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The approach, which was developed earlier for modeling chemical reactions in laser induced plasmas, is applied to radio-frequency discharge plasmas. The model is based on the assumption that all ionization processes and chemical reactions are at local thermodynamic equilibrium. A chemical composition of an argon-hydrogen plasma with an Addition of boron trichloride is studied as a function of plasma temperature and mole ratio H2∕BCl3. It is established that more than twenty simple and composite molecules and ions can be formed in the course of chemical reactions. The results are compared with those obtained earlier by means of another equilibrium model that uses ab-initio quantum chemical computations of thermochemical and kinetic data and a 0D thermochemical quilibrium solver.
Laser induced plasma (LIP) is a dynamic, short living event which presents significant difficulty for modeling. In this report, a collisional-dominated chemical model developed earlier* is expanded by the inclusion of a new method for calculation of chemical reactions. The model consists of the coupled Navier-Stokes, state, radiative transfer, material transport, and chemical equations. The latter are written in terms of atomic and molecular partition functions rather than reaction rates. Typically, a solution of such the system of chemical equations is difficult for the entire range of plasma temperatures and densities because reaction constants may vary by hundreds orders of magnitude owing to extreme plasma conditions. No numerical solver of non-linear systems of equations handles this situation with ease. We resolve the problem by using a hierarchical approach. First, we rank the reactions according to their ascendancy. Second, we exploit either the contraction or Newton-Raphson algorithms to solve the system of chemical equations. We illustrate the approach by performing a series of calculations for reacting species Si, C, N, Ca, Cl and their molecules in laser induced plasmas.
This course will provide an introduction to plasma diagnostic techniques. The major focus of the course will be on the discussions of the practical procedures as well as the underlying physical principles for the measurements of plasma fundamental characteristics (e.g., temperatures, thermodynamic properties, and electron number density). Particular emphasis will be placed on inductively coupled plasma–atomic emission spectrometry, but other analytical plasmas will also be used as examples when appropriate. Selected examples on how one can manipulate the operating conditions of the plasma source, based on the results of plasma diagnostic measurements, to improve its performance used for spectrochemical analysis will also be covered. Topics to be covered include thermal equilibrium, line profiles, temperatures, electron densities, excitation processes, microreactions, pump and probe diagnostics, tomography, temporal and spatial resolution. Basis of plasma computer modeling will be presented.
A collisional-dominated model of a laser induced plasma will be presented which includes the coupled Navier-Stokes, state, radiative transfer, and material transport equations and incorporates plasma chemistry through the equilibrium approach based on the use of atomic and molecular partition functions. Simple chemical systems are modeled including ablation of Si, C, SiC, CaCl2 in N2 or Ar atmospheres with the formation of molecules N2, C2, Si2, CN, Cl2, SiN, SiC, CaCl, CaCl2 and their corresponding positive and negative ions. The model is used to study evolution of number densities of atomic and molecular species in the expanding plasma plume. The distribution is compared to experimental observations obtained by optical imaging and tomography. The model and experiment serve to elucidate mechanisms of molecular formation in LIPs, the topic which has recently received much attention in the LIBS community.
A collisional-dominated model of a laser induced plasma will be presented which includes the coupled Navier-Stokes, state, radiative transfer, and material transport equations and incorporates plasma chemistry through the equilibrium approach based on the use of atomic and molecular partition functions. Simple chemical systems are modeled including ablation of Si, C, SiC, CaCl2 in N2 or Ar atmospheres with the formation of molecules N2, C2, Si2, CN, Cl2, SiN, SiC, CaCl, CaCl2 and their corresponding positive and negative ions1,2. The initial conditions are specially chosen to emulate the plasma state on the onset of expansion just after the laser pulse had ended.
The model is used to study evolution of number densities of atomic and molecular species in the expanding plasma plume. The distribution is compared to experimental observations obtained by optical imaging and tomography. The model and experiment serve to elucidate mechanisms of molecular formation in LIPs, the topic which has recently received much attention in the LIBS community.