Continuous bunch-by-bunch spectroscopic investigation of the micro-bunching instability

TL;DR

This paper introduces a high-speed spectrometer for real-time analysis of micro-bunching instability in electron accelerators, providing insights into bunch shape dynamics through terahertz spectral measurements.

Contribution

It presents a novel 4-channel single-shot THz spectrometer capable of streaming readout at 500 million spectra per second, enabling detailed time-resolved studies of micro-bunching phenomena.

Findings

Spectrometer captures detailed spectral evolution during micro-bunching events

Comparison with simulations enhances understanding of bursting dynamics

Results improve knowledge of bunch shape and sub-structure formation

Abstract

Electron accelerators and synchrotrons can be operated to provide short emission pulses due to longitudinally compressed or sub-structured electron bunches. Above a threshold current, the high charge density leads to the micro-bunching instability and the formation of sub-structures on the bunch shape. These time-varying sub-structures on bunches of picoseconds-long duration lead to bursts of coherent synchrotron radiation in the terahertz frequency range. Therefore, the spectral information in this range contains valuable information about the bunch length, shape and sub-structures. Based on the KAPTURE readout system, a 4-channel single-shot THz spectrometer capable of recording 500 million spectra per second and streaming readout is presented. First measurements of time-resolved spectra are compared to simulation results of the Inovesa Vlasov-Fokker-Planck solver. The presented results lead to a better understanding of the bursting dynamics especially above the micro-bunching instability threshold.