Isochronicity correction in the CR storage ring

Abstract

A challenge for nuclear physics is to measure masses of exotic nuclei up to the limits of nuclear existence which are characterized by low production cross sections and short half-lives. The large acceptance Collector Ring (CR) [1] at FAIR [2] tuned in the isochronous ion-optical mode offers unique possibilities for measuring short-lived and very exotic nuclides. However, in a ring designed for maximal acceptance, many factors limit the resolution. One point is a limit in time resolution inversely proportional to the transverse emittance. But most of the time aberrations can be corrected and others become small for large number of turns. We show the relations of the time correction to the corresponding transverse focusing and that the main correction for large emittance corresponds directly to the chromaticity correction for transverse focusing of the beam. With the help of Monte-Carlo simulations for the full acceptance we demonstrate how to correct the revolution times so that in principle resolutions of ∆m/m = 10 −6 can be achieved. In these calculations the influence of magnet inhomogeneities and extended fringe fields are considered and a calibration scheme also for ions with different mass-to-charge ratio is presented.

Storage ring mass spectrometry for nuclear structure and astrophysics research

“…The new driver accelerator, 100-Tm heavy ion synchrotron, SIS-100, will provide bunched high intensity primary beams of up to 5 • 10 11 238 U per bunch each 1/5 s. The secondary beams produced from these beams will be separated by the new high-acceptance fragment separator, Super-FRS, [207] which is designed to achieve a high transmission of fragments to the Collector Ring, CR, [208] . The CR is a dedicated isochronous ring [209,210] where lifetime and mass measurements of short-lived nuclei will be performed [58], see Figure 23. At the present FRS-ESR, the transmission of fragments from the FRS to the ESR in isochronous mode is less than a percent.…”

An improvement of isochronous mass spectrometry: Velocity measurements using two time-of-flight detectors

“…The nonlinear field is critical for the IMS experiment since it directly alter the orbital length variation and thus lead to a significantly lower mass resolving power [18]. However, high-order isochronous condition can be fulfilled via some isochronicity correction by means of sextupoles and octupoles [15,18,19]. Even though the momentum compaction factor can be corrected to be a constant within the Bρ-acceptance, we can still investigate the effect of α p1 on the relative variation of orbital length, which is the same magnitude as the relative variation of revolution period.…”

Toward precision mass measurements of neutron-rich nuclei relevant to r-process nucleosynthesis

“…The further the system is from the ideal isochronicity, the worse the mass resolving power becomes. Investigations on the isochronicity of storage rings are also under way to obtain the best mass resolving power [78][79][80].…”

“…FIG. 2: (Color online) Effects of the uncertainty in the neutron separation energy Sn for 78 Ni on the T9-nn conditions required by the N = 50 waiting point nuclei 80 Zn, 79 Cu and 78 Ni. The band between two curves of the same kind represents the conditions using different Sn of 78 Ni.…”