AUT, Tehran
Three-Dimensional simulation of Free-Electron Laser amplifiers at the presence of helical wiggler and ion-channel has been reported. The electromagnetic field is assumed to express in terms of the TE modes of a cylindrical waveguide in the absence of the electron beam. The final form of dynamical equations for the evolution of the slowly varying amplitude and wavenumber of TE mode is obtained by substitution of the vector potentials in to Maxwell’s equations. A cold, uniform, axisymmetric electron beam with a flat-top density profile has been considered for modeling the initial injection of the electron beam. The three-dimensional Lorentz force equation in the presence of a realistic helical magnetostatic wiggler, ion-channel electrostatic field and electromagnetic fields describes the electron dynamics. A set of coupled nonlinear first order differential equations is derived and solved numerically by Runge-Kutta method. The 10th-order Gussian quaderature technique is used for calculation of averages in the field equations. Finally, evolution of the radiation power and growth rate of the TE11 mode is shown.
AUT, Tehran
The dynamical stability of electron trajectories in a free-electron laser with planar wiggler is studied. The analysis is based on the numerical simulation of Kolmogorov entropy to investigate how the separation of the trajectories of two neighboring electrons in the six-dimensional phase space evolves along the undulator. Self-electric and self-magnetic fields are taken into account and an adiabatically tapered wiggler magnetic field is used in order to inject the electrons into the wiggler. A considerable decrease in the dynamical stability of electron trajectories was found near the resonance region. It was found that self-fields decrease the dynamical stability of electron trajectories in group I orbits and increase it in group II orbits. Furthermore, the electromagnetic radiation weakens the dynamical stability of electrons as it grows exponentially and become very intense near the saturation point.
ELETTRA, Basovizza
The advent of FEL sources has brought new possibilities for experimentalists performing measurements that are challenging in terms of time resolution, flux, coherence, and so on. One of the most important points, however, is the capability of characterizing the FEL photon beam so to determine the different parameters of each pulse hitting the system under investigation. For this reason it is mandatory to realize diagnostics sections along FEL user facilities recording beam pulse-resolved features such as the absolute intensity, the energy spectrum, the beam position, the time arrival, and the wavefront. For other parameters like the coherence and the pulse length, on the other side, a direct and online detection is not possible. At FERMI@Elettra, the Italian FEL facility, a dedicated diagnostic section called PADReS (Photon Analysis Delivery and Reduction System) will be installed after the undulatory' exit, and it will serve as a source of pulse-resolved informations for end-users. In this talk the instruments that are part of typical FEL diagnostic sections will be described using PADReS as a real example to see the roles of the different diagnostic tools.
