Design Study of a Re-bunching RFQ for the SPES Project

Abstract

An upgrade to the 2nd generation of the selective production of exotic species (SPES) to produce aradioactive ion beam (RIB) has been studied at the istituto nazionale di fisica nucleare − laboratorynazionali di Legnaro (INFN-LNL). Due to the long distance between the isotope separator online(ISOL) facility and the superconducting quarter wave resonator (QWR) cavity acceleratorelineare per ioni (ALPI), a new re-buncher cavity must be introduced to maintain the high beamquality during the beam transport. A particular radio frequency quadrupole (RFQ) structure hasbeen suggested to meet the requirements of this project. A window-type RFQ, which has a highmode separation, less power dissipation and compact size compared to the conventional normal4-vane RFQ, has been introduced. The RF design has been studied considering the requirementsof the re-bunching machine for high figures of merit such as a proper operation frequency, a highshunt impedance, a high quality factor, a low power dissipation, etc. A sensitivity analysis of thefabrication and the misalignment error has been conducted. A micro-movement slug tuner has beenintroduced to compensate for the frequency variations that may occur due to the beam loading, thethermal instability, the microphonic effect, etc.