Tuning an 81.25 MHz four-vane RFQ with a ramped field profile at RISP

Abstract

A radio-frequency quadrupole linear accelerator (RFQ) was developed and tuned for the heavy ion accelerator facility at Rare Isotope Science Project (RISP). The RISP RFQ has an 81.25 MHz operational frequency and a four-vane structure for a continuous-wave mode operation despite the fabrication difficulties of the huge cavity generated due to the brazing technology. The cavity is inherently insensitive to perturbations due to low frequency and a short cavity length. The linearly increasing profile of inter-vane voltage was tuned for all quadrants through not only movable slug tuners but also modification of the end-plate. In this study, a low-frequency RFQ with a novel, ramped field profile was tuned and the commissioning tests were conducted with a new tuning method compatible with the modification of the end-region geometry.