Development of Low Charge-to-Mass Ratio Post-Accelerator for the RIA Project

摘要

A post-accelerator for rare isotopes (RIB linac) which must produce high-quality beams of radioactive ions over the full mass range, including uranium, at energies above the coulomb barrier is being developed for the U.S. RIA facility. To provide highest possible intensity of rare isotopes with masses from 6 to 240, the linac will accept all ions in the 1+ charge state. A high resolution separator for purifying beams at the isobaric level precedes the RIB linac. Charge stripping in the linac takes place at two stages: helium gas stripping at energies of a few tens of keV/u, and an additional foil stripping at ～680-1700 keV/u for the heavier ions. The RIB linac will utilize existing superconducting heavy-ion linac technology for all but one exceptional piece, a very-low-charge-state injector, which is needed for the first ～9 MV of the accelerator. This section consists of a pre-buncher followed by three sections of cw, normally-conducting RFQ. The first section is a conventional RFQ operating at 12 MHz. The following two sections are hybrid RFQs operating at 12 and 24 MHz. A 1:2 scale cold model of 12 MHz RFQ was built and it is being studied in order to determine final specifications for the full power 12 MHz hybrid RFQ. This paper reports on the present status of the RIB linac development with particular attention paid to the very-low-charge-state injector section.