Experimental test of the inverse free-electron-laser accelerator principle

A free-electron laser was configured as an autoaccelerator to test the principle of accelerating electrons by stimulated absorption of radiation (λ=1.65 mm) by an electron beam (750 kV) traversing an undulator. Radiation is produced in the first section of a constant period undulator (${\mathit{l}}_{\mathit{w}1}$=1.43 cm) and then absorbed (∼40%) in a second undulator, having a tapered period (${\mathit{l}}_{\mathit{w}2}$=1.8–2.25 cm), which results in the acceleration of a subgroup (∼9%) of electrons to ∼1 MeV.