| Paper | Title | Page |
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| TU6RFP076 | Measurement of Longitudinal and Transverse Impedance of Kicker Magnets Using the Coaxial Wire Method | 1726 |
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Fast kicker magnets are used to inject beam into and eject beam out of the CERN SPS accelerator ring. These kickers are generally ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. Unless special precautions are taken the impedance of the ferrite yoke can provoke significant beam induced heating, even above the Curie temperature of ferrite. In addition the impedance can contribute to beam instabilities. In this paper different variants of the coaxial wire method, both for measuring longitudinal and transverse impedance, are briefly discussed in a tutorial manner and do's and don'ts are shown on practical examples. In addition we present the results of several impedance measurements for SPS kickers using the wire method and compare those results with theoretical models. |
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| TH5PFP015 | Recent Developments for the HEADTAIL Code: Updating and Benchmarks | 3220 |
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The HEADTAIL code models the evolution of a single bunch interacting with a localized impedance source or an electron cloud, optionally including space charge. The newest version of HEADTAIL relies on a more detailed optical model of the machine taken from MAD-X and is more flexible in handling and distributing the interaction and observation points along the simulated machine. In addition, the option of the interaction with the wake field of specific accelerator components has been added, such that the user can choose to load dipolar and quadrupolar components of the wake from the impedance database Z-BASE. The case of a single LHC-type bunch interacting with the realistic distribution of the kicker wake fields inside the SPS has been successfully compared with a single integrated beta-weighted kick per turn. The current version of the code also contains a new module for the longitudinal dynamics to calculate the evolution of a bunch inside an accelerating bucket. |
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| FR5RFP034 | Transverse Impedance Localization Using Dependent Optics | 4604 |
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Funding: This work has been partially performed under the auspices of US department of energy Measurements of transverse impedance in the SPS to track the evolution over the last few years show discrepancies compared to the analytical estimates of the major contributors. Recent measurements to localize the major sources of the transverse impedance using intensity dependent optics are presented. Some simulations using HEADTAIL to understand the limitations of the reconstruction and related numerical aspects are also discussed. |
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| FR5RFP048 | An Update of ZBASE, the CERN Impedance Database | 4643 |
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A detailed knowledge of the beam coupling impedance of the CERN synchrotrons is required in order to identify the impact on instability thresholds of potential changes of beam parameters, as well as additions, removal or modifications of hardware. To this end, an update of the impedance database was performed, so that impedance results from theoretical calculations using new multilayer models, impedance results from electromagnetic field simulations and impedance results from bench measurements can be compiled. In particular, the impedance database is now set to separately produce the dipolar and quadrupolar transverse impedance and wakes that the HEADTAIL simulation code needs to accurately simulate the effect of the impedance on the beam dynamics. |
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| FR5RFP047 | Analysis of the Transverse SPS Beam Coupling Impedance with Short and Long Bunches | 4640 |
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The upgrade of the CERN Large Hadron Collider (LHC) would require a four- to fivefold increase of the single bunch intensity presently obtained in the Super Proton Synchrotron (SPS). Operating at such high single bunch intensities requires a detailed knowledge of the sources of SPS beam coupling impedance, so that longitudinal and transverse impedance reduction campaigns can be planned and performed effectively if needed. In this paper, the transverse impedance of the SPS is studied by injecting a single long bunch into the SPS, and observing its decay without RF. This particular setup enhances the resolution of the frequency analysis of the longitudinal and transverse bunch signals acquired with strip line couplers connected to a fast data acquisition. It also gives access to the frequency content of the transverse impedance. Results from measurements with short and long bunches in the SPS performed in 2008 are compared with simulations and theoretical predictions. |
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| FR5RFP049 | Coupling Impedance of the CERN SPS Beam Position Monitors | 4646 |
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A detailed knowledge of the beam coupling impedance of the CERN Super Proton Synchrotron (SPS) is required in order to operate this machine with a higher intensity for the foreseen Large Hadron Collider (LHC) luminosity upgrade. A large number of Beam Position Monitors (BPM) is currently installed in the SPS, and this is why their contribution to the SPS impedance has to be assessed. This paper focuses on electromagnetic simulations and bench measurements of the longitudinal and transverse impedance generated by the horizontal and vertical BPMs installed in the SPS machine. |
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| FR5RFP047 | Analysis of the Transverse SPS Beam Coupling Impedance with Short and Long Bunches | 4640 |
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The upgrade of the CERN Large Hadron Collider (LHC) would require a four- to fivefold increase of the single bunch intensity presently obtained in the Super Proton Synchrotron (SPS). Operating at such high single bunch intensities requires a detailed knowledge of the sources of SPS beam coupling impedance, so that longitudinal and transverse impedance reduction campaigns can be planned and performed effectively if needed. In this paper, the transverse impedance of the SPS is studied by injecting a single long bunch into the SPS, and observing its decay without RF. This particular setup enhances the resolution of the frequency analysis of the longitudinal and transverse bunch signals acquired with strip line couplers connected to a fast data acquisition. It also gives access to the frequency content of the transverse impedance. Results from measurements with short and long bunches in the SPS performed in 2008 are compared with simulations and theoretical predictions. |
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| FR5RFP048 | An Update of ZBASE, the CERN Impedance Database | 4643 |
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A detailed knowledge of the beam coupling impedance of the CERN synchrotrons is required in order to identify the impact on instability thresholds of potential changes of beam parameters, as well as additions, removal or modifications of hardware. To this end, an update of the impedance database was performed, so that impedance results from theoretical calculations using new multilayer models, impedance results from electromagnetic field simulations and impedance results from bench measurements can be compiled. In particular, the impedance database is now set to separately produce the dipolar and quadrupolar transverse impedance and wakes that the HEADTAIL simulation code needs to accurately simulate the effect of the impedance on the beam dynamics. |
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| FR5RFP049 | Coupling Impedance of the CERN SPS Beam Position Monitors | 4646 |
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A detailed knowledge of the beam coupling impedance of the CERN Super Proton Synchrotron (SPS) is required in order to operate this machine with a higher intensity for the foreseen Large Hadron Collider (LHC) luminosity upgrade. A large number of Beam Position Monitors (BPM) is currently installed in the SPS, and this is why their contribution to the SPS impedance has to be assessed. This paper focuses on electromagnetic simulations and bench measurements of the longitudinal and transverse impedance generated by the horizontal and vertical BPMs installed in the SPS machine. |
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| FR5RFP050 | Beam Instabilities Studies at Transition Crossing in the CERN Proton Synchrotron | 4649 |
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The CERN PS crosses transition energy at about 6 GeV by using a second order gamma jump performed with special quadrupoles. However, for high-intensity beams, and in particular the single bunch beam for the neutron Time-of-Flight facility, a controlled longitudinal emittance blow-up is still needed to prevent a fast single-bunch vertical instability from developing near transition. A series of studies have been done in the PS in 2008 to measure the beam behaviour near transition energy for different settings of the gamma transition jump. The purpose of this paper is to compare those measurements with simulations results from the HEADTAIL code, which should allow to understand better the different mechanisms involved and maybe improve the transition crossing. |
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| FR5RFP052 | Impedance Studies for the Phase 2 LHC Collimators | 4655 |
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The LHC phase 2 collimation project aims at gaining a factor ten in cleaning efficiency, robustness and impedance reduction. From the impedance point of view, several ideas emerged during the last year, such as using dielectric collimators, slots or rods in copper plates, or Litz wires. The purpose of this paper is to discuss the possible choices, showing analytical estimates, electro-magnetic simulations performed using Maxwell, HFSS and GdFidL, and preliminary bench measurements. The corresponding complex tune shifts are computed for the different cases and compared on the stability diagram defined by the settings of the Landau octupoles available in the LHC at 7 TeV. |