The general objectives of recent work at GAPHYOR were the evaluation of pertinent atomic data based on experimental and theoretical studies, mainly of rare gas atoms and ions, and the use of those atomic data in plasma diagnostics and modeling applications. Plasma spectroscopy of Ne, Ar and Xe was carried out in various devices and conditions including a hollow cathode device available at the University of Ioannina, Greece, the DIVA reactor in LPGP, the WEGA stellarator of the IPPG of Greifswald, various plasma thrusters, and a beam-foil experiment specially conceived for the VUV region in IPNAS, Liège. The spectra were analyzed with line identification codes developed ‘ad hoc’ and compared with results from the GAPHYOR Collisional-Radiative (C-R) model. Systematic calculations and evaluations were carried out for atomic data pertaining to Ne, Ar and Xe atoms and their low ionization stages, which were used in the C-R models for diagnostics and modeling of plasmas of fusion interest.
Recent evaluations concerned the following:
(1) Structure and transition probabilities (Aij), which are important in optical diagnostics of emission lines of plasmas. Generation of a huge number of Aij is necessary for the complete C-R models. In evaluating these Aij we compare results calculated using mainly the following theoretical methods:
- Our Coulomb approximation code (CbA)
- The Cowan Atomic Structure (CATS) code of LANL
- The Superstructure (SST) code, installed in Meudon observatory
- The MCDF GRASP code available in the IAPCM of Beijing
Calculations II and III were carried out using different sets of configurations; we occasionally compared with results from IV, which describe the relativistic effects explicitly. Comparisons with the small number of available experimental data have also been made.
(2) Electron Collision Excitation Cross Sections (σEe) calculations and their corresponding Rate Coefficients (αEji) for various distribution functions. Special care was given to the αEji values because the theoretical spectra obtained by C-R models depend strongly on the accuracies of both transition probabilities and electron collision excitation data. We focused on the special case of electron impact excitation cross sections from the ground 2,3,5p and 3,4,6s transitory and metastable levels of the neutral Ne, Ar and Xe to the lowly excited levels of these three atoms. This work is now underway for argon and neon. In evaluating these σEe results calculations using the following theoretical methods were compared.
- Distorted Wave (DW) approximation using the Los Alamos ACE codes
- First Order Many Body Theory (FOMBT), also with the ACE code, especially near the threshold
- Quasi-classical evaluations following numerical solutions of the few body problem
- The semi-empirical formula introduced by H.W. Drawin, as adapted by K. Katsonis for the rare gas atoms
Calculations V and VI were carried out using different sets of configurations and the resulting cross sections compared. The comparisons of methods VII and VIII, which are based on experimental energies and on transition probabilities calculated with the Coulomb approximation, with NIST values, when available, are often satisfactory over the entire energy range and especially near threshold.
(3) Extension of the applicability of our ‘zero-dimension’ codes to treat the bulk of the plasma state and properties calls for their coupling with detailed kinetic codes such as EIRENE. Simplified C-R models of Ar and Ne, based on averaged structures of the atoms/ions, are under development.