Axial free-electron laser interaction between an annular electron beam and an axisymmetric TM mode

Free-electron lasers (FEL's) operating with helical wiggler fields and axial guide fields are subject to orbit instability which causes additional particle loss as saturation is reached, A new type of FEL interaction possible between an annular electron beam and a TM/sub 0m/ mode is described here. This interaction is between the axial electron motion and an RF mode that is radially "wiggled" a in periodically rippled waveguide. The net transverse force integrated over a wiggle period on each of the particles in this type of device can be made to vanish by choosing the proper waveguide radius. The resulting particle orbits are more stable than those in conventional FEL's with helical wiggler fields.<
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