A re-examination of scaling laws in the traveling wave interaction

A re-examination of traveling wave interactions (in the helix traveling wave tube and the free-electron laser) is performed 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.