Beam dynamics studies on a specific radio-frequency quadrupole injector for superconducting linacs

Abstract Radio-frequency quadrupole (RFQ) linear accelerators are widely used at the front end of large-scale hadron accelerator facilities owing to their extraordinary performance of progressive bunching, high-efficiency acceleration and low emittance growth. Meanwhile, it is worth noting that RFQ linacs gradually become the only normal conducting accelerators in modern continuous-wave high-power superconducting hadron linacs. As a result, high-quality beams at the exit of RFQ linacs with respect to more strict beam dynamics requirements are demanded, where minimizing the emittance growth is one of the most critical design targets. Not only a small rms emittance is required for an easy rms match to the following superconducting cavities but also a small total emittance is needed to reduce the beam loss in the superconducting cavities. In this paper, the design parameters of some typical RFQ injectors for superconducting linacs worldwide were compared, and the beam dynamics design of a 162.5 MHz, 2.1 MeV, continuous-wave RFQ linac was performed. Guided by the design approach called MEGLET (Minimizing Emittance Growth via Low Emittance Transfer), the beam dynamics design of the example RFQ injector was completed with high transmission efficiency, low emittance growth, and large error tolerance. The design result could be a reference for similar RFQ linacs, and the beam dynamics design approach is useful and applicable for other linacs intended to improve the figures of merit.