Modelling the electron temperature characteristic for discharges in electronegative recombination dominated gases

A model is developed for recombination dominated electronegative plasmas which allows the electron temperature (T-e) to be related to the similarity variable pressure x plasma dimension(pl). It is based on four relationships: (i) T-e > T-ec where T-ec is given by equating ionization and attachment rates; (ii) a relationship between the rate coefficients for ionization, attachment and recombination (k(iz), k(att) and k(rec)) and the central negative ion/electron density ratio alpha0 drop n(n0)/n(e0) set by the ion fluxes at the centre; (iii) a relationship between the attachment and recombination rates, k(att) and k(rec), the electronegativity, alpha (0), and X-0, the fractional size of the central negative ion-positive ion plasma, obtained by integrating the negative ion flux; and (iv) a plasma balance equation between the generation and loss rates and pL, effectively the integral of the positive ion flux. Since the underlying equations are nonlinear it is necessary to introduce another parameter. This is chosen to be the ratio of the central electron density (n(e0)) to the gas density (n(g)). Detailed results are given for chlorine and comparison is made with simulation and experiment in that, and other, gases. The paper brings into correspondence two different recent analytical/computational approaches to the subject.