| Paper | Title | Page |
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| MOP002 | A High Phase Advance Damped and Detuned Structure for the Main Linacs of CLIC | 49 |
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We report on the suppression of long-range wakefields in the main linacs of the CLIC collider. The wakefield is damped using a combination of detuning the frequencies of beam-excited higher order modes and by light damping, through slot-coupled manifolds. This unique accelerator, in the process of being fabricated, will be the first structure to demonstrate wakefield damping and the ability to sustain high accelerating gradients for CLIC. This serves as an alternative to the baseline CLIC design, which at present relies entirely on heavy damping. Detailed simulations are presented, on both the optimised surface fields resulting from the monopole mode, and from wakefield damping of the dipole modes. Preparations for the fabrication of a structure, suitable for high power testing, are also discussed. This design takes into account practical mechanical engineering issues and is the result of several optimisations since the original CLICDDS proposal[*]. *V.F. Khan and R.M. Jones, Presented at Particle Accelerator Conference (PAC 09), Vancouver, BC, Canada, 4-8 May 2009. |
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| MOP021 | Compensation of Transient Beam-Loading in the CLIC Main Linac | 94 |
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Compensating transient beam loading to maintain a 0.01% relative beam energy spread is a key issue for the CLIC two-beam acceleration technique. The combination of short pulses, narrow bandwidth rf components and the limited number of rf pulse shaping 'knobs' given by the drive beam generation scheme makes meeting this specification challenging. A dedicated model, which takes into account all stages of drive beam generation, including the delay loop and combiner rings, the single-bunch response of the power generation structure (PETS), the RF waveguide network transfer function and dispersive properties of the accelerating structure has been developed. The drive beam phase switching delays, resulting rf pulse shape, loaded and unloaded voltages and finally the energy spread are presented. |
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| MOP022 | Tuning of CLIC Accelerating Structure Prototypes at CERN | 97 |
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An RF measurement system has been set up at CERN for use in the X-band accelerating structure development program of the CLIC study. Using the system, S-parameters are measured and the field distribution is obtained automatically by using a bead-pull technique. The corrections for tuning the structure are calculated from the result. Integrated software guides cell-by-cell tuning to obtain the correct phase advance and minimum reflection at the operation frequency. The detailed configuration of the system, as well as the semi-automatic tuning procedure, is presented along with a few examples of measurement and tuning of CLIC accelerating structure prototypes. |
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| MOP023 | The Accelerating Structure for a 500 GeV CLIC | 100 |
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The rf design of an accelerating structure for the 500 GeV CLIC main linac is presented. The design takes into account both aperture and HOM damping requirements coming from beam dynamics as well as the limitations related to rf breakdown and pulsed surface heating. In addition, the constraints related to the compatibility with 3 TeV CLIC have been taken into account. The structure is designed to provide 80 MV/m averaged accelerating gradient at 12 GHz with an rf-to-beam efficiency as high as 39.8 %. |
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| MOP025 | ACE3P Computations of Wakefield Coupling in the CLIC Two-beam Accelerator | 106 |
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The Compact Linear Collider (CLIC) provides a path to a multi-TeV accelerator to explore the energy frontier of High Energy Physics. Its novel two-beam accelerator concept envisions rf power transfer to the accelerating structures from a separate high-current decelerator beam line consisting of power extraction and transfer structures (PETS). It is critical to numerically verify the fundamental and higher-order mode properties in and between the two beam lines with high accuracy and confidence. To solve these large-scale problems, SLAC's parallel finite element electromagnetic code suite ACE3P is employed. Using curvilinear conformal meshes and higher-order finite element vector basis functions, unprecedented accuracy and computational efficiency are achieved, enabling high-fidelity modeling of complex detuned structures such as the CLIC TD24 accelerating structure. In this paper, time-domain simulations of wakefield coupling effects in the combined system of PETS and the TD24 structures are presented. The results will help to identify potential issues and provide new insights on the design, leading to further improvements on the novel CLIC two-beam accelerator scheme. |
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| MOP067 | First High Power Tests of CLIC Prototype Accelerating Structures with HOM Waveguide Damping | 208 |
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Prototype accelerating structures for the Compact Linear Collider (CLIC) are being developed and high-power tested in a collaboration between SLAC, KEK and CERN. Several undamped, low group-velocity and strongly tapered prototypes (of the so-called T18 design) have been operated above 100 MV/m average gradient at a very low breakdown rates. Recently two new structures with the same iris apertures but now including higher order mode damping waveguides in each cell (TD18 design) have been tested at SLAC and KEK. The damped versions could be processed to similar gradients but an increased breakdown rate was observed. The damping waveguides lead to a magnetic field enhancement in the outer diameter of the cells which results in increased pulsed surface heating. The maximum pulsed temperature rise is 80 deg at the design gradient of 100 MV/m compared to only 20 deg for the undamped version. The high-power tests of the two TD18 structures are analyzed with special emphasis on the influence on breakdown rate of the enhanced magnetic field and consequent increased pulsed surface temperature rise. |
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| MOP068 | Design of the CLIC Main Linac Accelerating Structure for CLIC Conceptual Design Report | 211 |
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The design of the CLIC main linac accelerating structure has been refined based on an improved understanding of the high-gradient limits given by rf breakdown and pulsed surface heating. In addition, compact couplers have been developed and HOM damping loads have been designed. The rf design has also been made consistent with details of the present manufacturing procedure, based on bonded asymmetrical disks, and with requirements coming from integration of the accelerating structure in the two-beam module which includes all subsystems. This completion and refinement of the structure design has been made to produce the self-consistent parameter set required for preparation of the CLIC conceptual design report. |