P3-3: Measurement of loss in high power 170 GHz gyrotron transmission lines

Over-moded corrugated cylindrical waveguides are used for high power gyrotron radiation transmission applications, such as ITER, because of their low loss characteristics at millimeter wavelengths. Measurements on such over-moded systems are fraught with inaccuracies due to higher order modes. We report a new technique to accurately measure the inherent loss of an over-moded device in the desired operation mode. This technique is demonstrated successfully on low-power measurements at 170 GHz in 63.5 mm diameter corrugated ITER transmission lines. We find the miter bend loss to be 0.022 ± 0.008 dB (0.5 ± 0.2 %), in good agreement with theory.