DOW-UAP-D121: Pulsed High-Power Microwave Source Technology - Insulation, Switches, Cathodes and Antennas for Directed-Energy Weapons

Source file: DOW-UAP-D121_AAWSAP-DIRD-Pulsed-High-Power-Microwave-Source-Technology-January-28-2010.pdf Originating agency: Defense Intelligence Agency (DIA), Defense Warning Office, Directorate for Analysis; produced under the Advanced Aerospace Weapon System Applications (AAWSA) Program Document type: Defense Intelligence Reference Document (DIRD), "Acquisition Threat Support" series; control number DIA-08-0912-005 Date: 28 January 2010 (ICOD, the information cutoff date: 1 December 2009) Classification: UNCLASSIFIED//FOR OFFICIAL USE ONLY, with the "For Official Use Only" caveat struck through on every page; publicly released in 2026 Page count: 37 VIRIN: 260918-D-D0360-1110 PURSUE Release: 6

Summary

This DIRD is an engineer's guide to building pulsed high-power microwave (HPM) sources, devices that radiate very short, very intense electromagnetic pulses in order to upset or destroy electronics. It was prepared by the Acquisition Support Division (DWO-3) of DIA's Defense Warning Office. The author appears only as "AAP Person 64", and an administrative note directs comments to "AAP Person 1", the "AAWSA Program Manager", at DIA, "ATTN: CLAR/DWO-3, Bldg 6000, Washington, DC 20340-5100" (page 2). It is dated 28 January 2010, with an information cutoff date of 1 December 2009.

The paper runs to 29 numbered pages of text. A three-page summary sets out the military rationale, followed by "Critical Technologies" (insulation, cathode materials, high-voltage switching), "High-Voltage Pulse Sources", "Pulsed High-Power Microwave Sources", "HPM Antennas" and a one-paragraph conclusion. It has 13 figures (including photographs of the Orion test facility, the Active Denial System and the Jolt source) and three data tables.

The paper reads like a laboratory handbook: it is full of voltages, rise times and hands-on tricks. It serves the "armament" technical area of the AAWSAP Statement of Objectives (DOW-UAP-D110), with material on pulsed power that also touches "power generation", and its account of the Active Denial System touches "human effects". It never mentions UFOs or UAP.

Research Article

From Starfish Prime to the "ebomb"

The summary opens with history. Interest began with the high-altitude electromagnetic pulse (HEMP) produced by nuclear bursts, whose 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" (page 6). HEMP fields were measured at "several hundreds of kilovolts per meter" with rise times of a few nanoseconds. Testing in the 1960s and 1970s led to programs to reproduce such effects "without requiring a nuclear detonation", which the paper calls "the impetus for the advancement of pulsed HPM technologies for weapons."

The threat framing follows. HPM weapons, unlike HEMP, "are smaller in scale, involve a much lower level of technology, and are within the capability of almost any state," and their low cost and the vulnerability of U.S. electronics "could make small-scale HPM weapons attractive to terrorist groups" (page 6). Sources built for electronic attack, "what is referred to by the media as an 'ebomb'", deliver peak powers above 10 gigawatts. As an illustration the paper cites a report that on 28 May 2001 a U.S. Comanche helicopter (spelled "Commanche" in the text) testing HPM weapons in New York state generated a pulse that disrupted the GPS equipment used to land commercial aircraft at Albany (page 7). The paper gives no source for this report.

The physics of burning out a chip

The most analytical passage explains why so many different kinds of source can all do damage. Semiconductor junctions fail thermally above about 600 K. For pulses shorter than about 100 nanoseconds, heat cannot diffuse away, so the damage threshold power "varies as 1/t". Between 100 nanoseconds and 10 microseconds it scales as 1/t^1/2, and for longer pulses a constant power is needed (the text says the "power requirement scales as t", evidently meaning the energy). The consequence: "short pulses require very high power but little energy, while very long pulses require large amounts of energy but little power" (page 7). If pulses repeat faster than about once per millisecond, heat accumulates between them, which is why "the PRR capability is of extreme importance for any HPM source" (page 8).

The same pages note three practical limits. The assets tested include "those of friend and foe alike". Fratricide is a real risk: "Preventing harm to friendly assets is difficult and is a major reason why HPM has rarely been employed in actual battlefield settings." And the sources are hard to detect, because pulses last 1-500 nanoseconds, bursts usually under 10 seconds, and ultrawideband (UWB) sources have "nearly zero energy at any one frequency" and so would be missed by spectrum analyzers (page 8).

Critical technologies: insulation and cathodes

The author argues that insulation often sets the size and limits of a system, and that most published dielectric data are measured for the power industry at 50 or 60 hertz, so that "it is often up to diligent engineers to obtain materials data on their own" (page 9). Table 1 lists breakdown strengths of ten plastics, from 7.5 kV/mil for polysulfone (Ultrason S) to 0.4 kV/mil for polyphenylene sulfide (Ryton). Thin layers are far stronger than thick ones: polypropylene withstands 7,000 volts per mil at half a mil but only 900 volts per mil at one-eighth of an inch. That effect makes laminated insulation possible (page 10). The paper records that in the early 1980s plastics makers told Sandia they "could engineer plastics to meet any set of material properties desired," which proved untrue, and that "virtually no new plastics are being introduced today."

Other practical details follow. The best casting epoxies came from the car industry's push to fit an ignition coil into each spark-plug cap; some "have the viscosity of milk at about 100 degrees Fahrenheit" and reach more than 4 kV/mil at 0.125 inch (pages 11-12). Table 2 compares gases with air: sulfur hexafluoride is the only common electronegative gas, and hydrogen is only 65 percent as strong as air but is the only gas that allows repetition rates beyond 500-600 pulses per second (page 13). A plastic-paper-oil laminate with Shell Diala AX oil has reached more than 2.1 kV/mil and 1.3 MV, and "dielectric tapering" with coatings can cut peak field stress by 50 percent (pages 14-15).

On cathodes, the paper states the Child-Langmuir space-charge limit and quotes J. R. Pierce's 1946 list of the ideal cathode's qualities (emits freely, copiously, forever, uniformly), noting that the wish list "has not changed much in more than 60 years" (page 16). Velvet, the explosive-emission standard for 20 years, turns on at about 10 kV/cm but outgasses, lasts "only about 100 shots" in some grades and is not reproducible "even between one roll and the next" (page 17). Carbon closes the gap at 2-2.5 cm/µs; cesium-iodide-coated carbon slows closure to about 0.4 cm/µs, roughly a quarter of the velvet or bare carbon rate. The goal of current programs is "hundreds of kiloamps for tens of microseconds", giving gigawatt narrowband sources at perhaps 100 hertz and "100-megajoule energy output per burst" (page 18). Table 3 (page 19) records lifetimes from under 100 shots (F-Velvet) to more than 200,000 (CsI-carbon fiber tufts).

Switches, pulsed power and a Russian connection

The paper calls high-voltage switching "among the most challenging of technologies," and says the textbook Townsend-avalanche explanation for sub-nanosecond breakdown "is most likely incorrect", while runaway-electron models fit better (page 19). Because a pulse's spectrum is set by its rise time, "switching speed is the most important parameter of a UWB HPM source" (page 20). Hydrogen gas switches and liquid switches have reached rise times around 100 picoseconds at 1,500 pulses per second (pages 21-22). Solid-state switches still cannot hold the tens of kilovolts needed. The most promising advances, the paper says, rest on "physics pioneered by I. V. Grekhov and colleagues at the Ioffe Physical-Technical Institute in St. Petersburg", with whom AFRL and the University of New Mexico were collaborating; such devices gave 6-8 kV with 100-ps rise times (page 22). Photoconductive switches coated with "amorphic diamond" at the University of Texas at Dallas reached 150-ps switching at 100 kV with a lifetime of 10^5 shots (page 23).

For prime power the paper covers Marx generators, in which about half the energy is lost in charging resistors, and transformer drivers. It complains that ferrite research is neglected because programs are "under time or budget constraints", so "little or no progress in new ferrite materials for pulsed operation has been made" (page 24). It also covers explosively driven flux compression generators, which convert chemical energy into electromagnetic energy.

The source catalogue: from Orion to Jolt

The narrowband section compares tube types. Relativistic klystrons have reached the 10-GW level at 40-50 percent efficiency. Vircators tune from 300 MHz to 40 GHz but at 1-10 percent efficiency, which "poses real problems for weaponization". Relativistic magnetrons reach about 5 GW (pages 25-26). Two systems are described in detail:

• Orion (first fielded in 1995): a transportable test facility in five shipping containers, with four tunable magnetrons (1-3.3 GHz) and a beam spot of 7 x 15 meters at 100 meters (page 27).
• Active Denial System: "the only directed-energy weapon system known to be fielded today", a 95 GHz gyrotron of 100 kW with a range of "more than 750 meters", which deposits energy about 0.4 mm into skin to cause "a burning sensation sufficiently intense to trigger an involuntary reflex response" (page 28).

The impulse (ultrawideband) sources come with specifications. Sandia's SNIPER delivers 1.25 GW with a 150-ps rise time, and EMBL 11 GW at 750 kV. AFRL's H-series (H2, H3, H5) used 2,000-psi hydrogen switches; with H5, "personnel were isolated from the source whenever any pressure was in the switch." Phoenix, at about 5 GW with a 90-ps rise time, "had the fastest rise time of any HPM source to date." GEM II, built by Power Spectra in the mid-1990s, was a 12 x 12 steerable array whose "major problem" was that "typically, a few switches failed during each burst." Jolt is a 1.1-MV "hyperband" source feeding a half impulse radiating antenna (pages 28-32). The paper also notes that DIEHL in Germany sells mesoband sources "to the public", including "a suitcase-sized system" producing 70 kV/m at 2 meters, and that BAE Systems in the United Kingdom sells others (page 33).

Antennas and the half-wavelength wall

The final technical section explains why antennas are the stubborn bottleneck. Narrowband systems will eventually use phased arrays, since arrays "are the only antennas that are compatible with electronic control for tracking targets". Adapted designs such as the flat FLAPS reflector of the Active Denial System and the Vlasov antenna are described with figures (pages 33-35). For UWB the community measures sources by a "figure of merit" (peak field times distance, in volts). Typical UWB antenna gains are 3-4. The feed section is "possibly the most important factor in HPM sources" (pages 35-36).

Significance

Unlike the speculative-physics papers in the AAWSAP series, this one concerns a real, fielded class of weapon. It frames that class explicitly as a proliferation and terrorism concern, and it names foreign commercial and scientific players (DIEHL, BAE Systems, the Ioffe Institute). Its conclusion is sober: advances are needed in "advanced cathode materials, computer codes for more predictive ability in electron beam generation and propagation, high-speed switching at high power, and low-loss insulation", and if higher-voltage photoconductive switches arrive, "variations of the phased array will become the HPM source design of choice" (page 37).

Its limits should be stated. The paper cites no references, so figures such as the Albany GPS incident rest on its word alone. It gives no assessment of any specific foreign HPM program. Much of its data describes 1990s test hardware that the paper itself says is "currently inactive". It contains no forecast in years and no mention of UAP. A companion directed-energy survey in the same release is DOW-UAP-D137 on high-energy lasers.

Key People

Locations

Key Concepts

Notable Quotes

"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." -- page 6

"Technical accessibility, lower cost, and the vulnerability of U.S. electronic equipment could make small-scale HPM weapons attractive to terrorist groups." -- page 6

"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." -- page 7

"Preventing harm to friendly assets is difficult and is a major reason why HPM has rarely been employed in actual battlefield settings." -- page 8

"The UWB sources would be the most difficult to detect, since they have nearly zero energy at any one frequency and so would not be detected at all by instruments such as spectrum analyzers." -- page 8

"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." -- page 19

"Gyrotrons are important in narrowband HPM production because the only directed-energy weapon system known to be fielded today is based on them." -- page 28

"With demanding levels of directivity and gain also requirements, compact UWB antenna designs will continue to be difficult, if not impossible, to realize." -- page 37