitization, or serial processing would occur in the preprocessing state. High performance is expected, based on pulse coding of input currents down to one picoampere with noise referred to input of about 10 femtoamperes. Linear pulse coding has been observed for input currents ranging up to seven orders of magnitude. Low power requirements suggest utility in space and in conjunction with very large arrays. Very low dark current and multispectral capability are possible because of hardware compatibility with the cryogenic environment of high performance detector arrays. The aforementioned hardware development effort is aimed at systems which would integrate image acquisition and image processing.

Coon, Darryl D.↗
DOE OSTI2013

Benchmark Modeling of the Near-Field and Far-Field Wave Effects of Wave Energy Arrays

This project is an industry-led partnership between Columbia Power Technologies and Oregon State University that will perform benchmark laboratory experiments and numerical modeling of the near-field and far-field impacts of wave scattering from an array of wave energy devices. These benchmark experimental observations will help to fill a gaping hole in our present knowledge of the near-field effects of multiple, floating wave energy converters and are a critical requirement for estimating the potential far-field environmental effects of wave energy arrays. The experiments will be performed at the Hinsdale Wave Research Laboratory (Oregon State University) and will utilize an array of newly developed Buoys' that are realistic, lab-scale floating power converters. The array of Buoys will be subjected to realistic, directional wave forcing (1:33 scale) that will approximate the expected conditions (waves and water depths) to be found off the Central Oregon Coast. Experimental observations will include comprehensive in-situ wave and current measurements as well as a suite of novel optical measurements. These new optical capabilities will include imaging of the 3D wave scattering using a binocular stereo camera system, as well as 3D device motion tracking using a newly acquired LED system. These observing systems will capture the 3D motion history of individual Buoys as well as resolve the 3D scattered wave field; thus resolving the constructive and destructive wave interference patterns produced by the array at high resolution. These data combined with the device motion tracking will provide necessary information for array design in order to balance array performance with the mitigation of far-field impacts. As a benchmark data set, these data will be an important resource for testing of models for wave/buoy interactions, buoy performance, and far-field effects on wave and current patterns due to the presence of arrays. Under the proposed project we will initiate high-resolution (fine scale, very near-field) fluid/structure interaction simulations of buoy motions, as well as array-scale, phase-resolving wave scattering simulations. These modeling efforts will utilize state-of-the-art research quality models, which have not yet been brought to bear on this complex problem of large array wave/structure interaction problem.

16 TIDAL AND WAVE POWER↗
NASA NTRS2009

Microstrip Antenna for Remote Sensing of Soil Moisture and Sea Surface Salinity

This compact, lightweight, dual-frequency antenna feed developed for future soil moisture and sea surface salinity (SSS) missions can benefit future soil and ocean studies by lowering mass, volume, and cost of the antenna system. It also allows for airborne soil moisture and salinity remote sensors operating on small aircraft. While microstrip antenna technology has been developed for radio communications, it has yet to be applied to combined radar and radiometer for Earth remote sensing. The antenna feed provides a key instrument element enabling high-resolution radiometric observations with large, deployable antennas. The design is based on the microstrip stacked-patch array (MSPA) used to feed a large, lightweight, deployable, rotating mesh antenna for spaceborne L-band (approximately equal to 1 GHz) passive and active sensing systems. The array consists of stacked patches to provide dual-frequency capability and suitable radiation patterns. The stacked-patch microstrip element was designed to cover the required L-band center frequencies at 1.26 GHz (lower patch) and 1.413 GHz (upper patch), with dual-linear polarization capabilities. The dimension of patches produces the required frequencies. To achieve excellent polarization isolation and control of antenna sidelobes for the MSPA, the orientation of each stacked-patch element within the array is optimized to reduce the cross-polarization. A specialized feed-distribution network was designed to achieve the required excitation amplitude and phase for each stacked-patch element.

Ramhat-Samii, Yahya↗
DOE OSTI2015

Development of an accurate EPID-based output measurement and dosimetric verification tool for electron beam therapy

Purpose: To develop an efficient and robust tool for output measurement and absolute dose verification of electron beam therapy by using a high spatial-resolution and high frame-rate amorphous silicon flat panel electronic portal imaging device (EPID). Methods: The dosimetric characteristics of the EPID, including saturation, linearity, and ghosting effect, were first investigated on a Varian Clinac 21EX accelerator. The response kernels of the individual pixels of the EPID to all available electron energies (6, 9, 12, 16, and 20 MeV) were calculated by using Monte Carlo (MC) simulations, which formed the basis to deconvolve an EPID raw images to the incident electron fluence map. The two-dimensional (2D) dose distribution at reference depths in water was obtained by using the constructed fluence map with a MC simulated pencil beam kernel with consideration of the geometric and structural information of the EPID. Output factor measurements were carried out with the EPID at a nominal source–surface distance of 100 cm for 2 × 2, 3 × 3, 6 × 6, 10 × 10, and 15 × 15 cm{sup 2} fields for all available electron energies, and the results were compared with that measured in a solid water phantom using film and a Farmer-type ion chamber. The dose distributions at a reference depth specific to each energy and the flatness and symmetry of the 10 × 10 cm{sup 2} electron beam were also measured using EPID, and the results were compared with ion chamber array and water scan measurements. Finally, three patient cases with various field sizes and irregular cutout shapes were also investigated. Results: EPID-measured dose changed linearly with the monitor units and showed little ghosting effect for dose rate up to 600 MU/min. The flatness and symmetry measured with the EPID were found to be consistent with ion chamber array and water scan measurements. The EPID-measured output factors for standard square fields of 2 × 2, 3 × 3, 6 × 6, 10 × 10, 15 × 15 cm{sup 2} agreed with film and ion chamber measurements. The average discrepancy between EPID and ion chamber/film measurements was 0.81% ± 0.60% (SD) and 1.34% ± 0.75%, respectively. For the three clinical cases, the difference in output between the EPID- and ion chamber array measured values was found to be 1.13% ± 0.11%, 0.54% ± 0.10%, and 0.74% ± 0.11%, respectively. Furthermore, the γ-index analysis showed an excellent agreement between the EPID- and ion chamber array measured dose distributions: 100% of the pixels passed the criteria of 3%/3 mm. When the γ-index was set to be 2%/2 mm, the pass rate was found to be 99.0% ± 0.07%, 98.2% ± 0.14%, and 100% for the three cases. Conclusions: The EPID dosimetry system developed in this work provides an accurate and reliable tool for routine output measurement and dosimetric verification of electron beam therapy. Coupled with its portability and ease of use, the proposed system promises to replace the current film-based approach for fast and reliable assessment of small and irregular electron field dosimetry.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2021

Polarimetric calibration of the Multi-Angle Imager for Aerosols (MAIA)

NASA’s Multi-Angle Imager for Aerosols (MAIA) mission, under development at the Jet Propulsion Laboratory, is designed to study the adverse health effects of different types of particulate air pollution. Planned for launch in 2023 for a 3-year mission, the MAIA satellite instrument will focus on a selected set of metropolitan target areas, where air quality monitors and health data are available. Aerosol concentration and speciation are inferred from multi-angle measurements of backscattered sunlight in 14 spectral bands from 350-2200 nm, with bands near 442, 645 and 1040 nm measuring the degree (DoLP) and angle of linear polarization (AoLP) in addition to radiance. The pushbroom camera has a ~240-km cross-track field of view with a nadir resolution of ~200 m, and is mounted onto a biaxial gimbal to provide along-track view angles within ±60°, to extend the field of regard to ±48°, and to view the instrument’s onboard calibrator (OBC) and dark target. The OBC consists of a sunlit transmissive diffuser, followed by 12 polarizers at different orientations. MAIA’s polarimetry is implemented using miniature wire grid polarizers on the focal plane array, and dual photoelastic modulators (PEMs) and achromatic quarter-wave plates to rapidly rotate the polarization. The resulting ~26-Hz intensity modulation encodes the linearly polarized and total radiance in each pixel, leaving the DoLP and AoLP insensitive to gain calibration. We report on the polarimetric calibration of the MAIA camera using a vacuum-compatible polarization state generator, consisting of a 1600W Xenon lamp, 12-inch integrating sphere, and rotating high-extinction polarizer. Mueller-matrix-based calibration coefficients for each detector pixel are derived from measurements at multiple polarizer angles, and are used to correct the measurements for instrumental polarization aberrations. Prior to flight, the calibrated MAIA camera is panned across the OBC to characterize its output, using uniform illumination with an irradiance similar to the Sun.

Werne, Thomas↗
DOE OSTI2018

Diagnostic and Power Feed Upgrades to the MAIZE Facility

The Michigan Accelerator for Inductive Z-pinch experiments (MAIZE) is a one stage, 1 MA, Linear Transformer Driver (LTD) at the University of Michigan. The MAIZE facility has been the site of various experimental studies, including wire array z-pinches for x-ray source development and cylindrical foil loads for implosion stability analysis. Here, in order to better understand and investigate these and other experiments, a 4- frame extreme ultraviolet (EUV) camera was implemented, the optical stability of a 12-frame laser shadowgraphy system was improved, B-dot probes were upgraded, and a Rogowski coil was constructed. New conical load hardware was also developed to reduce the inductance of the transmission line and thus improve the current delivered to the loads.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1980

Coaxial phased array antenna

A coaxial antenna array for communicating circularly polarized electromagnetic radiation is disclosed. A pair of open ended antenna cavities is coaxially constructed and operates by excitation of linear radiation elements arranged within each of the cavities. A pair of crossed dipole radiation devices is centered within the inner cavity and operated by means of a phase shifting network circuit to transmit as well as receive circularly polarized radiation. Four monopole radiation devices are symmetrically arranged to operate in the outer cavity in phase quadrature by means of the phase shifting network circuit to both transmit and receive circularly polarized electromagnetic radiation. Combined operation of the two antenna cavities with a 180 deg phase differential between the fields related to the two antenna cavities provides a broad beam, relatively wide frequency bandwidth communication capability. Particular embodiments disclosed feature a generally square cavity array as well as a circular cavity array.

Ellis, H., Jr.↗
NASA NTRS2002

Ideal Integrating Bolometer

We describe a new 'ideal integrator' bolometer as a prototype for a new generation of sensitive, flexible far-IR detectors suitable for use in large arrays. The combination of a non-dissipative sensor coupled with a fast heat switch provides breakthrough capabilities in both sensitivity and operation. The bolometer temperature varies linearly with the integrated infrared power incident on the detector, and may be sampled intermittently without loss of information between samples. The sample speed and consequent dynamic range depend only on the heat switch reset cycle and can be selected in software. Between samples, the device acts as an ideal integrator with noise significantly lower than resistive bolometers. Since there is no loss of information between samples, the device is well-suited for large arrays. A single SQUID readout could process an entire column of detectors, greatly reducing the complexity, power requirements, and cost of readout electronics for large pixel arrays.

Kogut, Alan↗
NASA NTRS2004

Ideal Integrating Bolometer

We describe a new "ideal integrator" bolometer as a prototype for a new generation of sensitive, flexible far-IR detectors suitable for use in large arrays. The combination of a non-dissipative sensor coupled with a fast heat switch provides breakthrough capabilities in both sensitivity and operation. The bolometer temperature varies linearly with the integrated infrared power incident on the detector, and may be sampled intermittently without loss of information between samples. The sample speed and consequent dynamic range depend only on the heat switch reset cycle and can be selected in software. Between samples, the device acts as an ideal integrator with noise significantly lower than resistive bolometers. Since there is no loss of information between samples, the device is well-suited for large arrays. A single SQUID readout could process an entire column of detectors, greatly reducing the complexity, power requirements, and cost of readout electronics for large pixel arrays.

Kogut, A.↗
DOE OSTI2022

Anatomy of Protein Electrospray Ionization Mass Spectra by Superconducting Tunnel Junction Mass and Energy Spectrometry

Cryogenic superconducting tunnel junction (STJ) detectors have the advantage of single-particle sensitivity, high quantum efficiency, low noise, and the ability to detect the time and relative impact energy of deposited ions. This makes them attractive for use in mass spectrometry (MS) and as a form of energy spectrometry. STJ cryodetectors have been coupled to time-offlight (TOF) mass spectrometers equipped with a matrix-assisted laser desorption ionization (MALDI) source and to an electrospray ionization (ESI) TOF mass spectrometer. Here, a lab-made linear ion trap (LIT) mass spectrometer system was coupled to an ESI source and a 16-channel Nb-STJ array with improved readout electronics. The goal was to investigate fundamentals of ESI-generated protein ions by further exploiting the advantage of resolving these ions in a third dimension of the relative energy deposited into the STJs. The proteins equine cytochrome c, bovine carbonic anhydrase, bovine serum albumin, and murine immunoglobulin G were studied using this ESI-LIT-STJ-MS instrument. Multiply charged monomers, multimers, and fragments from metastable ions were resolved from monomer peaks by differences in ion deposition energy even when these ions have the same mass-to-charge ratio as the corresponding monomer. The determination of fragment mass from metastable decomposition is accomplished without knowing the charge state of the fragment. The average charge state of the multimers is reduced with each addition of a protein which is a direct reflection of the surface area available for charging. Multiply charged in-source fragments have also been observed and distinguished in the mass spectrum of carbonic anhydrase by using the differences in the energy deposited in the STJs.

42 ENGINEERING↗
DOE OSTI2011

Superfluidity of Bose-Einstein condensates in toroidal traps with nonlinear lattices

Superfluid properties of Bose-Einstein condensates (BEC) in toroidal quasi-one-dimensional traps are investigated in the presence of periodic scattering length modulations along the ring. The existence of several types of stable periodic waves, ranging from almost uniform to very fragmented chains of weakly interacting and equally spaced solitons, is demonstrated. We show that these waves may support persistent atomic currents and sound waves with spectra of Bogoliubov type. Fragmented condensates can be viewed as arrays of Josephson junctions and the current as a BEC manifestation of the dc-Josephson effect. The influence of linear defects on BEC superfluidity has been also investigated. We found that for subcritical velocities, linear defects that are static with respect to the lattice (while the condensate moves in respect to both the optical lattice and the defect) preserve the BEC superfluidity.

74 ATOMIC AND MOLECULAR PHYSICS↗