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This paper reports on nonlinear spectral broadening of 1.1 ps pulses in a gas‐filled multi‐pass cell to generate sub‐100 fs optical pulses at 1030 nm and 515 nm at pulse energies of 0.8 mJ and 225 µJ, respectively, for pump–probe experiments at the free‐electron laser FLASH. Combining a 100 kHz Yb:YAG laser with 180 W in‐burst average power and a post‐compression platform enables reaching simultaneously high average powers and short pulse durations for high‐repetition‐rate FEL pump–probe experiments. [ABSTRACT FROM AUTHOR]

Ronchi testing of a focused electromagnetic wave has in the last few years been used extensively at X‐ray free‐electron laser (FEL) facilities to qualitatively evaluate the wavefront of the beam. It is a quick and straightforward test, is easy to interpret on the fly, and can be used to align phase plates that correct the focus of aberrated beams. In general, a single Ronchigram is not sufficient to gain complete quantitative knowledge of the wavefront. However the compound refractive lenses that are commonly used at X‐ray FELs exhibit a strong circular symmetry in their aberration, and this can be exploited. Here, a simple algorithm that uses a single recorded Ronchigram to recover the full wavefront of a nano‐focused beam, assuming circular symmetry, is presented, and applied to experimental measurements at the Matter in Extreme Conditions instrument at the Linac Coherent Light Source. [ABSTRACT FROM AUTHOR]

User operation at the European X‐ray Free‐Electron Laser Facility started at the SASE1 undulator beamline in fall 2017. The majority of the experiments utilize optical lasers (mostly ultrafast) for pump–probe‐type measurements in combination with X‐ray pulses. This manuscript describes the purpose‐developed pump–probe laser system as installed at SASE1, implemented features and plans for further upgrades. The ultrafast pump–probe laser at the SASE1 undulator beamline of the European XFEL is described. [ABSTRACT FROM AUTHOR]

The Macromolecular Femtosecond Crystallography (MFX) instrument at the Linac Coherent Light Source (LCLS) is the seventh and newest instrument at the world's first hard X‐ray free‐electron laser. It was designed with a primary focus on structural biology, employing the ultrafast pulses of X‐rays from LCLS at atmospheric conditions to overcome radiation damage limitations in biological measurements. It is also capable of performing various time‐resolved measurements. The MFX design consists of a versatile base system capable of supporting multiple methods, techniques and experimental endstations. The primary techniques supported are forward scattering and crystallography, with capabilities for various spectroscopic methods and time‐resolved measurements. The location of the MFX instrument allows for utilization of multiplexing methods, increasing user access to LCLS by running multiple experiments simultaneously. A description of the Macromolecular Femtosecond Crystallography instrument at the Linac Coherent Light Source is given. Scientific capabilities are highlighted, performance parameters are presented along with some commissioning results. [ABSTRACT FROM AUTHOR]

X-ray focus optimization and characterization based on coherent scattering and quantitative speckle size measurements was demonstrated at the Linac Coherent Light Source. Its performance as a single-pulse free-electron laser beam diagnostic was tested for two typical focusing configurations. The results derived from the speckle size/shape analysis show the effectiveness of this technique in finding the focus' location, size and shape. In addition, its single-pulse compatibility enables users to capture pulse-to-pulse fluctuations in focus properties compared with other techniques that require scanning and averaging. [ABSTRACT FROM AUTHOR]

Here, it is shown that simulated native serial femtosecond crystallography (SFX) cathepsin B data can be phased by rapid ionization of sulfur atoms. Utilizing standard software adopted for radiation-damage-induced phasing (RIP), the effects on both substructure determination and phasing of the number of collected patterns and fluences are explored for experimental conditions already available at current free-electron laser facilities. [ABSTRACT FROM AUTHOR]

Abstract: To produce short X-ray pulses for SwissFEL 1 [1] FEL: Free Electron Laser; SITF: SwissFEL Injector Test Facility; OPCPA: Optical Parametric Chirped Pulse Amplifier; PLL: Phase Locked Loop. , it is necessary to compress the electron bunches by a factor of 300, down to sub-fs for the attosecond operational modes. To achieve stable FEL output accurate timing of the initial electron injection at the main linear accelerator is necessary. Tolerance studies show, that to reach the final performance goals, less than 40fs relative rms jitter is required from the electron gun, relative to the reference. Here we present independent residual RF phase noise measurements of the laser oscillators, showing an exceptional ~30fs integrated rms jitter. Moreover timing studies at the SwissFEL Injector Test Facility, based on charge detection at the sharp rising edge of the Schottky-scan were performed allowing for systematic correlation studies and showing a residual jitter of ~150fs at 10Hz from the pulsed laser system and beam transport respect to the reference. For future development, available relative jitter measurement techniques for pulsed laser systems will be reviewed and their applicability for laser arrival time monitoring and feedback for FEL applications will be discussed. [Copyright &y& Elsevier]

A three-cell 1.3 GHz, Normal Conducting (NC) buncher is designed for a possible future upgrade of the European X-ray Free Electron Laser (Eu-XFEL) to operate in a continuous-wave (CW)/ long pulse (LP) mode. The RF geometry of the buncher is optimized for high shunt impedance, large mode separation as well as multipacting free in the operation range. The nominal buncher voltage is 400 kV with an RF power dissipation of 14 kW, and its shunt impedance is ∼ 50% higher than existing CW bunchers. The RF power coupler cell is optimized for field symmetry to minimize coupler kick effect on beam dynamics. The thermal load due to RF power dissipation is analyzed using Multiphysics simulations in CSTMWS and a cooling scheme is designed. [ABSTRACT FROM AUTHOR]

Abstract: The electromechanical model of the TESLA cavity has been implemented in FPGA technology for real-time testing of the control system. The model includes Lorentz force detuning and beam loading effects. Step operation and vector stimulus operation modes are applied for the evaluation of a FPGA cavity simulator operated by a digital controller. The performance of the cavity hardware model is verified by comparing with a software model of the cavity implemented in the MATLAB system. The numerical aspects are considered for an optimal DSP calculation. Some experimental results are presented for different cavity operational conditions. [Copyright &y& Elsevier]

The Linac Coherent Light Source (LCLS) is a single pass X-ray FEL designed to produce very short (∼200 fs) and very high power (8 GW), short wavelength (1.5 A˚) pulses. The new facility to be built at SLAC as a multiple laboratory collaboration will have peak brilliance performance exceeding those obtained presently in third generation synchrotron radiation sources by 10 orders of magnitude. In this paper, we review the accelerator physics design challenges. We report on advances made in photo-injectors. We discuss the issues of Coherent Synchrotron Radiation produced in the bunch compressors and undulator vacuum chamber wakefields. [Copyright &y& Elsevier]

Part of the overall design effort for X-ray FELs such as the LCLS and TESLA projects has involved extensive use of particle simulation codes to predict their output performance and underlying sensitivity to various input parameters (e.g. electron beam emittance). This paper discusses some of the numerical issues that must be addressed by simulation codes in this regime. We first give a brief overview of the standard approximations and simulation methods adopted by time-dependent (i.e. polychromatic) codes such as ginger (LBNL Report No. LBNL-49625, 2002), genesis (Nucl. Instr. and Meth. A 429 (1999) 243), and fast3d (Nucl. Instr. and Meth. A 429 (1999) 233), including the effects of temporal discretization and the resultant limited spectral bandpass, and then discuss the accuracies and inaccuracies of these codes in predicting incoherent spontaneous emission (i.e. the extremely low gain regime). [Copyright &y& Elsevier]

The electron source still remains a major challenge for continuous-wave (CW) X-ray free-electron lasers (FELs). In this paper, we study the feasibility of an injection line based on a DC and superconducting radio-frequency (SRF) combined photocathode injector. We present a detailed investigation on the longitudinal phase space evolution of the electron beam along the injection line. We also analyze the main issues determining the high-order energy spread and current skewness. Based on the analysis, we propose to use a harmonic cavity as the buncher for the injection line. Simulation shows that an extracted electron beam with a normalized RMS emittance of 0.37 μ m, an RMS bunch length of 1.0 mm, a high-order RMS energy spread of 2.75 keV, and a current skewness of 0 can be obtained at the bunch charge of 100 pC. This study is meaningful to the design of the injection lines for short-wavelength CW FELs, including those based on normal-conducting very-high-frequency (VHF) guns or DC guns. [ABSTRACT FROM AUTHOR]

Effects producing gain dilution in Free Electron Laser devices are well documented. We develop here a unified point of view allowing the introduction of space charge effects, along with the gain deterioration due to inhomogeneous broadening contributions and discuss the relevant interplay. We outline future developments and comment on the possibility of including in the formalism effects of quantum mechanical nature. [ABSTRACT FROM AUTHOR]