GRADUATION THESIS

EFFICIENCY ENHANCEMENT OF A THREE-DIMENSIONAL FREE ELECTRON LASER WITH A RECTANGULAR WIGGLER

A Thesis Submitted in Partial Fulfillment of the Requirement for the Degree of Master of Science in Solid State Physics
By: Amirhossein Hosseinnezhad
Supervisor: Dr. Amirhossein Ahmadkhan Kordbacheh

Abstract:

The thesis investigates the non-linear three-dimensional free-electron laser simulation based on a rectangular wiggler for a prebunched electron beam to study efficiency enhancement. The Maxwell equations and the Lorentz equations of motion are used to derive a series of non-linear first-order differential equations within the gradually varying wave number approximation and amplitude. The equations are solved numerically by using utilizing the fourth-order Runge-Kutta method. It is assumed that the relativistic electron beam is cold; however, both the self-fields of the electron beam and the slippage of the radiation wave relative to the electron beam are ignored. The appropriate parameters are chosen in agreement with the Compton regime. Both TE and TM modes of a rectangular wiggler are reported. For the present waveguide size and a 35-GHz frequency, three modes are resonant: the TE01, TE11, and TM11 modes. The other modes like TE21 and TM21 modes either do not intersect the resonance line or intersect it at large wavenumbers. Besides, the results of a rectangular wiggler and a Planar wiggler with parabolic pole faces are compared. The effect of a prebunched electron beam on saturation is studied as well. It is found that by using a prebunched beam, saturation length can be decreased, and the radiation power is increased dramatically.


Keywords: Free-electron laser, three-dimensional, rectangular wiggler, a prebunched beam, TE and TM modes, the Compton regime