The floating potential of an emissive cylindrical probe in a plasma is calculated for an arbitrary ratio of Debye length to probe radius and for an arbitrary ion composition. In their motion to the probe the ions are assumed to be collisionless. For a small Debye length, a two-scale analysis for the quasineutral plasma and for the sheath provides analytical expressions for the emitted and collected currents and for the potential as functions of a generalized mass ratio. For a Debye length that is not small, it is demonstrated that, as the Debye length becomes larger, the probe potential approaches the plasma potential and that the ion density near the probe is not smaller but rather is larger than it is in the plasma bulk.

In the framework of a one-dimensional model for plasma flow in ablative capillary discharges, we use a consistent method for obtaining the appropriate boundary conditions, and a new method for describing the radiative energy flux from the plasma to the wall. Good agreement is reached between the calculated and the measured values for the temporal behaviour of the plasma's main parameters. The agreement is particularly satisfying for the plasma conductance (resistance), the voltage across the capillary, the total input energy, the maximum input power and the plasma pressure. This gives us confidence that the model also predicts correct values for the remaining plasma parameters that are difficult to measure accurately, such as the plasma density, the temperature and the velocity (inside the capillary as well as at its exit). The knowledge of these parameters is crucial in order to use the ablative capillary as an efficient plasma source for different applications.

The system of a high pressure discharge capillary connected to an ablative pipe is shown here to be an efficient and convenient plasma source. The characteristics of the source (mass and energy fluxes) are determined by the Joule energy supplied to the discharge section as well as by the wall material and, geometrical parameters of the discharge capillary and the ablative pipe. For a given wall material and fixed geometrical characteristics of the capillary, a large range of exit plasma parameters values can be obtained by varying either the length of the ablative pipe or the electrical current carried by the discharge. Useful information for the design of the proposed plasma source is given. It is based on consistent numerical solution of the quasi onedimensional continuity momentum and energy equations with non-ideal state equation and non-uniform ionization degree for the combined discharge unit and ablative pipe.

A study of spatial and temporal dependences of plasma-relevant parameters has been done in the frame of a general quasi-one-dimensional model for ablative capillary discharges and for a specific time-dependence of the input energy. Particular attention was given to the effect of the so-called 'second boost of input energy' that leads to a substantial increase of some of the main plasma parameters such as exit velocity (26%), mass flux (177%) and energy flux (exit power) (285%). Calculations and experiments are in good agreement. The reliabilities of the model and numerical approach are supported by energy conservation condition fulfilment and the critical value of the exit Mach number.

Quasi-one dimensional hydrodynamic continuity, momentum and energy equations describing the plasma flow in high-pressure-discharge ablative capillaries are derived. To overcome the formidable difficulties arising in the solution of a fully two-dimensional system of equations, experimental information on the structure (geometry) of the generated plasma is used. Thus the two-dimensional hydrodynamic equations are averaged over the cross-section of the capillary to obtain a quasi-one-dimensional system of equations in which, however, the essential two-dimensional features are present. These include the radial outwards radiative transfer of energy and the radial inwards ablative mass flow. Some particular cases, including their thermodynamical aspects, are discussed. Illustrative analytical and numerical solutions of the equations are also presented.

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A time-dependent quasi-one-dimensional model is developed for studying high- pressure discharges in ablative capillaries used, for example, as plasma sources in electrothermal launchers. The main features of the model are (i) consideration of ablation effects in each of the continuity, momentum and energy equations; (ii) use of a non-ideal equation of state; and (iii) consideration of space- and time-dependent ionization.

The non-ideal continuity, momentum and energy equations describing plasma characteristics in confined high-pressure discharges in cylindrical ablative capillaries were solved numerically. The model equations used included (a) viscous and radiative and thermal conduction effects, (b) space dependent ionization and correction to Spitzer's electrical conductivity, and (c) non-ideal equation of state, as provided by SESAME library. For illustration, the case of polyethylene capillaries and discharge parameters appropriate for electrothermal launchers were considered. Analysis of the results indicated the consideration of the non-ideal equation of state to have significant consequences on the plasma characteristics. The sensitivity of these effects to variations in the discharge parameters was then studied and the results are also presented here. In the last part of the work the authors present the results of the implementation of a method aimed to determine self-consistent boundary conditions at the ends of the capillary as well as of the investigation of their effect on the solutions obtained.