# The bunch current measurement using high-speed photodetector at HLS II

## TL;DR

This paper introduces a high-speed photodetector-based system for precise bunch current measurement at HLS II, achieving high resolution and accuracy suitable for various operational modes.

## Contribution

A novel measurement system utilizing ultra-fast photodetectors and high-speed digitizers with a dedicated sampling algorithm for high-precision bunch current measurement.

## Key findings

- Root-mean-square current error is 1.03% in tests.
- System achieves nearly 225 GS/s sampling rate.
- Effective in different operational modes, including beam top-up.

## Abstract

This contribution presents a novel bunch current measurement system based on an ultra-fast photodetector and a high-speed digitizer at Hefei Light Source II (HLS II). In order to achieve bunch-by-bunch resolution, the sampling rate of the system is nearly 225 GS/s via a dedicated equivalent sampling algorithm. According to preliminary tests of daily operation mode and single-bunch mode, the root-mean-square (rms) of current relative error distribution is 1.03%, which illustrates the new system satisfies requirements for high-precision bunch current measurement. In addition, experiment results of "HLS" Morse code fill pattern mode demonstrate this system also could be a convenient and robust tool for beam top-up mode in the future.

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Source: https://tomesphere.com/paper/1701.01790