As was discussed in Chapter 1, collisions do not play as central a role in plasmas as they
do in conventional neutral gases. Indeed, relatively hot, diffuse plasmas are essentially collisionless.
Probably the most significant effect of collisions is that they act to relax particle distribution functions toward Maxwellian
distributions. (See Section 3.11.) The aim of this chapter is to develop a theory of collisions that is applicable to a weakly coupled plasma.
The fact that the plasma in question is weakly coupled (i.e., the Debye length greatly exceeds
the distance of closest approach of colliding particles, which also implies that the mean-free-path between collisions greatly exceeds the Debye length) means that it is a good approximation to treat the collisions as occasional binary events. (See Sections 1.6 and 1.7.)
As we shall see, the long-range nature of the Coulomb force renders the theory of collisions in a plasma
significantly different from the corresponding theory for a neutral gas (where the inter-particle forces are invariably short-range in nature).
