Multipactor in Low Pressure Gas and in ... - of Richard Udiljak

methods are charge detection using a probe and optical monitoring and
these two methods will be described below.
Charge probe
A special case of the method of electron monitoring, which was described
in a previous subsection, is the use of a probe that monitors only a
certain position within the microwave device. A very common approach
used when detecting electrons inside a waveguide is to flush mount an
SMA connector and apply a positive potential to the centre pin. The
negatively charged electrons are attracted to the pin and causes a small,
but detectable, current to flow, which can serve as an indication of the
electron density.
The method is easy to implement and therefore it has been quite
common in many test setups. Unfortunately, it is also quite slow due
to the circuit used to amplify the weak current [14] and thus it is not
feasible for measuring fast multipactor events. In addition, it requires
modification of the component, which makes it useless when testing flight
hard ware. In such a case the EDDM is a better choice.
Optical detection
Optical detection is possible since the electrons that make up the multipactor
discharge can excite or ionise either the remaining gas molecules
within the device or the molecules in the device wall. It can be divided
into two groups, viz. photon detection via optical probe and photon
detection via photographs or video camera [72,73]. Both methods are
common, but the former seems to be more frequently used.
The main advantage with these methods is that they can be used to
pin-point the location of the discharge inside the device. A major disadvantage
is that they may be impossible to use for studying real parts,
as the devices may not have any suitable openings. This is especially
true for the methods based on photographic techniques.
6.2 Detection using RF Power Modulation
During verification of a test setup for multipactor at Saab Ericsson
Space, Göteborg, Sweden, an odd, spike-like phenomenon was found
in the noise generated by a discharge in a coaxial test sample. An ad-
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