The focusing properties of both normal and superconducting low energy CW proton Linacs

The continue wave (CW) high current proton linac has wide applications as the front end of the high power proton machines. The low energy part is the most difficult one and there is no widely accepted solution yet. Both normal conducting and superconducting acceleration structures are thought to be the possible solutions. Although the characteristics of normal conducting structures and superconducting ones are quite different, such as acceleration voltage, maximum electric field and so on, we found the focusing properties of the lattice composed by these two acceleration structures are quite similar for different reasons. The advantages and disadvantages of lattices composed of both the normal conducting and superconducting structures are analysed from the beam dynamics point of view, and their constraints on beam main parameters are discussed.