A new structure of linear collider

A new scheme is proposed for the muon collider cooling RF, on which the cavity is almost a simple pillbox. The principle is to divide the accelerating cells into three separate channels with a phase difference of 2{pi}/3 between each other. A special structure is designed in which each channel is like a side-coupled cavity structure operating at {pi}/2-mode, but an extra phase shift of {pi} is introduced so that the phase difference between two cells is 2{pi}. Therefore, the beam sees a 2{pi}/3-mode implying a high interaction between cavities and beam, while the RF system sees a {pi}/2-mode implying a high stability. In other words, it combines the advantages of both traveling wave and standing wave. The mechanical structure is also simple and compact because the side-coupled cavity is formed by a uniform rectangular-like waveguide, which is simply an arc section attached on the main cavities. The principle and the preliminary simulation are addressed in detail. This principle is also applicable for a 2{pi}/4 mode and other machine provided the coupling due to aperture is weak enough