The present paper describes a Monte Carlo code to simulate the cascade of electron-hole pairs and phonons generated when a low-energy X-ray photon is absorbed by a material. The model has been applied to study the response to UV or soft X-ray radiation of diamond and silicon, focused on the case of two-layer material made of diamond film grown on silicon. Typically the statistical distribution of the electron-hole cascade is macroscopically parameterized by the mean energy required to create an electron-hole pair W and the Fano factor F. The results for the pure materials are in agreement with the values present in the literature. Moreover we found an enhancement of the Fano factor and a super-Poissonian behaviour of the statistical distribution of the pairs, typical of correlated systems.

The paper presents three collisional-radiative models developed to investigate non-equilibrium chemistry andradiation in hypersonic shock tubes operating with different planetary atmospheres. An hybrid collisional-radiative model,employing the state-to-state kinetics of electronically excited states of molecules and the multi-temperature approximationfor the vibrational degree of freedom is presented first, and applied to the numerical rebuilding of experimental shock tubeemission spectra. Next, an hybrid collisional-radiative model for ionized air is presented. This model consider the state-tostateapproach for electronic states of atoms and the multi-temperature model for the vibrational populations of diatomicmolecules in their ground electronic state. A radiative transport equation is also solved to determine radiative source termsin the kinetic scheme and the enthalpy production due to radiation. The third model considers the state-to-state collisionalradiativemodel of Jupiter's atmosphere, self-consistently coupled with the Boltzmann equation for free electrons and theradiative transfer equation for the radiation transport in one-dimensional slab geometry.

An approximate method for calculating the electronic partition functions of atomic systems is reported. The method is based on the idea of combining a multitude of atomic energy levels into two or three grouped levels. Dimensionless formulation suitable for practical calculations is presented. Application to real systems shows that two grouped levels are enough to model hydrogen-like and noble gas atoms, whereas three grouped levels are required to describe atoms with low lying excited states. Two methods for the calculation of degeneracy and energy values of the grouped levels are investigated. Representative mono-atomic LTE plasma properties calculations are reported. The results agree with accurate computations using partition functions that include several thousands energy levels.

A collisional-radiative model (CRM) of a plasma composedof H2, H+2 , H, H+, He, He+, e?, is appliedto study the relaxation processes behind an hypersonicshock wave under conditions reproducing an atmosphericentry in Jupiter's atmosphere. The CRM is coupled witha Boltzmann equation solver, for the determination of theelectron energy distribution function, and with a radiativetransfer equation for calculating the specific intensityIn , radiative rate coefficients and radiative energy transferin one-dimensional slab geometry. The model predictshighly non-equilibrium electron and atomic distributionsas well as strong reabsorption of atomic radiationin the post-shock region. A comparison among distributionsobtained using optically thick and optically thinplasma approximation against the fully coupled calculationis also presented.

An advanced self-consistent plasma physics model including non-equilibrium vibrational kinetics, a collisional radiative model for atomic species, a Boltzmann solver for the electron energy distribution function, a radiation transport module coupled to a steady inviscid flow solver and, has been applied to study non-equilibrium in high enthalpy flows for Jupiter's atmosphere. Two systems have been considered, a hypersonic shock tube and nozzle expansion, emphasizing the role of radiation reabsorption on macroscopic and microscopic flow properties. Large differences are found between thin and thick plasma conditions not only for the distributions, but also for the macroscopic quantities. In particular, in the nozzle expansion case, the electron energy distribution functions are characterized by a rich structure induced by superelastic collisions between excited species and cold electrons.

Non-equilibrium effects in hydrogen plasmas have been investigated in different systems, ranging from RF plasmas to corona discharges. The existing measurements of vibrational and rotational temperatures, obtained by different spectroscopical techniques, are reported, rationalized by results calculated by kinetic models. Input data of these models are discussed with particular attention on the dependence of relevant cross sections on the vibrational quantum number. Moreover, the influence of the vibrational excitation of H(2) molecules on the translational distribution of atoms in ground and excited levels is shown. Finally, a collisional radiative model for atomic hydrogen levels, based on the coupling of the Boltzmann equation for electron energy distribution function (EEDF) and the excited state kinetics, is presented, emphasizing the limits of quasi-stationary approximation. In the last case, large deviations of the EEDF and atomic level distributions from the equilibrium are observed.

A zero-dimensional collisional-radiative (CR) model, coupled self-consistently with the electron Boltzmann equation, has been applied to the description of a metallic-laser induced plasma at experimental conditions typical of LIBS experiment. To take in account expansion effects, the experimental temperature and total number density as function of time have been used as input data. Plasma composition and the simultaneous time evolution of both heavy particle level distributions and the electron energy distribution function have been calculated by taking into account the most relevant collisional and radiative processes. This approach estimates the hierarchy of the elementary processes during the expansion and possible deviations from LTE conditions. The comparison of the experimental and theoretical results shows a good agreement, but at the same time new questions arise on the analysis of spectroscopic results and on the assumption generally made in LIBS.

The Two-Level Distribution (TLD) model has been improved for extension to air kinetics. The model is based on the evidence that rate coefficients are strictly correlated to the tail of the vibrational distribution rather than to vibrational temperature. TLD model reproduces, with high accuracy and low computational resources, the results obtained using detailed State-to-State (STS) kinetics. © 2012 American Institute of Physics.

A model to predict the emissivity and absorption coefficient of atomic hydrogen plasma is presented in detail. Non-equilibrium plasma is studied through coupling of the model with a collisional-radiative code for the excited states population as well as with the Boltzmann equation for the electron energy distribution function.

The space exploration is nowadays assisted by realistic modeling of re-entry conditions of space vehicles in planetary atmospheres, for the design of thermal protection systems. The detailed kinetic modeling relies on the accurate description of elementary process dynamics, including the role of the excitation of the internal degrees of freedom of chemical species. Efforts in the construction of a complete and consistent dynamical information are presented, focusing on hydrogen plasmas relevant to the Jupiter atmosphere. Examples of numerical experiments are given, emphasizing the relevance of the adopted state-to-state approach in reproducing the onset of non-equilibrium internal distributions governing the plasma system evolution. © Springer-Verlag 2011.

The space exploration is nowadays assisted by realisticmodeling of re-entry conditions of space vehicles inplanetary atmospheres, for design of thermal protection systems.The detailed kinetic modeling relies on the accuratedescription of elementary process dynamics, including therole of the excitation of the internal degrees of freedom ofchemical species. Efforts in the construction of a completeand consistent dynamical information are presented, focusingon hydrogen plasmas relevant to the Jupiter atmosphere.Examples of numerical experiments are given, emphasizingthe relevance of the adopted state-to-state approach inreproducing the onset of non-equilibrium internal distributionsgoverning the plasma-system evolution.

A state-to-state model of H-2/He plasmas coupling the master equations for internal distributions of heavy species with the transport equation for the free electrons has been used as a basis for implementing a multi-temperature kinetic model. in the multi-temperature model internal distributions of heavy particles are Boltzmann, the electron energy distribution function is Maxwell, and the rate coefficients of the elementary processes become a function of local temperatures associated to the relevant equilibrium distributions. The slatedo-state and multi-temperature models have been compared in the case of a homogenous recombining plasma, reproducing the conditions met during supersonic expansion though converging-diverging nozzles.

State-to-state non-equilibrium plasma kinetics is widely used to characterize cold molecular and reentry plasmas. The approach requires a high level of dynamical information, and demands a large effort in the creation of complete databases of state-resolved cross sections and rate coefficients. Recent results, emphasizing the dependence of elementary process probability on both the vibrational and rotational energy content of the H2 molecule, are presented for those channels governing the microscopic collisional dynamics in non-equilibrium plasmas, i.e. electron-impact induced resonant processes, vibrational deactivation and dissociation in atom-diatom collisions and atomic recombination at the surface. Results for H2 plasmas, i.e. negative ion sources for neutral beam injection in fusion reactors, RF parallel-plate reactors for microelectronics, atmospheric discharges and the shock wave formed in the hypersonic entry of vehicles in planetary atmosphere for aerothermodynamics, are discussed.

In this paper, the absorption coefficient and emissivity of non-equilibrium atomic hydrogen plasma have been calculated in the case of a steady state shock wave. For this purpose, the atomic level population profiles along the shock wave have been calculated using a collisional-radiative model coupled with the electron Boltzmann equation. The spectral coefficients are in turn the input for solving a one-dimensional radiative transfer equation, which allows to calculate the radiation intensity and radiative flux in the plasma slab. © 2011 American Institute of Physics.

The paper presents radiation models developed to investigate radiation in entry in Earth, Mars and Jupiteratmospheres. The capacity of ASTEROID computing code to simulate elementary radiative processes, calculate spectraland groups optical properties, and also solve simple radiative heat transfer problems is presented for Earth entry. Thelarge number of radiative processes involved in the radiative flux is put forward. The contributions of the differentradiative processes encountered in Mars entry are studied using the HTGR spectroscopic database. The validity of thisdatabase with respect to diatomic molecules systems and CO2 infrared radiation is illustrated through experimentalvalidations. The accuracy of statistical narrow-band model to predict radiative flux is illustrated for an afterbody. Finallyrecent improvements of the model developed for the calculation of radiative properties of high-temperature H2/Hemixtures representative of Jupiter atmosphere is presented. The model takes into account the most important radiativeprocesses.

The possibility of using reduced model, that account for non-Boltzmann vibrational distributions for nitrogen monoxide kinetics has been explored. The basic idea is that the rate coefficients, which are proportional to the tail of the vibrational distribution function, are strictly correlated to reactant density rather than to vibrational temperature, which depend on the low energy distribution. The model consider the rate coefficients as a function of the population of the last vibrational level of the relevant species, which evolution is calculated with a proper kinetic equation. © 2011 American Institute of Physics.

Four different types of macroscopic models developed for the vibration-chemistry coupling in nonequilibriumflows for re-entry applications are presented. First, using an approach based on nonequilibrium thermodynamics, globalrate coefficients of dissociation of N2 and O2 under parent molecular or atomic impact and backward molecularrecombination are determined. Then a Two-Level Distribution (TLD) model is developed, in which a relaxation equationfor vibrational temperature is solved as in the case of multi-temperature models but with the simultaneous solution of akinetic equation, as in the case of state-to-state models, but only for the last vibrational level. In a third approach, a multiinternaltemperature model is presented to describe accurately the vibrational distribution function in using several groupsof levels, within which the levels are assumed to follow a Boltzmann distribution at an internal temperature of the group.This multi-internal temperature model allows us to describe accurately the vibrational energy relaxation and dissociationprocesses behind a strong shock wave. Finally, a rovibrational collisional coarse-grain model is developed to reduce adetailed rovibrational mechanism for the internal energy excitation and dissociation processes behind a strong shock wavein a nitrogen flow.

A collisional-radiative model for hydrogen atom, coupled self-consistently with the Boltzmann equation for free electrons, has been applied to model a shock tube. The kinetic model has been completed considering atom-atom collisions and the vibrational kinetics of the ground state of hydrogen molecules. The atomic level kinetics has been also coupled with a radiative transport equation to determine the effective adsorption and emission coefficients and non-local energy transfer. © 2011 Elsevier B.V. All rights reserved.

In this paper we study non equilibrium level kineticsin a steady shock wave propagating in pure hydrogenplasma. The hydrodynamic description of the shock waveis achieved using the steady state continuity equationstaking into account radiative losses into the energy equation.Spectral properties of the (H, H+, e?) plasmahave been evaluated using a recently developed numericalmodel from the level population output of an advancedcollisional-radiative model which solves a Boltzmannequation for the non-equilibrium EEDF.

A collisional-radiative model for the H2/He plasma, coupled to a Boltzmann solver for the free electron kinetics is used to investigate the non-equilibrium conditions created in the expansion of an high-temperature plasma flow through a converging-diverging nozzle, starting from the steady state composition at T 0 = 10 000 K and p 0 = 1 atm in the reservoir. It is shown that the plasma optical thickness plays a major role on the evolution of macroscopic quantities and internal distributions along the nozzle axis. Structured electron energy distribution functions, characterized by long plateaux and humps, are created due to superelastic collisions of cold electrons and electronically excited atomic hydrogen. The magnitudes of the plateaux are orders of magnitude higher in an optically thick plasma compared with a thin plasma, while the electron-electron collisions play a role in smoothing the peaks created by superelastic collisions between cold electrons and H (n > 2).

Different mechanisms of CO<inf>2</inf> dissociation, in discharge and post-discharge conditions, have been computed by performing a parametric numerical solution of the electron Boltzmann equation as a function of the electric field, the ionization degree and the vibrational temperatures and by considering elastic, inelastic, superelastic and electron electron collisions. Emphasis is given to the role of superelastic electronic and vibrational collisions in affecting the electron energy distribution function and relevant rates. The results show that, at low E/N values, the dissociation rates from pure vibrational mechanism can overcome the corresponding rates of electron impact dissociation. In any case, the electron impact dissociation rates are largely dependent on the transitions from excited vibrational levels.