SiC resistive X-ray beam monitor for intensity and position control of synchrotron light

A silicon carbide (SiC) X-ray beam position monitor is presented, based on a resistive charge-division principle derived from lateral-effect photodiodes and specifically adapted for synchrotron radiation applications. This device, referred to as a resistive X-ray beam position monitor (rXBPM), exploits a free-standing SiC membrane combined with a resistive p⁺-doped layer, enabling transmission-mode operation while preserving high radiation hardness and mechanical robustness. In contrast to conventional segmented X-ray beam position monitors, whose response depends strongly on the beam spot size and is typically limited to narrow linear regions, the resistive architecture of the rXBPM provides an intrinsically beam-footprint-independent position signal with an extended linear response region. The detector was fabricated using selective electrochemical etching to realize a thin membrane structure and was experimentally characterized at the microfocus beamline (MiFo) in the PTB laboratory at the BESSY II synchrotron facility using 5.4 keV X-rays. An average transmission of approximately 61% was measured, with good spatial uniformity across the membrane area. Raster-scan measurements demonstrate a linear position response over ranges of ±500 µm and ±1 mm around the detector center, with position sensitivities exceeding 0.157 mm^-1 and estimated upper-limit noise-equivalent positions of a few micrometres. Three-dimensional COMSOL simulations were used to model charge transport and lateral charge division in the real device geometry, showing excellent agreement with experimental results and confirming the independence of the position sensitivity from the beam spot size over a wide range of operating conditions. These results establish SiC rXBPMs as a compact, beam spot size calibration-free and radiation-hard solution for beam diagnostics at modern synchrotron light sources, with particular relevance for applications requiring large active areas, extended linearity and minimal beam perturbation.