Stanford Research Systems RGA100, Operating Manual And Programming Reference

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2 Glossary of Terms
SRS Residual Gas Analyzer
Electron emission . The release of electrons from the heated filament in the ionizer. The
electrons are accelerated into the anode grid where the ionization of the gas molecules
occurs.
Electron emission current. The electron current from the filament to the grid in mAmps.
Ion current signals scale linearly with the electron emission current. Note : The available
emission current range in the SRS RGA is 0 to 3.5 mA.
Electron Energy . The kinetic energy of the electrons (in eV) used for electron
bombardment in the ionizer. Note: In the SRS RGA the Electron Energy is equal to the
voltage difference (in Volts) beween the filament and the anode grid.
Electronics Control Unit (abbreviation: ECU) . Electronics box that attaches directly to
the probes feedtrhu flange and contains all the necessary components to operate the
quadrupole mass spectrometer and communicate with a host computer.
Faraday Cup . A charged particle detector, consisting of a metal electrode, for the direct
collection and detection of charged particles. Note: Typical designs are cup shaped to
minimize secondary electron losses.
Filament (Ionizer Component). The source of the ionizing electrons. Thin, thoria
coated, Iridium wire that operates at a negative potential relative to ground and is
resistively heated to incandescence with an electrical current from the emission regulator.
The thermionically emitted electrons are accelerated towards the anode grid which is
positively charged with reference to the filament and ground.
Focus Plate (Ionizer component). Ionizer’’s electrode plate that serves the double
purpose of drawing the ions away from the anode grid, and containing the ionizing
electrons inside the source.
Fragment ion . An ion of mass smaller than that of the original parent molecule.
Fragmentation factor . The fragmentation factor of gas g at mass M is defined as the
ratio of ion signal at mass M to the ion signal at the principal mass peak of gas g.
Fragmentation of molecules : The breaking of multi-atomic molecules into units of
fewer atoms, some of which are usually electrically charged.
Fragmentation (or cracking) pattern . The fragment distribution of ionic species which
results from dissociation and ionization of multi-atomic molecules of given species in the
ionizer.
Head (also RGA Head). The combination of the Probe and the Electronics Control Unit.
Inert Gas . A gas that does not normally react chemically with other substances.
Example: He, Ar, Kr and Xe. Typically used for calibration purposes in RGA’’s.
Ion . An atom or molecule which has gained or lost one or more electrons and therefore
has a negative or positive charge. Note: Most RGA’’s use electron bombardment to ionize
molecules and detect only positive ions.