Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “FOCUSING”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Modification of the parallel scattering mean free path of cosmic rays in the presence of adiabatic focusing

The cosmic ray mean free path in a large-scale nonuniform guide magnetic field with superposed magnetostatic turbulence is calculated to clarify some conflicting results in the literature. A new, exact integro-differential equation for the cosmic-ray anisotropy is derived from the Fokker-Planck transport equation. A perturbation analysis of this integro-differential equation leads to an analytical expression for the cosmic ray anisotropy and the focused transport equation for the isotropic part of the cosmic ray distribution function. The derived parallel spatial diffusion coefficient and the associated cosmic ray mean free path include the effect of adiabatic focusing and reduce to the standard forms in the limit of a uniform guide magnetic field. For the illustrative case of isotropic pitch angle scattering, the derived mean free path agrees with the earlier expressions of Beeck and Wibberenz, Bieber and Burger, Kota, and Litvinenko, but disagrees with the result of Shalchi. The disagreement with the expression of Shalchi is particularly strong in the limit of strong adiabatic focusing.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Dynamics near equilibrium for intense beams in a nonlinear integrable focusing channel

Accelerator storage ring designs based on nonlinear integrable Hamiltonian systems provide a novel test-bed for studying the interplay between nonlinear dynamics and space charge at high intensity. In this work, the structure of beam Vlasov equilibria is explored for a constant focusing channel based on the nonlinear focusing potential of the Integrable Optics Test Accelerator. Finally, the dynamics of the single-particle orbits is explored in the combined space charge and external focusing fields as a function of beam current, and the self-consistent relaxation of a mismatched beam to equilibrium is characterized.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

SUPER-FOCUS: A tool for agile functional analysis of shotgun metagenomic data

Analyzing the functional profile of a microbial community from unannotated shotgun sequencing reads is one of the important goals in metagenomics. Functional profiling has valuable applications in biological research because it identifies the abundances of the functional genes of the organisms present in the original sample, answering the question what they can do. Currently, available tools do not scale well with increasing data volumes, which is important because both the number and lengths of the reads produced by sequencing platforms keep increasing. Here, we introduce SUPER-FOCUS, SUbsystems Profile by databasE Reduction using FOCUS, an agile homology-based approach using a reduced reference database to report the subsystems present in metagenomic datasets and profile their abundances. We tested SUPER-FOCUS with over 70 real metagenomes, the results showing that it accurately predicts the subsystems present in the profiled microbial communities, and is up to 1000 times faster than other tools.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Exact solutions for the electromagnetic fields of a flying focus

The intensity peak of a “flying” focus travels at a programmable velocity over many Rayleigh ranges while maintaining a near-constant profile. Assessing the extent to which these features can enhance laser-based applications requires an accurate description of the electromagnetic fields. Here we present exact analytical solutions to Maxwell’s equations for the electromagnetic fields of a constant-velocity flying focus, generalized for arbitrary polarization and orbital angular momentum. Furthermore, the approach combines the complex source-point method, which transforms multipole solutions into beam-like solutions, with the Lorentz invariance of Maxwell’s equations. Propagating the fields backward in space reveals the space-time profile that an optical assembly must produce to realize these fields in the laboratory. Comparisons with simpler paraxial solutions provide conditions for their reliable use when modeling a flying focus.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Spectral Galerkin solver for intense beam Vlasov equilibria in nonlinear constant focusing channels

Here a numerical method is described for producing stationary solutions of the Vlasov-Poisson system describing a relativistic charged-particle beam in a constant focusing accelerator channel, confined transversely by a general (linear or nonlinear) focusing potential. The method utilizes a variant of the spectral Galerkin algorithm to solve a nonlinear partial differential equation (PDE) in two degrees of freedom for the beam space charge potential in equilibrium. Numerical convergence with an increasing number of computed spectral modes is investigated for several benchmark problems. Preservation of the stationary phase space density is verified using a strongly nonlinear focusing channel based on the Integrable Optics Test Accelerator at Fermi National Accelerator Laboratory.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Streamer self-focusing in an external longitudinal magnetic field

The numerical simulation of the development of a streamer discharge in a gap with an external longitudinal magnetic field was used to demonstrate the self-focusing of such discharges. Self-focusing is caused by a sharp deceleration of the radial ionization wave due to a change in the electron energy distribution function, a decrease in the average electron energy, the rate of gas ionization, and the electron mobility in crossed electric and magnetic fields as compared to the case of the discharge development without a magnetic field. The self-focusing effect of a streamer discharge in an external longitudinal magnetic field is observed for both positive and negative pulse polarities. The work proposes an estimate of the critical value of the magnetic field, which makes it possible to control the development of pulsed high-voltage discharges at various gas pressures.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Photon Acceleration in a Flying Focus

A high-intensity laser pulse propagating through a medium triggers an ionization front that can accelerate and frequency-upshift the photons of a second pulse. Here, the maximum upshift is ultimately limited by the accelerated photons outpacing the ionization front or the ionizing pulse refracting from the plasma. Here we apply the flying focus—a moving focal point resulting from a chirped laser pulse focused by a chromatic lens—to overcome these limitations. Theory and simulations demonstrate that the ionization front produced by a flying focus can frequency-upshift an ultrashort optical pulse to the extreme ultraviolet over a centimeter of propagation. An analytic model of the upshift predicts that this scheme could be scaled to a novel table-top source of spatially coherent x-rays.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Dispersive X-ray absorption spectroscopy using independent grazing-incidence focusing and convexly bent Bragg-crystal dispersing optics

We present a modular instrument for dispersive X-ray absorption spectroscopy (DXAS) developed for the Advanced Spectroscopy Beamline at Sector 25 of the Advanced Photon Source. The setup employs a double-multilayer monochromator to provide X-rays with a broad energy bandwidth, Kirkpatrick–Baez mirrors for focusing, a convexly bent Bragg-crystal polychromator for energy dispersion, and a pixel-array detector to resolve all X-ray energies and collect their intensity simultaneously, thereby enabling acquisition of a full X-ray absorption spectrum in a single shot. The use of separate optics for X-ray focusing and energy dispersion provides high spatial resolution and avoids chromatic aberrations inherent in focusing bent-crystal optics, and a modular design makes implementation of the technique at other beamlines possible without requiring modifications to the upstream beamline configurations. Theoretical calculations are performed to determine optimal instrument operating parameters and demonstrate that an energy resolution better than the K-edge core-hole lifetime broadening can be maintained while providing a sufficient bandwidth for X-ray absorption near-edge structure spectroscopy through the full operating range of 5–11 keV. Additionally, instrument design, data analysis methods, and initial DXAS results on lithium–manganese–nickel oxide laminates are presented.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Rayleigh-scattering microscopy for tracking and sizing nanoparticles in focused aerosol beams

Ultra-bright femtosecond X-ray pulses generated by X-ray free-electron lasers (XFELs) can be used to image high-resolution structures without the need for crystallization. For this approach, aerosol injection has been a successful method to deliver 70–2000 nm particles into the XFEL beam efficiently and at low noise. Improving the technique of aerosol sample delivery and extending it to single proteins necessitates quantitative aerosol diagnostics. Here a lab-based technique is introduced for Rayleigh-scattering microscopy allowing us to track and size aerosolized particles down to 40 nm in diameter as they exit the injector. This technique was used to characterize the `Uppsala injector', which is a pioneering and frequently used aerosol sample injector for XFEL single-particle imaging. The particle-beam focus, particle velocities, particle density and injection yield were measured at different operating conditions. It is also shown how high particle densities and good injection yields can be reached for large particles (100–500 nm). It is found that with decreasing particle size, particle densities and injection yields deteriorate, indicating the need for different injection strategies to extend XFEL imaging to smaller targets, such as single proteins. This work demonstrates the power of Rayleigh-scattering microscopy for studying focused aerosol beams quantitatively. It lays the foundation for lab-based injector development and online injection diagnostics for XFEL research. In the future, the technique may also find application in other fields that employ focused aerosol beams, such as mass spectrometry, particle deposition, fuel injection and three-dimensional printing techniques.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Evaluation of neon focused ion beam milling for TEM sample preparation

Summary Gallium‐based focused ion beams generated from liquid–metal sources are widely used in micromachining and sample preparation for transmission electron microscopy, with well‐known drawbacks such as sample damage and contamination. In this work, an alternative (neon) focused ion beam generated by a gas field‐ionization source is evaluated for the preparation of electron‐transparent specimens. To do so, electron‐transparent sections of Si and an Al alloy are prepared with both Ga and Ne ion beams for direct comparison. Diffraction‐contrast imaging and energy dispersive x‐ray spectroscopy are used to evaluate the relative damage induced by the two beams, and cross‐sections of milled trenches are examined to compare the implantation depth with theoretical predictions from Monte Carlo simulations. Our results show that for the beam voltages and materials systems investigated, Ne ion beam milling does not significantly reduce the focused ion beam induced artefacts. However, the Ne ion beam does enable more precise milling and may be of interest in cases where Ga contamination cannot be tolerated.

PEKIN, T. C.↗
DOE OSTI2015

SU-E-J-32: Dosimetric Evaluation Based On Pre-Treatment Cone Beam CT for Spine Stereotactic Body Radiotherapy: Does Region of Interest Focus Matter?

Purpose: Spine stereotactic body radiotherapy requires very conformal dose distributions and precise delivery. Prior to treatment, a KV cone-beam CT (KV-CBCT) is registered to the planning CT to provide image-guided positional corrections, which depend on selection of the region of interest (ROI) because of imperfect patient positioning and anatomical deformation. Our objective is to determine the dosimetric impact of ROI selections. Methods: Twelve patients were selected for this study with the treatment regions varied from C-spine to T-spine. For each patient, the KV-CBCT was registered to the planning CT three times using distinct ROIs: one encompassing the entire patient, a large ROI containing large bony anatomy, and a small target-focused ROI. Each registered CBCT volume, saved as an aligned dataset, was then sent to the planning system. The treated plan was applied to each dataset and dose was recalculated. The tumor dose coverage (percentage of target volume receiving prescription dose), maximum point dose to 0.03 cc of the spinal cord, and dose to 10% of the spinal cord volume (V10) for each alignment were compared to the original plan. Results: The average magnitude of tumor coverage deviation was 3.9%±5.8% with external contour, 1.5%±1.1% with large ROI, 1.3%±1.1% with small ROI. Spinal cord V10 deviation from plan was 6.6%±6.6% with external contour, 3.5%±3.1% with large ROI, and 1.2%±1.0% with small ROI. Spinal cord max point dose deviation from plan was: 12.2%±13.3% with external contour, 8.5%±8.4% with large ROI, and 3.7%±2.8% with small ROI. Conclusion: A small ROI focused on the target results in the smallest deviation from planned dose to target and cord although rotations at large distances from the targets were observed. It is recommended that image fusion during CBCT focus narrowly on the target volume to minimize dosimetric error. Improvement in patient setups may further reduce residual errors.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Design and validation of an MR-conditional robot for transcranial focused ultrasound surgery in infants

Purpose: Current treatment of intraventricular hemorrhage (IVH) involves cerebral shunt placement or an invasive brain surgery. Magnetic resonance-guided focused ultrasound (MRgFUS) applied to the brains of pediatric patients presents an opportunity to treat IVH in a noninvasive manner, termed “incision-less surgery.” Current clinical and research focused ultrasound systems lack the capability to perform neonatal transcranial surgeries due to either range of motion or dexterity requirements. A novel robotic system is proposed to position a focused ultrasound transducer accurately above the head of a neonatal patient inside an MRI machine to deliver the therapy. Methods: A clinical Philips Sonalleve MRgFUS system was expanded to perform transcranial treatment. A five degree-of-freedom MR-conditional robot was designed and manufactured using MR compatible materials. The robot electronics and control were integrated into existing Philips electronics and software interfaces. The user commands the position of the robot with a graphical user interface, and is presented with real-time MR imaging of the patient throughout the surgery. The robot is validated through a series of experiments that characterize accuracy, signal-to-noise ratio degeneration of an MR image as a result of the robot, MR imaging artifacts generated by the robot, and the robot’s ability to operate in a representative surgical environment inside an MR machine. Results: Experimental results show the robot responds reliably within an MR environment, has achieved 0.59 ± 0.25 mm accuracy, does not produce severe MR-imaging artifacts, has a workspace providing sufficient coverage of a neonatal brain, and can manipulate a 5 kg payload. A full system demonstration shows these characteristics apply in an application environment. Conclusions: This paper presents a comprehensive look at the process of designing and validating a new robot from concept to implementation for use in an MR environment. An MR conditional robot has been designed and manufactured to design specifications. The system has demonstrated its feasibility as a platform for MRgFUS interventions for neonatal patients. The success of the system in experimental trials suggests that it is ready to be used for validation of the transcranial intervention in animal studies.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-J-29: Dosimetric Effect of Image Registration ROI Size and Focus in Automated CBCT Registration for Spine SBRT

Purpose: Spinal stereotactic body radiotherapy (SBRT) involves highly conformal dose distributions and steep dose gradients due to the proximity of the spinal cord to the treatment volume. To achieve the planning goals while limiting the spinal cord dose, patients are setup using kV cone-beam CT (kV-CBCT) with 6 degree corrections. The kV-CBCT registration with the reference CT is dependent on a user selected region of interest (ROI). The objective of this work is to determine the dosimetric impact of ROI selection. Methods: Twenty patients were selected for this study. For each patient, the kV-CBCT was registered to the reference CT using three ROIs including: 1) the external body, 2) a large anatomic region, and 3) a small region focused in the target volume. Following each registration, the aligned CBCTs and contours were input to the treatment planning system for dose evaluation. The minimum dose, dose to 99% and 90% of the tumor volume (D99%, D90%), dose to 0.03cc and the dose to 10% of the spinal cord subvolume (V10Gy) were compared to the planned values. Results: The average deviations in the tumor minimum dose were 2.68%±1.7%, 4.6%±4.0%, 14.82%±9.9% for small, large and the external ROIs, respectively. The average deviations in tumor D99% were 1.15%±0.7%, 3.18%±1.7%, 10.0%±6.6%, respectively. The average deviations in tumor D90% were 1.00%±0.96%, 1.14%±1.05%, 3.19%±4.77% respectively. The average deviations in the maximum dose to the spinal cord were 2.80%±2.56%, 7.58%±8.28%, 13.35%±13.14%, respectively. The average deviation in V10Gy to the spinal cord were 1.69%±0.88%, 1.98%±2.79%, 2.71%±5.63%. Conclusion: When using automated registration algorithms for CBCT-Reference alignment, a small target-focused ROI results in the least dosimetric deviation from the plan. It is recommended to focus narrowly on the target volume to keep the spinal cord dose below tolerance.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Spectrometer of Synchrotron Radiation Based on Diffraction Focusing a Divergent Beam Formed by a Compound Refractive Lens

The results of the first experimental realization of a spectrometer based on the effect of diffraction focusing of X rays by a flat single crystal are discussed. A secondary X-ray source with a relatively high angular divergence and small sizes was formed at the focus of a compound refractive lens having 50 beryllium biconcave elements with a curvature radius of 50 μm. The silicon spectrometer crystal was cut in the form of a wedge of variable thickness, oriented perpendicular to the diffraction plane. The reflection 111 was used for energies of 8.3 and 12 keV. To simulate the experiment, a computer program was developed, which takes into account accurately and for the first time the focusing of radiation by the lens and its subsequent diffraction in the crystal. A calculated curve for a monochromatic beam has made it possible to determine the monochromator spectrum with high resolution from experimental data for a polychromatic beam. It is shown that monochromator resolution increases with an increase in the distance from the compound refractive lens to the crystal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Phonon focusing and electron–phonon drag in semiconductor crystals with degenerate charge-carrier statistics

We study the effect of anisotropy in elastic properties on the electron–phonon drag and thermoelectric phenomena in gapless semiconductors with degenerate charge-carrier statistics. It is shown that phonon focusing leads to a number of new effects in the drag thermopower at low temperatures, when diffusive phonon scattering from the boundaries is the predominant relaxation mechanism. We analyze the effect of phonon focusing on the dependences of the thermoelectromotive force (thermopower) in HgSe:Fe crystals on geometric parameters and the heat-flow directions relative to the crystal axes in the Knudsen regime of the phonon gas flow. The crystallographic directions that ensure the maximum and minimum values of the thermopower are determined and the role of quasi-longitudinal and quasi-transverse phonons in the drag thermopower in HgSe:Fe crystals at low temperatures is analyzed. It is shown that the main contribution to the drag thermopower comes from slow quasi-transverse phonons in the directions of focusing in long samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Sagittally focusing X-ray spectrometer in asymmetric Laue geometry

A sagittally focusing transmission-diffraction X-ray spectrometer is proposed. Sagittal focusing is achieved using an asymmetric Laue reflection. The shape of the crystal is constructed to achieve sagittal focusing of the X-ray spectrum into a line on a flat detector pointed at the crystal. Here, we show that the resulting X-ray flux (photons/area) delivered to the detector can be greater by more than two orders of magnitude compared to that of a sagittally flat Laue spectrometer.

Webster, Lucas G. [University of New Mexico, Albuq↗
DOE OSTI2023

Role of the Porras factor in phase matching of high-order harmonic generation driven by focused few-cycle laser pulses

We investigate the role of the Porras factor (or laser focusing effect) on the macroscopic high-order harmonic generation (HHG) driven by a focused broadband few-cycle laser beam. By employing a non-adiabatic phase-matching analysis method, we reveal that phase mismatch due to the induced-dipole phase varies with the Porras factor, which is dominant in phase matching at low gas pressure. We also find that in a strongly ionized medium when gas pressure is high, the nonlinear propagation is dominated by a plasma effect such that the focusing effect is mitigated, resulting in similar poor phase matching of HHG regardless of the Porras factor. Our results are expected to assist experimentalists identifying optimal conditions for HHG using ultrashort laser pulses.

Optics↗
DOE OSTI2023

Experience from the US contribution to HL-LHC: Nb3Sn focusing quadrupoles and SRF crab cavities

The Interaction Regions (IR) of many colliders benefit from the application of leading-edge technologies to ensure the highest possible luminosity delivered to the experiments. Leading-edge low-beta focusing magnets and crab cavities to handle individual bunches are critically important to increase the instantaneous and integrated luminosity in future Colliders.The High-Luminosity LHC Upgrade, HL-LHC, with Nb3Sn Magnets (called MQXF) and Superconducting Radio Frequency (SRF) crab cavities (of two types, called DQW and RFD) is a world-wide collaborative project under construction in this decade to utilize the solutions mentioned above as key ingredients to increase tenfold the integrated luminosity delivered to the CMS and ATLAS experiments in the next decade. The HL-LHC AUP is the US effort to contribute approximately 50% of the low-beta focusing magnets and crab cavities for the HL-LHC.In this contribution we present the valuable lessons learned by the US efforts in the procurement, construction, and testing phases of the Nb3Sn focusing magnets and SRF crab cavities. We will report on the experience gathered by HL-LHC AUP in the production of the first half of deliverables (magnets MQXFA03 to MQXFA13). We will also report on the test of the first cryoassemblies and the status of the cavities’ development, production and testing.Both the technical and project management lessons-learned will inform applications of these technologies to future colliders and projects.

43 PARTICLE ACCELERATORS↗