The cavity-based x-ray free-electron laser (CBXFEL) R&D project utilizes a low-loss x-ray cavity (65.5 m long) to provide circulating monochromatized x-ray seeding for electrons from the Cu-linac at SLAC. The project aims to demonstrate the two-pass gain in x-ray regenerative amplifier and XFELO modes by 2024. Here, we report on the design, manufacture, and characterization of x-ray optical and diagnostic components for this project. The low-loss wavefront-preserving x-ray optical components include high-reflectivity C(400) diamond crystal mirrors, drumhead diamond crystal with thin membranes, beryllium refractive lenses, channel-cut Si monochromators, and exact-Backscattering C(440) diamond crystal. The x-ray diagnostics are designed to ensure the accuracy of beam alignment and to characterize and optimize CBXFEL performance. These include different types of x-ray beam position and profile monitors and x-ray beam intensity monitors, and a meV-resolution x-ray spectrograph. All x-ray optical and diagnostic components have been fully characterized with x-rays, and the mechanical installation of these components is expected to be finished soon.

Cavity-based X-ray free electron laser (CBXFEL) is the proposed scheme to dramatically improve stability and coherence of the existing XFELs. A project to demonstrate proof-or-principle CBXFEL is underway at SLAC National Accelerator Laboratory, in collaboration with Argonne National Lab (ANL, USA) and RIKEN Research Institute (Japan). CBXFEL is expected to operate at 9.831 keV photon energy, using synthetic diamonds as cavity Bragg mirrors. LCLS copper linac will deliver two electron bunches 624 RF buckets apart, resulting in the total X-ray cavity size of about 65500.87 mm. In this proceeding, we present the final design of the X-ray cavity, including photon and electron beam subsystems, and report on projected performance and current installation status.