Environmental Engineering Reference
In-Depth Information
Figure 1.3
Electron and gas temperatures of laboratory plasmas. The straight line corresponds
to an equilibrium plasma, whose electron and gas temperatures are equal.
takesplaceingasdischargeswhenanionizedgasisplacedinanexternalelectric
field. Moving in this field, electrons acquire energy from the field and transfer it
to the gas. As a result, the mean electron energy may exceed the thermal energy
of neutral particles of the gas, and they can produce the ionization which is nec-
essary for maintaining an electric current in the system. Thus, a gas discharge is
an example of a plasma which is maintained by an external electric field. If the
temperatures of electrons and neutral particles are identical, the plasma is called
an equilibrium plasma; in the opposite case, we have a nonequilibrium plasma.
Figure 1.3 gives some examples of equilibrium and nonequilibrium plasmas.
Thus, a plasma as a physical object has specific properties which characterize
it. Because of the presence of charged particles, various types of interaction with
external fields are possible and these lead to a special behavior of plasmas which is
absent in ordinary gaseous systems. Furthermore, there are a variety of means for
generation and application of plasmas, and these will be considered below.
