Paper  Title  Page 

WEPMN082  Global Scattering Matrix Technique Applied to the Calculation of Higher Order Modes for ILC Superconducting Cavities  2218 


A cascaded scattering matrix approach is used to determine the electromagnetic (e.m.) field in the main ILC cavities. This approach is used to compute higher order e.m. modes in the baseline configuration, and high gradient alternative configurations. We present results on three designs: TESLA, Cornell University's reentrant and, KEK's "Ichiro". This approach allows realistic experimental errors to be incorporated in the studies in an efficient manner and allows several cavities to be modelled en masse. Simulations are presented on the wakefields in superstructures and segments of entire modules. Details on trapped eigenmodes and means to avoid them are delineated. The influence of cell misalignments and cavity perturbations on the modes are also presented.  
WEPMN077  Impedance Measurements on a Test Bench Model of the ILC Crab Cavity  2206 


Funding: This work was supported by the EC under the FP6 'Research Infrastructure Action  Structuring the European Research Area' EUROTeV DS Project Contract no.011899, RIDS and PPARC. In order to verify detailed impedance simulations, the modes in an aluminium model of the ILC crab cavity were investigated using a beadpulling technique as well as a stretchedwire frequency domain measurement. The combination of these techniques allow for a comprehensive study of the modes of interest. For the wire measurement, a transverse alignment system was fabricated and rf components were carefully designed to minimize any potential impedance mismatches. The measurements are compared with direct simulations of the stretchedwire experiments using numerical electromagnetic field codes. High impedance modes of particular relevance to the ILC crab cavity are identified and characterized 

WEPMN078  RF Cavity Development for FFAG Application on ERLP at Daresbury  2209 


Funding for a nonscaling, Fixed Field Alternating Gradient (FFAG) facility has been approved for installation on the Energy Recovery Linac Prototype (ERLP) at Daresbury. The RF system specification for this project requires the development of a high efficiency, 1.3 GHz, normal conducting accelerating structure, capable of delivering the required accelerating voltage, whilst adhering to stringent space limitations imposed by the extremely compact nature of the FFAG ring. We have optimised a cavity design, providing the necessary acceleration and minimising the RF power requirements to match with commercially available power sources.  
THPMS049  Investigations of the Wideband Spectrum of Higher Order Modes Measured on TESLAstyle Cavities at the FLASH Linac  3100 


Funding: US DOE Contract #DEAC0276SF00515 Higher Order Modes (HOMs) excited by the passage of the beam through an accelerating cavity depend on the properties of both the cavity and the beam. It is possible, therefore, to draw conclusions on the inner geometry of the cavities based on observations of the properties of the HOM spectrum. A data acquisition system based on two 20 GS/s, 6 GHz scopes has been set up at the FLASH facility, DESY, in order to measure a significant fraction of the HOM spectrum predicted to be generated by the TESLA cavities used for the acceleration of its beam. The HOMs from a particular cavity at FLASH were measured under a range of known beam conditions. The dipole modes have been identified in the data. 3D simulations of different manufacturing errors have been made, and it has been shown that these simulations can predict the measured modes. 

THPAN081  Collimator Wakefields: Formulae and Simulation  3405 


The effect of a leading particle on a trailing particle due to resistive and geometric wakefields in collimators can be described by expanding in a series of angular mode potentials W_{m}(s). Several formulae for these are given in the literature. We compare these formulae with numerical predictions from codes that solve the EM field equations, and explore the claimed regions of validity. We also explore how the EM code results can be used to numerically obtain angular mode potentials suitable for use in tracking codes.  
FRPMN091  Simulation of HOM Wakefields in the Main ILC Cavities  4288 


We investigate the electromagnetic field (e.m.) excited by a train of multiple bunches in the main superconducting linacs of the ILC. These e.m. fields are represented as a wakefield. Detailed simulations are made for the modes which constitute the longrange wakefield in new high gradient cavity structures. In particular, we focus our study on the modes in reentrant and low loss Ichiro cavities. Modes trapped within a limited number of cells can give rise to a significant diminution in the emittance of the beam and we pay particular attention to these modes. Beam tracking simulations on the resulting emittance dilution over the entire length of the linac are made in order to provide details on the damping which is necessary for modes with particularly large kick factors.  
FRPMN092  Beam Coupling Impedance Simulations and Laboratory Measurements for the LHC FP420 Detector  4294 


The FP420 collaboration* aims at designing forward proton tagging detectors to be installed in the LHC sectors 420 meters downstream of the ATLAS detector and/or CMS detector. The experiment requires modification of the beam pipe material and geometry with a consequent impact on the LHC impedance budget and the circulating beam stability. This paper describes numerical simulations and laboratory measurements carried out to characterize the coupling impedance (longitudinal and transverse) and the associated loss factor of each insertion. The detectors are located in pockets of the beam tube. We study both single and multipocket configurations with a view to characterizing the impact on the beam dynamics. In addition, results are compared to available analytical calculations for the resistive wall impedance.
* Cox, Brian et al., "FP420 : An R&D Proposal to Investigate the Feasibility of Installing Proton Tagging Detectors in the 420 m Region of the LHC", CERNLHCC2005025 

FRPMS069  Simulations of Stretched Wire Measurements of 3.9GHz Cavities for the ILC  4177 


We present wakefield simulations on both the main superconducting cavities and on the beam delivery system crab cavities of the ILC. We utilize both finite difference and finite element computer codes to simulate the electromagnetic fields in these cavities in the presence of a stretched wire. This study is intended to both predict the wakefield in experiments on the modal characterisation of 3.9 GHz cavities in progress at the Cockcroft Institute and, to explore practical issues concerning the feasibility of using this stretched wire method to investigate modes in the ILC main cavities. Multicell scattering matrices and the modes in infinite periodic structures are calculated with a view to aiding the interpretation of experimental results. A modal convergence study is also included 