DIMOHA: A Time-Domain Algorithm for Traveling-Wave Tube Simulations

To simulate traveling-wave tubes (TWTs) in time domain and, more generally, the wave-particle interaction in vacuum devices, we developed the DIscrete MOdel with HAmiltonian approach (DIMOHA) model as an alternative to current particle-in-cell (PIC) and frequency approaches. Indeed, it is based on a longitudinal N-body Hamiltonian approach satisfying Maxwell's equations. Advantages of DIMOHA comprise: 1) it allows arbitrary waveform (not just field envelope), including continuous waveform (CW), multiple carriers, or digital modulations (shift keying); 2) the algorithm is much faster than PIC codes, thanks to a field discretization allowing a drastic degree-of-freedom reduction, along with a robust symplectic integrator; 3) it supports any periodic slow wave structure (SWS) design such as a helix or folded waveguides; 4) it reproduces harmonic generation, reflection, oscillation, and distortion phenomena; and 5) it handles nonlinear dynamics, including intermodulations, trapping, and chaos. DIMOHA accuracy is assessed by comparing it against measurements from a commercial Ku-band tapered helix TWT and against simulations from a subterahertz folded-waveguide TWT with a staggered double-grating SWS. The algorithm is also tested for multiple carriers simulations with success.