Study on high-precision diffusion bonding for X-band accelerator structure

In order to realize X-band accelerator structures for linear colliders, the fabrication process of a high-precision machining of disks followed by a reliable bonding with least deformation is one of the key issues to realize their tight tolerances. Through studies of various bonding technologies, we reached a copper to copper diffusion bonding technique as a suitable solution based on the present-day technologies. Based on the technique, a few structures, such as M2, with 1.3m in length and 80mm in diameter were fabricated successfully. Then aiming at a longer and thinner structure (1.8m long and 61mm in diameter), a new technique called 'pre-bonding' was invented to make the stacking/bonding technology more reliable. Main features obtained from 'pre-bonding' are a better straightness and a small disk to disk slippage by applying a large axial pressure while heating at much lower temperature than that of annealing for copper material. Key parameters, such as pressure, temperature and period were carefully studied and optimized. Based on the technology, two structures, DDS3 and RDDS1, were successfully fabricated. (author)