An S-band fluid-cooled helix TWT

The use of moving fluids in a hollow helix structure supported by hollow ceramics is shown to simultaneously provide helix cooling, selective losses for suppressing backward wave oscillations, and low dielectric loading. The same structure using a different fluid is a high-power attenuator. The 50 PSI input fluid passes through parallel hollow ceramic supports into and through a half-turn of the hollow helix and then out through other ceramic supports on the opposite side of the helix to the fluid output. The effect of the fluid in the helix is to provide excellent cooling (1500 watts/inch at 20°C rise in the fluid) with a large safety factor. The RF losses of the fluid in the ceramics are dependent upon the wall thickness of the ceramic and the electrical conductivity of the fluid. Using water as the coolant in a specific design provides a highly frequency-selective loss which prevents backward-wave oscillations. A slight modification of ceramic inner dimension and utilization of a higher conductivity fluid provides an attenuator capable of dissipating over 5 kilowatts.