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

Chapter 7
Conclusions and outlook
This thesis has presented basic theory as well as new developments concerning
the phenomenon called multipactor. Its deleterious effects on
microwave systems operating in a vacuum environment have been emphasised.
For satellites, the discharge can be catastrophic as basically no
means of repair or modification is available for parts in orbit. To avoid
the risks associated with vacuum discharges, lots of effort has been put
into studying the phenomenon and today well established engineering
methods exist, which are used by the microwave engineer when designing
hardware bound for space. However, the available methods are based
on the simple parallel-plate model, which in many instances is the worst
case. Thus, when designing important microwave features, in particular
such involving a nonuniform electromagnetic field, like e.g. irises and
coaxial lines, the parallel-plate model may not be applicable and there
is a risk of unnecessarily conservative designs. Such designs are often
large and heavy, which is a great disadvantage when it comes to devices
to be used in space. As a first attempt to establish new methods of
assessing the risk for having a discharge in such structures, a large part
of this thesis has been devoted to multipactor in irises and coaxial lines.
It has been shown that by only considering the random walk of the secondary
electrons in an iris, the threshold can be significantly increased
compared with the pure parallel-plate case. Many interesting aspects of
the phenomenon in a coaxial line have been found, e.g. the dual stable
regions of single-sided resonance and its unexpectedly low threshold
of the first order mode. In addition, the increased threshold for high
impedance coaxial lines that was found in experiments, was also found
in this study, both in the theoretical analysis and in the PIC-simulations.
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