Bunching coefficients in echo-enabled harmonic generation

Coulombian diffusion determines a dilution of bunching coefficients in free electron laser seeded devices. From the mathematical point of view the effect can be modeled through a heat-type equation, which can be merged with the ordinary Liouville equation, ruling the evolution of the longitudinal phase space beam distribution. We will show that the use of analytical tools like the generalized Bessel functions and algebraic techniques for the solution of evolution problems may provide a useful method of analysis and shine further light on the physical aspects of the underlying mechanisms.