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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 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Soft X-ray line profiles in the impulsive phase of electron-heated solar flares

Using a model of the hydrodynamic response of a flare loop to energy input in the form of a nonthermal electron beam, the predicted line profile of the Ca XIX resonance line at 3.177 A is computed. The results are compared with observations and are shown to generally agree, both qualitatively and quantitatively, with these observations. The model does, however, predict an overall blueshift in the line profile, a result which differs with earlier interpretations of the observations, and which remains to be tested by absolutely calibrated measurements of the Ca XIX spectrum. It is concluded that electron-heated models of solar flares quite naturally predict the observed features in the Ca XIX line profile, without the need to introduce nonthermal motions or an artificial division of the flare plasma into two distinct components, as suggested by previous authors.

Emslie, Gordon A.↗
DOE OSTI2014

SU-E-T-441: Comparison of Dose Distributions for Spot-Scanned Pencil-Beam and Scattered-Beam Proton Treatments of Ocular Tumors

Purpose: To study the cross-field and depth dose profiles of spot-scanned pencil beam configurations for the treatment of ocular tumors and to compare their performance to a simulated scattered beam. Methods: Dose distributions in a cubic water phantom were compared for beams that passed through a final 24mm diameter aperture to deposit maximum dose at 2.4cm depth. The pencil-beam spots formed a hexagonally-packed ring with a center-to-center spacing of 4mm. The protons exited the nozzle with energy 95.5MeV, traversed a 4.5cm water-equivalent range shifter, and travelled either 42.5cm or 100cm to the phantom surface. The aperture-to-phantom distance (APD) was 5.7cm to allow room for eye-tracking hardware. A configuration with APD=0 was also tested. The scattered beam was generated with energy 159MeV, passed through 127mm of Lexan, exited the final aperture, and travelled 5.7cm to the phantom surface. This latter configuration is comparable to the MGH single scattered beamline. All beams were modelled with TOPAS1.0-beta6 compiled with GEANT4.9.6p2. Results: The modeled scattered beam produced a distal fall-off along the central axis of zd90%-zd10%=3.6mm. For the pencil beam, the zd90%-zd10% was 1.6mm in all configurations. The scattered beam's cross-field penumbra at depth of maximum dose was r90%- r10%=1.9mm. For the spot-scanned configuration with the range-shifter-tophantom distance (RsPD) of 100cm, similar cross-field profiles were achieved with r90%-r10%=2.0mm. At shorter RsPD of 42.5cm, the crossfield penumbras were 5.6mm and 7.7mm for APD=0cm and APD=5.7cm, respectively. Conclusion: For proton treatments employing a range shifter, the cross-field and central axis dose profiles depend on the quality of the original beam, the size of the range shifter, the distance from the range shifter exit to the patient, and the distance from the final aperture to the patient. A spot-scanned pencil beam configuration can achieve cross-field penumbras equal to a scattered beam and superior distal gradients.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Nonlinear Dynamics and Phase Space Manipulations of High-Brightness Beams

The project consisted of two main tasks. Each task had several specific aims. The three main objectives of Task 1 were: 1. Investigation of the flat beam technique to produce high transverse emittance ratio longitudinally-compressed bunches, 2. Exploration of a new chicane-like transverse-to-longitudinal phase space exchanger for precise pulse shaping and emittance exchange, 3. Applications of flat-beam with shaped current profile(s) to dielectric wakefield acceleration in an asymmetric waveguide. The outcome of our research was to performed details simulations of flat-beam generation and compression. Some preliminary experiment on flat-beam generation and compression were conducted at the FAST-IOTA injector in parallel to commissioning activities. Likewise, the longitudinal phase-space transformation was not fully explored; we participated in experiments conducted at the Argonne Wakefield Accelerator and especially introduced a simple transverse-shaping technique.

43 PARTICLE ACCELERATORS↗
NASA NTRS2006

Improved Hurricane Boundary Layer Observations with the Imaging Wind and Rain Airborne Profiler

During the NOAA/NESDIS 2005 Hurricane Season (HS2005) and the 2006 Winter Experiment, the University of Massachusetts (UMass) installed two instruments on the NOAA N42RF WP-3D research aircraft: the Imaging Wind and Rain Airborne Profiler (IWRAP) and the Simultaneous Frequency Microwave Radiometer (SFMR). IWRAP is a dual-band (C- and Ku), dual-polarized pencil-beam airborne radar that profiles the volume backscatter and Doppler velocity from rain and that also measures the ocean backscatter response. It simultaneously profiles along four separate incidence angles while conically scanning at 60 RPM. SFMR is a C-band nadir viewing radiometer that measures the emission from the ocean surface and intervening atmosphere simultaneously at six frequencies. It is designed to obtain the surface wind speed and the column average rain rate. Both instruments have previously been flown during the 2002, 2003 and 2004 hurricane seasons. For the HS2005, the IWRAP system was modified to implement a raw data acquisition system. The importance of the raw data system arises when trying to profile the atmosphere all the way down to the surface with a non-nadir looking radar system. With this particular geometry, problems arise mainly from the fact that both rain and ocean provide a return echo coincident in time through the antenna s main lobe. This paper shows how this limitation has been removed and presents initial results demonstrating its new capabilities to derive the atmospheric boundary layer (ABL) wind field within the inner core of hurricanes to much lower altitudes than the ones the original system was capable of, and to analyze the spectral response of the ocean backscatter and the rain under different wind and rain conditions.

tropical cyclones↗
DOE OSTI2016

WE-AB-207A-12: HLCC Based Quantitative Evaluation Method of Image Artifact in Dental CBCT

Purpose: Image artifacts are usually evaluated qualitatively via visual observation of the reconstructed images, which is susceptible to subjective factors due to the lack of an objective evaluation criterion. In this work, we propose a Helgason-Ludwig consistency condition (HLCC) based evaluation method to quantify the severity level of different image artifacts in dental CBCT. Methods: Our evaluation method consists of four step: 1) Acquire Cone beam CT(CBCT) projection; 2) Convert 3D CBCT projection to fan-beam projection by extracting its central plane projection; 3) Convert fan-beam projection to parallel-beam projection utilizing sinogram-based rebinning algorithm or detail-based rebinning algorithm; 4) Obtain HLCC profile by integrating parallel-beam projection per view and calculate wave percentage and variance of the HLCC profile, which can be used to describe the severity level of image artifacts. Results: Several sets of dental CBCT projections containing only one type of artifact (i.e. geometry, scatter, beam hardening, lag and noise artifact), were simulated using gDRR, a GPU tool developed for efficient, accurate, and realistic simulation of CBCT Projections. These simulated CBCT projections were used to test our proposed method. HLCC profile wave percentage and variance induced by geometry distortion are about 3∼21 times and 16∼393 times as large as that of the artifact-free projection, respectively. The increase factor of wave percentage and variance are 6 and133 times for beam hardening, 19 and 1184 times for scatter, and 4 and16 times for lag artifacts, respectively. In contrast, for noisy projection the wave percentage, variance and inconsistency level are almost the same with those of the noise-free one. Conclusion: We have proposed a quantitative evaluation method of image artifact based on HLCC theory. According to our simulation results, the severity of different artifact types is found to be in a following order: Scatter>Geometry>Beam hardening>Lag>Noise>Artifact-free in dental CBCT.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1992

The kinematics of the molecular gas in Centaurus A

The CO (2-1) emission along the inner dust lane of Centaurus A, observed with the Caltech Submillimeter Observatory on Mauna Kea, shows the molecular gas to be in a thin disk, with a velocity dispersion of only about 10 km/s. The observed line profiles are broadened considerably due to beam smearing of the gas velocity field. The profile shapes are inconsistent with planar circular and noncircular motion. However, a warped disk in a prolate potential provides a good fit to the profile shapes. The morphology and kinematics of the molecular gas is similar to that of the ionized material, seen in H-alpha. The best-fitting warped disk model not only matches the optical appearance of the dust lane but also agrees with the large-scale map of the CO emission and is consistent with H I measurements at larger radii.

Quillen, A. C.↗
DOE OSTI2010

Perveance and ion bunch structure from a 'compact, high-pressure' laser ion source

The Dublin City University (DCU) laser ion source (LIS) is a 'compact high-pressure' laser ion source utilizing a table top Q-switched laser. The DCU-LIS combines high laser fluence (F>4 kJ cm{sup -2}), high laser intensity (I>10{sup 11} W cm{sup -2}) with a short field free region (L=48 mm) and high source potential (V{sub ext}>40 kV) in order to offset recombination losses within the plasma and maximize the proportion of highly charged ions which are extracted from the plasma plume. Such a configuration also provides high peak currents (I{sub p}>3 mA), high current densities (J>5 mA cm{sup -2}), and high charge states (Cu{sup 6+}) in the extracted ion-bunch train. However, to obtain and utilize these parameter values in a high pressure LIS requires characterization and control of a number of processes related to ion dynamics and space charge effects on the extracted ions at the plasma plume-anode-extraction gap interface. Relevant issues include electric field distortion, Debye shielding, beam divergence, overfocusing, and perveance (P) in addition to current density profiles for the extracted ion beam. In this paper we focus on these issues and their impact on charge particle extraction and acceleration with a view to elucidating the parameter regimes within which the DCU-LIS performance envelope is optimal.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Reflection of light beams from a chirped dielectric plane-layered structure

The reflection of light beams with various widths of the angular spectrum from a chirped plane-layered dielectric structure is numerically studied. For wide beams, the total lateral shift of the reflected beam depends on the position of the photonic barrier inside the structure and the value of the Goos – Hänchen shift. For narrow beams, the region of the interaction with the structure increases, the profile broadens and the reflected beam wavefront becomes phase modulated. It is shown that the light reflected from a quasi-periodic structure with negative spatial dispersion undergoes focusing. (light beams)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Calculation of the transverse kicks generated by the bends of a hollow electron lens

Electron lenses are pulsed, magnetically confined electron beams whose current-density profile is shaped to obtain the desired effect on the circulating beam in high-energy accelerators. They were used in the Fermilab Tevatron collider for abort-gap clearing, beam-beam compensation, and halo scraping. A beam-beam compensation scheme based upon electron lenses is currently being implemented in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. This work is in support of a conceptual design of hollow electron beam scraper for the Large Hadron Collider. It also applies to the implementation of nonlinear integrable optics with electron lenses in the Integrable Optics Test Accelerator at Fermilab. We consider the axial asymmetries of the electron beam caused by the bends that are used to inject electrons into the interaction region and to extract them. A distribution of electron macroparticles is deposited on a discrete grid enclosed in a conducting pipe. The electrostatic potential and electric fields are calculated using numerical Poisson solvers. The kicks experienced by the circulating beam are estimated by integrating the electric fields over straight trajectories. These kicks are also provided in the form of interpolated analytical symplectic maps for numerical tracking simulations, which are needed to estimate the effects of the electron lens imperfections on proton lifetimes, emittance growth, and dynamic aperture. We outline a general procedure to calculate the magnitude of the transverse proton kicks, which can then be generalized, if needed, to include further refinements such as the space-charge evolution of the electron beam, magnetic fields generated by the electron current, and longitudinal proton dynamics.

Stancari, Giulio↗
DOE OSTI2014

Electron Lenses for the Large Hadron Collider

Electron lenses are pulsed, magnetically confined electron beams whose current-density profile is shaped to obtain the desired effect on the circulating beam. Electron lenses were used in the Fermilab Tevatron collider for bunch-by-bunch compensation of long-range beam-beam tune shifts, for removal of uncaptured particles in the abort gap, for preliminary experiments on head-on beam-beam compensation, and for the demonstration of halo scraping with hollow electron beams. Electron lenses for beam-beam compensation are being commissioned in RHIC at BNL. Within the US LHC Accelerator Research Program and the European HiLumi LHC Design Study, hollow electron beam collimation was studied as an option to complement the collimation system for the LHC upgrades. This project is moving towards a technical design in 2014, with the goal to build the devices in 2015-2017, after resuming LHC operations and re-assessing needs and requirements at 6.5 TeV. Because of their electric charge and the absence of materials close to the proton beam, electron lenses may also provide an alternative to wires for long-range beam-beam compensation in LHC luminosity upgrade scenarios with small crossing angles.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Applications of electron lenses: scraping of high-power beams, beam-beam compensation, and nonlinear optics

Electron lenses are pulsed, magnetically confined electron beams whose current-density profile is shaped to obtain the desired effect on the circulating beam. Electron lenses were used in the Fermilab Tevatron collider for bunch-by-bunch compensation of long-range beam-beam tune shifts, for removal of uncaptured particles in the abort gap, for preliminary experiments on head-on beam-beam compensation, and for the demonstration of halo scraping with hollow electron beams. Electron lenses for beam-beam compensation are being commissioned in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). Hollow electron beam collimation and halo control were studied as an option to complement the collimation system for the upgrades of the Large Hadron Collider (LHC) at CERN; a conceptual design was recently completed. Because of their electric charge and the absence of materials close to the proton beam, electron lenses may also provide an alternative to wires for long-range beam-beam compensation in LHC luminosity upgrade scenarios with small crossing angles. At Fermilab, we are planning to install an electron lens in the Integrable Optics Test Accelerator (IOTA, a 40-m ring for 150-MeV electrons) as one of the proof-of-principle implementations of nonlinear integrable optics to achieve large tune spreads and more stable beams without loss of dynamic aperture.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

2D Optical Streaking for Ultra-Short Electron Beam Diagnostics

We propose a novel approach to measure short electron bunch profiles at micrometer level. Low energy electrons generated during beam-gas ionization are simultaneously modulated by the transverse electric field of a circularly-polarized laser, and then they are collected at a downstream screen where the angular modulation is converted to a circular shape. The longitudinal bunch profile is simply represented by the angular distribution of the electrons on the screen. We only need to know the laser wavelength for calibration and there is no phase synchronization problem. Meanwhile the required laser power is also relatively low in this setup. Some simulations examples and experimental consideration of this method are discussed. At Linac Coherent Light Source (LCLS), an S-band RF transverse deflector (TCAV) is used to measure the bunch length with a resolution 10 femtosecond (fs) rms. An X-band deflector (wavelength 2.6cm) is proposed recently to improve the resolution. However, at the low charge operation mode (20pC), the pulse length can be as short as fs. It is very challenging to measure femtosecond and sub-femtosecond level bunch length. One of the methods is switching from RF to {mu}m level wavelength laser to deflect the bunch. A powerful laser ({approx}10s GW) is required to deflect such a high energy beam (GeV) in a wiggler. Synchronization is another difficulty: the jitter between the bunch and the laser can be larger than the laser wavelength, which makes single-shot measurement impossible. To reduce the laser power, we propose to use ionized electrons from high energy electron beam and gas interaction for high energy electron bunch diagnostics. Similarly, the femtosecond X-ray streak camera uses X-ray ionization electrons to measure the X-ray pulse. The electrons generated by beam-gas ionization have low energy (eVs). Therefore, a lower laser power is possible to deflect such low energy electrons. Note that there is no field ionization in our case. To avoid field ionization, which occurs in plasma case, gases species with high field ionization threshold should be considered. For a linear polarized laser, the kick to the ionized electrons depends on the phase of the laser when the electrons are born and the unknown timing jitter between the electron beam and laser beam makes the data analysis very difficult. Here we propose to use a circular polarized laser to do a 2-dimensional (2D) streaking (both x and y) and measure the bunch length from the angular distribution on the screen, where the phase jitter causes only a rotation of the image on the screen without changing of the relative angular distribution. Also we only need to know the laser wavelength for calibration. A similar circular RF deflecting mode was used to measure long bunches. We developed a numerical particle-in-Cell (PIC) code to study the dynamics of ionization electrons with the high energy beam and the laser beam.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

MCNPX-CINDER'90 Simulation of Photonuclear Mo-99 Production Experiments

The MCNPX and CINDER'90 codes were used to support design of experiments investigating Mo-99 production with a 20-MeV electron beam. Bremsstrahlung photons produced by the electron beam interacting with the target drive the desired Mo-100({gamma},n)Mo-99 reaction, as well as many undesired reactions important to accurate prediction of radiation hazards. MCNPX is a radiation transport code and CINDER'90 is a transmutation code. They are routinely used together for accelerator activation calculations. Low energy neutron fluxes and production rates for nonneutron and high energy neutron induced reactions computed using MCNPX are inputs to CINDER'90. CINDER'90 presently has only a neutron reaction cross section library up to 25 MeV and normally the other reaction rates come from MCNPX physics models. For this work MCNPX photon flux tallies modified by energy response functions prepared from evaluated photonuclear cross section data were used to tally the reaction rates for CINDER'90 input. The cross section evaluations do not provide isomer to ground state yield ratios so a spin based approximation was used. Post irradiation dose rates were calculated using MCNPX with CINDER'90 produced decay photon spectra. The sensitivity of radionuclide activities and dose rates to beam parameters including energy, position, and profile, as well as underlying isomer assumptions, was investigated. Three experimental production targets were irradiated, two natural Mo and one Mo-100 enriched. Natural Mo foils upstream of the targets were used to analyze beam position and profile by exposing Gafchromic film to the foils after each irradiation. Activation and dose rate calculations were rerun after the experiments using measured beam parameters for comparison with measured Mo-99 activities and dose rates.

Accelerator Design, Technology, and Operations↗
DOE OSTI2018

Coherent combining of pulses amplified in wideband parametric amplifiers under multiple-beam pumping

The influence of fluctuations of pump beam parameters on the coherent combining efficiency of femtosecond pulses amplified in parametric amplifies based on LBO crystals under multiple- beam pumping is analysed. It is shown that in transition from a single-beam to two-beam pumping, the sensitivity of the parameters of amplified radiation to angular instability of the pump beams sharply increases. With increasing number of the pump beams, the sensitivity of the parameters to fluctuations of the pump beam propagation angle weakly varies. It is found that if a substantial number (n ≫ 1) of 2-cm-diameter beams amplified in parametric amplifiers under multiple-beam pumping are coherently combined, then obtaining the 98 % efficiency of this process requires the angular stabilisation of the pump beams better than 50 μrad. Fluctuations of other pump beam parameters such as energy, phase aberrations, and relative jitter either affect only the amplitude of the pulse amplified or the influence on the phase profile of the amplified beam is at most 10{sup −2} rad, which should not noticeably affect the coherent combining of amplified pulses. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Characterization of a multi-axis ion chamber array

Purpose: The aim of this work was to characterize a multi-axis ion chamber array (IC PROFILER; Sun Nuclear Corporation, Melbourne, FL USA) that has the potential to simplify the acquisition of LINAC beam data. Methods: The IC PROFILER (or panel) measurement response was characterized with respect to radiation beam properties, including dose, dose per pulse, pulse rate frequency (PRF), and energy. Panel properties were also studied, including detector-calibration stability, power-on time, backscatter dependence, and the panel's agreement with water tank measurements [profiles, fractional depth dose (FDD), and output factors]. Results: The panel's relative deviation was typically within ({+-}) 1% of an independent (or nominal) response for all properties that were tested. Notable results were (a) a detectable relative field shape change of {approx}1% with linear accelerator PRF changes; (b) a large range in backscatter thickness had a minimal effect on the measured dose distribution (typically less than 1%); (c) the error spread in profile comparison between the panel and scanning water tank (Blue Phantom, CC13; IBA Schwarzenbruck, DE) was approximately ({+-}) 0.75%. Conclusions: The ability of the panel to accurately reproduce water tank profiles, FDDs, and output factors is an indication of its abilities as a dosimetry system. The benefits of using the panel versus a scanning water tank are less setup time and less error susceptibility. The same measurements (including device setup and breakdown) for both systems took 180 min with the water tank versus 30 min with the panel. The time-savings increase as the measurement load is increased.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

3D printing of gas jet nozzles for laser-plasma accelerators

Recent results on laser wakefield acceleration in tailored plasma channels have underlined the importance of controlling the density profile of the gas target. In particular, it was reported that the appropriate density tailoring can result in improved injection, acceleration, and collimation of laser-accelerated electron beams. To achieve such profiles, innovative target designs are required. For this purpose, we have reviewed the usage of additive layer manufacturing, commonly known as 3D printing, in order to produce gas jet nozzles. Notably we have compared the performance of two industry standard techniques, namely, selective laser sintering (SLS) and stereolithography (SLA). Furthermore we have used the common fused deposition modeling to reproduce basic gas jet designs and used SLA and SLS for more sophisticated nozzle designs. The nozzles are characterized interferometrically and used for electron acceleration experiments with the SALLE JAUNE terawatt laser at Laboratoire d’Optique Appliquée.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1982

Molecular-beam sampling study of extinguishment of methane-air flames by dry chemicals

The use of Al2O3, NaHCO3, KHCO3, NH4H2PO4 and KCl powders for the inhibition of a methane/oxygen diffusion flame is studied through measurement of composition and temperature profiles, using a molecular beam mass spectrometer sampling system. In order to obtain significant inhibition without extinguishing the flame, a powder feeding rate of 2 mg/liter of gas was used for KCl and Al2O3, and of 3 mg/liter of gas for the remaining powders. CH4, O2, N2, H2O and CO2 concentrations were measured by the mass spectrometer, while temperature was measured by the time-of-flight technique. For the powder feeding rates used, Al2O3 was the least and KCl and NH2H4PO2 the most effective in reducing temperature; in reaction-inhibition effectiveness, Al2O3 was again lowest while KCl was superior to all others. Because the KCl concentration was only 2/3 that of NH4H2PO4, it is recommended as the most effective temperature reducer and reaction inhibitor.

Knuth, E. L.↗
DOE OSTI2014

Quasi-monoenergetic ion generation by hole-boring radiation pressure acceleration in inhomogeneous plasmas using tailored laser pulses

It is proposed that laser hole-boring at a steady speed in inhomogeneous overdense plasma can be realized by the use of temporally tailored intense laser pulses, producing high-fluence quasi-monoenergetic ion beams. A general temporal profile of such laser pulses is formulated for arbitrary plasma density distribution. As an example, for a precompressed deuterium-tritium fusion target with an exponentially increasing density profile, its matched laser profile for steady hole-boring is given theoretically and verified numerically by particle-in-cell simulations. Furthermore, we propose to achieve fast ignition by the in-situ hole-boring accelerated ions using a tailored laser pulse. Simulations show that the effective energy fluence, conversion efficiency, energy spread, and collimation of the resulting ion beam can be significantly improved as compared to those found with un-tailored laser profiles. For the fusion fuel with an areal density of 1.5 g cm{sup –2}, simulation indicates that it is promising to realize fast ion ignition by using a tailored driver pulse with energy about 65 kJ.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗