• Yu. Lurie, Y. Pinhasi
  Ariel University Center of Samaria, Faculty of Engineering, Ariel

In pulsed beam free-electron devices, longitudinal space-charge fields result in collective effects leading to expansion of short electron pulses along their trajectory. This effect restricts application of intense ultra-short electron pulses, and requests a careful theoretical description. In the present work, longitudinal space-charge fields are considered in the framework of a three-dimensional, space-frequency approach. The basic equations of the model, originally obtained as a solution of the wave equations for the electromagnetic field in an uniform waveguide, are shown to satisfy also Gauss's law. Longitudinal electric field was found in the model analytically for a point-like charge, moving along a waveguide with a constant velocity. This enables consideration and comparison of different components of the resulted longitudinal electric field, such as forward and backward going waves, near and under cut-off frequencies, and so on. Possible simplifications in evaluations of longitudinal space-charge fields in the model are discussed.

• Y. Pinhasi, Yu. Lurie
  Ariel University Center of Samaria, Faculty of Engineering, Ariel

Free-electron lasers (FELs) and masers, utilize distributed interaction between an electron beam and the electromagnetic field. Our space-frequency theory [*] is extended to consider collective effects emerging while ultra short electron pulses are propagating in the interaction region. The total electromagnetic field (radiation and space-charge) is presented in the frequency domain as an expansion in terms of transverse eigen-modes. The mutual interaction between the electron beam and the electromagnetic field is fully described by a set of coupled equations, expressing the evolution of mode amplitudes and electron beam dynamics. The model is used for the study of radiation excitation in pulsed beam free-electron lasers operating in millimeter wavelengths and Tera-Hertz frequencies. The approach is applied in a numerical particle code WB3D, simulating wide-band interaction of a free-electron laser operating in the linear and non-linear regimes, and is utilized to study spontaneous and super-radiant emissions radiated by a an electron bunch at the sub-millimeter regime, taking into account three dimensional space-charge effects playing a role in such ultra short bunches.

* Y. Pinhasi, Yu. Lurie, A. Yahalom: “Space-frequency model of ultra wide-band interactions in millimeter wave masers”, Phys. Rev. E 71, (2005), 036503- 1-8