| Paper | Title | Page |
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| MOP64 | Wire Measurement of Impedance of an X-Band Accelerating Structure | 165 |
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Several tens of thousands of accelerator structures will be needed for the next generation of linear collders known as the GLC/NLC (Global Linear Collider/Next Linear Collider). To prevent the beam being driven into a disruptive BBU (Beam Break Up) mode or at the very least, the emittance being signifcantly diluted, it is important to damp down the wakefield left by driving bunches to a manageable level. Manufacturing errors and errors in design need to be measurable and compared with predictions. We develop a circuit model of wire-loaded X-band accelerator structures. This enables the wakefield (the inverse transform of the beam impedance) to be readily computed and compared with the wire measurement. We apply this circuit model to the latest series of accelerating for the GLC/NLC. This circuit model is based upon the single-cell model developed in [1] extended here to complete, multi-cell structures.
[1] R.M. Jones et al, 2003, Proc. PAC2003 (also SLAC-PUB 9871) |
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| MOP40 | A Study Of Coupler-Trapped Modes In X-Band Linacs for the GLC/NLC | 129 |
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| Each of the X-band accelerating structures for the GLC/NLC consist of 55 cells which accelerate a train of charged particles. The cells are carefully designed to ensure that the transverse wakefield left behind each bunch does not disrupt the trailing bunches. However, unless attention is paid to the design of the fundamental mode coupler, then a dipole mode is trapped in the region of the coupler and cells. This mode can give rise to severe emittance dilution if care is not taken to avoid a region of resonant growth in the emittance. Here, we present results on HFSS simulations, cold test experimental measurements and beam dynamics simulations arising as a consequence of the mode trapped in the coupler. The region in which the trapped mode has little influence on the beam is delineated. | ||
| THP33 | Progress toward NLC/GLC Prototype Accelerator Structures | 675 |
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| The accelerator structure groups for NLC (Next Linear Collider) and GLC (Global Linear Colliders) have successfully collaborated on the research and development of a major series of advanced accelerator structures based on room-temperature technology at X-band frequency. The progress in design, simulation, microwave measurement and high gradient tests are summarized in this paper. The recent effort in design and fabrication of the accelerator structure prototype for the main linac is presented in detail including HOM (High Order Mode) suppression and couplers, fundamental mode couplers, optimized accelerator cavities as well as plans for future structures. We emphasize techniques to reduce the field on the surface of the copper structures (in order to achieve high accelerating gradients), limit the dipole wakefields (to relax alignment tolerance and prevent a beam break up instability) and improve shunt impedance (to reduce the RF power required). | ||
| THP87 | Accelerator Structure Bead Pull Measurement at SLAC | 803 |
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| Microwave measurement and tuning of accelerator structures are important issues for the current and next generation of high energy physics machines. Application of these measurements both before and after high power processing can reveal information about the structure but may be misinterpreted if measurement conditions are not carefully controlled. For this reason extensive studies to characterize the microwave measurements at have been made at SLAC. For the beadpull a reproducible measurement of less than 1 degree of phase accuracy in total phase drift is needed in order to resolve issues such as phase changes due to structure damage during high power testing. Factors contributing to measurement errors include temperature drift, mechanical vibration, and limitations of measurement equipment such as the network analyzer. Results of this continuing effort will be presented. |