Ka-Band Low-Voltage Multiple-Beam TWT Experiment

Multiple-beam vacuum electron devices are attractive for compact, high-power device applications because of the increased beam current that can be achieved with multiple beams at moderate or low operating voltages [1], [2]. We describe the design, development and initial testing of a proof-of-principle 4-beam, ~100 mA/beam, folded-waveguide TWT operating in Ka-band at 6.2 kV. From simulation using NRL codes, this TWT is predicted to generate an output power of about 300 W at a central frequency of 29 GHz. First, a 4-beam beamstick was built and tested, demonstrating 100 mA per beam and 400 mA total current. In the full TWT device tests, the beam current was reduced by about 30% from the design level, probably due to cathode surface contamination. This limited the output RF power of this device to 120 W, in good agreement with simulations at reduced current.