Microfabrication and cold testing of copper circuits for a 50 Watt, 220 GHz traveling wave tube

We present the microfabrication and cold test measurement results of serpentine waveguide amplifier circuits at 220 GHz. The circuits were fabricated using a novel embedded polymer monofilament technique combined with Ultraviolet-LIGA to simultaneously create both the beam tunnel and interaction circuits. We find remarkable characteristic matches between the measurements of the best circuits, illustrating that the process developed is able to create repeatable, highly precise circuits with high yield. It was found that slight beam tunnel misalignment can cause very strong stopbands to appear in the operating band due to bi- or quasi-periodicity. The NRL code TESLA-SW/FW has been used to rapidly simulate the as-built structure under a variety of conditions to accurately predict the performance with an electron beam. The tolerances needed on beam tunnel alignment are studied, with implications extending to the THz range.