5 – 2
Transpector CPM Operating Manual
5.2.1 The Ion Source
The Transpector CPM sensor closed ion source requires a pressure reducing
orifice because process pressures are typically far greater than the maximum at
which the closed ion source can operate. (See
Figure 5-2 Closed ion source
Inside the closed ion source, a heated filament emits electrons which bombard the
incoming gas molecules giving them an electrical charge. While this charge may
be either positive or negative, Transpector CPM detects only positive ions. Once a
molecule is charged (ionized), electric fields can be used to manipulate the
molecule.
The default filament is made of tungsten. Tungsten offers the best resistance to
aggressive gases, particularly those containing fluorine and chlorine. A yttria
coated iridium filament can be used in oxygen or water vapor heavy environments
(that will quickly oxidize the tungsten filament).
CAUTION
Tungsten filaments will be destroyed when operated at
high pressure because they react with oxygen and water
vapor at operating temperature.
Sealing Disk
Spring
Anode Cylinder
Filament Block
Shield Washer
Anode Plate
Insulator Rings
Focus Plates
Upper Tube Ring
Filament
(Electron Repeller not shown)
