CNC Machined Helically Corrugated Interaction Region for a THz Gyrotron Traveling Wave Amplifier

This paper reports the development of a helically corrugated interaction region (HCIR) for a 100 W gyrotron traveling wave amplifier operating at a central frequency of 0.37 THz. This HCIR has a corrugation amplitude of 42 μm, with a nominal waveguide diameter of 0.760 mm. The HCIR was made by electroforming copper on a sacrificial aluminum mandrel: the latter was precision CNC milled using a 0.2 mm diameter ball nose cutter. The dispersion characteristics of the HCIR were measured and found to be in good agreement with the analytical calculation and numerical simulation. Measured insertion loss was between 2 and 4 dB.