Experimental investigation of the transition energy γ_t in the isochronous mode of the HIRFL-CSRe

摘要

The Isochronous Mass Spectrometry (IMS) based on storage rings is a powerful technique for mass measurement of short-lived exotic nuclei. The transition energyγtof the storage ring is a vital parameter of the IMS technique. It is difficult to measure theγtand its relation to momentum spread or circulating length, especially to monitor the variation ofγtduring experiments. An experimental investigation on theγthas been performed for the IMS experiment at the Cooler Storage Ring of the Heavy Ion Research Facility in Lanzhou (HIRFL-CSRe). With the velocity measured by two time-of-flight (TOF) detectors, theγtas a function of orbital length can be determined. The influences of higher order magnetic field components on theγtfunction were inferred for isochronous correction. This paper introduces and investigates the influence of dipole magnetic fields, quadrupole magnetic fields and sextupole magnetic fields on theγtfunction. With the quadrupole magnets and sextupole magnets corrections, a mass resolution of 171332 (FWHM) andσ(T)∕T=1.34×10−6were reached, which shall be compared with 31319 (FWHM) andσ(T)∕T=7.35×10−6obtained without correction.