On the theory of short-wavelength lasers for recombining plasmas

Abstract

This thesis describes a theoretical simulation of the expansion phase of laser-produced plasmas. A set of nonlinear time dependent equations describing the flow of plasma has been solved numerically using Range-Kutta method. The. flow of ions and electrons in the expansion phase was modeled as a homogel}qu expansion, uniform temperatures for electrons and ions. This set of equations help us in the calculation of plasma parameters as a function of time, such. as) plasma density, electrons temperature, ions temperatures, average charge state of plasma ......etc.

Many processes effect on plasma parameters as Collisional i.QJ1i:i\a.tiQf}, Radiative recombination, Dielectronic recombination, and Three:b Cfy recombination (TBR). The most important process in the plasma expansion is three-body recombination, because . TBR release the excess energy of recombination to the plasma electrons, i.e. TBR is a source of heat, hence TBR not only alter the ion composition of the plasma but also is responsible for slowing the decrease of electrons temperature during the expansion phase. For example, in the absence of three-body recombination, from the calculations the • decrease of the electrons and ions temperatures with time t follow a t _, law, whereas, in the presence of three-body recombination the electrons temperature is founded to follow a law that is close tot_,.

The average charge state of the plasma ions has also been calculated during the expansion and was found to decrease with time at a rate that depended on the particle concentration in the initial plasma, decreasing more rapidly as the initial concentration increased. TBR also effect on the average charge state especially in the late time of expansion phase, it cause average charge state frozen in, i.e. Z does not change very much with time. Finally, in our discussion we do a simple comparison between our results and the published theoretical and practical data.