Fabrication of improved quadrant-type X-band high-gradient accelerating structures

A common normal-conducting high-gradient accelerating structure of particle accelerators is the 'disk type', which has dozens of machined, stacked, and bonded disks. In the disk type, surface currents associated with a magnetic field of an accelerating mode flow across disk-to-disk junctions. Another structure is the 'quadrant type', which is orthogonal to the above type. In the quadrant type, bonding planes are parallel to a beam axis, and therefore, this type has the remarkable feature that no such surface current flows across any junction. We proposed, designed, fabricated, and tested an improved quadrant-type X-band (11.4 GHz) single-cell standing-wave structure, and then demonstrated its efficacy and the potential for this structure to be successful for accelerating gradients of 100 MV/m or higher at sufficiently low breakdown rates. For a complete demonstration, we have fabricated a 24-cell traveling-wave structure based on the improved-quadrant-type fabrication method. (author)