Undulator For The CLIO Project At Orsay

The CLIO collaboration (Collaboration pour un Laser Infrarouge a Orsay) started in 1986, in order to build an infrared laser at LURE (Orsay). It includes the design and the construction of a new FEL dedicated RF linear accelerator, to make a tunable laser in a broad wavelength range (typically 2- 20 μm) with a peak power in the MW range and an average power of a few tens of watts. In order to obtain enough gain at low wavelength (λ≈2 μm) together with a good energy extraction at long wavelength, a two component undulator has been designed and built. It is made of two identical 1=0.96 m long undulators with a computer controlled and automatically adjustable magnetic gap, the second undulator being possibly tapered. The undulator period was chosen as λ0=4 cm. Preliminary calculations indicated that the regime in which a half length constant gap undulator is followed by a tapered one provides the best energy extraction. To adjust easily the FEL wavelength, the non hybrid technology was chosen. With a judicious choice of a few electron energies the spectral region from 2 to 20 μm can be spanned by varying the undulator gap between 10 and 30 mm.