Design of a 600 MeV Superconducting Microtron

The design of a 600 MeV racetrack microtron proposed for the University of Illinois consists of a 30 MeV superconducting linac operating at 1.3 GHz between two uniform field bending magnets about 6.4 meters apart. There will be 19 parallel return paths separated by 14.7 cm. Vertical focusing is provided on each return orbit by a quadrupole pair close to each magnet. For quadrupoles 20 cm long and separated by 10 cm, the gradients required to advance the vertical oscillation phase by 90° per revolution increase monotonically from 150 to 350 gauss per centimeter. Only very weak horizontal focusing powers are needed to keep the return beams within 2 mm of linac axis. The linac itself provides some focusing but two weak quadrupole singlets on the linac axis, one near each magnet, provide additional focusing. Electron trajectories for all traversals through the linac and the magnets have been calculated in detail, by a step by step procedure where required, and are presented here. These results confirm earlier, less complete, calculations indicating that the microtron design parameters are not critical and that an output energy resolution of one part in 104 is easily obtainable.