Research into the sampling methods of digital beam position measurement

TL;DR

This paper investigates various sampling methods for digital beam position measurement in accelerators, demonstrating that optimized sampling and interleaved distribution significantly improve resolution and accuracy in SSRF tests.

Contribution

It introduces and compares different ADC sampling modes and proposes an interleaved distribution scheme to enhance beam position measurement precision.

Findings

Turn-by-turn resolution better than 1 μm achieved

Slow-acquisition resolution improved from 4.28 μm to 0.17 μm

Interleaved distribution reduces long-term channel variation errors

Abstract

BPM (Beam Position Measurement) system is one of the most important beam diagnostic instruments in accelerators. A fully digital BPM (DBPM) has been designed for SSRF (Shanghai Synchrotron Radiation Facility). As Analog-to-Digital Converter (ADC) is one crucial part in the DBPM system, the sampling methods should be studied to achieve optimum performance. We implemented different sampling modes and compared them through tests. Meanwhile, long term variation among four sampling channels is another concern, which would introduce errors in beam position measurement. We designed an interleaved distribution scheme to address this issue. To evaluate these sampling methods, we conducted commissioning tests with the beam in SSRF. Test results indicate that with proper sampling methods, a turn-by-turn (TBT) position resolution better than 1 um is achieved, and the slow-acquisition (SA) position resolution is enhanced from 4.28 {\mu}m to 0.17 {\mu}m successfully with interleaved distribution applied, both beyond requirement.