Numerical simulations of gyro-devices with hybrid-PIC formulation

Summary form only given, as follows. Recent strong interest in the development of compact, efficient, high power, millimeter wave gyro-devices has accentuated the need for advanced design tools capable of accurately predicting the device actual performance. At the Naval Research Laboratory, the studies of the nonlinear saturation gain, efficiency, and bandwidth for gyro-devices are approached from two different formulations: (1) slow-time scale (SLT) formulation and (2) hybrid particle-in-cell (PIC) formulation. The SLT formulation is a computationally efficient, well-proven approach suitable for the accurate modeling of steady-state, single-mode, amplifier operations. For time-dependent multimode design problems where frequencies are arbitrary (e.g. mode competition and spurious oscillations), the hybrid -PIC formulation is the appropriate approach. This formulation is the basis for a 3-D, finite difference, time domain, PIC code recently developed at NRL. In both approaches, the transverse spatial profile of the electromagnetic fields is decomposed into a complete set of orthonormal basis functions (waveguide eigenmodes). For the hybrid-PIC formulation, the transverse modal expansion allows the reduction of Maxwell´s equations into a coupled set of 1-D (axial) equations which are self-consistently solved, directly both in time and real space, with a finite-difference algorithm. Numerical simulations of both gyrotron and peniotron interactions have been performed with the new hybrid-PIC code. Comparisons between the SLT and hybrid-PIC formulations in appropriate cases have shown good agreement. Current code modeling capabilities include uniform and vaned interaction circuits, gyro-traveling-wave amplifiers, gyro-klystron amplifiers, and gyro-oscillators.