High Power test of a low group velocity X-band Accelerator Structure for CLIC

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 has consequently designed a new prototype structure for CLIC with a very low group velocity, input power and average aperture (<a/λ> = 0.13). The 18 cell structure has a group velocity of 2.6 % at the entrance and 1 % at the last cell. Several of these structures have been made in a 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 the first KEK/SLAC built structure is presented which reached an unloaded gradient in excess of 100 MV/m at a pulse length of 230 ns with a breakdown rate below 10-6 per meter active length. The high-power testing was done using the NLCTA facility at SLAC.