Investigation of the effect of support rod permittivity on TWT performance

Summary form only given. The cold-test parameters including dispersion and on-axis interaction impedance, have been calculated for a Northrop-Grumman helical TWT slow-wave circuit using MAFIA, the three-dimensional electromagnetic finite integration computer code. The helix model includes tape thickness, dielectric support geometry and material properties consistent with the actual circuit. Measured and simulated cold-test data for the helical circuit will be presented, showing excellent agreement. These parameters will also be compared for several variations on the dielectric constant of the rods, including axially and azimuthally asymmetric configurations, consistent with likely variations occurring in actual manufactured TWTs. The large deviation in TWT performance due to these variations suggest a need for more accurate dielectric data and improved control of material fabrication processes.