Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Ionizer Degas 8-7
SRS Residual Gas Analyzer
Ionizer Degas
An Ionizer Degas program is built into the RGA head to clean up the filament and the
ionizer by Electron Impact Desorption. Degassing provides a fast way to clean up the ion
source, however, it compromises the lifetime of the thoria coating of the filaments and it
is no substitute for a complete bakeout of the probe. Its use is only recommended when
contamination of the probe is suspected and a long bakeout is not a practical option.
During the degas process the anode grid and the filament are bombarded by a 20 mA
current of 400 eV electrons. The complete process takes three minutes and can be
triggered directly from the RGA Windows software (Head Menu). The emission current
is ramped slowly during the first minute to eliminate sudden bursts of gases into the
vacuum system.
The electron multiplier is turned off at the beginning of the cycle. The emission current is
turned back to its pre-degas setting at the end of the degas cycle, but the electron
multiplier is always left off for additional protection. Overpressure protection is built into
the degas procedure and the filament will immediately shut down if a leak is detected.
For users developing their own software, the Degas process can be triggered with the DG
command described in the
RGA Command Set List, and Degas times as large as 20
minutes long can be selected.