Feasibility of using rf quadrupole focusing in proton linacs at energies above 100 MeV

Qualitative arguments and quantitative estimates are given concerning the use of rf quadrupole focusing in proton linacs at energies above 100 MeV. Radio-frequency quadrupole focusing is widely used in ion foreinjectors in linear accelerators to form and preaccelerate ion bunches to velocities of 0.06 to 0.08. Some success has been reported in the use of rf quadrupole focusing to accelerate protons to 30 MeV