Frequency and fields tuning of a heavy ion radio-frequency quadrupole accelerator

A continuous wave heavy ion four-vane Radio Frequency Quadrupole accelerator (RFQ) is under construction for the LEAF project in the Institute of Modern Physics, Chinese Academy of Sciences. The operation frequency is 81.25 MHz and the inter-vane voltage is 70 kV. To separate the adjacent dipole frequency from the operation frequency, the π-mode stabilizing loops (PISLs) are utilized. After optimization, the RFQ cavity is equipped with 6 pairs of PISLs and the frequency separation reaches 5.54 MHz. With low power test and careful tuning, the cavity achieved the desired frequency and field. The relative error of the quadrupole field is less than 1% and the admixtures of the two dipole modes are within 1.5% of the quadrupole field. In this paper, the effects of the PISLs in the RFQ will be studied. Meanwhile, the low power test and tuning of the LEAF RFQ are presented.