7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Collisional-radiative modeling for plasma population kinetics and spectroscopy
Yuri Ralchenko
National Institute of Standards and Technology, Gaithersburg, MD 20899, USAe-mail: yuri.ralchenko@nist.gov

The modern diagnostics of terrestrial and astrophysicalplasmas are based on variety of techniques. Particularly
important is the spectroscopic plasma diagnostics that isbased on measurements and analyses of line andcontinuum spectra in emission and absorption, line
intensity evolution, spectral line shapes and shifts and soon. These physical quantities may be very sensitive tocrucial plasma parameters such as particle densities andtemperatures, distributions of electromagnetic fields,
deviations from equilibrium (Maxwellian) energy
distributions of collisional partners, opacities, anisotropyof collisions, to name a few. To this end, a trustworthy
calculation of the radiation generated from plasmas
becomes a crucial task for reliable spectroscopic
diagnostics of diverse plasmas.
Such calculations involve different levels of complexity
depending upon plasma conditions. For dense plasmas inequilibrium, the simple Local Thermodynamic
Equilibrium (LTE) model may be well applicable. For theoptically thin LTE case, it only requires level energies,
their statistical weights, and the radiative transition
probabilities to generate complete spectra. For dilute
plasmas in equilibrium, the Coronal Equilibrium (CE)may provide reasonable results; however, it needs large
amounts of collisional data. The most general approachfor simulation of plasma emission is based on thecollisional-radiative (CR) model that attempts at accountof all major physical processes affecting populations ofatomic states (levels). These processes typically include
collisions with electrons (e.g., excitation, deexcitation,ionization;
3-body,radiativeanddielectronic
recombination), radiative processes (spontaneousemission, photoabsorption for opaque plasmas), and nonradiative processes (autoionization). For some plasmas,
other effects such as charge exchange with fast neutrals orother collisions with heavy particles may need to be added.
CR models typically require extensive sets of basic atomic
data (e.g., cross sections or rate coefficients for collisions)to be calculated with the state-of-the-art atomic structure
and collision codes.
In this talk we will present an overview of the modern
methods and techniques for CR modeling (see, e.g., Ref.
[1]). Special attention will be given to the atomic data
production and quality required by modern CR codes.
Over the recent years, a number of sophisticated atomicstructure and collision codes were developed that allow
CR modelers to quickly and reliably generate large sets ofquality data. Those may include energy levels, radiativeand autoionization transition probabilities, electron-impact cross sections and rate coefficients, heavy-particle
cross sections, and so on. The generated atomic data canthen be benchmarked against the available online
databases of evaluated and recommended data (e.g., theNIST Atomic Spectra Database [2]).
The examples of CR simulations in this presentation
will include several cases emphasizing the flexibility anduniversality of the CR approach. We will present theanalysis of x-ray/EUV spectra from highly-charged highZ ions produced in non-Maxwellian plasmas of electron
beam ion traps. Then, a CR model for the motional Stark
effect diagnostics in magnetic fusion devices will beoutlined [3]. Due to the induced electric field, this model
is built using parabolic rather then more common
spherically-symmetric atomic states which requires anovel approach to calculation of atomic data. Then, therecent results of simulations for the charge exchange
recombination spectroscopy in the hot plasma of ITER
(see fig. 1 below) will be discussed as well [4].

Figure 1. Comparison of the simulated spectra in thevisible range with and without neutral beam injection [4].
References[1] Modern Methods in Collisional-Radiative Modeling ofPlasmas, ed. by Yu. Ralchenko, Springer, 2016.
[2] A. Kramida, Yu. Ralchenko, J. Reader and the NISTASD Team, (2022). NIST Atomic Spectra Database(v.5.10), Available at: https://physics.nist.gov/asd[3] O. Marchuk et al, J. Phys. B 43, 011002 (2010); I.
Bespamyatnov et al, Nucl. Fusion 53, 123010 (2013).
[4] Dipti et al, Plasma Phys. Contr. Fusion 63, 115010(2021).