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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.
“The Times”17 pages
UNCLASSIFIED//Flilll. lilFFllil,t.k Wlilii lil•lklC appears to be hydrogen ions, which, because of their low mass, contribute to the problem of gap closure. The gap closure velocity using carbon cathodes quoted by most reports researched is 2-2.5 cm/μsec, and diode gaps from the same reports were 1-4 centimeters. Carbon cathodes also have much longer lifetime than velvet. However, one of the greatest advantages of carbon is the ever-expanding ability to form both macro- and nanostructures using it as a base or substrate. Structures formed using carbon include pyramids, fibers, microfibers, nanotubes, and tufts. Many possible carbon structures still have yet to be formed and tested. Thus far, structures with the most surface area appear to perform best. CERAMICS Ceramics, much like carbon, can be formed into at least microstructures and have some features that have attracted interest in them for a couple of decades. These include virtually unlimited lifetimes and extremely low outgassing. A problem with ceramics, however, is that very high threshold fields are required for diode operation. Coatings to improve the performance of ceramic cathode structures may exist, and research is continuing in this area. CESIUM IODIDE COATED One of the most recent and impressive materials to be used in cathodes for HPM tubes is cesium iodide. Cesium is a pure metal that has a work function of only 1.9 eV and a melting temperature of 28 °Celsius; thus, it is liquid at only slightly above room temperature. Cesium ions are quite heavy, and that is why this coating was used initially. It was believed that the gap closure rate would be slowed since the heavy cesium ions would progress much more slowly across the anode-cathode gap than would other ion species, given the same electric field. This has proved to be the case, and closure velocities that are about one-fourth those for velvet or bare carbon (0.4 cm/psec) have been attained. As a result, the HPM emission times have been extended. Typically, the cesium salt is dissolved in water as a saturated solution and then the carbon cathodes are dipped several times. Subsequently, the cathodes must be baked under vacuum for several hours to remove the water from the surface and leave the hardened cesium salt. Once completed, the cathodes have a very long lifetime unless contaminated by back splatter of material from the anode. At present, HPM programs investigating the performance of cathodes having some form of cesium coating over carbon nanostructures show the most potential for progress in the state of the art. The goal of these programs is hundreds of kiloamps for tens of microseconds, resulting in gigawatt narrow-band HPM sources running at repetition rates of possibly 100 hertz and thus capable of 100-megajoule energy output per burst. Also of great interest at present are cathodes termed "hybrids," which utilize multiple emission mechanisms in beam generation. The cathodes developed by these programs are to be used with the magnetically insulated line oscillator (Sandia National Laboratories [SNL]), the relativistic klystron oscillator (Kyle Hendricks, Air Force Research Laboratory [AFRL]), the reltron (Bruce Miller, SNL), and the super reltron, among others. 10 UNCLASSIFIED/1«F8R 8Ffl@Itllt ""I! one I
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Report, from the dia collection. The PDF is mirrored here; the original link is under it. 37 pages are in the text index: search them above, or from the library's search.