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This Defense Intelligence Reference Document from the Defense Intelligence Agency, dated 28 January 2010, surveys pulsed high-power microwave (HPM) source technology. It was produced under the Advanced Aerospace Weapon System Applications (AAWSA) program. It covers insulation, cathode materials, high-voltage switching, pulse generators, microwave sources such as magnetrons, gyrotrons and the Phoenix and Jolt sources, and antennas. The document concludes that progress depends on advances in cathodes, switching and insulation. It says compact ultrawideband antennas will remain difficult to build.
UNCLASSIFIED//F81il 8FFI1il.t.L Wfili &,•LY Table 3 shows findings of cathode material studies at SNL and at the AFRL. Table 3. Cathode Study Findings Material Emission Threshold Lifetime Outgassing (kV) (# of Shots) (Neutrals/Electron) Cs I-Carbon 72,000 4- 6.5 (substrate) Microfibers "Sandia Red" Velvet 8 kV/cm - 8,000 10 ".iW:ILO Green" Velvet 10 kV/cm - 4,000 10 - 14 Velveteen Low Low 12 F-Velvet Low 12 Ceramic Cloth > 120kV/crn --- --- Ceramic Felt > l00 kV/cm --- --- Carbon Pvramids >80kV/cm --- --- Carbon Nanotubes 20-50 kV/cm Arc rate of - -4 2% Bare Carbon 15-40 kV/cm > 36,000 4.3 - 6.5 Microfiber (substrate) (packing density) Csl-Carbon Fiber 2011.111111 -4 Tufts Metal I Ceramic 95 kV/cm (diode --- 8 collap:.e unless> 150 kV/cm) 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 true 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 begin at the cathode in an average electric field of only 20- 25 kV/cm and, by virtue of an enhanced electric field at their tip, progress in an orderly fashion to the anode. At this time, a heating phase begins, 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 determined by the width and rise time of the square pulse. The period of the lowest frequency is twice the pulse width, and the rise time is about one-quarter the period of the highest frequency. 11 UNCLASSIFIED/ ;CEiOAt OFFIQI.Ctk WfiEii &,•LY
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Report, from the dia collection. The PDF is mirrored here; the original link is above. 37 pages are in the text index: search them above, or from the library's search.