  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) 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: (i) it allows arbitrary waveform (not just field
envelope), including continuous waveform (CW), multiple carriers or digital
modulations (shift keying); (ii) 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; (iii) it supports any
periodic slow-wave structure design such as helix or folded waveguides; (iv) it
reproduces harmonic generation, reflection, oscillation and distortion
phenomena; (v) 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 sub-THz folded waveguide TWT with a staggered double-grating
slow-wave structure. The algorithm is also tested for multiple-carriers
simulations with success.
