A common approach to the achievement and sustainment of fusion reactions involves conditions in which the fuel mixture exists in a plasma state. Such a state of rapidly moving ions and electrons provides for extensive scattering due to Coulomb force effects. These are particularly important because they lead to kinetic energy variations amongst particles, and more importantly, to particle losses from the reaction region thereby affecting the energy viability of the plasma.

3.1 Collisional Processes

Collisions between atomic, nuclear, and subnuclear particles take many forms. The important process of fusion between light nuclides represents a "discrete" inelastic process of nucleon rearrangement in which the reactants lose their former identity. In contrast, Coulomb scattering among ions and electrons causes "continuous" changes in direction of motion and kinetic energy. All these phenomena occur in a plasma to a varying extent and are therefore important in all confinement devices.

There may also exist a need to describe other selected collisional events in a fully or partially ionized medium, requiring therefore that the distinguishing characteristics of various processes be identified. Among these we note atomic processes such as photo-ionization, electron impact excitation, fluorescence, charge transfer and recombination, among others. Nuclear processes include inelastic nuclear excitation, nuclear de-excitation and elastic scattering.

A commonly occurring and important type of collision in a plasma is charged particle scattering attributable to the mutual electrostatic force. Such Coulomb scattering can vary from the most frequently occurring small-angle "glancing" encounters due to long-range interactions, up to the least likely near "head-on" collisions. The Coulomb scattering probability for ions is much larger than that to undergo fusion. Note that the deflections encountered in scattering reactions may lead to significant bremsstrahlung radiation power losses which lower the plasma temperature.

In general, the complete analysis of charged particle scattering is physically complex and mathematically tedious. As a consequence, we chose here to employ selected reductions in order to convey some of the essential and dominant features of specific relevance for our purposes here.