Installation of a Four-Vane Radio-Frequency Quadrupole Accelerator for the Rare Isotope Science Project

A radio-frequency quadrupole (RFQ) linear accelerator has been fabricated and installed as the injector for the superconducting linear accelerator of the Rare Isotope Science Project (RISP) to accelerate particles from protons to uranium ions. In this paper, a new continuous-wave (CW) 4-vane RFQ with a low operational frequency of 81.25 MHz and a ramped inter-vane voltage profile was realized. A RFQ with octagonal cross section is composed entirely of oxygen-free electronic (OFE) copper and is fabricated using a three-step brazing process. The cavity length is 5 meters and the diameter is 1 meter. The RFQ consists of nine modules, and the length of each module is 0.56 meter, which was determined in consideration of the facility's capability. The machining tolerance and the final gaps between vanes were checked using pin gauges and a 3D coordinate measurement system (CMM) as the errors were less than ±30 μm and ±50 μm respectively. The fabrication technology experiences in this work can be applied to future heavy-ion CW RFQs.