AAWSAP DIRD, Pulsed High-Power Microwave Source Technology, January 2010

This Defense Intelligence Reference Document (DIA-08-0912-005) is dated 28 January 2010. The Defense Intelligence Agency's Defense Warning Office prepared it under the Advanced Aerospace Weapon System Applications Program. It gives an overview of pulsed high-power microwave sources and the technologies needed to build them, including insulation, cathode materials, high-voltage switching, pulse generators and antennas. The paper concludes that progress requires better cathodes, switching and insulation, and that compact ultrawideband antennas will remain difficult to build.

From the source:Release of 2026-09-18 Incident: 1/28/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys pulsed high-power microwave (HPM) source technology and argues that such systems remain of military interest because they can disrupt or damage electronic systems with short, intense electromagnetic pulses. The report reviews the main source types and the supporting technologies they depend on, including high-voltage insulation, switching, cathode materials, antennas, and pulse-power generation. It emphasizes the difficulty of building systems that are compact, efficient, and practical to field, since short pulse durations, antenna size, heating, detectability, and beam or signal quality all impose hard engineering limits. Its overall conclusion is that the technology has significant potential military value, but that further progress depends on advances in cathodes, predictive modeling, high-speed high-voltage switching, and low-loss insulation, while compact ultrawideband systems will remain difficult because of basic physical constraints on antenna design.

UNCLASSIFIED/} P'Olt OP'P'l@IAL l:ISE &P•LY
Table 3 shows findings of cathode material studies at SNL and at the AFRL.
Table 3. Cathode Study Findings
Material Emission Threshold
(kV)
Lifetime
(# of Shots)
Outgassing
(Neutrals/Electron)
Csl-Carbon
Micro.fibers
 72,000 4 - 6.5 (substrate)
"Sandia Red" Velvet 8 kV/cm - 8,000 10
"MILO Green" Velvet 10 kV/cm - 4,000 10-14
Velveteen Low Low 12
F-Velvet Low 12
Ceramic Cloth > 120 kV/cm --- ---
Ceramic Felt > 100 kV/cm --- ---
Carbon Pyramids > 80 kV/cm --- ---
Carbon Nanotubes 20-50 kV/cm Arc rate of -
2%
-4
Bare Carbon
Microfiber
(packing density)
15-40 kV/cm > 36,000 4.3 - 6.5
(substrate)
Csl-Carbon Fiber
Tufts
 200,000 -4
Metal I Ceramic 95 kV/cm (diode
collapse
unless> 150 kV/cm)
--- 8
HIGH-VOLTAGE SWITCHING
High-voltage switching is among the most challenging of technologies for HPM sources.
Although high-voltage switches have been used for several decades, and thousands of
experiments have been performed on the mechanisms involved in liquid and gaseous
breakdown, there are still many aspects of the phenomenon that defy explanation. This
is especially t rue as the time required to reach the fully conducting state becomes
extremely short. The usual explanation for this process involves Townsend avalanching,
whereby electron streamers beg in at the cathode in an average electric field of only 20-
25 kV/cm and, by virtue of an enhanced electric field at their t ip, progress in an orderly
fashion to the anode. At this time, a heating phase beg ins, and an increasing amount of
current is passed through the streamer until the switch finally reaches the fully
conducting state. The problem with this explanation is that it is most likely incorrect
and relies on exaggerated ion densities to explain how switches can reach full
conduction in less than a billionth of a second. Alternative explanations involving
runaway electron generation provide a better match to observations. Very fast
switching is critically important to the concept of UWB HPM. The basic concept is to
generate a square pulse with the fastest rise time possible. A Fourier transform of this
waveform results in a frequency spectrum containing frequencies determ ined by the
width and rise time of the square pulse. The period of the lowest frequency is tw ice the
pulse width, and the rise time is about one-quarter the period of the highest frequency.
UNCLASSIFIED/ ,<FQA OFFICIO I. Uili OPII.V
11