DOW-UAP-D121, AAWSAP DIRD, Pulsed High-Power Microwave Source Technology, January 2010

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.

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Defense
Intelligence
Reference
Document
Acquisition Threat Support
28 January 2010
!COD: 1 December 2009
DIA-08-0912-005
Pulsed High-Power Microwave
Source Technology
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Pulsed High-Power Microwave Source Technology
Prepared by:
Acquisition Support Division (DW0-3)
Defense Warning Office
Directorate for Analysis
Defense Intelligence Agency
Author:
AAP Person 64
Administrative Note
COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized.
This product is one in a series of advanced technology reports produced in FY 2009
under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace
Weapon System Applications (AAWSA) Program. Comments or questions pertaining to
I
this document should be addressed to !AAP Person 1 AAWSA Program
Manager, Defense Intelligence Agency, ATTN: CLAR/DW0-3, Bldg 6000, Washington,
DC 20340-5100.
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Contents
Summary................................................................................................................vi
Critical Technologies .............................................................................................. 1
Insulation .......................................................................................................... 1
Uniform Homogeneous....................................................................................... 2
Solid ................................................................................................................... 2
Plastics............................................................................................................ 2
Epoxies ................ ,..............................., .......................................................... 3
Urethanes and Silicones ................................................................................. 4
Liquids ............................................................................................................... 4
Gaseous .............................................................................................................. 4
Laminated .......................................................................................................... 6
Plastic-Paper-Oil ................................................................................................ 6
Plastic-Paper-Epoxy ........................................................................................... 6
Dielectric Tapering ............................................................................................. 7
Cathode Materials .............................................................................................. 7
Velvet................................................................................................................. 9
Carbon ............................................................................................................... 9
Ceramics .......................................................................................................... 10
Cesium Iodide Coated ...................................................................................... 10
High-Voltage Switching .................................................................................... 11
Gaseous Switching ........................................................................................... 12
High-Speed Liquid Switching............................................................................ 14
Solid-State Switching ....................................................................................... 14
High-Voltage Pulse Sources ................................................................................. 15
Marx Generators .............................................................................................. 15
Transformer Based Generators ........................................................................ 16
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Explosively Driven Generators ......................................................................... 16
Pulsed High-Power Microwave Sources................................................................ 17
Pulsed Electron Beam Sources ......................................................................... 17
BWOs, TWTs, and RKAs ..................................................................................... 17
Split-Cavity Oscillators ..................................................................................... 18
Virtual Cathode Oscillators............................................................................... 18
Magnetrons ...................................................................................................... 18
Gyrotrons ......................................................................................................... 19
Impulse HPM Sources ...................................................................................... 20
SNIPER............................................................................................................. 20
EMBL ................................................................................................................ 20
H-Series HPM Sources ...................................................................................... 20
The Phoenix HPM Source.................................................................................. 22
The GEM II HPM Source ................................................................................... 24
The Jolt HPM source ......................................................................................... 24
Mesoband Sources ........................................................................................... 24
HPM Antennas...................................................................................................... 25
Narrowband Antennas...................................................................................... 25
Wideband and Ultrawideband Antennas........................................................... 27
Conclusion............................................................................................................ 29
Figures
Figure 1. Paschen Curve for Air ............................................................................ 13
Figure 2. Example of Marx Generator Circuit ........................................................ 16
Figure 3. Orion HPM Testing Facility....................................................................... 19
Figure 4. Active Denial System With FLAPS Antenna ............................................ 20
Figure 5. H2 With Large TEM Horn and PGC Output.............................................. 21
Figure 6. Cross-Section Drawing of HS With Point Geometry Converter, Brewster
Angle Window, and Extended-Ground-Plane Antenna ........................... 21
Figure 7. HS Output Section With the Point Geometry Converter Feeding an
Extended-Ground-Plane Antenna Through a Brewster Angle Window ... 22
Figure 8. Phoenix Radiated Pulse at 8.5 Meters ................................................... 23
Figure 9. Phoenix Radiated Spectral Content ....................................................... 23
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Figure 10. Jolt Hyperband HPM Source................................................................. 24
Figure 11. Jolt Radiated Electric Field Waveform at 85 Meters ............................. 24
Figure 12. FLAPS Antenna With a Cross-Shorted Dipole Array ............................. 26
Figure 13. Mode Converter Vlasov Antenna and Vlasov Antenna Attached to a
Coaxial MILO ....................................................................................... 27
Tables
Table 1. Dielectric Properties of Some HPM Plastics............................................... 3
Table 2. Relative Spark Breakdown Strength of Gases ........................................... S
Table 3. Cathode Study Findings .......................................................................... 11
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Pulsed High-Power Microwave Source Technology
Summary
This paper provides an overview of the major types of high-power microwave
(HPM) sources and the critical technologies required to build them. Pulsed
HPM technology has been of scientific and military interest for several decades.
Originally, the interest focused on the area of high-altitude electromagnetic
pulse (HEMP) concerns.
HEMP is produced when a nuclear weapon is detonated high above the earth's
surface, creating gamma radiation that interacts with the atmosphere to
create an intense electromagnetic (EM) energy field that is harmless to people
as it radiates outward but can overload computer circuitry with effects similar
to, but causing damage more swiftly than, a lightning strike. HEMP effects
became fully known in 1962, when a high-altitude nuclear test (codenamed
"Starfish Prime") over the Pacific Ocean disrupted radio stations and
electronic equipment 800 miles away in Hawaii. The HEMP effect can span
thousands of miles, depending on the altitude, design, and power of the
nuclear burst. It is speculated that a single device detonated at high altitude
over the central United States could affect the entire country, since the HEMP
would be picked up by conductors, such as wires and power cables, acting as
antennas to conduct the electrical energy into various electronic systems. This
EM radiation was found to have field levels on the order of several hundreds of
kilovolts per meter with onset or rise times of a few nanoseconds and a
duration of nearly a microsecond. Fields of these magnitudes were found to
have severe detrimental effects on numerous electrical systems and items,
such as the power grid, automobiles, communications equipment, and aircraft.
Much testing was done in the 1960s and 1970s to determine vulnerabilities
and to find mitigation solutions. The HEMP is essentially a wideband
microwave pulse, and several EMP simulators were devised and built for use in
testing its effect on various electronic systems. In addition, several programs
were established to investigate the possibility of generating and radiating
other spectrums of EM radiation that may have some of these same effects
without requiring a nuclear detonation. This was the impetus for the
advancement of pulsed HPM technologies for weapons.
HPM radiation is composed of shorter waveforms at higher frequencies than is
HEMP, which makes it highly effective against electronic equipment and more
difficult to harden against. Whereas HEMP weapons are large in scale and
require a nuclear capability along with technology to launch high-altitude
missiles, HPM weapons are smaller in scale, involve a much lower level of
technology, and are within the capability of almost any state. HPMs can
damage computers and electronics similar to the way HEMP can, although the
effects are limited to a much shorter range. Technical accessibility, lower cost,
and the vulnerability of U.S. electronic equipment could make small-scale HPM
weapons attractive to terrorist groups. HPM devices are now categorized as
directed-energy weapons.
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One major use of HPM by the military is for electronic attack, or what is
referred to by the media as an "ebomb." HPM sources developed for this
purpose provide peak powers in excess of 10 gigawatts. The goal of such a
weapon is to disable communications and computer systems prior to any troop
movements and render the enemy unable to stage a response. The technology
used to drive such sources has its roots in pulsed power, and for narrowband
sources requires the use of tools that have been developed in the plasma
physics community. Reliance on microprocessors that have an increasing
density of circuits packaged onto each chip makes such systems ever-more
vulnerable to HPM effects. As an example of the possible effects of HPM
weapons, on 28 May 2001, a U.S. Commanche helicopter, flying in New York
state while performing tests involving HPM weapons, was reported to have
generated a low-level energy pulse that disrupted the Global Positioning
System devices used to land commercial aircraft in Albany.
The use of this type of weapon can be based on several scenarios, depending
on the asset it will be used against. Sometimes, it may only be necessary to
upset a data bus transfer to produce a success; other times, success may not
be so simple. Some of the kill mechanisms obtained from microwave weapons
include semiconductor overheating or burnout, arc generation, computer
upsets, voltage induction into sensitive circuits, display upset, and overvoltage
in discrete components. The asset to be neutralized will often determine the
specific type of microwave source to be used; for example, assets with slots
designed for communications purposes may be most vulnerable to narrowband
HPM of a specific frequency, while assets with several computers linked by a
communications bus may be more vulnerable to ultrawideband (UWB) pulses
of a specific pulse repetition rate (PRR). Often, the variety of EM radiation that
would be most effective is not obvious, and therefore several must be
evaluated.
If EM radiation is able to penetrate a target, the issue then becomes the
susceptibility of the many semiconductor devices, which make up the various
circuits of the target. Failures in semiconductors owing to thermal effects
occur when junction temperatures are raised above 600° Kelvin. Since thermal
energy diffuses through the semiconductor, failure mechanisms depend on the
microwave pulse duration. Ifthe pulse duration is short compared with
thermal diffusion times, then the temperature increases in proportion to the
deposited energy. Pulse durations (t) shorter than about 100 nanoseconds fall
into this regime, and the threshold power for damage varies as 1/t.
Experimental testing has shown that for pulse durations between 100
nanoseconds and 10 microseconds, the power required for damage scales as
1/t112• And for pulses longer than 10 microseconds, a steady state in which the
thermal diffusion rate equals the rate of energy deposition and temperature is
proportional to power, resulting in a constant power requirement for damage.
In this case, the power requirement scales as t. The consequence of these
scaling factors is that short pulses require very high power but little energy,
while very long pulses require large amounts of energy but little power. This
analysis results in a vast range of HPM sources capable of damaging
semiconductor devices. The above appli