  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.

Accelerator Physics