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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/ ,.. r,u, 8FFIIItliL ~81!! SHLY ray production, and beam breakup. The combination of x-rays and the high base pressures has led to breakdowns in the cavities and unstable beam propagation. SPLIT-CAVITY OSCILLATORS Split-cavity oscillators (SCOs) utilize transit-time bunching of the beam to generate microwave energy. They can generate microwave pulses of about 100 MW for durations on the order of 100 nanoseconds (ns). The SCO can be very compact since no magnetic field is required and low beam quality requiring only basic pulse power sources is adequate. Complete systems, including a power supply and mode-converting antenna, have been built on roll-around laboratory carts. VIRTUAL CATHODE OSCILLATORS Virtual cathode oscillators (vircators) operate because of a phenomenon of intense beam physics. They have no conventional counterpart. They have operating frequencies tunable from 300 MHz to 40 GHz, no required magnetic field, simple construction, and low efficiency. Power output varies from 200 MW to 15 GW, and efficiencies range from 1 to 10 percent. Operation is typically in a TM mode in a cylindrical geometry with mode conversion necessary for efficient radiation. The frequency of oscillation of a free- running vircator is related to the relativistic beam plasma frequency and typically chirps upward during the pulse. Plasma closure effects limit the pulse length. Containing the oscillating beam in a resonant cavity can stabilize the frequency. If the resonant cavity is driven by an external source, the vircator can be made to lock to the external signal. Although vircators' simplicity is a major advantage, their very low efficiency poses real problems for weaponization. They have been used as sources for testing, where efficiency and size are not an issue. MAGNETRONS HPM magnetrons are basically relativistic, cold-cathode versions of their conventional counterparts. They are characterized by relatively high efficiency, low power densities internal to the tube, robust operation, and compact size. Their modulators and power supplies are simple and inexpensive compared with BWOs, TWTs, and RKAs. Relativistic magnetrons have achieved efficiencies of 10-30 percent in the bands from 0.5 to 10 GHz at power levels of about 5 GW. Pulse widths are on the order of 100 ns, limited by plasma closure of the anode-cathode gap. Magnetrons may be phase locked for higher output power. The magnetically insulated line oscillator (MILO) is essentially a magnetron that uses the magnetic field of the beam current to provide magnetic insulation between the cathode and anode. This eliminates the need for pulsed magnets and their power supplies while also reducing the size and weight of the system. No mode conversion is required with the MILO. 18 UNCLASSIFIED//EiOAt OEiEil&l11J.k W&liii ,Ulklf
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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.