No abstract

A simple phenomenological model is established to determine the temporal evolution of spark gap channel radius and electrical conductivity during the resistive phase period. The present determination is based on the Braginskii’s equation for the channel radius which includes the electrical conductivity of the discharge channel as a constant quantity. In the present model, however, the electrical conductivity is regarded as a time varyingquantity. Basing on this, a mathematical formulation for the channel radius as a function of time was derived, and this has made possible the derivation of an explicit expression for the conductivity as a function of time as well. Taking the temporal average of the electrical conductivity offers an alternative mathematical formulation for the instantaneous radius based on a steady conductivity value that can be determined according to some experimental parameters. It has been verified that both of the channel radius formulations mentioned above lead to similar results for the temporal evolution. The obtained results of the channel radius were used to determine the instantaneous inductance of the spark channel. The present model was used to examine the role of gas pressure and gap width on the temporal evolutions of the channel radius, conductivity, and inductance in nanosecond spark gaps.

A theoretical model is developed to determine time evolution of temperature at the surface of an opaque target placed in air for cases characterized by the formation of laser supported absorption waves (LSAW) plasmas. The model takes into account the power temporal variation throughout an incident laser pulse, (i.e. pulse shape, or simply: pulse profile).Three proposed profiles are employed and results are compared with the square pulse approximation of a constant power.

A simple computational model is established to simulate a capacitor discharge process through a spark gap. The model constitutes of three intervals, the first one is concerned with charging the capacitor by a D.C. voltage source, where the voltage across the capacitor raises to a certain critical value regarded as the breakdown voltage of the spark gap. The second interval describes the gap breakdown where the resistance of the ionized gas in the gap decreases very sharply as a result of heating the plasma by the electrical current. This interval is denoted as the resistive phase of the discharge. The third interval describes the discharge through the previously heated plasma in the gap; for this interval the plasma resistance is assumed to have a constant value which is considered as the minimum value obtained at the end of the previous interval (the resistive phase interval). The temporal evolution curves obtained from the model exhibit reasonable trends that conform to the physical situation under study. Also, the comparison made with published data shows an acceptable agreement. The model is employed to perform a parametric comparison to examine the rule of the gap parameters on the voltage and current evolution curves.