Microbunching - or short-wavelength – instabilities are well-known for drastic reduction of the beam quality, its filamentation and strong amplification of the noise in a beam. Space charge and coherent synchrotron radiation (CSR) are the leading causes for such instability. I will present rigorous 3D theory of such instabilities driven by the space-charge forces and define the condition when...
A nanosecond multi-bunch mode in FEL extends the laser capabilities. There are several critical components to be added to a baseline of the multi bunch FEL (for example, LCLS/LCLS-II). One of the components is the system that properly control the individual bunch orbit in the linac. The individual bunch orbit control based on the RF amplitude and phase modulation is limited by the bandwidth....
Laser-wake field accelerators (LWFAs) are potential candidates to produce intense relativistic electron beams to drive compact free electron lasers (FELs) in VUV and X-ray regions. The High-Field Physics and Ultrafast Technology Laboratory at National Central University (NCU) is actively developing a compact LWFA-based high gain harmonic generation (HGHG) FEL aim at coherent extreme...
The Circular Electron Positron Collider (CEPC) is a large-scale scientific project consisting of three accelerators: a 30 GeV Linac, a full-energy booster, and a collider operating at four different energy modes. The CEPC Linac is a normal-conducting linear accelerator with an energy of 30 GeV and repetition frequency of 100 Hz. To fully utilize the potential of the Linac, during the injection...
Understanding the electron beam distribution in the longitudinal phase space (LPS) is crucial for Free Electron Laser (FEL) facilities. Conventionally, LPS diagnostics utilize radio frequency (RF) deflecting structures to streak the electron beam transversely, mapping the longitudinal bunch distribution onto a transverse plane for observation. However, RF structures are complex and costly,...
State-of-the-art XFELs generate bright, ultrashort X-ray pulses enabling cutting-edge sub-femtosecond resolution time-resolved pump-probe experiments. Key requirement is an utmost precise timing distribution and synchronization between pulsed lasers and microwave sources distributed across a km-scale facility. Fiber-based pulsed optical timing distribution systems (TDS) are an ideal solution...
Current x-ray free-electron lasers (XFELs) rely on single-pass amplification starting from noise or a seed and require long undulator lines to reach saturation. An oscillator configuration allows for multi-pass amplification, using shorter undulator lines, and the filtering properties of both the resonator and the gain will improve the transverse and longitudinal coherence. Here we consider a...
Achieving lower beam emittance through effective space charge compensation is critical for enhancing beam brightness and luminosity in accelerator physics. Traditional solenoid-based methods are limited to linear compensation and often introduce chromatic aberrations. Our study aims to develop novel techniques that compensate for both linear and non-linear space charge forces. As a first step,...
Bunch compressors are frequently employed to boost beam brightness in accelerator facilities such as e+e-
linear colliders and free electron lasers (FELs). However, the energy chirp or correlated energy spread intro-
duced into the beam by the chirper linac remained after bunch compression is undesirable in some applica-
tions. Wakefield structures known as dechirpers are designed to...
SLAC and RadiaSoft are partnering to provide integration support for two parallel workflows that support end-to-end modeling and machine learning integration for accelerators. LUME, Light Source Unified Modeling Environment, has been developed by SLAC to facilitate end-to-end modeling for machine tuning and optimization. This workflow includes the integration of machine learning surrogate...
Many applications in modern accelerators require short electron bunches with high peak current. To achieve this high current, a large energy chirp must be imposed on the bunch so that the electrons are compressed when they pass through a chicane. In existing linear accelerators, this energy chirp is imposed by accelerating the beam off-crest from the peak fields of the RF cavities, thereby...
Despite the good short-term performance of electron beam control, the long-term stability and control accuracy of the particle beams still limit the performance and application range of the FEL due to the thousands of coupling parameters as well as the uncertainty and time-varying nature of the electron distribution generated by the photocathode. Many challenges are still faced when confronted...
As a scheme to increase longitudinal coherence in SASE based FELs, hard X-ray self-seeding (HXRSS) has demonstrated its capability of delivering above 1mJ/eV peak pulse intensity in the hard X-ray range. To further increase its operational range and tunability, several advanced HXRSS operation schemes are under investigation at the European XFEL. The studies on 2nd harmonic generation, two...
This study presents a comprehensive analysis of user operations at the FERMI free-electron laser (FEL) facility spanning a period of 10 years. Located in Trieste, Italy, FERMI is the first seeded FEL light source dedicated to users, delivering since 2011 high quality extreme ultraviolet and soft X-ray beams for a wide range of scientific experiments based on diffraction, scattering and...
We perform analysis of a typical practical case of FLASH operation with the number of radiation modes in the range pulse M ~ 4 ... 8. Standard tuning procedure (for maximum pulse energy at full undulator length) results in visible energy chirp along the electron bunch such that spectrum bandwidth is increased to about 1% fwhm, visibly wider than natural FEL bandwidth. These features were taken...
Planar corrugated wakefield structures are widely used in X-ray FEL facilities for passive dechirping and transverse deflecting. The wakefields of these structures have previously been analytically studied, assuming the electron beam is short and has a small transverse beam size. However, the transverse beam size can be notably large in some practical cases, for example, when a slotted foil is...
Within the FLASH 2020+ upgrade project of the FLASH facility in Hamburg, the original FLASH beamline (FLASH1) will be completely remodelled and equipped with variable gap APPLE-III undulators, capable of controlling the polarization state of the FEL radiation.In the course of enhancing the operability of FLASH, the influence of the variable undulator focusing in both planes will be...
Attosecond X-ray pulses carrying orbital angular momentum (OAM) are as a powerful tool for investigating various ultrafast phenomena, offering unique insights into the dynamics of matter at the atomic and molecular level. The self-seeded FEL with OAM (SSOAM) method providing a new way to produce attosecond X-ray vortices pulses with high intensity. In this study, we present our recent progress...
Precise alignment of the undulator trajectory onto a straight line is a per-requisite for high fidelity SASE operation, which in turn also enables non-standard operation modes like self-seeding or two-color operation. At European XFEL electron and photon beam based method are combined with a step-by-step performance based optimization to ensure that the trajectory is on a straight line over...
Low-emittance electron beams play an essential role in improving the machine performance and extending the capabilities of existing free-electron lasers. The generation of such high-quality electron bunches relies on an overall optimization of the photoinjector, and most importantly, on the desired properties of the cathode drive laser. Appropriate shaping of the drive laser, namely,...
Knowledge of the beam energy is important for practically all particle accelerators. This contribution presents the method used at the European XFEL since more than 8 years. It relies on high-performance trajectory fitting of beam position monitor data against an online model of the accelerator lattice. Unlike most other methods, it can be applied to virtually any section of the lattice with...
The bunch-to-bunch energy control of the electron beam is crucial in the continuous wave X-ray free-electron lasers facility(XFEL). Recently, a delay system based on double bend achromat (DBA) was proposed for the Shanghai High-Repetition-Rate XFEL and Extreme Light Facility(SHINE) to achieve this goal. On this basis, we further optimize this structure to realize the bunch length control while...
The PolFEL THz free electron laser project comprises 80 MeV cw-linac furnished with warm S-band electron gun and 2 Rossendorf-like cryomodules. Besides bringing the beam to undulator, inverse Compton scattering interaction point, and finally to the dump, the beam diagnostics system is dedicated to metallic superconducting photocathodes development, in particular gun performance...
The design and tuning of a storage ring for a fourth-generation synchrotron light source is very demanding. Recently, some research groups have considered techniques based on quasi-invariants of motion to address this task. This contribution presents tools, based on a quasi-invariant of motion method, for the description and optimisation of the quality of electron dynamics in a storage ring....
We present a study that characterizes synchrotron radiation in the presence of a waveguide (the vacuum pipe). Building on previous work*, we have developed a code for calculating synchrotron radiation (SR) that accounts for boundary conditions. Our approach employs the Green's function technique to solve field equations under a paraxial approximation. We cross-checked the outputs of our code...
Echo-enabled harmonic generation (EEHG) has been proposed as a seeding method for free-electron lasers but can also be employed to generate ultrashort radiation pulses at electron storage rings. With a twofold laser-electron interaction in two undulators (the modulators), each followed by a magnetic chicane, an electron phase space structure with a high harmonic content is produced, which...
Dalian Coherent Light Source (DCLS), a vacuum ultraviolet free-electron laser (FEL) facility, has been delivering high-brightness FEL pulses to the scientific community for over seven years. To further enhance the electron bunch quality and consequently improve FEL lasing performance, an X-band system for linear bunch compression has been recently installed and commissioned at DCLS. This...
Free-electron-lasers fill a critical gap in the space of THz-sources as they can reach high average and peak powers with spectral tunability. Using a waveguide in a THz FEL significantly increases the coupling between the relativistic electrons and electromagnetic field enabling large amounts of radiation to be generated in a single passage of electrons through the undulator. In addition to...
FEL Seeding in High Gain Harmonic Generation scheme has been used for more than a decade with excellent results. The shortest wavelength delivered for user operation is so far around 4 nm based on double-cascade fresh bunch seeding at the FERMI FEL2. The implemented seed wavelength range in this case is 240-267 nm, which provides a good compromise between not too high harmonic order to reach 4...
Single-spike SASE radiation exhibits partial temporal coherence, creating an opportunity to compress pulses below the slippage length limit. In this case, the FEL pulse length will be limited by the coherent bandwidth. We consider how arbitrary control of the electron beam chirp can be used to first create a large coherent bandwidth through the chirp-taper dynamics; and secondly to compress...
X-ray free-electron laser is developing towards the sources with ultra-high intensity and ultra-short duration. The SXFEL facility is operated to generate the soft x-ray FEL with sub-GW-level peak power and nearly 100 fs pulse duration. It also has taken into consideration to shorten the pulse duration and increase the peak power. In this contribution, we analyzed the schemes possibility of...
Imposing a density modulation, or microbunching, on an electron beam may improve the brightness of an inverse Compton scattering (ICS) source by orders of magnitude via superradiant emission. We analytically and numerically analyze a new method, termed ponderomotive bunching, to create microbunching on a relativistic electron beam. Here, an electron beam interacts with a copropagating beat...
The room temperature VHF RF gun which can provide high brightness beams with MHz repetition rate is one of the candidates for the electron source of a high-repetition-rate FELs.The VHF RF gun operates at continuous wave (CW) mode with high cathode gradient and high accelerating voltage. The dark current is critical to the performance of the downstream SRF cavities, undulators and beam line...
An infrared free electron laser user device will be constructed at the Anhui University in Hefei. The facility integrate free electron laser, strong magnetic field, and low-temperature environment aiming at materials science and other fields research. It consists of two FEL oscillators driven by one normal-conducting S-band linac and five experimental stations. The two oscillators generate the...
FELiChEM is an infrared free electron laser (FEL) user facility located in China, covering a wavelength range of 2-200 μm. Many spectral gaps were measured which the user experiments did not expect, especially in the far-infrared wavelength region from 50-200 μm. In this paper, we propose to apply a bow-tie cavity resonator instead of the conventional resonators to eliminate all the spectral...
Circularly polarized free electron laser (FEL) pulses are strongly demanded to satisfy plenty of experiments, but static magnetic elliptically polarized undulators(EPU) are too limited to achieve shorter undulator periods. In this paper, the potential of polarization control using the radio frequency (RF) undulator afterburner is discussed for Shanghai soft X-ray FEL user facility(SXFEL-UF)....
The operation of X-ray free-electron laser facilities necessitates the use of electron beams characterized by both high repetition rates and high energy, thereby elevating radiation safety concerns attributable to potential beam loss. Beam collimation is employed to protect the undulator and other elements by removing the beam halo in operation, as well as absorbing the off-axis beam during...
The extraction efficiency is one of the key parameters of an FEL oscillator. In the conventional way of extraction efficiency measurement in Kyoto University FEL (KU-FEL), temporal evolutions of the electron beam energy distribution in a macro-pulse with and without FEL lasing were measured by a Faraday cup placed after an energy analyzer[1]. Then the extraction efficiency is evaluated from...
The Shanghai soft X-ray Free-Electron Laser facility (SXFEL) is a fourth-generation linac-based light source, capable of producing X-ray pulses with duration of tens of femtosecond. The photocathode laser and the seed laser for external seeding FEL therefore have tight requirements for relative arrival time to the machine and electron bunch. To reach required energy and wavelength to drive...
DESY is developing different scenarios for a high-duty-cycle upgrade of the superconducting linac of the European XFEL. These scenarios include the current 10-Hz “burst mode” at 16.5 GeV (~1% duty cycle) up to full CW operation at ~7 GeV (100% duty cycle), with an intermediate 10% duty cycle option which could achieve ~15 GeV. The linac upgrade itself requires an additional sixteen CW-ready...
Coherent Synchrotron Radiation (CSR) is regarded as one of the most important reasons that limit beam brightness in modern accelerators. Current numerical packages containing CSR wake fields generally use 1D models, which can become invalid in extreme compression regimes. On the other hand, the existing 2D or 3D codes are often slow. Here we report DFCSR, a novel particle tracking codes which...
The Korea Atomic Energy Research Institute has developed a 5-MeV compact microtron accelerator to construct a high-power terahertz (THz) free electron laser (FEL) for field use. Good quality electron beam is essential for generating strong THz laser beam. Optimizing the electron beam was a priority for ensuring the performance and stability of the final THz FEL beam. The compact microtron...
Fermi is a seeded FEL and has been operating in High Gain Harmonic Generation mode for more than a decade. Recently, the FERMI FEL-1 line, which normally delivers photons from 100 nm to 20 nm, has been upgraded to operate in Echo Enabled Harmonic Generation mode, extending the spectral range down to 10 nm and even beyond.
A measurement campaign was carried out to characterise the FEL...
Plasma-driven FELs require electron beams of high quality to facilitate effective FEL amplification, mirroring the stringent beam property requirements of FELs driven by radio frequency structures. Unique to plasma accelerators, however, are specific challenges such as dealing with the small beam size in the plasma, and managing a significant energy chirp within the beam. The study offers a...
SwissFEL has been in user operation since 2019. Central to its ongoing success and enhancement is the continuous development of the properties of the electron beam, which requires ever more accurate instrumentation. This poster provides a comprehensive overview of the latest advancements in electron beam instrumentation at SwissFEL. which are pivotal for improving the facility's operational...
The pulse duration of the X-ray free-electron laser (XFEL) relies on the pulse duration of the electron bunch. The energy distribution of the electron bunch can be manipulated by using the laser heater in the purpose of generating attosecond pulse duration electron bunch current profile. Therefore, the resultant electron bunch current profile after the bunch compressor chicanes is programmable...
All XFEL machines utilize multiple magnetic Bunch Compressors (BC) for e-bunch compression. Since the non-linear energy chirp among bunch slices, current peaks occur in the head and tail of bunches, which generate collective effects spoiling the core slices. To remove current peaks, collimators at BCs are used to collimate head and tail slices in FEL machines operating at an approximate...
The PITZ Facility at DESY Zeuthen focuses on the development & optimization of high-brightness e-beam sources for FELs like the Eu-XFEL. The main scientific program is generation of intense e-beams characterized by small transverse emittance from the photo injector, a critical requirement for modern FELs. At PITZ, a thorough study of factors influencing emittance growth is carried out....
Free-electron lasers in the terahertz region that produce high peak and average power require small diameter, low-emittance, high voltage electron beams. This paper presents a 1.5-2 MV, 100-200 A thermionic cathode e-beam source for compact megawatt range peak power, multi-kilowatt average power, high repetition rate THz FELs. The beam generation system includes a high-quality Pierce gun...
Ever since the first pump-probe experiment at LCLS in 2009, it has been clear that determining X-ray/optical relative arrival times is critical to performing precision measurements. In the decade of ensuing developments at LCLS, we have pioneered many of the XFEL timing measurement schemes used across the world. Currently, to measure timing at the soft x-ray end stations, an incident optical...
High-brightness electron bunches with small transverse emittance are required to drive X-ray free-electron lasers (FELs). For the measurement of the transverse emittance, the quadrupole scan and multi-profiles method are the two most common methods. The quadrupole scan method is more flexible in freely choosing the data points during the scan, while the multi-screen method allows on-line...
DESY and PhLAM are developing electro-optical measurements systems aiming at single-shot operation and high (MHz+) acquisition rates to characterize electron bunch shapes of short wavelength FELs as well as the temporal properties of pulsed THz sources. We review here the design strategies developed at DESY, and that allow the latest high-resolution measurements strategy based on diversity...
We investigated the versatility of manipulating the nonlinear longitudinal phase space for an electron injector including a VHF gun, bunch compressor cavities and a booster section. The research focuses on minimising the bunch length through RF compression while preserving the emittance produced after the gun. We will present the best results obtained from the OPAL simulations. The findings...
The FAST facility at Fermilab provides particle accelerator R&D with > 150 MeV electrons from an RF linac out of a PITZ style photoinjector. The TESSA tapered undulator FEL experiment [1] will make use of the FAST accelerator and requires careful control of beam properties with small emittances. We present modeling studies of the photoinjector electron beam dynamics using the Opal code,...
The regenerative amplifier FEL (RAFEL) promises to greatly increase the brightness and stability of single pass x-ray FELs. One of the critical challenges of the x-ray RAFEL is maintaining electron-optical overlap over the relatively large (hundreds of meters) footprint of the system. Numerical modeling of x-ray RAFELs with angular and positional errors is critical for designing stable...
FERMI has started the upgrade phase to FERMI 2.0. The ultimate goal of the upgrade plan is to extend the spectral range of the facility to cover the water window and beyond, and to reduce the minimum pulse duration below the characteristic lifetime of the light element core hole electrons. One of the main requirements of this upgrade is to preserve the uniqueness of FERMI: the possibility to...
SABINA (Source of Advanced Beam Imaging for Novel Applications) is a new IR/THz FEL source under construction at the INFN Laboratori Nazionali di Frascati (LNF). The FEL is a single-pass amplifier designed to operate in the 10-100 THz spectral range using the SPARC_LAB infrastructure. The amplifier, consisting of three Apple-X undulator modules built by KYMA S.p.A., will deliver pulse energies...
External seeding via Echo-Enabled Harmonic Generation (EEHG) has been established for the first time at FLASH. This major achievement is a critical milestone towards FLASH2020+, the upgrade project for the FLASH facility, which will enable external seeding at MHz repetition rates at a user facility. Compared to standard SASE operation, the spectral quality and the longitudinal coherence are...
We present first light emission from the Israeli THz superradiant FEL based on the ORGAD accelerator. The source was designed to operate beyond 1 THz. However, we measured superradiant emission near 0.6 THz with radiative energy output of 1.5 uJ.
This FEL operates in the FEL center of Ariel and Tel-Aviv universities. Designed and constructed in collaboration with UCLA, it is a hybrid RF gun...
The Photo Injector Test facility at DESY in Zeuthen (PITZ) develops a prototype tunable high-power THz source for pump-probe experiments at the European XFEL. A single-pass high gain THz free-electron laser (FEL) was realized at PITZ. A THz beam line based on a strongly focusing planar LCLS-I undulator is used for proof-of-principle experiments. The first lasing at the center frequency of ~3...
Kyoto University Free Electron Laser (KU-FEL) achieved a record high extraction efficiency of 9.4% [1]. For further increase of the extraction efficiency, reduction of the optical cavity loss or increase of the FEL gain is required [2]. One possible way to reduce the optical cavity loss while keeping the reflection bandwidth of the cavity mirror is changing the out-coupling way from current...
Simulations of particle accelerators are fundamentally important both to help in understanding measurements, and to plan future experiments. Start-to-end simulations, which begin with the initial generation of a particle distribution in a gun, up to the final beam energy, often require switching between codes to account for the differences between models. Tools which are able to switch between...
A flat dechirper is used for fresh-slice generation of hard X-ray FEL pulses at PAL-XFEL. The electron beam is transversely deflected with a 1m long corrugated plate positioned just before the undulator beamline. The beamline is divided into two parts that contain respectively 8 and 13 undulator modules, and between which a self-seeding chicane introduces a variable electron beam time delay....
This work presents measurements of the GR05+ Gamma Spectrometers placed in two different undulator cells of the SASE1 Undulator System at the European X-Ray Free Electron Laser (XFEL). Because of their small size, it is possible to register energy spectra near the beam pipe and undulator permanent magnets. Additionally, the characterization of this CZT solid-state detector is included, as well...
Coherent, wide-tunable frequency and high intensi-ty terahertz (THz) source is under preparation at the Shanghai Soft X-ray free-electron laser facility (SXFEL). The electron bunches modulated by frequen-cy beating light can generate coherent, wide-tunable, high intensity THz radiation from 0.1 to 30 THz through wigglers. The electromagnetic wiggler with peak magnetic field up to 1.75 T is...
Plasma wakefield accelerators (PWFA) have showcased remarkable acceleration gradients, reaching tens of GeV per meter. In this method, the accelerating structure is a highly nonlinear charge-density wave in a plasma, which is excited by an ultrarelativistic electron beam. Advancements in generating FEL-quality, attosecond electron beams represent the forefront of this field. In this work, we...
X-ray beams, carrying orbital angular momentum (OAM), are emerging as a powerful tool to probe matter. Recently, the self-seeded FEL with OAM (SSOAM) method has been proposed to generate high-power X-ray OAM pulses, which places the traditional optical elements in the linear regime of the FEL amplification process before saturation to reduce the thermal load of the optical element. In this...
FLASH is an XUV and soft X-ray free-electron laser user facility at DESY. In the FLASH2 main undulator beamline radiation down to 3.2 nm wavelength in the fundamental has been demonstrated. In order to efficiently generate soft X-ray radiation at the third harmonic of the FLASH2 main undulator wavelength with tunable polarization, an additional APPLE-III type undulator has been installed...
Ultrashort, intense terahertz radiation sources hold tremendous potential for various industrial and scientific applications. However, the bandwidth of FEL based pulses is limited due to slippage effects in the undulator. In this paper we study a solution to generate very short and intense THz pulses using chirped microbunching combined with tapered undulators in order to effectively compress...
Terawatt XFELs represent the frontier in further development of x-ray sources and require high current densities with strong transverse focusing. In this paper, we investigate the implications/potentialities of TW XFELs on the generation of harmonics at still shorter wavelengths and higher photon energies. The simulations indicate that significant power levels are possible at high harmonics...
The use of an external laser to initialize the FEL process at the harmonics of the laser has been demonstrated to be very efficient for improving the FEL performance. Thanks to the external seeding FEL can reach saturation in a shorted undulator compared to SASE FELs, but also gain in terms of FEL spectral brightness and stability.
An efficient harmonic conversion in the FEL process requires...
In the realm of Free Electron Laser (FEL) research, the accurate characterization of radiation pulse profiles is crucial for optimizing beam quality and experimental outcomes. Our presentation introduces a pioneering approach utilizing machine learning techniques for virtual diagnostic profiling of FEL radiation pulses. Our innovative Artificial Intelligence (AI) diagnostic tool leverages...
Research into high-harmonic generation (HHG) from solid-state and gas targets holds significant importance in advancing high-field photon science, particularly in the realm of attosecond VUV and X-ray pulse generation. Thanks to the recent advancements in few-cycle pulse generation in superradiant FEL oscillators [*], HHG photon sources driven by infrared FEL pulses are becoming feasible....
In molecular systems, quantum-level electron motions occur on the sub-femtosecond timescale. In order to probe such dynamics, high energy attosecond pulses are required to provide the necessary spatial and temporal resolutions. At LCLS, the X-ray Laser-Enhanced Attosecond Pulses (XLEAP) collaboration develops operation modes for attosecond pulses in the soft and hard X-ray regimes for these...
FELs have made tremendous progress in the last fifty years, but the energy conversion efficiency is still in the order of 1%. The ORGAD is a hybrid S-band (2856 MHz) RF photo-cathode accelerator located at the Schlesinger Compact Accelerator Center at Ariel University, a collaborative project with Tel Aviv University. A longitudinally bunched electron beam is then injected into an undulator...
Cavity-based x-ray free electron lasers (CBXFELs) such as the x-ray regenerative amplifier FEL (XRAFEL) and the XFEL oscillator (XFELO) have been proposed to produce stable, fully-coherent, hard x-ray unreachable with the current XFELs. XRAFEL approach employs high-current, short-bunch electron beams to support a high-gain FEL process, resulting in substantial pulse energy. On the other hand, ...
In this paper, the results of high-resolution X-ray topography characterization of monocrystal diamond plate with (100) crystal surface orientation used as high-quality monochromator of high-heat-load free electron lasers are reported. The monocrystal diamond plate was grown using high-pressure high-temperature method and fabricated by laser-cutting. The intrinsic crystal quality of the...
Experimental studies on THz FELs at the Photo Injector Test facility at DESY in Zeuthen (PITZ) have revealed that the THz radiation pulse energy is significantly higher than predictions by Genesis1.3 simulation using the standard shot noice model. To understand the underlying mechanism, the bunching factors of individual slices with a length of the resonant wavelength (local bunching factors),...
Superconducting materials are more and more widely used in FEL-s accelerators, which proper work strongly depends on their properties, very sensitive to the irradiation effects. The ionizing irradiation occuring in FEL-s influences the subtle structure of superconductors, especially of layered form, damaging it, which effect will have negative influence on superconducting parameters. From the...
In 2023, LINAC Coherent Light Source II achieved first light, spanning over 5 km. The goal of achieving 10fs relative jitter between the experiment laser and the x-ray led to the development of new systems. We will present the timing system design, architecture, and key commission results.
The challenge of reference distribution in the hostile environment of LCLS II was addressed by using a...
The transverse beam envelope matching inside undulators is important for XFELs. SACLA operates two XFEL beamlines, and the beam energy and longitudinal compression are adjusted bunch-by-bunch in accordance with the XFEL parameters of each beamline. Since transverse focusing strengths depend on the beam energy and RF phases, the transverse envelope varies from bunch to bunch, and mismatch...
We investigate an iris waveguide designed for installation in the long halls of free-electron laser facilities for THz radiation propagation for pump-probe experiments. We approach this problem theoretically and validate our results using numerical wavefront propagation techniques. An iris line, optimised for 3 THz, can propagate radiation over 370 m with a transmission coefficient (T) of...
Shanghai soft X-ray free electron laser facility(SXFEL) is the first coherent X-ray light source in China with a wavelength covering the water window. With the help of a pair of elliptically polarized undulators(EPU) in the seeding line, the output laser can be switched between linear polarization and circular polarization, meeting the needs of different users. After tuning the planar...
Time-resolved diagnostics at Free-Electron Laser (FEL) facilities, in particular electron beam longitudinal phase space (LPS) and FEL power profile measurements, provide information highly valuable for users, machine development studies, and beam setup. We investigate the slice energy resolution of passive streaker setups, in particular the effect of an energy chirp on the measured slice...
The European XFEL at DESY is a world-leading research infrastructure in Hamburg (Germany),
enabling scientists to observe and investigate microstructural processes and phenomena with spa-
tial and temporal resolutions on the atomic and femtosecond scale. To improve the performance
of the accelerator and also to ensure its competitiveness with other facilities, it is essential
to optimize...
Coherent synchrotron radiation (CSR) has been an important consideration for design of bunch compressors and other beam manipulating sections in FEL linacs. There has been increasing interest and need to move from the most common 1D CSR models to consider 2D and even 3D CSR modeling. However, these simulations are very slow and computationally intensive. Machine learning models are capable of...
SABINA (Source of Advanced Beam Imaging for Novel Applications) is a new IR/THz FEL source under construction at the INFN Laboratori Nazionali di Frascati (LNF). The FEL will be driven by the SPARC_LAB* linac, a normal conducting linear accelerator delivering high-brightness beams generated in a photo catode gun. The beam peak current is increased by compression in velocity bunching regime,...
The MAX IV linac is used to provide sub-100 fs pulses for a Short Pulse Facility (SPF). In order to form this beam, two bunch compressors at 245 MeV and 3.0 GeV are used. The properties of these compressors have been studied and simulated in the past, but lacking longitudinal diagnostics in their proximity, measurements of their effect on the beam have been limited. We seek to ascertain the...
RF electron guns can produce higher quality electron beams due to their high accelerating gradients, and semiconductor photocathodes have higher quantum efficiencies. However, the thermionic emission of the material can affect the beam emittance. Therefore, it is necessary to develop cathodes with lower thermionic emission, and to measure the thermionic emission, especially under high power...
Recent results of short-range longitudinal wake calculations in the undulator lines at the European XFEL predicted strong wakefield effect. Design of the vacuum system of FLASH 2 undulator is pretty much similar to that of the European XFEL. Bunch charge and the peak current are also in the same range as well. Thus, we expect comparable effects of the wakefields for both machines. Relevant...
Caustic theory has been applied to electron trajectories in particle accelerators and has been used to describe current spike formation in bunch compressors. Current spike development is sensitive to small changes in the initial longitudinal phase space distribution and longitudinal dispersion (R56, T566 and U5666) of bunch compressors. The caustic theory can be used to describe current horn...
An accurate knowledge of the slice electron beam parameters such as energy spread and seed laser induced energy modulation is very critical for an optimal setting of the EEHG parameters and FEL optimization. In this work we report about a method that, based on a fitting of experimental parameters scans in coherent harmonic generation with numerical simulations or models, can provide accurate...
We demonstrate the feasibility of measuring the spatial intensity correlation function of synchrotron radiation at free-electron laser facilities. For this technique, it is sufficient to use a synchrotron radiation imager paired with an undulator commissioning crystal monochromator at Bragg's angle. By measuring the transverse intensity correlation, we retrieved the electron beam size at the...
In order to improve the stability of the accelerator system and to have the ability to further compress the electron beam, the space for installing a third magnetic compressor was reserved at the beginning of the physical design of SHINE. However, the three-stage compression of the microbunching instability is prone to cause the three-stage cascade amplification, and therefore it is necessary...
The microbunching instability (MBI) has become a critical issue in advanced X-ray free-electron lasers, posing a considerable challenge to achieving the desired beam quality and coherence. In the multi-bend beamlines of the beam switchyard system, the MBI effect can have a large gain because of the coherent synchrotron radiation (CSR). We have performed a comprehensive simulation with...
As part of the collaboration building a set of detectors for the new collider, our group was tasked with designing and building a large-scale cosmic ray detector, which was to complement the capabilities of the MPD (Dubna) detector set. The detector was planned as a trigger for cosmic ray particles and to be used to calibrate and test other systems. Additional functions were to be the...
The main purpose of Beam Loss Monitor (BLM) system is the early detection of incorrect beam propagation inside the beamline and, therefore, the protection of machine, its vacuum and electronic components. The beam parameters within the PolFEL facility induces the need of such a system. Each of the proposed beam loss detector, which are distributes along the PolFEL device, is built of miniature...
The emittance exchange (EEX) beamline provides a unique capability in transferring transverse beam density modulation into longitudinal bunching. This process can be advantageous for rapidly starting the FEL process reducing the effective length of the undulators. We investigate the feasibility of creating nanometer-scale longitudinal density modulation at the Argonne Wakefield Accelerator. We...
We present a high-slippage concept of SASE FEL that can produce narrow-band spectra at 13.5 nm for Extreme Ultraviolet Lithography (EUVL). The narrow-band SASE FEL differs from the seeded FEL which involves spectrally filtering the SASE output to produce a monochromatic seed and amplifying the coherent seed with additional undulators. Seeded FELs have been experimentally demonstrated to...
We present an algorithm for modelling single instances of partially coherent radiation using their Wigner distribution. This algorithm is based on an approach for simulating Gaussian random fields, where randomly generated noise is constrained by the effective radiation size in the conjugate Fourier domains. This approach, utilizing Fourier transform methods, significantly enhances...
For enabling attosecond X-ray pulse generation via high harmonic generation in rare gases driven by free electron laser (FEL)[1], nonlinear compression of long-wavelength-infrared (LWIR) pulses from an oscillator-type FEL in a thick Germanium plate has been demonstrated[2]. LWIR-FEL pulses with the peak wavelength in 8.5 micro-m and the pulse duration of 146 fs in full width at half maximum...
It has been reported that cavity-type free-electron laser (FEL) oscillations cause shape distortion in an electron bunch depending on a detuning length of an optical cavity [1]. We have studied the FEL-induced bunch distortion by observing coherent edge radiation (CER) generated at an FEL facility of Kyoto University, which has the highest extraction efficiency of an FEL oscillation [2]. We...
Finding a temporally overlapping condition is necessary for pump-probe experiments. This can be achieved by obtaining sum frequency generation (SFG) signal. Our attempt proceeded using a mid-infrared free electron laser (MIR-FEL) of 12.5 micro-m, ps-Nd:YVO4 laser of 1064 nm from Kyoto University free electron laser (KU-FEL) facility, and a polycrystalline ZnS plate at room temperature. An...
Attosecond physics is an emerging as one of the fastest-growing, highest-impact, areas of science at FELs. In this proceeding, we compare several methods for generating single-spike attosecond soft x-ray pulses at LCLS. Over the last several years we have measured more than 30 independent attosecond SXR configurations, across which we can explore a variety of techniques, including:...
Externally seeded Free Electron Lasers (FELs), such as the upgraded FLASH1 at DESY, utilize external lasers to initiate bunching, contrasting with the self-amplification of spontaneous emission (SASE). This upgraded facility will offer simultaneous seeded and SASE pulses. Introducing a chirped electron bunch and high repetition rate seed lasers with unique spectral features will significantly...
Experimental investigations of terahertz (THz) free electron lasers (FELs) at the Photo Injector Test Facility at DESY in Zeuthen (PITZ) have demonstrated the feasibility and substantial potential of high-power tunable THz sources driven by a PITZ-like accelerator. Preliminary seeding experiments indicate improvements in the lasing process, such as earlier saturation and reduced fluctuations...
Next generation X-ray FELs (XFELs) are rapidly moving towards CW operation, which brings the new requirements on high quality of the CW electron sources. such as a superconducting RF (SRF) electron gun. While operation in SRF environment can be quite challenging, the quality of the generated beams is rather rewarding [1-4].
We report on our unique experience with the record performing SRF...
The APEX gun experiments at LBNL have demonstrat-ed the average beam current up to 0.3 mA. The VHF band normal conducting RF gun indicates the potential to provide both high brightness and high average current beams. R&D activities for the mA-scale average beam current by using the VHF gun started in our laboratory. In this paper, the RF design, multipacting simulations, vacuum calculations,...
Slice and normalize emittancies are the critical parameters that dictate the efficiency of SASE FEL mechanism and advanced FEL lasing schemes. The control of the emittance has been notoriously difficult and requires substantial efforts to transport a high-brightness electron beam from the cathode to the undulator. In this communication, we introduce the concept of a ponderomotive laser lens...
Shenzhen Superconducting Soft X-Ray Free-electron Laser (S3FEL) is a newly proposed high-repetition-rate X-ray FEL facility in China, which will be located at Guangming Science City in Shenzhen. The superconducting RF structure will provide electron beams with a few hundred kW of beam power at beam energies up to 2.5 GeV and repetition rates up to 1 MHz. The design of the dump line from the...
X-ray laser oscillator, dubbed XLO, is an ongoing project at SLAC National Accelerator Laboratory. XLO employs atomic gain medium pumped by an XFEL, to generate hard x-ray coherent, transform limited light. XLO has unique properties of very high gain per pass (similarly to the case of an undulator-/cavity- based high gain XFEL, while maintaining narrow bandwidth of XFELO. Current effort is...
Kyoto University Free Electron Laser (KU-FEL) facility has been developed for energy-related research by the Institute of Advanced Energy, Kyoto University. There are two accelerator-driven infrared coherent light sources in the facility. One is the oscillator-type FEL whose wavelength range is 3.4 to 26 micro-m[1]. The other one is the THz-Coherent Undulator Radiation (THz-CUR) source whose...
Cavity-based free-electron lasers (CBXFELs) have the potential to dramatically improve the stability and coherence of FELs. The CBXFEL project is a collaboration between SLAC, Argonne, and RIKEN to build a 65 m rectangular X-ray cavity at the LCLS, with the goal of demonstrating low-loss cavity ring-down and, ultimately, two-pass FEL gain. This paper describes recent simulation and...
At MAX IV laboratory the linac is used to inject into the two rings but also to drive the FemtoMAX beamline, which is a source of (incoherent) short pulses in the Hard X-ray range.
In this contribution we present the design and simulations for a new mode of operation of the linac that would allow to generate coherent ultra-short FEL pulses in the soft X-ray domain. Preliminary simulations...
In the PolFEL team, we are working on developing a new, more precise method of undulator tuning. Our method is based on an accurate model of the undulator's magnetic field distribution, described using approximation-free analytical expressions derived directly from the Biot-Savart equation. Having an accurate description of the magnetic field allows tuning to be carried out in two phases: (1)...
There is an increasing demand for coherent extreme ultraviolet (EUV) radiation in imaging and spectroscopy, particularly as the next generation of EUV lithography requires high-power EUV light sources. Experimental results demonstrate that harmonic lasing in a free-electron laser (FEL) is an effective method for extending the wavelength range and producing narrow bandwidth FEL. In this...
The development of short-wavelength, fully coherent Free Electron Lasers (FELs) represents a pivotal direction for advancing X-ray source technology. Promising solutions under consideration include cavity-based X-ray Free Electron Lasers (CBXFELs), such as the X-ray Regenerative Amplifier FEL (XRAFEL) and the X-ray FEL Oscillator. We are pursuing the development of advanced FEL schemes and the...
An afterburner consisting of four APPLE-X undulator modules has recently been re-installed downstream of the planar undulator in the soft x-ray beamline (SASE3) at the European XFEL. The modules were removed shortly after initial installation because of damage to electrical components caused by the spontaneous radiation produced in the planar undulator. After the damage became apparent, a...
Optical Stochastic Cooling (OSC) is a state-of-the-art beam cooling technology first demonstrated in 2021 at the IOTA storage ring at Fermilab's FAST facility. A second phase of the research program is planned to run in early 2025 and will incorporate an optical amplifier to enable significantly increased cooling rates and greater operational flexibility.
In addition to beam cooling, an OSC...
Dalian Coherent Light Source (DCLS) is a free-electron laser (FEL) user facility in the vacuum ultraviolet wavelength region, operating in high-gain harmonic generation (HGHG) mode. Accurate diagnosis of the longitudinal phase space of electron bunch plays a critical role in beam tuning and FEL optimizing. Additionally, advanced user experiments have demonstrated a demand for determining the...
Due to their excellent photoemissive properties, especially low thermal emittance and high sensitivity in the green wavelength, multi-alkali antimonide photocathode, particularly potassium-cesium-antimonide, have emerged as prominent photoemissive materials for the electron sources of high-repetition-rate FEL applications. To explore their feasibility of operating in a high-gradient RF gun,...
To produce nearly fully coherent hard X-ray self-seeded (HXRSS) free-electron laser (FEL) pulses, the forward Bragg-diffraction (FBD) monochromator is utilized at PAL-XFEL. These HXRSS FEL pulses exhibited exceptional peak-brightness and a narrow spectrum, demonstrating outstanding performance across a wide photon energy range from 3.5keV to 14.6keV. To further decrease the spectral bandwidth,...
The next generation of X-ray free-electron lasers (XFELs) research is focused on the investigation of self-seeding techniques, and, more recently, X-ray cavity designs. Here, we explore the capabilities of the X-ray self-seeding (HXRSS) setup at LCLS. The self-seeding mechanism is initiated by generating SASE in the first undulator section, followed by monochromatization and seeding in the...
It is a critical challenge to meet the requirements for XFEL operation modes and photon properties across different undulator lines simultaneously. We propose a solution to this challenge by introducing a dipole-kicker combination in the bunch compressors, allowing for the variation of electron bunch length in continuous-wave XFEL facilities driven by a superconducting linac. Through...
The LAM system in XFELs is crucial for measuring and compensating for time jitter in laser transmission. The EOM encodes phase information onto the reference pulse amplitude, but amplitude noise can affect measurement accuracy. In this study, we analyzed the spectral characteristics of the optical pulse signal output from the EOM using FFT, identifying primary noise sources. We then compared...
We present an electromagnetic characterization and optimization study of nanostructured photocathodes for electron gun applications. The study concentrates on photocathodes operated at visible to infrared wavelengths, for which an accurate simulation model is constructed. We apply a customized dispersion model for the cathode material, which can describe the measured permittivity data over a...
Generating so-called ‘laser-like’ X-ray in the full X-ray band has been a long-term challenge for seeded free electron lasers (FELs), which is generally limited by the up-frequency conversion efficiency and the materials of optical monochromators. Here, we demonstrate a reverse tapered undulator-enhanced harmonic lasing mechanism to possibly extend the photon coverage of the seeded FELs for...
High-brilliance X-ray beams provided by large-scale synchrotron facilities allow detailed visualization of the structure of materials and tissues, making them indispensable for the development of new high-tech materials in the broadest sense of the word. Unfortunately, however, because of the size and costs of these big facilities they are scarce and not very accessible, with long waiting...
Externally seeded FEL schemes with harmonic up-conversion, e.g. Echo-Enabled Harmonic Generation (EEHG), deliver pulses with improved spectro-temporal properties and shot-to-shot stability at wavelengths down to the XUV and X-ray range. Such schemes rely on the manipulation of the longitudinal phase space of the electron beam at the wavelength of the seed laser, for which it is crucial that...
In the application of FELs for the EUV lithography, an important question is how the coherence of the FEL light affects the imaging of the mask. As is well known, coherent light produces speckles which, in lithographic process, can distort the mask image. An effective way to suppress the speckes was pointed out in Ref. [1]. It is based on splitting the FEL beam into multiple beamlets in a way...
Cesium telluride (Cs-Te) photocathodes are the current workhorse in high repetition rate free-electron lasers (FELs) around the world. Unfortunately, they are chemically highly reactive, which limits their operational lifetime and require frequent interventions for Cs-Te film replacement or rejuvenation. The precise control of the Cs-Te deposition stoichiometry ratio during the photocathode...
We propose a scheme for coherently shaping attosecond x-ray pulses at free-electron lasers. We show that by seeding an FEL with a short coherent seed that overfills the amplification bandwidth, one can shape the wigner function of the pulse by controlling the undulator taper profile. The examples of controllable coherent pulse pairs and trains, as well as isolated spectrotemporally shaped...
One option being considered to meet the needs of the XFEL user community within the UK is a new national facility capable of producing photon beams with properties identified in the UK XFEL Science Case. The case calls for a high-efficiency facility with a step-change increase in the simultaneous operation of multiple end stations, with high-repetition rate near-transform limited x-ray pulses...
XPD project - photon data base for the European XFEL is a joint effort of DESY and European XFEL*. The project has been launched in 2009, and is in use by users since 2012. The goal of the XPD project is to provide users with full temporal, spatial, and spectral patterns of the radiation fields for different regimes of the European XFEL operation. Tracing of these fields with advanced user...
We present a simulation study of a tapered FEL oscillator, which aims at delivering high average power in the extreme ultraviolet wavelength region. The setup relies on the combination of three critical elements: a pre-buncher, a strongly tapered undulator and an optical cavity enclosing them. Such a configuration allows for efficient power extraction
from a high-brightness electron beam.
We...
A new 1.6-cell photocathode RF gun has been installed to improve the performance of Kyoto University free electron laser (KU-FEL). A test operation using a copper cathode has been completed, and the electron bunch charge of 60 pC with 120 bunches in a macro-pulse was obtained. However, due to the copper cathode's low quantum efficiency, the electron beam performance could not reach the target...
At SwissFEL we employ photocathode temporal shaping to produce sub-femtosecond X-ray FEL pulses. Two optical laser pulses arrive on the photocathode with a time delay of few picoseconds, resulting in a notch at the center of the generated electron current profile. Longitudinal space charge and coherent synchrotron radiation effects that occur during beam transport and bunch compression then...
The preparation of a superconducting photocathode for a sc electron gun, composed of a photoemission lead layer deposited on niobium substrate must fulfil strict requirements not only in terms of photoemission efficiency, operation in ultra high vacuum and high-power electromagnetic field. Of fundamental importance is the practical requirement for strong adhesion of the Pb layer. It yields...
The future upgrades of the European XFEL (EuXFEL) foresees continuous wave (CW) and High-Duty-Cycle (HDC) operation requiring a CW electron photoinjector. Motivated by this, a 1.6-cell superconducting radio frequency (SRF) electron gun cavity is under development at DESY. Recently, the DESY CW SRF gun cavities out of niobium with a copper cathode screwed directly to the cavity’s back wall...
The waveguide free electron laser has demonstrated the ability to efficiently convert relativistic electron beam energy into THz radiation in a single passage through a tapered helical undulator. An oscillator configuration can further boost energy extraction efficiency surpassing single-pass state-of-the-art. Embedding the undulator in an oscillator cavity is particularly useful in...
Radiation from SASE FEL with planar undulator contains visible contribution of the odd harmonics. Comprehensive studies of the nonlinear harmonic generation mechanism have been performed in * in the framework of the one-dimensional model. General features of harmonic radiation have been determined. It was found that coherence time at saturation falls inversely proportional to harmonic number,...
PolFEL stands for Polish Free Electron Laser, the first FEL research infrastructure in Poland. It will be based on a superconducting linear accelerator using Tesla-type resonant cavities with fundamental RF frequency of 1.3 GHz. Each superconducting cavity will operate in closed loop driven by individual Solid-State Amplifier (SSA) in single cavity regulation mode. The amplifiers have been...
Longitudinal wake fields are generated when relativistic electron beams pass through the narrow undulator vacuum chambers. The wake field, and the relatively weaker longitudinal space charge field, may cause considerable energy variations along the beam and influence the FEL radiation process. In this work, the wake field due to finite conductivity of the vacuum chamber material and the inner...
FLASH, the XUV and soft X-ray free-electron laser user facility at DESY, is in the transitional period between two substantial upgrade shutdowns within the FLASH2020+ upgrade project.FLASH consists of a common injector and linac and drives 3 different beamlines of which the two FEL beamlines FLASH1/2 can be operated simultaneously at 10 Hz with subtrains of typically 1 to 500 bunches within...
The SASE2 undulator of the European XFEL is equipped with a fully operational Hard X-Ray Self-Seeding (HXRSS) system. HXRSS pulses are delivered on a regular basis to users [1] and together with the high rep-rate capabilities of European XFEL linac allowed already for innovative applications [2]. Recently we have delivered HXRSS with pulse energy up to 1.4 mJ at 9 keV and investigated...
Traditionally, the optimization of Free-Electron Laser (FEL) facilities has been performed manually by the FEL operators. This approach proves to be time-consuming due to the multitude number of parameters that require adjustments. The results of this manual optimization are highly contingent upon the operator’s experience. To address these challenges, the implementation of machine learning...
The proposed Shenzhen Superconducting Soft X-Ray Free-electron Laser (S$^3$FEL) is a high-repetition-rate FEL facility which is currently commencing civil construction. The overlap between the electron beam and the radiation field is one of the critical determinants during the FEL amplification process, exerting a significant influence on the quality of FEL performance. The stringent...
The UK is conducting a multi-stage project to analyse the case for major investment into XFELs, through either developing its own facility or by investing at existing machines. The project’s 2020 Science Case identified a clear need for ‘next-generation’ XFEL capabilities including near-transform limited x-ray pulses across a wide range of photon energies and pulse durations; evenly spaced...
In the long wavelength range of FEL oscillator, especially in FIR & THz, the vacuum chamber is designed as waveguide to suppress the diffraction effect during propagation. Meanwhile it will also bring some other effect, such as frequency shift, spectral gap, truncation loss and so on. The waveguide effect is studied mostly based on simple parallel plate situation by setting the horizontal size...
Externally seeded FELs deliver fully coherent radiation down to the soft X-Rays with high shot-to-shot stability. They are, however, limited in repetition rate by the available seed laser systems and highest achievable harmonic.
Cavity-based FELs, on the other hand, have the potential to generate fully coherent FEL radiation at the maximum repetition rate supported by superconducting...
Theoretical analysis and design considerations of a THz superradiant FEL are presented. The superradiant emission scales like the number of electrons N squared, enhancing spontaneous emission by a factor N. The longitudinal dimension (duration) of the beam diminishes the excited mode energy at high frequencies through the bunching coefficient.
We demonstrate the design considerations...
Flat corrugated structures designed to generate strong wakefields are used for various purposes in X-ray FEL facilities, in particular for longitudinal and transverse electron beam shaping and for diagnostics. In this contribution we present time-resolved measurements of transverse (dipole and quadrupole) wakefield effects produced in flat corrugated structures by electron bunches with typical...
The AQUA beamline of the EuPRAXIA@SPARC_LAB free-electron laser facility is a SASE FEL designed to operate in the water window, in the 3-4 nm spectral range. The beam driving this FEL is accelerated up to 1-1.2 GeV FEL by an X-band normal conducting linear accelerator followed by a plasma wakefield acceleration stage.
The main radiator consists of an array of ten APPLE-X permanent magnet...
The Klein – Gordon equation of motion in the transition layer of a free-electron laser of the relativistic strophotron type is studied. The condition of suddenly switching-on interaction is found: a smallness of the transition layer at the entrance compared to the distance traveled by the electron in longitudinal direction in one period of transverse oscillations in strophotron. The results...
The X-ray free-electron laser (FEL) FLASH in Hamburg I currently installing installing a new FLASH1 beamline incorporating external seeding using High Gain Harmonic Generation (HGHG) and Echo Enabled Harmonic Generation (EEHG). Our novel UV seed laser system matches FLASH burst operation pattern with 1 MHz pulse trains and 600 µs duration at 10 Hz (6000 pulses/sec). It features two beams: Seed...
The Shenzhen Superconducting Soft X-Ray Free-electron Laser (S3FEL) is a newly proposed high repetition-rate X-ray FEL facility. In this contribution, we have presented various two-color FEL schemes based on this facility, including undulator splitting, fresh slice, and afterburner configurations. Based on these schemes, there is a promising prospect to generate high-brightness two-color soft...
In this letter, we proposed a new scheme to generate femtosecond-level high peak current electron beam, compressed from a flat-top beam, through energy modulation based on dielectric-loaded circular waveguide is numerically implemented.. With the advantage of passiveness and dephasingless self-modulation at terahertz frequency, stable electron beam and free electron laser radiation can be...
The recent development of advanced black box optimization algorithms has promised order of magnitude improvements in optimization speed when solving accelerator physics problems. These algorithms have been implemented in the python package Xopt, which has been used to solve online and offline accelerator optimization problems at a wide number of facilities, including at SLAC, Argonne, BNL,...
NSRRC high brightness photo-injector has been built to generate intense ultrashort electron bunches for novel accelerator-based light source development. The injector is equipped with a laser-driven photocathode rf gun and a 5.2-m long S-band traveling-wave linac for beam acceleration. The electron bunch is compressed near the linac rf zero crossing phase by the so-called velocity bunching...
Corrugated structures have recently been utilized for the time-resolved diagnostics of electron bunches in the several GeV energy range and free-electron-laser (FEL) pulses across several FEL facilities: SwissFEL at PSI and European XFEL at DESY. This approach is simple and cost-effective, based on the self-streaking of electrons with a transverse wakefield enhanced in such structures.
In...
After six years of user operation, the x-ray photon diagnostics system [1] at the European XFEL has matured and contributes daily to reliable beam delivery to users with exquisite tailored x-ray pulses at MHz repetition rates in the range from below 500 eV to above 24 keV at pulse energies up to 4 mJ in the hard x-ray and > 10 mJ in the soft x-ray range, with pulse durations from ~100 fs down...
