Environmental Engineering Reference
In-Depth Information
6.2.2
Trapped Ions of Low-Density Plasma in a Particle Field
In an ionized gas of low density along with ion trajectories that correspond to ion
capture by the particle surface and free trajectories that correspond to ion removal,
capture of ions in closed trajectories is of importance for screening of the particle
field [77]. These trajectories are different for the Coulomb (Figure 6.3) and screened
Coulomb (Figure 6.4) fields [70, 78]. In the case of the Coulomb field, a captured
ion moves along the same elliptic orbit after each period, whereas for the screened
Coulomb field the elliptic orbit of the ion rotates after each period. Formation of
trapped ions results from the resonant charge exchange process
A
C
C
!
A
A
C
,
A
C
(6.41)
where
A
represents one of colliding particles. In analyzing of the behavior of
trapped ions, it is of importance that the cross section of resonant charge exchange
σ
res
exceeds significantly that of elastic ion-atom scattering, and therefore an ion
and an atom involved in this process move along straight trajectories [79, 80]. The
parameters that determine the subsequent ion behavior are given in Figure 6.5
and include
R
, the point where this process takes place,
ε
, the atom energy at this
Figure 6.3
Trajectories of motion of a captured ion in the Coulomb field of the particle.
Figure 6.4
Trajectories of motion of a captured ion in a screened particle field.
