Linear theory of gyrotron traveling wave tubes with nonuniform and lossy interaction structures

A linear theory model is developed to analyze gyrotron traveling wave tubes ~gyro-TWT! employing nonuniform interaction structures, which can be tapered wall waveguide, severed tubes, or distributed lossy wall waveguides. Effects of the wall loss, reflections caused by the nonuniformity of the waveguide, and beam–wave interactions inside the sever region are incorporated in this theory. In addition, self-excited oscillations in the gyro-TWT induced by absolute instabilities or reflections can also be studied by the same theory. Good agreements with the self-consistent particle-tracing code have been achieved. This theory can be used to provide a first-cut design of a stable gyro-TWT. © 1998 American Institute of Physics. @S1070-664X~98!02906-1#