Novel deuteron RFQ design with trapezoidal electrodes and double dipole four-vane structure

RFQ-based neutron sources for various applications are being developed and constructed worldwide. To simplify RFQ structure and increase the effective shunt impedance, some novel design strategies have been investigated, including trapezoidal electrode modulations, the double dipole (DD) RFQ structure and use of an internal buncher dynamics strategy. Trapezoidal modulations based on 2TERM profiles are proposed to compensate for the variation of inter-vane capacitance, which helps to simplify rf electromagnetic design and field tuning. The double dipole (DD) four-vane structure increases mode separation without adding other equipment by modifying the RFQ undercut scheme. Furthermore, the entrance gap electric field between endplate and electrodes is designed as a longitudinal buncher, which makes the RFQ bunching section much shorter. By applying these considerations, a novel RFQ has been designed. It operates at 162.5 MHz with a duty factor of 1%, and can accelerate the 10 mA deuteron beam to 1.5 MeV. We have reduced the length of electrodes from 2.2 m to 1.8 m while maintaining transmission efficiency above 98.5%. The rf electromagnetic design has been carried out to fulfill the requirements of the resonant frequency, flat longitudinal field distribution and field tuning.