Fast electrical energy storage or Voltage-Driven Technology (VDT) has dominated fast, high-voltage pulsed power systems for the past six decades. Fast magnetic energy storage or Current-Driven Technology (CDT) is characterized by 10,000 X higher energy density than VDT and has a great number of other substantial advantages, but it has all but been neglected for all of these decades. The uniform explanation for neglect of CDT technology is invariably that the industry has never been able to make an effective opening switch, which is essential for the use of CDT. Most approaches to opening switches have involved plasma of one sort or another. On a large scale, gaseous plasmas have been used as a conductor to bridge the switch electrodes that provides an opening function when the current wave front propagates through to the output end of the plasma and fully magnetizes the plasma - this is called a Plasma Opening Switch (POS). Opening can be triggered in a POS using a magnetic field to push the plasma out of the A-K gap - this is called a Magnetically Controlled Plasma Opening Switch (MCPOS). On a small scale, depletion of electron plasmas in semiconductor devices is used to affect opening switch behavior, but these devices are relatively low voltage and low current compared to the hundreds of kilo-volts and tens of kilo-amperes of interest to pulsed power. This work is an investigation into an entirely new approach to opening switch technology that utilizes new materials in new ways. The new materials are Ferroelectrics and using them as an opening switch is a stark contrast to their traditional applications in optics and transducer applications. Emphasis is on use of high performance ferroelectrics with the objective of developing an opening switch that would be suitable for large scale pulsed power applications. Over the course of exploring this new ground, we have discovered new behaviors and properties of these materials that were here to fore unknown. Some of these unexpected discoveries have lead to new research directions to address challenges.
The Radiatively Driven Hypersonic Wind Tunnel (RDHWT) program requires an unprecedented 2-3 MeV electron beam energy source at an average beam power of approximately 200MW. This system injects energy downstream of a conventional supersonic air nozzle to minimize plenum temperature requirements for duplicating flight conditions above Mach 8 for long run-times. Direct-current electron accelerator technology is being developed to meet the objectives of a radiatively driven Mach 12 wind tunnel with a free stream dynamic pressure q=2000 psf. Due to the nature of research and industrial applications, there has never been a requirement for a single accelerator module with an output power exceeding approximately 500 kW. Although a 200MW module is a two-order of magnitude extrapolation from demonstrated power levels, the scaling of accelerator components to this level appears feasible. Accelerator system concepts are rapidly maturing and a clear technology development path has been established. Additionally, energy addition experiments have been conducted up to 800 kW into a supersonic airflow. This paper will discuss progress in the development of electron beam accelerator technology as an energy addition source for the RDHWT program and results of electron beam energy addition experiments conducted at Sandia National Laboratories.
Experimental results are presented that provide design guidelines for high repetition rate, long-life pulsed power magnetic modulators. Fault mechanisms that occurred during a series of 32 million shots at 100 pps, with continuous runs of up to 5.7 million shots (~16 hours) on the Dos Lineas magnetic modulator are described. An effort to explain the fault mechanisms and how to avoid them is made. Factors that limit the long life performance of a variety of components including switches, cables and oil are encountered. The high reliability of the magnetic switch technology is demonstrated.
In applications where multiple magnetic modulators are used to drive a single Linear Induction Voltage Adder (LIVA) or Linear Accelerator (LINAC), it is essential that the outputs of the modulators be synchronized. Output rise times are typically in the 10 ns to 20 ns range, often making it necessary to synchronize to within less than 1 ns. Microprocessor and electronic feedback schemes have been developed and demonstrated that achieve the required level of synchronization, however, they are sophisticated and potentially complex. In a quest for simplicity, this work seeks to determine the achievable level of modulator to modulator timing jitter that can be obtained with simple design practices and passive techniques. Sources of output pulse time jitter in magnetic modulators are reviewed and some basic modulator design principles that can be used to minimize the intrinsic time jitter between modulators are discussed. A novel technique for passive synchronization is presented.