Perspectives towards Sub-Ångström Working Regime of the European X-ray Free-Electron Laser with Low-Emittance Electron Beams

Ye Chen,Matthias Scholz,Winfried Decking,Lutz Winkelmann,Frank Brinker

doi:10.3390/app112210768

Ye Chen, Matthias Scholz + Show 3 more

Open Access

https://doi.org/10.3390/app112210768

Copy DOI

Journal: Applied sciences	Publication Date: Nov 15, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: Deutsches Elektronen-Synchrotron DESY

Abstract

Sub-ångström working regime refers to a working state of free-electron lasers which allows the generation of hard X-rays at a photon wavelength of 1 ångström and below, that is, a photon energy of 12.5 keV and above. It is demonstrated that the accelerators of the European X-ray Free-Electron Laser can provide highly energetic electron beams of up to 17.5 GeV. Along with long variable-gap undulators, the facility offers superior conditions for exploring self-amplified spontaneous emission (SASE) in the sub-ångström regime. However, the overall FEL performance relies quantitatively on achievable electron beam qualities through a kilometers-long accelerator beamline. Low-emittance electron beam production and the associated start-to-end beam physics thus becomes a prerequisite to dig in the potentials of SASE performance towards higher photon energies. In this article, we present the obtained results on electron beam qualities produced with different accelerating gradients of 40 MV/m–56 MV/m at the cathode, as well as the final beam qualities in front of the undulators via start-to-end simulations considering realistic conditions. SASE studies in the sub-ångström regime, using optimized electron beams, are carried out at varied energy levels according to the present state of the facility, that is, a pulsed mode operating with a 10 Hz-repetition 0.65 ms-long bunch train energized to 14 GeV and 17.5 GeV. Millijoule-level SASE intensity is obtained at a photon energy of 25 keV at 14 GeV electron beam energy using a gain length of about 7 m. At 17.5 GeV, half-millijoule lasing is achieved at 40 keV. Lasing at up to 50 keV is demonstrated with pulse energies in the range of a few hundreds and tens of microjoules with existing undulators and currently achievable electron beam qualities.

Highlights

Linear accelerator based free-electron lasers [1,2,3,4,5] produce extremely short, brilliant and coherent X-ray pulses [6,7] and have become an enabling technology for interdisciplinary experiments worldwide
At a typical electron beam energy of 14 GeV, stable, high-intensity self-amplified spontaneous emission (SASE [6]) performance is achieved for 0.6–14 keV in routine user runs [9,10,11], while in test runs, good lasing signals towards 25 keV were achieved with only limited tuning time
Perspectives towards the sub-ångström working regime of the European XFEL are given based on the present state of the facility

Summary

Introduction

Linear accelerator based free-electron lasers [1,2,3,4,5] produce extremely short, brilliant and coherent X-ray pulses [6,7] and have become an enabling technology for interdisciplinary experiments worldwide. Using the optimized electron bunches, SASE performance in the sub-ångström working regime of the facility, here covering a photon energy range from 9.3 to 45 keV is explored based on existing undulators at the European XFEL. This considers a typical electron energy of 14 GeV as in routine user runs as well as a full beam energy of 17.5 GeV which was demonstrated in previous operation.

Near-Cathode Particle Dynamics

Budgeting Emittance at Multiple Accelerating Gradients at the Cathode

Start-to-End Beam Physics

SASE Performance in the Sub-Ångström Regime

Findings

Conclusions