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

The Isochronous Mass Spectrometry (IMS) based on storage rings is a powerful technique for mass measurement of short-lived exotic nuclei. The transition energy γt of the storage ring is a vital parameter of the IMS technique. It is difficult to measure the γt and its relation to momentum spread or circulating length, especially to monitor the variation of γt during experiments. An experimental investigation on the γt has 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, the γt as a function of orbital length can be determined. The influences of higher order magnetic field components on the γt function were inferred for isochronous correction. This paper introduces and investigates the influence of dipole magnetic fields, quadrupole magnetic fields and sextupole magnetic fields on the γt function. With the quadrupole magnets and sextupole magnets corrections, a mass resolution of 171332 (FWHM) and σ(T)∕T=1.34×10−6 were reached, which shall be compared with 31319 (FWHM) and σ(T)∕T=7.35×10−6 obtained without correction.