SLAC, Menlo Park, California
Under the support of the U. S. DOE SciDAC program, SLAC has been developing a suite of 3D parallel finite-element codes aimed at high-accuracy, high-fidelity electromagnetic and beam physics simulations for the design and optimization of next-generation 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, self-consistent Particle-In-Cell (PIC) particle dynamics as well as thermal, mechanical, and multi-physics 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.
LLNL, Livermore, California
SLAC, Menlo Park, California
Stanford University, Stanford, Califormia
Fundamental power couplers for superconducting accelerator applications like the ILC are complicated RF transmission line assemblies due to their having to simultaneously accommodate demanding RF power, cryogenic, and cleanliness constraints. When these couplers are RF conditioned, the observed response is an aggregate of all the parts of the coupler and the specific features that dominate the conditioning response are unknown. To better understand and characterize RF conditioning phenomena toward improving performance and reducing conditioning time, a high-power coupler component test stand has been built at SLAC. Operating at 1.3 GHz, this test stand was designed to measure the conditioning behavior of select components of the TTFIII coupler independently, including outer-conductor bellows, diameter changes, copper plating and surface preparations, and cold window geometries and coatings. A description of the test stand, the measurement approach, and a summary of the results obtained are presented.
SLAC, Menlo Park, California
LLNL, Livermore, California
The TTF-III 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 high-power 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.
SLAC, Menlo Park, California
KEK, Ibaraki
Jefferson Lab, Newport News, Virginia
DESY, Hamburg
The Low-Loss 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 higher-order 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 9-cell 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 end-groups of the cavity. In this paper, we will present the optimization results of the end-groups for the Low-Loss shape for effective HOM damping and alleviation of multipacting. Comparisons of simulation results with measurements will also be presented.