DIA, 2010: estudo do AAWSAP descreve armas de micro-ondas que queimam eletrônicos e são difíceis de detectar

UNCLASSIFIED//[FOR OFFICIAL USE ONLY, struck through] Defense Intelligence Reference Document Acquisition Threat Support 28 January 2010 ICOD: 1 December 2009 DIA-08-0912-005 Pulsed High-Power Microwave Source Technology

Pulsed High-Power Microwave Source Technology Prepared by: Acquisition Support Division (DWO-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 this document should be addressed to [AAP Person 1], AAWSA Program Manager, Defense Intelligence Agency, ATTN: CLAR/DWO-3, Bldg 6000, Washington, DC 20340-5100.

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. One major use of HPM by the military is for electronic attack, or what is referred to by the media as an "e-bomb." 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. If the 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/t^1/2 • 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 applies to single-shot pulse durations, but if a PRR is applied such that there is insufficient time for thermal diffusion between pulses (about 1 millisecond), then there will be an overall constant rise in temperature. For this reason, the PRR capability is of extreme importance for any HPM source. As a matter of course, assets to be tested include those of friend and foe alike, the goal being to find vulnerabilities in both and correcting those found in our own assets. Several techniques are employed to mitigate vulnerabilities found in assets, including filtering of conductor lines, using metallic enclosures, eliminating any unnecessary openings in the outer enclosure, and using ferrite or other magnetic materials. Any electronics inside a completely sealed metallic container (Faraday cage) would have no vulnerability to HPM of any variety; however, such a scenario is also of little or no use, since there could be no communication to or from the enclosure. Assets therefore must include some openings for communications, instruments, air flow, and sensors, sometimes as a matter of fulfilling their function. From the HPM source perspective, care must be taken to prevent fratricide and harm to friendly assets. To prevent fratricide, all connections to the source must be filtered to prevent fast transients from returning to the control unit. Some signals can be transmitted using fiber-optic cable; however, there is usually a piece of equipment at the source end that must be filtered. Some connections, such as the high-voltage power supplies, can make good use of high inductance filtering to eliminate fast transients, while others, such as trigger lines, must make use of other filtering means, such as transformer coupling, lightning arrestors, transorbs, and fast-acting, high-voltage diodes. Preventing harm to friendly assets is difficult and is a major reason why HPM has rarely been employed in actual battlefield settings. To ensure there is no harm to friendly assets, all assets would have to be tested for vulnerabilities, something that is not done at present. The antenna is a major factor in this matter. Unfocused antennas radiate a pattern that spreads as it progresses outward and, thus, the area subjected to the EM fields increases with distance. It is then harder to separate one's own assets from the radiated fields. In addition, it is very difficult to detect these sort of pulsed sources, since the pulses are very short (typically 1-500 nanoseconds), and even in burst mode, the bursts are usually less than 10 seconds. The short burst mode operation is necessary because of the high peak powers and subsequent heating of key components such as switches. 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.

Conclusion This paper provided an overview of the current state of HPM sources and the technologies driving their development. 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 techniques are just a few of the areas where advancement clearly is needed for progress to occur. Advancements in photoconductive solid-state (PCSS) and other solid-state switching and sharpening devices appear to finally be reaching a level of development such that they may soon be of use in high-voltage systems. If PCSS switching devices capable of higher operating voltage and extended lifetime are made available, variations of the phased array will become the HPM source design of choice, given the inherent advantages. More compact antennas are greatly desired; however, the physics of the radiation process requires structure sizes on the order of one-half wavelength of the lowest radiated frequency. With demanding levels of directivity and gain also requirements, compact UWB antenna designs will continue to be difficult, if not impossible, to realize.