Paper Title Page
Study of the Next Major Flash Upgrade: FLASH2020  
  • B. Faatz
    DESY, Hamburg, Germany
  The FLASH facility has delivered beam to two experiments simultaneously since Spring 2016. Both users can request a large variety of parameters independently, without interfering with the other experiment and the setup for both users can take place in parallel. For several years, a study has started to plan for the next major upgrade, referred to as FLASH2020. The ultimate goal is a CW version of FLASH with up to 1 million bunches per second which should be able to go down in wavelength to cover the complete water window. In this presentation we will present the different upgrade scenarios that are under discussion. Also we present tests already performed and planned for the near future to optimize the design and maximize the flexibility of the new facility.  
MOP031 First Operation of a Harmonic Lasing Self-Seeded FEL 1
  • E. Schneidmiller, B. Faatz, M. Kuhlmann, J. Rönsch-Schulenburg, S. Schreiber, M. Tischer, M.V. Yurkov
    DESY, Hamburg, Germany
  Harmonic lasing is a perspective mode of operation of X-ray FEL user facilities that allows it to provide brilliant beams of higher-energy photons for user experiments. Another useful application of harmonic lasing is so called Harmonic Lasing Self-Seeded Free Electron Laser (HLSS FEL), that allows it to improve spectral brightness of these facilities. In the past, harmonic lasing has been demonstrated in the FEL oscillators in infrared and visible wavelength ranges, but not in high-gain FELs and not at short wavelengths. In this paper, we report on the first evidence of the harmonic lasing and the first operation of the HLSS FEL at the soft X-ray FEL user facility FLASH in the wavelength range between 4.5 nm and 15 nm. Spectral brightness was improved in comparison with Self-Amplified Spontaneous emission (SASE) FEL by a factor of six in the exponential gain regime. A better performance of HLSS FEL with respect to SASE FEL in the post-saturation regime with a tapered undulator was observed as well. The first demonstration of harmonic lasing in a high-gain FEL and at a short wavelength paves the way for a variety of applications of this new operation mode in X-ray FELs.  
MOP032 Reverse Undulator Tapering for Polarization Control and Background-Free Harmonic Production in XFELs: Results from FLASH 1
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
  Baseline design of a typical X-ray FEL undulator assumes a planar configuration which results in a linear polarization of the FEL radiation. However, many experiments at X-ray FEL user facilities would profit from using a circularly polarized radiation. As a cheap upgrade, one can consider an installation of a short helical afterburner, but then one should have an efficient method to suppress powerful linearly polarized background from the main undulator. There is an efficient method for such a suppression: an application of the reverse taper in the main undulator.* In this contribution, we present the results of experiments with reverse taper at FLASH2 where a high contrast between FEL intensities from the afterburner and from the reverse-tapered main undulator was demonstrated. Another important application of the reverse taper is a possibility to produce FEL harmonics in the afterburner (or in the last part of baseline gap-tunable undulator). We present recent results from FLASH2 where the second and the third harmonics were efficiently generated with a low background at the fundamental.
* E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13-080702 (2013).
MOP033 Baseline Parameters of the European XFEL 1
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
  We present the latest update of the baseline parameters of the European XFEL. It is planned that the electron linac will operate at four fixed electron energies of 8.5, 12, 14, and 17.5 GeV. Tunable gap undulators provide the possibility to change the radiation wavelength in a wide range. Operation with different bunch charges (0.02, 0.1, 0.25, 0.5 and 1 nC) provides the possibility to operate XFEL with different radiation pulse duration. We also discuss potential extension of the parameter space which does not require new hardware and can be realized at a very early stage of the European XFEL operation.  
XFEL Photon Pulses Database (XPD) at the European XFEL  
  • M. Manetti, L. Samoylova, H. Sinn, J. Szuba, K. Wrona
    XFEL. EU, Schenefeld, Germany
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
  The best way to plan user experiments would be performing start-to-end simulations tracing a radiation pulse from its origin (undulator) through a beamline (mirrors, monochromators, etc.) to a target, simulations of physical processes of the radiation interaction with a sample, and simulations of detection processes of related debris (photon, electrons, ions, etc.) by detectors. Modern FEL simulation codes allow prediction of all details of the output radiation pulses from x-ray FEL (3D maps of radiation fields for the fundamental and higher frequency harmonics). We present an XFEL photon pulses simulation database accessible through public web-server that allows access to the data produced by the time-dependent FEL simulation code FAST. A web application allows pick-up of selected photon pulse data in the hdf5 format for any given XFEL operation mode (electron energy, charge/photon pulse duration, active undulator range, etc.) suitable for statistical analysis, including propagation through the optical system, interaction with the sample, etc. The pulse post-processing data, including the gain curve, time structure, source size and far-field angular divergence are also provided.  
Optimum Undulator Tapering of SASE FEL: Theory and Experimental Results From FLASH2  
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
  Optimization of the amplification process in FEL amplifier with diffraction effects taken into account results in a specific law of the undulator tapering.* It is a smooth function with quadratic behavior in the beginning of the tapering section which transforms to a linear behavior for a long undulator. In practice, an undulator consists of a sequence of modules of fixed length separated with intersections. Two modes of undulator tapering can be implemented: step tapering and smooth tapering. Step tapering uses a step change of the undulator gap from module to module, while smooth tapering assumes additional linear change of the gap along each module. In this report, we simulate the performance of both experimental options and compare with theoretical limit.
* E.A. Schneidmiller and M.V. Yurkov, Optimization of a high efficiency free electron laser amplifier, Phys. Rev. ST Accel. Beams 18-030705 (2015).
MOP036 Frequency Doubling Mode of Operation of Free Electron Laser FLASH2 1
  • M. Kuhlmann, E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
  We report on the results of the first operation of a frequency doubler at free electron laser FLASH2. The scheme uses the feature of the variable-gap undulator. The undulator is divided into two parts. The second part of the undulator is tuned to the double frequency of the first part. The amplification process in the first undulator part is stopped at the onset of the nonlinear regime, such that nonlinear higher-harmonic bunching in the electron beam density becomes pronouncing, but the radiation level is still small to disturb the electron beam significantly. The modulated electron beam enters the second part of the undulator and generates radiation at the second harmonic. A frequency doubler allows operation in a two-color mode and operation at shorter wavelengths with respect to standard SASE scheme. Tuning of the electron beam trajectory, phase shifters and compression allows tuning of intensities of the first and the second harmonic. The shortest wavelength of 3.1 nm (photon energy 400 eV) has been achieved with a frequency doubler scheme, which is significantly below the design value for the standard SASE option.  
MOP037 Opportunities for Two-Color Experiments at the SASE3 Undulator Line of the European XFEL 1
  • S. Serkez, G. Geloni, T. Mazza, M. Meyer
    XFEL. EU, Schenefeld, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  As is well known, the installation of a simple magnetic chicane in the baseline undulator of an XFEL allows for producing two-color FEL pulses. In this work we discuss the possibility of applying this simple and cost-effective method at the SASE3 soft X-ray beamline of the European XFEL. We consider upgrades of this method that include the further installation of a mirror chicane. We also discuss the scientific interest of this upgrade for the Small Quantum Systems (SQS) instrument, in connection with the high-repetition rate of the European XFEL, and we provide start-to-end simulations up to the radiation focus on the sample, proving the feasibility of our concept. Our proposed setup has been recently funded by the Finnish Research Infrastructure (FIRI) and will be built at SASE3 in 2020-2021.  
poster icon Poster MOP037 [1.844 MB]  
MOP038 Overview of the Soft X-Ray Line Athos at SwissFEL 1
  • R. Ganter, S. Bettoni, H.-H. Braun, M. Calvi, P. Craievich, R. Follath, C.H. Gough, F. Löhl, M. Paraliev, L. Patthey, M. Pedrozzi, E. Prat, S. Reiche, T. Schmidt, A.C. Zandonella
    PSI, Villigen PSI, Switzerland
  The Athos line will cover the photon energy range from 250 to 1900 eV and will operate parallel to the hard x-ray line Aramis of SwissFEL. Athos consists of fast kicker magnets, a dog-leg transfer line, a small linac and 16 APPLE undulators. The Athos undulators follow a new design: the so-called APPLE X design where the 4 magnet arrays can be moved radially in a symmetric way. Besides mechanical advantages of such a symmetric distribution of forces, this design allows for easy photon energy scans at a constant polarization or for the generation of transverse magnetic gradients. Another particularity of the Athos FEL line is the inclusion of a short magnetic chicane between every undulator segment. These chicanes will allow the FEL to operate in optical klystron mode, high-brightness SASE mode, or superradiance mode. A larger delay chicane will split the Athos line into two sections such that two colors can be produced with adjustable delay. Finally a post undulator transverse deflecting cavity will be the key tool for the commissioning of the FEL modes. The paper will present the current status of this four years project started in 2017.  
MOP039 Possible Method for the Control of SASE Fluctuations 1
  • N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  It is well known that because the SASE FEL starts up from the intrinsic electron beam shot noise, there are corresponding fluctuations in the useful properties of the output pulses which restrict their usability for many applications. In this paper, we discuss possible new methods for controlling the level of fluctuations in the output pulses.  
TUA01 Recent FEL Experiments at FLASH 1
  • S. Schreiber, E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
  The FLASH free-electron laser user facility at DESY (Hamburg, Germany) provides high brilliance SASE FEL radiation in the XUV and soft X-ray wavelength range. With the recent installation of a second undulator beamline (FLASH2), variable-gap undulators are now available. They now allow various experiments not possible with the FLASH1 fixed gap undulators. We report on experiments on tapering, harmonic lasing, reverse tapering, frequency doubling at FLASH2 and experiments using double pulses for specific SASE and THz experiments at FLASH1.  
Design and Modelling of the Baseline Layout for the Soft X-Ray Laser (SXL) at MAX IV Laboratory  
  • F. Curbis, S. Werin
    MAX IV Laboratory, Lund University, Lund, Sweden
  The Soft X-ray Laser (SXL) is a project aiming to build a new beamline that will exploit the potential of the MAX IV 3 GeV linac and its Short Pulse Facility (SPF). In fact, this injector, which is routinely used as an electron source for the two rings in the laboratory, is capable of delivering ultra-brilliant electron pulses and possibly driving a Free Electron Laser (FEL). While the necessary technical improvements and features of the linac are described in another contribution, this paper presents the baseline layout of the SXL FEL and point out the features of the photon source that should deliver brilliant pulses between 1 and 5 nm. The baseline design consists of a SASE FEL with variable polarization undulators. However, the plan is to develop a comprehensive system of external sources at various wavelength in order to enable various pump-probe schemes, thereby satisfying the requests of the users community. Moreover the design needs to take into account the possibility of accommodating two-pulse-two-color capability and the production of femtosecond or even attosecond pulses.  
slides icon Slides TUA02 [2.345 MB]  
Generation of High Power, Short X-Ray FEL Pulses  
  • M.W. Guetg, F.-J. Decker, Y. Ding, Z. Huang, A.A. Lutman, T.J. Maxwell
    SLAC, Menlo Park, California, USA
  X-ray Free Electron Lasers combine high pulse power, short pulse length, narrow bandwidth and a high degree of transverse coherence. Increasing the photon pulse power, while shortening the pulse length, is of key importance on the way to single molecule imaging. This letter shows experimental results at the Linac Coherent Light Source improving its power to more than 300 GW, while reducing the photon pulse length to 10fs. This was achieved by removing residual transverse-longitudinal centroid beam offsets and correction of dispersion when operating over 6 kA peak current.  
TUA04 Suppression of the CSR Effects at a Dogleg Beam Transport Using DBA Lattice 1
  • T. Hara, T. Inagaki, C. Kondo, H. Maesaka, Y. Otake, H. Tanaka, K. Togawa
    RIKEN SPring-8 Center, Hyogo, Japan
  • K. Fukami
    JASRI/SPring-8, Hyogo, Japan
  • T. Hasegawa, O. Morimoto, S. Nakazawa, M. Yoshioka
    SES, Hyogo-pref., Japan
  Multi-beamline, multi-user operation is an important issue of linac-based XFELs to improve usability and efficiency of facilities. At SACLA, the multi-beamline operation had been tested since 2015 using two beamlines (BL2 and BL3). But the CSR effects at a 3-degree dogleg beam transport of BL2 caused a projected emittance growth and instability of the beam orbit due to a high peak current of 10 kA and a short bunch duration of SACLA. Consequently, stable lasing was obtained only for elongated electron bunches with low peak currents below 3 kA. To mitigate the CSR effects, the beam optics of the dogleg was rearranged. The new beam optics are based on two DBA (double bend achromatic) structures and the transverse effects of CSR are cancelled between four bending magnets. To avoid the bunch length change, the electron beam passes an off-center orbit at the quadrupole magnets of DBA. Under the new beam optics, stable lasing has been successfully obtained with 10 kA electron bunches, and the parallel operation of the two beamlines will be started in September 2017 for user experiments.  
slides icon Slides TUA04 [7.330 MB]  
Generating Subfemtosecond Hard X-Ray Pulses with Optimized Nonlinear Bunch Compression  
  • S. Huang
    PKU, Beijing, People's Republic of China
  • Y. Ding, Y. Feng, E. Hemsing, Z. Huang, J. Krzywinski, A.A. Lutman, A. Marinelli, T.J. Maxwell, D. Zhu
    SLAC, Menlo Park, California, USA
  Funding: This work is supported by the U.S. Department of Energy Contract No. DE-AC02-76SF00515 and the National Key Research and Development Program of China (Grant No. 2016YFA0401904).
A simple method for generating single-spike hard x-ray pulses in free-electron lasers (FELs) has been developed at the Linac Coherent Light Source (LCLS). By optimizing the electron bunch compression in experiments, we have obtained half of the hard x-ray FEL shots containing single-spike spectrum. At 5.6-keV photon energy, the single-spike shots have a mean pulse energy of about 10 J with 70% intensity fluctuation and the pulse width (full width at half maximum) is evaluated to be at 200-attosecond level.