Nuclear Instruments and Methods in Physics Research A 331 (1993) 3-5 North-Holland NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH Section A FEL development at the Budker Institute of Nuclear Physics N.A. Vinokurov Budker Institute of Nuclear Physics, Lavrentyeu pr., 11, Novosibirsk 630090, Russian Federation There are three different FEL projects at the Budker Institute of Nuclear Physics: 1) the FEL on the VEPP-3 storage ring which operates in the visible and ultraviolet region; 2) the high power FEL using a racetrack microtron recuperator (this machine will provide an average power of about tens of kilowatt in the infrared region); and 3) the compact infrared FEL project, using a microton, and a powerful FEL on a dedicated superconducting storage ring, which is under consideration now. The free electron lasers (FEL) is a new type of laser. In principle, an FEL may produce radiation tunable in wavelength in the 0.1 to 1000 ~xm range at a mean power of up to 1 MW (and possibly higher). Radiation generated by an FEL can find its application in science (physics, chemistry, biology), medicine, and modern technology. Tunability, high technical effi- ciency, high mean power and a radiation divergence close to the diffraction limit are features of FEL that compare favorably with other powerful lasers. To produce electron beams for FELs, different kinds of accelerators are used. From the point of view of engineering and cost aspects, accelerators are the ma- jor components of FELs, whose radiation is deter- mined by the parameters of the electron beams. This motivates the development of dedicated electron accel- erators optimized for the present problem. This clari- fies why the Budker Institute of Nuclear Physics is a convenient site for this kind of activity. The Institute has great experience in development, building and performance of various accelerators for physics of ele- mentary particles (colliding electron-positron beams, electron cooling of protons, project for a linear col- lider), technology (industrial accelerators for irradia- tion of various materials, ion implantation), and syn- chrotron radiation generation (dedicated storage rings, insertion devices, beamlines). Work on FEL develop- ment is carried out in several directions. Just after the exciting experiments of Elias et al. [1] the idea came up to install an FEL on storage ring VEPP-3. The modification of an FEL with sufficiently higher gain, the optical klystron, was proposed [2], manufactured, installed on the storage ring, and the spectrum of the spontaneous emission and gain had been measured [3]. At the same time the storage ring FEL power limitations had been understood [4] and the technique of the mirror reflectivity measurements was developed [5]. To increase the gain hybrid perma- nent magnet undulators were proposed and used in the second modification of the optical klystron [6]. In order to increase the gain further a third magnetic system with a larger aperture and larger undulators' length was build [7]. The undulators had wedge shape poles to decrease the Stray fields. After the big fire in 1985 we began to design the fourth version of the optical ldystron to be installed on the dedicated bypass. It has long (3.4 m) electromag- netic undulators [8], a zero ~-function and optimized /3-functions in the FEL straight section, good vacuum pumping near the mirrors and an improved mirror alignment system [9). The FEL for visible and ultraviolet wavelength range (0.69-0.24 p.m) has been in operation on the VEPP-3 electron storage ring since 1988 [10]. For the time being, this is the FEL with the shortest wavelength. After a Fabry-Perot etalon was installed inside the exceptionally narrow optical cavity for the FEL, a generation line (AA/A = 4 × 10 -6) was obtained [11]. FEL generation with a confocal optical cavity inside was realized [12]. This work is of importance for the creation of a powerful FEL with long cavities. The scheme of radiation extraction from a powerful FEL was also modeled (the so-called "electron radiation extraction" earlier suggested at the Institute) [13-15]. The experiments with this system have confirmed the correctness of the computations, i.e. they have shown that there is the possibility of creating a powerful FEL with this kind of radiation extraction. At present work is in progress on further shortening the radiation wave- length (to 0.21 txm). This is complicated by the absence of mirrors whose reflection factor is close to unity ( ~ 99%) in this spectral range. Recently we tested here the technique to modify the angular distribution of the planar undulator radiation [16], which permits one to remove the short-wavelength part of the radiation from the center of the FEL resonator mirror, which results 0168-9002/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved I. MEMORIAL LECTURES