Research on Quasi-in-Situ Calibration Method for Multi-Channel Mismatches in Beam Signal Processors

Abstract

The multi-channel beam signal acquisition and processing system is a core component of beam position monitoring (BPM) systems and their related diagnostics in particle accelerators. Its channel mismatches directly affect the measurement accuracy of key parameters such as beam position, bunch length, and charge. To address the challenge that existing calibration methods struggle to achieve calibration results consistent with online operation, this article proposes a quasi-in-situ calibration method for multi-channel mismatches based on the beam signal itself. Using the quasi-periodic characteristic of the beam signal, this method employs equivalent-time sampling combined with a waveform reconstruction algorithm to reconstruct the complete waveform for each channel with sufficient time resolution. It precisely calibrates the amplitude gains, time delays, and DC offsets between channels, enabling a correction for the entire analog signal processing chain, including the beam pickups, the signal cables, and the analog front-end (FE) electronics. Numerical simulations are performed to systematically analyze the influence of channel mismatches on the measured beam parameters, and an experimental verification is conducted at Hefei Light Source II (HLS-II) storage ring. The results demonstrate that this method significantly enhances the channel matching of the BPM signal processors in the time and frequency domains, providing a practical and reliable quasi-in-situ calibration method for high-accuracy beam measurements.