A study of an ablation-derived plasma in an acceleration device

Abstract

The results of a study of non-thermal Carbon and Fluorine plasmas in an electromagnetic acceleration device are presented, the plasmas being created by ablation from the surface of a solid dielectric. The dielectric is close to a steady discharge through which ablated material, on entry, is heated and accelerated, and it is concluded that the high level of radiative power loss, which consists mainly of optically thick resonance line radiation, is in part responsible for the uniformity and stability of the plasma plume. Plasma velocities around 1-2 x 106 cm/s. are attained.

In addition to conventional electrical and spectroscopic diagnostic methods, several new spectroscopic techniques are described, providing greater accuracy in the measurement of particle temperatures and densities in non-thermal, non-hydrogenic plasmas. In order to make these methods possible, as well as allowing estimates of the radiation losses, a model describing the papulation distribution among the bound ionic states was constructed and solved for a wide range of plasma conditions. From these results new values of collisional-radiative ionization and recombination coefficients are obtained, which are in broad agreement with experimental values.

A model was developed which described the rate of ablation from the solid and which formed part of a larger numerical scheme for calculating the temperature, density and velocity of the plasma plume. This model gives results which are in good agreement with the observations and is used to predict the plasma behaviour under different operating conditions and with different dielectric materials.

The extension of certain parts of this work to other situations is also discussed, in particular, laser heating of plasmas, problems of ablation in high-temperature plasma containment devices, and as a source for selective excitation spectroscopy. The possibility of using the device as a soft X-ray laser is also investigated.