PlasmaQuant MS Series
Mass
Spectrometer
127
The exit plate orifice is positioned at the exit to, and on axis with the quadrupole. This
lens is connected to the mass analyzer chassis and maintained electrically at earth
(ground) potential. The exit plate is an important component in creating the geometry
of the electrostatic field at the exit to the quadrupole. The surface of the exit plate also
traps any unwanted metastable atoms or photons preventing them from entering the
detector. This process assists in minimizing background interference. It performs a
similar function to the entrance lens. The exit plate orifice is 6 mm in diameter.
Although most of the unwanted atoms are extracted from the plasma by the ion
optics, intermolecular collisions within the second vacuum chamber can create
additional unwanted atoms. For this reason, the fringe filter contains ‘curved’ rods.
Figure 8-20 - The terminal block provides the interface for the fringe bias, entrance plate, entrance lens
and exit lens supplies
The terminal block provides an electrical interface for the DC supplies for the entrance
lenses, and the fringe bias. The four gold plated pins are spring loaded and provide an
electrical connection to the vacuum chamber top panel.
The exit lens is connected to the mass spectrometer chassis earth. It attracts and traps
unwanted particles, and metastables which may have been generated inside the
quadrupole through ion collisions.
The detector focus lens is located inside the detector. It is a flat plate containing a
4mm diameter hole through which the ions pass on route to the first dynode. It serves
two functions. Primarily it protects the detector from damage due to excessive ion
counts. It also creates an electrostatic field that improves the efficiency of transferring
ions from the quadrupole exit and into the detector.
Exit plate
Detector focus lens
Terminal Block