Mechanical design and performance evaluation of KB mirror system for the ARPES beamline at SSRF

A new angle resolved photoelectron energy spectrum (ARPES) beamline is designed as a branch of the photoelectron experimental system (dreamline) at Shanghai Synchrotron Radiation Facility (SSRF). Its purpose is to provide a powerful instrument to conduct ARPES experiments for users from all over the world. During the design and construction of the beamline, many technical difficulties needed to be solved because of its high energy resolution, high photon flux and high focusing quality, including the design of monochromator, the design of Kirkpatrick-Baez (KB) mirror system and the manufacture of the optics. In this paper, the KB mirror system is described, including its principle and design scheme. The practical significance of displacement function is discussed. For vertical linear driving mechanism, the variation of resolution and repeatability induced by its axial deformation and radial deformation is analyzed. The results show that it is within the scope of permissible error. Linear resolution and repeatability, and angle resolution and repeatability are tested as 0.56 μm, 1.6 μm, 0.6″ and 1.08″, which guarantee the high accurate motion of KB mirrors and further improve the performance of the beamline. The simulation and ray tracing results of the beamline show that the energy resolution is better than 11.2 meV at 1000 eV, the photon flux is higher than 1011 phs/s/0.01%BW and the spot size on sample is about 15 μm × 4.7 μm (FWHM), demonstrating that the performance is beyond prediction.