Preliminary design of a dedicated proton therapy linac (S-band) is describe
d. The short beam pulse width and high repetition rate make the linac simil
ar to the electron linacs now used for cancer therapy. This linac consists
of ion source, RFQ, DTL, SCDTL, and SCL. Its tatol length is 26m. The final
energy of the output proton beam is 70-200 MeV, with average beam cut-rent
of 10-40nA.