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

creasing ratio Ri/Ro was observed. It was also found that the first multipactor
zone became narrower for decreasing Ri/Ro. This behaviour
was seen in the analytical analysis and it is evident also in the PICsimulations.
Figure 5.16 shows the result of a simulation for Z = 174 Ω
(Ro/Ri = 18.26). The agreement between simulations and experiments
is good. The multipactor zone becomes narrower and the threshold increases.
The position of the zone is slightly shifted compared with the
experimental data and the reason for this deviation may partly be explained
by an inaccuracy of the dimensions of the copper electrodes.
The main reason, however, seems to be related to the SEY-model and
the description of the initial velocity of the secondary electrons, but a
more detailed study will be necessary to settle this matter.
log 10 (Amplitude) [V]
3.2
3
2.8
2.6
2.4
2.2
2
1.8
−1.6 −1.4 −1.2 −1 −0.8 −0.6
log (Frequency) [GHz]
10
Figure 5.16: Ratio of power deposited on the inner and outer conductors
due to electron impacts (log-scale) for the same parameters and
SEY-formula as in Fig. 5.15 except that Ro/Ri = 18.26.
In the section summarizing the main findings of the analytical part,
it was mentioned that no single-sided multipactor was noted in the experiments.
This is in agreement with the PIC-simulations and shows
that no measurements were made at high enough voltage and frequency,
where single sided multipactor would be the main phenomenon (the dark
blue regions in Fig. 5.16).
90
0
−0.5
−1
−1.5
−2
−2.5
−3
−3.5
−4
−4.5