Performance of a precise isochronous magnetic field over a wide momentum range in the Rare-RI Ring

The Rare-RI Ring is the isochronous storage ring constructed at the RIKEN radioactive isotope beam factory for high-precision mass measurements of extremely short-lived and rarely produced exotic nuclei via time-of-flight mass spectrometry. This is the only cyclotron-like heavy-ion storage ring that can satisfy the isochronous condition over a wide momentum range. The magnetic field is created with the assistance of 10 trim coils. A particle-tracking simulation was developed for tuning the magnetic field to reach high-precision isochronism. We successfully performed a commissioning experiment for the precise mass measurement of rarely produced nuclei, established by newly developed techniques: self-triggered injection together with in-flight particle identification, and high-precision isochronous adjustment. Experimental isochronism was obtained to be 4.7×10−6 for the standard deviation within ±0.3% of momentum range. The results showed that the high-precision isochronous magnetic field over a wide momentum range enabled precise mass determination.