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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

Interaction-Point Phase-Space Characterization using Single-Beam and Luminous-Region Measurements at PEP-II

Description: We present an extensive experimental characterization of the e{sup {+-}} phase space at the interaction point of the SLAC PEP-II B-Factory, that combines a detailed mapping of luminous-region observables using the BABAR detector, with stored-beam measurements by accelerator techniques.
Date: September 9, 2008
Creator: Kozanecki, W; /Saclay; Bevan, A.J.; /Queen Mary, U. of London; Viaud, B.F.; U., /Montreal et al.
Partner: UNT Libraries Government Documents Department

The 2mrad horizontal crossing angle IR layout for a TeV ILC

Description: The current status of the 2mrad crossing angle layout for the ILC is reviewed. The scheme developed in the UK and France is described and the performance discussed for a TeV machine. Secondly, the scheme developed at SLAC and BNL is then studied and modified for a TeV machine. We find that both schemes can handle the higher energy beam with modifications, and share many common features.
Date: July 27, 2005
Creator: Appleby, R.; Angal-Kalinin, D.; /Daresbury; Bambade, P.; Mouton, B.; /Orsay, LAL et al.
Partner: UNT Libraries Government Documents Department

Measurements of the Transverse Wakefields Due to Varying Collimator Characteristics

Description: We report on measurements of the transverse wakefields induced by collimators of differing characteristics. An apparatus allowing the insertion of different collimator jaws into the path of a beam was installed in End Station A (ESA) in SLAC. Eight comparable collimator geometries were designed, including one that would allow easy comparison with previous results, and were installed in this apparatus. Measurements of the beam kick due to the collimator wakefields were made with a beam energy of 28.5 GeV, and beam dimensions of 100 microns vertically and a range of 0.5 to 1.5 mm longitudinally. The trajectory of the beam upstream and downstream of the collimator test apparatus was determined from the outputs of ten BPMs (four upstream and six downstream), thus allowing a measurement of the angular kick imparted to the beam by the collimator under test. The transverse wakefield was inferred from the measured kick. The different aperture designs, data collection and analysis, and initial comparison to theoretical and analytic predictions are presented here.
Date: July 6, 2007
Creator: Molloy, S.; Seletskiy, Sergei; Woods, Mike; /SLAC; Smith, Jonathan David Andrew; Tech., /Cockcroft Inst. Accel. Sci. et al.
Partner: UNT Libraries Government Documents Department

Disruption of Particle Detector Electronics by Beam Generated EMI

Description: The possibility that radio frequency beam generated electromagnetic interference (EMI) could disrupt the operation of particle detector electronics has been of some concern since the inception of short pulse electron colliders more than 30 years ago [1]. Some instances have been reported where this may have occurred but convincing evidence has not been available. This possibility is of concern for the International Linear Collider (ILC). We have conducted test beam studies demonstrating that electronics disruption does occur using the vertex detector electronics (VXD) from the SLD detector which took data at the SLC at SLAC. We present the results of those tests, and we describe the need for EMI standards for beam and detector instrumentation in the IR region at the ILC.
Date: June 27, 2007
Creator: Bower, G.; /SLAC; Sugimoto, Y.; /KEK, Tsukuba; Sinev, N.; U., /Oregon et al.
Partner: UNT Libraries Government Documents Department

Status of the ILC Main Linac Lattice Design

Description: The report describes the present design of the ILC Main Linac lattice. The topics covered include basic element layout, optical functions, and issues centered around the linac following of the Earth's curvature.
Date: October 9, 2007
Creator: Valishev, A.; Solyak, N.; /Fermilab; Woodley, M. & /SLAC
Partner: UNT Libraries Government Documents Department

Magnetic Measurements and Simulations for a 4-magnet Dipole Chicane for the International Linear Collider

Description: T-474 at SLAC is a prototype BPM-based energy spectrometer for the ILC. We describe magnetic measurements and simulations for the 4-magnet chicane used in T-474.
Date: December 17, 2007
Creator: Schreiber, H.J.; Viti, M.; /DESY; Duginov, V.N.; Kostromin, S.A.; Morozov, N.A. et al.
Partner: UNT Libraries Government Documents Department

Wakefield Calculations for 3D Collimators

Description: Using a recently developed time domain numerical approach we calculate the short-range geometric wakefields of 3D collimators and compare with analytical models. We find, in the diffractive regime, that the transverse mode kick factor can be approximated from the change in field energy between the beam pipe and the collimator if the collimator is long, or using a ''field clipping'' estimate if it is short. For collimators of past and present measurements at SLAC, numerical, analytical, and measurement results are compared.
Date: July 17, 2006
Creator: Zagorodnov, I.; /DESY; Bane, K.L.F. & /SLAC
Partner: UNT Libraries Government Documents Department

Emittance and Phase Space Exchange

Description: Alternative chicane-type beam lines are proposed for exact emittance exchange between horizontal phase space (x; x{prime}) and longitudinal phase space (z; {delta}). Methods to achieve exact phase space exchanges, i.e. mapping x to z, x{prime} to {delta}, z to x and {delta} to x{prime} are suggested. Methods to mitigate the thick-lens effect of the transverse cavity on emittance exchange are discussed. Some applications of the phase space exchanger and the feasibility of an emittance exchange experiment with the proposed chicane-type beam line at SLAC are discussed.
Date: August 19, 2011
Creator: Xiang, Dao & Chao, Alex
Partner: UNT Libraries Government Documents Department

Status of the E166-Experiment

Description: The E166 experiment is a proof-of-principle experiment to demonstrate the production of polarized positrons with a helical undulator. The experiment has taken first data in June 2005 at SLAC. This article gives a short overview of the performance of various components of the experiment.
Date: August 23, 2005
Creator: Poeschl, R.
Partner: UNT Libraries Government Documents Department

Collective Effects in the SuperB Collider

Description: Some collective effects have been studied for the SuperB high luminosity collider. Estimates of the effect of Intra Beam Scattering (IBS) on the emittance and energy spread growths have been carried up for both the High Energy (HER, positrons) and the Low Energy (LER, electrons) rings. Electron cloud build up simulations for HER were performed with the ECLOUD code, developed at CERN, to predict the cloud formation in the arcs, taking into account possible remediation techniques such as clearing electrodes. The new code CMAD, developed at SLAC, has been used to study the effect of this electron cloud on the beam and assess the thresholds above which the electron cloud instability would set in.
Date: June 25, 2012
Creator: Demma, Theo; /INFN, Rome; Pivi, Mauro & /SLAC
Partner: UNT Libraries Government Documents Department

Intensity Effects of the FACET Beam in the SLAC Linac

Description: The beam for FACET (Facility for Advanced aCcelerator Experimental Tests) at SLAC requires an energy-time correlation ('chirp') along the linac, so it can be compressed in two chicanes, one at the midpoint in sector 10 and one W-shaped chicane just before the FACET experimental area. The induced correlation has the opposite sign to the typical used for BNS damping, and therefore any orbit variations away from the center kick the tail of the beam more than the head, causing a shear in the beam and emittance growth. Any dispersion created along the linac has similar effects due to the high (>1.2% rms) energy spread necessary for compression. The initial huge emittances could be reduced by a factor of 10, but were still bigger than expected by a factor of 2-3. Normalized emittance of 3 {micro}m-rad in Sector 2 blew up to 150 {micro}m-rad in Sector 11 but could be reduced to about 6-12 {micro}m-rad, for the vertical plane although the results were not very stable. Investigating possible root causes for this, we found locations where up to 10 mm dispersion was created along the linac, which were finally verified with strong steering and up to 7 mm settling of the linac accelerator at these locations.
Date: July 3, 2012
Creator: Decker, F.-J.; Lipkowitz, N.; Sheppard, J.; White, G.R.; Wienands, U.; Woodley, M. et al.
Partner: UNT Libraries Government Documents Department

LLRF System Upgrade for the SLAC Linac

Description: The Linac Coherent Light Source (LCLS) at SLAC is in full user operation and has met the stability goals for stable lasing. The 250pC bunch can be compressed to below 100fS before passing through an undulator. In a new mode of operation a 20pC bunch is compressed to about 10fS. Experimenters are regularly using this shorter X-ray pulse and getting pristine data. The 10fS bunch has timing jitter on the order of 100fS. Physicists are requesting that the RF system achieve better stability to reduce timing jitter. Drifts in the RF system require longitudinal feedbacks to work over large ranges and errors result in reduced performance of the LCLS. A new RF system is being designed to help diagnose and reduce jitter and drift in the SLAC linac.
Date: July 6, 2012
Creator: Hong, Bo; /SLAC; Akre, Ron; /SLAC; Pacak, Vojtech & /SLAC
Partner: UNT Libraries Government Documents Department

Higher Order Modes Damping Analysis for the SPX Deflecting Cavity Cyromodule

Description: A single-cell superconducting deflecting cavity operating at 2.815 GHz has been proposed and designed for the Short Pulse X-ray (SPX) project for the Advanced Photon Source (APS) upgrade. A cryomodule of 4 such cavities will be needed to produce the required 2-MV deflecting voltage. Each deflecting cavity is equipped with one fundamental power coupler (FPC), one lower order mode (LOM) coupler, and two higher order mode (HOM) couplers to achieve the stringent damping requirements for the unwanted modes. The damping of the LOM/HOM below the beampipe cutoff has been analyzed in the single cavity geometry and shown to meet the design requirements. The HOM above the beampipe cutoff in the 4-cavity cyromodule, however, may result in cross coupling which may affect the HOM damping and potentially be trapped between the cavities which could produce RF heating to the beamline bellows. We have evaluated the HOM damping in the 4-cavity cryomodule using the parallel finite element EM code suite ACE3P developed at SLAC. We will present the results of the cryomodule analysis in this paper.
Date: June 6, 2012
Creator: Xiao, L; Li, Z.; Ng, C.; /SLAC; Nassiri, A.; Waldschmidt, G. et al.
Partner: UNT Libraries Government Documents Department

Experiment to Detect Accelerating Modes in a Photonic Bandgap Fiber

Description: An experimental effort is currently underway at the E-163 test beamline at Stanford Linear Accelerator Center to use a hollow-core photonic bandgap (PBG) fiber as a high-gradient laser-based accelerating structure for electron bunches. For the initial stage of this experiment, a 50pC, 60 MeV electron beam will be coupled into the fiber core and the excited modes will be detected using a spectrograph to resolve their frequency signatures in the wakefield radiation generated by the beam. They will describe the experimental plan and recent simulation studies of candidate fibers.
Date: November 21, 2011
Creator: England, R.J.; /SLAC; Colby, E.R.; /SLAC; Ischebeck, R.; /Munich, Max Planck Inst. Quantenopt. et al.
Partner: UNT Libraries Government Documents Department

Performance of the PEP-II B-Factory Collider at SLAC

Description: PEP-II is an e{sup +}e{sup -} asymmetric B-Factory Collider located at SLAC operating at the Upsilon 4S resonance (3.1 GeV x 9 GeV). It has reached a luminosity of 9.21 x 10{sup 33}/cm{sup 2}/s and has delivered an integrated luminosity of 710 pb{sup -1} in one day. PEP-II has delivered, over the past six years, an integrated luminosity to the BaBar detector of over 262 fb{sup -1}. PEP-II operates in continuous injection mode for both beams boosting the integrated luminosity. The peak positron current has reached 2.45 A in 1588 bunches. Steady progress is being made in reaching higher luminosity. The goal over the next several years is to reach a luminosity of 2.1 x 10{sup 34}/cm{sup 2}/s. The accelerator physics issues being addressed in PEP-II to reach this goal include the electron cloud instability, beam-beam effects, parasitic beam-beam effects, high RF beam loading, shorter bunches, lower {beta}*{sub y} interaction region operation, and coupling control. Figure 1 shows the PEP-II tunnel.
Date: March 3, 2006
Creator: Seeman, J.; Browne, M.; Cai, Y.; Colocho, W.; Decker, F.J.; Donald, M.H. et al.
Partner: UNT Libraries Government Documents Department

Field Ionization of Neutral Litium Vapor Using a 28.5 GeV Electron Beam

Description: The E164/E164X plasma wakefield experiment studies beam-plasma interactions at the Stanford Linear Acceleration Center (SLAC). Due to SLAC's recent ability to variably compress bunches longitudinally from 650 {micro}m down to 20 {micro}m, the incoming beam is sufficiently dense to field ionize the neutral lithium (Li) vapor. The field ionization effects are characterized by the beams energy loss through the Li vapor column. Experiment results are presented.
Date: January 30, 2006
Creator: O'Connell, C.L.; Barnes, c.D.; Decker, F.-J.; Hogan, M.J.; Iverson, R.; Krejcik, P. et al.
Partner: UNT Libraries Government Documents Department

Field Ionization using a 28.5 GeV Electron Beam

Description: The E164/E164X plasma wakefield experiment studies beam-plasma interactions at the Stanford Linear Acceleration Center (SLAC). Due to SLAC's recent ability to variably compress bunches longitudinally from 650 {micro}m down to 20 {micro}m, the incoming beam is sufficiently dense to field ionize the neutral lithium (Li) vapor. The field ionization effects are characterized by the beams energy loss through the Li vapor column. Experiment results are presented.
Date: June 7, 2005
Creator: O'Connell, C.; Barnes, C.D.; Decker, F.-J.; Hogan, M.J.; Iverson, R.; Krejcik, P. et al.
Partner: UNT Libraries Government Documents Department

Optical Effects of Wakefields in the PEP-II Stanford Linear Accelerator Center B Factory

Description: Wakefields defining beam stability affect also the beam optics and beam properties in high current machines. In this paper we present observations and analysis of the optical effects in the PEP-II SLAC B-factory, which has the record in achievement of high electron and positron currents. We study the synchronous phase and the bunch length variation along the train of bunches, overall bunch lengthening and effects of the wakes on the tune and on the Twiss parameters. This analysis is being used in upgrades of PEP-II and may be applied to future B-factories and damping rings for Linear Colliders.
Date: January 29, 2007
Creator: Heifets, S.; Novokhatski, S.; Teytelman, D. & /SLAC
Partner: UNT Libraries Government Documents Department

Electromagnetic Interference from the ILC Beams

Description: Electromagnetic interference is an emerging problem of the future. This investigation analyzed the data collected from airborne radiation waves that caused electronic devices to fail. This investigation was set up at SLAC in End Station A and the data collected from the electromagnetic waves were received from antennas. In order to calibrate the antennas it required a signal generator to transmit the signals to the antenna and a digital oscilloscope to receive the radiation waves from the other antenna. The signal generator that was used was only able to generate signals between 1 and 1.45 GHz; therefore, the calibrations were not able to be completed. Instead, excel was used to create a curve fitting for the attenuation factors that were already factory calibrated. The function from the curve fitting was then used to extend the calibrations on the biconical and yagi antennas. A fast Fourier Transform was then ran in Matlab on the radiation waves received by the oscilloscope; in addition, the attenuation factors were calculated into the program to show the actual amplitudes of these radiation waves. For future research, the antennas will be manually calibrated and the results will be reanalyzed.
Date: November 7, 2007
Creator: Brown, LaVonda N. & /SLAC, /Norfolk State U.
Partner: UNT Libraries Government Documents Department

Summary of the Optics, IR, Injection, Operations, Reliability and Instrumentation Working Group

Description: The facilities reported on are all in a fairly mature state of operation, as evidenced by the very detailed studies and correction schemes that all groups are working on. First- and higher-order aberrations are diagnosed and planned to be corrected. Very detailed beam measurements are done to get a global picture of the beam dynamics. More than other facilities the high-luminosity colliders are struggling with experimental background issues, mitigation of which is a permanent challenge. The working group dealt with a very wide rage of practical issues which limit performance of the machines and compared their techniques of operations and their performance. We anticipate this to be a first attempt. In a future workshop in this series, we propose to attempt more fundamental comparisons of each machine, including design parameters. For example, DAPHNE and KEKB employ a finite crossing angle. The minimum value of {beta}*{sub y} attainable at KEKB seems to relate to this scheme. Effectiveness of compensation solenoids and turn-by-turn BPMs etc. should be examined in more detail. In the near future, CESR-C and VEPP-2000 will start their operation. We expect to hear important new experiences from these machines; in particular VEPP-2000 will be the first machine to have adopted round beams. At SLAC and KEK, next generation B Factories are being considered. It will be worthwhile to discuss the design issues of these machines based on the experiences of the existing factory machines.
Date: April 20, 2012
Creator: Wienands, U.; /SLAC; Funakoshi, Y. & /KEK, Tsukuba
Partner: UNT Libraries Government Documents Department

Structure Loaded Vacuum Laser-Driven Particle Acceleration Experiments at SLAC

Description: We present an overview of the future laser-driven particle acceleration experiments. These will be carried out at the E163 facility at SLAC. Our objectives include a reconfirmation of the proof-of-principle experiment, a staged buncher laser-accelerator experiment, and longer-term future experiments that employ dielectric laser-accelerator microstructures.
Date: April 9, 2007
Creator: Plettner, T.; Byer, R.L.; Colby, E.R.; Cowan, B.M.; Ischebeck, R.; McGuinness, C. et al.
Partner: UNT Libraries Government Documents Department

Coupler Design for the LCLS Injector S-Band Structures

Description: The LCLS injector is required to provide a 1-nC, 10-ps bunch with a normalized rms transverse projected emittance of less than 1 micron. The LCLS beam is generated and accelerated in a 1.6-cell S-band RF gun at 120 MV/m up to 6 MeV. The gun is followed by two SLAC 3-m S-band accelerator structures to further accelerate the beam to 135 MeV which moves the beam out of the space-charge dominated regime. In the SLAC S-band structures, the RF power feed is through a single coupling-hole (single-feed coupler) which results in a field asymmetry. The time dependent multipole fields in the coupler induce a transverse kick along the bunch and cause the emittance to increase above the LCLS specification. To meet the stringent emittance requirements for the injector, the single-feed couplers will be replaced by a dual-feed racetrack design to minimize the multipole field effects. We will present detailed studies of the multipole fields in the SLAC linac RF coupler and the improvements with the dual-feed ractrack design using the parallel finite element S-parameter solver S3P.
Date: March 3, 2006
Creator: Li, Z.; Bentson, L.D.; Chan, J.; Dowell, D.H.; Limborg-Deprey, C.; Schmerge, J.F. et al.
Partner: UNT Libraries Government Documents Department

Measurement of Electron Clouds in Large Accelerators by Microwave Dispersion

Description: Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation at high currents. Furthermore, it is difficult to probe their density over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave transmitted over a section of the accelerator and used it to measure the average electron cloud density over a 50 m section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center.
Date: March 19, 2008
Creator: De Santis, S.; Byrd, J.M.; /LBL, Berkeley; Caspers, F.; /CERN; Krasnykh, A. et al.
Partner: UNT Libraries Government Documents Department