Evanescent-wave proton postaccelerator driven by intense THz pulse

Hadron therapy motivates research dealing with the production of particle beams with $\ensuremath{\sim}100\text{ }\text{ }\mathrm{MeV}/\text{nucleon}$ energy and relative energy fluctuation on the order of 1%. Laser-driven accelerators produce ion beams with only tens of $\mathrm{MeV}/\text{nucleon}$ energy and an extremely broad spectra. Here, a novel method is proposed for postacceleration and monochromatization of particles, leaving the laser-driven accelerator, by using intense THz pulses. It is based on further developing the idea of using the evanescent field of electromagnetic waves between a pair of dielectric crystals. Simple model calculations show that the energy of a proton bunch can be increased from 40 to 56 MeV in five stages and its initially broad energy distribution can be significantly narrowed down.