NONLINEAR-THEORY OF A FOLDED WAVE-GUIDE GYROTRON TRAVELING-WAVE TUBE AMPLIFIER

We have developed a three-dimensional nonlinear theory for broadband g yrotron traveling-wave amplification in an H-plane-bend folded wavegui de. The H-plane-bend configuration is formed by folding a rectangular waveguide so that the orientation of the magnetic field changes along the bend in contrast to the conventional E-plane bend, where the orien tation of the electric field changes. Calculations show the feasibilit y of amplifier operation with large instantaneous bandwidth and modera te efficiency both in the slow wave region and the reduced dispersion fast wave region. Numerical results for a cold beam show an efficiency of 26% with 11% bandwidth in the slow wave region and an efficiency o f 47% with 10% bandwidth in the fast wave region. For an electron beam with 2% velocity spread and 2% guiding center spread, the slow wave e fficiency drops to 6% but the bandwidth increases to 16% whereas the e fficiency and bandwidth of the fast waves decrease by a small amount t o 42% and 9.5%, respectively. The efficiency is more sensitive to the axial beam velocity spread in the slow wave region due to larger Doppl er shift.