PROPOSAL FOR NOVEL FEL OPERATION

It is shown that a free-electron laser operation is possible in a novel wiggler, proposed in a previous paper. A single-particle approach is used to derive the small-signal gain equation at the fundamental harmonic in this configuration for a(omega)2/2(1 + a(omega)2 << 1. 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 in the two cases. The maximum value of the small-signal gain is proportional to the cube of the interaction region length in our case, as in the ordinary linearly polarized FEL. For a given magnetostatic-field amplitude in the ordinary linearly polarized FEL and a given amplitude of the zero-order trajectory's transverse component in our case and for the same electron-beam energy, resonant radiation wavelength, interaction region length, and electron-beam density in the two cases, the maximum value of the small-signal gain in our case is greater than that of the ordinary linearly polarized FEL for large enough surface current density in our case and for small enough wiggler period in the ordinary linearly polarized FEL.