Fig. 1. Schematic of the MRTOF-MS: Ions ejected from the flat trap are
accelerated via three thin plates A1, A2 and A3 (each with a 4 mm bore
inside), and after passing through a steerer section, ion transport
continues through the drift tubes DT1, DT2, and DT3 before reaching the
inner of the MRTOF-MS.
The typical measurement cycle
proceeds as follows: First, reference and analyte ions accumulate in the
linear Paul traps on either side of the flat ion trap (FLT) and are
individually transferred to the FLT for a final cooling process. This
process takes about 5 ms at a pressure of 10-2~10-1 mbar. Ions are orthogonally
ejected towards the MRTOF-MS, accelerated by three accelerating lenses
(AC), steered by two pairs of steerers (ST), and transported to a system
of drift tubes (DT). The tube DT1 is pulsed to adjust the potential
energy of the ions due to downstream voltage-supply limitations.
However, in the simulation, this is simplified by shifting the whole
potential of the MRTOF-MS. Then ions pass through DT2 and DT3. Before
injecting ions into the MR analyzer, the voltage applied to the
outermost electrode of the injection-side mirror is reduced to allow
ions to pass (switching of the end-cap mirror’s bias). The ions then
reflect between the mirrors for a chosen duration, ensuring that ions
with a specific A/q undergo a predetermined number of reflections
(where A represents the atomic mass number and qrepresents the electric charge). After the ions have undergone the
desired number of reflections and are near the turning point of the
injection-side mirror, the voltage applied to the outermost electrode of
the ejection-side mirror is reduced to allow the ions to pass. The ions
will then travel to the ion detector and generate the stop signals for
time-to-digital converter (TDC).
While the start signal is the
ejection of ions from the FLT. To achieve excellent performance, the
electrostatic lenses in-between should be precisely optimized. This will
allow the ion pulse to fly close to the optical axis, resulting in a
narrow time-of-flight (TOF) focus on the detector.
Simulation setting