Reliable, highly reproducible plasma injectors for ET and ETC launchers

The plasma injector is a major component within electrothermal (ET) or electrothermal-chemical (ETC) launcher. Soreq NRC has promoted for years the SPETC (solid-propellant ETC) gun concept, where the generated plasma jet serves to ignite the charge and to control its burning rate (for example, to eliminate the effect of the initial charge temperature on the propellant burning rate). From a system engineering point of view there is an advantage in using small size plasma injectors. Such injectors have been designed, built and tested in our laboratory for many years. In this paper we report about "free jet" (the plasma is injected to the atmosphere and not into propellant charge) experiments performed with certain models of such injectors. These injectors were designed for electrical energies in the range of hundreds of kilojoules and several hundreds MW. The dependence of the mass losses from the ablative capillary and anode on the total electrical energy and power are presented. Although the limited scope of this presentation one can grasp from these data indications regarding the differences between the thermodynamic properties (temperature, density) of plasma jets produced by capillaries with different geometries, operated at various electrical energies and powers. A comparison between the energy carried by the plasma and metal droplets (resulting from anode melting) may give an indication about the relative contribution of these two factors to the propellant ignition.