Thermo Scientific DSQ II, Hardware Manual

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7
Ion Detector
Electron Multiplier
Thermo Scientific DSQ II Hardware Manual 189
Electron Multiplier
An electron multiplier amplifies a current by generating an electron cascade from an
oxide-coated surface of an electrode. The two components of an electron multiplier are the
cathode and anode.
Figure 104. ETP Electron Multiplier
Cathodes serve as the electrode the electron multiplier uses to generate the electron cascade. It
receives a potential of up to -2.5 kV from the high voltage ring. The anode is near ground
potential.
Secondary particles from the conversion dynode strike near the inner walls of the electron
multiplier cathode with sufficient energy to eject electrons. The ejected electrons are
accelerated farther into the cathode, drawn by the increasingly positive potential gradient.
Due to the design of the eletron multiplier, the ejected electrons do not travel far before they
again strike a surface, causing the emission of more electrons. Thus, a cascade of electrons is
created that finally results in a measurable current at the anode. The current collected by the
anode is proportional to the number of secondary particles striking the cathode.
Typically, the electron multiplier has a gain of about 10
5
. If the current of ions entering the
electron multiplier from the conversion dynode is 10
-12
A, and the gain of the electron
multiplier is 10
5
, then a current of 10
-7
A leaves the electron multiplier through the anode.
This current is converted to a voltage by the electrometer circuit and recorded by the data
system.