Design of a miniaturized terahertz traveling wave tube with embedded single-walled carbon nanotubes cold cathode

In this paper, a miniaturized terahertz traveling wave tube (TWT) based on the embedded single-walled carbon nanotubes (SWCNTs) cold cathode electron source is studied. The cold cathode suitable for the terahertz TWT requires stable high emission current density and enhanced electron beam focusing performance due to the small size of the electron beam tunnel and the long beam-wave interaction length of the terahertz TWT. Firstly, a stable SWCNTs cold cathode is fabricated by an improved screen-printing method, which achieves a low turn-on field of 0.78 V/µm and a high emission current density of 11 A/cm². Then, a grid-free electron gun with the embedded planar SWCNTs cold cathode is designed, which reduces the beam radius by 11 times compared with the planar cold cathode with non-embedded structure. The beam waist can reach 0.016 mm under the action of the periodic permanent magnet (PPM) focusing system, and the electron beam is well confined within the radius of 0.05 mm without interception. Finally, a G-band folded waveguide TWT based on the SWCNTs cold cathode electron source with the output power of 807 mW at 220 GHz is designed. This design is promising for the application of terahertz communication, such as 6G.