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This paper expands upon previous research into developing a numerical model of a capillary plasma source for application to electrothermal--chemical (ETC) guns. The capillary model is comprised of a kinetic model simulating polyethylene ablation coupled to a 1-D time-dependent hydrodynamic model to determine the capillary outflow parameters. As input, the simulation requires the capillary internal radius, length, and applied electrical current. Previous work found that best agreement with experimentally measured ablated mass could be achieved with the application of a backflux parameter, representing the percentage of the ablated material that was allowed to return to the polyethylene surface and form a film. Using the model, a parameter study is conducted to determine the effects that varying the peak electrical current, internal capillary radius, and backflux parameter has on the plasma temperature, peak outflow pressure, and total ablated mass. A sinusoidal electrical current is assumed in this paper, with the peak current and discharge time taken over a range typically encountered in ETC gun application. An analysis of the dependence of total ablated mass and peak capillary pressure on the deposited electrical energy yields insight into nonlinearities in the capillary energy equation. Index Terms--Capillary, electrothermal chemical (ETC), energy density, modeling.

Much progress has been made in the last few years toward the development of an end-to-end computer model of an electrothermal chemical gun. Phenomena that must be considered in an electrothermal chemical gun model include the initial capillary plasma properties, the plasma-air interaction, plasma sheath effects, and the plasma-propellant interaction itself. This paper presents an overview of recent progress made modeling these various phenomena. Also discussed are methods under consideration to incorporate surface chemistry effects into the plasma-propellant interaction model. Index Terms--Capillary, ETC, heat flux, modeling, plasma, plasma chemistry, plasma sheath.

Plasma-propellant interaction for application to an electrothermal gun is studied theoretically. Electrothermal-chemical (ETC) guns are used for enhancement of the ignition and combustion of the energetic propellant. A detailed understanding of the dynamics of the plasma-propellant interaction is considered one of the key elements to the future success of practical ETC gun implementation. A model of the propellant ablation under plasma effect is developed based on the kinetic theory of ablation. The ablation model is coupled with a model of the plasma generation in the capillary discharge that allows calculation of the effective heat flux from the plasma. Calculations are performed for specific experimental conditions in which ablated mass of a double-base and a nitramine composite propellant are studied. An ablation model is used to predict the ablation rate of the propellant for different bulk plasma densities. An effective heat flux from the plasma is found which yields the experimentally determined ablated mass. One representative solution reproduces the experimentally determined ablated mass for the double-base propellant of 5.3 mg via an effective heat flux on the order of 4 x [10.sup.8] J/[m.sup.2] s. The effective heat flux that corresponds to the experimentally measured ablated mass is determined for different propellants. Differences in the calculated effective heat flux between different propellants indicate that although heat convection from the plasma is the dominant source of energy, plasma radiation, and the optical properties of the propellants themselves cannot be ignored. The difference in plasma heat flux between propellants can readily be explained by partial absorption of plasma radiation consistent with the optical properties of the propellants. Index Terms--Electrothermal chemical (ETC), heat flux, modeling, plasma, propellant.