A new multi-harmonic buncher for the LEAF project

A new multi-harmonic buncher (MHB) was designed to improve the acceleration efficiency by producing a saw-tooth signal containing three-harmonic signal with 40.625 MHz fundamental frequency in front of a heavy ion Radio Frequency Quadrupole accelerator (RFQ) for improving longitudinal beam matching and acceleration efficiency in the Low Energy Accelerator Facility (LEAF) in the Institute of Modern Physics (IMP), Chinese Academy of Sciences. In order to achieve a higher bunching efficiency for MHB, we use a three-harmonic scheme with the bunching efficiency of 70%. Based on the requirement of high quality factor (Q) and multiple harmonics, we developed a special double quarter wave resonator (QWR) structure. The beam commissioning results showed the acceleration efficiency of N+2+ beam was around 86% by measurement. In this paper, the electromagnetic of MHB was introduced in detail, and the effect of MHB on acceleration efficiency was evaluated by beam testing.