Proposal for novel FEL operation

It is shown that free-electron-laser (FEL) operation in a novel wiggler, proposed in a previous paper by the author (1990), is possible. A single-particle approach is used to derive the small-signal gain equation at the fundamental harmonic in this configuration for sufficiently small a_ω. The small-signal gain curve has the same shape as that of the ordinary linearly polarized FEL, but the expressions for the resonance parameter and for the multiplying coefficient in the small-signal gain equation are different. The maximum value of the small-signal gain is proportional to the cube of the interaction region length in the present case, as in the ordinary linearly polarized FEL, but the maximum value of the small-signal gain is greater than that of the ordinary linearly polarized FEL for large enough surface current density