Gas-filled linear quadrupole trap with axial emission as an ion source for multiple-reflection time-of-flight mass spectrometer

To combine a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) with continuous mode ion sources such as those of electrospray type, it has been proposed to accumulate ions in a trap in the intervals between rare accelerator pulses. The ion accumulation scheme offered in the present paper consists of a gas-filled segmental quadrupole with radio-frequency entrainment and axial emission. The paper presents the necessary calculations for the ion trap and analysis of processes of ion capture, collisional cooling, and pulsed emission. Experimental studies of the storage trap have shown almost complete transformation of a continuous ion beam into a pulsed one and the possibility of long-time (for up to a few seconds) ion holding. Satisfactory beam parameters are achieved at sufficient cooling (defined by the dwell time and pressure in the trap, 5 ms∙mtorr), low gas pressure collisions, and at a low trap load (below 100 000 charges). The combination of these two requirements limits the total beam current at which the ion flux can be converted into minimum width pulses to 3 nA.