Design and performance of the inter-RFQ beam transport and matching section for the SAIC PET isotope production accelerator

The SAIC PET isotope production accelerator is comprised of a 1 MeV ³He⁺ radio-frequency quadrupole (RFQ) accelerator followed by a charge-doubler and pair of RFQ accelerators to produce 8 MeV ³He⁺⁺ ions. The inter-RFQ section consists of a stripper and a transport system in order to match the beam into the following RFQ. This inter-RFQ section is functionally equivalent to a single-sided beam funnel where the bend magnet has been replaced with a stripper cell. The operating frequency is doubled from 212.5 MHz to 425 MHz and the beam must be matched transversely and longitudinally to the 425 MHz RFQ acceptance. The transverse matching is accomplished using permanent magnet quadrupoles and the longitudinal matching is accomplished using a buncher cavity. Our particular design is unique in that the transverse x:y diameter ratio can be as high as 4:1. Initially this asymmetry was thought to complicate the transport, however the system can be designed to exploit the unique features of a large aspect ratio and has important implications at other facilities