Center for Underground Physics

Beam position monitors (BPMs) are indispensable components of modern particle accelerators,

providing real-time diagnostics to ensure precise beam control, stability, and quality. As accelerators

such as the International Linear Collider (ILC) aim for nanometer-scale beam sizes at the interac-

tion point, stringent requirements on position resolution arise. Specifically, the main linac of the

ILC demands a BPM resolution better than 5 µm to support stable beam transport and minimize

emittance growth. To address this, we have developed an L-band cavity BPM optimized for the

beam conditions of the ILC. In this presentation, we introduce a prototype of an L-band cavity BPM

and its signal processing system, describe the methodology for position resolution measurements,

discuss the problems and solutions encountered in the past experiment, and report the projected

position resolutions of about 300 nm at best.