C. Georgiades

The inductance of the discharge in a spark gap

The inductance of an arc discharge has been modeled and a mathematical formula given for the arc inductance in terms of its geometrical dimensions. This formula agrees with the experimental results and is used to determine the arc‐channel radius. Inductance measurements have been taken for various values of pressure, interelectrode distance and applied voltage in a triggered spark gap. The dependence of inductance upon these parameters has been explained through the existing variations of the arc‐channel cross section. Two mechanisms are responsible for the variations of inductance. The first is diffusion and the second is the tendency of the current channel to vary diameter with pressure, interelectrode distance, and applied voltage. The time history of the arc‐channel inductance has been investigated. Finally, the ambipolar diffusion coefficient and the total charge number of the arc channel has been obtained.

The influence of the external circuit on arc-discharge of a spark-gap: its application to a pulsed gas laser

An investigation of the influence of the driving circuit on the arc-discharge of a spark-gap takes place in this work. The two most common types of circuits used in pulsed gas lasers have been studied for all possible combinations of capacitance allocation. In these circuits the spark-gap is used as ignition system and participates in the electric circuit through its resistance and inductance. This consideration shows that capacitances act as charge containers and feed the arc-discharge in the spark-gap independently of their positions in the circuit. Their values influence the total charge contained in the arc discharge and this, in its turn, influences the discharge resistance. On the other hand, total charge flows through the discharge at a rate determined by the coupling of the circuit loops, namely, by the circuit type. Thus, circuit type influences the drift velocity and this, in its turn, influences the channel radius, which determines the discharge inductance. >

Electrical discharges investigation in gas-pulsed laser

The electrical discharges which exist in a gas-pulsed laser (ignition system and laser tube) constitute an additional problem to the study of the whole laser system. This is due to their time-dependent behavior during the discharge. An electrical discharge can be symbolized as time-dependent resistance and inductance in the laser electric circuit. The analysis of the circuit is impossible if the resistance and inductance functions in relation to time are not known. This work illustrates a very easy way of finding the resistance and inductance functions in relation to time. This can be achieved by measuring only the waveform of the voltage across the capacitors of the system. By combining this waveform with the differential equation of the system performance, the evolution of the resistance and the inductance in relation to time can be determined. The quantities which can be calculated after that, in relation to time, are the oscillatory frequencies, the damping constants as well as the impedances of the discharges.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electrical characteristics of the discharge in a pulsed gas laser

The resistance and inductance of a laser discharge in a pulsed gas laser are considered theoretically in this paper. The total charge and the dimensions of the discharge volume are responsible for the resistance and inductance of the laser channel respectively. Generally, the inductance increases either decreasing electrode length or discharge thickness, or increasing the interelectrode distance. The direct dependence of the resistance and inductance with the microscopically plasma parameters, total charge and drift velocity, was discovered in this paper through the external driving circuit and especially through its capacitance. The values of the capacitors form the total charge while the coupling of the capacitors in the circuits forms the drift velocity. These are inferred dealing with the two most common circuits used in a pulsed gas laser, namely the doubling circuit and the charge transfer circuit for all possible combinations of capacitance allocation.

Comments on "The time evolution of the resistances and inductances of the discharges in a pulsed gas laser through its current waveforms" [with reply]

Persephonis et al. (see ibid., vol.24, p.1208-14 (1996)) present a method for calculating the time evolution of the resistance and inductance from the measured current and voltage waveforms of a circuit. As it was pointed out by Fridman (1997), from those measurements, it is impossible to obtain a unique time evolution of the resistance and inductance; further hypothesis are needed to solve the problem. In this comment we analyze the results presented in the above paper and find several contradictory features, like violations to the Kirchoffs law. Finally, we stress the fact that during the fast breakdown of a gas gap characterized by large, fast varying values of the resistivity, it is impossible to meaningfully and separately define a resistance and an inductance as lumped parameters of a circuit.The opportunity of definition of the time evolution of the resistance and inductance through the oscillograms of a current and voltage is discussed. It is shown that this problem is not single-valued, and it has a set of solutions. The restrictions are established, which should be in accordance with these solutions. An example of various temporary dependencies of inductance and resistance is indicated, which corresponds to the identical current and voltage oscillograms. The above paper 1 considers a problem of calculation of the time evolution of the inductance and resistance of the pulse discharge channels through oscillograms of the current .I t is a question of high priority, and interests the experimenters studying the high current pulsed discharges. However, methods used in the paper and received results cause a number of objections. 1) In the paper the pulse process in the double electrical circuit (see Fig. 1 of the paper ) is considered, which is described by the following system of differential equations:

The electric behavior of a capacity-transfer-type pulsed gas laser

In the present work the electric behavior of a Capacity-Transfer-Type N2 laser has been studied in relation to storage and peaking capacitors. The results showed that the resistance and inductance of discharges in the ignition system and in the laser chamber vary as the values of the capacitors change. This occurs because the driving circuit, and particularly its capacitances, affect the formation of the two discharges and finally the laser output. The coupling of the two circuit loops is weak and is achieved through laser channel inductance. Finally, the behavior of the laser output versus storage and peaking capacitors is determined from a) the electric energy deposited in the laser channel, as a short pumping pulse and b) the laser oscillation time delay which depends on the upper laser level and the Q factor of the cavity.

Determination of the electrical characteristics of the discharges in a pulsed gas laser through its current waveforms

A method of finding the time dependent resistance and inductance of the discharges in the switch system and laser chamber in pulsed gas lasers is described in the present work. According to this method the current waveform is digitized and the first and second derivative is calculated through a computer. For a certain time instant, substituting the value of the current and its first and second derivative into the integrodifferential equations describing the performance of the circuit loops, we form relationships which connect the values of the resistance and inductance for this particular time instant. Combining relationships originated from very closed adjacent time instants, the values of the resistance and inductance can be found. Scanning the entire time region of the discharge, the time history of the resistances and inductances of the discharges are revealed. Their behavior shows for the resistances an abrupt drop while for the inductances a sharp peak, both during the formation phase. After that the above characteristic quantities fluctuate slowly around constant values.

Method of measuring currents in pulsed gas lasers

The comprehension of the performance of pulsed gas lasers requires knowledge of several parameters which are time dependent and consequently difficult to measure. These parameters are mainly influenced by the two electric discharges which take place during the laser performance, namely by the ignition system and laser tube. The present work illustrates a new method to determine the most fundamental of these parameters, the current. This can be achieved exploiting only the voltage waveform on which much concealed information exists about all the time dependent parameters. The revelation of these parameters can be achieved by further elaboration of the waveforms of the high voltages. This elaboration, in our case, leads to finding the current and is described in this paper. The method is applied to a simple RLC circuit, to a doubling, and to a C-to-C circuit and it is delivered from experimental errors existing in other methods achieving the best accuracy to date.