# Button-Type Beam Position Monitor Development for Fourth-Generation Synchrotron Light Sources: Numerical Modeling and Test Bench Measurements

## TL;DR

This paper develops a new beam position monitor for advanced X-ray storage rings using simulations and experiments.

## Contribution

The novel contribution is the design and testing of a button-type BPM optimized for fourth-generation synchrotron light sources.

## Key findings

- Rhomboidal BPM structures were analyzed and compared to traditional round geometries.
- A microwave test bench validated the radio frequency behavior of the BPM prototype.
- Wakefields and signal extraction were studied to optimize performance and practicality.

## Abstract

This paper addresses the design of beam position monitor (BPM) devices suitable for fourth-generation diffraction-limited X-ray storage rings. Detailed investigations of the electromagnetic (EM) phenomena occurring inside the component under various working conditions are carried out by considering different BPM EM models defined by their geometry and materials. Moving from a theoretical characterization of the common round geometry, rhomboidal structures are studied through a careful numerical analysis relying on advanced computer-aided tools. Several critical elements, such as wakefields, pick-up signal extraction, and trapped and propagating modes, are explored from the simulation point of view and from the experimental one, by deploying a manufactured microwave test bench, which is employed to measure the radio frequency behavior of a BPM prototype built at Elettra Sincrotrone Trieste. The aim of the proposed study is to identify a satisfactory tradeoff between achievable performance and practical realizability for BPM devices operating in last-generation light sources.