Multi-Reflection TOF Mass Spectrometer

• Multi-Reflection TOF Mass Spectrometer is an electrostatic time-of-flight analyzer that uses repeated ion reflections to significantly enhance mass resolution within compact setups.
• It achieves high resolving power through optimized ion preparation, precise voltage control, and advanced calibration methods, enabling accurate measurements even with low ion counts.
• The instrument is pivotal in nuclear physics, providing rapid mass measurements and effective beam purification for studies of rare isotopes and short-lived nuclei.

A multi-reflection time-of-flight mass spectrometer (MR-ToF-MS), also written MRTOF-MS and in some contexts termed a multi-reflection time-of-flight mass spectrograph, is an electrostatic time-of-flight analyzer in which ions are stored between two opposing electrostatic mirrors and reflected many times through a compact drift region. The repeated reflections fold a very long effective flight path into an apparatus of roughly meter scale, so that small differences in mass-to-charge ratio produce progressively larger time-of-flight differences. In practice, MR-ToF-MS combines high resolving power, millisecond-scale measurement times, high sensitivity at very low ion counts, simultaneous observation of multiple species, and compatibility with short-lived radioactive beams, which has made it a central instrument for precision mass spectrometry, beam purification, and isomer-resolved studies in rare-isotope physics (Ito et al., 2013, Schury et al., 2015).

1. Principle, terminology, and flight-time scaling

The defining feature of MR-ToF-MS is repeated axial reflection between electrostatic mirrors. Ions are injected as a short bunch, oscillate between the mirrors for a selected number of laps or revolutions, and are then ejected to a detector. Because the total flight time scales approximately with $\sqrt{m/q}$, the measured time of flight can be converted into mass by reference to a calibrant. A standard relation used in multiple implementations is

$$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$

with $t_0$ the offset between the trigger and the actual ion ejection. The corresponding mass resolving power is commonly written as

$R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$

or, equivalently, $R_m=\tfrac{1}{2}R_t$ when time resolving power $R_t=t/\Delta t$ is used (Ito et al., 2013, Schlaich et al., 2023).

Several papers emphasize that MR-ToF-MS is a true mass spectrograph rather than merely a single-species timing device. Multiple species can be recorded simultaneously, and in principle mass determination can be performed with very few detected ions. This characteristic is especially important for heavy and superheavy nuclei, where yields are low and half-lives are short. The same property also underlies the use of MR-ToF-MS as a separator, since different $m/q$ species separate in time inside the analyzer and may then be selected or rejected (Schury et al., 2015, Maier et al., 19 Sep 2025).

A central complication is that ions with sufficiently different $m/q$ do not necessarily execute the same number of laps during the same storage interval. Wide-band studies showed that this can scramble the monotonic ordering of peaks in time-of-flight spectra. Theoretical mass bandwidth therefore differs from useful bandwidth, and the effective bandwidth was found to be only about $60\%$ of the theoretical bandwidth because ions near the switched ejection mirror experience field perturbations during extraction. This corrects a common oversimplification: high nominal resolving power does not by itself guarantee straightforward broadband interpretation unless lap-number ambiguity and switching-field effects are explicitly handled (Schury et al., 2013).

2. Ion preparation, trapping, and analyzer architectures

MR-ToF-MS performance depends as much on the front-end ion preparation chain as on the mirror optics. In online rare-isotope installations, ions are commonly produced at high energy, separated in flight, stopped in helium gas, extracted as low-energy ions, cooled, accumulated, and only then injected into the analyzer. The GARIS-II plus gas-cell plus MRTOF-MS arrangement demonstrated this end-to-end workflow for heavy fusion-evaporation products, while the SLOWRI and BigRIPS installations at RIKEN used gas-cell stopping, RF transport, and trap-based preparation to deliver short, cold bunches to the spectrograph (Schury et al., 2015, Rosenbusch et al., 2021).

A particularly influential preparation system is the two-stage trap described for the RIKEN MRTOF. It combines an asymmetric taper trap and a flat trap. The taper trap provides pre-cooling and an effective axial drag force without rod segmentation, improving transfer into the second stage. The flat trap, built from two segmented printed-circuit boards separated by 4 mm and using orthogonal ejection through small plated holes, prepares a low-emittance bunch suitable for precision timing. In that system, ions were fully cooled within $2~\mathrm{ms}$ in the flat trap, the operational duty cycle was approximately $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$0, the combined trapping efficiency reached $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$1 for $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$2 and $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$3 for $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$4, and the flat-trap capacity was approximately $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$5 ions (Ito et al., 2013).

Analyzer geometries vary across facilities, but a recurring pattern is a central drift region bounded by mirror stacks with shaped potentials for near-isochronous motion. The PUMA offline-source MR-ToF-MS, a further development of the Greifswald design, uses six electrodes per mirror, a field-free drift region, an in-trap lift electrode, and in-trap deflectors for contaminant rejection. The IGISOL instrument uses two identical six-electrode mirror stacks separated by a 47 cm drift tube and traps ions by pulsing the central drift tube. The newer RIKEN ZeroDegree spectrometer installation adds a pulsed drift tube upstream of the analyzer in order to vary ion kinetic energy systematically and measure the instrument’s dispersion function directly (Schlaich et al., 2023, Virtanen et al., 12 Aug 2025, Rosenbusch et al., 2021).

These architectures make clear that “multi-reflection” is not a single hardware blueprint but a family of related electrostatic analyzers. A plausible implication is that front-end design choices—gas-cell extraction, bunch width, orthogonal ejection, in-trap lifts, and deflection or retrapping stages—are best regarded as integral parts of MR-ToF-MS performance rather than ancillary beamline details.

3. Calibration, referencing, and spectral inference

The precision of MR-ToF-MS depends on how reference information is incorporated into the time-of-flight analysis. Early high-precision operation at RIKEN demonstrated a single-reference method using only $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$6 to measure $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$7, with flight times of about $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$8, $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$9, and a relative mass uncertainty of $t_0$0. In that study, the offset $t_0$1 was measured to be about $t_0$2, with a conservative systematic uncertainty of $t_0$3, and validation measurements on $t_0$4 and $t_0$5 confirmed the reliability of the single-reference approach (Ito et al., 2013).

For long runs and wide-band measurements, drift correction becomes decisive. A major methodological development was concomitant referencing, in which reference and analyte are interleaved cycle by cycle on a timescale of about 15 ms. In that mode, the two species experience nearly identical voltage and temperature histories, and the spectra are separately tagged in the TDC. Benchmarking with rubidium and cesium ions showed that the standard deviation of the circulation-time data decreased from $t_0$6 for consecutive analysis to $t_0$7 for concomitant analysis, while the Birge ratio improved from $t_0$8 to $t_0$9. The same work reported a relative deviation of $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$0 for the new mode, compared with $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$1 for the older consecutive method (Schury et al., 2018).

Modern analyses also rely heavily on time-resolved calibration and asymmetric peak-shape modeling. At TITAN, MR-ToF-MS spectra were calibrated with a quadratic relation $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$2, with $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$3, and corrected by time-resolved calibration implemented in the acquisition software. Peak centroids were extracted with hyper-EMG line shapes using the emgfit library. At the FRS Ion Catcher, a more elaborate pipeline combined time-resolved calibration, Hyper-EMG($R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$4) functions, and weighted maximum-likelihood estimation. For overlapping peaks, an iterative simulation-based correction improved the effective resolution of low-lying isomers by a factor of up to three compared with standard analysis (Porter et al., 2022, Ayet et al., 2019).

Finite field-transition times during trap ejection introduce a subtler systematic. A dedicated study showed that non-instantaneous switching violates the textbook $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$5 law by adding a small mass-dependent correction. In extreme short-time systems the resulting mass deviation can reach about one percent, but for typical single-reference MR-ToF-MS with millisecond flight times the deviation usually remains below the $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$6 level. If calibration with two or more ion species is possible during the measurement, the effect becomes negligible for appropriate reference choices (Rosenbusch et al., 2019).

4. Resolving power, stability, and non-ideal effects

The highest resolving powers reported for MR-ToF-MS are not determined by geometry alone. Voltage stability, temperature drift, energy spread, non-ideal switching, and high-order aberrations all contribute directly to $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$7. This is especially acute near the turning points in the electrostatic mirrors, where ions spend much of their time and where tiny voltage changes can induce disproportionate time-of-flight shifts. One high-stability power-supply study quantified this sensitivity by noting that a $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$8 change in a single electrode voltage can induce about a $R=\frac{m}{\Delta m}=\frac{t}{2\Delta t},$9 shift in ion time of flight. Using that mapping, the authors argued that, in the idealized limit where only the most sensitive electrode matters, $R_m=\tfrac{1}{2}R_t$0 would be required to reach $R_m=\tfrac{1}{2}R_t$1, and $R_m=\tfrac{1}{2}R_t$2 for $R_m=\tfrac{1}{2}R_t$3; real instruments require stricter stability because multiple electrodes contribute independently (Schury et al., 2019).

The same work demonstrated an active high-voltage system based on a 20-bit DAC, a very low-noise 5 V reference formed from four parallel LTC6655-5 references, and an optically isolated high-voltage amplifier with closed-loop gain $R_m=\tfrac{1}{2}R_t$4. In bench tests up to $R_m=\tfrac{1}{2}R_t$5, the output stability in the $R_m=\tfrac{1}{2}R_t$6 band was on the level of $R_m=\tfrac{1}{2}R_t$7 during one hour, with only slightly more output variation across 3 days; the output was largely free of noise in the 1–200 Hz band; and after a 100 V step the supply settled to the ppm level within about 1 minute. When 16 such supplies biased a half-scale MR-ToF-MS, the instrument reached a time resolving power of about $R_m=\tfrac{1}{2}R_t$8 and maintained it for 36 hours, with measured peak drift below $R_m=\tfrac{1}{2}R_t$9 over that period (Schury et al., 2019).

Energy spread and time focus define an additional limitation. The IGISOL commissioning paper modeled the total flight time with explicit linear and quadratic energy terms and showed that the time focus is achieved only for specific combinations of trapping energy and revolution number. The fitted second-order coefficient was $R_t=t/\Delta t$0, the longitudinal emittance for $R_t=t/\Delta t$1 was estimated as $R_t=t/\Delta t$2, close to the expected $R_t=t/\Delta t$3, and the measured time-of-flight temperature sensitivity was $R_t=t/\Delta t$4. The same study reported time-of-flight peak widths down to $R_t=t/\Delta t$5 FWHM and mass resolving powers of about $R_t=t/\Delta t$6 within 20 ms, while also showing that larger revolution numbers eventually magnify aberrations and broaden the packet again (Virtanen et al., 12 Aug 2025).

High-end designs now treat non-ideal effects as a first-class design problem. The new MRTOF at RIKEN estimated that to reach $R_t=t/\Delta t$7, average voltage fluctuations must be on the order of $R_t=t/\Delta t$8. Simulations for FRIB’s proposed 30 keV high-voltage MR-ToF-MS went further: long-term $R_t=t/\Delta t$9 drifts in mirror voltages would reduce the ideal asymptotic resolving power from $m/q$0 to $m/q$1, modern active stabilization at about $m/q$2 would give $m/q$3, $m/q$4 would require about $m/q$5, and $m/q$6 about $m/q$7. The same simulations proposed active time-centroid correction via a pickup electrode, with 1 mV voltage precision corresponding to about $m/q$8 centroid stabilization and roughly $m/q$9 (Rosenbusch et al., 2021, Ireland et al., 10 Oct 2025).

A recurrent misconception is that mirror-temperature drift can be ignored if the analyzer is mechanically rigid. The literature suggests otherwise: temperature affects both dimensions and voltages, and in practical systems those electrical effects often dominate unless the power supplies and divider chains are stabilized on the ppm scale.

5. Nuclear-physics applications and representative measurements

MR-ToF-MS became established in nuclear physics because it can reach high precision within milliseconds, making it useful where Penning-trap observation times become too long. The first online RIKEN demonstration measured $m/q$0 with $m/q$1 after about $m/q$2 of flight time and obtained a mass excess of $m/q$3. That result was presented as a worst-case test in a light system, where the speed advantage over Penning traps is smaller than it would be for heavier ions (Ito et al., 2013).

For heavy nuclei, the GARIS-II-coupled MRTOF-MS showed that online measurements can be performed even with very low statistics. Time-of-flight spectra for the isobar chains $m/q$4–$m/q$5–$m/q$6–$m/q$7, $m/q$8–$m/q$9–$60\%$0, and $60\%$1–$60\%$2–$60\%$3–$60\%$4 were observed, with precision atomic mass values determined for $60\%$5, $60\%$6, and $60\%$7. The same work reported $60\%$8 at 148 laps and a total cycle from accumulation to detection of 30 ms, illustrating the suitability of MR-ToF-MS for short-lived nuclei in the heavy region (Schury et al., 2015).

At TITAN, MR-ToF-MS became a high-throughput precision tool for short-lived, contaminated beams. The first scientific TITAN campaign with the newly commissioned instrument measured $60\%$9, reached a mass resolving power of about $2~\mathrm{ms}$0 with a $2~\mathrm{ms}$1 flight time and $2~\mathrm{ms}$2 peak width, and was cross-checked with the MPET Penning trap where yields allowed. Later TITAN work on neutron-rich Ca, Ti, and V isotopes reported 13 mass measurements in total, eight of which improved on previous precision, with agreement between MR-ToF-MS and LEBIT at the $2~\mathrm{ms}$3, $2~\mathrm{ms}$4, and $2~\mathrm{ms}$5 levels for $2~\mathrm{ms}$6, $2~\mathrm{ms}$7, and $2~\mathrm{ms}$8, respectively. These data supported the disappearance of the $2~\mathrm{ms}$9 shell closure with increasing proton number and did not support an $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$00 shell closure (Leistenschneider et al., 2017, Porter et al., 2022).

The FRS Ion Catcher MR-ToF-MS pushed the method into the regime of few-event spectroscopy and low-lying isomers. It measured 31 ground-state masses of 15 different elements, with half-lives down to 17.9 ms and count rates as low as 11 events per nuclide, achieved a relative uncertainty of $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$01, performed the first direct mass measurement for seven nuclides, and extracted six isomeric excitation energies with excitation energies down to about $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$02. For nuclides with known literature masses, the average relative deviation was $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$03 (Ayet et al., 2019).

Correlated decay spectroscopy extends these capabilities further. An MRTOF-MS equipped with an $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$04-TOF detector directly measured $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$05 and $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$06, reached $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$07 after 266 laps, determined $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$08, obtained an excitation energy $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$09, and extracted a directly measured $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$10-decay branching ratio $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$11, thereby confirming $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$12 for $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$13 (Niwase et al., 2021).

More recent TITAN measurements of $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$14 show the continued maturation of the method. Using mass-selective retrapping followed by 756–842 isochronous laps, the experiment achieved $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$15–$$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$16, obtained the first ground-state mass measurement of $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$17, and improved the precision of $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$18 and $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$19, enabling the first evaluation of the IMME coefficients at $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$20 and refined analysis of the $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$21 doublet (Hockenbery et al., 12 Jan 2025).

6. Beam purification, specialized detectors, and high-voltage extensions

Although MR-ToF-MS is often introduced through precision mass measurements, the literature shows that it also functions as a beam purifier, isobar separator, ion counter, and diagnostic instrument. The PUMA offline-source system is an explicit example: the MR-ToF-MS is placed upstream of the RFQ cooler/buncher in order to remove contaminants early, speed the accumulation of up to $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$22 ions, and deliver mass-selected stable-ion bunches for antiproton-annihilation studies. During commissioning with $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$23, the device achieved $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$24 at 150 revolutions, corresponding to $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$25, with the limitation traced to chopping of the continuous beam rather than to the analyzer itself. In xenon tests, the in-trap deflector, switched with rise and fall times below $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$26 and a $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$27 potential difference, isolated specific isotopes such as $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$28 and $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$29 (Schlaich et al., 2023).

The same multifunctional trend appears in specialized detector development. The $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$30-TOF detector replaced the usual impact plate of a MagneToF detector by a silicon surface barrier detector so that a single device could provide the TOF stop signal, implanted-decay energy, and decay time. Offline tests reported more than $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$31 timing efficiency for $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$32 $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$33 rays, an intrinsic time resolution of $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$34, and an energy resolution of $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$35. Two-dimensional $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$36-ToF spectra resolved mixed $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$37 sources better than one-dimensional TOF spectra alone, demonstrating a route to background suppression and state assignment in extremely low-yield experiments (Niwase et al., 2019).

MR-ToF-MS has also been proposed outside rare-isotope mass spectroscopy in the narrow sense. For barium tagging in xenon-based neutrinoless double beta decay searches, a designed MR TOF would study ion-extraction efficiency and provide secondary isotope identification. Simulations suggested a mass-resolving power of $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$38, with a quickly adjustable tradeoff between broadband operation $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$39 to $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$40 at $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$41 to $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$42, and high-resolution mode at $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$43 with mass range about $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$44. The same design noted an acceptance of about $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$45 when the ion beam is collimated to a maximum diameter of 2 mm in order to suppress aberrations (Murray et al., 2019).

Facility-scale high-voltage developments now extend the separator role into a broader beam-delivery function. The commissioned IGISOL MR-ToF-MS is already used as a fast mass separator, beam purifier, and ion counter for laser spectroscopy and yield measurements, while the proposed FRIB high-voltage instruments are designed to store ions at 30 keV, increase ion throughput by two orders of magnitude compared with current devices, and deliver isobarically and isomerically purified beams to downstream stations. In ideal simulations, the optimized FRIB design reaches $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$46, while even the lower-energy $$m = m_{\mathrm{ref}}\left(\frac{t-t_0}{t_{\mathrm{ref}}-t_0}\right)^2,$$47 version remains useful for many applications (Virtanen et al., 12 Aug 2025, Maier et al., 19 Sep 2025).

These developments suggest that the modern MR-ToF-MS should be understood not only as a compact precision spectrometer, but as a reconfigurable electrostatic platform that can alternate between metrology, purification, and correlated spectroscopy. The precise balance among those modes depends on the same factors that govern resolving power elsewhere in the field: bunch quality, mirror tuning, voltage stability, and the treatment of non-ideal switching and drift.