Ablation Study in the Capillary Discharge for Electrothermal Guns

Summary form only given. Electrothermal-chemical (ETC) accelerators are designed to introduce electrical energy into the chamber of a conventional chemical gun system. An ETC system has the potential to improve the performance of conventional guns by enhancing the ignition and combustion characteristics of propellants. An ETC system has two components, namely a plasma source and a chemical propellant system. In this system the propellant is usually ignited with plasma introduced by a jet from a capillary discharge. The plasma-propellant interactions are dependent on the plasma properties that are determined by the plasma source. Therefore accurate prediction of plasma properties from the capillary discharge is important for understanding plasma-propellant interactions. The main physical processes occurs in the capillary in a similar way to an ablation controlled discharge. Rapid heating of a thin dielectric surface layer leads to ablation of the material of the wall. Different characteristic sub-regions near the ablated surface namely space-charge sheath, Knudsen layer, presheath and a hydrodynamic layer are considered. The ablation rate is determined by the parameters at the edge of the Knudsen layer. The kinetic approaches namely bi-modal distribution function and direct simulation Monte-Carlo are used to determine the parameters at the interface between the kinetic Knudsen layer and the hydrodynamic layer. Coupling solution of the non-equilibrium, Knudsen layer, with hydrodynamic layer and presheath provides self-consistent solution for the ablation rate. An example of discharge in the polyethylene capillary for plasma-propellant interaction is considered. It was predicted that typically during the 300 mus discharge the ablated mass is about 22 mg, while carbon electrode erosion mass is about 3 mg. The pressure peaks at about 10 MPa and electron temperature peak is about 1.4 eV