Trajectories through a cylindrically symmetric LEF TOF analyzer for electrons, neutrals, and positive and negative ions. The drift region length is given by , an ST trajectory path length by , and the front and rear voltage potentials by and .
Data recorded concurrently by ST and LEF detectors for three ion species. (a) The C, N, and O neutrals recorded by the ST detector had low flight times and comparatively broad distributions. Echo peaks of LEF ions were measured at higher flight times. (b) The LEF detector recorded the high-resolution distributions of LEF ions with a mass resolution of .
Simulation of secondary electron trajectories that could be created when an LEF ion impacts a metal plate. Electrostatic potential contours are also shown. (a) The sensor without inner rings does not show any substantial focusing of secondary electrons. (b) With inner focusing rings, the secondary electrons are guided toward the center of the ST MCP detector and can be distinguished from other ST signals by their impact position.
In the MCP detector assembly, the start signal for a timing measurement is triggered by a pulse read off of the anode-facing side of the MCP stack, while the impact position is recorded by the delay-line anode.
Monte Carlo simulations of secondary electron focusing for incident ions. (a) In this two-dimensional histogram of the ST detector impact positions, the broad neutral peak is visible as well as the centered LEF echo peak. (b) The flight times are shown for the neutral and positive LEF charge states, along with their mass resolution. (c) The flight times recorded within the central 4-mm radius area of the detector show a strong LEF echo signal. Note that due to the broad spatial scattering of neutrals, they land within the central area, but with a flux that no longer dominates the measurement.
Measurement of secondary electron focusing in an LEF TOF sensor. (a) The broad neutral peak and the centered echo peak can be seen in this image of the detector. (b) TOF peaks for the entire detector, with the neutral and the LEF echo peak labeled. (c) TOF peaks from the inner 4-mm radius area show that the LEF echo peak is clearly dominant, and background has been substantially reduced.
Simulation (a) and measurement (b) of TOF start electrons emitted from the carbon foil, showing that they are concentrated toward the edge of the MCP.
Measurement of associated daughter products from the parent molecule . When the TOF of one daughter product in the central region of the detector is isolated and plotted against the TOF of its companion in the outer region, the identity of the parent molecule can be found.
Article metrics loading...
Full text loading...