Towards Cleaner Ion Beams: Contaminant Removal Study for FRIB's future MR–ToF mass separator

The Facility for Rare Isotope Beams (FRIB) is a state–of–the–art rare–isotope beam facility capable of producing short–lived, ultra–rare nuclides whose study advances our understanding of nuclear structure, astrophysical processes, and fundamental nuclear interactions. However, production of these nuclides is accompanied by contaminating ion species which prevent many scientific investigations. To address this issue, a Multi-Reflection Time–of–Flight (MR-ToF) mass separator is in development at FRIB storing ions at 30 keV beam energy. It will enable a highly selective and high–flux mass separation to provide cleaner beams to subsequent experiments [1].

As the ions bounce back and forth between the two electrostatic mirrors of the MR-ToF device, they separate in time–of–flight according to their mass–to–charge ratio. Once contaminants are separated from the ions of interest, they need to be removed. Various methods exist for current state–of–the–art MR–ToF devices storing ions at < 2 keV beam energies, see e.g. Ref [2,3], but their performance at higher beam energies was unexplored.

We performed comprehensive ion–optical simulations and physical laboratory tests to quantify their performance at our increased beam energy of 30 keV. The presentation provides an evaluation of each method, detailing successes and limitations. Based on these findings, we identify and recommend the optimal contaminant removal solution for FRIB’s future highly selective and high–flux MR–ToF device.

[1] Maier, F.M.M. et al., NIMA 1056, 168545 (2023).

[2] Wolf, R. N et al, IJMS, 349–350, 123–133 (2013).

[3] Wienholtz, F. et al, IJMS, 421, 285–293 (2017).