R&D of an ultrafast X-ray beam size monitor for SuperKEKB

SuperKEKB is a high luminosity electron-positron collider that aims to achieve an instantaneous luminosity ten times higher than the present world luminosity record by SuperKEKB itself. However, stable operation is hampered by a phenomenon known as Sudden Beam Loss (SBL), where beam instability occurs within tens of microseconds, resulting in significant beam loss and triggering a beam abort. It has been suggested that a fast increase in beam size may accompany SBL events. To study this rapidly evolving beam size instability and to gain deeper insights into SBL, we are developing a new bunch-by-bunch X-ray beam size monitor. It uses a silicon strip sensor to read the synchrotron radiation from the bending magnet and can record the transverse size of all bunches arriving at least 4 ns intervals. This presentation will detail the development of the X-ray beam size monitor and report on preliminary performance tests using laser light as a proxy for synchrotron radiation.