Paper  Title  Page 

TUZBC01  Towards Simulation of Electromagnetics and Beam Physics at the Petascale  889 


Funding: Work supported by DOE contract DEAC0276SF00515. Under the support of the U. S. DOE SciDAC program, SLAC has been developing a suite of 3D parallel finiteelement codes aimed at highaccuracy, highfidelity electromagnetic and beam physics simulations for the design and optimization of nextgeneration particle accelerators. Running on the latest supercomputers, these codes have made great strides in advancing the state of the art in applied math and computer science at the petascale that enable the integrated modeling of electromagnetics, selfconsistent ParticleInCell (PIC) particle dynamics as well as thermal, mechanical, and multiphysics effects. This paper will present 3D results of trapped mode calculations in an ILC cryomodule and the modeling of the ILC Sheet Beam klystron, shape determination of superconducting RF (SCRF) cavities and multipacting studies of SCRF HOM couplers, as well as 2D and preliminary 3D PIC simulation results of the LCLS RF gun. 

Slides  
TUODC03  Parallel Finite Element ParticleInCell Code for Simulations of Spacecharge Dominated BeamCavity Interactions  908 


Funding: U. S. DOE contract DEAC00276SF00515 Over the past years, SLAC's Advanced Computations Department (ACD) has developed the parallel finite element particleincell code Pic3P (Pic2P) for simulations of beamcavity interactions dominated by spacecharge effects. As opposed to standard spacecharge dominated beam transport codes, which are based on the electrostatic approximation, Pic3P (Pic2P) includes spacecharge, retardation and boundary effects as it selfconsistently solves the complete set of MaxwellLorentz equations using higherorder finite element methods on conformal meshes. Use of efficient, largescale parallel processing allows for the modeling of photoinjectors with unprecedented accuracy, aiding the design and operation of the nextgeneration of accelerator facilities. Applications to the Linac Coherent Light Source (LCLS) RF gun are presented. 

Slides  
WEPMS041  Multipacting Simulations of TTFIII Coupler Components  2436 


Funding: This work was supported by US DOE contract No. DEAC0276SF00515. This work was performed under the auspices of the US DOE by the University of California, LLNL under Contract No. W7405Eng48. The TTFIII coupler adopted for the ILC baseline cavity design has shown a tendency to have long initial high power processing times. A possible cause for the long processing times is believed to be multipacting in various regions of the coupler. To understand performance limitations during high power processing, SLAC has built a flexible highpower coupler test stand. The plan is to test individual sections of the coupler, which includes the cold and warm coaxes, the cold and warm bellows, and the cold window, using the test stand to identify problematic regions. To provide insights for the high power test, detailed numerical simulations of multipacting for these sections will be performed using the 3D multipacting code Track3P. The simulation results will be compared with measurement data. 

WEPMS042  Optimization of the LowLoss SRF Cavity for the ILC  2439 


Funding: Work supported by DOE contract DEAC0276SF00515. The LowLoss shape cavity design has been proposed as a possible alternative to the baseline TESLA cavity design for the ILC. The advantages of this design over the TESLA cavity are its lower cryogenic loss, and higher achievable gradient due to lower surface fields. High gradient prototypes for such designs have been tested at KEK (ICHIRO) and JLab (LL). However, issues related to HOM damping and multipacting (MP) still need to be addressed. Preliminary numerical studies of the prototype cavities have shown unacceptable damping for some higherorder dipole modes if the typical TESLA HOM couplers are directly adapted to the design. The resulting wakefield will dilute the beam emittance thus reduces the machine luminosity. Furthermore, high gradient tests on a 9cell prototype at KEK have experienced MP barriers although a single LL cell had achieved a high gradient. From simulations, MP activities are found to occur in the endgroups of the cavity. In this paper, we will present the optimization results of the endgroups for the LowLoss shape for effective HOM damping and alleviation of multipacting. Comparisons of simulation results with measurements will also be presented. 

WEPMS048  Modelling Imperfection Effects on Dipole Modes in TESLA Cavity  2454 


Funding: Work supported by DOE contract DEAC0276SF00515 The actual cell shape of the TESLA cavities differ from the ideal due to fabrication errors, the addition of stiffening rings and the frequency tuning process. Cavity imperfection shift the dipole mode frequencies and alter the Qext's from those computed for the idea cavity. A Qext increase could be problematic if its value exceeds the limit required for ILC beam stability. To study these effects, a cavity imperfection model was established using a mesh distortion method. The eigensolver Omega3P was then used to find the critical dimensions that contribute to the Qext spread and frequency shift by comparing predictions to TESLA cavity measurement data. Using the imperfection parameters obtained from these studies, artificial imperfection models were generated and the resulting wakefields were used as input to the beam tracking code Lucretia to study the effect on beam emittance. In this paper, we present the results of these studies and suggest tolerances for the cavity dimensions. 