Nonlinear wave-particle interaction in helix traveling-wave tubes using N-body simulations in time domain

Introduction Momentum exchange between waves and particles caused by nonlinear synchronisation is a key process, responsible for Landau damping as well as for the amplification in devices like gyrotrons, free-electron devices or traveling wave tubes (TWTS) [1, 2, 3]. But a complete description of the wave-particle interaction is a challenge due to the large number of parameters involved. To model TWTs, we use the N-body (many-body) description of wave-particle interaction. This description is often deemed impossible in classical electrodynamics and for microscopic dynamics of plasmas, but we show that it is, in fact, a viable alternative to the traditional vlasovian (kinetic) approach, especially for time simulations of turbulence and instabilities generated by nonlinear particle dynamics (trapping, chaos, threeor four-wave couplings). Combined with a model reduction to decrease the number of degrees of freedom, this description enables us to accurately study periodic structures.