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

(cf. Fig. 2.7). When taking the envelope of these zones, the differences
in the right boundaries of the main zones, between the constant initial
velocity and the constant k approaches, become negligible. This can be
seen clearly in Fig. 2.7 [40]. The existence of the hybrid modes requires
Figure 2.7: Vacuum multipactor with the main zones as well as a few hybrid
zones [40]. With the envelope of the hybrid zones included
the resemblance between the Sombrin chart and the Hatch and
Willams chart (cf. Fig. 2.5) is striking.
phase stability, just as for the classical zones discussed above. However,
the width of each hybrid zone is very small and thus it is very sensitive
to an initial velocity spread. On the other hand, there are many hybrid
zones very close to one other and this spread will result in a mixing or
overlapping of the resonances [39].
2.1.3 Factors effecting the threshold
There are many different aspects that need to be considered when determining
the multipactor threshold. The most important and most obvious
ones are type of material, gap size, and amplitude and frequency
of the electric field. These are all part of the basic theory as described
above. Apart from these there are other more or less important factors.
The supply of primary electrons does not effect the theoretical
threshold, which can be determined with methods described earlier in
this thesis. Nevertheless, a weak source of seed electrons can result in
an apparent higher threshold during testing. In a typical test setup for
determination of the breakdown amplitude, an electric field is applied
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