## 4 New Beamlines  
Figure 3 shows the schematic view of the current SACLA facility with three beamlines. In 2015, we constructed a second hard X-ray FEL beamline, BL2, and tested pulse-to-pulse switching operations between BL2 and BL3, the first hard XFEL beamline, by using a fast kicker magnet in the upstream location of the undulator lines [28]. At that time, we found that the quality of an electron beam was degraded at a dog-leg transport with a deflection angle of \(\pm\)3 degrees to the BL2 undulators.  
The highly compressed electron beam with a peak current greater than 10 kA produced unwanted coherent synchrotron radiation (CSR), which significantly enlarged the electron beam emittance through large energy modulation in the dipole magnets. To resolve this issue, we redesigned the optics of the dog-leg transport to include a combination of two double-bend achromat structures while maintaining high symmetry. Furthermore, we developed a pulsed high power supply to increase the deflection angle of the switching magnet. In February 2017, we tested this system and found that high pulse energies of several hundred microjoules were simultaneously generated at the two beamlines by employing the highly compressed electron beam. Later in 2017, we plan to offer simultaneous operations of these beamlines for users.  
In 2015, we also upgraded the broadband spontaneous radiation beamline BL1 to a soft X-ray FEL beamline. A key machine used for this project was the SPring-8 Compact SASE Source (SCSS) test accelerator [4]. This machine was built in 2005 with a beam energy of 250 MeV, originally for performing proof-of-principle tests for the compact XFEL scheme. Following the first lasing at 49 nm in 2006, SCSS was also used for R&D on FEL utilization and experiments with intense FEL radiation in the extreme ultraviolet (EUV) region. In 2013, SCSS was decommissioned after the successful inauguration of SACLA. However, we found space in the upstream position of the BL1 undulator to accommodate this machine as a compact electron beam driver dedicated to BL1. In the summer of 2015, we relocated the accelerator components of SCSS while increasing the beam energy to 450 MeV. This upgraded  
Figure 3: (**a**) Schematic top view of the SACLA facility. Purple bars in (**a**) indicate linacs and green bard indicate undulators. OH: optics hutch; EH: experimental hutch; LH: laser hutch; SR: synchrotron radiation from SPring-8. (**b**) Schematic bird’s eye view of the SACLA experimental hall.  
machine is called SCSS+. In October 2015, we achieved first lasing at a photon energy of 37 eV, and started user operations the following July. In the summer of 2016, we further added two accelerator units to increase the beam energy to 800 MeV. We observed a high pulse energy above 100 uJ at a photon energy around 100 eV before the winter shutdown of 2016. The typical energy resolution is \(\sim\)2%. Since we use an in-vacuum variable-gap undulator for BL1, i.e., the same as that used for BL2 and BL3, we can cover a higher photon energy up to \(\sim\)150 eV by opening the undulator gap while maintaining pulse energy above \(\sim\)10 uJ. It should be emphasized that SCSS+ and SACLA are operated independently, so we are able to increase the available user time of soft X-ray FEL without limiting the availability of hard X-ray FEL at BL2 and BL3.