The Ultraviolet and Soft X-Ray FEL in Hamburg
The idea to use a long linear accelerator (linac) for providing the drive beam for an X-ray free-electron laser was conceived at the Stanford Linear Accelerator Center SLAC. In the Linac Coherent Light Source (LCLS) project [1] a 1km long section of the S
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8.1 Introductory Remarks The idea to use a long linear accelerator (linac) for providing the drive beam for an X-ray free-electron laser was conceived at the Stanford Linear Accelerator Center SLAC. In the Linac Coherent Light Source (LCLS) project [1] a 1 km long section of the SLAC electron linac, which has been the major facility for elementary particle physics at Stanford since 1965, will deliver the beam needed in the FEL. The SLAC machine is based on normal-conducting accelerating structures working at 3 GHz. The world’s first linear collider SLC was realized utilizing this linac to accelerate electrons and positrons to 46 GeV and collide them after the traversal of an arc to study electro-weak physics at the Z 0 resonance. Since more than 15 years large groups of particle and accelerator physicists have been working on the development of linear electron-positron colliders in the TeV regime. While at Stanford and in Japan normal-conducting machines were designed the TESLA collaboration decided for superconducting cavities as the acceleration devices. After a decade of intense R&D the collaboration succeeded in raising the accelerating field from a few Megavolts per meter to more than 35 MV/m in multi-cell niobium cavities [2]. The success of the TESLA cavity program was the essential motivation to base the future International Linear Collider ILC on the superconducting TESLA technology. The TESLA Test Facility TTF was built at DESY with the intention to investigate the performance of superconducting cavities with an accelerated electron beam and to study whether the high beam quality needed in a collider could be achieved. Already at an early stage the decision had been taken to couple the envisaged TESLA collider with an X-ray free-electron laser [3, 4]. As a first test of this concept, the TTF machine was augmented with a 13.5 m long undulator magnet. In February 2000 the worldwide first ultraviolet FEL began its operation at wavelengths between 80 and 180 nm. Meanwhile the TTF linac has been upgraded in two steps to a maximum energy of 1 GeV by adding more cavities, and the undulator was extended to a length of 27 m. The
P. Schm¨ user, et al.: The Ultraviolet and Soft X-Ray FEL in Hamburg, STMP 229, 121–148 (2008) c Springer-Verlag Berlin Heidelberg 2008 DOI 10.1007/978-3-540-79572-8 8
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8 The Ultraviolet and Soft X-Ray
new FEL facility has been named FLASH.1 The shortest wavelength achieved up to now is 6.5 nm in the first harmonic. Presently, there are several FEL projects underway all aiming at femtosecond FEL pulses in the UV and soft X-ray regime. They are facing similar scientific and technological challenges as met at FLASH. To some extent the FLASH facility can serve as a blue-print for a new class of accelerator-driven light sources, and the physical considerations and technical solutions described in this chapter are of interest for the envisaged new sources as well.
8.2 Layout of the Free-Electron Laser FLASH The vacuum-ultraviolet and soft X-ray Free-Electron Laser FLASH is shown schematica
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