| Paper |
Title |
Page |
| MOPP128 |
Comparison of Stretched-wire, Bead-pull and Numerical Impedance Calculations on 3.9 GHz Dipole Cavities
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859 |
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- P. Goudket, C. D. Beard, P. A. McIntosh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
- G. Burt, A. C. Dexter
Cockcroft Institute, Lancaster University, Lancaster
- R. M. Jones
Cockcroft Institute, Warrington, Cheshire
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In order to verify detailed impedance and wakefield simulations, the resonant modes in an aluminium model of the 9-cell ILC crab cavity were investigated using a stretched-wire frequency domain measurement, as well as frequency-domain bead-pull measurements. These measurements were compared to numerical simulations in order to verify that the complete cavity mode spectrum could be experimentally characterised for this high frequency structure. The analysis of the results and the accuracy and/or limitations of each method is presented.
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| MOPP034 |
Large Scale Linac Simulations Using a Globalised Scattering Matrix Approach
|
619 |
| |
- I. R.R. Shinton, R. M. Jones
UMAN, Manchester
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A globalised cascaded scattering matrix scheme serves as practical method to simulate the electromagnetic (e.m.) fields in the groups of cavities which constitute the main accelerating structures of a linac. The cascaded scattering matrix technique is a well-proven method which allows realistic fabrication errors to be incorporated in an efficient manner without the necessity to re-mesh the entire geometry. Once the unit cell structures have been determined using a numerical scheme, such as finite element method utilized here, the overall cascaded scattering matrix calculation requires little in the way of computational resources or time and is consequently an efficient means of characterizing the e.m. field. Details of the e.m. field, shunt impedance and trapped modes for large scale linac simulations applied to the baseline and alternate high gradient cavities for the ILC and applications to XFEL are presented.
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| TUPP062 |
Beam Coupling Impedance Studies on LHC FP420 Multi-pocket Beam Pipe Prototype
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1682 |
| |
- F. Roncarolo, R. Appleby, R. M. Jones
UMAN, Manchester
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The LHC FP420 collaboration is assessing the feasibility of installing forward proton detectors 420m from the ATLAS and/or CMS interaction points. The latest prototype of a FP420 station consists of a modified LHC beam pipe in which two pockets hosting the detectors introduce an abrupt cross-section variation of the pipe. During the FP420 proposed operation, each station is moved towards the beam as close as 3 mm (~ 10 σx). The impact on the LHC beam coupling impedance has been evaluated with a laboratory wire measurement and a suite of numerical simulations. In addition, we describe a proposed modification of the beam pipe design which minimizes the impedance of the resonances without compromising the FP420 detector signal to background ratio.
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| TUPP063 |
Characterization of the ATLAS Roman Pots Beam Coupling Impedance and Mechanics
|
1685 |
| |
- F. Roncarolo, R. M. Jones
UMAN, Manchester
- F. Caspers, B. Di Girolamo, T. Kroyer
CERN, Geneva
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At the LHC, four Roman Pot (RP) type detectors will be installed on both sides of the ATLAS experiment with the aim of measuring elastic scattering at very small angles and determining the absolute luminosity at the interaction point. During dedicated LHC runs, the detectors will be positioned at about 1 mm from the nominal beam orbit. Numerical simulations and laboratory measurements were carried out to characterize the RP impact on the total LHC beam coupling impedance. The measurement results assess the effectiveness of RF-absorbing ferrite plates that have been mounted in convenient locations in order to damp high Q resonances of the RP structure. In addition, we review the RP mechanics emphasizing the accuracy and reproducibility of the positioning system.
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| WEPP081 |
Wake-fields and Beam Dynamics Simulations for ILC ACD Accelerating Cavities
|
2707 |
| |
- C. J. Glasman, R. M. Jones
UMAN, Manchester
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The ILC aims at colliding bunches of electrons and positrons at a centre of mass energy of 0.5 TeV and in a proposed upgrade to 1 TeV. These bunches of charged particle are accelerated in superconducting linacs. The baseline design for the ILC relies on the relatively mature TESLA-style cavities, with a proposed gradient of more than 30 MV/m and is known as the baseline configuration document (BCD). However, here we investigate electromagnetic fields in superconducting cavities, with the potential to reach accelerating gradients in excess of 50 MV/m, and these are the subject of the alternative configuration document (ACD). We analyse the band structure and necessary damping requirement of the wake-fields in two design configurations: Cornell's re-entrant cavity and KEK's Ichiro cavity. The emittance dilution arising from beams subjected to injection offsets and from cavity misalignments are studied in beam dynamics simulations.
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| WEPP085 |
RF Coupler Kicks and Wake-fields in SC Accelerating Cavities
|
2719 |
| |
- N. Juntong, R. M. Jones, I. R.R. Shinton
UMAN, Manchester
- C. D. Beard
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
- G. Burt
Cockcroft Institute, Warrington, Cheshire
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The main accelerating cavities of the ILC provide acceleration of both positron and electron beams to 250 GeV per beam and 500 GeV per beam in a proposed upgrade. The wake-field excited by each ultra-relativistic beam in the accelerating cavities can seriously dilute the emittance of the particles within the beams. Each cavity is supplied with both fundamental and higher order mode couplers. The geometrical configuration of these RF couplers results in an asymmetrical field and this gives rise to both an RF kick being applied to the beam and transverse wake-field. Detailed e.m. fields are simulated in the vicinity of the couplers in order to assess the impact on the beam dynamics. We investigate modified geometries with a view to alleviating the emittance dilution resulting from the e.m. field associated with the RF couplers.
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| WEPP089 |
Wake-field Suppression in the CLIC Main Linac
|
2725 |
| |
- V. F. Khan, R. M. Jones
UMAN, Manchester
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The CLIC linear collider aims at accelerating multiple bunches of electrons and positrons and colliding at a centre of mass energy of 3 TeV. These bunches are accelerated through X-band linacs operating at an accelerating frequency of 12 GHz. Each beam readily excites wake-fields in the accelerating cavities of each linac. The transverse components of the wake-fields, if left unchecked, can dilute the beam emittance. The present CLIC design relies on heavy damping of these wake-fields in order to ameliorate the effects of the wake-field on the beam emittance. Here we present initial results on a modified design which combines both damping and detuning of the cell frequencies of each cavity structure in order to enhance the overall decay of the wake-field. Interleaving of cell frequencies is explored as a means to improve the damping.
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