Equilibrium orbit analysis in a free-electron laser with a coaxial wiggler

An analysis of single-electron orbits in combined coaxial wiggler and axial guide magnetic fields is presented. Solutions of the equations of motion a re developed in a form convenient for computing orbital velocity components and trajectories in the radially dependent wiggler. Simple analytical solu tions are obtained in the radially-uniform-wiggler approximation and a form ula for the derivative of the axial velocity v(\\) with respect to the Lore ntz factor gamma is derived. Results of numerical computations are presente d and the characteristics of the equilibrium orbits are discussed. The thir d spatial harmonic of the coaxial wiggler field gives rise to group III orb its which an characterized by a strong negative mass regime.