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

only model, the inclusion of ionisation and thermal spread leads to a
decreased threshold with increasing pressure.
Thresholds as in Fig. 3.7 can be found for all impact velocities between
W1 and W2 and by constructing the envelope of all these curves
for each order of resonance, the complete, classical multipactor zones can
be found for a given pd-product for each zone. This is done in Fig. 3.8,
which shows the complete zones for three different pd-values. The drawback
with this chart is that the model does not account for the hybrid
zones and thus the right boundary of each zone will not accurately reflect
the true multipactor threshold for those fd-values. The model can,
however, be extended to include also the hybrid modes, but due to the
increased complexity, this is left as future work
Voltage [V]
10 3
10 2
pd=10 Pa mm
10 0
pd=4 Pa mm
Frequency−Gap product [GHz⋅mm]
pd=2 Pa mm
Figure 3.8: Multipactor susceptibility zones in low pressure argon (solid lines)
together with vacuum zones (dotted lines) for comparison. Parameters
used are: W1 = 23 eV, W2 = 1000 eV, W0 = 3.68 eV,
σse,max(0) = 3 and ɛ0 = 0.
3.2.4 Key findings
Among the main results is that the friction force dominates the low
pressure multipactor threshold for materials with a low first cross-over
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