Electron beam profile imaging in the presence of coherent optical radiation effects

Christopher Behrens,Bernhard Schmidt,Stephan Wesch,Gero Kube,Christopher Gerth,Minjie Yan

doi:10.1103/physrevstab.15.062801

Abstract

High-brightness electron beams with low energy spread at existing and future x-ray free-electron lasers are affected by various collective beam self-interactions and microbunching instabilities. The corresponding coherent optical radiation effects, e.g., coherent optical transition radiation, render electron beam profile imaging impossible and become a serious issue for all kinds of electron beam diagnostics using imaging screens. Furthermore, coherent optical radiation effects can also be related to intrinsically ultrashort electron bunches or the existence of ultrashort spikes inside the electron bunches. In this paper, we discuss methods to suppress coherent optical radiation effects both by electron beam profile imaging in dispersive beamlines and by using scintillation imaging screens in combination with separation techniques. The suppression of coherent optical emission in dispersive beamlines is shown by analytical calculations, numerical simulations, and measurements. Transverse and longitudinal electron beam profile measurements in the presence of coherent optical radiation effects in non-dispersive beamlines are demonstrated by applying a temporal separation technique.

Highlights

X-ray free-electron lasers (FELs) offer a brilliant tool for science at atomic length and ultrafast time scales [1], and they have been realized with the operation of the FreeElectron Laser in Hamburg (FLASH) [2], the Linac Coherent Light Source (LCLS) [3], and the SPring-8 Angstrom Compact Free Electron Laser (SACLA) [4]
In the case of the lutetium aluminum garnet (LuAG) imaging screen recorded with a time delay, the dependence of the integrated intensity is entirely linear in the bunch charge, which verifies the power of the temporal separation technique
Electron beam profile imaging is crucial for many applications in electron beam diagnostics at FELs, and required to perform single-shot diagnostics

Summary

Introduction

X-ray free-electron lasers (FELs) offer a brilliant tool for science at atomic length and ultrafast time scales [1], and they have been realized with the operation of the FreeElectron Laser in Hamburg (FLASH) [2], the Linac Coherent Light Source (LCLS) [3], and the SPring-8 Angstrom Compact Free Electron Laser (SACLA) [4]. The x-ray FEL driving electron bunches are subject to several collective effects, e.g., microbunching instabilities or coherent synchrotron radiation (CSR), which degrade the required high transverse and longitudinal beam brightness [5,6,7,8]. These instabilities may result in significant deteriorations of the FEL performance [9] and in coherent radiation effects [10,11,12,13,14,15,16] such as coherent optical transition radiation (COTR) or CSR in the optical wavelength range [17] (abbreviated as COSR).

Methods

Results

Conclusion