This blog provides an in-depth look at some of APELC’s single-pulse pulsed power systems. These systems are designed for applications requiring precisely controlled, non-repetitive high-power pulses, typically operating at repetition rates of less than 1 Hz and often firing just once every few minutes depending on their use. To understand the capabilities and applications of this technology, we will explore the essential components and subsystems that constitute a complete turn-key single-pulse pulsed power system offered by APELC.
Single-Pulse System Architecture
The single-pulse systems offered by APELC are categorized by a repetition rate of <1Hz, and more typically, are only fired once every few minutes based upon the applications they are used in. Before diving deeper into this technology, it is important to first understand the typical components and subsystems that comprise a complete turn-key single-pulse pulsed power system. The diagram below demonstrates the major subsystems, which are as follows:
- Power and Control Rack
- Marx Generator
- Pulse-forming/peaking
- Energy delivery
- Load
- Diagnostics
Figure 1 Typical APELC single-pulse turn-key system
A brief explanation of each of these subsystems is presented below to help understand their function and how they operate within the entire turn-key single-pulse system.
1. Power & Control Rack
The power & control rack pictured in the figure above is typical of most all APELC turn-key systems. It provides a controller (typically PLC-based touchscreen control) that interefaces with each component of the rack to give the user control over charging (high-voltage power supply), pressure regulation (electronic pressure regulators), triggering (trigger generator), and safety/interlock functions. The rack can be operated locally from the touch-screen interface or remotely from a computer, laptop, tablet, or phone.
2. Marx Generator
The Marx generator is the core technology for APELC systems. As described in our blog “5 Things to Know About APELC Marx Generators”, the Marx generator is a high-voltage circuit containing individual capacitor stages, isolated by high-impedance charging elements, that are charged in parallel and then fired/erected in series. The result is a high-pulse that has an amplitude defined by the number of stages (Verected = Nstages X Vcharge) and a pulse-width defined by the erected series capacitance and the load impedance (T= Zload X Cerected), where the erected capacitance is the stage capacitance divided by the number of stages.
3. Pulse-forming/peaking
Many of the single-pulse systems built by APELC are for MIL-STD testing requiring a very specific pulse shape, with an emphasis on the rising edge. Most of the Marx generators offered by APELC have inherent rise-times in the range of 5-20ns, which is limited by the series inductance of the Marx generator. To overcome this limitation, a pulse-forming or “peaking circuit” can be added between the Marx generator and the load. In the case of a peaking circuit, a small capacitance is pulse charged by the erected voltage of the Marx, and a gas or oil switch with a very low series inductance holds off the peak voltage and then releases the energy from the peaking capacitance into the load, followed by the remaining energy from the Marx. The resulting pulse is a superposition of the fast energy from the peaking circuit and the energy from the Marx (which defines the pulse width). This results in a fast-rising (in some cases <1ns) pulse.
4. Energy delivery
While the diagram above shows a coaxial cable as the means of delivering energy from the Marx generator and peaking circuit to the load, this portion of the system can also be comprised of a transition from coaxial to planar in the case of APELC’s RS-105 systems or in any system where the pulse is being delivered onto a planar antenna structure (e.g. Ultrawideband).
5. Load
The load shown in the figure above depicts an APELC coaxial dummy load used for characterizing the output of the Marx generator. However, the load can also be the customer’s equipment or a subsytem provided by APELC. Examples of this can include and RS105 TEM structure, high-power microwave diode, or flash x-ray diode. In most cases, the load impedance should be matched to the source impedance to ensure minimal reflected energy coming back to the Marx generator.
6. Diagnostics
APELC can supply custom diagnostics for all of our systems to characterize the current, voltage and pulse shape. The figure above depicts a calibrated current-viewing-resistor (CVR) on the end of our coaxial dummy load. This set-up is often used to calibrate additional sensors between the output and load, such as b-dots, d-dots or rogowski coils.
Applications of APELC Single-Pulse Systems
1. MIL-STD-461G RS-105 HEMP Testing
APELC single-pulse systems are most often used in applications where the temporal characteristics of the pulse are critical to the end-user, with an emphasis on the rise-time of the pulse. A good example of this is the APELC 2m RS105 system shown in the figure below.
Figure 2 APELC 2m RS105 system
The 2m RS105 system is part of our line of test equipment for MIL-STD testing of assets in a “fast pulse” or E1 high-altitude nuclear EMP (HEMP) environment. A description of this is provided in greater detail in past blog entries. In the example of MIL-STD-461G, RS105 testing, the standard defines a pulse that has a 50 kV/m electric-field strength, a 1.8-2.8ns risetime, and a 18-28ns FWHM pulse-width. Meeting these specifications is somewhat difficult and requires not only a well-designed peaking circuit, but also necessitates a well-designed transition to the transverse electromagnetic wave (TEM) structure used to radiate the 50 kV/m field and pulse onto the test article.
2. Low-jitter Testing Scenarios
APELC single-pulse systems are often used by our customers at the DOE labs for tests requiring extremely precise timing to coordinate multiple events. Some examples of this include combined environment HEMP testing (E1 pulse + Gamma radiation or E2) or triggering of larger pulsed power systems where the firing of APELC’s single-pulse system needs to be coordinated in time with other pulsed power components (e.g. laser-triggered spark gaps) to ensure reliable and repeatable performance.
Since the beginning of APELC’s Marx generator development, one of our strong-suits has been the design and manufacturing of Marx generators with incredibly low timing jitter, in some cases as a low as <300ps. This unique capability makes APELC single-pulse systems ideal for customers requiring precise control over the timing of their entire system, and APELC prides ourselves on the ability to deliver easy-to-use, low-maintenance, and highly reliable solutions to these difficult problems.
Conclusion
APELC prides ourselves on working with our customers prior to a contract/purchase order to ensure we are meeting their needs and stringent requirements. Understanding these requirements helps us to provide the best possible and easiest to use system for delivering extremely precise pulses for some of the most important applications involved in our nation’s defense.
