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TOFMS Source Modules


Electron Ionisation and Pulsed Extraction of Gas Sample

Electron Impact TOF Source Schematic

This TOFMS source features:

  1. An electron impact ionisation source, with a repeller and focussing electrode to produce a high flux sheet of electrons into the TOFMS source.

  2. A multi-electrode TOFMS source designed to create a pulse of ions for injection into a TOF analyser. The source has a backplate, a pulse-out electrode, and two further electrodes to accelerate the ion pulse up to the flight energy of the TOF analyser.

In this type of TOFMS source ions are created at near ground potential from gas molecules using electron impact ionisation (EI). The ions are then extracted and accelerated to their flight energy in such a way as to come to a sharp time focus at an adjustable position some way down the flight tube. Any ion optical elements following the TOFMS source, such as deflectors, must float at the potential of a field-free region that preceeds the detector and reflectron, if used.

The filament is intended to operate at 70eV, and drive electronics are also available from Kore. Similarly, the TOF pulser is designed for pulse-out with a fast voltage edge up to 400V in amplitude. Flight potentials of 1-3 kV are typical in TOF instruments, and the final element of the TOF source is maintained at the same potential as the 'field-free region' (FFR) that follows the source and any deflectors. It is best if the pulser is located near the pulsing electrode, and a Kore pulser box is available to fit to a feedthrough flange onto which the TOF source is mounted.

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Orthogonal Pulsing Of Ion Beam (EI not required)

Orthogonal pulsed extraction schematic

This multi-electrode TOFMS source is designed to receive a continuous (already ionised) ion stream and create pulses of ions for injection into a TOF analyser. The source has a backplate, a pulse-out electrode, and two further electrodes to accelerate the ion pulse up to the flight energy of the TOF analyser.

This type of TOFMS source is able to extract ions from a continuous ion stream of up to 100 volts potential (in combination with the Kore floating pulser supply). The ions are then accelerated to their flight energy in such a way as to come to a sharp time focus at an adjustable position some way down the flight tube. Any ion optical elements following the TOF source, such as deflectors, must float at the potential of a field-free region that preceeds the detector and reflectron, if used.

The TOFMS source is designed for pulse-out with a fast, 300-400 volt edge. Flight energies of 1-3 keV are typical in TOF instruments, and the final element of the TOF source is maintained at the same potential as the 'field-free region' (FFR) that follows the source and any deflectors. It is best if the pulser is located near the pulsing electrode, and a Kore pulser box is available to fit to a feedthrough flange onto which the TOF source is mounted.

If the ionisation source provides a divergent beam, it will be advantageous to consider a lensing system that will focus and transfer it into the source with minimal ion losses (high transmission). An example of suitable transfer optics / lens system is described in the section on 'Matching Optics'.


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Last updated: 16:22 19/02/2014

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