A free-electron laser with a rotating quadrupole wiggler

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Abstract
A new rotating quadrupole wiggler configuration for free‐electron lasers is proposed. The stability analyses of the particle trajectories in a continuously rotating quadrupole magnetic field and self‐fields of a solid beam are performed. The resulting orbit equations are solved exactly and it is shown that high‐current beams can be confined. To analyze the potential of this wiggler for free‐electron lasers, a set of nonlinear orbit equations is derived which averages over the fast time variation in both the wiggler and radiation fields. By integrating these equations, the linearized single particle gain of the free‐electron laser is calculated. It is shown that, at comparable wiggler strengths, the rotating quadrupole wiggler and conventional wiggler give similar gains.