Abstract
We achieved stable operation of a free-electron laser (FEL) based on the self-amplified spontaneous-emission (SASE) scheme at the SPring-8 Compact SASE Source (SCSS) test accelerator in the extremely ultraviolet region. Saturation of the SASE FEL power has been achieved at wavelengths ranging from 50 to 60 nm. The pulse energy has reached ∼30 μJ at 60 nm. The observed fluctuation of the pulse energy is about 10% (standard deviation) for several hours, which agrees with the expectation from the SASE theory showing the stable operation of the accelerator. The SASE FEL has been routinely operated to provide photon beams for user experiments over a period of a few weeks. Analysis on the experimental data gave the normalized-slice emittance at the lasing part is around 0.7π mm mrad. This result indicates that the normalized-slice emittance of the initial electron beam, 0.6π mm mrad in a 90% core part, is kept almost unchanged after the bunch compression process with a compression factor of approximately 300. The success of the SCSS test accelerator strongly encourages the realization of a compact XFEL source.9 MoreReceived 6 February 2009DOI:https://doi.org/10.1103/PhysRevSTAB.12.070701This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Highlights
An x-ray free-electron laser (XFEL), which generates coherent and brilliant x-ray beams with ultrashort pulse duration, will innovate research activities in various fields, such as materials science, molecular biology, catalysis engineering, environmental research, and medical science
We present the SASE FEL performance achieved at the SPring-8 Compact SASE Source (SCSS) test accelerator and discuss perspectives of the compact SASE source
This stable operation has successfully provided photon beams to experimental users with the SASE FEL, which is characterized by a pulse energy of a few tens of J with a fluctuation of $10% in standard deviation (STD)
Summary
An x-ray free-electron laser (XFEL), which generates coherent and brilliant x-ray beams with ultrashort pulse duration, will innovate research activities in various fields, such as materials science, molecular biology, catalysis engineering, environmental research, and medical science. In the XFEL projects in Europe [3] and the U.S [4], the accelerator system has been designed based on the photocathode rf gun and multistage bunch compression, followed by the out-of-vacuum undulators In these projects, a high-energy (15 to 20 GeV) electron beam is employed for producing FEL radiation in an angstrom wavelength range. A reduction of the facility scale gives a significant advantage [10], a new technical challenge was requested for generating and accelerating the extremely high-quality electron beam with a small normalized-slice emittance of less than 1 mm mrad For this purpose, we proposed to use a thermionic cathode gun [11], which has a stable emission property and a long lifetime compared to photocathode rf guns.
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