90 degrees-Apart-stem RFQ structure for wide range of frequencies

At present, many different resonant RFQ structures for accelerating both light and heavy ions are successfully used. Usually they are divided into two well known groups: 4-vane and 4-rod structures, each of them having its merits and drawbacks. In this paper a new resonant structure is considered, which combines the advantages of both. It may be seen as a 4-vane structure with holes (open-quotes windowsclose quotes) in the vanes, or as a 4-rod one having stems located 90 degrees apart from each other and from the beam direction. Thus, changing the window size, such a structure can be modified from a typical 4-rod resonator, working at 50 MHz or less, to a typical 4-vane one, working at higher frequencies (up to 500 MHz) and having a better frequency distinction between operating and unwanted dipole modes, due to the magnetic coupling between neighboring quadrants through the holes. It also should be noted that no voltage arises on the beam axis in the gap between end plate and electrodes, provided that horizontal and vertical windows have the same longitudinal position. Computer simulations with MAFIA codes are presented and compared with cold model measurements