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New concepts for damping rings

Description: The requirements for very low emittance and short damping time in the damping rings of future linear colliders, naturally lead to very small beta functions and dispersion in the ring arcs. This makes it difficult to make chromatic correction while maintaining good dynamics. We have therefore developed a lattice with very simple arcs (designed to give the best product of emittance and damping time), and with separate chromatic correction in a dedicated section. The chromatic correction is achieved using a series of non-interleaved sextupole pairs. The performance of such a solution is comparable to that of current damping ring designs, while there are a number of potential advantages.
Date: May 30, 2002
Creator: Raimondi, P. & Wolski, A.
Partner: UNT Libraries Government Documents Department

A new lattice design for the NLC positron pre-damping ring

Description: The positron source for the Next Linear Collider (NLC) will produce a beam larger than the acceptance of the main damping rings, which are optimized for low extracted emittance. A pre-damping ring, with large acceptance, is therefore needed to reduce the emittance of the beam from the source, so it can be accepted by the main damping ring with minimal particle loss. Previous designs, based on a racetrack structure with TME cells in the arcs, have proven difficult to tune for the required dynamic aperture, in part because of the low symmetry. We report here on a new design, with a 10-fold symmetric DBA structure, which meets the principal parameter specifications, and has much greater tuning flexibility.
Date: May 30, 2002
Creator: Wolski, A.
Partner: UNT Libraries Government Documents Department

Tracking Studies to Determine the Required Wiggler Aperture forthe ILC Damping Rings

Description: The injection efficiency of an ILC damping ring is closely tied to its acceptance. To maximize both, one wants a physical aperture as large as possible in the wiggler magnets, as these are likely to be the limiting physical apertures in the ring. On the other hand, a small aperture in the wiggler magnets is needed to achieve the required field profile, a high magnetic field that is very linear over the whole physical aperture of the magnet. Tracking studies were done for all proposed ILC damping ring lattices to determine their required physical apertures. Although a half-aperture of 8 or 10mm had been proposed, our studies showed that, for most lattices, a 16mm half-aperture is required. For some lattices a 12mm half aperture might suffice. We present here the results of our studies, which led to adopting a 16mm half-aperture in the current ILC damping ring baseline design.
Date: June 21, 2006
Creator: Reichel, I. & Wolski, A.
Partner: UNT Libraries Government Documents Department

Intrabeam Scattering Studies for the ILC Damping Rings Using a NewMATLAB Code

Description: A new code to calculate the effects of intrabeam scattering (IBS) has been developed in MATLAB based on the approximation suggested by K. Bane. It interfaces with the Accelerator Toolbox but can also read in lattice functions from other codes. The code has been benchmarked against results from other codes for the ATF that use this approximation or do the calculation in a different way. The new code has been used to calculate the emittance growth due to intrabeam scattering for the lattices currently proposed for the ILC Damping Rings, as IBS is a concern, especially for the electron ring. A description of the code and its user interface, as well as results for the Damping Rings, will be presented.
Date: June 21, 2006
Creator: Reichel, I. & Wolski, A.
Partner: UNT Libraries Government Documents Department

Ion Effects in the Electron Damping Ring of the International Linear Collider

Description: Ion-induced beam instabilities and tune shifts are critical issues for the electron damping ring of the International Linear Collider (ILC). To avoid conventional ion trapping, a long gap is introduced in the electron beam by omitting a number of successive bunches out of a long train. However, the beam can still suffer from the fast ion instability, driven by ions that last only for a single passage of the electron bunches. Our study shows that the ion effects can be significantly mitigated by using multiple gaps, so that the stored beam consists of a number of relatively short bunch trains. The ion effects in the ILC damping rings are investigated using both analytical and numerical methods.
Date: July 17, 2006
Creator: Wang, L.; Raubenheimer, T.; /SLAC; Wolski, A. & U., /Liverpool
Partner: UNT Libraries Government Documents Department

A Lattice with Larger Momentum Compaction for the NLC Main Damping Rings

Description: Previous lattice designs for the Next Linear Collider Main Damping Rings [1] have met the specifications for equilibrium emittance, damping rate and dynamic aperture. Concerns about the effects of the damping wiggler on the beam dynamics [2] led to the aim of reducing the total length of the wiggler to a minimum consistent with the required damping rate, so high-field dipoles were used to provide a significant energy loss in the arcs. However, recent work has shown that the wiggler effects may not be as bad as previously feared. Furthermore, other studies have suggested the need for an increased momentum compaction (by roughly a factor of four) to raise the thresholds of various collective effects. We have therefore developed a new lattice design in which we increase the momentum compaction by reducing the field strength in the arc dipoles, compensating the loss in damping rate by increasing the length of the wiggler. The new lattice again meets the specifications for emittance, damping rate and dynamic aperture, while having the benefit of significantly higher thresholds for a number of instabilities.
Date: March 17, 2008
Creator: Woodley, M.; Raubenheimer, Tor O.; Wu, J.; Wolski, A. & /SLAC /LBL, Berkeley
Partner: UNT Libraries Government Documents Department

Achieving Large Dynamic Aperture in the ILC Damping Rings

Description: The Damping Rings for the International Linear Collider have challenging requirements for the acceptance, because of the high average injected beam power and the large beam produced from the positron source. At the same time, the luminosity goals mean that the natural emittance must be very small, and this makes it particularly difficult to achieve a good dynamic aperture. We describe design approaches and lattice designs that meet the emittance specification and have very promising dynamic aperture.
Date: May 27, 2005
Creator: Wolski, A.; Cai, Y & /LBL, Berkeley /SLAC
Partner: UNT Libraries Government Documents Department

Multi-Stage Bunch Compressors for the International Linear Collider

Description: We present bunch compressor designs for the International Linear Collider (ILC) which achieve a reduction in RMS bunch length from 6 mm to 0.3 mm via multiple stages of compression, with stages of acceleration inserted between the stages of compression. The key advantage of multi-stage compression is that the maximum RMS energy spread is reduced to approximately 1%, compared to over 3% for a single-stage design. Analytic and simulation studies of the multi-stage bunch compressors are presented, along with performance comparisons to a single-stage system. Parameters for extending the systems to a larger total compression factor are discussed.
Date: May 27, 2005
Creator: Tenenbaum, P.; Raubenheimer, T.O.; /SLAC; Wolski, A. & /LBL, Berkeley
Partner: UNT Libraries Government Documents Department

Beam based alignment at the KEK accelerator test facility

Description: The KEK Accelerator Test Facility (ATF) damping ring is a prototype low emittance source for the NLC/JLC linear collider. To achieve the goal normalized vertical emittance {gamma}{var_epsilon}{sub {gamma}} = 20 nm-rad, magnet placement accuracy better than 30 mm must be achieved. Accurate beam-based alignment (BBA) is required. The ATF arc optics uses a FOBO cell with two horizontally focusing quadrupoles, two sextupoles and a horizontally defocusing gradient dipole, all of which must be aligned with BBA. BBA at ATF uses the quadrupole and sextupole trim windings to find the trajectory through the center of each magnet. The results can be interpreted to assess the accuracy of the mechanical alignment and the beam position monitor offsets.
Date: June 14, 2002
Creator: Ross, M.; Nelson, J.; Woodley, M. & Wolski, A.
Partner: UNT Libraries Government Documents Department

Initial results from model independent analysis of the KEK ATF

Description: Model Independent Analysis (MIA) has shown the potential to be a useful tool for diagnostics and optics verification. The Accelerator Test Facility (ATF) prototype damping ring at KEK has a diagnostic system with the ability to collect data allowing the application of MIA for analysis of the injection stability, and the storage ring optics and diagnostics. Understanding of all these issues will be important for improving the operational performance of a damping ring. We report here the results of a first attempt to apply MIA to the ATF.
Date: May 30, 2002
Creator: Wolski, A.; Ross, M.C.; Woodley, M.D. & Nelson, J.
Partner: UNT Libraries Government Documents Department

Overview of collective effects in the NLC main damping rings

Description: The present design for the NLC Main Damping Rings (MDRs) meets the specifications for acceptance and extracted emittance, in the limit of zero current. However, the relatively large bunch charge and moderate energy mean that a variety of collective effects can impact the beam dynamics, leading to loss of stability or increase of equilibrium emittance. These effects include intrabeam scattering, impedance from numerous sources, fast ion instability, and (in the positron ring) electron cloud. In this note, we survey the expected impact on damping ring performance from each of a number of collective effects, and discuss the priorities for future studies in this area.
Date: May 30, 2002
Creator: Wolski, A. & de Santis, S.
Partner: UNT Libraries Government Documents Department

Harmonic cavities for the NLC damping rings

Description: To achieve high luminosity, a linear collider needs damping rings to produce beams with very small transverse emittances. In the NLC, design constraints place the Main Damping Rings in a parameter regime where intrabeam scattering (IBS) is likely to be a limitation on the emittance, and hence on the final luminosity. It is possible to mitigate the effects of IBS by lengthening the bunch: this may be achieved by redesigning the lattice with higher momentum compaction, or by use of higher harmonic cavities. Here, we consider the latter approach. We estimate the required bunch lengthening that might be needed, outline some appropriate parameters for the harmonic cavities, and discuss some of the effects that might be introduced or exacerbated by the cavities, such as synchronous phase variation along the bunch train.
Date: May 29, 2003
Creator: de Santis, S. & Wolski, A.
Partner: UNT Libraries Government Documents Department

Beam Conditioning for Free Electron Lasers:Consequences and Methods

Description: The consequences of beam conditioning in four example cases [VISA, a soft x-ray free-electron laser (FEL), LCLS, and a 'Greenfield' FEL] are examined. It is shown that in emittance limited cases, proper conditioning reduces sensitivity to the transverse emittance and, furthermore, allows for stronger focusing in the undulator. Simulations show higher saturation power, with gain lengths reduced by a factor of 2 or more. The beam dynamics in a general conditioning system are studied, with 'matching conditions' derived for achieving conditioning without growth in the effective emittance. Various conditioning lattices are considered, and expressions derived for the amount of conditioning provided in each case when the matching conditions are satisfied. These results show that there is no fundamental obstacle to producing beam conditioning, and that the problem can be reduced to one of proper lattice design. Nevertheless, beam conditioning will not be easy to implement in practice.
Date: December 14, 2010
Creator: Wolski, A.; Penn, G.; Sessler, A.; Wurtele, J. & /LBL, Berkeley /UC, Berkeley, Astron. Dept.
Partner: UNT Libraries Government Documents Department

Analysis of KEK-ATF optics and coupling using orbit response matrix analysis

Description: LOCO is a code for analysis of the linear optics in a storage ring based on the closed orbit response to steering magnets. The analysis provides information on focusing errors, BPM gain and rotation errors, and local coupling. Here, we report the results of an application of LOCO to the KEK-ATF. Although the analysis appears to have provided useful information on the optics of the machine, it appears that one of the main aims of the study--to reduce the vertical emittance by correcting the local coupling--was not successful, and we discuss some possible reasons for this.
Date: January 1, 2004
Creator: Wolski, A.; /LBL, Berkeley; Nelson, J.; Ross, M.; Woodley, M.; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Analysis of KEK-ATF Optics And Coupling Using Orbit Response Matrix Analysis

Description: LOCO is a code for analysis of the linear optics in a storage ring based on the closed orbit response to steering magnets. The analysis provides information on focusing errors, BPM gain and rotation errors, and local coupling. Here, we report the results of an application of LOCO to the KEK-ATF. Although the analysis appears to have provided useful information on the optics of the machine, it appears that one of the main aims of the study--to reduce the vertical emittance by correcting the local coupling--was not successful, and we discuss some possible reasons for this.
Date: October 13, 2006
Creator: Wolski, A.; /LBL, Berkeley; Nelson, J.; Ross, M.; Woodley, M.; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Coupling Correction and Beam Dynamics at Ultralow Vertical Emittance in the ALS

Description: For synchrotron light sources and for damping rings of linear colliders it is important to be able to minimize the vertical emittance and to correct the spurious vertical dispersion. This allows one to maximize the brightness and/or the luminosity. A commonly used tool to measure the skew error distribution is the analysis of orbit response matrices using codes like LOCO. Using the new Matlab version of LOCO and 18 newly installed power supplies for individual skew quadrupoles at the ALS the emittance ratio could be reduced below 0.1% at 1.9 GeV yielding a vertical emittance of about 5 pm. At those very low emittances, additional effects like intra beam scattering become more important, potentially limiting the minimum emittance for machine like the damping rings of linear colliders.
Date: March 17, 2008
Creator: Steier, Christoph; Robin, D.; Wolski, A.; Portmann, G.; Safranek, J. & /LBL, Berkeley /SLAC
Partner: UNT Libraries Government Documents Department

Collective effects analysis for the Berkeley femtosource

Description: We present an overview of the collective effects in a proposed ultrafast x-ray facility, based on a recirculating linac. The facility requires a small vertical ewmittance of 0.4 mm-mrad and is designed to operate with a ''flat bunch'' with a large aspect ratio of emittances. Emittance control from the electron source at the RF photocathode to the photon production chain of undulators, and understanding and the mitigation of collective effects is critical to a successful machine operation. Key aspects of accelerator physics involved in beam break-up, coherent synchrotron radiation, resistive wall impedance and other effects have been addressed and reported here.
Date: May 1, 2003
Creator: Corlett, J.; De Santis, S.; Wolski, A. & Zholents, A.
Partner: UNT Libraries Government Documents Department

Beam Conditioning and Harmonic Generation in Free ElectronLasers

Description: The next generation of large-scale free-electron lasers (FELs) such as Euro-XFEL and LCLS are to be devices which produce coherent X-rays using Self-Amplified Spontaneous Emission (SASE). The performance of these devices is limited by the spread in longitudinal velocities of the beam. In the case where this spread arises primarily from large transverse oscillation amplitudes, beam conditioning can significantly enhance FEL performance. Future X-ray sources may also exploit harmonic generation starting from laser-seeded modulation. Preliminary analysis of such devices is discussed, based on a novel trial-function/variational-principle approach, which shows good agreement with more lengthy numerical simulations.
Date: July 5, 2004
Creator: Charman, A.E.; Penn, G.; Wolski, A. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Orbit Response Matrix Analysis Applied at PEP-II

Description: The analysis of orbit response matrices has been used very successfully to measure and correct the gradient and skew gradient distribution in many accelerators. It allows determination of an accurately calibrated model of the coupled machine lattice, which then can be used to calculate the corrections necessary to improve coupling, dynamic aperture and ultimately luminosity. At PEP-II, the Matlab version of LOCO has been used to analyze coupled response matrices for both the LER and the HER. The large number of elements in PEP-II and the very complicated interaction region present unique challenges to the data analysis. All necessary tools to make the analysis method useable at PEP-II have been implemented and LOCO can now be used as a routine tool for lattice diagnostic.
Date: May 17, 2005
Creator: Steier, C.; Wolski, A.; /LBL, Berkeley; Ecklund, S.; Safranek, J.A.; Tenenbaum, P. et al.
Partner: UNT Libraries Government Documents Department

Simulation of the Electron Cloud for Various Configurations of a Damping Ring for the ILC

Description: In the beam pipe of the positron damping ring of the International Linear Collider (ILC), an electron cloud may be first produced by photoelectrons and ionization of residual gases and then increased by the secondary emission process. This paper reports the assessment of electron cloud effects in a number of configuration options for the ILC baseline configuration. Careful estimates were made of the secondary electron yield threshold for electron cloud build-up, and the related single- and coupled-bunch instabilities, as a function of beam current and surface properties for a variety of optics designs. When the configuration for the ILC damping rings was chosen at the end of 2005, the results from these studies were important considerations. On the basis of the theoretical and experimental work, the baseline configuration currently specifies a pair of 6 km damping rings for the positron beam, to mitigate the effects of the electron cloud that could present difficulties in a single 6 km ring.
Date: June 23, 2006
Creator: Pivi, M.; Wang, L.; /SLAC; Ohmi, K.; /KEK, Tsukuba; Wanzenberg, R. et al.
Partner: UNT Libraries Government Documents Department

Impedance and instabilities in the NLC damping rings

Description: We report on impedance calculations and single-bunch and multi-bunch instabilities in the NLC damping rings. Preliminary designs of vacuum chambers and major components have addressed beam impedance issues, with the desire to increase instability current thresholds and reducing growth rates. MAFIA calculations of short-range and long-range wakefields have allowed computations of growth rates and thresholds, which are presented here. Resistive wall instability dominates long-range effects, and requires a broadband feedback system to control coupled-bunch motion. Growth rates are within the range addressable by current feedback system technologies. Single-bunch instability thresholds are safely above nominal operating current.
Date: June 12, 2001
Creator: Corlett,J.; Li, D.; Pivi, M.; Rimmer, R.; DeSantis, S.; Wolski, A. et al.
Partner: UNT Libraries Government Documents Department

Symplectic models for general insertion devices

Description: A variety of insertion devices (IDs), wigglers and undulators, linearly or elliptically polarized,are widely used as high brightness radiation sources at the modern light source rings. Long and high-field wigglers have also been proposed as the main source of radiation damping at next generation damping rings. As a result, it becomes increasingly important to understand the impact of IDs on the charged particle dynamics in the storage ring. In this paper, we report our recent development of a general explicit symplectic model for IDs with the paraxial ray approximation. High-order explicit symplectic integrators are developed to study real-world insertion devices with a number of wiggler harmonics and arbitrary polarizations.
Date: June 1, 2001
Creator: Wu, Y.; Forest, E.; Robin, D. S.; Nishimura, H.; Wolski, A. & Litvinenko, V. N.
Partner: UNT Libraries Government Documents Department

Beam-based alignment at the KEK-ATF damping ring

Description: The damping rings of a future linear collider will have demanding alignment and stability requirements in order to achieve the low vertical emittance necessary for high luminosity. The Accelerator Test Facility (ATF) at KEK has successfully demonstrated the vertical emittance below 5 pm that is specified for the GLC/NLC Main Damping Rings. One contribution to this accomplishment has been the use of Beam Based Alignment (BBA) techniques. The mode of operation of the ATF presents particular challenges for BBA, and we describe here how we have deduced the offsets of the BPMs with respect to the quadrupoles. We also discuss a technique that allows for direct measurements of the beam-to-quad offsets.
Date: June 30, 2004
Creator: Woodley, Mark D.; Nelson, Janice; Ross, Marc; Turner, James; Wolski, A. & Kubo, Kiyoshi
Partner: UNT Libraries Government Documents Department