A REEXAMINATION OF THE TRAVELING-WAVE INTERACTION

A re-examination of the traveling wave interaction (in the helix traveling wave tube and the free-electron laser) is performed using three-dimensional linear stability analyses for an idealized annular electron beam model in order to investigate the validity of the well-known scaling laws in which the gain varies as the cube (fourth) root of the current when space-charge effects are negligible (dominant). The results indicate that these scaling laws are simplistic generalizations which break down for; broad bandwidth interactions, and that the actual variation of the gain with the current can be more complex. A three-dimensional nonlinear analysis of a free-electron laser using a more realistic electron beam model is also discussed in which these scaling laws are also shown to break down.