The NRL Fluid-Cooled Helix Traveling-Wave Tube.
NAVAL RESEARCH LAB WASHINGTON D C
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In the conventional helix traveling wave tube the helix is supported by three or four ceramic rods between the helix and tube shell. The amount of average power attainable is limited by the amount of heat that can be conducted along the helix and across the ceramic supports. A fluid-cooled helix was designated that employs a helix made of copper tubing supported by hollow ceramic tubing brazed at each half turn of the helix. Several geometries of fluid flow and their effect on the RF design of the tube were tested. The cooling analyses indicate that it should be possible to dissipate at least five times as much power with the fluid cooling as with conventional thermal conduction for frequencies up through S-band. For some fluids the circuit RF losses increase rapidly with frequency above the operating frequency. This is useful for suppressing unwanted backward-wave oscillations. Experimental tubes were built and tested. Four kilowatts of average power was attained at 3 GHz in a design that was capable of octave bandwidth operation.
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