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Probing the Geometry and Physics of the Emission Region in Active Galactic Nuclei using hard X-ray & Gamma-ray Observations

Description: The X-ray spectra of {approx}200 AGN collected from Swift-BAT were analyzed to test the Unified Model for AGN. Specifically, the photon indices, high energy cutoffs, and reflection components of Sy1 and Sy2 were compared. Under the Unified Model, the photon indices and reflection components for Sy1 should be larger than Sy2 and the high energy cutoffs should be the same. Fitting a simple power law model to the sample spectra proved to be insufficient. The PEXRAV model fit the spectra of the Sy1 and Sy2 significantly better, indicating that a reflection component and/or high energy cutoff exists as the Unified Model expects. Using both the simple power law and PEXRAV models it was concluded that in the population studied, Sy1 had a larger photon index than Sy2, as expected by the Unified Model. For Sy1 and Sy2, the reflection components were found to be compatible, but given the large errors, this finding cannot be said to be evidence against the Unified Model. However, it was concluded that Sy1 and Sy2 have different high energy cutoffs, which is unexpected under the Unified Model.
Date: August 25, 2010
Creator: Woods, Natasha & /Texas U., Dallas /SLAC /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Operating the LCLS Gas Attenuator and Gas Detector System with Apertures of 6mm Diameter

Description: The possibility of increasing the apertures of the LCLS gas attenuator/gas detector system is considered. It is shown that increase of the apertures from 3 to 6 mm, together with 4-fold reduction of the operation pressure does not adversely affect the vacuum conditions upstream or downstream. No change of the pump speed and the lengths of the differential pumping cells is required. One minor modification is the use of 1.5 cm long tubular apertures in the end cells of the differential pumping system. Reduction of the pressure does not affect performance of the gas attenuator/gas detector system at the FEL energies below, roughly, 2 keV. Some minor performance degradation occurs at higher energies.
Date: November 17, 2010
Creator: Ryutov, D.D.; Bionta, R.M.; Hau-Riege, S.P.; Kishiyama, K.I.; Roeben, M.D.; Shen, S. et al.
Partner: UNT Libraries Government Documents Department

Optimal Model-Based Fault Estimation and Correction for Particle Accelerators and Industrial Plants Using Combined Support Vector Machines and First Principles Models

Description: Timely estimation of deviations from optimal performance in complex systems and the ability to identify corrective measures in response to the estimated parameter deviations has been the subject of extensive research over the past four decades. The implications in terms of lost revenue from costly industrial processes, operation of large-scale public works projects and the volume of the published literature on this topic clearly indicates the significance of the problem. Applications range from manufacturing industries (integrated circuits, automotive, etc.), to large-scale chemical plants, pharmaceutical production, power distribution grids, and avionics. In this project we investigated a new framework for building parsimonious models that are suited for diagnosis and fault estimation of complex technical systems. We used Support Vector Machines (SVMs) to model potentially time-varying parameters of a First-Principles (FP) description of the process. The combined SVM & FP model was built (i.e. model parameters were trained) using constrained optimization techniques. We used the trained models to estimate faults affecting simulated beam lifetime. In the case where a large number of process inputs are required for model-based fault estimation, the proposed framework performs an optimal nonlinear principal component analysis of the large-scale input space, and creates a lower dimension feature space in which fault estimation results can be effectively presented to the operation personnel. To fulfill the main technical objectives of the Phase I research, our Phase I efforts have focused on: (1) SVM Training in a Combined Model Structure - We developed the software for the constrained training of the SVMs in a combined model structure, and successfully modeled the parameters of a first-principles model for beam lifetime with support vectors. (2) Higher-order Fidelity of the Combined Model - We used constrained training to ensure that the output of the SVM (i.e. the parameters of the beam lifetime model) are ...
Date: August 25, 2010
Creator: Sayyar-Rodsari, Bijan; Schweiger, Carl & /SLAC /Pavilion Technologies, Inc., Austin, TX
Partner: UNT Libraries Government Documents Department

Optimization of the LCLS Single Pulse Shutter

Description: A mechanical shutter which operates on demand is used to isolate a single pulse from a 120 Hz X-ray source. This is accomplished with a mechanical shutter which is triggered on demand with frequencies ranging from 0 to 10 Hz. The single pulse shutter is an iron blade that oscillates on a pivot in response to a force generated by a pair of pulsed electromagnets (current driven teeter-totter). To isolate an individual pulse from the X-ray beam, the motion of the mechanical shutter should be synchronized in such a way that it allows a single pulse to pass through the aperture and blocks the other incoming pulses. Two consecutive pulses are only {approx} 8 ms apart and the shutter is required to complete one full cycle such that no two pulses pass through the opening. Also the opening of the shutter blade needs to be at least 4 mm so that a 1 mm diameter rms Gaussian beam can pass through without modulation. However, the 4 mm opening is difficult to obtain due to blade rebound and oscillation of the blade after colliding with the electromagnet. The purpose of this project is to minimize and/or totally eliminate the rebound of the shutter blade in pursuit of maximizing the aperture while keeping the open window interval < {approx}12 ms.
Date: August 25, 2010
Creator: Adera, Solomon & /Georgia Tech., Atlanta /SLAC
Partner: UNT Libraries Government Documents Department

LHC RF System Time-Domain Simulation

Description: Non-linear time-domain simulations have been developed for the Positron-Electron Project (PEP-II) and the Large Hadron Collider (LHC). These simulations capture the dynamic behavior of the RF station-beam interaction and are structured to reproduce the technical characteristics of the system (noise contributions, non-linear elements, and more). As such, they provide useful results and insight for the development and design of future LLRF feedback systems. They are also a valuable tool for the study of diverse longitudinal beam dynamics effects such as coupled-bunch impedance driven instabilities and single bunch longitudinal emittance growth. Results from these studies and related measurements from PEP-II and LHC have been presented in multiple places. This report presents an example of the time-domain simulation implementation for the LHC.
Date: September 14, 2010
Creator: Mastorides, T.; Rivetta, C. & /SLAC
Partner: UNT Libraries Government Documents Department

Model of gamma sky for the Fermi Gamma-ray Space Telescope (FGST)

Description: A number of important parameters of cosmic-ray distribution, propagation, and interaction in the Milky Way can be predicted through the comparison of measured cosmic-ray and gamma-ray spectra to the spectra of simulated Galaxies. These predictions are made by altering the physical parameters governing Galaxy simulations until a best-fit set of parameters is found. Since the accuracy of this method is limited by the quality of available data, the exceptional precision of recent FGST gamma-ray measurements makes unprecedented galactic model refinement possible. Consequently, this data was used as a benchmark in optimizing galactic models derived by GALPROP. An in-depth investigation was performed on a wide range of galactic models, and improvement or degeneration in each was gauged through specialized analysis using novel GaDGET software. By analyzing individual galactic parameters and their effects on observed spectra, a new optimized set of parameters was found that better fits the Fermi data than previous GALPROP models. This result is especially important in refining previous estimates of galactic parameters that cannot be measured directly. It also provides an important check on known galactic parameters and enhances GALPROPs value as a high-level modeling tool.
Date: August 25, 2010
Creator: McLeod, Andrew & /UC, San Diego /SLAC /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

QM02 Strength Measurement

Description: In late April, Paul Emma reported that his orbit fitting program could find a reasonably good fit only if the strength of QM02 was changed from design value of -5.83 kG to -6.25 kG - a strength change of 7.3%. In late May, we made a focal length measurement of QM02 by turning off all focusing optics between YC07 and BPMS1 (in the spectrometer line) except for QM02 and adjusted the strength of QM02 so that vertical kicks by YC07 did not produce any displacements at BPMS1 (see Figure 1). The result was quoted in the LCLS elog was that QM02 appeared to 6% too weak, and approximately agreed with Paul's observation. The analysis used for the entry in the log book was based on the thin lens approximation and used the following numbers: Distance YC07 to QM02 - 5.128 m; Distance QM02 to BPMS1 - 1.778 m; and Energy - 135 MeV. These distances were computed from the X,Z coordinates given the on the large plot of the Injector on the wall of the control room. On review of the MAD output file coordinates, it seems that the distance used for QM02 to BPMS1 is not 1.778 m. The correct value is Distance, center of QM02 to BPMS1 - 1.845 m. There may be a typo on the wall chart values for the coordinates of BPMS1, or perhaps there was a misinterpretation of edge versus center of QM02. In any case, the effect of this change is that the thin lens estimate changes from 6% too weak to 9% too weak. At John Galayda's suggestion, we looked into the thin lens versus thick lens approximation. A Mathematica program was written to solve for the K value of the QM02, in the thick lens approximation, that provides point to point ...
Date: November 24, 2010
Creator: Welch, J; Wu, J.; /SLAC & ,
Partner: UNT Libraries Government Documents Department

Report on Modifications to the BX12 and BX13 BC1 Dipoles

Description: Emittance growth seen during the last commissioning run in the bunch compressor optics section, BC1, was blamed on inadequate dipole field quality. The significant linear and nonlinear field non-uniformities generated large horizontal dispersion errors beyond BC1. The linear dispersion after BC1 was corrected using two small 'corrector' quadrupoles placed in BC1 for this purpose, but the remaining nonlinear field caused growth of the normalized horizontal emittance of 40% or more. At best {gamma}{epsilon}{sub x} went from 1.2 {micro}m before BC1 up to 1.7 {micro}m after BC1. The problem was magnified by the larger-than-design energy spread in BC1 due to a long initial bunch length. To improve the field quality we decided to modify the two 'inner dipoles', BX12 and BX13, of the four magnet chicane during the four month down time in the Fall of 2007. Only the two inner dipoles were chosen because of the limited time available and the fact that the beam is particularly sensitive to field quality of the inner dipoles due to its very large transverse size when going through them. The modifications were completed in November and included new poles and a new pinning scheme. The outer dipoles were left unchanged.
Date: November 23, 2010
Creator: Welch, James; DeBarge, S.; Emma, P.; Fisher, A.; Li, N.; Wu, J. et al.
Partner: UNT Libraries Government Documents Department

Retrofitting and the mu Problem

Description: One of the challenges of supersymmetry (SUSY) breaking and mediation is generating a {mu} term consistent with the requirements of electro-weak symmetry breaking. The most common approach to the problem is to generate the {mu} term through a SUSY breaking F-term. Often these models produce unacceptably large B{mu} terms as a result. We will present an alternate approach, where the {mu} term is generated directly by non-perturtative effects. The same non-perturbative effect will also retrofit the model of SUSY breaking in such a way that {mu} is at the same scale as masses of the Standard Model superpartners. Because the {mu} term is not directly generated by SUSY breaking effects, there is no associated B{mu} problem. These results are demonstrated in a toy model where a stringy instanton generates {mu}.
Date: August 26, 2010
Creator: Green, Daniel; Weigand, Timo & /SLAC /Stanford U., Phys. Dept.
Partner: UNT Libraries Government Documents Department


Description: The authors have searched for an asymmetry in the inelastic scattering of electrons from a polarized proton target in the region of resonance excitation, at values of four-momentum transfer squared of 0.4, 0.6 and 1.0 (GeV/c){sup 2}. Data were also taken using an incident positron beam in order to distinguish any possible effect of time-reversal violation from that due to higher-order ({alpha}{sup 3}) contributions to the scattering. No sizeable violation of time-reversal invariance was found.
Date: March 1, 1970
Creator: Rock, Stephen; Borghini, Michel; Chamberlain, Owen; Fuzesy,Raymond Z.; Morehouse, Charles C.; Powell, Thomas et al.
Partner: UNT Libraries Government Documents Department

First Results of the LCLS Laser-Heater System

Description: The Linac Coherent Light Source (LCLS) is an x-ray Free-Electron Laser (FEL) project that has just achieved its first lasing at 1.5 {angstrom} radiation wavelength. The very bright electron beam required to drive this FEL is susceptible to a microbunching instability in the magnetic bunch compressors that may increase the slice energy spread beyond the FEL tolerance. To control the slice energy spread and to suppress the microbunching instability, a laser heater (LH) system is installed in the LCLS injector area at 135 MeV, right before the RF deflector that is used for the time-resolved electron diagnostics. This unique component is used to add a small level of intrinsic energy spread to the electron beam in order to Landau damp the microbunching instability before it potentially breaks up the high brightness electron beam. The system was fully installed and tested in the fall of 2008, and effects of heating on the electron beam and the x-ray FEL were studied during the 2009 commissioning period. The laser heater system is composed of a 4-dipole chicane; a 9-period, planar, permanent-magnet, adjustable-gap undulator at the center of the chicane; one OTR screen on each side of the undulator for electron/laser spatial alignment; and an IR laser (up to 15-MW power) which co-propagates with the electron beam inside the undulator generating a 758-nm energy modulation along the bunch. The final two dipoles of the 4-dipole chicane time-smear this modulation leaving only a thermal-like intrinsic energy spread within the bunch. Table 1 lists the main parameters for this system. The very bright electron beam required for an x-ray free-electron laser (FEL), such as the LCLS, is susceptible to a microbunching instability in the magnetic bunch compressors, prior to the FEL undulator. The uncorrelated electron energy spread in the LCLS can be increased by an order ...
Date: December 16, 2011
Creator: Emma, P; Boyce, R.F.; Brachmann, A.; Carr, R.; Decker, F.-J.; Ding, Y. et al.
Partner: UNT Libraries Government Documents Department

Betatron-Function Measurement in Lattices with 90-Degrees Sections

Description: Lattice functions derived from betatron phase-advance measurements have been used successfully at many e{sup +}-e{sup -} facilities in the world, including at the PEP-II High Energy Ring. For the Low energy Ring of PEP-II, however, extraction of meaningful beta functions is hampered by the 90{sup o} phase advance/cell in the arcs, which causes a singularity in the expressions for beta. An algorithm has been developed calculating beta functions based on {beta} and {alpha} at the beginning of an arc and tracking the Twiss parameters through the arc while matching the observed phase advance/cell. Stability of the algorithm is improved by doing the same calculation 'backward' as well as forward and averaging the result. The algorithm allows estimating beta functions at bad BPMs in many cases. The paper presents the algorithm used as well as examples of use in PEP.
Date: April 24, 2012
Creator: Wienands, U.; /SLAC; Biagini, M.E. & /Frascati
Partner: UNT Libraries Government Documents Department

Representing Range Compensators with Computational Geometry in TOPAS

Description: In a proton therapy beamline, the range compensator modulates the beam energy, which subsequently controls the depth at which protons deposit energy. In this paper, we introduce two computational representations of range compensator. One of our compensator representations, which we refer to as a subtraction solid-based range compensator, precisely represents the compensator. Our other representation, the 3D hexagon-based range compensator, closely approximates the compensator geometry. We have implemented both of these compensator models in a proton therapy Monte Carlo simulation called TOPAS (Tool for Particle Simulation). In the future, we will present a detailed study of the accuracy and runtime performance trade-offs between our two range compensator representations.
Date: September 7, 2012
Creator: Iandola, Forrest N. & /Illinois U., Urbana /SLAC
Partner: UNT Libraries Government Documents Department

Research and Design of a Sample Heater for Beam Line 6-2c Transmission X-ray Microscope

Description: There exists a need for environmental control of samples to be imaged by the Transmission X-Ray Microscope (TXM) at the SSRLs Beam Line 6-2c. In order to observe heat-driven chemical or morphological changes that normally occur in situ, microscopes require an additional component that effectively heats a given sample without heating any of the microscope elements. The confinement of the heat and other concerns about the heaters integrity limit which type of heater is appropriate for the TXM. The bulk of this research project entails researching different heating methods used previously in microscopes, but also in other industrial applications, with the goal of determining the best-fitting method, and finally in designing a preliminary sample heater.
Date: August 27, 2012
Creator: Policht, Veronica & /Loyola U., Chicago /SLAC
Partner: UNT Libraries Government Documents Department

Resolving Lifshitz Horizons

Description: Via the AdS/CFT correspondence, ground states of field theories at finite charge density are mapped to extremal black brane solutions. Studies of simple gravity + matter systems in this context have uncovered wide new classes of extremal geometries. The Lifshitz metrics characterizing field theories with non-trivial dynamical critical exponent z {ne} 1 emerge as one common endpoint in doped holographic toy models. However, the Lifshitz horizon exhibits mildly singular behaviour - while curvature invariants are finite, there are diverging tidal forces. Here we show that in some of the simplest contexts where Lifshitz metrics emerge, Einstein-Maxwell-dilaton theories, generic corrections lead to a replacement of the Lifshitz metric, in the deep infrared, by a re-emergent AdS{sub 2} x R{sup 2} geometry. Thus, at least in these cases, the Lifshitz scaling characterizes the physics over a wide range of energy scales, but the mild singularity is cured by quantum or stringy effects.
Date: April 24, 2012
Creator: Harrison, Sarah; Kachru, Shamit; Wang, Huajia & /Stanford U., ITP /Stanford U., Phys. Dept. /SLAC
Partner: UNT Libraries Government Documents Department

Section on Supernova Remnants and Cosmic Rays of the White Paper on the Status and Future of Ground-Based Gamma-Ray Astronomy

Description: This is a report on the findings of the SNR/cosmic-ray working group for the white paper on the status and future of ground-based gamma-ray astronomy. The white paper is an APS commissioned document, and the overall version has also been released and can be found on astro-ph. This detailed section of the white paper discusses the status of past and current attempts to observe shell-type supernova remnants and diffuse emission from cosmic rays at GeV-TeV energies. We concentrate on the potential of future ground-based gamma-ray experiments to study the acceleration of relativistic charged particles which is one of the main unsolved, yet fundamental, problems in modern astrophysics. The acceleration of particles relies on interactions between energetic particles and magnetic turbulence. In the case of SNRs we can perform spatially resolved studies in systems with known geometry, and the plasma physics deduced from these observations will help us to understand other systems where rapid particle acceleration is believed to occur and where observations as detailed as those of SNRs are not possible.
Date: November 9, 2011
Creator: Pohl, M.; U., /Iowa State; Abdo, Aous A.; U., /Michigan State; Atoyan, A.; U., /McGill et al.
Partner: UNT Libraries Government Documents Department

Reference Undulator Measurement Results

Description: The LCLS reference undulator has been measured 22 times during the course of undulator tuning. These measurements provide estimates of various statistical errors. This note gives a summary of the reference undulator measurements and it provides estimates of the undulator tuning errors. We measured the reference undulator many times during the tuning of the LCLS undulators. These data sets give estimates of the random errors in the tuned undulators. The measured trajectories in the reference undulator are stable and straight to within {+-}2 {micro}m. Changes in the phase errors are less than {+-}2 deg between data sets. The phase advance in the cell varies by less than {+-}2 deg between data sets. The rms variation between data sets of the first integral of B{sub x} is 9.98 {micro}Tm, and the rms variation of the second integral of B{sub x} is 17.4 {micro}Tm{sup 2}. The rms variation of the first integral of B{sub y} is 6.65 {micro}Tm, and the rms variation of the second integral of B{sub y} is 12.3 {micro}Tm{sup 2}. The rms variation of the x-position of the fiducialized beam axis is 35 {micro}m in the final production run This corresponds to an rms uncertainty in the K value of {Delta}K/K = 2.7 x 10{sup -5}. The rms variation of the y-position of the fiducialized beam axis is 4 {micro}m in the final production run.
Date: August 18, 2011
Creator: Wolf, Zachary; Levashov, Yurii; /SLAC & ,
Partner: UNT Libraries Government Documents Department

Using Dynamic Quantum Clustering to Analyze Hierarchically Heterogeneous Samples on the Nanoscale

Description: Dynamic Quantum Clustering (DQC) is an unsupervised, high visual data mining technique. DQC was tested as an analysis method for X-ray Absorption Near Edge Structure (XANES) data from the Transmission X-ray Microscopy (TXM) group. The TXM group images hierarchically heterogeneous materials with nanoscale resolution and large field of view. XANES data consists of energy spectra for each pixel of an image. It was determined that DQC successfully identifies structure in data of this type without prior knowledge of the components in the sample. Clusters and sub-clusters clearly reflected features of the spectra that identified chemical component, chemical environment, and density in the image. DQC can also be used in conjunction with the established data analysis technique, which does require knowledge of components present.
Date: September 7, 2012
Creator: Hume, Allison & /SLAC, /Princeton U.
Partner: UNT Libraries Government Documents Department

Channeling through Bent Crystals

Description: Bent crystals have demonstrated potential for use in beam collimation. A process called channeling is when accelerated particle beams are trapped by the nuclear potentials in the atomic planes within a crystal lattice. If the crystal is bent then the particles can follow the bending angle of the crystal. There are several different effects that are observed when particles travel through a bent crystal including dechanneling, volume capture, volume reflection and channeling. With a crystal placed at the edge of a particle beam, part of the fringe of the beam can be deflected away towards a detector or beam dump, thus helping collimate the beam. There is currently FORTRAN code by Igor Yazynin that has been used to model the passage of particles through a bent crystal. Using this code, the effects mentioned were explored for beam energy that would be seen at the Facility for Advanced Accelerator Experimental Tests (FACET) at a range of crystal orientations with respect to the incoming beam. After propagating 5 meters in vacuum space past the crystal the channeled particles were observed to separate from most of the beam with some noise due to dechanneled particles. Progressively smaller bending radii, with corresponding shorter crystal lengths, were compared and it was seen that multiple scattering decreases with the length of the crystal therefore allowing for cleaner detection of the channeled particles. The input beam was then modified and only a portion of the beam sent through the crystal. With the majority of the beam not affected by the crystal, most particles were not deflected and after propagation the channeled particles were seen to be deflected approximately 5mm. After a portion of the beam travels through the crystal, the entire beam was then sent through a quadrupole magnet, which increased the separation of the channeled particles ...
Date: September 7, 2012
Creator: Mack, Stephanie & /SLAC, /Ottawa U.
Partner: UNT Libraries Government Documents Department