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Operational Radiation Protection in Synchrotron Light and Free Electron Laser Facilities
The 3rd generation synchrotron radiation (SR) facilities are storage ring based facilities with many insertion devices and photon beamlines, and have low injection beam power (< few tens of watts), but extremely high stored beam power ({approx} 1 GW). The 4th generation x-ray free electron laser (FEL) facilities are based on an electron Linac with a long undulator and have high injection beam power (a few kW). Due to its electron and photon beam characteristics and modes of operation, storage ring and photon beamlines have unique safety aspects, which are the main subjects of this paper. The shielding design limits, operational modes, and beam losses are first reviewed. Shielding analysis (source terms and methodologies) and interlocked safety systems for storage ring and photon beamlines (including SR and gas bremsstrahlung) are described. Specific safety issues for storage ring top-off injection operation and FEL facilities are discussed. The operational safety program, e.g., operation authorization, commissioning, training, and radiation measurements, for SR facilities is also presented.
Date:
December 11, 2009
Creator:
Liu, James C.; Rokni, Sayed H. & Vylet, Vaclav
System:
The UNT Digital Library
PROJECTED IMPACT OF SULFATE ATTACK ON THE LONG-TERM PERFORMANCE OF A CONCRETE REPOSITORY
Saltstone is a cementitious waste form made by mixing salt solution originating from liquid waste storage tanks at the DOE Savannah River Site with a dry mix containing blast furnace slag, fly ash, and cement or lime. The wet mix is poured into a concrete repository for on-site disposal. Solidified Saltstone is a dense, alkaline, reducing, micro-porous, monolithic, cementitious matrix, containing a solution of salts within its pore structure. Sodium sulfate concentrations in the pore fluid are around 0.15 mol/L, and external sulfate attack on concrete barriers is expected to occur over time. To predict the long-term performance of concrete repositories, the STADIUM{reg_sign} code was used to simulate the reactive transport processes leading to formation of ettringite, an expansive mineral phase often associated with spalling or cracking. STADIUM{reg_sign} is a multi-ionic transport model based on a split operator approach that separates ionic movement and chemical reactions. Ionic transport is described by the extended Nernst-Planck equation for unsaturated media, and accounts for electrical coupling between ionic species, chemical activity, transport due to water content gradient, and temperature effects. STADIUM{reg_sign} does not predict whether physical damage will occur, or the impact on transport properties should fracturing occur. Thus the presence of ettringite …
Date:
December 11, 2009
Creator:
Flach, G.
System:
The UNT Digital Library
Special Issue for the 9th International Conference on Carbonaceous Particles in the Atmosphere
Carbonaceous particles are a minor constituent of the atmosphere but have a profound effect on air quality, human health, visibility and climate. The importance of carbonaceous particles has been increasingly recognized and become a mainstream topic at numerous conferences. Such was not the case in 1978, when the 1st International Conference on Carbonaceous Particles in the Atmosphere (ICCPA), or ''Carbon Conference'' as it is widely known, was introduced as a new forum to bring together scientists who were just beginning to reveal the importance and complexity of carbonaceous particles in the environment. Table 1 lists the conference dates, venues in the series as well as the proceedings, and special issues resulting form the meetings. Penner and Novakov (Penner and Novakov, 1996) provide an excellent historical perspective to the early ICCPA Conferences. Thirty years later, the ninth in this conference series was held at its inception site, Berkeley, California, attended by 160 scientists from 31 countries, and featuring both new and old themes in 49 oral and 83 poster presentations. Topics covered such areas as historical trends in black carbon aerosol, ambient concentrations, analytic techniques, secondary aerosol formation, biogenic, biomass, and HULIS1 characterization, optical properties, and regional and global climate effects. …
Date:
December 11, 2009
Creator:
Strawa, A.W.; Kirchstetter, T.W. & Puxbaum, H.
System:
The UNT Digital Library
The Surface Activation Layer of GaAs Negative Electron Affinity Photo cathode Activated by Cs, Li and NF3
The lifetime of GaAs photocathodes can be greatly improved by introducing Li in the Cs+NF{sub 3} activation process. The surface activation layer of such photocathodes is studied by synchrotron radiation photoemission and is compared with GaAs photocathodes activated without Li. The charge distributions of N, F and Cs experience significant changes when Li is added in the activation. In addition, the presence of Li causes NF{sub x} molecules to take an orientation with F atoms on top. All these changes induced by Li hold the key for the lifetime improvement of GaAs photocathodes.
Date:
December 11, 2009
Creator:
Sun, Yun; Kirby, R. E.; Maruyama, T.; Mulhollan, G. A.; Bierman, J. C. & Pianetta, P.
System:
The UNT Digital Library
Using Atom Interferometry to Search for New Forces
Atom interferometry is a rapidly advancing field and this Letter proposes an experiment based on existing technology that can search for new short distance forces. With current technology it is possible to improve the sensitivity by up to a factor of 10{sup 2} and near-future advances will be able to rewrite the limits for forces with ranges from 100 {micro}m to 1km.
Date:
December 11, 2009
Creator:
Wacker, Jay G.
System:
The UNT Digital Library
X-ray Absorption Spectroscopy Characterization of Zn Underpotential Deposition on Au(111) from Phosphate Supporting Electrolyte
Zn K-edge X-ray absorption spectroscopy (XAS) has been used to investigate the structure of Zn monolayers prepared on Au(111) electrodes via underpotential deposition (UPD) from phosphate supporting electrolyte. Theoretical modeling of the XAS data indicates that the Zn adatoms adopt a commensurate ({radical}3x{radical}3)R30{sup o} ({mu}{sub sc} = 0.33) adlayer structure and reside within the 3-fold hollow sites of the Au(111) surface. Meanwhile, phosphate counter-ions co-adsorb on the UPD adlayer and bridge between the Zn adatoms in a ({radical}3x{radical}3)R30{sup o} ({mu}{sub sc} = 0.33) configuration, with each phosphorous atom residing above a vacant 3-fold hollow site of the Au(111). Significantly, this surface structure is invariant between the electrochemical potential for UPD adlayer formation and the onset of bulk Zn electrodeposition. Analysis of the Zn K-edge absorption onset also presents the possibility that the Zn adatoms do not fully discharge during the process of UPD, which had been proposed in prior voltammetric studies of the phosphate/Zn(UPD)/Au(111) system.
Date:
December 11, 2009
Creator:
Lee, J. R.; O'Malley, R. L.; O'Connell, T. J.; Vollmer, A. & Rayment, T.
System:
The UNT Digital Library
XAL Adoption Experience at LCLS
XAL is a high level accelerator application framework originally developed by the Spallation Neutron Source (SNS), Oak Ridge National Laboratory. The XAL framework provides generic hierarchical view for an accelerator as well as many utility tools. In XAL, a built-in physics model calculates either single particle or beam envelope tracking for physics parameters. Modifications to the original XAL model are necessary for the Linac Coherent Light Source (LCLS). Work was done to manipulate MAD deck output within a database in support of the XAL configuration and model. The XAL graphical user interface has been replaced by a SLAC specific design. New applications based on the framework are also discussed in this paper.
Date:
December 11, 2009
Creator:
Chu, P.; Woodley, M.; Chan, A.; Chevtsov, S.; Fairley, D.; Grunhaus, E. et al.
System:
The UNT Digital Library
XAL-Based Applications and Online Models for LCLS
XAL, a high-level accelerator application framework originally developed at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory, has been adopted by the Linac Coherent Light Source (LCLS) project. The work includes proper relational database schema modification to better suit XAL configuration data requirement, addition of new device types for LCLS online modeling purpose, longitudinal coordinate system change to better represent the LCLS electron beam rather than proton or ion beam in the original SNS XAL design, intensively benchmark with MAD and present SLC modeling system for the online model, and various new features to the XAL framework. Storing online model data in a relational database and providing universal access methods for other applications is also described here.
Date:
December 11, 2009
Creator:
Chu, P.; Woodley, M.; Iverson, R.; Krejcik, P.; White, G.; Wu, J. et al.
System:
The UNT Digital Library
Interpretation of Wild 2 Dust Fine Structure: Comparison of Stardust Aluminium Foil Craters to the Three-Dimensional Shape of Experimental Impacts by Artificial Aggregate Particles and Meteorite Powders
New experimental results show that Stardust crater morphology is consistent with interpretation of many larger Wild 2 dust grains being aggregates, albeit most of low porosity and therefore relatively high density. The majority of large Stardust grains (i.e. those carrying most of the cometary dust mass) probably had density of 2.4 g cm{sup -3} (similar to soda-lime glass used in earlier calibration experiments) or greater, and porosity of 25% or less, akin to consolidated carbonaceous chondrite meteorites, and much lower than the 80% suggested for fractal dust aggregates. Although better size calibration is required for interpretation of the very smallest impacting grains, we suggest that aggregates could have dense components dominated by {micro}m-scale and smaller sub-grains. If porosity of the Wild 2 nucleus is high, with similar bulk density to other comets, much of the pore-space may be at a scale of tens of micrometers, between coarser, denser grains. Successful demonstration of aggregate projectile impacts in the laboratory now opens the possibility of experiments to further constrain the conditions for creation of bulbous (Type C) tracks in aerogel, which we have observed in recent shots. We are also using mixed mineral aggregates to document differential survival of pristine composition and …
Date:
December 10, 2009
Creator:
Kearsley, A T; Burchell, M J; Price, M C; Graham, G A; Wozniakiewicz, P J; Cole, M J et al.
System:
The UNT Digital Library
The neuroprotective properties of palmitoylethanolamine against oxidative stress in a neuronal cell line
This article discusses the neuroprotective properties of palmitoylethanolamine against oxidative stress in a neuronal cell line.
Date:
December 10, 2009
Creator:
Duncan, Scott R.; Chapman, Kent D. & Koulen, Peter
System:
The UNT Digital Library
Sum frequency generation and catalytic reaction studies of the removal of the organic capping agents from Pt nanoparticles by UV-ozone treatment
We report the structure of the organic capping layers of platinum colloid nanoparticles and their removal by UV-ozone exposure. Sum frequency generation vibrational spectroscopy (SFGVS) studies identify the carbon-hydrogen stretching modes on poly(vinylpyrrolidone) (PVP) and tetradecyl tributylammonium bromide (TTAB)-capped platinum nanoparticles. We found that the UV-ozone treatment technique effectively removes the capping layer on the basis of several analytical measurements including SFGVS, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The overall shape of the nanoparticles was preserved after the removal of capping layers, as confirmed by transmission electron microscopy (TEM). SFGVS of ethylene hydrogenation on the clean platinum nanoparticles demonstrates the existence of ethylidyne and di-{sigma}-bonded species, indicating the similarity between single-crystal and nanoparticle systems.
Date:
December 10, 2009
Creator:
Aliaga, Cesar; Park, Jeong Y.; Yamada, Yusuke; Lee, Hyun Sook; Tsung, Chia-Kuang; Yang, Peidong et al.
System:
The UNT Digital Library
Three-fold diffraction symmetry in epitaxial graphene and the SiC substrate
The crystallographic symmetries and spatial distribution of stacking domains in graphene films on 6H-SiC(0001) have been studied by low energy electron diffraction (LEED) and dark field imaging in a low energy electron microscope (LEEM). We find that the graphene diffraction spots from 2 and 3 atomic layers of graphene have 3-fold symmetry consistent with AB (Bernal or rhombohedral) stacking of the layers. On the contrary, graphene diffraction spots from the buffer layer and monolayer graphene have apparent 6-fold symmetry, although the 3-fold nature of the satellite spots indicates a more complex periodicity in the graphene sheets.
Date:
December 10, 2009
Creator:
Siegel, D A; Zhou, S Y; El Gabaly, F; Schmid, A K; McCarty, K F & Lanzara, A
System:
The UNT Digital Library
Absolute Bunch Length Measurements by Incoherent Radiation Fluctuation Analysis
By analyzing the pulse to pulse intensity fluctuations of the radiation emitted by a charge particle in the incoherent part of the spectrum, it is possible to extract information about the spatial distribution of the beam. At the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory, we have developed and successfully tested a simple scheme based on this principle that allows for the absolute measurement of the rms bunch length. A description of the method and the experimental results are presented.
Date:
December 9, 2009
Creator:
Sannibale, F.; /LBL, Berkeley; Stupakov, G.V.; /SLAC; Zolotorev, M.S.; /LBL, Berkeley et al.
System:
The UNT Digital Library
Beam Echo Effect for Generation of Short-Wavelength Radiation
The Echo-Enabled Harmonic Generation (EEHG) FEL uses two modulators in combination with two dispersion sections to generate a high-harmonic density modulation starting with a relatively small initial energy modulation of the beam. After presenting the concept of the EEHG, we address several practically important issues, such as the effect of coherent and incoherent synchrotron radiation in the dispersion sections. Using a representative realistic set of beam parameters, we show how the EEHG scheme enhances the FEL performance and allows one to generate a fully (both longitudinally and transversely) coherent radiation. We then discuss application of the echo modulation for generation of attosecond pulses of radiation, and also using echo for generation of terahertz radiation. We present main parameters of a proof-of-principle experiment currently being planned at SLAC for demonstration of the echo modulation mechanism.
Date:
December 9, 2009
Creator:
Stupakov, G.
System:
The UNT Digital Library
Calculation of Coherent Synchrotron Radiation Impedance Using the Mode Expansion Method
We study an impedance due to coherent synchrotron radiation (CSR) generated by a short bunch of charged particles passing through a dipole magnet of finite length in a vacuum chamber of a given cross section. In our method we decompose the electromagnetic field of the beam over the eigenmodes of the toroidal chamber and derive a system of equations for the expansion coefficients in the series. The general method is further specialized for a toroidal vacuum chamber of a rectangular cross section where the eigenmodes can be computed analytically. We also develop a computer code that calculates the CSR impedance for a toroid of rectangular cross section. Numerical results obtained with the code are presented in the paper.
Date:
December 9, 2009
Creator:
Stupakov, G. V. & Kotelnikov, I. A.
System:
The UNT Digital Library
Design Considerations for a PEBB-Based Marx-Topology ILC Klystron Modulator
The concept of Power Electronic Building Blocks (PEBBs) has its origin in the U.S. Navy during the last decade of the past century. As compared to a more conventional or classical design approach, a PEBB-oriented design approach combines various potential advantages such as increased modularity, high availability and simplified serviceability. This relatively new design paradigm for power conversion has progressively matured since then and its underlying philosophy has been clearly and successfully demonstrated in a number of real-world applications. Therefore, this approach has been adopted here to design a Marx-topology modulator for an International Linear Collider (ILC) environment where easy serviceability and high availability are crucial. This paper describes various aspects relating to the design of a 32-cell Marx-topology ILC klystron modulator. The concept of nested droop correction is introduced and illustrated. Several design considerations including cosmic ray withstand, power cycling capability, fault tolerance, etc., are discussed. Details of the design of a Marx cell PEBB are included.
Date:
December 9, 2009
Creator:
Macken, K.; Beukers, T.; Burkhart, C.; Kemp, M. A.; Nguyen, M. N. & Tang, T.
System:
The UNT Digital Library
FEL and Optical Klystron Gain for an Electron Beam with Oscillatory Energy Distribution
If the energy spread of a beam is larger then the Pierce parameter, the FEL gain length increases dramatically and the FEL output gets suppressed. We show that if the energy distribution of such a beam is made oscillatory on a small scale, the gain length can be considerably decreased. Such an oscillatory energy distribution is generated by first modulating the beam energy with a laser via the mechanism of inverse FEL, and then sending it through a strong chicane. We show that this approach also works for the optical klystron enhancement scheme. Our analytical results are corroborated by numerical simulations.
Date:
December 9, 2009
Creator:
Stupakov, G.; Ding, Y. & Huang, Z.
System:
The UNT Digital Library
Heavy-Quarkonium Production in High Energy Proton-Proton Collisions at RHIC
We update the study of the total {psi} and {Upsilon} production cross section in proton-proton collisions at RHIC energies using the QCD-based Color-Singlet (CS) Model, including next-to-leading order partonic matrix elements. We also include charm-quark initiated processes which appear at leading order in {alpha}{sub s}, but which have so far been overlooked in such studies. Contrary to earlier claims, we show that the CS yield is consistent with measurements over a broad range of J/{psi} rapidities. We also find that charm-quark initiated processes, including both intrinsic and sea-like charm components, typically contribute at least 20 % of the direct J/{psi} yield, improving the agreement with data both for the integrated cross section and its rapidity dependence. The key signature for such processes is the observation of a charm-quark jet opposite in azimuthal angle {phi} to the detected J/{psi}. Our results have impact on the proper interpretation of heavy-quarkonium production in heavy-ion collisions and its use as a probe for the quark-gluon plasma.
Date:
December 9, 2009
Creator:
Brodsky, Stanley J. & Lansberg, Jean-Philippe
System:
The UNT Digital Library
Light-Front Holography, AdS/QCD, and Hadronic Phenomena
AdS/QCD, the correspondence between theories in a modified five-dimensional anti-de Sitter space and confining field theories in physical space-time, provides a remarkable semiclassical model for hadron physics. Light-front holography allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time, thus providing a relativistic description of hadrons at the amplitude level. We identify the AdS coordinate z with an invariant light-front coordinate {zeta} which separates the dynamics of quark and gluon binding from the kinematics of constituent spin and internal orbital angular momentum. The result is a single-variable light-front Schroedinger equation with a confining potential which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The mapping of electromagnetic and gravitational form factors in AdS space to their corresponding expressions in light-front theory confirms this correspondence. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates. The distinction between static structure functions, such as the probability distributions computed from the square of the light-front wavefunctions, versus dynamical structure functions which include the effects of rescattering, is emphasized. A new method for computing the hadronization of quark and …
Date:
December 9, 2009
Creator:
Brodsky, Stanley J. & de Teramond, Guy F.
System:
The UNT Digital Library
Light-Front Holography and Gauge/Gravity Duality: The Light Meson and Baryon Spectra
Starting from the bound state Hamiltonian equation of motion in QCD, we derive relativistic light-front wave equations in terms of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. These equations of motion in physical space-time are equivalent to the equations of motion which describe the propagation of spin-J modes in anti-de Sitter (AdS) space. Its eigenvalues give the hadronic spectrum, and its eigenmodes represent the probability amplitudes of the hadronic constituents at a given scale. An effective classical gravity description in a positive-sign dilaton background exp(+{kappa}{sup 2}z{sup 2}) is given for the phenomenologically successful soft-wall model which naturally encodes the internal structure of hadrons and their orbital angular momentum. Applications to the light meson and baryon spectrum are presented.
Date:
December 9, 2009
Creator:
de Teramond, Guy F.; U., /Costa Rica & Brodsky, Stanley J.
System:
The UNT Digital Library
Light-Front Holography and Non-Perturbative QCD
The combination of Anti-de Sitter space (AdS) methods with light-front holography leads to a semi-classical first approximation to the spectrum and wavefunctions of meson and baryon light-quark bound states. Starting from the bound-state Hamiltonian equation of motion in QCD, we derive relativistic light-front wave equations in terms of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. These equations of motion in physical space-time are equivalent to the equations of motion which describe the propagation of spin-J modes in anti-de Sitter (AdS) space. Its eigenvalues give the hadronic spectrum, and its eigenmodes represent the probability distribution of the hadronic constituents at a given scale. Applications to the light meson and baryon spectra are presented. The predicted meson spectrum has a string-theory Regge form M{sup 2} = 4{kappa}{sup 2}(n + L + S = 2); i.e., the square of the eigenmass is linear in both L and n, where n counts the number of nodes of the wavefunction in the radial variable {zeta}. The space-like pion form factor is also well reproduced. One thus obtains a remarkable connection between the description of hadronic modes in AdS space and …
Date:
December 9, 2009
Creator:
Brodsky, Stanley J. & de Teramond, Guy F.
System:
The UNT Digital Library
Measurements of Charmless B Decays Related to alpha at BaBar
We report recent measurements of the CKM angle {alpha} using data collected by the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} collider at the SLAC National Accelerator Laboratory. In addition to improved constraints on {alpha} from the decays B{sup {+-}} {yields} {rho}{sup {+-}}{rho}{sup 0}, we also present preliminary results of neutral and charged B meson decays to K{sub 1}(1270){pi} and K{sub 1}(1400){pi} and its impact on the estimate for the CKM angle {alpha} based on time-dependent analysis of CP-violating asymmetries in B{sup 0} {yields} a{sub 1}(1260){sup {+-}} {pi}{sup {-+}}. Moreover we report the first observation of the decay B {yields} a{sub 1}(1260){sup {+-}}a{sub 1}(1260){sup {-+}}; this mode can be used, in principle, to provide an independent measurement of {alpha}.
Date:
December 9, 2009
Creator:
Lombardo, Vincenzo & /INFN, Milan
System:
The UNT Digital Library
Measurements of Time-Dependent CP Asymmetries in b\to s Penguin Dominated Hadronic B Decays at BaBar
We report measurements of Time-Dependent CP asymmetries in several b {yields} s penguin dominated hadronic B decays, where New Physics contributions may appear. We find no significant discrepancies with respect to the Standard Model expectations.
Date:
December 9, 2009
Creator:
Biassoni, Pietro
System:
The UNT Digital Library
Multi-Device Knob Utility for LCLS
At the SLAC National Accelerator Laboratory (SLAC) the Controls Department (CD) has developed a new Multi-Device Knob Utility (MKB) based on the Experimental Physics and Industrial Control System (EPICS) toolkit for controlling one or more Process Variables (PVs) in unison, or simultaneously, from a physical knob located in the control room, or from various software tools such as the EPICS Extensible Display Manager (EDM) or a Swing slider in Java. A group of devices are hooked up to a knob, and then the value written to the devices is a simple function of the value of the knob. This is used, most commonly, to create a bump in the electron beam for the Linac Coherent Light Source (LCLS). Control system variables typically controlled are magnetic fields, phases, and timing offsets. This paper describes the technologies used to implement this utility.
Date:
December 9, 2009
Creator:
Zelazny, Michael; Chevtsov, Sergei; Chu, Chungming Paul; Fairley, Diane; Krejcik, Patrick; Rogind, Deborah et al.
System:
The UNT Digital Library