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Electrothermal-chemical (ETC) propulsion with the control of a combustion process yet requires large electrical energies for an appreciable effect. Referring to the changed tendency of focusing ETC researches on the early ignition phase, the Agency for Defense Development (ADD), Korea, has been studying an electrothermal ignition for a 120-mm gun using a capillary plasma injector. Under the condition of a limited capillary geometry, design efforts with various liner materials have been done to achieve robust capillary discharges capable of transferring energies around 100 kJ. Electrical properties were estimated with the help of plasma theories and compared with experimental results. Experiments using a closed vessel and a gun-chamber simulator have been done to investigate the burning behaviors and the early phase of an electrothermal ignition, respectively. The closed vessel was designed for both a plasma and a conventional ignition. The burning rates could be obtained up to 70 MPa. The gun-chamber simulator was designed in the shape of the chamber of a 120-mm gun except for an acrylic chamber wall withstanding up to 30 MPa. Through prior tests using the closed vessel and the gun-chamber simulator, appropriate electrical energies and propellant have been selected. Firings of the full-scale 120-mm gun have been done using JA2 propellant. Electrical pulses of 1-2.5-ms duration in the energy from 20 to 120 kJ were applied. Aside from ignition capability, the results showed a possibility of a control on the peak pressure. Currently, ADD, Korea, continues the research to enhance the efficiency of the plasma injector, to compact the pulse forming network, and to investigate the electrothermal ignition properties of LOVA propellant. Index Terms--Capillary, electrothermal, propellant.

It is important to understand the physical processes contributed by the plasma injector in the development of an electrothermal-chemical (ETC) gun. To investigate basic properties of a capillary discharge, an injector was discharged in open air. Comparing the measured and the calculated plasma resistivities, the state of power balance was investigated. The capillary plasma discharged in open air showed large ejection of plasma without power-balancing, while the capillary plasma produced in the ETC gun experiment reaches near balanced steady-state as the pressure of the combustion chamber becomes appreciable. The ejected flames were monitored with a high-speed camera. Typically the observed flames were about 50 cm ~1 m long and 25 cm wide. To estimate temperature and density, a preliminary measurement of time-resolved spectra in the visible wavelength region was done. Index Terms--Capillary discharge, electrothermal chemical propulsion, plasma resistivity.

In order to maximize electrothermal-chemical (ETC) gun performance, the power supply for the ETC gun driver needs to have a capability of producing a flexible current pulse. This current pulse forming can be realized by a combination of current pulses from multiple modularized capacitor banks. For this purpose, a 2.4-MJ pulse power system (PPS) has been developed. The 2.4-MJ PPS consists of eight modular 300-kJ capacitor banks (CBs). The 300-kJ CB modules are designed to operate independently and have a charging voltage of 22 kV and a current capability of 150 kA. Operation characteristics of 2.4-MJ PPS have been investigated. Various shapes of current pulse have been tried to a dummy resistive load and an ETC gun load. In this paper, we discuss some problems that take place during multiple modules operation and suggest solutions for these problems. We also show some experimental results when the 2.4-MJ PPS was applied to resistive dummy load and a 30-mm ETC gun load. Index Terms--Capacitor bank, ETC gun, 2.4-MJ pulse power system, 30-mm electrothermal-chemical (ETC) gun, 300-kJ pulse power module.

In late 2000, an experimental 30-mm electrothermal-chemical (ETC) gun, a data acquisition system, and a 2.4-MJ pulse-forming network (PFN) consisting of eight 300-kJ modules were constructed, and serious research projects were started. During the past years, basic studies on the effect of the electric pulse in the process of ignition and propulsion of the gun have been done. Two types of ammunition, an exploding wire cartridge and a capillary plasma injector cartridge, were used in the experiments. The load resistance should-be estimated well in order to deliver electric energies into the combustion chamber as a desired form in time. For that purpose, there has been an effort to model the load resistance of the ETC gun, which shows the dependence on the pressure of the combustion chamber. A study on a capillary plasma itself is also an important topic and is now in the beginning stage of research using spectroscopic diagnostics. The capillary plasma discharged in the open air provides useful information through the comparison with that discharged in the ETC gun. In the development and operation of the PFN, some problematic characteristics such as a high-voltage surge leading to a destruction of crowbar diodes occurred. A countermeasure was presented to solve the problem. High-current switches are also being studied. Vacuum rotary arc gap switch, pseudospark switch, triggered vacuum switch, and inverse-pinch switch are being studied for better and reliable operations. The ETC program in Korea is currently concentrating on the detailed investigation on the interaction of a plasma with propellants. Index Terms--Electrothermal-chemical propulsion, pulse-forming network.