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electromagnetic-fields

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TUPAN047 Beam-beam Effects in Crab Crossing and Crab Waist Schemes sextupole, resonance, emittance, betatron 1493
 
  • K. Ohmi
  • M. E. Biagini, P. Raimondi, M. Zobov
    INFN/LNF, Frascati (Roma)
  • Y. Funakoshi
    KEK, Ibaraki
  To boost up the luminosity performance in B factories, crab crossing and crab waist schemes are proposed. The crab crossing scheme compensates crossing angle, while the crab waist scheme compensates nonlinear tems induced by crossing angle with sextupole magnets. We discuss which nonlinear terms in the beam-beam map are enhanced by the crossing angle and which terms are compensated by the crab waist sextupole.  
 
WEPMN041 Reduction of RF Skin Loss with Thin Foils impedance, resonance, controls, linac 2134
 
  • Y. Iwashita
  • H. Fujisawa, M. Ichikawa, Y. Tajima
    Kyoto ICR, Uji, Kyoto
  Reduction of RF power loss caused by skin effect has been studied. Some measurement results on a coaxial cavity with thin foils are described. Application to another type of RF devices will be discussed.  
 
WEPMN082 Global Scattering Matrix Technique Applied to the Calculation of Higher Order Modes for ILC Superconducting Cavities scattering, simulation, dipole, linac 2218
 
  • I. R.R. Shinton
  • R. M. Jones
    Cockcroft Institute, Warrington, Cheshire
  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 re-entrant 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 wake-fields in super-structures and segments of entire modules. Details on trapped eigen-modes and means to avoid them are delineated. The influence of cell misalignments and cavity perturbations on the modes are also presented.  
 
WEPMN111 3.9 GHz Superconducting Accelerating 9-cell Cavity Vertical Test Results simulation, resonance, pick-up, vacuum 2295
 
  • T. N. Khabiboulline
  • C. A. Cooper, N. Dhanaraj, H. Edwards, M. Foley, E. R. Harms, D. V. Mitchell, A. M. Rowe, N. Solyak
    Fermilab, Batavia, Illinois
  • W.-D. Moller
    DESY, Hamburg
  The 3rd harmonic 3.9GHz accelerating cavity was proposed to improve beam performances of the FLASH (TTF/DESY) facility. In the frame of collaboration Fermilab will provide DESY with a cryomodule containing a string of four cavities. In addition, a second cryomodule with one cavity will be fabricated for installation in the Fermilab photo-injector, which will be upgraded for the ILC accelerator test facility. The first results of vertical tests of 9-cell Nb cavities didn?t reached the designed accelerating gradient. The main problem is multipactoring in HOM couplers, which leads to quenching and overheating of the HOM couplers. New HOM couplers with improved design integarated to next 9-cell cavities. In this paper we present all results of vertical tests.  
 
WEPMS004 Deflecting Cavity for Beam Diagnostics in ERL Injector impedance, diagnostics, gun, emittance 2331
 
  • S. A. Belomestnykh
  • V. D. Shemelin, K. W. Smolenski, V. Veshcherevich
    CLASSE, Ithaca
  Funding: Work is supported by the National Science Foundation grant PHY 0131508.

A 1300 MHz deflecting cavity will be used for beam slice emittance measurements, and to study the temporal response of negative electron affinity photocathodes in the ERL injector currently under construction at Cornell University. A single-cell TM110-mode cavity was designed to deflect the beam vertically. The paper describes the cavity shape optimization procedure, its mechanical design and performance at low RF power.

 
 
WEPMS071 EVIDENCE FOR FOWLER-NORDHEIM BEHAVIOR IN RF BREAKDOWN electron, vacuum, ion, superconductivity 2499
 
  • M. BastaniNejad
  • M. Alsharo'a, P. M. Hanlet, R. P. Johnson, M. Kuchnir, D. J. Newsham
    Muons, Inc, Batavia
  • C. M. Ankenbrandt, A. Moretti, M. Popovic, K. Yonehara
    Fermilab, Batavia, Illinois
  • A. A. Elmustafa
    Old Dominion University, Norfolk, Virginia
  • D. M. Kaplan
    Illinois Institute of Technology, Chicago, Illinois
  Funding: Supported in part by DOE STTR grant DE-FG02-05ER86252

Microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 800 MHz RF cavity experiments are used to investigate the mechanism of RF breakdown. The images show evidence for melting and boiling in small regions of ~10 micron diameter on tungsten, molybdenum, and beryllium electrode surfaces. In these experiments, the dense hydrogen gas in the cavity prevents electrons or ions from being accelerated to high enough energy to participate in the breakdown process so that the only important variables are the fields and the metallic surfaces. The distributions of breakdown remnants on the electrode surfaces are compared to the maximum surface gradient E predicted by an ANSYS model of the cavity. The surface local density of spark remnants, presumably the probability of breakdown, shows a power law dependence on the maximum gradient, with E10 for tungsten and molybdenum and E7 for beryllium. This is reminiscent of Fowler-Nordheim behavior of electron emission from a cold cathode, which is explained by the quantum-mechanical penetration of a barrier that is characterized by the work function of the metal.

 
 
THPMN028 Development of the Strip-line Kicker System for ILC Damping Ring kicker, extraction, power-supply, damping 2772
 
  • T. Naito
  • H. Hayano, K. Kubo, M. Kuriki, N. Terunuma, J. Urakawa
    KEK, Ibaraki
  The performance of the kicker system for the International Linear collider(ILC) is the one of the key component to determine the damping ring(DR) circumference and the train structure. The parameters are discussing at the baseline configuration design for the ILC. The bunch trains in the linac are 2820(5640) bunches with 308(154) ns spacing and the repetition rate is 5Hz. The bunch spacing in the DR is 6(3) ns. The kicker has to have fast rise and fall times of 6(3) ns and the repetition rate of 3.25(6.5) MHz. The development work of the kicker system using multiple strip-lines is carried out at KEK-ATF. The beam test result of the single unit is described. Also Experimental results on new scheme to improve the rise and fall times will be presented.  
 
THPAN021 Analysis of a Particle-In-Cell Code Based on a Time-Adaptive Mesh simulation, cathode, space-charge, laser 3271
 
  • S. Schnepp
  • E. Gjonaj, T. Weiland
    TEMF, Darmstadt
  Funding: This work was partially funded by HGF (VH-FZ-005) and DESY Hamburg.

For the coupled simulation of charged particles and electromagnetic fields several techniques are known. In order to achieve accurate results various parameters have to be taken into account. The number of macro-particles per cell, the resolution of the computational grid, and other parameters strongly affect the accuracy of the results. In the code tamBCI, based on a time-adaptive mesh, additional variables related to the adaptive grid refinement have to be chosen appropriately. An analysis of these values is carried out and the results are applied to the self-consistent simulation of the injector section of FLASH in 3D.

 
 
THPAN045 Explicit Time Domain Boundary Element Scheme for Dispersion-free Wake Field Calculation of Long Accelerator Structures simulation, linac, scattering, electron 3330
 
  • K. Fujita
  • T. Enoto, S. Tomioka
    Hokkaido University, Sapporo
  • R. Hampel, W. F.O. Muller, T. Weiland
    TEMF, Darmstadt
  • H. Kawaguchi
    Muroran Institute of Technology, Department of Electrical and Electronic Engineering, Muroran
  This paper introduces a new explicit scheme with a moving window option for wake field calculation of long accelerator structures. This scheme is based on a time domain boundary element method (TDBEM) which uses a retarded Kirchhoff boundary integral equation on interior region problems. As a corollary of this boundary integral equation, our approach allows a conformal modeling of a structure and time domain wake field simulation without numerical grid dispersion errors in all spatial directions. The implementation of a moving window technique in the framework of TDBEM is presented and it is shown that this moving window technique allows to significantly reduce memory requirement of the TDBEM scheme in the short range wake field calculation. Several numerical examples are demonstrated for the TESLA 9-cell cavity and tapered collimators. The results of the new TDBEM scheme are compared with that of finite difference codes.  
 
THPAN046 Extension of Napoly Integral for Transverse Wake Potentials to General Axisymmetric Structure dipole 3333
 
  • Y. Shobuda
  • Y. H. Chin, K. Takata
    KEK, Ibaraki
  The Napoly integral for wake potential calculations in the axisymmetric structure is a very useful method because the integration of Ez field can be confined in a finite length instead of infinite length by deforming the integration path, which reduces CPU time for accurate calculations. However, his original method cannot be applied to the transverse wake potentials in a structure where the two beam tubes on both sides have unequal radii. In this case, the integration path needs be a straight line and the integration stretches out to an infinite in principle. We generalize the Napoly integrals so that integrals are always confined in a finite length even when the two beam tubes have unequal radii, for both longitudinal and transverse wake potential calculations. The extended method has been successfully implemented to ABCI.  
 
THPAN081 Collimator Wakefields: Formulae and Simulation simulation, damping, collimation 3405
 
  • R. J. Barlow
  • A. Bungau, R. M. Jones
    Cockcroft Institute, Warrington, Cheshire
  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 Wm(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.  
 
THPAN090 Fourier Spectral Simulation for Wake Field in Conducting Cavities simulation, impedance, vacuum, coupling 3432
 
  • M. Min
  • Y.-C. Chae, P. F. Fischer, K.-J. Kim
    ANL, Argonne, Illinois
  • Y. H. Chin
    KEK, Ibaraki
  Recent demand of short-bunch beams poses high-order computational tools for investigating beam dynamics in order to improve the beam quality. We have studied a new computational approach with spectrally accurate high-order approximation for wake field calculations. The technique employs the standard Fourier basis combined with a post-processing procedure for noise reduction by Gegenbauer reconstruction. We integrate this scheme into the existing 2D wake field calculation code ABCI and investigate possible enhancemance of its performance on the same grid base. We will demontrate 2D wake potential simulations for various cylindrically symmetric structures with the quality improvement in comparison to the conventional lower-order method.  
 
THPAN091 Spectral-Element Discontinuous Galerkin Simulations for Wake Potential Calculations: NEKCEM simulation, impedance, coupling, storage-ring 3435
 
  • M. Min
  • Y.-C. Chae, P. F. Fisher
    ANL, Argonne, Illinois
  The demand for short bunches of 1 ps or less poses not only technical challenges in order to deliver the beams for leading-edge research but also poses computational challenges when it comes to investigating bunched multi-particle beam dynamics in order to improve the beam quality. We introduce a powerful high-order numerical tool based on spetral-element discretizations with discontinuous Galerkin approximation approach, which includes spectral element time domain solver for Maxwell's equation and electrostatic Poisson solver. We will demonstrate 3D simulations for wakefield and wake potential calculations in conducting cavity structures, as well as meshing and visualization components. We will discuss the overcome of the computational bottleneck by widely-used low-order finite difference programs for calculating wake field excited by 1-ps bunches, provided with performance and accuracy comparison.  
 
THPAS010 A Multislice Approach for Electromagnetic Green's Function Based Beam Simulations electron, simulation, space-charge, cathode 3531
 
  • M. Hess
  • C. S. Park
    IUCF, Bloomington, Indiana
  Funding: This research is supported in part by the Department of Energy under grant DE-FG0292ER40747 and in part by the National Science Foundation under grant PHY-0552389.

We present a multislice approach for modeling the space-charge fields of bunched electron beams that are emitted from a metallic cathode using electromagnetic Green's function techniques. The multislice approach approximates a local region of the beam density and current with a slice of zero longitudinal thickness. We show examples of how the multislice approach can be used to accurately compute the space-charge fields for electron bunch lengths in the regime of photocathode sources, i.e. (<10 ps).

 
 
THPAS012 Computational Requirements for Green's Function Based Photocathode Source Simulations simulation, space-charge, electron, cathode 3537
 
  • C. S. Park
  • M. Hess
    IUCF, Bloomington, Indiana
  Funding: This work is supported by the National Science foundation under contract PHY-0552389 and by the Department of Energy under contract DE-FG02-92ER40747.

We demonstrate the computational requirements for a Green's function based photocathode simulation code called IRPSS. In particular, we show the necessary conditions, e.g. eigenmode number and integration time-step, for accurately computing the space-charge fields in IRPSS to less than 1 % error. We also illustrate how numerical filtering methods can be applied to IRPSS in conjunction with a multislice approach, for dramatically improving computational efficiency of electromagnetic field calculations.

 
 
THPAS067 Adaptive Impedance Analysis of Grooved Surface Using the Finite Element Method impedance, dipole, controls, linear-collider 3639
 
  • L. Wang
  Funding: Work supported by the U. S. Department of Energy under contract DE-AC02-76SF00515

Grooved surface is proposed to reduce the secondary emission yield in a dipole and wiggler magnet of International Linear Collider. An analysis of the impedance of the grooved surface based on adaptive finite element is presented in this paper. The performance of the adaptive algorithms, based on an element-element h-refinement technique, is assessed. The features of the refinement indictors, adaptation criteria and error estimation parameters are discussed.

 
 
FRPMN051 Design of S-band Cavity BPM for HLS pick-up, monitoring, resonance, gun 4102
 
  • Q. Luo
  • H. He, P. Li, P. Lu, B. Sun, J. H. Wang
    USTC/NSRL, Hefei, Anhui
  Funding: Supported by 985 Project of USTC 173123200402002

For the development of accelerators we require increasingly precise control of beam position. Cavity BPMs promise a much higher position resolution compared to other BPM types and manufacture of cavity BPMs is in general less complicated. The cavity BPM operating at S-band for HLS (Hefei Light Source) was designed. It consists of two cavities: a position cavity tuned to TM110 mode and a reference cavity tuned to TM010 mode. To suppress the monopole modes we use waveguides as pickups. Superheterodyne receivers are used in electronics for many cavity BPMs while we decide to use chip AD8302 produced by Analog Devices to process the signals. To simulate and calculate the electromagnetic field we use MAFIA.

 
 
FRPMS075 Modeling of the Sparks in Q2-bellows of the PEP-II SLAC B-factory simulation, vacuum, radiation, luminosity 4213
 
  • A. Novokhatski
  • J. Seeman, M. K. Sullivan
    SLAC, Menlo Park, California
  Funding: Work supported by USDOE contract DE-AC02-76SF00515

The PEP-II B-factory at SLAC has recently experienced unexpected aborts due to anomalously high radiation levels at the BaBar detector. Before the problem was finally traced we performed the wake field analysis of the Q-2 bellows, which is situated at a distance of 2.2 m from the interaction point. Analysis showed that electric field in a small gap between a ceramic tile and metal flange can be high enough to produce sparks or even breakdowns. Later the traces of sparks were found in this bellows.