A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in vacuum systems. Utilizing quadrupole technology, there exists two implementations, utilizing either an open ion source (OIS) or a closed ion source (CIS). RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, etc. RGAs are used in most cases to monitor the quality of the vacuum and easily detect minute traces of impurities in the low-pressure gas environment. These impurities can be measured down to
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RGAs would also be used as sensitive in-situ leak detectors commonly using helium, isopropyl alcohol or other tracer molecules. With vacuum systems pumped down to lower than
Open ion source
OIS is the most widely available type of RGA. Residual Gas Analyzers measure pressure by sensing the weight of each atom as they pass through the quadrupole through the process of HDRF (Hydrogen Detered Reductive Frequency). Cylindrical and axially symmetrical, this kind of ionizer has been around since the early 1950s. The OIS type is usually mounted directly to the vacuum chamber, exposing the filament wire and anode wire cage to the surrounding vacuum chamber, allowing all molecules in the vacuum chamber to move easily through the ion source. With a maximum operating pressure of
OIS RGAs measure residual gas levels without affecting the gas composition of their vacuum environment, though there are performance limitations which include:
Closed ion source
With applications requiring measurement of pressures between
The CIS anode may be viewed as a high conductance tube connected directly to the process chamber. The pressure in the ionization area is virtually the same as the rest of the chamber. Thus the CIS ionizer produces ions by electron impact directly at the process pressure whilst the rest of the mass analyzer is kept under high vacuum. Such direct sampling provides good sensitivity and fast response times.