Recombination and energy balance in a decaying plasma I. H—H+— e plasma

The thermal economy of a decaying H — H+ — e plasma is discussed in detail, particular attention being paid to a plasma which is magnetically confined so that only the atoms can strike the containing walls. It is pointed out that the relaxation times for the temperatures, Te and Ti of electrons and ions are commonly shorter than the relaxation times for the number densities, n(c) and n(1), of electrons and atoms, so that as the plasma decays these temperatures fall through quasi-equilibrium values. The quasi-equilibrium Te and Ti and the corresponding collisional-radiative recombination coefficient a are calculated for a wide range of optically thin and optically thick plasmas. A comparison is made with the experimental data of Hinnov & Hirschberg (1962). Satisfactory agreement is obtained. Very dense plasmas in which ionizing collisions are important are briefly considered.