Surface impedance formalism for a metallic beam pipe with small corrugations
Not Available
Stupakov, G.↗
Engineering topics
Bane, K L.F.
Publications and source records attributed to Bane, K L.F..
Multiparticle Simulation of Intrabeam Scattering for SuperB
In this communication we present the structure of a multiparticle tracking code to investigate intrabeam scattering effects in low emittance colliders. Simulation results obtained with particular reference to the SuperB parameters are compared with those of conventional IBS theories.and with those of a novel semi-analythical model able to predict IBS effect in terms of emittance growths. Intrabeam scattering (IBS) is associated with multiple small angle scattering events leading to emittance growth. In most electron storage rings, the growth rates arising from IBS are usually much longer than damping times due to synchrotron radiation, and its effect is not observed. However, IBS growth rates increase with bunch charge density, and for machines such as SuperB, that operate with high bunch charges and very low emittances, the IBS growth rates can be large enough to observe significant emittance increase. Several formalisms have been developed for calculating IBS growth rates in storage rings, notably those by Piwinski, Bjorken and Mtingwa, and their high energy approximations. Calculations show that IBS should be manageable in both SuperB rings. However these analytical models, based on Gaussian bunch distributions, cannot investigate some interesting aspects of IBS such as its impact during the damping process and its effect on the beam distribution. We developed a multiparticle tracking code, based on the Zenkevich-Bolshakov algorithm, to investigate these effects. In this communication we present the structure of the code and some simulation results obtained with particular reference to the SuperB parameters. Simulation results are compared with those of conventional IBS theories.
43 PARTICLE ACCELERATORS↗
Lattice Design for PEP-X Ultimate Storage Ring Light Source
SLAC expertise in designing and operating high current storage rings and the availability of the 2.2-km PEP-II tunnel present an opportunity for building a next generation light source - PEP-X - that would replace the SPEAR3 storage ring in the future. The PEP-X 'baseline' design, with 164 pm-rad emittance at 4.5 GeV beam energy and a current of 1.5 A, was completed in 2010. As a next step, a so-called 'ultimate' PEP-X lattice, reducing the emittance to 11 pm-rad at zero current, has been designed. This emittance approaches the diffraction limited photon emittance for multi-keV photons, providing near maximum photon brightness and high coherence. It is achieved by using 7-bend achromat cells in the ring arcs and a 90-m damping wiggler in one of the 6 long straight sections. Details of the lattice design, dynamic aperture, and calculations of the intra-beam scattering effect and Touschek lifetime at a nominal 0.2 A current are presented. Accelerator-based light sources are in high demand for many experimental applications. The availability of the 2.2-km PEP-II tunnel at SLAC presents an opportunity for building a next generation light source - PEP-X - that would replace the existing SPEAR3 light source in the future. The PEP-X study started in 2008, and the 'baseline' design, yielding 164 pm-rad emittance at 4.5 GeV beam energy and a current of 1.5 A, was completed in 2010. This relatively conservative design can be built using existing technology. However, for a long term future, it is natural to investigate a more aggressive, so-called 'ultimate' ring design. The goal is to reduce the electron emittance in both x and y planes to near the diffraction limited photon emittance of 8 pm-rad at hard X-ray photon wavelength of 0.1 nm. This would provide a near maximum photon brightness and significant increase in photon coherence. This study was motivated by the advances in low emittance design at MAX-IV. The latter was used as a starting point for the PEP-X arc lattice, however new features were included into the design for better tuning capabilities and compensation of non-linear optics effects. Further emittance reduction is achieved with a 90-m damping wiggler. Finally, intra-beam scattering (IBS) and Touschek lifetime effects were estimated and cross-checked using various codes.
43 PARTICLE ACCELERATORS↗
Ideas for a Future PEP-X Light Source
SLAC is developing a long-range plan to transfer the evolving scientific programs at SSRL from the SPEAR3 light source to a much higher performing synchrotron source -- PEP-X -- a new storage ring that would occupy the existing PEP-II tunnel and support two experimental halls, each containing 16 x-ray beam lines. Operating at 4.5 GeV and 1.5 A with a horizontal emittance of 0.14 nm-rad, reached using 90 m of damping wigglers, PEP-X would have an order of magnitude higher average brightness and flux in the 1-{angstrom} x-ray range than any existing or planned future storage ring sources. Higher brightness in the soft x-ray regime might be reached with partial lasing in long undulators, and high peak brightness could be reached with seeded FEL emission. The status of preliminary studies of PEP-X is presented.
43 PARTICLE ACCELERATORS↗
Simulations of Bunch Precompression at High Currents in the SLC Damping Rings
In the Stanford Linear Collider (SLC) each beam, after leaving a damping ring, is compressed in the Ring-to-Linac (RTL) transfer line before entering the linear accelerator. At a bunch population of 4.0 x 10{sup 10} particles, due to the limited energy acceptance of the RTL, approximately 15% of the beam has normally been lost. During the 1996 run, however, to eliminate this loss the bunch was partially precompressed in the damping ring, just before extraction; the beam loss in the RTL was reduced to almost zero. The operation and performance of precompression are presented by Minty et al. (1999). Also given is an analysis which, however, does not include the effects of the longitudinal wakefield on the beam dynamics. In this report we extend that analysis to include these effects.
43 PARTICLE ACCELERATORS↗
IMPEDANCE CONSIDERATIONS FOR THE DESIGN OF THE VACUUM SYSTEM OF THE CERN PS2
In order for the LHC to reach an ultimate luminosity goal of 10{sup 35}/cm{sup 2}/s, CERN is considering upgrade options for the LHC injector chain, including a new 50 GeV synchrotron of about 1.3 km length for protons and heavy ions, to be called the PS2 [1]. The proton energy will be ramped from 4 GeV to 50 GeV in 1.2 s, and the design proton current for LHC operation is 2.7 A. In the LARP framework, we are studying the instability thresholds and the impedance requirements of the vacuum system for the PS2. Goal of this study is to develop an impedance budget for the machine. We consider the standard single and multi-bunch collective effects that may be an issue in the PS2. For single bunch, we study the microwave instability and the transverse mode coupling instability (TMCI); for multi-bunch, the transverse coupled bunch instability. While the impedance budget will include many components in the machine, at present, we only have sufficient information to include the resistance of the beam pipe, the vacuum flanges that connect the various pieces of the vacuum chamber, and space charge impedance in our estimate. Note that earlier estimates of the impedance and its effects in the PS2 can be found in Ref. [2]. Table 1 presents selected PS2 parameters that will be used in the calculations. The equations used, unless indicated otherwise, can be found in Ref. [3].
43 PARTICLE ACCELERATORS↗
PEP-X IMPEDANCE AND INSTABILITY CALCULATIONS
PEP-X, a next generation, ring-based light source is designed to run with beams of high current and low emittance. Important parameters are: energy 4.5 GeV, circumference 2.2 km, beam current 1.5 A, and horizontal and vertical emittances, 185 pm by 8 pm. In such a machine it is important that impedance driven instabilities not degrade the beam quality. In this report they study the strength of the impedance and its effects in PEP-X. For the present, lacking a detailed knowledge of the vacuum chamber shape, they create a straw man design comprising important vacuum chamber objects to be found in the ring, for which they then compute the wake functions. From the wake functions they generate an impedance budget and a pseudo-Green function wake representing the entire ring, which they, in turn, use for performing microwave instability calculations. In this report they, in addition, consider in PEP-X the transverse mode-coupling, multi-bunch transverse, and beam-ion instabilities.
43 PARTICLE ACCELERATORS↗
COMPARISON OF SIMULATION CODES FOR MICROWAVE INSTABILITY IN BUNCHED BEAMS
In accelerator design, there is often a need to evaluate the threshold to the (longitudinal) microwave instability for a bunched beam in an electron storage ring. Several computational tools are available that allow them, once given the wakefield representing a ring, to numerically find the threshold current and to simulate the development of the instability. In this work, they present results of coputer simulations using two codes recently developed at the SLAC National Accelerator Laboratory: a Vlasov-Fokker-Planck (VFP) solver based on an algorithm by Warnock and Ellison, and a program that find the threshold from the linearized Vlasov equation. They apply the programs to find the instability threshold for three models of ring impedances: that of a Q = 1 resonator, of shielded coherent synchrotron radiation (CSR), and of a resistive wall. The first example is wel-bheaved, but the other two are singular wakes that need special care. Note that similar numerical studies of the threshold of a Q = 1 resonantor wake have been performed by Oide and Yokova, and others. They compare the results of the two programs and discuss their respective capabilities and limitations. In this report they assume the slippage factor {eta} is always positive. They work in Gaussian units.
43 PARTICLE ACCELERATORS↗