• 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.

• 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.