Development and beam commissioning of a continuous-wave four-vane heavy ion radio-frequency quadrupole accelerator based on stable operation

A continuous-wave (CW) heavy ion radio frequency quadrupole (RFQ) accelerator was developed for the Low Energy Accelerator Facility (LEAF) at IMP. The RFQ accelerator is the most effective accelerator for accelerating the low energy high intensity beam, but there are challenges achieving the stable CW operation. This paper presents the development of the LEAF RFQ based on the stable CW operation. In the beam dynamics design, a multi-harmonic buncher is utilized to reduce the longitudinal emittance and the constant-voltage design is applied for low RF power loss. In the radio frequency (RF) design, the constant-voltage four-vane RFQ is selected to reduce the power dissipation. The π-mode stabilizing loop (PISL) is employed to reduce the admixture of the dipole field. In order to ensure the stability of the cavity structure, the multi-physics of the cavity are analysed. The resonant frequency sensitivities of the cooling water temperature are studied to tune the cavity frequency during operation. Through low power test and tuning, the resonance frequency and field distributions are optimized. The beam commissioning (4He1+,14N2+ and86Kr13+) and some radiation experiments have been performed. The entire processes of the LEAF RFQ development, such as, beam dynamics design, RF design, multi-physics analysis, low power test, high power conditioning, beam commissioning and some radiation experiments, will be detailed presented in this paper. The results of testing and commissioning indicate that the development of the LEAF RFQ has succeeded. And the design scheme for RFQ with stable CW operation in this work can be applied to other future CW RFQs.