RF field measurement of an RFQ cold model cavity for the JHP

A radio-frequency quadrupole (RFQ) linac will be constructed as a preinjector linac for the Japanese Hadron Project (JHP). Its resonant frequency, injection and final energies are determined from beam-optics considerations of the entire system to be 432 MHz, 50 keV and 3 MeV, respectively. In order to achieve these requirements, keeping the maximum surface electric field to less than 1.8-times the Kilpatrick limit, the RFQ becomes about 2.7 m long. In order to examine the field stability of such a long RFQ cavity, a cold model cavity without vane modulation or a side-tuner was constructed with relative intervane-distance errors of less than ±30 μm. The measurements showed that a good longitudinal and azimuthal field uniformity within ±3.5% could be achieved by adjusting only end tuners