| 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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| 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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| 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. |
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| MOP070 | Breakdown Studies for the CLIC Accelerating Structures | 217 |
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Optimizing the design and the manufacturing of the CLIC RF accelerating structures for achieving the target value of breakdown rate at the nominal accelerating gradient of 100 MV/m requires a detailed understanding of all the steps involved in the mechanism of breakdown. These include surface modification under RF fields, electron emission and neutral evaporation in the vacuum, arc ignition and consequent surface modification due to plasma bombardment. Together with RF tests, experiments are conducted in a simple DC test set-up instrumented with electrical diagnostics and optical spectroscopy. The results are also used for validating simulations which are performed using a wide range of numerical tools (MD coupled to electrostatic codes, PIC plasma simulations) able to include all the above phenomena. Some recent results are presented in this paper. |
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| MOP074 | High Power Evaluation of X-band High Power Loads | 226 |
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Several types of X-band high power loads developed for several tens of MW range were designed, fabricated and used for high power tests at X-band facility of KEK. Some of them have been used for many years and some show possible deterioration of RF performance. Recently revised-design loads were made by CERN and the high power evaluation was performed at KEK. In this paper, the main requirements are recalled, together with the design features. The high power test results are analysed and presented. |
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| MOP075 | Breakdown Characteristics in DC Spark Experiments of Copper Focusing on Purity and Hardness | 229 |
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To investigate the breakdown characteristic related to the differences in purity and hardness, four types of oxygen-free copper (OFC) materials, usual class 1 OFC with/without diamond finish, 7-nine large-grain copper and 6-nine hot-isotropic-pressed copper, were tested with the DC spark test system at CERN. Measurements of beta, breakdown fields and breakdown probability are discussed followed by the surface inspection mostly with SEM on the tested materials. |
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| MOP076 | An Experimental Investigation on Cavity Pulsed Heating | 232 |
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Cavity pulsed heating experiments have been conducted at SLAC National Accelerator Laboratory in collaboration with CERN and KEK. These experiments were designed to gain a better understanding on the impact of high power pulsed magnetic fields on copper and copper alloys. The cavity is a one port hemispherical cavity that operates in the TE013-like mode at 11.424 GHz. The test samples are mounted onto the endcap of the cavity. By using the TE013 mode, pulsed heating information can be analyzed that is based only on the impact of the peak magnetic field which is much bigger in value on the test sample than on any other place in the cavity. This work has shown that pulsed heating surface damage on copper and copper alloys is dependent on processing time, pulsed heating temperature, material hardness, and crystallographic orientation and that initial stresses occur along grain boundaries which can be followed by pitting or by transgranular microfractures that propagate and terminate on grain boundaries. The level of pulsed heating surface damage was found to be less on the smaller grain samples. This is likely due to grain boundaries limiting the propagation of fatigue cracks. |