RIKEN SPring-8 Center (RSC) constructed a new XFEL beamline, “BL2”, at SACLA in FY2013, and started commissioning in October 2014. BL2 will be open for users in March 2015.

【Outline】
RIKEN, in collaboration with JASRI, constructed the SACLA facility from FY2006 to FY2010, and started user operations in March 2012 with two beamlines: XFEL (BL3) and wide-range spontaneous (BL1). BL3 provides XFEL light in the shortest wavelength region with high reliability. A number of significant results have been reported recently (http://xfel.riken.jp/research/index01.html). However, beamtime availability has become a serious problem. This is a common concern for XFEL activities around the world, because the only hard X-ray FEL facilities currently in operation are SACLA and LCLS in the US. We have received many requests from current and potential users to expand experimental capacity. To address this problem, in FY2013 the RSC constructed a new beamline, BL2, as the second XFEL beamline at SACLA. Commissioning for the beamline started in October 2014 and the opening for user operations is expected in March 2015. In addition, the RSC has conducted upgrades of the experimental stations at the existing beamline, BL3.

【Targets at BL2】
So far, experiments in a broad range of fields, including biology, materials science, and science at extreme conditions, have been conducted at BL3, SACLA’s original XFEL beamline. The flexible design of BL3 has enabled various trials, though efficiency has been limited due to requirements for the exchange of instrument configurations for each experiment. At the new beamline, BL2, experimental platforms developed at BL3 will be fully exploited for performing experiments mainly in biological fields with much greater efficiency. With the help of SACLA’s supercomputer system, a large number of samples will be able to be efficiently analyzed. Also, the experimental platform will mitigate the hurdles for performing experiments at SACLA for a broad range of researchers, including those who are non-expert in XFEL.

【BL2 experimental stations (for users)】】
BL2 includes two experimental stations: EH3 and EH4b. The main instrument or chamber is installed in EH3, while detectors for measuring X-ray signals in a small angle region, if required, are set up in EH4b (Fig. 1). In EH3, a 1-um focusing system is permanently installed. The system is an improved version of that developed in collaboration with a team headed by Prof. Kazuto Yamauchi at Osaka University (H. Yumoto et al., "Focusing of X-ray free-electron laser pulses with reflective optics", Nature Photonics, 7, 43-47 (2013)). The system offers increased stability and an expanded effective aperture to enhance intensity. Also, femtosecond optical lasers are available, similar to those installed at BL3. Note that the arrival timing system (see next section) will not yet have been installed at BL2. Thus we recommend users to apply to BL3 if they require temporal resolution better than 500 fs. The current experimental methods and related publications expected to be conducted at BL2 are listed as follows.

Coherent Diffractive Imaging (CDI)

	R. Xu et al., "Single-shot three-dimensional structure determination of nanocrystals with femtosecond X-ray free-electron laser pulses ", Nature Commun. 5, 4061 (2014).
	M. G.-Jones et al., "Macromolecular structures probed by combining single-shot free-electron laser diffraction with synchrotron coherent X-ray imaging ", Nature Commun. 5, 3798 (2014).
	C. Song et al., "Multiple application X-ray imaging chamber for single-shot diffraction experiments with femtosecond X-ray laser pulses ", J. Appl. Cryst. 47, 188-197 (2014).
	T. Kimura et al., "Imaging live cell in micro-liquid enclosure by X-ray laser diffraction ", Nature Commun. 5, doi:10.1038/ncomms4052 (2014).
	Y. Takahashi et al., "Coherent Diffraction Imaging Analysis of Shape-Controlled Nanoparticles with Focused Hard X-ray Free-Electron Laser Pulses ", Nano Letters 13, 6028 (2013).
	M. Nakasako, et al., "KOTOBUKI-1 apparatus for cryogenic coherent X-ray diffraction imaging", Rev. Sci. Instrum. 84, 093705 (2013).

Serial Femtosecond Crystallography (SFX)

Fixed-target Protein Crystallography (FPX)

K. Hirata et al, "Determination of damage-free crystal structure of an X-ray-sensitive protein using an XFEL ", Nature Methods 11, 734-736 (2014).

【BL3 experimental stations (for users)】
The RSC completed upgrades for the experimental stations at the existing beamline, BL3, during the summer shutdown of 2014. First, the 1-um focusing system was upgraded to be similar to that in BL2, and moved from EH3 to EH4c. Second, an arrival timing system to achieve a higher timing resolution in pump-probe experiments was permanently installed at EH1. Third, an access mode was prepared for EH2 to enable experiment preparation in a hutch while conducting other experiments in downstream hutches. We note that EH3 has become an experimental hutch dedicated to BL2.

【Perspective】
We started the commissioning of BL3 in October 2014. We will periodically report progress on this website. We plan to commence user operations at BL2 in March 2015. Initially, the beamline to be operated will be selected by switching the route of the electron beam using a switching magnet located upstream of the undulator trains. We expect to significantly improve operational efficiency, as users will now be able to set-up for experiments at one beamline while conducting other experiments at the other beamline. In the near future, we will conduct pulse operations for the switching magnet to achieve pulse-to-pulse dynamical switching for the electron beam. Since the SACLA system allows us to change the electron beam energy in pulse-to-pulse operated at a repetition rate of 60 Hz, we will be able to operate multiple beamlines simultaneously with a single accelerator as a first XFEL machine (T. Hara et al., "Time-interleaved multi-energy acceleration for an x-ray free-electron laser facility", Phys. Rev. ST. Accel. Beams, 16, 080701 (2013)). The large enhancement of experimental capacities at SACLA will contribute significantly to the development of many fields of science and technology.

Fig. 1 Schematic for SACLA beamlines.