  Non-linear simulation results for a 220-GHz rectangular dielectric-loaded
traveling wave amplifier are presented. Simulations are used to check a linear
theory that is developed by phenomenological introduction of an effective
dielectric parameter for electron beam channel, and it is found that the RF
power gains from Pierce three-wave theory and particle simulations are in
reasonable agreement. It is shown that the RF power gain during initial
beam-wave interaction is positive; the falling on the initial RF power profile,
which has been thought to be the RF power transferred to the beam for bunching
buildup (negative gain effect), is probably resulting from numerical errors.
Beam-wave interaction mechanism is analyzed by examining the evolution of beam
bunching centers. Influences of various parameters on amplifier performance are
examined, and transverse space-charge effect is analyzed. A symmetric
excitation scheme for RF couplers is proposed, and RF field jumps on the common
intersection line of vacuum, dielectric, and metal wall, which is found in RF
simulations, are explained theoretically.

Accelerator Physics