Diagnostics of low-temperature neon plasma through a fine-structure resolved collisional–radiative model

A collisional–radiative (CR) model for low-temperature Ne plasma is developed. Various radiative and collisional processes involving the ground 2p ⁶ and the excited 2p ⁵3s, 2p ⁵3p, 2p ⁵ 3d, 2p ⁵4s and 2p ⁵4p states are considered in the plasma. First, we calculate a complete set of required electron-impact excitation cross-sections of Ne, which is an important process in such low-temperature plasma. We used the relativistic distorted wave (RDW) theory and calculated electron excitation cross-sections for the transitions from the ground 2p ⁶ state to the excited 2p ⁵3s, 2p ⁵3p, 2p ⁵ 3d, 2p ⁵4s and 2p ⁵4p states, as well as from the excited state 2p ⁵3s to the 2p ⁵3p and 2p ⁵4p excited states of the Ne atom in a wide range of incident electron energies from the threshold to 500 eV. The ground and different excited states of the Ne are represented through the multiconfiguration Dirac–Fock wave functions, which are obtained using the GRASP2K code. To ascertain the reliability of the obtained wave functions, we calculated the oscillator strengths for different dipole allowed transitions, and compared them with the available experimental and theoretical results. Further, the calculated detailed RDW cross-sections are presented and compared with the available experimental and other theoretically calculated values. The cross-sections for 2p ⁵ 3s to 2p ⁵4p and 2p ⁵3s (J = 1 only) to 2p ⁵3p are reported for the first time. The complete set of calculated electron excitation cross-sections of different transitions of Ne along with other processes are used to develop the CR model. The model has been applied to the diagnostics of low-temperature Ne plasma by coupling it to the optical emission and absorption measurements of Boffard et al (2012 J. Phys. D: Appl. Phys. 45 382001, and 2009 Plasma Sources Sci. Technol. 18 035017). The extracted values of electron density, electron temperature and the calculated 1s _i level populations have been compared with the corresponding measurements available in the pressure range of 5–25 mTorr and are found to be in excellent agreement. (paper)