Ring-Double-Bar Slow Wave Structure for High Power TWTs

The electromagnetic properties of a ring-double-bar (RDB) slow wave structure are investigated. Use of two bars to connect neighboring rings instead of one as in a conventional ring-bar (RB) structure leads to the splitting E- and H-waves, with the H-wave concentrated in thin layers near the rings. This effect leads to the flattening of the dispersion characteristic, similar to that in a helix with longitudinal vanes. Prototype RDB structures have been fabricated, measured, and compared with the conventional helix and RB circuits. Analysis, simulation, and cold test measurements demonstrate that the use of an RDB structure may make it possible to increase the maximum stable operating voltage of wideband traveling-wave tubes to 30-40 kV, enabling an order of magnitude increase in output power without the danger of backward wave oscillation.