The new MRTOF spectrograph for nuclear masses following RIBF's ZeroDegree spectrometer, featuring new methodologies for ion selection and mirror optimization

A newly assembled multi-reflection time-of-flight mass spectrograph (MRTOF-MS) at RIKEN's RIBF facility became operational in spring 2020. The setup underwent an initial online commissioning at the BigRIPS facility in the end of 2020 where more than 70 nuclear masses have been measured accurately with high precision. Further modifications and performance tests using stable ions were completed in early 2021. Recently a new optimization procedure for electrostatic mirror voltages has been implemented, which employs a pulsed drift to modify the ions' energy in a wide range and provides simplified access to the characteristic dispersion function of the system. Thus far, a mass resolving power of $R_m > 1\,000\,000$ is reached within a total time-of-flight of only $12.5\,\mathrm{ms}$ making the spectrometer capable of studying short-lived nuclei possessing low-lying isomers. Furthermore, a new in-MRTOF ion selection scheme to remove molecular contaminants will be reported, which has been developed for the online commissioning run. With uranium beam intensities reaching $100\,\mathrm{pnA}$ the production of short-lived rare isotopes at the RIBF is expanding, where recent developments allow for neutron-rich nuclei up to the $N=126$ shell closure, as a unique feature at present. The high resolution reached with MRTOF systems allows to separately observe nuclear states of many nuclei, which provides important input to tackle long standing questions in nuclear structure as well as the making of the chemical elements via nucleosynthesis.