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Emittance and trajectory control in the main linacs of the NLC

Description: The main linacs of the next generation of linear colliders need to accelerate the particle beams to energies of up to 750 GeV while maintaining very small emittances. This paper describes the main mechanisms of static emittance growth in the main linacs of the Next Linear Collider (NLC). The authors present detailed simulations of the trajectory and emittance control algorithms that are foreseen for the NLC. They show that the emittance growth in the main linacs can be corrected down to about 110%. That number is significantly better than required for the NLC design luminosity.
Date: September 1, 1996
Creator: Assmann, R.; Adolphsen, C.; Bane, K.; Raubenheimer, T.O. & Thompson, K.
Partner: UNT Libraries Government Documents Department

LIAR -- A new program for the modeling and simulation of linear accelerators with high gradients and small emittances

Description: Linear accelerators are the central components of the proposed next generation of linear colliders. They need to provide acceleration of up to 750 GeV per beam while maintaining very small normalized emittances. Standard simulation programs, mainly developed for storage rings, do not meet the specific requirements for high energy linear accelerators. The authors present a new program LIAR (LInear Accelerator Research code) that includes wakefield effects, a 4D coupled beam description, specific optimization algorithms and other advanced features. Its modular structure allows to use and to extend it easily for different purposes. They present examples of simulations for SLC and NLC.
Date: September 1, 1996
Creator: Assmann, R.; Adolphsen, C.; Bane, K.; Raubenheimer, T.O.; Siemann, R. & Thompson, K.
Partner: UNT Libraries Government Documents Department

Ion effects in the SLC electron damping ring

Description: The authors report on the ion-related beam behavior in the electron damping ring during unusually poor vacuum conditions in the weeks that followed a catastrophic kicker chamber failure that contaminated the ring vacuum system. The vacuum gradually improved over several months of beam operation, during which time the vertical emittance remained blown up by a factor of 2. The emittance blowup was accompanied by a transverse instability that produced jitter in the extracted beam size. Both the characteristic spectrum of self-excited betatron sidebands and the emittance blowup exhibited a threshold behavior with beam current and vacuum pressure. This behavior depended strongly on the betatron tune and it was found that the ion effects could be minimized by operating just below the 1/2 integer resonance.
Date: May 1, 1997
Creator: Krejcik, P.; Pritzkau, D.; Raubenheimer, T.; Ross, M. & Zimmermann, F.
Partner: UNT Libraries Government Documents Department

Observation and analysis of static deflections from transverse long-range wakefields in the SLC

Description: In the SLC main linac a train of three bunches is accelerated. The leading positron bunch is followed by two bunches of electrons. When the positron bunch passes off-axis through the Rf structures, it excites dipole modes in the structures, for example long-range transverse wakefields which deflect the subsequent electron bunches. Although the magnitude of the deflections is small one can infer the deflections by measuring the trajectory differences while changing the spacing between the positron and electron bunches. Knowing the positron trajectory the misalignments of the accelerating RF structures with respect to the BPM`s can be calculated. The authors present measurements from the SLC linac and discuss the data analysis and errors.
Date: July 1, 1997
Creator: Assmann, R.W.; Decker, F.J.; Raimondi, P. & Raubenheimer, T.O.
Partner: UNT Libraries Government Documents Department

Alignment tolerance of accelerating structures and corrections for future linear colliders

Description: The alignment tolerance of accelerating structures is estimated by tracking simulations. Both single-bunch and multi-bunch effects are taken into account. Correction schemes for controlling the single and multi-bunch emittance growth in the case of large misalignment are also tested by simulations.
Date: June 1, 1995
Creator: Kubo, K.; Adolphsen, C.; Bane, K.L.F.; Raubenheimer, T.O. & Thompson, K.A.
Partner: UNT Libraries Government Documents Department

Diagnostic for dynamic aperture

Description: In large accelerators and low beta colliding beam storage rings, the strong sextupoles, which are required to correct the chromatic effects, produce strong nonlinear forces which act on particles in the beam. In addition in large hadron storage rings the superconducting magnets have significant nonlinear fields. To understand the effects of these nonlinearities on the particle motion there is currently a large theoretical effort using both analytic techniques and computer tracking. This effort is focused on the determination of the 'dynamic aperture' (the stable acceptance) of both present and future accelerators and storage rings. A great deal of progress has been made in understanding nonlinear particle motion, but very little experimental verification of the theoretical results is available. In this paper we describe 'dynamic tracking', a method being studied at the SPEAR storage ring, which can be used to obtain experimental results which are in a convenient form to be compared with the theoretical predictions.
Date: April 1, 1985
Creator: Morton, P.L.; Pellegrin, J.L.; Raubenheimer, T.; Rivkin, L.; Ross, M.; Ruth, R.D. et al.
Partner: UNT Libraries Government Documents Department

A damping ring design for future linear colliders

Description: In this paper we present a preliminary design of a damping ring for the TeV Linear Collider (TLC), a future linear collider with an energy of 1/2 to 1 TeV in the center of mass. Because of limits on the emittance, repetition rate and longitudinal impedance, we use combined function FODO cells with wigglers in insertion regions; there are approximately 22 meters of wigglers in the 155 meter ring. The ring has a normalized horizontal emittance, including the effect of intrabeam scattering, which is less than 3 /times/ 10/sup /minus/6/ and an emittance ratio of epsilon/sub x/ approx. 100epsilon/sub y/. It is designed to damp bunches for 7 vertical damping times while operating at a repetition rate of 360 Hz. Because of these requirements on the emittance and the damping per bunch, the ring operates at 1.8 GeV and is relatively large, allowing more bunches to be damped at once. 10 refs., 5 figs., 2 tabs.
Date: March 1, 1989
Creator: Raubenheimer, T.O.; Gabella, W.E.; Morton, P.L.; Lee, M.J.; Rivkin, L.Z. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Beam parameters of a possible emittance-dynamics test area for NLC studies at the SLC

Description: A group at SLAC has studied the possibility of using the Stanford Linear Collider (SLC) to generate short-bunch small-emittance beams similar to those required for the Next Linear Collider (NLC). The conclusion is that such beams are feasible and that an experimental area for testing many concepts related to NLC beams can be provided with a reasonable addition of hardware to the existing SLC Linac. Some of the concepts that can be tested are: (1) effect tolerances of double bunch length compression, (2) wakefields of ultra-short bunches in accelerating structures, (3) the acceleration of short intense multiple bunches, (4) the generation and preservation of bunches with 100 to 1 emittances ratios, (5) beam deflections by collimators, (6) energy and energy spread control of multiple short bunches, and (7) vibration effects and trajectory stability for low emittance beams.
Date: August 1, 1992
Creator: Seeman, J. T.; Fieguth, T.; Kheifets, S.; Raubenheimer, T. & Yeremian, A. D.
Partner: UNT Libraries Government Documents Department

Suppression of Secondary Electron Emission using Triangular Grooved Surface in the ILC Dipole and Wiggler Magnets

Description: The development of an electron cloud in the vacuum chambers of high intensity positron and proton storage rings may limit machine performance. The suppression of electrons in a magnet is a challenge for the positron damping ring of the International Linear Collider (ILC) as well as the Large Hadron Collider. Simulation show that grooved surfaces can significantly reduce the electron yield in a magnet. Some of the secondary electrons emitted from the grooved surface return to the surface within a few gyrations, resulting in a low effective secondary electron yield (SEY) of below 1.0 A triangular surface is an effective, technologically attractive mitigation with a low SEY and a weak dependence on the scale of the corrugations and the external magnetic field. A chamber with triangular grooved surface is proposed for the dipole and wiggler sections of the ILC and will be tested in KEKB in 2007. The strategy of electron cloud control in ILC and the optimization of the grooved chamber such as the SEY, impedance as well as the manufacturing of the chamber, are also discussed.
Date: July 6, 2007
Creator: Wang, L.; Bane, K.; Chen, C.; Himel, T.; Munro, M.; Pivi, M. et al.
Partner: UNT Libraries Government Documents Department

Secondary Electron Yield Measurements and Groove Chambers Tests in the PEP-II Beam Line Straights Sections

Description: Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron Damping Ring (DR) of future Linear Colliders such as ILC and CLIC [1, 2]. In the Positron Low Energy Ring (LER) of the PEP-II accelerator, we have installed vacuum chambers with rectangular grooves in a straight magnetic-free section to test this promising possible electron cloud mitigation technique. We have also installed a special chamber to monitor the secondary electron yield of TiN and TiZrV (NEG) coating, Copper, Stainless Steel and Aluminum under the effect of electron and photon conditioning in situ in the beam line. In this paper, we describe the ongoing R&D effort to mitigate the electron cloud effect for the ILC damping ring, the latest results on in situ secondary electron yield conditioning and recent update on the groove tests in PEP-II.
Date: July 3, 2008
Creator: Pivi, M.T.F.; King, F.; Kirby, R.E.; Markiewicz, T; Raubenheimer, T.O.; Seeman, J. et al.
Partner: UNT Libraries Government Documents Department

Conceptual Design of the Drive Beam for a PWFA-LC

Description: Plasma Wake-Field Acceleration (PWFA) has demonstrated acceleration gradients above 50 GeV/m. Simulations have shown drive/witness bunch configurations that yield small energy spreads in the accelerated witness bunch and high energy transfer efficiency from the drive bunch to the witness bunch, ranging from 30% for a Gaussian drive bunch to 95% for bunch with triangular shaped longitudinal profile. These results open the opportunity for a linear collider that could be compact, efficient and more cost effective than the present microwave technologies. A concept of a PWFA-based Linear Collider (PWFA-LC) has been developed by the PWFA collaboration. Here we will describe the conceptual design and optimization of the drive beam, which includes the drive beam linac and distribution system. We apply experience of the CLIC drive beam design and demonstration in the CLIC Test Facility (CTF3) to this study. We discuss parameter optimization of the drive beam linac structure and evaluate the drive linac efficiency in terms of the drive beam distribution scheme and the klystron/modulator requirements.
Date: August 3, 2009
Creator: Pei, S.; Hogan, M.J.; Raubenheimer, T.O.; Seryi, A.; /SLAC; Braun, H.H. et al.
Partner: UNT Libraries Government Documents Department

Observation of Beam ION Instability in Spear3

Description: Weak vertical coupled bunch instability with oscillation amplitude at {mu}m level has been observed in SPEAR3. The instability becomes stronger when there is a vacuum pressure rise by partially turning off vacuum pumps and it becomes weaker when the vertical beam emittance is increased by turning off the skew quadrupole magnets. These confirmed that the instability was driven by ions in the vacuum. The threshold of the beam ion instability when running with a single bunch train is just under 200 mA. This paper presents the comprehensive observations of the beam ion instability in SPEAR3. The effects of vacuum pressure, beam current, beam filling pattern, chromaticity, beam emittance and bunch-by-bunch feedback are investigated in great detail. In an electron accelerator, ions generated from the residual gas molecules can be trapped by the beam. Then these trapped ions interact resonantly with the beam and cause beam instability and emittance blow-up. Most existing light sources use a long single bunch train filling pattern, followed by a long gap to avoid multi-turn ion trapping. However, such a gap does not preclude ions from accumulating during one passage of the single bunch train beam, and those ions can still cause a Fast Ion Instability (FII) as predicted by Raubenheimer and Zimmermann. FII has been observed in ALS, and PLS by artificially increasing the vacuum pressure by injecting helium gas into the vacuum chamber or by turning off the ion pumps in order to observe the beam ion instability. In some existing rings, for instance B factory, the beam ion instability was observed at the beginning of the machine operation after a long period of shutdown and then it automatically disappeared when the vacuum was better. However, when the beam emittance becomes smaller, the FII can occur at nominal conditions as observed in PLS, SOLEIL ...
Date: December 14, 2011
Creator: Teytelman, D.; Cai, Y.; Corbett, W. J.; Raubenheimer, T. O.; Safranek, J. A.; Schmerge, J. F. et al.
Partner: UNT Libraries Government Documents Department

Experimental Measurements of the Secondary Electron Yield in the Experimental Measurement of the Secondary Electron Yield in the PEP-II Particle Accelerator Beam Line

Description: Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron Damping Ring (DR) of future Linear Colliders (LC) such as ILC and CLIC. To test a series of promising possible electron cloud mitigation techniques as surface coatings and grooves, in the Positron Low Energy Ring (LER) of the PEP-II accelerator, we have installed several test vacuum chambers including (i) a special chamber to monitor the variation of the secondary electron yield of technical surface materials and coatings under the effect of ion, electron and photon conditioning in situ in the beam line; (ii) chambers with grooves in a straight magnetic-free section; and (iii) coated chambers in a dedicated newly installed 4-magnet chicane to study mitigations in a magnetic field region. In this paper, we describe the ongoing R&D effort to mitigate the electron cloud effect for the LC damping ring, focusing on the first experimental area and on results of the reduction of the secondary electron yield due to in situ conditioning.
Date: August 25, 2010
Creator: Pivi, M.T.F.; Collet, G.; King, F.; Kirby, R.E.; Markiewicz, T.; Raubenheimer, T.O. et al.
Partner: UNT Libraries Government Documents Department

The computer program LIAR for the simulation and modeling of high performance linacs

Description: High performance linear accelerators are the central components of the proposed next generation of linear colliders. They must provide acceleration of up to 750 GeV per beam while maintaining small normalized emittances. Standard simulation programs, mainly developed for storage rings, did not meet the specific requirements for high performance linacs with high bunch charges and strong wakefields. The authors present the program. LIAR (LInear Accelerator Research code) that includes single and multi-bunch wakefield effects, a 6D coupled beam description, specific optimization algorithms and other advanced features. LIAR has been applied to and checked against the existing Stanford Linear Collider (SLC), the linacs of the proposed Next Linear Collider (NLC) and the proposed Linac Coherent Light Source (LCLS) at SLAC. Its modular structure allows easy extension for different purposes. The program is available for UNIX workstations and Windows PC`s.
Date: July 1, 1997
Creator: Assmann, R.; Adolphsen, C.; Bane, K.; Emma, P.; Raubenheimer, T.O.; Siemann, R. et al.
Partner: UNT Libraries Government Documents Department

Collective effects in the NLC damping ring designs

Description: In this paper, we give an overview of collective effects and related issues in the damping rings for the NLC. The main damping ring will have a maximum average current of 1 A in four bunch trains which are separated by 60-80 ns, allowing the fast kickers to inject and extract individual trains. Each bunch train consists of 75-90 bunches, separated by 1.4 ns, with a maximum bunch population of 1.5 x 10{sup 10}. Because of the large average current, coupled bunch instabilities are a potential problem; these can be driven by the ring impedance or by a collective beam-ion instability. In addition, because the ring has a very small momentum compaction and synchrotron tune, potential well distortion and the microwave instability could be important. Finally, because of the very small beam emittances, the intrabeam scattering is significant. In the next sections, we will describe the present state of our calculations. We begin by describing the vacuum chamber design and RF cavities. We then discuss the longitudinal and transverse coupled bunch instabilities, the potential well distortion and the microwave instability, and finally, mode-coupling, ion effects, and intrabeam scattering.
Date: June 1995
Creator: Raubenheimer, T.; Bane, K. L. F.; Berg, J. S.; Byrd, J.; Corlett, J.; Furman, M. et al.
Partner: UNT Libraries Government Documents Department

Emittance and energy control in the NLC main linacs

Description: The authors discuss tolerances and correction schemes needed to control single- and multi-bunch emittance in the NLC main linacs. Specifications and design of emittance diagnostic stations will be presented. Trajectory correction schemes appropriate to simultaneously controlling the emittance of a multibunch train and the emittance of individual bunches within the train will be discussed. The authors discuss control of bunch-to-bunch energy spread using a ramped RF pulse generated by phase-modulating the SLED-II input. Tolerances on ions, wake fields, quadrupole alignment, and accelerating structure alignment will be given.
Date: June 1, 1995
Creator: Adolphsen, C.; Bane, K.L.F.; Kubo, K.; Raubenheimer, T.; Ruth, R.D.; Thompson, K.A. et al.
Partner: UNT Libraries Government Documents Department

LIAR -- A computer program for the modeling and simulation of high performance linacs

Description: The computer program LIAR (LInear Accelerator Research Code) is a numerical modeling and simulation tool for high performance linacs. Amongst others, it addresses the needs of state-of-the-art linear colliders where low emittance, high-intensity beams must be accelerated to energies in the 0.05-1 TeV range. LIAR is designed to be used for a variety of different projects. LIAR allows the study of single- and multi-particle beam dynamics in linear accelerators. It calculates emittance dilutions due to wakefield deflections, linear and non-linear dispersion and chromatic effects in the presence of multiple accelerator imperfections. Both single-bunch and multi-bunch beams can be simulated. Several basic and advanced optimization schemes are implemented. Present limitations arise from the incomplete treatment of bending magnets and sextupoles. A major objective of the LIAR project is to provide an open programming platform for the accelerator physics community. Due to its design, LIAR allows straight-forward access to its internal FORTRAN data structures. The program can easily be extended and its interactive command language ensures maximum ease of use. Presently, versions of LIAR are compiled for UNIX and MS Windows operating systems. An interface for the graphical visualization of results is provided. Scientific graphs can be saved in the PS and EPS file formats. In addition a Mathematica interface has been developed. LIAR now contains more than 40,000 lines of source code in more than 130 subroutines. This report describes the theoretical basis of the program, provides a reference for existing features and explains how to add further commands. The LIAR home page and the ONLINE version of this manual can be accessed under: http://www.slac.stanford.edu/grp/arb/rwa/liar.htm.
Date: April 1, 1997
Creator: Assmann, R.; Adolphsen, C.; Bane, K.; Emma, P.; Raubenheimer, T.; Siemann, R. et al.
Partner: UNT Libraries Government Documents Department

Physics goals for the planned next linear collider engineering test facility.

Description: The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well as of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.
Date: July 17, 2001
Creator: Bohn, C.; Michelotti, L.; Ostiguy, J.-F.; Syphers, M.; Bluem, H.; Todd, A. et al.
Partner: UNT Libraries Government Documents Department

First observations of a fast beam-ion instability at the ALS

Description: The authors report the results of experiments on a fast beam-ion instability at the Advanced Light Source (ALS). This ion instability, which can arise even when the ions are not trapped over multiple beam passages, will likely be important for many future accelerators. In the experiments, the authors filled the ALS storage ring with helium gas, raising the pressure approximately two orders of magnitude above the nominal pressure. With gaps in the bunch train large enough to avoid conventional (multi-turn) ion trapping, they observed a factor 2--3 increase in the vertical beam size along with coherent beam oscillations which increased along the bunch train.
Date: May 1, 1997
Creator: Byrd, J.; Thomson, J.; Chao, A.; Heifets, S.; Minty, M.; Seeman, J. et al.
Partner: UNT Libraries Government Documents Department

Modeling Incoherent Electron Cloud Effects

Description: Incoherent electron effects could seriously limit the beam lifetime in proton or ion storage rings, such as LHC, SPS, or RHIC, or blow up the vertical emittance of positron beams, e.g., at the B factories or in linear-collider damping rings. Different approaches to modeling these effects each have their own merits and drawbacks. We describe several simulation codes which simplify the descriptions of the beam-electron interaction and of the accelerator structure in various different ways, and present results for a toy model of the SPS. In addition, we present evidence that for positron beams the interplay of incoherent electron-cloud effects and synchrotron radiation can lead to a significant increase in vertical equilibrium emittance. The magnitude of a few incoherent e+e- scattering processes is also estimated. Options for future code development are reviewed.
Date: June 18, 2007
Creator: Vay, Jean-Luc; Benedetto, E.; Fischer, W.; Franchetti, G.; Ohmi, K.; Schulte, D. et al.
Partner: UNT Libraries Government Documents Department