The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results.

The SwissFEL Injector Test Facility operated at the Paul Scherrer Institute between 2010 and 2014, serving as a pilot plant and testbed for the development and realization of SwissFEL, the X-ray Free-Electron Laser facility under construction at the same institute. The test facility consisted of a laser-driven rf electron gun followed by an S-band booster linac, a magnetic bunch compression chicane and a diagnostic section including a transverse deflecting rf cavity. It delivered electron bunches of up to 200 pC charge and up to 250 MeV beam energy at a repetition rate of 10 Hz. The measurements performed at the test facility not only demonstrated the beam parameters required to drive the first stage of an FEL facility, but also led to significant advances in instrumentation technologies, beam characterization methods and the generation, transport and compression of ultra-low-emittance beams. We give a comprehensive overview of the commissioning experience of the principal subsystems and the beam physics measurements performed during the operation of the test facility, including the results of the test of an in-vacuum undulator prototype generating radiation in the vacuum ultraviolet and optical range.

Abstract. The goal of SwissFEL is to provide a source of extremely bright and short X-ray pulses enabling scientific discoveries in a wide range of disciplines, from fundamental research to applied science. To accelerate the electrons to an energy of up to 5.8 GeV a linear accelerator (LINAC) consisting of 104 C-band (5.712 GHz) accelerating structures each of a length of 2m is foreseen. We present the mechanical design of the accelerating structures. High precision manufacturing is applied in order to avoid a tuning step during fabrication. Following this production process several 0.3 m test structures have been produced and tested. First results including RF power tests are presented. Description of linear accelerator (LINAC) of SwissFEL and of its general requirementsThe LINAC is used to accelerate an electron bunch to an energy of 5.8 GeV before the lasing process is initiated in the undulator section. One module consists of 4 C-band (5.7 GHz) structures made of copper which are fed by one pulse compressor connected to one modulator and to one klystron (figure 1). 26 modules or 104 C-band structures aligned along a row of 300 m are required to accelerate the electrons up to 5.8 GeV.To minimize cost and to achieve an economical series production of the C-band accelerating structures fabrication has to meet stringent requirements.• Precision of one single copper cell is of 1 µm and has a surface roughness R a of 25 nm.• Concentricity is 50 µm of a 2m C-band structure before and after vacuum brazing together in one step the J-shaped input and output couplers and the 113 copper cells (table 1).• No additional mechanical tuning of a 2m long C-band structure is required after brazing since all individual volumes of the 113 copper cells match the specified frequency (5.712 GHz) and the nominal phase advance of 120°.