摘要：Beam dynamics and rf design have been performed of a new type trapezoidal IH-rfQ operating at 104 MHz for acceleration of 14C+ in the framework of rfQ based 14C AMS facility at Peking University. Low energy spread rfQ beam dynamics design was approached by the method of internal discrete bunching. 14C+ will be accelerated from 40 keV to 500 keV with the length of about 1.1 m. The designed transmission efficiency is better than 95% and the energy spread is as low as 0.6%. Combining the beam dynamics design, a trapezoidal IH-rfQ structure was proposed, which can be cooled more easily and has better mechanical performance than traditional rfQ. Electromagnetic field distribution was simulated by using CST Microwave Studio (MWS). The specific shunt impedance and the quality factor were optimized primarily.