The actual cell shapes of the TESLA cavities differ from the ideal ones due to fabrication errors, the addition of stiffening rings and the frequency tuning process. Cavity imperfections shift the dipole mode frequencies and alter the Qext's from those of the ideal cavity. The 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, cavity imperfection models will be generated for the study of wakefield impact on beam transport.
The linacs proposed for the Next Linear Collider (NLC) and Japanese Linear Collider (JLC) would contain several thousand X-Band accelerator structures that would operate at a loaded gradient of 50 MV/m. An extensive experimental and theoretical program is underway at SLAC, FNAL and KEK to develop structures that reliably operate at this gradient. The development of standing wave structures is a part of this program. The properties of standing wave structures allow them to operate at the loaded gradient in contrast to traveling wave structures that need conditioning to the unloaded gradient (65 MV/m for NLC/JLC). The gradients in the standing structures tested thus far have been limited by input coupler breakdowns. The behavior of these breakdowns is consistent with a model of pulsed heating due to high magnetic fields. New input couplers have been designed to reduce maximum magnetic fields. This paper discusses design considerations related to high power performance, wakefield suppression and results of high power tests of prototype standing wave structures.
High performance linear accelerators are the central components of the proposed next generation of linear colliders. They must provide acceleration of up to 750 GeV per beam while maintaining small normalized emittances. Standard simulation programs: mainly developed for storage rings, do not meet the specific requirements for high performance linacs with high bunch charges and strong wakefields. We present the program LIAR (" LInear Accelerator Research code") that includes single and multi-bunch wakefield effects, a 6D coupled beam description, specific optimization algorithms and other advanced features. LIAR has been applied to and checked against the existing Stanford Linear Collider (SLC), the linacs of the proposed Next Linear Collider (NLC) and the proposed Linac Coherent Light Source (LCLS) at SLAC. Its modular structure allows easy extension for different purposes. The program is available for UNIX workstations and Windows PC's. They must provide acceleration of up to 750 GeV per beam while maintaining small normalized emittances. Standard simulation programs, mainly developed for storage rings, do not meet the specific requirements for high performance linacs with high bunch charges and strong wakefields. We present the program LIAR ("LInear Accelerator Research code") that includes single and multi-bunch wakefield effects, a 6D coupled beam description, specific optimization algorithms and other advanced features. LIAR has been applied to and checked against the existing Stanford Linear Collider (SLC), the linacs of the proposed Next Linear Collider (NLC) and the proposed Linac Coherent Light Source (LCLS) at SLAC. Its modular structure allows easy extension for different purposes. The program is available for UNIX workstations and Windows PC's.A major objective of the LIAR project is to provide an open programming platform for the accelerator physics community. We invite interested scientists to join this project. The LIAR home page and the ONLINE version of the user's manual can be accessed under:
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