Novel theoretical approaches in Thomson laser scattering measurements in weakly nonideal, collisional and inhomogenous arc plasma jets

In this thesis we present a novel analysis of the Thomson scattered light from arc plasma jets. This analysis goes beyond the standard random phase approximation (RPA) for plasmas that are weakly non-ideal and collisional. Since these plasmas are characterized by a low number of electrons in the Debye sphere, the usual approach of assuming that each charged particle is surrounded by a well defined screening cloud is questionable. In addition, frequent electron-ion collisions may alter the form for the dynamic structure factor in a more fundamental way than the commonly used Bhatnagar-Gross-Krook (BGK) approximation could predict. Indeed, the failure of the RPA and the BGK approximations in the interpretation of the light scattered data in thermal plasma jet is reported. The novel suggested approach is based on a memory function formalism (MFF) for the spectral density function, which is used to describe the spectrum of the scattered light under a wider range of conditions than the RPA or the BGK approximation. The MFF technique is constructed on a series expansion which preserves the three lowest order frequency-moment sum rules. Simplified forms for these sum rules are introduced in the linear Debye-Huckel (D-H) limit. Possible extensions to the non-linear D-H limit are also discussed and compared with molecular dynamics simulations. In addition, corrections to the proposed form for the sum-rules in highly inhomogeneus systems are derived.; Experimental results from arc plasma jets at different operating conditions are then compared with the MFF theory. With this approach self-consistent values for the electron temperature and density in arc plasma jets are obtained. Electron temperature values are compared with a series of spectroscopic measurements that we have performed on the same plasma. Results show that spectroscopic temperatures are lower than the temperatures obtained with Thomson scattering at the same plasma conditions, suggesting a possible departure from the condition of local thermodynamic equilibrium (LTE). A particle heating model is used to explain such a departure from LTE in terms of three-body electron-ion recombination reactions.; Finally, the experimental techniques developed here are used to study the formation of large-scale hydrodynamic instabilities in the jet.