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| MOPWA022 | Influence of Transient Beam Loading on the Longitudinal Beam Dynamics at BESSY VSR | 141 |
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BESSY VSR, a scheme where 1.7 ps and 15 ps long bunches (rms) can be stored simultaneously in the BESSY II storage ring has recently been proposed *. The strong longitudinal bunch focusing is achieved by superconducting high gradient RF cavities. If the bunch fill pattern exhibits a significant inhomogeneity, e.g. due to gaps, transient beam loading causes a distortion of the longitudinal phase space which is different for each bunch. The result are variations along the fill pattern in synchronous phase, synchrotron frequency and bunch shape. This paper presents investigations of transient beam loading and depicts the consequences on bunch length, phase stability and longitudinal multi-bunch oscillations for the projected setup of BESSY VSR.
* G. Wüstefeld, A. Jankowiak, J. Knobloch, M. Ries, Simultaneous Long and Short Electron Bunches in the BESSY II Storage Ring, Proceedings of IPAC2011, San Sebastián, Spain |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA022 | |
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| MOPWA032 | Aspects of SRF Cavity Optimization for BESSY-VSR Upgrade | 171 |
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Funding: Work supported by Federal Ministry for Research and Education BMBF under contract 05K13HR1. In this work we present a preliminary study of a long chain of cavities and some aspects involved in the optimization procedure. It is important to numerically model and optimize the SRF cavities with respect to external quality factors of the most dangerous higher order modes. BESSY-VSR is an upgrade scheme for the existing BESSY II storage ring aiming to simultaneously support variable electron pulse lengths. Currently, BESSY II supports long 15 ps bunches in the standard user optics configuration and short 1.5 ps bunches in a so-called low-α optics mode. In order to develop BESSY II into a variable electron pulse length storage ring, additional two sets of SRF higher-harmonic cavities will be installed. The present RF acceleration system operates at 0.5 GHz and the additional 3rd harmonic and 3rd sub-harmonic cavities will operate at 1.5 GHz and 1.75 GHz, respectively. These cavities are essential to produce short 1.5 ps bunches with a design current of up to 0.8 mA per bunch. The total current in the storage ring is limited by the higher order mode damping capabilities of the SRF cavities. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA032 | |
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| MOPWA033 | Yacs - A New 2.5D FEM Eigenmode Solver for Axisymmetric RF-Structures | 175 |
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Funding: Work supported by the BMBF under contract no. 05K13PEB Most feasibility studies for modern accelerator concepts, including superconducting multicell RF-cavity-resonators in circular accelerators, depend on computing a large number of eigenmode frequencies and field patterns to obtain typical figures of merit. This task includes computational intensive numerical studies. To obtain the full eigenfrequency spectra most of these studies are performed in 3D, require a great amount of computation resources and thus are limited to a few hundred or thousand eigenmodes. To overcome this issue, some codes make use of the axisymmetric geometry of most of the RF-cavity-resonator structures and solve the problem in 2D. Solving in 2D however reduces the eigenmode spectra to eigenmodes with no azimuthal dependencies (so called monopole-modes). Due to the lack of freely available and easy to use 2.5D eigenmode solvers which are able to solve for the full 3D field in a reduced 2.5 dimensional problem, we developed yet another cavity solver (Yacs), a simple FEM based solver capable of solving for the full 3D eigenmodes of axisymmetric problems while only requiring a fraction of the computation resources required by most modern 3D codes. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA033 | |
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| MOPWA034 | Coupled-Bunch Instability Suppression Using RF Phase Modulation at the DELTA Storage Ring | 179 |
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Funding: Work supported by the BMBF under contract no. 05K13PEB The upcoming upgrade of BESSY II, called BESSY-VSR*, involves the utilization of superconducting multicell RF-resonators with high accelerating gradients to provide short and long bunches in an electron storage ring simultaneously. Even under the assumption of strongest available damping of beam induced modes, the residual impedances of the cavities may cause collective multibunch instabilities at the frontier of stability available from current bunch-by-bunch feedback systems. At the DELTA electron storage ring, a phase modulation of the driving RF is used to suppress coupled-bunch instabilities and to increase the lifetime. The time dependent frequency variation in the order of the synchrotron frequency gives rise to additional damping of the bunch oscillators by decoherence and Landau damping. The behaviour and the additional damping of the bunch oscillators is investigated by the existing bunch-by-bunch feedback system e.g. the increase of the overall damping might support the capability of feedback systems under extreme operating conditions of BESSY-VSR. * G. Wüstefeld et al., Proc. of IPAC'11, San Sebastián, THPC014 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA034 | |
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| MOPWA035 | Two General Orbit Theorems for Efficient Measurements of Beam Optics | 183 |
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| Closed-orbit perturbations and oscillating beam solutions in storage rings are closely related. While techniques exist to fit accelerator models to closed-orbit perturbations or to oscillation data, the exploitation of their relation has been limited. In this work, two orbit theorems that allow an efficient computation of optical parameters in storage rings with older hardware are derived for coupled linear beam motion. The monitor theorem is based on an uncoupled case study described by the author in an earlier work and has been generalized as well as simplified in mathematical abstraction to provide a reliable and computationally stable framework for beam optics measurements. It is based on a closed-orbit measurement utilizing 4 dipole correctors (2 for each plane). The corrector theorem allows to obtain parameters of these dipole correctors using two turn-by-turn monitors at almost arbitrary positions in the ring (which do not need to be located in a drift space), so that it is possible to uniquely resolve closed orbits into optical parameters without sophisticated lattice models. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA035 | |
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| MOPHA024 | A Novel Transverse Deflecting Cavity for Slice Diagnostics at BERLinPro | 827 |
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Funding: Work supported by BMBF under contract no. 05K10PEA BERLinPro is an energy-recovery linac project to be realized at the Helmholtz-Zentrum Berlin (HZB) for an electron beam with 1mm mrad normalized emittance and 100 mA average current. The initial beam parameters are determined by the performance of the electron source, an SRF photo-electron injector. The development auf this SRF photon-electron injector is a main task of BERLinPro. Especially the beam emittance is basically defined by the SRF photogun. For beam diagnostics time dependent effects from the RF curvature and space charge must be taken into account and a sophisticated slice diagnostics is required. To perform this type of diagnostics a transverse deflecting cavity has been designed, characterized and is presently under construction.. This single cell cavity operates in a TM110-like mode at 1.3 GHz optimized for high transverse shuntimpedance of appr. 3.2 MOhm by a concentration of fields near the beam axis. The cavity has a novel geometry that allows for an operation with both polarizations of the TM110-Mode. The layout of the deflecting cavity will be presented together with the results of the low RF characterization. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPHA024 | |
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| WEPMA026 | Higher Order Mode Propagation and Damping Studies on Axisymmetric Superconducting Multicell RF-Resonators | 2812 |
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Funding: Work supported by the BMBF under contract no. 05K13PEB Higher order mode (HOM) propagation and damping is a major concern in feasibility studies regarding the upcoming upgrade of BESSY II, named BESSY-VSR*, which involves the utilization of superconducting multicell RF-resonators in a storage ring while maintaining a reasonably high beam current typical for third generation synchrotron radiation facilities. In addition to the computation of the typical figures of merit, we focus on studies of the mode propagation in axisymmetric structures. Due to the focus on axisymmetric studies we are able to use 2D codes to investigate in eigenmodes with substantial higher frequencies than usually considered with full 3D codes in parametric studies. In this work we present preliminary studies involving mode propagation in superconducting elliptical multicell cavities. * G. Wüstefeld et al., Proc. of IPAC'11, San Sebastián, THPC014 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMA026 | |
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