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Injection Related Background due to the Transverse Feedback

Description: The background in the BaBar detector is especially high during injection, when most components are actually having reduced voltages. The situation is worse for the beam in High Energy Ring (HER) when the LER beam is present. It was found that the transverse feedback system plays an important role when stacking more charge on top of existing bunches. Lowering the feedback gain helped and it was realized later that the best scenario would be to gate off the feedback for only the one bunch, which got additional charge injected into it. The explanation is that the blown-up, but centered, original HER bunch plus the small injected off-axis bunch (each with half the charge) would stay in the ring if not touched, but the feedback system sees half the offset and wants to correct it, therefore disturbing and scraping the blown-up part.
Date: March 18, 2008
Creator: Decker, F.J.; Akre, R.; Fisher, A.; Iverson, R.; Weaver, M. & /SLAC
Partner: UNT Libraries Government Documents Department

Radiation safety considerations for the parasitic Final Focus Test Beam at SLAC

Description: A low intensity electron beam parasitic to the operation of the Stanford Linear Collider (SLC) has been transported through the Final Focus Test Beam (FFTB) facility making secondary test beams available for users. Photons generated in collimation of the SLC electron and positron beams in the linac pass through a splitter magnet that deflects the primary beams away from the linac axis into the SLC beam lines. These photons are converted to electrons and positrons in a secondary production target located down beam on the linac axis. The secondary electrons are then transported through the FFTB beam line onto experimental detectors. The average power of the parasitic beam is very low, thus, it presents no hazards. However, various accident scenarios involving failure of the splitter magnet and the active protection devices could send much more powerful SLC beams (up to 90 kilo-watts) into this zero-degree secondary beam line. For the accident cases, the average power in the transmitted beam was calculated using the Monte Carlo programs EGS4 and TURTLE. Results from analysis of the radiation protection systems that assure safety during the parasitic operation are presented.
Date: November 1, 1996
Creator: Rokni, S.H.; Iverson, R.H. & Keller, L.P.
Partner: UNT Libraries Government Documents Department

Commissioning and operation of the Nuclear Physics Injector at SLAC

Description: The new Nuclear Physics Injector (NPI) approved for construction in October of 1983 was completed by September of 1984, and delivered short pulse beams for SPEAR ring checkout in mid-October. Long pulse beams of up to 1.6 microsecond length were also demonstrated. The paper describes the startup operation, reviews the performance characteristics, and discusses the beam transport optics used to deliver 1 to 4 GeV beams to nuclear physics experiments in End Station A.
Date: March 1, 1985
Creator: Koontz, R.F.; Miller, R.H.; Leger, G.K. & Iverson, R.
Partner: UNT Libraries Government Documents Department

Dual Power Supplies for PEP-II Injection Kickers

Description: Originally the PEP-II injection kickers were powered by one power supply. Since the kicker magnets where not perfectly matched, the stored beam got excited by about 7% of the maximum kicker amplitude. This led to luminosity losses which were especially obvious for trickle injection when the detector is on for data taking. Therefore two independent power supplies with thyratrons in the tunnel next to the kicker magnet were installed. This also reduces the necessary power by about a factor of four since there are no long cables that have to be charged. The kickers are now independently adjustable to eliminate any non-closure of the kicker system and therefore excitation of the stored beam. Setup, commissioning and fine tuning of this system are discussed.
Date: May 25, 2005
Creator: Olszewski, J; Decker, F.-J.; Iverson, R.H.; Kulikov, A.; Pappas, C. & /SLAC
Partner: UNT Libraries Government Documents Department

XAL-Based Applications and Online Models for LCLS

Description: 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.
Partner: UNT Libraries Government Documents Department

Diagnosing the PEP-II Injection System

Description: The injection of beam into the PEP-II B-Factory, especially into the High Energy Ring (HER) has some challenges. A high background level in the BaBar detector has for a while inhibited us from trickling charge into the HER similar to the Low Energy Ring (LER). Analyzing the injection system has revealed many issues which could be improved. The injection bump between two kickers was not closed, mainly because the phase advance wasn't exactly 180{sup o} and the two kicker strengths were not balanced. Additionally we found reflections which kick the stored beam after the main kick and cause the average luminosity to drop about 3% for a 10 Hz injection rate. The strength of the overall kick is nearly twice as high as the design, indicating a much bigger effective septum thickness. Compared with single beam the background is worse when the HER beam is colliding with the LER beam. This hints that the beam-beam force and the observed vertical blow-up in the HER pushes the beam and especially the injected beam further out to the edge of the dynamic aperture or beyond.
Date: May 9, 2005
Creator: Decker, F.-J.; Donald, M.H.; Iverson, R.H.; Kulikov, A.; Pappas, G.C.; Weaver, M. et al.
Partner: UNT Libraries Government Documents Department

ESTB: A New Beam Test Facility at SLAC

Description: End Station A Test Beam (ESTB) is a beam line at SLAC using a small fraction of the bunches of the 13.6 GeV electron beam from the Linac Coherent Light Source (LCLS), restoring test beam capabilities in the large End Station A (ESA) experimental hall. ESTB will provide one of a kind test beam essential for developing accelerator instrumentation and accelerator R&D, performing particle and particle astrophysics detector research, linear collider machine and detector interface (MDI) R&D studies, development of radiation-hard detectors, and material damage studies with several distinctive features. In the past, 18 institutions participated in the ESA program at SLAC. In stage I, 4 new kicker magnets will be added to divert 5 Hz of the LCLS beam to the A-line. A new beam dump will be installed and a new Personnel Protection System (PPS) is being built in ESA. In stage II, a secondary hadron target will be installed, able to produce pions up to about 12 GeV/c at 1 particle/pulse.
Date: April 5, 2011
Creator: Pivi, M.; Fieguth, T.; Hast, C.; Iverson, R.; Jaros, J.; Jobe, K. et al.
Partner: UNT Libraries Government Documents Department

XAL Adoption Experience at LCLS

Description: 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.
Partner: UNT Libraries Government Documents Department

Beam-based optical tuning of the final focus test beam

Description: In order to reduce the SLAC 46.6 GeV beam to submicron sizes, the Final Focus Test Beam (FFTB) must meet tight tolerances on many aberrations. These aberrations include: mismatch and coupling of the incoming beam; dispersion; chromaticity; lattice errors in the chromatic correction sections; lattice coupling; and residual sextupole content in the quadrupoles. In order to address these aberrations, the authors have developed a procedure which combines trajectory analysis, use of intermediate wire scanners, and a pair of novel beam size monitors at the IP. This procedure allows the FFTB IP spot to be reduced to sizes under 100 nanometers.
Date: May 1, 1995
Creator: Tenenbaum, P.; Burke, D.; Hartman, S.; Helm, R.; Irwin, J.; Iverson, R. et al.
Partner: UNT Libraries Government Documents Department

A beam energy analysis and monitoring system for linear accelerators

Description: A model-based beam orbit simulation program has been used successfully to analyze the beam energy errors at the two-mile linear accelerator during commissioning of the SLC system. This simulation program has also been used to develop a nondestructive beam energy error monitoring system. The method of analysis, the simulation program, and a beam energy analysis and monitoring system using expert systems techniques will be described.
Date: February 1, 1988
Creator: Lee, M.J.; Kleban, S.D.; Zambre, Y.B.; Seeman, J.T.; Adolphsen, C.E.; Abrams, G.S. et al.
Partner: UNT Libraries Government Documents Department

Commissioning the LCLS Injector

Description: The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. The injector section, from drive laser and RF photocathode gun through first bunch compressor chicane, was installed in fall 2006. Initial system commissioning with an electron beam was completed in August 2007, with the goal of a 1.2-micron emittance in a 1-nC bunch clearly demonstrated. The second phase of commissioning, including second bunch compressor and full linac, is planned for 2008, with FEL commissioning in 2009. We report experimental results and experience gained in the first phase of commissioning, including the photo-cathode drive laser, RF gun, photocathode, S-band and X-band RF systems, first bunch compressor, and the various beam diagnostics.
Date: November 28, 2007
Creator: Akre, R.; Dowell, D.; Emma, P.; Frisch, J.; Gilevich, S.; Hays, G. et al.
Partner: UNT Libraries Government Documents Department

Modeling TeV Class Plasma Afterburners

Description: Plasma wakefield acceleration can sustain acceleration gradients three orders of magnitude larger than conventional RF accelerator. In the recent E164X experiment, substantial energy gain of about 3-4 GeV has been observed. Thus, a plasma afterburner, which has been proposed to double the incoming beam energy for a future linear collider, is now of great interest. In an afterburner, a particle beam drives a plasma wave and generates a strong wakefield which has a phase velocity equal to the velocity of the beam. This wakefield can then be used to accelerate part of the drive beam or a trailing beam. Several issues such as the efficient transfer of energy and the stable propagation of both the drive and trailing beams in the plasma are critical to the afterburner concept. We investigate the nonlinear beam-plasma interaction in such scenario using the 3D computer modeling code QuickPIC. We will report on the preliminary simulation results of both 100 GeV and 1 TeV plasma afterburner stages for electrons including the beam-loading of a trailing beam. Analytic analysis of hosing instability in this regime will be presented.
Date: January 30, 2006
Creator: Huang, C.; Clayton, C.; Johnson, d.; Joshi, C.; Lu, W.; Mori, W. et al.
Partner: UNT Libraries Government Documents Department

Picosecond Bunch length and Energy-z correlation measurements at SLAC's A-Line and End Station A

Description: We report on measurements of picosecond bunch lengths and the energy-z correlation of the bunch with a high energy electron test beam to the A-line and End Station A (ESA) facilities at SLAC. The bunch length and the energy-z correlation of the bunch are measured at the end of the linac using a synchrotron light monitor diagnostic at a high dispersion point in the A-line and a transverse RF deflecting cavity at the end of the linac. Measurements of the bunch length in ESA were made using high frequency diodes (up to 100 GHz) and pyroelectric detectors at a ceramic gap in the beamline. Modeling of the beam's longitudinal phase space through the linac and A-line to ESA is done using the 2-dimensional tracking program LiTrack, and LiTrack simulation results are compared with data. High frequency diode and pyroelectric detectors are planned to be used as part of a bunch length feedback system for the LCLS FEL at SLAC. The LCLS also plans precise bunch length and energy-z correlation measurements using transverse RF deflecting cavities.
Date: June 27, 2007
Creator: Molloy, Stephen; Emma, P.; Frisch, J.C.; Iverson, R.H.; Ross, M.; McCormick, D.J. et al.
Partner: UNT Libraries Government Documents Department

Trickle-Charge: a New Operational Mode for PEP-II

Description: In regular top-up-and-coast operation, PEP-II average luminosity is about 70-75% of the peak luminosity due to detector ramp-down and ramp-up times plus the time it takes to top-up both beams. We recently commissioned a new operational mode where the Low Energy Ring is injected continuously without ramping down the detector. The benefits--increased luminosity lifetime and roughly half the number of top-ups per shift--were expected to give an increase in delivered luminosity of about 15% at the same peak luminosity; this was confirmed in test runs. In routine trickle operation, however, it appears that the increase in delivered luminosity is more than twice that due to an increase in availability credited to the more stable operating conditions during trickle operation. Further gains were made when continuous injection was extended to the high energy ring as well. In this paper we will present our operational experience as well as some of the diagnostics we use to monitor and maintain tuning of the machine in order to control injection background and protect the detector.
Date: May 9, 2005
Creator: Kozanecki, W.; Colocho, W. S.; Decker, F. -J.; Ecklund, S.; Fisher, A. S.; Iverson, R. H. et al.
Partner: UNT Libraries Government Documents Department

The SLAC linac as used in the SLC collider

Description: The linac of the SLAC Linear Collider (SLC) must accelerate three high intensity bunches on each linac pulse from 1.2 GeV to 50 GeV with minimal increase of the small transverse emittance. The procedures and adjustments used to obtain this goal are outlined. Some of the accelerator parameters and components which interact are the beam energy, transverse position, component alignment, RF manipulation, feedback systems, quadrupole lattice, BNS damping, energy spectra, phase space matching, collimation, instrumentation and modelling. The method to bring these interdependent parameters collectively into specification has evolved over several years. This review is ordered in the sequence which is used to turn on the linac from a cold start and produce acceptable beams for the final focus and collisions. Approximate time estimates for the various activities are given. 21 refs.
Date: June 1, 1989
Creator: Seeman, J.T.; Abrams, G.; Adolphsen, C.; Atwood, W.; Bane, K.L.F.; Iverson, R. 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