Fabrication and cold test of prototype of spatially periodic radio frequency quadrupole focusing linac

TL;DR

This paper details the design, fabrication, and testing of a 325 MHz aluminum prototype of a spatially periodic RF quadrupole focusing linac, demonstrating its feasibility for high-current linac front ends.

Contribution

It introduces a novel spatially periodic RF quadrupole structure, with detailed mechanical design, fabrication process, and validation through cold testing, advancing high-current linac technology.

Findings

Field errors within acceptable range

Successful fabrication and assembly

Effective tuning scheme verified

Abstract

A 325 MHz aluminum prototype of a spatially periodic rf quadrupole focusing linac was developed at the Institute of Modern Physics, Chinese Academy of Sciences, as a promising candidate for the front end of a high-current linac. It consists of an alternating series of crossbar H-type drift tubes and rf quadrupole sections. Owing to its special geometry, cavity fabrication is a major hurdle for its engineering development and application. In this paper, we report the detailed mechanical design of this structure and describe its fabrication process, including machining, assembly, and inspection. The field distribution was measured by the bead-pull technique. The results show that the field errors of both the accelerating and focusing fields are within an acceptable range. A tuning scheme for this new structure is proposed and verified. The cold test process and results are presented in detail. The development of this prototype provides valuable guidance for the application of the spatially periodic rf quadrupole structure.