STUDY OF TRANSVERSE EFFECTS IN THE PRODUCTION OF X-RAYS WITH A FREE-ELECTRON LASER BASED ON AN OPTICAL UNDULATOR

The interaction between high-brilliance electron beams and counter-propagating laser pulses produces X rays via Thomson back-scattering. If the laser source is long and intense enough, the electrons of the beam can bunch and a regime of collective effects can establish. In this case of dominating collective effects, the FEL instability can develop and the system behaves like a free-electron laser based on an optical undulator. Coherent X-rays can be irradiated, with a bandwidth very much thinner than that of the corresponding incoherent emission. The emittance of the electron beam and the distribution of the laser energy are the principal quantities that limit the growth of the X-ray signal. In this work we analyse with a 3-D code the transverse effects in the emission produced by a relativistic electron beam when it is under the action of an optical laser pulse and the X-ray spectra obtained. The scalings typical of the optical wiggler, characterized by very short gain lengths and overall time durations of the process make possible considerable emission also with emittance of the order of 1mm mrad.

Download Full-text

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

Applied Sciences ◽

10.3390/app112210768 ◽

2021 ◽

Vol 11 (22) ◽

pp. 10768

Author(s):

Ye Chen ◽

Frank Brinker ◽

Winfried Decking ◽

Matthias Scholz ◽

Lutz Winkelmann

Keyword(s):

Electron Beam ◽

Photon Energy ◽

Free Electron ◽

Free Electron Laser ◽

Electron Beams ◽

Energy Levels ◽

Energetic Electron ◽

X Rays ◽

X Ray ◽

Low Emittance

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.

Download Full-text

Scaling of Beam Collective Effects with Bunch Charge in the CompactLight Free-Electron Laser

Photonics ◽

10.3390/photonics7040125 ◽

2020 ◽

Vol 7 (4) ◽

pp. 125

Author(s):

Simone Di Mitri ◽

Andrea Latina ◽

Marcus Aicheler ◽

Avni Aksoy ◽

David Alesini ◽

...

Keyword(s):

Free Electron ◽

Free Electron Laser ◽

Recent Literature ◽

Collective Effects ◽

X Rays ◽

X Ray ◽

Coherent Synchrotron Radiation ◽

X Band ◽

Efficient Lasing ◽

Pulse Energies

The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges in the range 75–300 pC. Space-charge forces in the injector, linac transverse wakefield, and coherent synchrotron radiation in bunch compressors are all taken into account. The study confirms efficient lasing in the soft X-rays regime with pulse energies up to hundreds of microjoules at repetition rates as high as 1 kHz.

Download Full-text

Focusing X-ray free-electron laser pulses using Kirkpatrick–Baez mirrors at the NCI hutch of the PAL-XFEL

Journal of Synchrotron Radiation ◽

10.1107/s1600577517016186 ◽

2018 ◽

Vol 25 (1) ◽

pp. 289-292 ◽

Cited By ~ 22

Author(s):

Jangwoo Kim ◽

Hyo-Yun Kim ◽

Jaehyun Park ◽

Sangsoo Kim ◽

Sunam Kim ◽

...

Keyword(s):

Free Electron ◽

Free Electron Laser ◽

Laser Pulses ◽

Mirror System ◽

X Rays ◽

X Ray ◽

Fixed Sample ◽

Scattering Geometry ◽

Diffraction Imaging ◽

Pal Xfel

The Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL) is a recently commissioned X-ray free-electron laser (XFEL) facility that provides intense ultrashort X-ray pulses based on the self-amplified spontaneous emission process. The nano-crystallography and coherent imaging (NCI) hutch with forward-scattering geometry is located at the hard X-ray beamline of the PAL-XFEL and provides opportunities to perform serial femtosecond crystallography and coherent X-ray diffraction imaging. To produce intense high-density XFEL pulses at the interaction positions between the X-rays and various samples, a microfocusing Kirkpatrick–Baez (KB) mirror system that includes an ultra-precision manipulator has been developed. In this paper, the design of a KB mirror system that focuses the hard XFEL beam onto a fixed sample point of the NCI hutch, which is positioned along the hard XFEL beamline, is described. The focusing system produces a two-dimensional focusing beam at approximately 2 µm scale across the 2–11 keV photon energy range. XFEL pulses of 9.7 keV energy were successfully focused onto an area of size 1.94 µm × 2.08 µm FWHM.

Download Full-text