Implementation of electron–X-ray beam overlap diagnostic instrument at LCLS

We report on the commissioning results of the newly implemented Beam Overlap Diagnostic (BOD) instrument, known as Station F, at the hard X-ray line of the Linac Coherent Light Source (LCLS). As part of the CBXFEL project at SLAC, Station F is designed to facilitate alignment between the relativistic electron beam entering the undulator hall and the X-rays returning from the CBXFEL cavity via the return line. The station features two interchangeable targets: (1) a diamond screen for direct imaging of the LCLS electron beam, enabling measurement of its transverse size and position; and (2) a YAP:Ce scintillator for detecting faint returning X-rays when the diamond’s sensitivity is insufficient. Emission from either target, whether generated by electron-induced cathodoluminescence or X-ray-induced scintillation, is captured using a fast-gated optical/UV camera. We present results from recent commissioning runs, including direct electron beam imaging, beam size and position characterization in both single- and two-bunch modes, and observations of coherent radiation linked to early microbunching, with implications for the laser heater configuration.