A W-band extended interaction oscillator (EIO) driven by a pseudospark-sourced sheet electron beam (PS-SEB) is demonstrated in this letter. The idea of combining the advantages of a pseudospark-sourced electron beam (high beam current density), a sheet electron beam geometry (large beam cross-sectional area) and a ladder-like slow wave structure (high gain per unit length) to generate powerful millimeter-wave radiation was experimentally verified. The PS-SEB based EIO produced ~1.2 kW peak output power, an increase of six times in the measured power from an EIO based on a pseudospark-sourced pencil electron beam. Such a methodology offers a promising solution for portable, low-cost and powerful millimeter-wave and terahertz-wave radiation sources.

The study of a planar G-band extended interaction oscillator (EIO) driven by a pseudospark-sourced (PS) sheet electron beam is presented. This enables the advantages of a planar interaction circuit combined with the merits of a PS sheet electron beam, including large beam cross section, high current density and the fact that a PS electron beam does not require the use of an external focusing magnetic field. Beam-wave interaction simulations for this planar EIO predicted a peak output power of 2.1 kW at ~0.2 THz. Investigations indicate that this planar EIO has a better tube performance with a higher radiation power compared with the PS pencil electron beam EIO.

We have recently proposed to combine the advantages of a pseudospark-sourced sheet electron beam (PS-SEB) with a planar slow wave structure to generate high power terahertz radiation. To verify this idea, experimental investigation of an extended interaction oscillator based on the PS-SEB has been conducted and presented. A PS-SEB of approximately 1.0 mm × 0.17 mm in size with 21.5 A peak current (1.26 × 10⁴ A/cm² beam current density) and 34.5 kV peak voltage was measured after propagating a distance of 10-mm without the need of an external focusing magnetic field. A radiation pulse of ∼35 ns in duration and an output power of over 10 W at a frequency of ∼0.2 THz were measured.

To accurately measure the performance of dielectric loaded circuits for gyrotron traveling wave tubes, a novel topological structure to generate the TE ₂₁ ^O or TE ₀₁ ^O (superscript represents circular waveguide) mode is proposed and verified in this paper. The topology is constituted by an overmoded TE ₁₀ ^□ to TE ₂₀ ^□ (superscript represents rectangular waveguide) mode converter with multiple matching steps and a taper from TE20 ^□ to TE ₂₁ ^O or TE ₀₁ ^O mode. This topology allows the TE ₂₁ ^O or TE ₀₁ ^O mode to be excited by changing the taper dimensions. Simulation results reveal that the TE ₂₁ ^O and TE ₀₁ ^O mode converters, respectively, have a 1-dB bandwidth of 12.8 and 9.3 GHz with an excellent performance. Converters for the back-to-back millimeter-wave measurements were fabricated with computerized numerical control and wire cutting techniques. Vector network analyzer measurements are in good agreement with the simulations.

A high-power Ku-band TE01 mode gyro-traveling wave tube (gyro-TWT) with a loss loading structure is designed, fabricated, and tested. A high beam quality magnetron injection gun generating 68-kV, 20-30-A electron beam is optimized to provide a high power radiation. A novel lossy ceramic loaded structure with mode selective attenuation ability is proposed to suppress the potential backward wave oscillation. The interaction circuit is analyzed by linear, nonlinear self-consistent theory, and experiment. An improved wideband input structure design is proposed accordingly. In the hot test, the proposed gyro-TWT produces a 420-kW maximum peak power, about 35-dB saturated gain, 23% efficiency, and more than 1.6 GHz (10%)-1-dB bandwidth in a stable operating condition.