Challenge to a straight structure for X-band linear collider

The structure of the X-band main linac for the linear collider requires a stringent straightness of the order of several microns. Especially the misalignment from cell-to-cell to over twenty cells should be minimized. An one-shot diffusion bonding technology has been developed at KEK aiming at this requirement. Two 1.3 m-long detuned structures have been made with a gentle bow of 20 microns. Recently the technology was applied to the main body bonding of an 1.8 m-long damped-detuned structure, DDS3. It resulted in a much larger bow but the cell misalignment showed very smooth behavior and can later be corrected mechanically. The technique is being refined to obtain a better performance of the main body of the round DDS structure, RDDS1. In the present paper are described the studies on the basic techniques applied for DDS3