Experimental Investigation of the Transition Energy ${\gamma }_t$ in the Isochronous Mode of the HIRFL-CSRe

Abstract

The Isochronous Mass Spectrometry (IMS) based on storage rings is a powerful technique for mass measurement of short-lived exotic nuclei. The transition energy ${\gamma }_t$ of the storage ring is a vital parameter of the IMS technique. It is difficult to measure the ${\gamma }_t$ and its relation to momentum spread or circulating length, especially to monitor the variation of ${\gamma }_t$ during experiments. An experimental investigation on the ${\gamma }_t$ 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 ${\gamma }_t$ as a function of orbital length can be determined. The influences of higher order magnetic field components on the ${\gamma }_t$ 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 ${\gamma }_t$ function. With the quadrupole magnets and sextupole magnets corrections, a mass resolution of 171332 (FWHM) and $\sigma (T)/T=1.34\times 10^{-6}$ were reached, which shall be compared with 31319 (FWHM) and $\sigma (T)/T=7.35\times 10^{-6}$ obtained without correction.

10 figures,19 pages