Composition of homogeneous quasi-stationary nitrogen arc plasma by collisional–radiative model

Abstract

A collisional–radiative model (CRM) is developed to study nitrogen arc plasma. The model is based on solution of the rate equations of ν species chosen for the study. The species chosen are: electrons e, atomic ions N + , atoms N, diatomic molecules N 2, and molecular ions N 2 + , we have then ν=5 species. The CRM is applied to homogeneous and quasi-stationary state (HQSS) plasma for electron temperature T e upto 12 000 K. All heavy particles are assumed to have the same kinetic temperature T g such that T g = T e , this means the temperature of the all five species is identical and is called plasma temperature T. The total pressure of the plasma is considered between 1 and 4 atm. The plasma composition is calculated taking into account all significant collisional and radiative mechanisms. The local effect of radiation absorption is described by the optical escape factors Λ j and Λ jk for free–bound and bound–bound transitions. Results show significant deviation from local thermodynamic equilibrium (LTE). It was also shown that the plasma pressure p has a strong influence on deviation from LTE. To assess the relative speeds of recombination reactions in nitrogen arc plasma we have calculated the relaxation time τ (or time constant) as a function of temperature.