Cause of unexpectedly high ion flux at 3 keV operation

Determine the physical and ion-optical factors responsible for the observation that the FRIB Multi-Reflection Time-of-Flight mass spectrometer (MR-ToF MS), when operated with ions stored at 3 keV beam energy, exhibits on average an order-of-magnitude higher maximal ion flux than existing low‑energy MR-ToF MS instruments. Ascertain whether this difference arises from optimization of the MR-ToF geometry and applied bias voltages, or from other mechanisms beyond the expected linear scaling of ion flux with beam energy.

Background

Ion flux is a critical performance metric for MR-ToF mass separation, directly impacting the delivery of high‑intensity isobarically and isomerically purified beams to downstream experiments. In this work, the authors simulate and compare ion flux for operation at 3, 15, and 30 keV storage energies and report substantial gains at higher energies, as expected from increased energy spread tolerance and reduced space‑charge effects.

However, even at the low storage energy of 3 keV, the FRIB device simulations show ion flux values that are, on average, an order of magnitude larger than those reported for other low‑energy MR‑ToF MSs. This unexpected difference remains unresolved, and the authors hypothesize it may be due to design and voltage optimizations favoring high ion flux, underscoring the need to identify and quantify the underlying causes.