Physics of Nonthermal Plasmas - Nonthermal Plasma Chemistry and Physics - page 122

energies at the wall or the target surface. The density of chemically active free radicals
and dissociation products is comparatively high caused by the shape of the electron
energy distribution function (EEDF) with a high concentration of electrons in the
higher energy range. The EEDF is more a Maxwellian than the EEDF in a low-
frequency plasma [81-83]. Microwave discharges can be generated in closed or open
structures or on a plasma resonance [84]. In the low-pressure regime the ignition and
sustaining of a microwave discharge can be supported by magnetic fields.
A simple kind of plasma generation by microwaves is achieved by the coupling
of the discharge tube with a rectangular waveguide (Figure 3.45). An example for
plasma generation in open configurations is the slow wave structure (Figure 3.46),
Magnetron
Waveguide
rectangular
Discharge tube
FIGURE 3.45 Coupling of discharge tube with a rectangular wave guide.
Discharge tube
Slow wave
structure
Microwave
FIGURE 3.46 Microwave plasma generation by a slow wave structure. (From Bosisio, R.G.
et al., J. Phys. E Sci. Instrum ., 6, 628, 1973.)