electron multiplier


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electron multiplier

A detection device inside the vacuum of a mass spectrometer which converts ions impacting on its front dynodes into a detectable, amplified electron current at the back lead of the device, with an overall gain (signal out/signal in) as high as 104–108.

Positive ions exiting the mass analyser impact the first dynode’s surface, triggering the release of several electrons, which are then accelerated through a potential to the next electrode, where each electron impact triggers the release of several secondary electrons; these are accelerated into the next dynode, leading to further impact (release events). A cascade of electrons is produced, generating a current that is further amplified and then sampled by an analog-to-digital converter to be recorded by the data system.
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During the RF sweep, which progressively destabilizes ions for ejection from the ion trap to the electron multiplier, the axial modulation RF enhances the movement of ions away from the center of the ion trap where magnetic field strength is low and ion density is high.
Six RGAs with electron multiplier detectors and 100 amu ranges will also be used to monitor the gas composition within the beam pipe vacuum volume.

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