Proposal and design of an 81.25 MHz interdigital H-mode dual-beam drift tube linac

A novel type dual-beam drift tube linac (DB-DTL) was proposed at the Institute of Modern Physics for ultra-high intensity heavy-ion acceleration. With two identical beam apertures located in the vertical direction with the same off-set from the cavity axis, two beams could be accelerated simultaneously by the DB-DTL and then be merged to one, thus double the current beam intensity limit, which is of great significance for ultra-high intensity heavy-ion acceleration. An 81.25 MHz proof-of-principle cavity was developed to demonstrate this new concept. Designed and optimized with the alternative phase focusing (APF) scheme, this prototype cavity was supposed to accelerate 10 mA protons beam from 0.56 MeV to 2.5 MeV in one meter with transmission efficiency more than 90%. Inter-digital H-mode (IH) structure was adopted by this DB-DTL, thus high shunt impedance could be achieved which significantly reduce the power loss. With efficient cooling, this cavity was capable to work at the pulsed mode with a maximum duty cycle of 10%. Beam dynamics simulations, electromagnetic design and optimization of the prototype cavity, and multi-physics analyses of this DB-DTL will be presented in this paper.