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Wuensch, W.

Paper Title Page
TUP055 Optimum Frequency and Gradient for the CLIC Main Linac Accelerating Structure 527
 
  • A. Grudiev, H.-H. Braun, D. Schulte, W. Wuensch
    CERN, Geneva
 
 

Recently the CLIC study has changed the operating frequency and accelerating gradient of the main linac from 30 GHz and 150 MV/m to 12 GHz and 100 MV/m, respectively. This major change of parameters has been driven by the results from a novel main linac optimization procedure. The procedure allows simultaneous optimization of operating frequency, accelerating gradient, and many other parameters of CLIC main linac. It takes into account both beam dynamics (BD) and high power rf constraints. BD constraints are related to emittance growth due to short- and long-range transverse wakefields. Rf constraints are related to rf breakdown and pulsed surface heating of the accelerating structure. The optimization figure of merit includes the power efficiency, measured as a ratio of luminosity to the input power as well as a quantity proportional to investment cost.

 
TUP057 Design and Fabrication of CLIC Test Structures 533
 
  • R. Zennaro, A. Grudiev, G. Riddone, A. Samoshkin, W. Wuensch
    CERN, Geneva
  • T. Higo
    KEK, Ibaraki
  • S.G. Tantawi, J.W. Wang
    SLAC, Menlo Park, California
 
 

Demonstration of a gradient of 100 MV/m at a breakdown rate of 10-7 is one of the key feasibility issues of the CLIC project. A high power rf test program both at X-band (SLAC and KEK) and 30 GHz (CERN) is under way to develop accelerating structures reaching this performance. The test program includes the comparison of structures with different rf parameters, with/without wakefield damping waveguides, and different fabrication technologies namely quadrant bars and stacked disks. The design and objectives of the various X-band and 30 GHz structures are presented and their fabrication methods and status is reviewed.

 
THP062 Design of an X-Band Accelerating Structure for the CLIC Main Linac 933
 
  • A. Grudiev, W. Wuensch
    CERN, Geneva
 
 

The rf design of an accelerating structure for the CLIC main linac is presented. The structure is designed to provide 100 MV/m averaged accelerating gradient at 12 GHz with an rf-to-beam efficiency as high as 27.7%. 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.

 
THP063 A New Local Field Quantity Describing the High Gradient Limit of Accelerating Structures 936
 
  • A. Grudiev, W. Wuensch
    CERN, Geneva
 
 

A new local field quantity which gives the high gradient performance limit of accelerating structures in the presence of vacuum rf breakdown is presented. A model of the breakdown trigger based on the pulsed heating of a potential breakdown site by the field emission currents and driven by a new field quantity, a modified Poynting vector, has been derived. The field quantity Sc takes into account both active and reactive power flow on the surface. This new quantity has been evaluated for many X-band and 30 GHz rf tests, both travelling wave and standing wave, and the value of Sc achieved in the experiments agrees well with analytical estimates.

 

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Slides

 
THP061 High Power Test of a Low Group Velocity X-Band Accelerator Structure for CLIC 930
 
  • S. Döbert, A. Grudiev, G. Riddone, M. Taborelli, W. Wuensch, R. Zennaro
    CERN, Geneva
  • C. Adolphsen, V.A. Dolgashev, L. Laurent, J.R. Lewandowski, S.G. Tantawi, F. Wang, J.W. Wang
    SLAC, Menlo Park, California
  • S. Fukuda, Y. Higashi, T. Higo, S. Matsumoto, K. Ueno, K. Yokoyama
    KEK, Ibaraki
 
 

In recent years evidence has been found that the maximum sustainable gradient in an accelerating structure depends on the rf power flow through the structure. The CLIC study group consequently designed a new prototype structure for CLIC with a very low group velocity, input power and average aperture (a/λ = 0.12). The 18 cell structure has a group velocity of 2.4% at the entrance and 1% at the last cell. Several of these structures have been made in collaboration between KEK, SLAC and CERN. A total of five brazed-disk structures and two quadrant structures have been made. The high power results of some of these structures are presented. The first KEK/SLAC built structure reached an unloaded gradient in excess of 100 MV/m at a pulse length of 230 ns with a breakdown rate below 10-6. The high-power testing was done using the NLCTA facility at SLAC.