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

Abstract

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 5 3s, 2p 5 3p, 2p 5 3d, 2p 5 4s and 2p 5 4p 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 5 3s, 2p 5 3p, 2p 5 3d, 2p 5 4s and 2p 5 4p states, as well as from the excited state 2p 5 3s to the 2p 5 3p and 2p 5 4p 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 5 4p and 2p 5 3s (J=1 only) to 2p 5 3p 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.

Diagnostics of Ne–Ar mixture plasma using a fine‐structure resolved collisional radiative model

“…The corresponding rates are calculated at the extracted T e values. The rates are obtained by using Equation (2) with our calculated EIE cross‐sections [ 19 ] and the non‐Maxwellian EEDF with x = 1.2 in Equation (3). We can see from Figure 5 that the overall excitation rates from the ground to the 2 p i and 1 s i states are lower than from the 1 s i levels to the 2 p i levels.…”

“…This depopulating channel of metastable atoms is included in the model through the seventh term of the particle balance equation. The diffusion rates were calculated as described in our previous paper of Baghel et al [ 19 ] However, we found the diffusion contributions were not very significant. The last term of the particle balance equation includes quenching of the Ne 1 s i atoms, which is a very significant process in the mixture plasma.…”

“…We have used a complete and consistent set of EIE cross‐sections of Ne from its ground to 1 s i , 2 p i , 3 d i , 3 s i , 3 p i levels and from 1 s i to 2 p i and 3 p i levels for projectile electron energy from 0 to 500 eV calculated by us. [ 19 ] The RDW EIE cross‐sections are in sufficient wide impact energy to account for the respective contributions coming from EIE/de‐excitation processes that affect population‐kinetics of 2 p i and 1 s i levels. The f ( E ) is the EEDF, which has been considered of the following non‐Maxwellian parametric form, [ 26 ] where, …”

“…In this light, our group has produced a consistent dataset of electron impact excitation cross‐sections for many atoms, including inert gases, which have been obtained from the RDW approach. [ 19 ] These cross‐sections are made available through an open‐source LxCat database. [ 24 ] In various modelling and diagnostic studies, these cross‐sections were employed.…”

Electron Impact Excitation of Extreme Ultra-Violet Transitions in Xe7–Xe10 Ions

“…It is clear from the above discussion that most of the previous experimental or theoretical studies on Xe 7+ -Xe 10+ ions have focused on their spectroscopic properties, while the electron impact cross section data are scarcely reported. However, various studies in the past have clearly demonstrated that using accurate cross section results in a collisional radiative model provides a better agreement with the measurements on the plasma parameters, viz., electron temperature and density [17][18][19][20]. Therefore, reliable cross sections are essential for the success of any plasma model.…”