1) What is Pulse Power?
Pulse power, also known as “pulsed power”, is the compression of electrical energy in both time and space with the goal of delivering fast, intense pulses of energy to a load. The best way to think about this from a basic engineering perspective is by considering peak power, and the relation between energy and time: Power=Energy/Time. As shown in the table below, If we consider a 10-stage Marx generator circuit, with 1kJ worth of energy storage charged using a high-voltage power supply over the course of 1 second, the corresponding power would be 100W. If we are able to release this same amount of energy in 10ns, then the peak power would be 10GW (10E9 Watts)!
Table 1 10-stage Marx Example
Figure 1 Power vs. Time for 10-stage Marx Example
2) Where and how did pulse power begin?
While capacitive discharge experiments were happening in the late 19th and early 20th century for the study of electrical breakdown, the compression of electrical energy to generate fast high-voltage transients began in-earnest with the invention of the Marx Generator by the German scientist, Erwin Otto Marx in 1924 [1]. As described in our blog post, “5 Things to Know About APELC Marx Generators” the Marx Generator charges a bank of capacitors in parallel and then discharges them in a series configuration, thereby adding the voltage of each “stage” to create a high-voltage pulse. Erwin Marx was initially using the Marx Generator for studies of electrical phenomena in high-voltage transmission.
J.C. “Charlie” Martin joined the Atomic Weapons Research Establishment (AWRE) in the UK in 1949 to study Nuclear Weapons design and saw the need to use flash radiography to study implosion phenomena, and by 1960 had developed a radiography and pulse power (later called “pulsed power”) facility, utilizing accelerators and high-voltage discharges to create intense pulses of X-ray energy. Ian Smith, one of the other progenitors of pulse power also joined AWRE around this time and began working with Martin on the development of radiographic and pulse power systems [2].
The work of J.C. Martin and Ian Smith found its way to the USA during the 1960’s when Department of Defense (DoD) funded contractors, such as Ion Physics, Physics International and EG&G began working with AWRE researchers to understand and later develop systems for the Air Force Weapons Laboratory (AFWL) and Sandia National Laboratories. Initially, many of these systems were used after the Nuclear Test Ban Treaty of 1963 to study weapons effects, though later Sandia, and other National Labs, such as Lawrence Livermore National Laboratories, Los Alamos National Laboratories and the Naval Research Laboratories were using pulse power and accelerator systems to study controlled fusion experiments.
From the 1960’s to present day Sandia has developed about a dozen large pulse power systems ranging from kilojoules to megajoules of electrical energy, with the largest to-date being the Z-Machine used to study inertial confinement fusion [3].
Figure 2 Sandia National Laboratories’ Z-Machine
3) How has APELC played into the history of pulse power?
Dr. Jon Mayes started APELC out of graduate school in 1998 utilizing the “wave-erection” Marx generator pioneered by David Platts (LANL) and Jerald Buchenauer (UNM). Mayes matured the design to create commercially available coaxial Marx generators for the generation of ultra-wideband (UWB) RF, High-power microwaves (HPM), materials studies and many other applications (Figure 3). Dr. Mayes brought his academic advisor, Dr. William Nunnally on as Chief Scientist. Dr. Nunnally has a long background in the design of pulse power systems, beginning with early compact Marx generator work at LANL, such as the 200kV, 10 nanosecond Marx Generator shown below in Figure 4.
Figure 3 APELC MG15-3C-940PF as an example of an APELC compact Marx Generator
Figure 4 LANL 200kV 10ns Marx Generator (c/o Dr. William Nunnally)
4) Is Pulse Power used for things other than weapons effects testing and fusion experiments?
Pulse power has found a large number of different uses over the decades from water purification to metal forming. As mentioned in the beginning of this blog, pulse power is the compression and delivery of intense bursts of energy into a load. As “work” is a synonym for energy, we can think of power as work done per unit time. So pulse power allows for a great degree of work to be done in a very short amount of time. This work can be applied to the chemical bonds in water or air-borne pathogens to break them down into benign compounds, or similarly, the work can be applied as a magnetic force to form metal into specific shapes in very short amounts of time. From a productivity perspective, this can mean high throughput, and in some cases, higher efficiency. This makes pulse power an incredibly powerful tool in both research and industrial applications.
5) Where is the field of pulse power headed now?
Uniquely, pulse power has utilized some of the same technology since Erwin Marx’s first experiments nearly 100 years ago- specifically, the spark gap. Switching high voltages (>1kV) in nanoseconds is extremely difficult to do using any technology other than gaseous switches (spark gaps and vacuum tubes- e.g. thyratrons), because of the physical limitations of materials in regards to charge transfer and high-voltage hold-off (i.e. insulation). While spark gaps and certain types of other gaseous switches have made their way into commercial and industrial applications, they can be prone to limited lifetimes and may require specialized knowledge by the operator. However, recent developments in semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) are bringing nanosecond switching at high voltages into the realm of solid-state devices. This means that some of the abovementioned applications can be made smaller, easier to use, and have longer lifetimes. That said, spark-gap-based pulse power is still the most robust, practical and sometimes only means of switching the extreme voltages and currents used in systems such as EMP simulators, large fusion experiments, HPM systems, and many of the other applications often required by the US Department of Energy (DOE) or Department of Defense.
Figure 5 APELC Solid-state Marx Generator
REFERENCES
- https://en.wikipedia.org/wiki/Marx_generator
- Smith, Ian. “The early history of western pulsed power.” IEEE transactions on plasma science5 (2006): 1585-1609.
- Van Arsdall, Anne. Pulsed Power at Sandia National Laboratories: The first forty years. Sandia National Laboratories, 2007.
