• A. Samoshkin, D. Gudkov, G. Riddone
  CERN, Geneva

The CLIC (Compact LInear Collider) design is based on two-beam acceleration concept developed at CERN, where the RF power is generated by a high current electron-beam (Drive Beam) running parallel to the Main Beam. The Drive Beam is decelerated in special power extraction structures (PETS) and the generated RF power is transferred via waveguides to the accelerating structures (AS). The accelerating gradient must be very high (100 MV/m) to reach the high energy for the electron-positron collisions. To facilitate the matching of the beams, components are assembled in 2-m long modules, of few different types. In some of them the AS are replaced by quadrupoles used for the beam focusing. Their alignment and positioning is made by using the signals from the beam-position monitors (BPM). Special modules are needed in damping region or to carry out dedicated instrumentation and vacuum equipment. The module design and integration has to cope with challenging requirements from the different technical systems. This paper reports the status of the engineering design and reports on the main technical issues.

• S. Döbert, A. Grudiev, G. Riddone, W. Wuensch, R. Zennaro
  CERN, Geneva
• C. Adolphsen, F. Wang, J.W. Wang
  SLAC, Menlo Park, California
• T. Higo, S. Matsumoto, K. Yokoyama
  KEK, Ibaraki

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.

• S. Matsumoto, T. Higo
  KEK, Ibaraki
• G. Riddone, I. Syratchev, W. Wuensch
  CERN, Geneva

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.

• J. Huopana
  HIP, University of Helsinki
• S. Atieh, G. Riddone
  CERN, Geneva
• K. Österberg
  Helsinki University, Department of Physics, University of Helsinki

The Compact Linear Collider (CLIC) is currently under development at CERN as a potential multi-TeV e+e' collider. The manufacturing and assembly tolerances for the required RF components are essential for the final efficiency and for the operation of CLIC. The proper function of an accelerating structure is sensitive to mechanical errors in the shape and the alignment of the accelerating cavity. The current tolerances are in the micron range. This raises challenges in the field of mechanical design and demands special manufacturing technologies and processes. Currently the mechanical design of the accelerating structures is based on a disk design. Alternatively, it is possible to create the accelerating assembly from quadrants, which has the potential to be favoured for the mass production due to simplicity and cost. In this case, the functional shape inside of the accelerating structure remains the same and a single assembly uses less parts. This paper focuses on the development work done in design and simulation for prototype accelerating structures and describes its application to series production.

• R.J. Nousiainen, K. Osterberg
  HIP, University of Helsinki
• G. Riddone
  CERN, Geneva

To fulfill the mechanical requirements set by the luminosity goals of the CLIC collider, currently under study, the 2-m two-beam modules, the shortest repetitive elements in the main linac, have to be controlled at micrometer level. At the same time these modules are exposed to variable high power dissipation while the accelerator is ramped up to nominal power as well as when the mode of CLIC operation is varied. This will result into inevitable temperature excursions driving mechanical distortions in and between different module components. A FEM model is essential to estimate and simulate the fundamental thermo-mechanical behavior of the CLIC two-beam module to facilitate its design and development. Firstly, the fundamental thermal environment is created for different RF components of the module. Secondly, the first thermal and structural contacts for adjacent components as well as idealized kinematic coupling for the main module components are introduced. Finally, the thermal and structural results for the studied module configuration are presented showing the fundamental thermo-mechanical effects of primary CLIC collider operation modes.

• F. Peauger, W. Farabolini, P. Girardot
  CEA, Gif-sur-Yvette
• A. Andersson, G. Riddone, A. Samoshkin, A. Solodko
  CERN, Geneva
• R.J.M.Y. Ruber
  Uppsala University, Uppsala
• R. Zennaro
  PSI, Villigen

To achieve high luminosity in CLIC, the accelerating structures must be aligned to an RMS accuracy of 5 μm with respect to the beam trajectory. Position detectors called Wakefield Monitors (WFM) are integrated to the structure for a beam based alignment. This paper describes the requirements of such monitors. The development plan and basic feature of the WFM as well as the accelerating structure working at 12 GHz and 100 MV/m are shortly described. Then we focus on detailed electromagnetic simulations and design of the WFM itself. In particular, time domain computations are performed and an evaluation of the intrinsic resolution is done for two higher order modes at 17 and 24 GHz. The mechanical design of the accelerating structure with WFM is also presented. Precise machining with a tolerance of 2.5 μm and a surface roughness of 0.025 μm is demonstrated. The fabrication status of three complete accelerating structures with WFM is finally presented for a feasibility demonstration with beam in CTF3 at CERN.