Equilibrium (or LTE) plasmas are characterized, deriving thermodynamic, transport properties and equilibrium composition, in a wide range of pressure and temperatures, ranging from technological applications to planetary atmospheres and stellar plasmas.
Thermodynamics and Transport in Equilibrium Plasmas
Thermodynamic properties and equilibrium chemical composition of complex gas mixtures (Earth, Mars and Jupiter atmospheres) have been calculated in the framework of the statistical thermodynamics, exploiting a fast and stable algorithm for the solution of the chemical equilibrium composition with the hierarchical approach. A simplified model, the two-level approach, to calculate partition functions and thermodynamic properties of atomic species has been proposed, reducing the number of the true atomic states in few virtual levels through a grouping procedure.
Transport coefficients (thermal conductivity λ, viscosity η and electrical conductivity σe) for plasmas generated in the impact of space vehicles on different planetary atmospheres (Earth, Jupiter, Mars), have been derived, in the framework of the Chapman Enskog theory, considering a high-order approximation and including also minor species. The core of the calculation is represented by the characterization of binary interactions, i.e. the derivation of collision integrals, describing the microscopic dynamics. The phenomenological approach has been proposed and validated for a number of different systems, that is based on modeling the average interparticle interaction with a phenomenological potential, whose parameters can be estimated through correlation formulas from physical properties of the collisional partners. Moreover a novel efficient algorithm has been implemented based on fractal integration.
The web-access computational tool EquilTheta, that calculates chemical equilibrium product concentrations, thermodynamic and transport properties for a given mixture in wide temperature and pressure ranges, is the focus of a business plan for the creation of a CNR-UniBAS spin-off.
The thermodynamic properties and the electrical conductivity of non-ideal, high-density hydrogen plasma have been investigated, accounting for quantum effects due to the change in the energy spectrum of atomic hydrogen when the electron-proton interaction is considered embedded in the surrounding particles. High-density conditions have been simulated assuming a simple confined-atom model, with the atom fixed in the centre of a spherical box, or atomic hydrogen subject to a screened Coulomb potential.
Laser induced plasma, LIP, is a technique of growing interest in different fields such as material processing, diagnostic, chemical analysis and space applications (Mars Curiosity Rover). Theoretical investigations have been dedicated to verify the assumption of local thermodynamic equilibrium (LTE), commonly considered for calibration-free LIBS.
- titanium laser-induced plume expansion
Nanosecond laser pulsed have been used to evaporate metal and metal oxides, in different environments, such as vacuum chamber, free air and water, in this last case also simulating the bubble dynamics. The role of chemical reactions in the dynamics of plume expansion has been investigated under different assumptions, such as LTE, free flow (without reactions) and chemical kinetics.
- collisional-radiative (CR) model of aluminium-laser induced plasma
A deeper analysis can be carried out by considering a collisional radiative model for atomic metals, using experimental values of plume parameters such as pressure and temperature.
- electron and phonon dynamics in metals
A similar approach can be used to investigate electron and phonon gas in a solid hitted by a fs laser pulse, exciting the electrons, which relax in ps range exchanging energy with the phonon-lattice.
Fluctuations in Gases and Plasmas
Fluctuation theory describes fundamental plasma processes and also provides expressions for the spectral densities of fluctuating plasma quantities as function of the averaged distribution function. This particular outcome of the fluctuation framework constitutes the basis of a number of independent diagnostics that can be implemented in diverse plasma environments. While fluctuation theory is rigorous for collisionless fully ionized plasmas, there exist regimes where approximate methods have to be invoked. Numerical experiments, which are performed by mean of Molecular Dynamics simulations, allows us to explore such regimes which are intractable by the analytical approach.
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