Fermi LAT Observations of the Vela Pulsar (open access)

Fermi LAT Observations of the Vela Pulsar

None
Date: May 15, 2009
Creator: Abdo, Aous A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /SLAC; Atwood, W.B.; /UC, Santa Cruz et al.
Object Type: Article
System: The UNT Digital Library
Fermi Discovery of Gamma-Ray Emission from NGC 1275 (open access)

Fermi Discovery of Gamma-Ray Emission from NGC 1275

We report the discovery of high-energy (E > 100 MeV) {gamma}-ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made with the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope. The positional center of the {gamma}-ray source is only {approx}3{prime} away from the NGC 1275 nucleus, well within the 95% LAT error circle of {approx}5{prime}. The spatial distribution of {gamma}-ray photons is consistent with a point source. The average flux and power-law photon index measured with the LAT from 2008 August 4 to 2008 December 5 are F{sub {gamma}} = (2.10 {+-} 0.23) x 10{sup -7} ph (>100 MeV) cm{sup -2} s{sup -1} and {Gamma} = 2.17 {+-} 0.05, respectively. The measurements are statistically consistent with constant flux during the four-month LAT observing period. Previous EGRET observations gave an upper limit of F{sub {gamma}} < 3.72 x 10{sup -8} ph (>100 MeV) cm{sup -2} s{sup -1} to the {gamma}-ray flux from NGC 1275. This indicates that the source is variable on timescales of years to decades, and therefore restricts the fraction of emission that can be produced in extended regions of the galaxy cluster. Contemporaneous …
Date: May 15, 2009
Creator: Abdo, Aous A.; Ackermann, M.; Ajello, M.; Asano, K.; Baldini, L.; Ballet, J. et al.
Object Type: Article
System: The UNT Digital Library
Fermi Large Area Telescope Bright Gamma-ray Source List (open access)

Fermi Large Area Telescope Bright Gamma-ray Source List

Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than {approx}10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.
Date: May 15, 2009
Creator: Abdo, Aous A.; Ackermann, M.; Ajello, M.; Atwood, W. B.; Axelsson, M.; Baldini, L. et al.
Object Type: Article
System: The UNT Digital Library
Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey (open access)

Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey

None
Date: May 15, 2009
Creator: Abdo, Aous A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L. et al.
Object Type: Article
System: The UNT Digital Library
Fermi/LAT Discovery of Gamma-Ray Emission From the Flat-Spectrum Radio Quasar PKS 1454-354 (open access)

Fermi/LAT Discovery of Gamma-Ray Emission From the Flat-Spectrum Radio Quasar PKS 1454-354

None
Date: May 15, 2009
Creator: Abdo, Aous A.; Ackermann, M.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J. et al.
Object Type: Article
System: The UNT Digital Library
The Fermi Gamma Ray Space Telescope discovers the Pulsar in the Young Galactic Supernova-Remnant CTA 1 (open access)

The Fermi Gamma Ray Space Telescope discovers the Pulsar in the Young Galactic Supernova-Remnant CTA 1

Energetic young pulsars and expanding blast waves (supernova remnants, SNRs) are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 ms, a period derivative of 3.614 x 10{sup -13} s s{sup -1}. Its characteristic age of 10{sup 4} years is comparable to that estimated for the SNR. It is conjectured that most unidentified Galactic gamma ray sources associated with star-forming regions and SNRs are such young pulsars.
Date: May 15, 2009
Creator: Abdo, Aous A.; Ackermann, M.; Atwood, W.B.; Baldini, L.; Ballet, J.; Barbiellini, G. et al.
Object Type: Article
System: The UNT Digital Library
Discovery of Pulsed Gamma Rays from the Young Radio Pulsar PSR J1028-5819 with the Fermi Large Area Telescope (open access)

Discovery of Pulsed Gamma Rays from the Young Radio Pulsar PSR J1028-5819 with the Fermi Large Area Telescope

Radio pulsar PSR J1028-5819 was recently discovered in a high-frequency search (at 3.1 GHz) in the error circle of the Energetic Gamma-Ray Experiment Telescope (EGRET) source 3EG J1027-5817. The spin-down power of this young pulsar is great enough to make it very likely the counterpart for the EGRET source. We report here the discovery of {gamma}-ray pulsations from PSR J1028-5819 in early observations by the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope. The {gamma}-ray light curve shows two sharp peaks having phase separation of 0.460 {+-} 0.004, trailing the very narrow radio pulse by 0.200 {+-} 0.003 in phase, very similar to that of other known {gamma}-ray pulsars. The measured {gamma}-ray flux gives an efficiency for the pulsar of {approx}10-20% (for outer magnetosphere beam models). No evidence of a surrounding pulsar wind nebula is seen in the current Fermi data but limits on associated emission are weak because the source lies in a crowded region with high background emission. However, the improved angular resolution afforded by the LAT enables the disentanglement of the previous COS-B and EGRET source detections into at least two distinct sources, one of which is now identified as PSR J1028-5819.
Date: May 15, 2009
Creator: Abdo, Aous A.; Ackermann, M.; Atwood, W.B.; Baldini, L.; Ballet, J.; Barbiellini, Guido et al.
Object Type: Article
System: The UNT Digital Library
Evaluate the Life History of Native Salmonids in the Malheur Subbasin, Fiscal Year 2008 Annual Report. (open access)

Evaluate the Life History of Native Salmonids in the Malheur Subbasin, Fiscal Year 2008 Annual Report.

This report has the following chapters: (1) Synopsis of 2000-2008 Stream Temperature Monitoring with Implications for Bull Trout Recovery in the Upper Malheur Logan Valley Wildlife Mitigation Property, 2008; (2) Bull Trout Spawning Survey Report, 2008; (3) 2008 Efforts to Trap and Haul Entrained Bull Trout Salvelinus confluentus over Agency Valley Dam on the North Fork Malheur River, Oregon; (4) Distribution and Abundance of Redband Trout Oncorhynchus mykiss in the Malheur River Basin, 2008; and (5) Spatial Patterns of Hybridization between Bull Trout, Salvelinus confluentus, and Brook Trout, Salvelinus fontinalis in an Oregon Stream Network.
Date: July 15, 2009
Creator: Abel, Chad; Brown, Daniel & Schwabe, Lawrence
Object Type: Report
System: The UNT Digital Library
Hot Electron Generation and Transport Using K(alpha) Emission (open access)

Hot Electron Generation and Transport Using K(alpha) Emission

We have conducted experiments on both the Vulcan and Titan laser facilities to study hot electron generation and transport in the context of fast ignition. Cu wires attached to Al cones were used to investigate the effect on coupling efficiency of plasma surround and the pre-formed plasma inside the cone. We found that with thin cones 15% of laser energy is coupled to the 40{micro}m diameter wire emulating a 40{micro}m fast ignition spot. Thick cone walls, simulating plasma in fast ignition, reduce coupling by x4. An increase of prepulse level inside the cone by a factor of 50 reduces coupling by a factor of 3.
Date: October 15, 2009
Creator: Akli, K. U.; Stephens, R. B.; Key, M. H.; Bartal, T.; Beg, F. N.; Chawla, S. et al.
Object Type: Article
System: The UNT Digital Library
Targeted discovery of glycoside hydrolases from a switchgrass-adapted compost community (open access)

Targeted discovery of glycoside hydrolases from a switchgrass-adapted compost community

Development of cellulosic biofuels from non-food crops is currently an area of intense research interest. Tailoring depolymerizing enzymes to particular feedstocks and pretreatment conditions is one promising avenue of research in this area. Here we added a green-waste compost inoculum to switchgrass (Panicum virgatum) and simulated thermophilic composting in a bioreactor to select for a switchgrass-adapted community and to facilitate targeted discovery of glycoside hydrolases. Small-subunit (SSU) rRNA-based community profiles revealed that the microbial community changed dramatically between the initial and switchgrass-adapted compost (SAC) with some bacterial populations being enriched over 20-fold. We obtained 225 Mbp of 454-titanium pyrosequence data from the SAC community and conservatively identified 800 genes encoding glycoside hydrolase domains that were biased toward depolymerizing grass cell wall components. Of these, {approx}10% were putative cellulases mostly belonging to families GH5 and GH9. We synthesized two SAC GH9 genes with codon optimization for heterologous expression in Escherichia coli and observed activity for one on carboxymethyl cellulose. The active GH9 enzyme has a temperature optimum of 50 C and pH range of 5.5 to 8 consistent with the composting conditions applied. We demonstrate that microbial communities adapt to switchgrass decomposition using simulated composting condition and that full-length genes can …
Date: November 15, 2009
Creator: Allgaier, M.; Reddy, A.; Park, J. I.; Ivanova, N.; D'haeseleer, P.; Lowry, S. et al.
Object Type: Article
System: The UNT Digital Library
The Slow:Fast substitution ratio reveals changing patterns of natural selection in gamma-proteobacterial genomes (open access)

The Slow:Fast substitution ratio reveals changing patterns of natural selection in gamma-proteobacterial genomes

Different microbial species are thought to occupy distinct ecological niches, subjecting each species to unique selective constraints, which may leave a recognizable signal in their genomes. Thus, it may be possible to extract insight into the genetic basis of ecological differences among lineages by identifying unusual patterns of substitutions in orthologous gene or protein sequences. We use the ratio of substitutions in slow versus fast-evolving sites (nucleotides in DNA, or amino acids in protein sequence) to quantify deviations from the typical pattern of selective constraint observed across bacterial lineages. We propose that elevated S:F in one branch (an excess of slow-site substitutions) can indicate a functionally-relevant change, due to either positive selection or relaxed evolutionary constraint. In a genome-wide comparative study of gamma-proteobacterial proteins, we find that cell-surface proteins involved with motility and secretion functions often have high S:F ratios, while information-processing genes do not. Change in evolutionary constraints in some species is evidenced by increased S:F ratios within functionally-related sets of genes (e.g., energy production in Pseudomonas fluorescens), while other species apparently evolve mostly by drift (e.g., uniformly elevated S:F across most genes in Buchnera spp.). Overall, S:F reveals several species-specific, protein-level changes with potential functional/ecological importance. As microbial …
Date: April 15, 2009
Creator: Alm, Eric & Shapiro, B. Jesse
Object Type: Article
System: The UNT Digital Library
The use of microarrays in microbial ecology (open access)

The use of microarrays in microbial ecology

Microarrays have proven to be a useful and high-throughput method to provide targeted DNA sequence information for up to many thousands of specific genetic regions in a single test. A microarray consists of multiple DNA oligonucleotide probes that, under high stringency conditions, hybridize only to specific complementary nucleic acid sequences (targets). A fluorescent signal indicates the presence and, in many cases, the abundance of genetic regions of interest. In this chapter we will look at how microarrays are used in microbial ecology, especially with the recent increase in microbial community DNA sequence data. Of particular interest to microbial ecologists, phylogenetic microarrays are used for the analysis of phylotypes in a community and functional gene arrays are used for the analysis of functional genes, and, by inference, phylotypes in environmental samples. A phylogenetic microarray that has been developed by the Andersen laboratory, the PhyloChip, will be discussed as an example of a microarray that targets the known diversity within the 16S rRNA gene to determine microbial community composition. Using multiple, confirmatory probes to increase the confidence of detection and a mismatch probe for every perfect match probe to minimize the effect of cross-hybridization by non-target regions, the PhyloChip is able to …
Date: September 15, 2009
Creator: Andersen, G. L.; He, Z.; DeSantis, T. Z.; Brodie, E. L. & Zhou, J.
Object Type: Book
System: The UNT Digital Library
The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission (open access)

The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission

The Large Area Telescope (Fermi/LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view (FoV), high-energy {gamma}-ray telescope, covering the energy range from below 20 MeV to more than 300 GeV. The LAT was built by an international collaboration with contributions from space agencies, high-energy particle physics institutes, and universities in France, Italy, Japan, Sweden, and the United States. This paper describes the LAT, its preflight expected performance, and summarizes the key science objectives that will be addressed. On-orbit performance will be presented in detail in a subsequent paper. The LAT is a pair-conversion telescope with a precision tracker and calorimeter, each consisting of a 4 x 4 array of 16 modules, a segmented anticoincidence detector that covers the tracker array, and a programmable trigger and data acquisition system. Each tracker module has a vertical stack of 18 (x, y) tracking planes, including two layers (x and y) of single-sided silicon strip detectors and high-Z converter material (tungsten) per tray. Every calorimeter module has 96 CsI(Tl) crystals, arranged in an eight-layer hodoscopic configuration with a total depth of 8.6 radiation lengths, giving both longitudinal and transverse information about the energy deposition …
Date: May 15, 2009
Creator: Atwood, W. B.; /UC, Santa Cruz; Abdo, Aous A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. et al.
Object Type: Article
System: The UNT Digital Library
Analysis of the growth of strike-slip faults using effective medium theory (open access)

Analysis of the growth of strike-slip faults using effective medium theory

Increases in the dimensions of strike-slip faults including fault length, thickness of fault rock and the surrounding damage zone collectively provide quantitative definition of fault growth and are commonly measured in terms of the maximum fault slip. The field observations indicate that a common mechanism for fault growth in the brittle upper crust is fault lengthening by linkage and coalescence of neighboring fault segments or strands, and fault rock-zone widening into highly fractured inner damage zone via cataclastic deformation. The most important underlying mechanical reason in both cases is prior weakening of the rocks surrounding a fault's core and between neighboring fault segments by faulting-related fractures. In this paper, using field observations together with effective medium models, we analyze the reduction in the effective elastic properties of rock in terms of density of the fault-related brittle fractures and fracture intersection angles controlled primarily by the splay angles. Fracture densities or equivalent fracture spacing values corresponding to the vanishing Young's, shear, and quasi-pure shear moduli were obtained by extrapolation from the calculated range of these parameters. The fracture densities or the equivalent spacing values obtained using this method compare well with the field data measured along scan lines across the faults …
Date: October 15, 2009
Creator: Aydin, A. & Berryman, J.G.
Object Type: Article
System: The UNT Digital Library
The NAS Parallel Benchmarks (open access)

The NAS Parallel Benchmarks

The NAS Parallel Benchmarks (NPB) are a suite of parallel computer performance benchmarks. They were originally developed at the NASA Ames Research Center in 1991 to assess high-end parallel supercomputers. Although they are no longer used as widely as they once were for comparing high-end system performance, they continue to be studied and analyzed a great deal in the high-performance computing community. The acronym 'NAS' originally stood for the Numerical Aeronautical Simulation Program at NASA Ames. The name of this organization was subsequently changed to the Numerical Aerospace Simulation Program, and more recently to the NASA Advanced Supercomputing Center, although the acronym remains 'NAS.' The developers of the original NPB suite were David H. Bailey, Eric Barszcz, John Barton, David Browning, Russell Carter, LeoDagum, Rod Fatoohi, Samuel Fineberg, Paul Frederickson, Thomas Lasinski, Rob Schreiber, Horst Simon, V. Venkatakrishnan and Sisira Weeratunga. The original NAS Parallel Benchmarks consisted of eight individual benchmark problems, each of which focused on some aspect of scientific computing. The principal focus was in computational aerophysics, although most of these benchmarks have much broader relevance, since in a much larger sense they are typical of many real-world scientific computing applications. The NPB suite grew out of the …
Date: November 15, 2009
Creator: Bailey, David H.
Object Type: Report
System: The UNT Digital Library
Pre-launch Estimates for GLAST Sensitivity to Dark Matter Annihilation Signals (open access)

Pre-launch Estimates for GLAST Sensitivity to Dark Matter Annihilation Signals

We investigate the sensitivity of the Gamma-ray Large Area Space Telescope (GLAST) to indirectly detect weakly interacting massive particles (WIMPs) through the {gamma}-ray signal that their pair annihilation produces. WIMPs are among the favorite candidates to explain the compelling evidence that about 80% of the mass in the Universe is non-baryonic dark matter (DM). They are serendipitously motivated by various extensions of the standard model of particle physics such as Supersymmetry and Universal Extra Dimensions (UED). With its unprecedented sensitivity and its very large energy range (20 MeV to more than 300 GeV) the main instrument on board the GLAST satellite, the Large Area Telescope (LAT), will open a new window of discovery. As our estimates show, the LAT will be able to detect an indirect DM signature for a large class of WIMP models given a cuspy profile for the DM distribution. Using the current state of the art Monte Carlo and event reconstruction software developed within the LAT collaboration, we present preliminary sensitivity studies for several possible sources inside and outside the Galaxy. We also discuss the potential of the LAT to detect UED via the electron/positron channel. Diffuse background modeling and other background issues that will be …
Date: May 15, 2009
Creator: Baltz, E. A.; Berenji, B.; Bertone, G.; Bergstrom, L.; Bloom, E.; Bringmann, T. et al.
Object Type: Article
System: The UNT Digital Library
New Berkeley Lab Report Tracks a Decade of PV Installed Cost Trends (open access)

New Berkeley Lab Report Tracks a Decade of PV Installed Cost Trends

Installations of PV systems have been expanding at a rapid pace in recent years. In the United States, the market for PV is driven by national, state, and local government incentives, including upfront cash rebates, production-based incentives, requirements that electricity suppliers purchase a certain amount of solar energy, and Federal and state tax benefits. These programs are, in part, motivated by the popular appeal of solar energy and by the positive attributes of PV - e.g., modest environmental impacts, avoidance of fuel price risks, coincidence with peak electrical demand, and the location of PV at the point of use. Given the relatively high cost of PV, however, a key goal of these policies is to encourage cost reductions over time. Therefore, as policy incentives have become more significant and as PV deployment has accelerated, so too has the desire to track the installed cost of PV systems over time, by system characteristics, by system location, and by component. A new Lawrence Berkeley National Laboratory report, 'Tracking the Sun: The Installed Cost of Photovoltaics in the U.S. from 1998-2007', helps to fill this need by summarizing trends in the installed cost (i.e., the cost paid by the system owner) of grid-connected …
Date: April 15, 2009
Creator: Barbose, Galen; Peterman, Carla & Wiser, Ryan
Object Type: Article
System: The UNT Digital Library
Final Report: Experimental and Theoretical Studies of Surface Oxametallacycles - Connections to Heterogeneous Olefin Epoxidation (open access)

Final Report: Experimental and Theoretical Studies of Surface Oxametallacycles - Connections to Heterogeneous Olefin Epoxidation

This project has aimed at the rational design of catalysts for direct epoxidation of olefins. This chemistry remains one of the most challenging problems in heterogeneous catalysis. Although the epoxidation of ethylene by silver catalysts to form ethylene oxide (EO) has been practiced for decades, little progress has been made in expanding this technology to other products and processes. We have made significant advances through the combination of surface science experiments, Density Functional Theory (DFT) calculations, and catalytic reactor experiments, toward understanding the mechanism of this reaction on silver catalysts, and to the rational improvement of selectivity. The key has been our demonstration of surface oxametallacycle intermediates as the species that control reaction selectivity. This discovery permits the influence of catalyst promoters on selectivity to be probed, and new catalyst formulations to be developed. It also guides the development of new chemistry with potential for direct epoxidation of more complex olefins. During the award period we have focused on 1. the formation and reaction selectivity of complex olefin epoxides on silver surfaces, and 2. the influence of co-adsorbed oxygen atoms on the reactions of surface oxametallacycles on silver, and 3. the computational prediction, synthesis, characterization and experimental evaluation of bimetallic …
Date: September 15, 2009
Creator: Barteau, Mark A.
Object Type: Report
System: The UNT Digital Library
Radiation Chemistry 2008 Gordon Research Conference - July 6-11, 2008 (open access)

Radiation Chemistry 2008 Gordon Research Conference - July 6-11, 2008

Radiation Chemistry is chemistry initiated by ionizing radiation: i.e. photons or particles with energy sufficient to create charge pairs and/or free radicals in a medium. The important transients include conduction band electrons and 'holes', excitons, ionic and neutral free radicals, highly excited states, and solvated electrons. Effects of radiation span timescales from the energy deposition in femtoseconds, through geminate recombination in picoseconds and nanoseconds, to fast radical chemistry in microseconds and milliseconds, and ultimately to processes like cancer occurring decades later. The radiation sources used to study these processes likewise run from femtosecond lasers to nanosecond accelerators to years of gamma irradiation. As a result the conference has a strong interdisciplinary flavor ranging from fundamental physics to clinical biology. While the conference focuses on fundamental science, application areas highlighted in the present conference will include nuclear power, polymer processing, and extraterrestrial chemistry.
Date: May 15, 2009
Creator: Bartels, David M.
Object Type: Article
System: The UNT Digital Library
Sage-Grouse and Wind Energy: Biology, Habits, and Potential Effects from Development (open access)

Sage-Grouse and Wind Energy: Biology, Habits, and Potential Effects from Development

Proposed development of domestic energy resources, including wind energy, is expected to impact the sagebrush steppe ecosystem in the western United States. The greater sage-grouse relies on habitats within this ecosystem for survival, yet very little is known about how wind energy development may affect sage-grouse. The purpose of this report is to inform organizations of the impacts wind energy development could have on greater sage-grouse populations and identify information needed to fill gaps in knowledge.
Date: July 15, 2009
Creator: Becker, James M.; Tagestad, Jerry D.; Duberstein, Corey A. & Downs, Janelle L.
Object Type: Report
System: The UNT Digital Library
The Ultraviolet Behavior of N (open access)

The Ultraviolet Behavior of N

We describe the construction of the complete four-loop four-particle amplitude of N = 8 supergravity. The amplitude is ultraviolet finite, not only in four dimensions, but in five dimensions as well. The observed extra cancellations provide additional non-trivial evidence that N = 8 supergravity in four dimensions may be ultraviolet finite to all orders of perturbation theory.
Date: May 15, 2009
Creator: Bern, Z.; Carrasco, J.J.; Dixon, L.J.; Johansson, H. & Roiban, R.
Object Type: Article
System: The UNT Digital Library
Quasi-static analysis of elastic behavior for some systems having higher fracture densities. (open access)

Quasi-static analysis of elastic behavior for some systems having higher fracture densities.

Elastic behavior of geomechanical systems with interacting (but not intersecting) fractures is treated using generalizations of the Backus and the Schoenberg-Muir methods for analyzing layered systems whose layers are intrinsically anisotropic due to locally aligned fractures. By permitting the axis of symmetry of the locally anisotropic compliance matrix for individual layers to differ from that of the layering direction, we derive analytical formulas for interacting fractured regions with arbitrary orientations to each other. This procedure provides a systematic tool for studying how contiguous, but not yet intersecting, fractured domains interact, and provides a direct (though approximate) means of predicting when and how such interactions lead to more dramatic weakening effects and ultimately to failure of these complicated systems. The method permits decomposition of the system elastic behavior into specific eigenmodes that can all be analyzed, and provides a better understanding about which of these specific modes are expected to be most important to the evolving failure process.
Date: October 15, 2009
Creator: Berryman, J.G. & Aydin, A.
Object Type: Article
System: The UNT Digital Library
A Simple, Low Cost Longitudinal Phase Space Diagnostic (open access)

A Simple, Low Cost Longitudinal Phase Space Diagnostic

For proper operation of the LCLS [1] x-ray free-electron laser (FEL), and other similar machines, measurement and control of the electron bunch longitudinal phase space is critical. The LCLS accelerator includes two bunch compressor chicanes to magnify the peak current. These magnetic chicanes can generate significant coherent synchrotron radiation (CSR), which can distort the phase space distribution. We propose a diagnostic scheme by exciting a weak skew quadrupole at an energy-chirped, high dispersion point in the first LCLS bunch compressor (BC1) to reconstruct longitudinal phase space on an OTR screen after BC1, allowing a time-resolved characterization of CSR effects.
Date: May 15, 2009
Creator: Bertsche, Kirk; Emma, Paul & Shevchenko, Oleg
Object Type: Article
System: The UNT Digital Library
A Proposed Fast Luminosity Feedback for the Super-B Accelerator (open access)

A Proposed Fast Luminosity Feedback for the Super-B Accelerator

We present a possible design for a fast luminosity feedback for the SuperB Interaction Point (IP). The design is an extension of the fast luminosity feedback installed on the PEP-II accelerator. During the last two runs of PEP-II and BaBar (2007-2008), we had an improved luminosity feedback system that was able to maintain peak luminosity with faster correction speed than the previous system. The new system utilized fast dither coils on the High-Energy Beam (HEB) to independently dither the x position, the y position and the y angle at the IP, at roughly 100 Hz. The luminosity signal was then read out with three independent lock-in amplifiers. An overall correction was computed based on the lock-in signal strengths and beam corrections for position in x and y and in the y angle at the IP were simultaneously applied to the HEB. With the 100 times increase in luminosity for the SuperB design, we propose using a similar fast luminosity feedback that can operate at frequencies between DC and 1 kHz, high enough to follow any beam motion from the final focusing magnets.
Date: May 15, 2009
Creator: Bertsche, Kirk; Field, R.Clive; Fisher, Alan; Sullivan, Michael & Drago, Alessandro
Object Type: Article
System: The UNT Digital Library