Linac coherent light source: status and prospects

Abstract

The Linac Coherent Light Source (LCLS) Project will be an x-ray free-electron laser. It is intended to produce pulses of 800-8,000 eV photons. Each pulse, produced with a repetition frequency of up to 120 Hz, will provide >10 12 photons within a duration of less than 200 femtoseconds. The project employs the last kilometer of the SLAC linac to provide a low-emittance electron beam in the energy range 4-14 GeV to a single undulator. Two experiment halls, located 100m and 350m from the undulator exit, will house six experiment stations for research in atomic/molecular physics, pumpprobe dynamics of materials and chemical processes, x-ray imaging of clusters and complex molecules, and plasma physics. Engineering design activities began in 2003, and the project is to be completed in March 2009. The project design permits straightforward expansion of the LCLS to multiple undulators. Keywords: Free-electron laser, FEL, self-amplified spontaneous emission, SASE, Linac Coherent Light Source, ultrafast science PROJECT HISTORYThe scope and goals of the Linac Coherent Light Source have changed considerably since it was first conceived in 1992 1 . At this time, alternatives for design goals were considered 2 ; 2-4 nanometers would cover the "water window," permitting single-shot imaging and holography of biological samples. Operation at 0.1 nanometer wavelength was considered feasible if the full energy capability of the SLAC linac could be harnessed. The earliest proposals were predicated on minimum cost and maximal use of Stanford Linear Accelerator Center facilities. For example, the Final Focus Test Beam (FFTB) enclosure was to house the undulator. A single experiment station, set up adjacent to the FFTB, was similarly modest in scope. As interest in the proposal grew and scientific opportunities came into focus 3 , a target operating range of 1.5-0.15 nanometers was chosen, to be achieved using the last kilometer of the SLAC linac and 1/3 of its maximum operating energy 4 . The LCLS Conceptual Design Report 5 describes the more extensive facilities proposed in 2002, with six experiment stations located in two experiment halls. Meanwhile, The TESLA Linear Collider program at DESY was expanded to include a VUV/soft x-ray FEL in the TESLA Test Facility 6 , and the TESLA Linear Collider concept was expanded to include a large-scale light source facility with ten undulators fed by beams up to 50 GeV extracted from the collider linac 7 . The TESLA concept inspired the LCLS team to anticipate the need for expansion. The layout of the LCLS has been revised to permit straightforward expansion, preserving the facilities of the initial construction. PROJECT BUDGET, ORGANIZATION AND PROGRESS TO DATEThe total estimated cost of the construction project includes engineering design, purchase of hardware, installation, and system checkout.