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

accurately describes the cross-section for the entire measurement range
can be given by (cf. Fig. 3.6)
σiz = q1
ln ɛ/ɛi
�
ɛ/ɛi + 0.1(ɛ/ɛi) 2
[m 2 ] (3.23)
where ɛi is the ionisation threshold of argon and q1 = 4.8 × 10 −20 m 2 .
Ionisation Cross Section [m 2 ]
10 −19
10 −20
10 −21
10 −22
Ionisation cross section for Argon
10 2
Electron energy [eV]
S.C.Brown
H.C.Straub
Analytical approximation
Figure 3.6: Ionisation cross-section for electron-argon collisions. The circles
and stars indicate measurement data by S. C. Brown [58] and
Straub et al. [59] respectively and the solid line is an analytical
approximation given by Eq. (3.23).
3.2.3 Multipactor boundaries
In the following section the above model will be used to determine the
multipactor boundaries. The best accuracy is attained when solving
the basic differential equations numerically while using good approximate
formulas for the different parameters. However, such computation
takes very long time, since both the initial and the final multipactor
conditions have to be fulfilled. Faster computation can be achieved
by using different approximations, e.g. constant parameters as shown
in Eqs. (3.10)-(3.12), Eq. (3.13), and Eq. (3.14). Two different implementations
are used in paper C, one purely numerical and one semi-
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