STATUS OF 5MW INDUCTIVE STORAGE FACILITY AT SOREQ NRC * A. Pokryvailo † , I. Ziv, E. Shviro Propulsion Physics Laboratory, Soreq NRC Yavne 81800, Israel * Work supported in part by the Israeli MOD. † Email: alex@soreq.gov.il Abstract 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 500kJ 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 5MW and was able to charge a cylindrical coil to 700kJ. 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 50kA, 7kV 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 1-2ms 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. I. INTRODUCTION ETC propulsion technology, recognized as a probable near-midterm candidate for gunnery upgrading, deals now mainly with plasma-assisted ignition of solid propellant [1]. An estimated energy demand is several hundreds kJ per pulse, with 400kJ defined as a near-term goal. Capacitive, inductive and kinetic energy storage methods are viable for electric guns. Many works are devoted to comparison of these methods (see, e.g., [2]-[3]). Inductive energy storage possesses high energy density, low cost and a long life. It is simple, has static structure and requires low-voltage prime power, which serves to improved safety compared with capacitive and inertial storage. Good coupling can be achieved to an ETC load. Similar to capacitive systems, an IPS may be built in modules, enabling flexible integration. IPS is especially attractive in view of the short charging time of the inductor that can be considered as a part of the firing sequence. Thus, the silent watch capability is an inherent feature of IPS. This appears to be a major advantage over capacitive and inertial storage. The IPS battery may be a dual-use source, supplying electricity also to high-power actuators. The IPS technology is not yet mature. It lacks commercially available high power density batteries; the problem of compact repetitive opening switch (OS) we consider as solved in general (see Section V). Unclear is the situation regarding the influence of stray electromagnetic fields on electronics and related issues. This paper updates our previous publications [1], [3]- [10], with the emphasis on repetitive switching. II. GENERAL A generic IPS (Fig. 1) includes four main components: the battery, the inductor, the opening switch (OS) and the control system. The OS and the closing switch (CS) may be physically combined in one switch or may exist as two independent units. Upon the CS/OS closure, the inductor L is charged to the desired current following an approximately exponential curve. When the OS interrupts the current, the inductor energy is transferred to the load, or in case of a load malfunction, dumped via an additional CS onto an emergency load R d . i n d u c t o r b a t t e r y V b R b R I R L D i L V L CS/OS I ch CS R d Figure 1. Basic circuit of IPS. 0-7803-7915-2/03/$17.00 ©2003IEEE. 445