This contribution describes, on behalf of the HXRSS team, design, installation, commissioning and operation of the Hard X-Ray Self-Seeding (HXRSS) system at the SASE2 FEL line of the European XFEL. We have reached up to mJ-level self-seeded pulses at 9-10 keV and the tested operational range is 6-13 keV. The setup can work in burst mode, that is following the bunch pattern of the European...
Athos is the soft X-ray FEL beamline of SwissFEL at PSI in Switzerland. Its novel undulator layout consists of short Apple-X modules, capable of providing full polarization control, interleaved with short magnetic chicanes. This flexible configuration allows for many unique operational modes, giving control over FEL properties such as peak power, pulse duration and longitudinal coherence. This...
We report on the first observation of short, single-spike events generated at the SASE3 beamline of European XFEL via the “attosecond at harmonics method”. The approach was first proposed in [1]. We created bunching in the linear regime at around 0.5 keV and then, after bunching optimization by means of a magnetic chicane, we amplified the 4th harmonic bunching with a part of the undulator set...
The COXINEL line has been designed at Synchrotron SOLEIL for electron beam manipulation in view of a seeded free electron laser using Laser plasma acceleration (LPA). After first studies on electron beam transport and undulator radiation in the spontaneous emission regime using LPA from Laboratoire d’Optique Appliquée (Ecole Polytechnique, France), the line has been moved to the HZDR, Dresden,...
We report on our first SASE and Seeded lasing achieved with electron beam accelerated with beam driven plasma wake-field acceleration technique.
Here we report on the first lasing of the high efficiency THz FEL operating at the UCLA Pegasus laboratory. The FEL is operated in the zero-slippage regime where a circular waveguide is used to match the radiation and electron-beam velocities in a 0.96 m long tapered helical undulator, allowing resonant interaction with the ultrashort 200-pC 5.5-MeV electron beam from the RF photogun over an...
Here we report on the first lasing of the Shanghai Soft X-ray FEL user facility (SXFEL). We have achieved the saturation of SASE at 2 nm based on FEL-I and saturation of harmonic lasing self-seeding at 3 nm based on FEL-II. We have also achieved the first lasing of EEHG with a wavelength as short as 5.3 nm.
The Photo Injector Test Facility at DESY in Zeuthen (PITZ) develops a prototype of an accelerator-based high-power tunable THz source for pump-probe experiments at the European XFEL. The PITZ injector is also the site for the development and preparation of the high-brightness electron source for the main linac of the European XFEL and has the same pulse train structure as the X-ray photon...
In recent years, echo-enabled harmonic generation (EEHG) demonstrated that it is capable to upshift the seed frequency in an FEL by almost two orders of magnitude. In this presentation, I will talk about the EEHG concept in FELs and show its connection to the echo effect known in other areas of physics (such as spin echo, plasma echo, echo in accelerators, etc.). The physics of the EEHG will...
The use of external lasers to initiate the FEL process has been introduced as a way to prepare the electron beam before entering the FEL radiator and to allow the generation of radiation pulses with increased brightness in shorter undulator. Over the recent years, new methods have been proposed and implemented to extend the capabilities of external seeding toward shorter wavelengths.
The...
One of the fundamental facets of microbunching in relativistic electron beams is the potential for generation of coherent radiation at the wavelengths that characterize that periodic longitudinal modulation. This microbunching is an inherent process in the free-electron laser (FEL) mechanism for both single-pass and oscillator configurations. Besides the FEL output, diagnostics of these...
Laser manipulation of electron beams is important for controlling free-electron lasers. In this talk, I will discuss how strong seeding can enable powerful, efficient FELs and high gradient acceleration when paired with strong tapering. I will then show how laser driven optical compression led to attosecond X-ray FEL pulses at LCLS and plans to use lasers to generate high repetition rate...
Laser assisted beam manipulation has been extensively used in modern high gain FELs to tailor the output properties. In this talk, I will focus on several advanced techniques on high harmonic generation and ultrashort pulse generation with assistant of external UV or IR lasers. With the help of state-of-the-art laser technologies, it’s very likely these techniques will open new opportunities...
Cavity-based XFEL systems will potentially offer much higher spectral quality of the hard x-ray beam compared to traditional XFEL SASE and self-seeded sources. A promising cavity-based concept is the population inversion x-ray laser oscillator, dubbed XLO, where the SASE beam is used as a pump, and a transition metal serves as a gain medium. We will report on the progress in design and...
Polarization is a fundamental property of light used in experiments to probe various properties of matter such as the chirality of molecules and crystal structures. There is increasing interest in generating bespoke radiation pulses for experiments with increasingly complex structures of polarization. At short wavelengths, free electron lasers offer an avenue to control the polarization...
Operation of a Quantum Free-Electron Laser (QFEL) could provide fully coherent X- and gamma-rays in a compact setup. Imperative to experimental realization is allowing for decoherence of either spontaneous emission or space-charge to take place, having opposing constraints [1]. Here, for the first time, we discuss a comprehensive QFEL model that takes into account both decoherence effects....
Quantum diffusion is caused by the recoil effect that a particle experiences when it emits a photon [1]. Quantum diffusion due to the synchrotron radiation in high-energy electron and positron circular accelerators defines the main parameters of the beam: its energy spread and hence the bunch length, as well as the horizontal emittance. It is calculated as a single particle effect assuming...
The free-electron laser FLASH at DESY can produce SASE-FEL pulses in the extreme ultraviolet to the soft X-ray region. The flexibility of the variable gap undulators in the FLASH2 beamline opens a wide range of scientific opportunities. Different advanced lasing schemes have been tested in the past years, like the frequency doubler scheme, two-color lasing, and ``harmonic lasing...
In Self-Amplified Spontaneous Emission Free Electron Laser (SASE FEL) based short-pulse schemes, pulse duration is limited by FEL coherence time. For hard X-ray FELs, coherence time is in a few hundred attosecond range while for XUV and soft X-ray FELs it is in the femtosecond regime. In this paper the modification of so-called chirp-taper scheme is developed that allows to overcome the...
X-ray free-electron lasers (FELs) rely on SASE due to the lack of seed lasers and the difficulty in obtaining mirrors. Progress in diamond crystal Bragg mirrors enables the design of x-ray FEL oscillators. Regenerative amplifiers (RAFELs) are high gain/low-Q oscillators that out-couple most of the optical power. An x-ray RAFEL based on the LCLS-II at SLAC using a six-mirror resonator...
This paper provides a summary of the analyses that led to the definition of the 2-color upgrade of the IR FEL at FHI Berlin. We briefly cover several different aspects of the design, beginning with the beam dynamics of the second far-IR beamline, engineering considerations of that physics design, and the FEL physics that defined the short-Rayleigh range undulator as well as aspects of the...
Free-electron lasers (FELs) operate at wavelengths from millimeter waves through hard x-rays. At x-ray wavelengths, FELs typically rely on self-amplified spontaneous emission SASE emission which contains multiple temporal “spikes” that limit the longitudinal coherence of the optical output; hence, alternate methods that improve on the longitudinal coherence of the SASE emission are of...
Genesis is widely used in the free electron laser community as a simulation tool for studying both simple and complex FEL systems. Until now, this has necessitated learning the command line interface, which can be challenging for new users. Sirepo Genesis provides an intuitive graphic interface for building Genesis simulations in the browser that can then be run using our cloud computing...
Fresh-slice lasing using wakefield induced time-dependent orbit oscillation is capable of producing high intensity two-color XFEL pulses and high power short pulses at femtosecond level. At the European XFEL, a corrugated structure system for fresh-slice applications for both the hard x-ray beamline SASE1 and the soft x-ray SASE3 beamline is being developed and implemented. In this...
X-ray absorption spectroscopy (XAS) with a SASE signal can be improved if the full XAS and reference spectrum are taken on a shot-to-shot basis, thus eliminating the impact of the intrinsic SASE fluctuations in the spectrum. This can be further improved if the FEL pulse has the frequency information encoded in its spatial position. The spatial encoding is achieved when a spatially tilted...
THz free electron laser at SANKEN, Osaka university generates a train of THz pulses with the interval of 27 MHz in the repetition of 5 Hz. The number of pulses in a train is about 100. Single pulse energy exceeds 200 \muJ at the carrier frequency of 4.5 THz. To extract a single pulse from the train, the reflective switch of the electron-hole plasma on the surface of Gallium Arsenide wafer...
The typical layout adopted in a seeded harmonic generation free-electron laser is based on radiator undulators placed immediately after the dispersive section, where the bunching is created.
With the advent of new and more complex seeding schemes, this solution cannot always be implemented and cases, where the bunched beam needs to be propagated in free space before entering the radiator,...
The AQUA beamline of the EuPRAXIA@SPARC_LAB infrastructure consists of a Free-Electron Laser facility driven by an electron beam with 1 GeV energy, produced by an X-band normal conducting LINAC followed by a plasma wakefield acceleration stage, with the goal to deliver variable polarization photons in the 3-4 nm wavelength range. Two undulator options were considered for the AQUA FEL...
Research and development of an accelerator-based THz source prototype for pump-probe experiments at the European XFEL are ongoing at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). A proof-of-principle experiment to generate THz SASE FEL radiation using an LCLS-I undulator driven by an electron bunch from the PITZ accelerator has been prepared. After four years of designs and...
We report on the first demonstration of generating high-power and short FEL pulses using the fresh-slice multi-stage amplification scheme at Athos, the soft X-ray beamline of SwissFEL. We use a transversely tilted electron beam traveling through the unique Athos layout with magnetic chicanes between every two undulator modules. Our first results show the production of FEL radiation with pulse...
A major challenge in single-linac - multiple undulator setups like EuXFEL is the generation of individual shaped photon pulses, in particular, when working in a mode where a single pulse train, or cw stream, feeds all undulator lines. This work presents the experimental verification of a flexible delivery scheme producing photon pulses for each of the three undulator lines with their electron...
We propose a computationally-efficient algorithm to calculate the field of partially coherent synchrotron radiation pulses from undulators. Wavefront propagation simulations play a pivotal role in designing beamline optics at new synchrotron radiation sources. However, they do not account for the stochastic behaviour of the initial radiation field, which is due to shot noise in the electron...
Light with orbital angular momentum (OAM) provides new insights into a wide range of physical phenomena and has engendered advanced applications in various fields. Additionally, research interest in X-ray OAM has been rapidly increasing. Here, we report a straightforward method capable of generating intense OAM beams from an X-ray free-electron laser oscillator (XFELO). This method leverages...
We (PAL-XFEL) have improved the PAL-XFEL performances remarkably since the user-service operation in 2017. We achieved the self-seeded XFEL with a peak brightness of 3.2 × 10^35, the highest to date, and reached a SASE FEL intensity of 3.2 mJ due to the improved beam emittance of 0.3 mm-mrad. The statistics of the SASE FEL intensities over the past three years show that the SASE FEL...
Laser-induced breakdown has been observed in various combination of gases and lasers. It is known from previous studies that breakdown occurs when the number of electrons exceeds a threshold value through the following stages: generation of seed electrons, acceleration of electrons by inverse Bremsstrahlung, and avalanche multiplication of electrons by impact ionization.
We have observed...
The European XFEL operates with 3 different SASE FELs served by variable gap undulators. In addition, the electron energy of the superconducting linear accelerator is varied between 8.5 and 16.5 GeV to cover a photon energy range from 500 eV to 30 keV. We will present SASE performance data collected over the past 5 years of operation and compare them with theoretical predictions.
The SACLA linear accelerator has been successfully used as a full-energy injector of the SPring-8 storage ring since 2020. In order to perform the beam injection in parallel with XFEL operation, three accelerators are virtually constructed in a control system. Thus the electron beam parameters, such as the beam energy, are independently tuned for the beam injection and the two XFEL beamlines....
MINERVA is a 3-D, time-dependent simulation code of FEL amplifiers, low-gain/high-Q and high-gain/low-Q oscillators, optical klystrons (including high-gain harmonic generation) and SASE configurations [1-7]. Oscillator simulations are done in conjunction with OPC [8]. MINERVA uses the Message Passing interface on Linux, Macintosh and Windows systems and has been successfully benchmarked...
Previous studies of FEL oscillators typically use averaged simulation codes which cannot model sub-wavelength effects, such as Coherent Spontaneous Emission from the electron pulse. In this paper, the unaveraged FEL simulation code Puffin is used with the optics code Optical Propagation Code to model the FEL in three dimensions, enabling sub-wavelength effects to be modelled at the FEL...
TeraFERMI is a THz beamline at the free-electron laser (FEL) FERMI. After passing the FEL's undulator, the electron bunches are refocused on a thin dielectric slab and generate coherent transition radiation (CTR), namely strong THz pulses. TeraFERMI provides single-cycle pulses with a broadband spectrum in the range from 0.1 THz to 6 THz and strong peak electric fields with up to 4 MV/cm or...
More and more high-gain SASE FELs operate at high repetition rates, either in burst or in continuous wave mode of operation, offering an unprecedented number of electron bunches per second. External seeding techniques provide high quality FEL pulses of full coherence and shot-to-shot stability but cannot keep up with MHz repetition rates of such FELs due to their dependence on the seed laser...
At KAERI we are developing compact Terahertz(THz) Free Electron Laser(FEL) for a commercial application like security inspection. We are using a waveguide-based optical resonator for our FEL system. Firstly, we report on the selection of low loss and small cross-section waveguide candidate to enhance the gain of THz FEL. We performed a detailed analysis of waveguides with different shapes and...
Echo-Enabled Harmonic Generation (EEHG) became a very promising and very popular technique after original publication [1]. As it commonly happens, this was the reinvention of already known technique, which was not broadly known in FEL community. EEHG vaguely reminded me of theory developed at Novosibirsk Institute of Nuclear Physics (BINP), but I was not sure that my memory is correct....
Infrared FEL oscillators generally use hole-coupling to extract intracavity laser power. The hole-coupling inherently causes a non-Gaussian beam profile at user stations, which are more than 10 m apart from the coupling hole. It is due to the existence of the Airy pattern in the extracted laser beam. We demonstrated that the beam profile can be changed from a non-Gaussian to a nearly Gaussian...
Compact sources offering high-brightness radiation in the EUV to X-ray regime are highly desired. Thomson scattering, in which an electron beam colliding with a laser pulse produces radiation, is a source of X-rays of increasing prevalence in modern labs, complementing large scale facilities like synchrotrons and X-ray free electron lasers. By imposing a density modulation on the electron beam...
The existing MAX IV 3 GeV linac could drive, with minor improvements, a soft X-ray Free Electron Laser and the aim of the SXL project has been so far to deliver a conceptual design of such a facility in the 1—5 nm wavelength range.
The project was initiated by a group of Swedish users of FEL radiation and the design work was supported by the Knut and Alice Wallenberg foundation and by...
In a storage ring free-electron laser (FEL) the cavity mirrors have to resist the harsh operational conditions due to high-energetic and background radiation in an ultra-high vacuum environment. For the wavelength between 120 and 190 nm only fluoride materials are suitable as coating material for high reflective mirrors. However, used in the bare form, they are not stable for extreme FEL...
The coherence of free-electron laser (FEL) radiation has so far been accessed mainly through first and second order correlation functions. Instead, we propose to reconstruct the energy state occupation number distribution of FEL radiation, avoiding the photo-counting drawbacks with high intensities, by means of maximum likelihood techniques based on the statistics of no-click events. The...
The FELIX Laboratory, located at Radboud University in Nijmegen, The Netherlands, is operating a suite of FELs serving an international user community with infrared and THz radiation from 5 to 1500 micron operating three FELs in parallel and providing beam to 16 dedicated user end stations. Recently, FELIX has upgraded its most frequently used FEL-2 beamline. The 38 period, 65 mm Halbach-type...
The free-electron laser FLASH at DESY can produce SASE-FEL pulses in the extreme ultraviolet to the soft X-ray regime. A superconducting linear accelerator drives two undulator lines (FLASH1 and
FLASH2). The FLASH1 undulator beam line contains six fixed gap undulator which implies that the SASE wavelength can only be changed via the electron beam energy, while FLASH2 contains twelve variable...
High-resolution emission/absorption spectroscopy with picosecond time resolution appears to be strategic in fundamental matter physics investigation as well as in functional materials characterization. Such a method typically requires a pulsed radiation source and high energy resolution, along with a large data statistic. In this work we demonstrate the possibility to retrieve high resolution...
FEL pulses with an easily tunable duration are of great benefit to user experiments with high requirements on the temporal resolution. A transverse beam tilt is well suited to shorten the pulse duration in a controlled manner. We consider three methods of tilt generation: rf deflecting structures, lattice dispersion in combination with an energy chirp, and transverse wakefields from C-band...
Cavity-based x-ray free-electron lasers (CBXFEL) will allow use of
optical cavity feedback to support generation of fully coherent x-rays
of high brilliance and stability by electrons in undulators. CBXFEL
optical cavities comprise Bragg-reflecting flat crystal mirrors, which
ensure x-rays circulation on a closed orbit, and x-ray refractive
lenses, which stabilize the orbit and refocus...
Intense attosecond pulses generated by x-ray free-electron lasers (XFEL) are promising for attosecond science, for example, to study the quantum mechanical motion of electrons in molecules. This paper presents numerical simulations of the generation of attosecond soft and hard x-ray FEL pulses with the chirp-taper and Enhanced SASE schemes, based on the parameters of the European XFEL. To...
European XFEL is a multi-beamline x-ray free-electron laser (FEL) user facility driven by a superconducting accelerator with a nominal photon energy range from 250 eV to 25 keV. An afterburner undulator based on superconducting undulator technology is currently being planned to enable extension of the photon energy range towards harder x-rays. This afterburner undulator would be installed...
A tunable, tabletop, Inverse Compton Scattering (ICS) hard X-ray source is being designed and built at Eindhoven University of Technology as part of a European Interreg program between The Netherlands and Belgium. This compact X-ray source will bridge the gap between conventional lab sources and synchrotrons: The X-ray photon energy will be generated between 1 and 100 keV with a brilliance...
Accurate measurements of the x-ray pulse duration produced by x-ray free-electron lasers (XFELs) typically rely on longitudinal electron beam phase space diagnostics, e.g. in a transverse deflecting cavity or TCAV, or from measurements of spectral correlations. All of the known spectral methods share the weakness that they will underestimate the pulse length in the case that the FEL spectrum...
FLASH, the free-electron laser user facility at DESY, delivers XUV and soft X-ray radiation for photon experiments since 2005. It is driven by a superconducting linear accelerator, and has two undulator lines (FLASH1 and FLASH2). A third electron beam line hosts the plasma wakefield experiment FLASHForward. Presently, the FLASH facility is undergoing an extensive refurbishment and a...
Laser pulses of sub-femtosecond duration can be used to track the motion of electrons in the inner shell, which is needed in a variety of advanced experiments. Although this has been accomplished in XUV and hard X-rays in a free-electron-laser facility, it remains a challenge in the soft X-ray region due to the relatively high photon energies and large slippage in the undulator. In this...
Topological insulators are a class of materials which have raised a great interest over the last decade, thanks to their intriguing conduction properties. Indeed, they are insulating in the bulk and metallic at the surface. Moreover, these metallic surface states have linear Dirac dispersion [1], thanks to which topological insulators show nonlinear THz behaviour similar to the case of...
Since coming on-line in November 2013, the Fritz-Haber-Institut (FHI) der Max-Planck-Gesellschaft (MPG) Free-Electron Laser (FEL) has provided intense, tunable infrared radiation to FHI user groups. It has enabled experiments in diverse fields ranging from bio-molecular spectroscopy to studies of clusters and nanoparticles, nonlinear solid-state spectroscopy, and surface science, resulting in...
A novel and noninvasive method for two-color x-ray emission is demonstrated at SwissFEL. In the setup, a laser emittance spoiler pulse is overlapped with the primary photocathode laser to locally spoil the beam emittance and the FEL emission. This results, together with a chirped electron pulse, in X-ray emission at two colors. High-energy, high stability, independent control of the duration...
Generation of few-cycle FEL pulses with a high extraction efficiency was achieved at JAERI-FEL [1] and KU-FEL [2]. The observed lasing can be understood as superradiance, radiation from bunched electrons in the slippage region. In the superradiance FEL oscillators, the high-extraction efficiency is accompanied by significant energy variation of the electrons during the undulator. Therefore,...
Free-electron lasers (FELs) produce different optical polarizations including linear, elliptic and circular polarizations corresponding to the polarizations of the undulators used. X-ray FELs depend upon long undulator lines consisting of a sequence of short undulators. Linearly polarized undulators are most commonly used; hence the optical output is linearly polarized. Elliptic or circular...
Networking, access and project opportunities for FEL and Laser research in Europe
Networking, access and project opportunities for FEL and Laser research in Europe
Networking, access and project opportunities for FEL and Laser research in Europe.
The natural time scale of valence electronic motion in molecular systems is on the order of hundreds of attoseconds. Consequently, the time-resolved study of electronic dynamics requires a source of sub-femtosecond pulses. Pulses in the soft x-ray domain can access core-level electrons, enabling the study of site-specific electron dynamics through attosecond pump/probe experiments. As...
European XFEL offers a unique combination of high electron
energy and soft X-ray SASE3 undulator resonant to low photon energies with
high K parameter. The long undulator allows us to employ split-undulator
scheme to deliver pump-probe radiation to users. Pulse energies depend on
photon energy and range from 100uJ at 2200eV to 900uJ at 600eV per pulse
respectively. We plan to install...
This contribution presents the experimental demonstration of improved performance of an X-ray free-electron-laser (FEL) using the optical klystron mechanism and helical undulator configuration in comparison to a standard planar undulator without optical klystron. The demonstration has been carried out at Athos, the soft X-ray beamline of SwissFEL. Athos has variable-polarization undulators and...
Phase shifters at undulator line are usually used for optimizing FEL intensity by setting 'in-phase' by matching the FEL pulse and electrons phases. π-offset so called ‘out-phase’ may suppress FEL intensity at the resonant frequency, therefore the 'out-phase' condition is an unwanted state. However, this 'out-phase' setting can arise side band spectrums. This phenomena can be explained by the...
Shanghai Soft X-ray FEL facility (SXFEL) is the first X-ray FEL facility in China. Various external seeding techniques have been adopted for improving the performance of SXFEL. Here we report on the first demonstration of echo-enabled harmonic cascade (EEHC) for generating coherent and ultrashort soft X-ray pulses. Benefiting from the superiority of low sensitivity to the electron beam...
We describe a new method to produce intensity stable, highly coherent, narrow-band x-ray pulses in self-seeded free electron (FEL) lasers. The approach uses an ultrashort electron beam to generate a single spike FEL pulse with a wide coherent bandwidth. The self-seeding monochromator then notches out a narrow spectral region of this pulse to be amplified by a long portion of electron beam to...
The transverse coherence of the source is an important property for FEL experiments. Theory and simulations indicated different features for seeded and unseeded FELs but so far no direct comparison has been pursued experimentally on the same facility.
At FERMI one has the unique possibility to test both configurations (SASE and seeding) within the same operating conditions.
In this...
Recently, a self-modulation scheme was proposed and experimentally demonstrated for enhancing energy modulation in seeded FELs [1], thereby significantly reducing the requirement of an external laser system. Driven by this scheme, an electron beam with a laser-induced energy modulation as small as 1.8 times the slice energy spread is used for lasing at the 7th harmonic of a 266-nm seed laser...
At the mid-infrared free electron laser oscillator in Kyoto University (KU-FEL), high extraction efficiency (9.4%) operation has been achieved [1] by introducing the dynamic cavity desynchronization technique [2] and photocathode operation of a thermionic RF gun [1]. Because of the interaction between the electron beam and FEL electromagnetic field, a maximum electron energy decrease of 16%...
While the linac based single-pass FEL has been successfully operated
in the EUV and x-ray regions for about two decades, the oscillator
FEL has been limited to operating in the longer wavelength region
due to the limitation of high-reflectivity, thermally stable, and
radiation-resistant short-wavelength mirrors. With Duke storage ring FEL,
we have recently extended the shortest lasing...
The THz gap is a region of the electromagnetic spectrum where high average and peak power radiation sources are scarce while scientific and industrial applications grow in demand. Free-electron laser coupling in a magnetic undulator can provide radiation generation in this frequency range, but slippage effects require the use of relatively long and low current electron bunches in the THz FEL,...
We present a scheme to generate synchronized THz and Soft X-ray radiation pulses by using a Free-Electron Laser Oscillator driven by a high repetition rate energy recovery linac. The backward THz radiation in the oscillator cavity produces naturally synchronized Soft/Hard X rays via Thomson back-scattering by interacting with a successive electron bunch. The performances of this dual source...
In this paper, a cathode laser pulse shaper at 515 nm is presented that will be used for emittance optimizations. In case alkali antimonide photocathodes are used, the shaped green pulses can be applied directly for photoemission while Cs2Te photocathodes requires second harmonic generation to provide UV laser pulses. Recent tests of CsK2Sb photocathodes in the high...
At Eindhoven university an inverse Compton scattering (ICS) source is being built. The ICS source consists of a 100kV photo gun electron injector, X-band accelerator, and interaction laser. One of the first upgrades for this ICS source is operating in a so-called burst mode. In burst mode, the electron injector is replaced by the advanced continuous electron (ACE) injector and a Fabry-Perot...
An X-ray free-electron laser oscillator (XFELO) is a next generation X-ray source promising radiation with full three-dimensional coherence, nearly constant pulse to pulse stability and more than an order of magnitude higher spectral flux compared to SASE FELs. In this contribution, the concept of an R&D project for installation of an XFELO demonstrator experiment at the European XFEL facility...
Recently, Hard x-ray self-seeding (HXRSS) operations at the European X-ray free-electron laser (EuXFEL) opened a pathway towards the application of pulses with high spectral density (in terms of ph/eV per pulse) in the fields of applied physics, chemistry and biology, where the coherent radiation spectrum is essential. The spectrum of hard x-ray self seeding pulses is generally accompanied by...
EuPRAXIA@SPARC_LAB is a new Free Electron Laser (FEL) facility that is currently
under construction at the Laboratori Nazionali di Frascati of the INFN. The electron
beam driving the FEL will be delivered by an X-band normal conducting LINAC followed
by a plasma wakefield acceleration stage. It will be characterized by a small
footprint and include two different plasma-driven photon...
Laser Wakefield Accelerators are now sufficiently mature to provide GeV scale/high-brightness electron beams capable of driving Free Electron Laser (FEL) sources. Here, we show start-to-end simulations carried out in the framework of the EuPRAXIA project of a Free Electron Laser driven by an LWFA accelerator in the Resonant Multi-Pulse Ionisation Injection (ReMPI) framework. Simulations...
Externally seeded FELs can produce fully coherent short-wavelength pulses with the advantage of higher shot-to-shot stability and spectral intensity than SASE radiation. For the FLASH2020+ project, the Echo-Enabled Harmonic Generation (EEHG) seeding technique achieves seeded FEL radiation in the XUV and soft X-ray range down to wavelengths of 4 nm. The implementation of the EEHG requires...
Over the last few years tremendous progress has been gained in the theoretical understanding and experimental demonstration of seeded FELs . The ultimate spectral limit of seeded FEL, however, remains unclear, because of the broadening and distortions induced in the output spectrum by residual broadband energy modulations in the electron beam.
In this talk, we present the mathematical...
In optical conventional lasers, chirped pulse amplification (CPA) has become an extremely powerful technique for the generation of ultrashort pulses in the infrared and visible spectral ranges. In this contribution we report the successful implementation of CPA in a seeded XUV FEL. A second experiment, using a two-stage harmonic generation scheme (FERMI FEL-2) has the objective to generate...
The external seeding scheme Echo-Enabled Harmonic Generation (EEHG) utilizes two modulators and two chicanes to manipulate the longitudinal phase space of an electron beam to achieve bunching at higher harmonics of the seed laser wavelength. Different combinations of energy modulation and longitudinal dispersion can result in the same amount of bunching at a certain harmonic. This study...
ERMI is the seeded Free Electron Laser (FEL) user facility at Elettra laboratory in Trieste, operating in the VUV to soft X-rays spectral range. In order to extend the FEL spectral range to shorter wavelengths, an upgrade plan for increasing the Linac energy from 1.5 GeV to 2.0 GeV is actually going on. After successful testing of the short prototype of new high gradient S-band accelerating...
Improvement of the longitudinal coherence in the proposed Soft Xray FEL, the SXL, for the MAX IV Laboratory is an important design aspect to enhance the user case. One of the main considered methods is HBSASE. However the final compression in the MAX IV acceleratos is done at full energy, and thus leaving an energy chirp in the electron pulse. This chirp in longitudinal phase space has to be...
A new concept of a high repetition rate VUV FEL is discussed. The FEL is envisioned to operate in the wavelength range from 50 to 250 nm with pulse energies of about 30 µJ throughout the wavelength range, and a pulse length of a few 100 fs. The SRF LINAC technology developed and used at the Helmholtz-Zentrum Dresden-Rossendorf for the Radiation Source ELBE is planned to be used for the...
Multi-alkali antimonide photocathodes can have high quantum efficiency similar as UV sensitive (Cs2Te) photocathodes, but with the advantages of photoemission sensitivity in the visible region of the light spectrum and a significant reduction in the mean transverse energy of photoelectrons. A batch of three KCs2Sb photocathodes was grown on molybdenum substrates via a sequential deposition...
In order to improve the brightness and coherence of the soft x-ray FEL line of SwissFEL (Athos), components for an Echo Enabled Harmonic Generation (EEHG) scheme are currently in preparation. The first components have been installed to allow first ESASE operation test in Spring 2022. This first stage consists in a 10 mJ class seed laser, a U200 modulator with individual control of each half...
Cavity-based X-ray Free Electron Lasers (FELs) such as the X-ray regenerative amplifier FEL (XRAFEL) [1] and the X-ray FEL oscillator [2] have drawn great interest as a means of producing high-brightness, fully coherent and stable hard x-ray pulses for high-repetition rate FELs [3]. However, high efficiency outcoupling of the stored cavity x-ray radiation remains challenging. Here we present a...
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In early 2019, the UK initiated a project to develop the science case for a UK XFEL, featuring a diverse team of UK scientists and international advisors. Accelerator scientists were engaged to highlight potential future accelerator developments and to develop concept outlines for a facility design meeting the requirements for world-leading capabilities. The UK XFEL Science Case, featuring the...
In this paper we'll describe the status of the FAST-GREENS experimental program where a 4 m-long strongly tapered helical undulator with a seeded prebuncher is used in the high gain TESSA regime to convert a significant fraction (up to 10 %) of energy from the 240 MeV electron beam from the FAST linac to coherent 515 nm radiation. We'll also discuss the longer term plans for the setup where by...
In order to meet the user request of extending the FERMI FEL spectral range over the whole water window, we are developing an upgrade strategy that is based on the implementation of the Echo Enabled Harmonic Generation (EEHG) scheme.
The FERMI upgrade strategy is structured as follow: during a first phase, the single cascade FEL-1 branch will be adapted to operate either in EEHG or in HGHG....
The FLASH facility houses a superconducting linac powering two FEL beamlines with MHz repetition rate in 10 Hz bursts. Within the FLASH2020+ project, which is taking care of facility development, one major aspect is the transformation of one of the two FEL beam lines to deliver externally seeded fully coherent FEL pulses to photon user experiments. At the same time the second beam line will...
The FLASH2020+ project has started to transform the FLASH facility to broaden the facility profile and meet demands of future user experiments.
In a nine-month lasting shutdown until August 2022 the linear accelerator of the FLASH facility has, among others, been upgraded with a laser heater, new bunch compressors and new modules. The latter results in an energy upgrade to 1.35 GeV allowing...
The possibility of using a plasma accelerated electron beam to generate Free Electron Laser (FEL) radiation has recently been proven. In the plasma acceleration process an intense broadband spectrum radiation in the X ray region, the betatron radiation, is produced by the electron beam passing through the ionized gas.
In this paper it is proposed to use this radiation, suitably...
Frequency mixing was studied experimentally at SASE3, the soft X-ray undulator of the European XFEL. Two frequencies were generated in the first part of the undulator in alternating K configuration. The mixing process occurred in the second part with detuned undulator segments used to generate R56. Finally, the difference frequency was radiated and amplified in a third part of the SASE3...
Free-electron lasers producing ultrashort pulses with high peak power are a resource to extend ultrafast non-linear spectroscopic techniques into the extreme-ultraviolet–X-ray regime. A super radiant cascade was proposed as a method to shorten the pulse duration in seeded FEL. Pulses shorter than the typical duration supported by the FEL gain bandwidth of the FEL amplifier in the linear regime...
ABSTRACT: FERMI is implementing a development plan to keep the facility in a world-leading position on the base of the requests coming from the user community and the advises from the Scientific Advisory Council and the Machine Advisory Committee. The ultimate goal of this plan consists in doubling the maximum photon energy available and in reducing the pulse duration below the characteristic...
The biggest benefit of DC photoelectron-gun driven by the sub-picosecond laser is that such type of guns can be operated with the current density much higher than the Child’s low limitation. We demonstrated 0.3 nC bunch generation by irradiating a 100 fs Ti:sapphire laser focused to 0.1 square-cm area onto a tangsten photocathode installed in a diode type 40 kV DC gun. The drawback is the...
The generation of x-ray pulses carrying orbital angular momentum from an x-ray free-electron laser (FEL) has attracted considerable attention due to the ability to directly change atomic states and develop new material characterization techniques. In this contribution, we report a new method for generating intense x-ray vortices. The method is based on the widely used self-amplified...
Nearly fully coherent hard X-ray self-seeded (HXRSS) free-electron laser (FEL) pulses with an unprecedented peak-brightness and a narrow spectrum using the forward Bragg-diffraction (FBD) monochromator has been provided. We have achieved outstanding performance of HXRSS FEL over photon energy range covering from 3.5 keV to 14.6 keV at PAL-XFEL. Furthermore, an averaged energy of seed FEL of...
Attosecond laser pulses in the extreme ultraviolet/soft X-ray (XUV/SXR) spectral regions are presently available for attosecond pump-probe spectroscopy and extreme ultraviolet lithography for chip manufacturing, ultrafast atomic-scale microscopy, and nonlinear X-ray optics. There are two main approaches to produce attosecond light pulses: high-harmonic generation (HHG) in gas-phase or...
External seeding techniques like high-gain harmonic generation (HGHG) and echo-enabled harmonic generation (EEHG) have been proven to be able to generate fully coherent radiation in the EUV and X-ray range. However, towards seeding at a high repetition rate, the repetition rate of current laser systems with sufficient power for seeding is limited to the kilohertz range. One attractive solution...
Within the FLASH2020+ project the FLASH VUV/XUV FEL facility at DESY (Hamburg, Germany) is currently undergoing a major upgrade to become the first high repetition rate, fully coherent FEL light source worldwide [1]. To reach this goal, one of the two in parallel operated FEL branches will be seeded at a fixed wavelength at 343 nm in a first step (SEED 1) and tunable between 297 nm to 317 nm...
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Beam-driven plasma wakefield accelerators (PWFAs) offer a unique regime for the generation and acceleration of high-quality electron beams to multi-GeV energies. Here we present an innovative hybrid staging approach, deploying electron beams generated in a laser-driven wakefield accelerator (LWFA) as drivers for a PWFA, integrated in a particularly compact setup. This scenario exploits the...
External seeding schemes allow the generation of stable and fully coherent free electron laser (FEL) radiation but can be limited in repetition rates in orders of tens of Hz. This limitation is mainly posed by limited average power of the seed lasers that are required to provide hundreds of MW peak power to modulate the electron bunches. An optical-klystron-based high gain harmonic generation...
A tunable and multicolor light source with near Fourier-limited pulses, controlled delay, and fully coherent beam with precisely adjustable phase profiles enables state-of-the-art measurements and studies of femtosecond dynamic processes with high elemental sensitivity and contrast. The start-to-end simulations efforts aim to take advantage of the available global pool of software and past and...
The LAPLACIAN (Laser Acceleration Platform as a Coordinated Innovation Anchor) experimental facility inside the MIRAI project framework is the Japanese answer to the global effort for the development of compact accelerators based on laser plasma acceleration (LPA) for its application to free electron laser (FEL). Situated in the SPRING-8 site, LAPLACIAN aims for the generation of X-ray FEL...
In the scope of the HERO ERC project, we are implementing a laser-based seeding scheme at the SwissFEL soft X-ray Athos beamline to generate fully coherent X-ray FEL pulses. With this perspective, we designed and built a new laser facility. It consists of a terawatt-class, femtosecond laser system based on Titanium Sapphire technology with wavelength tuning capability, an optical transfer line...
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Shaping techniques traditionally used to produce few femtosecond and even sub femtosecond soft X-ray FEL pulses at LCLS do not scale well to high repetition rates. Here we present the progress of the LCLS-II X-ray temporal shaping project which uses infrared and ultraviolet picosecond lasers to shape the electron beam of the LCLS-II superconducting linac. Quickly switching these shaping lasers...
The slice energy spread of the electron beam is one of the key parameters for high performance of linac-driven free electron lasers (FELs). The simulated uncorrelated energy spread in modern XFEL photoinjectors with beam energies of many tens of MeV is on the order of a few keV or even less. Thus, accurate measurement of the slice energy spread is not trivial. Two recent studies on high energy...
The advent of free electron lasers (FELs) in the soft and hard X-ray spectral region has opened the possibility to probe electronic, magnetic and structural dynamics, in both diluted and condensed matter samples, with femtosecond time resolution. In particular, FELs strongly enhanced the capabilities of several analytical techniques, which took advantage of the high degree of transverse...
The FAST-GREENS FEL experiment is aimed at demonstrating extraction efficiencies of greater than 10%. This is accomplished with a high-power seed laser and an aggressively tapered undulator to compensate for the energy loss in the electron beam. A proof of concept experiment will be conducted at the Fermilab Accelerator Science and Technology Facility (FAST) using an undulator specifically...
Phase-locked pulses are important for coherent control experiments. Here we present theoretical analyses and start-to-end simulation results for the generation of phase-locked pulses using the Hard X-ray Self-Seeding (HXRSS) system at the European XFEL. As proposed in Ref. [1], the method is based on a combination of self-seeding and fresh-slice lasing techniques. However, at variance with...
The photoinjectors of FLASH at DESY (Hamburg, Germany) and the European XFEL are operated by laser driven RF-guns. In both facilities cesium telluride photocathodes are successfully used since several years. We present recent data on the lifetime, quantum efficiency (QE), and dark current of the photocathodes currently in operation. In addition we present recent design changes in the...
We are developing an ultrafast and Ultracold Electron Source (UCES), based on near-threshold, two-step, femtosecond photoionization of laser-cooled rubidium gas in a grating Magneto Optical Trap (MOT). This source delivers stable ultrafast electron bunches with a unique combination of high bunch charge and low transverse emittance ~1.9 nm·rad, demonstrating the cold electron temperature ~25...
At DELTA, a 1.5-GeV electron storage ring operated by the TU Dortmund University, the seeding scheme CHG (coherent harmonic generation), the counterpart to HGHG (high-gain harmonic generation) without FEL gain, is used to provide ultrashort pulses in the femtosecond regime at harmonics of the seedlaser wavelength. To provide higher harmonics and thus shorter wavelengths, it is planned to...
We present a theory for free electrons interaction with radiation in both classical and quantum regimes and delineate their transition, based on a model of quantum electron wavepacket (QEW). The theory has general validity for a wide range of free electron interaction and radiation sources, including Free Electron Lasers, Cerenkov radiation, and transition radiation. We exemplify our analysis...
A numerical study is carried out on the quality of the electron bunch train produced from a photoinjector based on a frequency-detuning dependent gun coupler kick. The impact of the kick on the emittance of the bunch train is modelled via three-dimensional electromagnetic field maps calculated at detuned frequencies of the gun cavity within
long radio-frequency pulses. Beam dynamics...
The next generation of augmented brightness XFELs, such as LCLS-II, promises to address current challenges associated with systems with low X-ray cross-sections. Typical photoinjector lasers produce coherent ultraviolet (UV) pulses via nonlinear conversion of an infrared (IR) laser. Fast and active beam manipulation is required to capitalize on this new generation of XFELs, and controlling the...
The local laser synchronization is known to be of high importance for Free Electron facilities, affecting both machine performance and pump-probe FEL-external laser experiments. So, there has been a continuous effort to improve the timing jitter of all machine lasers. One of the main contributions to the overall timing jitter comes from the locking of the local laser oscillators to the...
A new generation of high-gradient normal conducting 1.3 GHz RF gun with 1% duty factor was developed to provide a high-quality electron source for superconducting linac driven free-electron lasers like FLASH and European XFEL. Compared to the Gun4 series, Gun5 aims for a ~50% longer RF pulse length (RF pulse duration of up to 1 ms at 10 Hz repetition rate) combined with high gradients (up to...
The external seeding technique Echo-Enabled Harmonic Generation (EEHG) consists of two undulators which are used to imprint energy modulations to an electron bunch via interaction with a seed laser. Each of these so-called modulators is followed by a chicane introducing longitudinal dispersion. Proper adjustment of the amplitudes of the energy modulations and dispersive strengths allows to...
A THz FEL is in preparation at PITZ as a proof-of-principle experiment for a high power and high repetition rate THz source and as an option for THz-driven experiments at the European XFEL. Some of these experiments require excellent coherence and CEP stable THz pulses. In SASE regime the coherent properties of the FEL radiation are limited. A seeding scheme can be used instead of SASE to...
Plasma photocathode injectors may enable electron beams with normalised emittance at the nm-rad level from a Plasma Wakefield Acceleration (PWFA) stage [1]. These electron beams typically have kA-level peak currents leading to ultrahigh 5D brightness beams with the potential to drive advanced light sources [1]. The feasibility of the plasma photocathode was demonstrated at FACET-I at SLAC [2]....
S.Y. Teng(1,2), S.H. Chen(1), W.Y. Chiang(2), M.C. Chou(2), H.P. Hsueh(2), W.K. Lau(2), A.P. Lee(2), P.T. Lin(3)
1 Department of Physics, NCU, Taoyuan, Taiwan
2 NSRRC, Hsinchu, Taiwan
3 Department of Engineering and System Science, NTHU, Hsinchu, Taiwan.
Intense coherent THz radiation has been generated from an 18-period, hybrid-type U100 planar undulator as it is driven by short...
At the 1.5 GeV synchrotron light source DELTA operated by the TU Dortmund University, the short-pulse facility employs the seeding scheme coherent harmonic generation (CHG) to produce ultrashort pulses in the vacuum ultraviolet and terahertz regime. This is achieved via a laser-induced electron energy modulation and a subsequent microbunching in a dispersive section. The spectro-temporal...
We report on the operation of the DRACO Laser Driven electron source for stable multi-day operation for FEL applications. The nC-class accelerator delivers charge densities around 10 pC/MeV , <1 mrad rms divergence at energies up to 0.5 GeV and peak currents of over 10 kA [1].
Precise characterisation is paramount for controlled operation, including: spectrally resolved charge diagnostic,...
In the framework of the FLASH2020+ project, the FLASH1 beamline will be upgraded to deliver seeded FEL pulses for users. This upgrade will be achieved by combining high gain harmonic generation and echo-enabled harmonic generation with a wide-range wavelength-tunable seed laser, to efficiently cover the 60-4 nm wavelength range. The undulator chain will also be refurbished entirely using new...
FEL basic theory indicates that the output wavelength of a seeded FEL operated in the HGHG configuration is determined by the wavelength of the seed laser and light is emitted when undulators are tuned to one of the harmonics of the seed laser. In a more realistic case, when taking into account the electron beam imperfections and the finite bandwidths of the seed and of the amplification...
Attosecond pulse production is an important development focus for most major FEL facilities. Chirp/taper and eSASE schemes, both of which will shorten the pulses well below the femto-second level for both hard and soft x-rays, are proposed for implementation at EuXFEL. As a high repetition rate super conducting linac that feeds three 200m long undulator lines for parallel operation, EuXFEL...
The 2nd stage of the FLASH2020+ project at DESY will be an upgrade of the FLASH1 beamline to enable HGHG and EEHG seeding with two modulator-chicane stages, and a radiator section with 11 Apple-III undulators to enable FEL radiation with controllable polarization. A key feature of FLASH, namely the capability of providing several thousand FEL pulses in the extreme UV and soft X-ray must not be...
FLASH2020+ is an upgrade project for the FLASH facility at Hamburg. A main goal of the project is to generate fully coherent soft X-ray FEL radiation at a high repetition rate (MHz). The project will utilize two external laser seeding principles in order to produced Seeded FEL with tunable wavelength from 4-60 nm. In order to achieve this goal, both HGHG (High Gain Harmonic Generation) and...
The extension of four-wave mixing (FWM) technique to the extreme ultraviolet and soft X-ray ranges allows to monitor the dynamics of coherent excitations of matter, when realized with the exquisite coherent property of bright FEL pulses. We show for the first time a scheme to provide transversally separated pulses with parallel or crossed linear polarizations, realized at FERMI FEL. This...
A unique platform for a Tera Hertz Transmission Line design for a superradiant FEL is present. The smart line is controlled by Artificial Intelligence (AI) intended for a wide tunable broad-spectrum THz radiation propagation. The main goal is to transfer radiation in the most efficient way. A 3D analysis and diagnostic of radiation space-frequency tool was developed. The AI changes the...
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Photocathodes are routinely used as a source of electrons in high brightness beam photoinjectors. The properties of the photocathode have a significant influence on the parameters of the electron beams and on the operation of the machines. The choice of photocathode materials is an important step in reaching the challenging requirements of modern accelerators. Recent advancements towards more...
The 1-MeV LCLS-II electron source including CW RF gun and buncher was successfully commissioned 2018-2020. Since then, a few upgrades has been implemented. Full scale of LCLS-II injector including the upgraded 1-MeV electron source, one standard 100-MeV Cryomodule, essential diagnostics for beam performance characterizations is being commissioned since late March 2022. This report will present...
DC-SRF gun, a DC and superconducting rf (SRF) combined photocathode electron source, has been developed at Peking University for nearly 20 years. Recently, a low-emittance version of DC-SRF gun, DC-SRF-II, was brought into stable CW operation with a DC voltage of 100 kV and an SRF cavity gradient of 13 MV/m, under which condition the dark current was measured to be lower than 0.001 nA....
Photoemission laser shaping is essential for both beam brightness and advanced accelerator concepts, therefore is an important R&D at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The laser pulse shaper presented here is based on spectral amplitude modulation of chirped laser pulses. In this approach one can do temporal-spatial coupled laser shaping, i.e. 3D shaping. The laser...
Good understanding of the underlying beam dynamics is mandatory for the successful design and operation of Free-Electron Lasers. In particular, it is important that all physically relevant collective effects are adequately represented in simulation codes so that their influence on the phase-space evolution of the bunch can be calculated with sufficient accuracy at all relevant length scales. ...
To date, the main obstacle to the extension of free electron lasers’ longitudinal coherence to the water window and beyond is the detrimental effect of spurious harmonic content in the longitudinal profile of electron bunches, namely the microbunching instability.
Intra-beam scattering is another (less known) collective effect that consists of multiple (small-angle) soft Coulomb scattering...
High-resolution measurements of the uncorrelated energy spread at SwissFEL indicate energy spread levels much larger than predicted by state-of-the-art particle tracking. This contribution presents measurements of the energy spread at the SwissFEL injector as a function of the electron bunch charge, the optics and the longitudinal dispersion of the lattice. The results indicate that both...
One of the serious issues for short electron bunches in electron beam accelerators is the microbunching instability driven by longitudinal wake fields along the accelerator. Over the last decades a tremendous effort has been made in the theoretical understanding and experimental study of the microbunching instability impact on free electron laser performances. At the European XFEL, the...
Laser wakefield accelerators can sustain accelerating gradients more than three orders of magnitude higher than those of radio-frequency accelerators, and are regarded as an attractive option for driving compact X-ray free-electron lasers. However, the realization of such devices remains a challenge owing to the relatively poor quality of electron beams that are based on a laser wakefield...
The breakthrough provided by plasma-based accelerators enabled unprecedented accelerating fields by boosting electron beams to GeV energies within few cm.
This enables the realization of table-top accelerators able to drive a Free-Electron Laser (FEL), a formidable tool to investigate matter at sub-atomic level by generating X-UV coherent light pulses with fs and sub-fs durations.
So...
We report the first lasing of a seeded FEL fully driven by a laser plasma accelerator. The experiment was performed at HZDR (Germany), coupling the high quality electron beams of the HZDR laser plasma accelerator with the versatile COXINEL beam manipulation line. Using an external seed at 270 nm, the FEL signal was observed at 275 nm. We explain how this slight red-shift confirms previous...
High-gain free-electron lasers (FELs) are driven by short, high-charge density electron beams as only produced at dedicated single pass or recirculating linear accelerators. We describe new conceptual, technical, and modeling solutions to produce subpicosecond, up to ∼100 μJ-energy extreme ultra-violet and soft x-ray FEL pulses at high and tunable repetition rates, from a diffraction-limited...
A high temporal stability of produced photon pulses is a key parameter for some classes of experiments, e.g., those using a pump-probe scheme. A longitudinal intra bunch-train feedback system, that reduces the intra bunch-train and the train-to-train arrival time fluctuations down to the sub-10 fs level was implemented at the European X-ray free electron laser (EuXFEL). The low arrival time...
This project describes different techniques to manufacture THz mirrors with arbitrary surfaces. The research is part of the development of THz transmission line for the compact FEL-THz accelerator.
As an initial phase flat mirrors were 3D printed with FFF (Fused Filament Fabrication) and SLA (Stereolithography Apparatus). The impact of material, layer height and layer direction to mirror’s...
Free electron lasers (FEL) serve a broad user community in many scientific fields ranging from
atomic and molecular physics to plasma and solid state physics as well as chemistry and biology.
Many experiments could benefit from a non-destructive online photon diagnostic of the provided
x-ray pulses. Especially, for free-electron lasers that are operated in the self-amplified sponta-
neous...
For a free-electron laser facility, the longitudinal phase space of the beam is essential to the FEL lasing performance. However, the commonly-used diagnostics device such as the transverse deflecting cavity provides a destructive way to measure the beam longitudinal properties, which is not available during beam delivery. Thus, the convolutional neural network is introduced to construct a...
Optimal FEL gain in a seeded FEL requires the careful alignment of different components. As for SASE FELs, the gain is optimized when the electron bunch travels in a straight line along the axis of each undulator in the radiator section. We have recently developed an alignment strategy for the optimization of the FERMI FELs which combines the beam-based alignment of the magnetic elements...
X-ray absorption spectroscopy (XAS) enables the study of the electronic and geometric structural properties of matter. Such investigations can now be realized with femtosecond temporal resolution owing to the availability of X-ray free-electron lasers (XFELs) [1]. However, most XFELs currently utilize self-amplified spontaneous emission (SASE), which causes strong shot-to-shot fluctuations of...
The European X-ray Free-Electron Laser (EuXFEL) is a unique FEL facility that provides X-ray pulses of high spectral brilliance and high photon flux at MHz repetition rate. However, the high peak power, produced in trains of up 2700 femtosecond pulses at a rate of 10 Hz, induces a periodic temperature increase of the hard X-ray monochromators, thereby reducing their transmitted intensity. To...
PolFEL will be the first free-electron laser facility in Poland. It will be driven with RF continuous-wave superconducting linac including an SRF injector furnished with a lead film superconducting photocathode. PolFEL will provide a wide wavelength range of electromagnetic radiation from 0.6 mm down to 60 nm. The linac will be split into three branches. Two of them will feed undulators chains...
The electron-beam properties needed for successful implementation of a free-electron-laser oscillator (FELO) on a superconducting TESLA-type linac at the Fermilab Accelerator Science and Technology (FAST) facility include the intrinsic normalized emittance and the submacropulse centroid stability. We have demonstrated that short-range wakefields (SRWs) and long-range wakefields including...
A helical undulator provides a stronger FEL coupling than common planar geometries as the beam’s transverse velocity never vanishes. However, a significant challenge lies in tuning and measuring the fields with limited access to the beam axis along the undulator. Confirming the good field region off axis is difficult without space for 3D hall probe scans, and is important for low energy beams...
We present experimental observation for the impact of an introduced orbit disturbance in the photoinjector section on the SASE performance at the European XFEL. An orbit bump is first created and then closed by the orbit feedback downstream, that is, the orbit leaving the injector section stays the same while presumably only causing a disturbance to the bunch. With the same orbit launched into...
Electrons in a X-ray free electron laser (XFEL) develop periodic density fluctuations, known as microbunches, which enable the exponential gain of X-ray power in an XFEL. When an electron beam microbunched at a hard X-ray wavelength is kicked, microbunches are often washed out due to the dispersion and R56 of the bend. An achromatic (dispersion-free) bend with small R56, however, can...
It has been proposed that a new arc, called T20, should be installed for a third fan of undulators at the EuXFEL in the next decade. Due to geometric constraints this arc will need to be at a much larger angle than for the existing arc (T1). It is expected therefore that coherent synchrotron radiation effects in T20 on the bunch emittances will be considerable. To preserve the x-ray beam...
It is planned to extend SwissFEL by a third beamline, named Porthos, operating in the hard X-ray regime. Three bunches will be accelerated within one RF pulse and distributed into the different beamlines with resonant kickers operating at the bunch spacing of a few tens of nanoseconds.
While the full extent of Porthos will not be realized before the end of this decade the extraction line from...
The ORGAD Hybrid RF-gun which was commissioned in Ariel University is based on a smaller-scale prototype built at UCLA's Particle Beam Physics Laboratory (PBPL) as an on-going collaboration between the Universities. The main beamline of the hybrid S-band (2856 [MHz]) photo injector is currently driving a 150[kW], short pulse THz-FEL. In order to use the RF gun for other applications, a new and...
EuPRAXIA@SPARC_LAB is a new Free Electron Laser (FEL) facility that is currently under construction at the Laboratori Nazionali di Frascati of the INFN. Fermilab is contributing to the project with the design, manufacturing and qualification of a prototype conduction cooled superconducting undulator (SCU) that, if successful, could be integrated in the final machine.
The design of the SCU...
Terahertz (THz) radiation may pass through dielectric materials, and this ability can be used for a variety of applications. Terahertz (THz) radiation is located between infrared and microwave radiations in the electromagnetic spectrum. FEL produces brief, high-power THz single pulses, and we provide a diagnostic approach for them. The electro optic efficacy is used as a detection method. For...
Development and characterization of an angle-resolved photo-electron spectrometer, based on the electron Time-of-Flight concept, designed for hard X-ray photon diagnostics at the European free-electron laser is described. The objective with the instrument is to provide beamline users and operators with pulse resolved, non-invasive spectral distribution diagnostics, which in the hard X-ray...
We were able to realize a compact microtron accelerator with 5 MeV electron beam acceleration energy and a hybrid electro-magnetic undulator that can vary the magnetic field of 1.07 T at 0.74 T. The electron beam is accelerated by an RF electric field of a 1-cell acceleration cavity and recirculated by a uniform magnetic field of the microtron main chamber. Through the re circulation process,...
FELs deliver rapid pulses on the femtosecond scale, and high peak intensities that fluctuate strongly on a pulse-to-pulse basis. The fast drift velocity and high radiation tolerance properties of chemical vapor deposition (CVD) diamonds make these crystals a good candidate material for developing a high frame rate pass-through diagnostic for the next generation of XFELs. We report on two...
PolFEL stands for Polish Free Electron Laser, the first FEL research infrastructure in Poland. This facility is under development, and it will operate in three wavelength ranges: IR, THz and VUV, using different types of undulators. Machine will be driven by 200 MeV linear superconducting accelerator, which will operate in both, pulsed wave (PW) and continuous wave (CW) modes. This...
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At the Photo Injector Test facility at DESY in Zeuthen (PITZ) photo electron guns for the use at the X-ray free-electron laser (FEL) facilities FLASH and European XFEL are conditioned. An electron beam with high current and low transverse emittance is required for high performance in an X-ray FEL.
As the lasing process occurs on the part of the electron bunch with the highest charge density...
Diffraction gratings are an essential instrument used at free-electron laser facilities in soft and tender x-ray ranges. Their application ranges from monochromators and analyzers to self-seeding and pulse compression. These gratings are typically around 50-200 mm, up to 500mm in length with pitches from a few micrometers down to a few 100 nm, made on flat or curved substrates. Blazed gratings...
Co-propagating a relativistic electron beam and a high-power laser pulse through a short undulator (modulator) provides an energy modulation which can be converted to a periodic longitudinal density modulation (or microbunching) via the R56 term of a chicane. Such pre-bunching of a beam at the resonant wavelength and the harmonics of a subsequent free-electron laser (FEL) amplifier seeds the...
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The presence of microbunching in the FERMI FEL electron beam is a known nuisance that can impact the performance of the FEL. Microbunching is generated by complex dynamics along the machine where there are several amplification sources. The use of a laser heater, at the cost of an increased energy spread, can improve the quality of the electron beam mitigating the modulation due to...
Intrabeam scattering (IBS) causes growth of the uncorrelated energy spread of electron bunches due to multiple small-angle Coulomb collisions over long propagation distances. As such, this effect may be a limiting factor for the beam current and therefore for the achievable photon energy in the SASE process. In addition, IBS influences the noise spectrum of the bunch, thus, interfering with...
The European X-Ray Free Electron Laser (XFEL) operates three Undulator Systems to generate high-brilliance and high repetition X-ray pulses. Each System consists of multiple 5-m long undulator segments separated by 1.1-m long intersections. Such intersections contain vacuum systems, diagnostic and correction equipment for the electron's trajectory, and phase shifters (PS) [1] to match the...
Ultra-short X-ray pulses in an XFEL can be generated by means of a slotted foil inserted into a bunch compressor. There is an ongoing study into whether such a technique could be used at the European XFEL. One important factor that must be considered is whether the additional beam losses and radiation load caused by the foil is acceptable with a high repetition rate of up to 4.5MHz at the...
The tremendous developments on Laser Plasma Accelerators (LPAs) have significantly improved the electron beam properties and stability making it possible to drive a Free Electron Laser (FEL). We report on the electron beam transport and manipulation using the COXINEL beamline implemented at HZDR that has recently led to the first measurements of an LPA-based seeded FEL in the UV region. Our...
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CLARA is an electron beam test facility being developed in phases at STFC Daresbury Laboratory. The first phase, with up to 35 MeV electron beam energy, has been operated since 2018 for a wide range of accelerator applications. The second phase, presently being installed, will expand the range of applications by taking the beam to 250 MeV energy and via a dog-leg to an experimental station...
The superconducting undulator (SCU) based on the second-generation high-temperature superconducting (HTS) tapes is a promising application for building tabletop free-electron lasers (FELs). The short period < 10 mm undulators with a narrow magnetic gap < 4 mm are especially relevant. The advantage of the HTS tape is that it shows both high critical current density and high critical magnetic...
Orbit response measurements in the soft X-ray beamline of Athos have shown coupling of the beam transport between the transverse planes, which is influenced by the on-axis field strength of the Apple-X undulator modules. A model reproduces this observation if a coupling term is included in the transport matrix of the undulator module. The presentation shows the estimate of the coupling...
Ultracold plasmas (UCPs) form a new exotic category of plasmas that can be produced by photo-ionizing laser-cooled atoms in a magneto-optical trap (MOT) near-threshold. With densities up to $10^{18}$ m$^{-3}$, temperatures as low as $\sim$100 $\mu$K for the ions, and $\sim$1 K for the electrons, they are the ideal model plasmas to study fundamental processes in plasma physics, such as (the...
Electromagnetic wave undulators have the advantage of a shorter period compared with the permanent magnet undulators when operating at high frequency, therefore producing FEL radiation at the same wavelength with less electron energy. This paper investigates the properties of a Ka-band microwave undulator, and the factors that affect the choice of the high-power drive sources, through the...
Despite the use in machine physics of high-performance software for calculating and predicting machine parameters, when these are applied to the real world, optimal operating point search is often necessary to obtain the desired performance.
Furthermore, small configuration changes required by FEL Users during running experiments ,lead to search new good working points in a short time.
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Currently 26 RF stations are in operation at the European X-ray Free Electron Laser (XFEL) and all RF stations can deliver sufficient power to reach maximum gradients in the accelerating modules, limited only by cavity and coupler properties. It was demonstrated that by activating a dynamic frequency shift (DFS) of the RF drive signal, the requested klystron power can be reduced by up to 20%,...
With the beam synchronous readout of the beam position measurement at the hard X-ray FEL beamline Aramis at SwissFEL we analyze the intrinsic orbit jitter, using a classification algorithm and Principal Component Analysis (PCA). The method sorts the jitter in a set of eigenvectors and -values. With the magnitude of the eigenvalues the impact of the different jitter sources can be estimated....
The undulators in the European XFEL are made of permanent magnets that need to be protected from beam losses that could cause demagnetisation. Under current operating conditions, beam losses in the undulators are prevented by a collimation section downstream of the main Linac and upstream of the switchyard. In the future, a slotted foil may be installed in the European XFEL to reduce the X-ray...
In January 2021 two X-band (12 GHz) PolariX Transverse Deflecting Structures with variable streak polarization were installed into the FLASH2 beamline at FLASH. Since none of the RF components for the FLASH2-PolariX RF-distribution system nor the two PolariX structures could be pre-conditioned, RF-conditioning was and is quite tedious. Nevertheless, after 6 weeks of conditioning, we have...
In 2017, a collaboration between DESY, PSI and CERN was established with the aim of developing and building seven advanced X-Band Transverse Deflection Structure (TDS) with the new feature of variable polarization of the deflecting force. Seven deflectors were produced by PSI of which five were installed in three experiments at DESY, while the remaining two were installed in the ATHOS soft...
We present the study for a short period Apple-X variable polarizing undulator, with small gap of operation and high magnetic field, which will be the base module for the AQUA line of the EuPRAXIA@SPARC_LAB FEL facility, of next realization at INFN Laboratory of Frascati. The undulator allows to achieve radiation between 3 and 5 nm, the so called water-window, with a 1 GeV electron beam energy,...
In this report, we present a simulation study of dielectric beam energy dechirper designed for the proposed NSRRC EUV FEL facility. As revealed from ELEGANT simulation of the high brightness driver linac system, a residual energy chirp of about 42 keV/m is left after bunch compression. It can be corrected by a capacitive dechirper structure when the bunch is slightly over-compressed. We...
The free-electron laser in Hamburg (FLASH) operates in the extreme ultraviolet (XUV) and soft X-ray region, providing photon pulses of few femtosecond (fs) duration and unprecedented intensity [1]. FLASH operates in the self-amplified spontaneous emission (SASE) regime, meaning that every pulse has a unique combination of energy, spectrum, arrival time and pulse duration. Therefore, it is...
We propose to develop an energy-recovery-linac (ERL)-based X-ray free-electron laser (FEL). Taking advantage of the demonstrated high-efficiency energy recovery of the beam power in the ERL, the proposed concept offers the following benefits: i) recirculating the electron beam through high-gradient SRF cavities shortens the linac, ii) energy recovery in the SRF linac saves the klystron power...
KAOS is the flagship optics of FERMI, the first - and presently only - fully seeded Free Electron Laser facility in the world. The name stands for Kirkpatrick-Baez Active Optical System, and it has been entirely developed in-house. After progressive revisions and upgrades, it presently empowers three out of six beamlines at FERMI, and it also serves two beamlines at FLASH, Hamburg (DiProI,...
The SASE3 soft X-ray beamline at the European XFEL is equipped with the grating monochromator allowing to reduce SASE FEL bandwidth and to improve longitudinal coherence at the experiments in the photon energy range 250 eV - 3000 eV. The design of the monochromator is challenged by a demand to control both photon energy resolution and temporal resolution; the aim to transport close to...
DEIMOS (Dichroism Experimental Installation for MagnetOptical Spectroscopies) is the beamline built at French Synchrotron SOLEIL facility intended for soft X-rays magnetic and natural dichroism spectroscopies. It has been designed to enable most challenging measurements in terms of X-rays sample sensitivity and signal detection level. The energies accessible on DEIMOS beamline rank from 350 eV...
Good control over the transverse distribution of an electron bunch is crucial for optimising the beam transport through a linear accelerator, and for improving the energy transfer of electrons to photons within the undulators of a free-electron laser (FEL). In order to achieve this, it is necessary to match, as closely as possible, the Twiss parameters of the electron bunch to the design...
Accurate and high resolution detection of the Longitudinal Phase Space (LPS) of the electron beam is a great advantage for operating and setting up a FEL. In the case of the soft X-ray FEL being proposed at the MAX IV synchrotron facility in Lund, this information is mainly supplied by a Transverse Deflecting Cavity (TDC) which is currently being installed and scheduled for commissioning in...
In free electron lasers (FEL) the accumulative effects of wakefields always lead to critical impacts on the electron bunch, resulting in an energy spread and deviation of transverse position. Thus the lasing performance will be decreased. The Shanghai high-repetition-rate XFEL and extreme light facility (SHINE) is under construction and the wakefields estimations are required. The SHINE...
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What is the best place where you can publish your FEL-related research? Should your target be the FEL community, or do your results deserve the attention of a broader audience? How to write a perfect paper, taking advantage of the interaction with editors and referees?
What is the best place where you can publish your FEL-related research? Should your target be the FEL community, or do your results deserve the attention of a broader audience? How to write a perfect paper, taking advantage of the interaction with editors and referees?
Existing beam diagnostics are invasive, and oftentimes cannot operate at the required resolution. In this work we present a Machine learning-based Virtual Diagnostic (VD) tool to accurately predict the Longitudinal phase space (LPS) for every shot using spectral information collected non-destructively from the radiation of a relativistic electron beam. VD is a computational tool based on deep...
Recent breakthroughs in laser wakefield accelerator (LWFA) technology have allowed them to drive free-electron lasers [1]. This is a significant accomplishment as LWFA electron beams are not as well controlled as beams from conventional accelerators. However, longitudinal structure in LWFA beams could be harnessed to accelerate the self-amplified spontaneous emission (SASE) process....
Temporal diagnostics of FEL pulses are generally of great benefit to FEL facilites, in particular to provide information to users and for the setup of special modes such as fresh-slice schemes. In this contribution we present FEL power profile measurements with femtosecond resolution at SwissFEL. The FEL temporal profiles are obtained from the longitudinal phase-space of the electrons after...
Recent advances in bunch compression and FEL schemes have enabled ultrashort sub-fs electron and X-ray pulses. The timing jitter is, at best, one order of magnitude larger that the pulse duration. This can be handled by high precision pump-probe delay measurements and data sorting. However, only a small fraction of the pulses will be in the relevant time window.
The acceleration and...
The implementation of a helical afterburner undulator at DESY's VUV-FEL source is part of the current FLASH2020+ upgrade program. The device shall be installed downstream of the present FLASH2 SASE undulators and will provide radiation with variable polarization from 1.33 nm to 1.77 nm (890-700eV) and thus also cover the L-edges of the 3d transition metals Fe, Co, and Ni. Despite a moderate...
The XFELs with an anomalously high peak brilliance are opening the way to a number of novel X-ray photon research paths. At SPring-8 Angstrom Compact Free-Electron Laser (SACLA) [1], the XFEL pulses with high stability and short pulse duration (6-7 fs) have been regularly provided thanks to the unique electron gun, accelerator, and undulator systems [2]. By focusing these XFELs to 1um-100nm,...
Cavity-Based X-ray Free-Electron Lasers (CBXFELs) employ an X-ray cavity formed by crystal mirrors such that X-ray pulses receive periodic FEL-amplification and Bragg-monochromatization. CBXFELs enable improved longitudinal coherence and spectral brightness over single-pass self-amplification of spontaneous radiation (SASE) FELs [1,2] for high-repetition rate FELs. Construction and alignment...
Free-electron lasers (FELs) are currently the most advanced class of light sources, by virtue of their unique capability to lase high-brightness and ultrashort pulses characterized by wavelengths spanning the Extreme-Ultraviolet (EUV), the Soft (SXR) and Hard (HXR) X-Ray spectral domains, alongside with temporal duration lying in the femtosecond (fs) timescale [1]. Specifically, the advent of...
We report on our recent experimental results of single-shot and single-particle X-ray diffraction of nanoparticles at SACLA. The single-shot diffraction data provided insights into the crystallization kinetics of Xe nanoparticles, where the nanoparticles initially crystallize in the metastable stacking-disordered phase and then transform into the stable fcc phase. In addition, we investigated...
There has been growing interest in using ultrafast light pulses to drive materials into nonequilibrium states with novel properties. Using time-resolved X ray scattering, I demonstrated that SnSe, one of the IV-VI resonantly bonded compounds, hosts a novel photo-induced lattice instability associated with an orthorhombic distortion of the rock-salt structure with space group Immm [1]. The new...
Dimensionality plays a key role for the emergence of ordered phases such as charge-density-waves (CDW), which can couple to, and modulate, the topological properties of matter.
In this work, we study the out-of-equilibrium dynamics of the paradigmatic quasi-one-dimensional material (TaSe$_4$)$_2$I, that exhibits a transition into an incommensurate CDW phase when cooled just below room...
Time-resolved experiments are increasingly relevant in modern FEL user facilities. With the FLASH2020+ upgrade project, the pump-probe capabilities of the FLASH will be extended. Besides offering fixed wavelengths (1030 nm fundamental and its harmonics), tunable wavelengths are under development: sub-150 fs long tunable mid-infrared (2-5 microns) pulses for the solid-state community and sub-40...
The FERMI Free Electron Laser in Trieste (Italy) has been designed and built as a seeded source, for precise control of the properties of its light pulses. Its excellent longitudinal coherence is inherited from the seed laser, and is its uppermost distinctive feature. In the realm of atomic, molecular and optical science, the use of longitudinal coherence of laboratory lasers as a time...
Electron motion is a key ingredient of every chemical processes. The natural timescale for such electronic dynamics in small molecular systems is typically in the range of tens to hundreds of attoseconds. Here I will present recent experimental results using attosecond x-ray free electron laser pulses and pulse pairs to probe ultrafast electronic motion. X-ray free-electron lasers offer...
The use of light beams possessing orbital angular momentum (OAM) is rapidly becoming a way for probing condensed-matter systems, even in the XUV range [1]. The wavefronts of such beams are characterized by an azimuthal angular dependence of the electric field phase, associated with an OAM topological charge $\ell \neq 0$. For imaging purposes, it has been shown that OAM beams can overcome the...
Brilliant, ultrashort, and coherent X-ray FEL pulses allow investigations of dynamics at the inherent time and length scale of atoms. However, the user community still lacks access to phase-locked X-ray pulses, desirable for time domain correlation spectroscopies and coherent quantum control. Based on selective electron-bunch degradation in the accelerator, combined with two-stage, self-seeded...
