Modified contra-wound helix circuits for high-power traveling-wave tubes

Experiments performed on modified forms of the Chodorow-Chu contra-wound helix circuit are presented with emphasis on those properties useful in the design of high voltage, high power traveling-wave tubes. Velocity and impedance measurements are shown for a fair range of pitches, crossover angles, wire widths, and wire thicknesses. Impedances are compared with those of a circuit having ideal fields (and the same phase and group velocities) and are found to be very good. Loading effects of glass and metal cylinders (envelopes), current paths, a second mode, and transitions from helix to waveguide are described. It is shown that periodic supports (stubs), used to make the structure much more rugged mechanically and capable of large heat dissipation, also increase the (already high) impedance almost as much as they decrease the group velocity, implying that the stubs add but little stored energy.