Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CRAB”

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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Hard X-ray Variations in the Crab Nebula

In the first two years of science operations of the Fermi Gamma-ray Burst Monitor (GBM), August 2008 to August 2010, approximately 7% (70 mcrab) decline was discovered in the overall Crab Nebula flux in the 15 - 50 keV band, measured with the Earth occultation technique. This decline was independently confirmed with four other instruments: the RXTE/PCA, Swift/BAT, INTEGRAL/IBIS, and INTEGRAL/SPI. The pulsed flux measured with RXTE/PCA from 1999-2010 was consistent with the pulsar spin-down, indicating that the observed changes were nebular. From 2001 to 2010, the Crab nebula flux measured with RXTE/PCA was particularly variable, changing by up to approximately 3.5% per year in the 15-50 keV band. These variations were confirmed with INTEGRAL/SPI starting in 2003, Swift/BAT starting in 2005, and Fermi GBM starting in 2008. Before 2001 and since 2010, the Crab nebula flux has appeared more stable, varying by less than 2% per year. I will present updated light curves in multiple energy bands for the Crab nebula, including recent data from Fermi GBM, Swift/BAT, INTEGRAL and MAXI, and a 16-year long light curve from RXTE/PCA.

Wilson-Hodge, Colleen A.↗
NASA NTRS2013

Hard X-ray Variations in the Crab Nebula

In the first two years of science operations of the Fermi Gamma-ray Burst Monitor (GBM), August 2008 to August 2010, approximately 7% (70 mcrab) decline was discovered in the overall Crab Nebula flux in the 15 - 50 keV band, measured with the Earth occultation technique. This decline was independently confirmed with four other instruments: the RXTE/PCA, Swift/BAT, INTEGRAL/IBIS, and INTEGRAL/SPI. The pulsed flux measured with RXTE/PCA from 1999-2010 was consistent with the pulsar spin-down, indicating that the observed changes were nebular. From 2001 to 2010, the Crab nebula flux measured with RXTE/ PCA was particularly variable, changing by up to approximately 3.5% per year in the 15-50 keV band. These variations were confirmed with INTEGRAL/SPI starting in 2003, Swift/BAT starting in 2005, and Fermi GBM starting in 2008. Before 2001 and since 2010, the Crab nebula flux has appeared more stable, varying by less than 2% per year. I will present updated light curves in multiple energy bands for the Crab Nebula, including recent data from Fermi GBM, Swift/BAT, INTEGRAL and MAXI, and a 16-year long light curve from RXTE/PCA.

Wilson-Hodge, Colleen A.↗
DOE OSTI2011

Status of the ILC Crab Cavity Development

The International Linear Collider (ILC) will require two dipole cavities to 'crab' the electron and positron bunches prior to their collision. It is proposed to use two 9 cell SCRF dipole cavities operating at a frequency of 3.9 GHz, with a transverse gradient of 3.8MV/m in order to provide the required transverse kick. Extensive numerical modelling of this cavity and its couplers has been performed. Aluminium prototypes have been manufactured and tested to measure the RF properties of the cavity and couplers. In addition single cell niobium prototypes have been manufactured and tested in a vertical cryostat. The International Collider (ILC) [1] collides bunches of electrons and positrons at a crossing angle of 14 mrad. The angle between these bunches causes a loss in luminosity due to geometric effects [2]. The luminosity lost from this geometric effect can be recovered by rotating the bunches into alignment prior to collision. One possible method of rotating the bunches is to use a crab cavity [3]. A crab cavity is a transverse defecting cavity, where the phase of the cavity is such that the head and tail of the bunch receive equal and opposite kicks. As the bunches are only 500 nm wide in the horizontal plane, the cavity phase must be strictly controlled to avoid the bunch centre being deflected too much. In order to keep the phase stability within the required limits it is required that the cavity be superconducting to avoid thermal effects in both the cavity and its RF source. At the location of the crab cavity in the ILC there is only 23 cm separation between the centre of the cavity and the extraction line, hence the cavity must be small enough to fit in this space. This, along with the difficulty of making high frequency SRF components, set the frequency of the cavity to 3.9 GHz.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Crab Crossing Schemes and Studies for Electron Ion Collider

This report shows our progress in crab crossing consideration for future electron-ion collider envisioned at JLab. In this design phase, we are evaluating two crabbing schemes viz., the deflecting and dispersive. The mathematical formulations and lattice design for these schemes are discussed in this paper. Numerical simulations involving particle tracking through a realistic deflecting RF cavity and optics illustrate the desired crab tilt of 25 mrad for 1.35 MV. Evolution of beam propagation are shown which provides the physical insight of the crabbing phenomenon.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Wakefield Damping for the CLIC Crab Cavity

A crab cavity is required in the CLIC to allow effective head-on collision of bunches at the IP. A high operating frequency is preferred as the deflection voltage required for a given rotation angle and the RF phase tolerance for a crab cavity are inversely proportional to the operating frequency. The short bunch spacing of the CLIC scheme and the high sensitivity of the crab cavity to dipole kicks demand very high damping of the inter-bunch wakes, the major contributor to the luminosity loss of colliding bunches. This paper investigates the nature of the wakefields in the CLIC crab cavity and the possibility of using various damping schemes to suppress them effectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

CLIC Crab Cavity Design Optimisation for Maximum Luminosity

The bunch size and crossing angle planned for CERN's compact linear collider CLIC dictate that crab cavities on opposing linacs will be needed to rotate bunches of particles into alignment at the interaction point if the desired luminosity is to be achieved. Wakefield effects, RF phase errors between crab cavities on opposing linacs and unpredictable beam loading can each act to reduce luminosity below that anticipated for bunches colliding in perfect alignment. Unlike acceleration cavities, which are normally optimised for gradient, crab cavities must be optimised primarily for luminosity. Accepting the crab cavity technology choice of a 12 GHz, normal conducting, travelling wave structure as explained in the text, this paper develops an analytical approach to optimise cell number and iris diameter.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Mechanical Analysis of the 400 MHz RF-Dipole Crabbing Cavity Prototype for LHC High Luminosity Upgrade

The proposed LHC high luminosity upgrade requires two crabbing systems in increasing the peak luminosity, operating both vertically and horizontally at two interaction points of IP1 and IP5. The required system has tight dimensional constraints and needs to achieve higher operational gradients. A proof-of-principle 400 MHz crabbing cavity design has been successfully tested and has proven to be an ideal candidate for the crabbing system. The cylindrical proof-of-principle rf-dipole design has been adapted in to a square shaped design to further meet the dimensional requirements. The new rf-dipole design has been optimized in meeting the requirements in rf-properties, higher order mode damping, and multipole components. A crabbing system in a cryomodule is expected to be tested on the SPS beam line prior to the test at LHC. The new prototype is required to achieve the mechanical and thermal specifications of the SPS test followed by the test at LHC. This paper discusses the detailed mechanical and thermal analysis in minimizing Lorentz force detuning and sensitivity to liquid He pressure fluctuations.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Crab cavities: Past, present, and future of a challenging device

In two-ring facilities operating with a crossing-angle collision scheme, luminosity can be limited due to an incomplete overlapping of the colliding bunches. Crab cavities then are introduced to restore head-on collisions by providing the destined opposite deflection to the head and tail of the bunch. An increase in luminosity was demonstrated at KEKB with global crab-crossing, while the Large Hardron Collider (LHC) at CERN currently is designing local crab crossing for the Hi-Lumi upgrade. Future colliders may investigate both approaches. In this paper, we review the challenges in the technology, and the implementation of crab cavities, while discussing experience in earlier colliders, ongoing R&D, and proposed implementations for future facilities, such as HiLumi-LHC, CERN’s compact linear collider (CLIC), the international linear collider (ILC), and the electron-ion collider under design at BNL (eRHIC).

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Design and prototyping of HL-LHC double quarter wave crab cavities for SPS test

The LHC high luminosity project envisages the use of the crabbing technique for increasing and levelling the LHC luminosity. Double Quarter Wave (DQW) resonators are compact cavities especially designed to meet the technical and performance requirements for LHC beam crabbing. Two DQW crab cavities are under fabrication and will be tested with beam in the Super Proton Synchrotron (SPS) at CERN by 2017. This paper describes the design and prototyping of the DQW crab cavities for the SPS test.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Understanding to Hierarchical Microstructures of Crab (Chinese hairy) Shell as a Natural Architecture

This work was done to better understand the microstructures, composition and mechanical properties of Chinese hairy crab shell. For fully revealing its hierarchical microstructure, the crab shell was observed with electron microscope under different magnifications from different facets. XRD, EDS, FTIR and TGA techniques have been used to characterize the untreated and chemically-treated crab shells, which provided enough information to determine the species and relative content of components in this biomaterial. Combined the microstructures with constituents analysis, the structural principles of crab shell was detailedly realized from different structural levels beyond former reports. To explore the relationship between structure and function, the mechanical properties of shell have been measured through performing tensile tests. The contributions of organics and minerals in shell to the mechanical properties were also discussed by measuring the tensile strength of de-calcification samples treated with HCl solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Physicochemical, Microstructural and Thermal Characterization of Chitosan from Blue Crab Shell Waste and Its Bioactivity Characteristics

The aim of the present study was to characterize the chitosan synthesized from blue crab (Callinectes sapidus, Rathbun, 1986) shell waste and to investigate its physicochemical and microstructural analyses as well as its antioxidant and antibacterial potentials. Microstructural and elemental characterization of the synthesized and commercial chitosan powders were performed using fourier transform infra-red spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Thermal analysis were done using thermogravimetric analysis. Antioxidant and antimicrobial analysis were done using by DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical scavenging assay and agar well diffusion assay, respectively. The yield of the synthesized chitosan was calculated as 7.47% with moisture and ash contents of 0.151 ± 0.0025% and 0.19 ± 0.01%, respectively. Synthesized chitosan demonstrated the values of degree of deacetylation (71%), water (620.029 ± 52.59%) and fat (437.93 ± 15.92%) binding capacities, solubility (94.15 ± 2.84%), viscosity (463.25 ± 13.10 cPs) and whiteness (90.23 ± 0.27%). Antioxidant activity of synthesized chitosan was found to be moderate (55.30 ± 5.05%) when compared to ascorbic acid standard (87.61 ± 1.34). Chitosan obtained from blue crab shell also showed moderate antibacterial activity against Staphylococcus aureus and Escherichia coli. The findings of the study indicated that blue crab shell waste might be a potentially effective biopolymer source for commercial applications especially in food industry.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Sterol regulatory element binding protein-1: Molecular cloning, tissue distribution and gene expression level in response to nutritional regulation in mud crab, Scylla paramamosain

Highlights: • The complete SREBP-1 cDNA sequence was cloned from the hepatopancreas of mud crab based on the RACE technology. • Tissue distribution analysis revealed that SREBP-1 transcripts were widely distributed in various organs, with higher mRNA levels in the eyestalk and cranial ganglia. • The expression level of SREBP-1 mRNA were up-regulated in proportion to the replacement of dietary fish oil with soybean oil. In the present study, SREBP-1 cDNA was cloned from the hepatopancreas of mud crab (Scylla paramamosain) and characterized by performing rapid-amplification of cDNA ends. The 3361bp long full-length cDNA encodes a polypeptide with 1039 amino acids. Tissue distribution analysis revealed that SREBP-1 transcripts were widely distributed in various organs, with higher mRNA levels in the eyestalk and cranial ganglia. Further, expression level of SREBP-1 mRNA were up-regulated in proportion to the replacement of dietary fish oil (FO) with soybean oil (SO). These results may contribute to better understanding of the long-chain polyunsaturated fatty acids (LC-PUFA) biosynthetic pathway and regulation mechanism in mud crab.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Spectrum and extension of the inverse-Compton emission of the Crab Nebula from a combined Fermi -LAT and H.E.S.S. analysis

The Crab Nebula is a unique laboratory for studying the acceleration of electrons and positrons through their non-thermal radiation. Observations of very-high-energy γ rays from the Crab Nebula have provided important constraints for modelling its broadband emission. We present the first fully self-consistent analysis of the Crab Nebula’s γ-ray emission between 1 GeV and ∼100 TeV, that is, over five orders of magnitude in energy. Using the open-source software package GAMMAPY, we combined 11.4 yr of data from the Fermi Large Area Telescope and 80 h of High Energy Stereoscopic System (H.E.S.S.) data at the event level and provide a measurement of the spatial extension of the nebula and its energy spectrum. We find evidence for a shrinking of the nebula with increasing γ-ray energy. Furthermore, we fitted several phenomenological models to the measured data, finding that none of them can fully describe the spatial extension and the spectral energy distribution at the same time. Especially the extension measured at TeV energies appears too large when compared to the X-ray emission. Our measurements probe the structure of the magnetic field between the pulsar wind termination shock and the dust torus, and we conclude that the magnetic field strength decreases with increasing distance from the pulsar. We complement our study with a careful assessment of systematic uncertainties.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

CHANDRA PHASE-RESOLVED X-RAY SPECTROSCOPY OF THE CRAB PULSAR

We present a new study of the X-ray spectral properties of the Crab Pulsar. The superb angular resolution of the Chandra X-Ray Observatory enables distinguishing the pulsar from the surrounding nebulosity. Analysis of the spectrum as a function of pulse phase allows the least-biased measure of interstellar X-ray extinction due primarily to photoelectric absorption and secondarily to scattering by dust grains in the direction of the Crab Nebula. We modify previous findings that the line of sight to the Crab is underabundant in oxygen and provide measurements with improved accuracy and less bias. Using the abundances and cross sections from Wilms et al. we find [O/H] = (5.28 {+-} 0.28) Multiplication-Sign 10{sup -4} (4.9 Multiplication-Sign 10{sup -4} is solar abundance). We also measure for the first time the impact of scattering of flux out of the image by interstellar grains. We find {tau}{sub scat} = 0.147 {+-} 0.043. Analysis of the spectrum as a function of pulse phase also measures the X-ray spectral index even at pulse minimum-albeit with increasing statistical uncertainty. The spectral variations are, by and large, consistent with a sinusoidal variation. The only significant variation from the sinusoid occurs over the same phase range as some rather abrupt behavior in the optical polarization magnitude and position angle. We also compare these spectral variations to those observed in gamma-rays and conclude that our measurements are both a challenge and a guide to future modeling and will thus eventually help us understand pair cascade processes in pulsar magnetospheres. The data are also used to set new, and less biased, upper limits to the surface temperature of the neutron star for different models of the neutron star atmosphere. We discuss how such data are best connected to theoretical models of neutron star cooling and neutron star interiors. The data restrict the neutrino emission rate in the pulsar core and the amount of light elements in the heat-blanketing envelope. The observations allow the pulsar, irrespective of the composition of its envelope, to have a neutrino emission rate higher than {approx}0.2 of the standard rate of a non-superfluid star cooling via the modified Urca process. The observations also allow the rate to be lower but now with a limited amount of accreted matter in the envelope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

EXTREME PARTICLE ACCELERATION IN MAGNETIC RECONNECTION LAYERS: APPLICATION TO THE GAMMA-RAY FLARES IN THE CRAB NEBULA

The gamma-ray space telescopes AGILE and Fermi detected short and bright synchrotron gamma-ray flares at photon energies above 100 MeV in the Crab Nebula. This discovery suggests that electron-positron pairs in the nebula are accelerated to PeV energies in a milligauss magnetic field, which is difficult to explain with classical models of particle acceleration and pulsar wind nebulae. We investigate whether particle acceleration in a magnetic reconnection layer can account for the puzzling properties of the flares. We numerically integrate relativistic test-particle orbits in the vicinity of the layer, including the radiation reaction force, and using analytical expressions for the large-scale electromagnetic fields. As they get accelerated by the reconnection electric field, the particles are focused deep inside the current layer where the magnetic field is small. The electrons suffer less from synchrotron losses and are accelerated to extremely high energies. Population studies show that, at the end of the layer, the particle distribution piles up at the maximum energy given by the electric potential drop and is focused into a thin fan beam. Applying this model to the Crab Nebula, we find that the emerging synchrotron emission spectrum peaks above 100 MeV and is close to the spectral shape of a single electron. The flare inverse Compton emission is negligible and no detectable emission is expected at other wavelengths. This mechanism provides a plausible explanation for the gamma-ray flares in the Crab Nebula and could be at work in other astrophysical objects such as relativistic jets in active galactic nuclei.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

PROPERTIES AND SPATIAL DISTRIBUTION OF DUST EMISSION IN THE CRAB NEBULA

Recent infrared (IR) observations of freshly formed dust in supernova remnants have yielded significantly lower dust masses than predicted by theoretical models and measured from high-redshift observations. The Crab Nebula's pulsar wind is thought to be sweeping up freshly formed supernova (SN) dust along with the ejected gas. The evidence for this dust was found in the form of an IR excess in the integrated spectrum of the Crab and in extinction against the synchrotron nebula that revealed the presence of dust in the filament cores. We present the first spatially resolved emission spectra of dust in the Crab Nebula acquired with the Infrared Spectrograph on board the Spitzer Space Telescope. The IR spectra are dominated by synchrotron emission and show forbidden line emission from S, Si, Ne, Ar, O, Fe, and Ni. We derived a synchrotron spectral map from the 3.6 and 4.5 {mu}m images, and subtracted this contribution from our data to produce a map of the residual continuum emission from dust. The dust emission appears to be concentrated along the ejecta filaments and is well described by an amorphous carbon or silicate grain compositions. We find a dust temperature of 55 {+-} 4 K for silicates and 60 {+-} 7 K for carbon grains. The total estimated dust mass is (1.2-12) Multiplication-Sign 10{sup -3} M{sub Sun }, well below the theoretical dust yield predicted for a core-collapse supernova. Our grain heating model implies that the dust grain radii are relatively small, unlike what is expected for dust grains formed in a Type IIP SN.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The dust and gas content of the Crab Nebula

We have constructed mocassin photoionization plus dust radiative transfer models for the Crab Nebula core-collapse supernova (CCSN) remnant, using either smooth or clumped mass distributions, in order to determine the chemical composition and masses of the nebular gas and dust. We computed models for several different geometries suggested for the nebular matter distribution but found that the observed gas and dust spectra are relatively insensitive to these geometries, being determined mainly by the spectrum of the pulsar wind nebula which ionizes and heats the nebula. Smooth distribution models are ruled out since they require 16–49 M {sub ⊙} of gas to fit the integrated optical nebular line fluxes, whereas our clumped models require 7.0 M {sub ⊙} of gas. A global gas-phase C/O ratio of 1.65 by number is derived, along with a He/H number ratio of 1.85, neither of which can be matched by current CCSN yield predictions. A carbonaceous dust composition is favored by the observed gas-phase C/O ratio: amorphous carbon clumped model fits to the Crab’s Herschel and Spitzer infrared spectral energy distribution imply the presence of 0.18–0.27 M {sub ⊙} of dust, corresponding to a gas to dust mass ratio of 26–39. Mixed dust chemistry models can also be accommodated, comprising 0.11–0.13 M {sub ⊙} of amorphous carbon and 0.39–0.47 M {sub ⊙} of silicates. Power-law grain size distributions with mass distributions that are weighted toward the largest grain radii are derived, favoring their longer-term survival when they eventually interact with the interstellar medium. The total mass of gas plus dust in the Crab Nebula is 7.2 ± 0.5 M {sub ⊙}, consistent with a progenitor star mass of ∼9 M {sub ⊙}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Synchrotron self-Compton emission from the Crab and other pulsars

Results of a simulation of synchrotron self-Compton (SSC) emission from a rotation-powered pulsar are presented. The radiating particles are assumed to be both accelerated primary electrons and a spectrum of electron–positron pairs produced in cascades near the polar cap. They follow trajectories in a slot gap using 3D force-free magnetic field geometry, gaining pitch angles through resonant cyclotron absorption of radio photons, radiating and scattering synchrotron emission at high altitudes out to and beyond the light cylinder. Full angular dependence of the synchrotron photon density is simulated in the scattering and all processes are treated in the inertial observer frame. Spectra for the Crab and Vela pulsars as well as two energetic millisecond pulsars, B1821–24 and B1937+21, are simulated using this model. The simulation of the Crab pulsar radiation can reproduce both the flux level and the shape of the observed optical to hard X-ray emission assuming a pair multiplicity of M{sub +}=3×10{sup 5}, as well as the very-high-energy emission above 50 GeV detected by MAGIC and VERITAS, with both the synchrotron and SSC components reflecting the shape of the pair spectrum. Simulations of Vela, B1821−24, and B1937+21, for M{sub +} up to 10{sup 5}, do not produce pair SSC emission that is detectable by current telescopes, indicating that only Crab-like pulsars produce significant SSC components. The pair synchrotron emission matches the observed X-ray spectrum of the millisecond pulsars, and the predicted peak of this emission at 1–10 MeV would be detectable with planned Compton telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗