Characterisation of microbunching instability with 2D Fourier analysis

Alexander Brynes ,L Giannessi,C Spezzani,G Gaio,M Veronese,G Penco,S Spampinati,P Rebernik,E Allaria,David Gauthier ,L Badano,M Trovò ,I Akkermans,S Brussaard,G De Ninno,Giovanni Perosa ,A Wolski,Peter H Williams ,I.d Setija ,Najmeh Mirian ,S Di Mitri

doi:10.1038/s41598-020-61764-y

Abstract

The optimal performance of high-brightness free-electron lasers (FELs) is limited by the microbunching instability, which can cause variations in both the slice energy spread and longitudinal profile of electron beams. In this paper, we perform 2D Fourier analysis of the full bunch longitudinal phase space, such that modulations in both planes can be studied simultaneously. Unlike the standard 1D analysis, this method is able to reveal modulations in a folded phase space, which would otherwise remain uncovered. Additionally, the plasma oscillation between energy and density modulations is also revealed by this method. The damping of the microbunching instability, through the use of a laser heater, is also analysed with this technique. We confirm a mitigation of the amplitude of modulation and a red-shift of the microbunching frequency as the energy spread added increases. As an outcome of this work, a systematic experimental comparison of the development of the instability in the presence of different compression schemes is here presented for the first time.

Highlights

The microbunching instability[1,2,3,4,5,6,7] is a collective effect that can develop due to either shot noise or a non-uniform intensity profile of the photo-cathode laser[8,9,10] in the injector of high-brightness electron accelerators, such as free-electron lasers (FELs)
Since the wavelength of the laser is much shorter than the electron bunch length, the paths travelled by particles with different energies through the second half of this chicane will overlap in longitudinal phase space
The influence of the laser heater on the bunch can be quantified both in terms of the slice energy spread (SES) increase that is imposed on the bunch, and of the effect that this added energy spread has on the microbunching parameters of the beam

Summary

Introduction

The microbunching instability[1,2,3,4,5,6,7] is a collective effect that can develop due to either shot noise or a non-uniform intensity profile of the photo-cathode laser[8,9,10] in the injector of high-brightness electron accelerators, such as free-electron lasers (FELs). The influence of the laser heater on the bunch can be quantified both in terms of the SES increase that is imposed on the bunch, and of the effect that this added energy spread has on the microbunching parameters of the beam.

Results

Conclusion