ETC research at Soreq NRC, Israel
An overview of the electro-thermal-chemical launcher (ETC) research program at the Propulsion Physics Laboratory, Soreq NRC, Israel is presented. The main avenue explored is a detailed study of solid propellant ETC (SPETC) performance and optimization. A better knowledge of the physical phenomena taking place inside the device and in parallel efforts to tackle the engineering aspects of specific weapon systems based on the SPETC concept. Theoretical and experimental tools have been developed. Permanent efforts towards developing optimal and efficient components for such systems are invested. A second avenue is the design and the construction of a small caliber ETC demonstrator, as an answer for present military demands for urban combat conditions. All system options are dealt with including a novel inductive pulse power supply.
Status of 5 MW inductive storage facility at SOREQ NRC
A laboratory repetitive inductive storage power supply (IPS) for the ignition of an electrothermal chemical (ETC) gun is described. Eight years ago, it was designed for delivering to an ET load the energy of 500 kJ in a shot. This paper gives an updated status of this facility. The IPS is battery-based. Originally, the battery had a peak power of 5 MW and was able to charge a cylindrical coil to 700 kJ. The batteries degradation during the years was observed and documented. Fringe fields of Brooks-type coils with and without screens were analyzed. A conclusion is drawn that a screen of reasonable weight cannot reduce the stray field below a susceptibility level of electronic devices that should be shielded individually. A major facility improvement was in the field of switching. A compact hybrid repetitive opening switch (HOS) rated 50 kA, 7 kV was developed. This HOS can be used in long-charge inductive storage systems that look promising for many applications, such as uninterruptible power supplies, driving ET loads, protection of DC circuits, etc. The HOS design and testing is given in detail. The design limitations and trade-offs are discussed. A commercial vacuum circuit breaker serves as the first stage. It provides the high-current carrying capability during the inductor charge. At a desired moment, it is opened, and the current is transferred to the second stage comprising two gate commutated thyristors (GCTs) connected in series; they break the current during several microseconds. A pause of l-2 ms is provided for the vacuum breaker recovery. A novel approach allowing the enhancement of an order of magnitude of the turn-off capability of fully-controlled semiconductor devices was developed. It comprises the inverse current injection into the second stage assisted by a precisely timed gate turn-off. The main benefit of this technique is the reduction of the quantity of the semiconductor devices in the second stage.
Effect of a non-ideal state equation on the steady state critical flow characteristics in ablative capillaries
The non-ideal continuity, momentum and energy equations describing plasma characteristics in confined high-pressure discharges in cylindrical ablative capillaries were solved numerically. The model equations used included (a) viscous and radiative and thermal conduction effects, (b) space dependent ionization and correction to Spitzer's electrical conductivity, and (c) non-ideal equation of state, as provided by SESAME library. For illustration, the case of polyethylene capillaries and discharge parameters appropriate for electrothermal launchers were considered. Analysis of the results indicated the consideration of the non-ideal equation of state to have significant consequences on the plasma characteristics. The sensitivity of these effects to variations in the discharge parameters was then studied and the results are also presented here. In the last part of the work the authors present the results of the implementation of a method aimed to determine self-consistent boundary conditions at the ends of the capillary as well as of the investigation of their effect on the solutions obtained.