Novel Concepts and Techniques
Paper Title Page
THP012 Compact FEL-Driven Inverse Compton Scattering Gamma-Ray Source 617
 
  • M. Placidi, G. Penn
    LBNL, Berkeley, California, USA
  • S. Di Mitri
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • C. Pellegrini
    UCLA, Los Angeles, California, USA
  • C. Pellegrini
    SLAC, Menlo Park, California, USA
 
  We explore the feasibility of a compact source of quasi-monochromatic, multi-MeV gamma-rays based on Inverse Compton Scattering (ICS) from a high intensity ultra-violet (UV) beam generated in a free-electron laser by the electron beam itself.[1] This scheme introduces a stronger relationship between the energy of the scattered photons and that of the electron beam, resulting in a device much more compact than a classic ICS for a given scattered energy. The same electron beam is used to produce gamma-rays in the 10-20 MeV range and UV radiation in the 10-15 eV range, in a ~4x22 m2 footprint system.
[1] M. Placidi et al., NIM A 855 (2017) 55-60.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP012  
About • paper received ※ 19 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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THP047 Laser-Driven Compact Free Electron Laser Development at ELI-Beamlines 680
 
  • A.Y. Molodozhentsev
    Czech Republic Academy of Sciences, Institute of Physics, Prague, Czech Republic
  • J.T. Green, J. Hawke, M. Kaur, D. Kocon, G. Korn, K.O. Kruchinin
    ELI-BEAMS, Prague, Czech Republic
  • A.R. Maier
    University of Hamburg, Hamburg, Germany
 
  Funding: Advanced research using high-intensity laser produced photons and particles (CZ.02.1.01/0.0/0.0/16019/0000789) from the European Regional Development Fund.
The ELI-Beamlines Centre, located near Prague (Czech Republic) is an international user facility for fundamental and applied research. Using the optical parametric chirped-pulse amplification (OPCPA) technique, the ELI-Beamlines laser system will provide the laser pulse energy up to 10 Joules with the repetition rate up to 25 Hz. Combination of new laser development with constant improvement of the LWFA electron beam parameters has great potential in future development of the compact high repetition rate Free Electron Laser. The LWFA-driven FEL project, called "LUIS", is currently under preparation at ELI-Beamlines in collaboration with the University of Hamburg. The goal of the project is the improvement of the electron beam parameters in order to demonstrate the amplification and saturation of the SASE-FEL photon power in a single unit of the FEL undulator. A successful realization of the LUIS project will open a way to a next generation of laser-driven X-FELs. An overview of the LUIS project including design features and a description of all instrumentations used to characterize the laser, plasma, electron beam, photon generation will be presented in frame of this report.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP047  
About • paper received ※ 15 August 2019       paper accepted ※ 16 September 2019       issue date ※ 05 November 2019  
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THP048 Progress Towards Laser Plasma Electron Based Free Electron Laser on COXINEL 684
 
  • M.-E. Couprie, T. André, F. Blache, F. Bouvet, F. Briquez, Y. Dietrich, J.P. Duval, M. El Ajjouri, A. Ghaith, C. Herbeaux, N. Hubert, M. Khojoyan, C.A. Kitégi, M. Labat, N. Leclercq, A. Lestrade, A. Loulergue, O. Marcouillé, F. Marteau, D. Oumbarek Espinos, P. Rommeluère, M. Sebdaoui, K.T. Tavakoli, M. Valléau
    SOLEIL, Gif-sur-Yvette, France
  • I.A. Andriyash, V. Malka, S. Smartzev
    Weizmann Institute of Science, Physics, Rehovot, Israel
  • C. Benabderrahmane
    ESRF, Grenoble, France
  • S. Bielawski, C. Evain, E. Roussel, C. Szwaj
    PhLAM/CERLA, Villeneuve d’Ascq, France
  • S. Corde, J. Gautier, J.-P. Goddet, O.S. Kononenko, G. Lambert, K. Ta Phuoc, A. Tafzi, C. Thaury
    LOA, Palaiseau, France
 
  Laser plasma acceleration (LPA) with up to several GeV beam in very short distance appears very promising. The Free Electron Laser (FEL), though very challenging, can be viewed as a qualifying application of these new emerging LPAs. The energy spread and divergence, larger than from conventional accelerators used for FEL, have to be manipulated to fulfil the FEL requirements. On the test experiment COXINEL (ERC340015), the beam is controlled in a manipulation [1,2] line, using permanent magnet quadrupoles of variable strength [3] for emittance handing and a decompression chicane equipped with a slit for the energy selection, enabling FEL amplification for baseline reference parameters [2]. The electron position and dispersion are independently adjusted [4]. The measured spontaneous emission radiated by a 2 m long 18 mm period cryo-ready undulator exhibits the typical undulator spatio-spectral pattern, in agreement with the modelling of the electron beam travelling along the line and of the afferent photon generation. The wavelength is easily tuned with undulator gap variation. A wavelength stability of 2.6% is achieved. The undulator linewidth can be controlled.
[1] A. Loulergue et al., New J. Phys. 17 023028 (2015)
[2] M. E. Couprie et al., PPCF 58, 3 (2016)
[3] F. Marteau et al., APL 111, 253503 (2017)
[4] T. André et al., Nature Comm. 1334 (2018)
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP048  
About • paper received ※ 13 August 2019       paper accepted ※ 16 September 2019       issue date ※ 05 November 2019  
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THP049 A Versatile THz Source for High-Repetition Rate XFELs 688
 
  • F. Lemery, M. Dohlus, K. Flöttmann, M. Marx
    DESY, Hamburg, Germany
  • M. Ivanyan, V.M. Tsakanov
    CANDLE, Yerevan, Armenia
 
  Funding: FL was partially funded by the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No. 730871
The development of high-repetition rate XFELs brings an exciting time for novel fundamental science exploration via pump-probe interactions. Laser-based pump sources can provide a wide range of wavelengths (200-10000~nm) via various gain media. These sources can also be extended with optical parametric amplifiers to cover a largely versatile spectral and bandwidth range. However beyond 10~μm, toward the THz regime, there exists no suitable gain media, and optical-to-THz efficiencies are limited below 1\%. In this paper we discuss the use of Cherenkov-based radiators with conventional electron bunches to generate high-power THz radiation over a wide range of parameters for existing and future XFEL facilities.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP049  
About • paper received ※ 25 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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THP051 Generating Trains of Attosecond Pulses with a Free-Electron Laser 692
 
  • S. Serkez, G. Geloni
    EuXFEL, Schenefeld, Germany
  • M.H. Cho, H.-S. Kang, G. Kim, J.H. Ko, C.-K. Min, I.H. Nam, C.H. Shim
    PAL, Pohang, Republic of Korea
  • F.-J. Decker
    SLAC, Menlo Park, California, USA
  • J.H. Ko, C.H. Shim
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • Yu. Shvyd’ko
    ANL, Lemont, Illinois, USA
 
  Recently, a Hard X-ray Self-Seeding setup was commissioned at PAL XFEL. Its main purpose is to increase the temporal coherence of FEL radiation in an active way. We report another application of this setup to generate trains of short sub-femtosecond pulses with linked phases. We discuss preliminary results of both experiment and corresponding simulations as well as indirect diagnostics of the radiation properties.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP051  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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THP054 Nanosecond Pulse Enhancement in Narrow Linewidth Cavity for Steady-State Microbunching 697
 
  • Q.H. Zhou
    Southwest University of Science and Technology, Mianyang, Sichuan, People’s Republic of China
 
  Funding: The National Natural Science Foundation of China under Grant No.11875227.
In steady-state microbunching (SSMB), nanosecond laser pulse with megawatt average power is required. We build up a theoretic model to enhance such pulse in a narrow linewidth (e.g. kHz level) cavity for this demand, which shows that a mode-locked mechanism in frequency domain should be considered. Simulations indicate that such pulse can be enhanced sufficiently under this condition. And we also propose some experimental schematics to realize it.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP054  
About • paper received ※ 25 August 2019       paper accepted ※ 22 October 2019       issue date ※ 05 November 2019  
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THP055 A Storage Ring Design for Steady-State Microbunching to Generate Coherent EUV Light Source 700
 
  • Z. Pan, X.J. Deng, W.-H. Huang, T. Rui, C.-X. Tang, Y. Zhang
    TUB, Beijing, People’s Republic of China
  • A. Chao
    SLAC, Menlo Park, California, USA
  • W. Wan
    ShanghaiTech University, Shanghai, People’s Republic of China
 
  The proposal of Steady State Microbunching (SSMB) makes it available to generate high average power coherent radiation, especially has the potential to generate kW level of EUV source for lithography. In order to achieve and maintain SSMB, we propose several concepts. One is that a very short electron bunch below 100 nm is stored in the ring, inserting a strong focusing part to compress the bunch to ~3 nm, then radiating coherently, which is called longitudinal strong focusing (LSF) scheme. We have optimized the candidate lattice to achieve the very short electron bunch storage and microbunching for electron beam. The tracking results show the equilibrium length of the electron bunch is about 400 nm and no particles lose after 4.3 damping time while only single-particle effect is considered. More optimization and some new design based on the simulation results are still implementing.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP055  
About • paper received ※ 19 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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THP060 Development of RF-Undulators and Powering Sources for Compact Efficient Compton FEL-Scattrons 704
 
  • A.V. Savilov, E.D. Abubakirov, N.S. Ginzburg, S.V. Kuzikov, N.Yu. Peskov, A.A. Vikharev, V.Yu. Zaslavsky
    IAP/RAS, Nizhny Novgorod, Russia
 
  Conception of Compton-type FELs operating up to X-ray band is under development currently at IAP RAS (N.Novgorod). This concept is aimed at reducing energy of a driving relativistic electron beam and thereby increasing efficiency of the electron-wave interaction in FEL, as well as achieving relative compactness of the generator. The basis of this concept is RF-undulators of a new type - the so-called ’flying’ undulators. Results of current research of these RF-undulators, their simulations and ’cold’ tests in the Ka-band are presented. For powering RF-undulators spatially-extended narrow-band Cerenkov masers are developed in the specified frequency range. In order to achieve the required sub-gigawatt power level of the pumping wave in a strongly oversized oscillator, we exploit the original idea of using two-dimensional distributed feedback implemented in the 2D doubly-periodical slow-wave structures. The design parameters of Ka-band surface-wave oscillator intended for powering RF-undulators, results of its simulation and initial experimental studies are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP060  
About • paper received ※ 15 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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THP061 Bayesian Optimisation for Fast and Safe Parameter Tuning of SwissFEL 707
 
  • J. Kirschner, A. Krause, M. Mutný, M. Nonnenmacher
    ETH, Zurich, Switzerland
  • A. Adelmann, N. Hiller, R. Ischebeck
    PSI, Villigen PSI, Switzerland
 
  Parameter tuning is a notoriously time-consuming task in accelerator facilities. As tool for global optimization with noisy evaluations, Bayesian optimization was recently shown to outperform alternative methods. By learning a model of the underlying function using all available data, the next evaluation can be chosen carefully to find the optimum with as few steps as possible and without violating any safety constraints. However, the per-step computation time increases significantly with the number of parameters and the generality of the approach can lead to slow convergence on functions that are easier to optimize. To overcome these limitations, we divide the global problem into sequential subproblems that can be solved efficiently using safe Bayesian optimization. This allows us to trade off local and global convergence and to adapt to additional structure in the objective function. Further, we provide slice-plots of the function as user feedback during the optimization. We showcase how we use our algorithm to tune up the FEL output of SwissFEL with up to 40 parameters simultaneously, and reach convergence within reasonable tuning times in the order of 30 minutes (< 2000 steps).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP061  
About • paper received ※ 13 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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THP065 Multi-Objective FEL Design Optimisation Using Genetic Algorithms 711
 
  • D.J. Dunning, H.M. Castañeda Cortés, J.K. Jones, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • J.K. Jones, N. Thompson
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
 
  Simulation studies were carried out to optimise the performance of various FEL designs, with examples including longitudinal current profile shaping for a seeded FEL, and selection of the chicane delays for the High-Brightness SASE technique. In these examples multi-objective genetic algorithms were applied to a single section of the overall facility simulation, i.e. the undulator, as is the common approach. Further studies are also reported in which a full start-to-end simulation chain was optimised, with the aim of delivering a more holistic facility design optimisation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP065  
About • paper received ※ 20 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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THP068 LCLS-II Extruded Aluminum Undulator Vacuum Chambers — New Approaches to an Improved Aperture Surface Finish 719
 
  • G.E. Wiemerslage, P.K. Den Hartog, J. Qian, M. White
    ANL, Lemont, Illinois, USA
 
  Funding: Work at Argonne National Laboratory is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract # DE-AC02-06CH11357.
The Linac Coherent Light Source, (LCLS) the world’s first x-ray free electron laser (FEL) became operational in 2009. The Advanced Photon Source contributed to the original project by designing and building the undulator line. Two slightly different variations of these chambers were required for LCLS-II: one for a soft X-ray (SXR) undulator line, and one for a hard X-ray (HXR) undulator line. Because of the extremely short electron bunch length, a key physics requirement was to achieve the best possible surface finish within the chamber aperture. Improvements to our earlier fabrication methods allowed us to meet the critical surface roughness finish defined by RF impedance requirements. We were able to improve the surface finish from an average of 812 nm rms to 238 nm rms. The average longitudinal surface roughness slope of all chambers was to be less than 20 mrad. We achieved an average longitudinal surface roughness slope of 8.5 mrad with no chamber exceeding 20 mrad. In the end, sixty-four undulator vacuum chambers and alignment systems were delivered to SLAC for the LCLS-II Upgrade project. Here we will report on the process improvements for the fabrication of these chambers.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP068  
About • paper received ※ 16 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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THP069 Observations on Microbunching of Electrons in Laser-Driven Plasma Accelerators and Free-Electron Lasers 722
 
  • A.H. Lumpkin
    Fermilab, Batavia, Illinois, USA
  • M. Downer, M. LaBerge
    The University of Texas at Austin, Austin, Texas, USA
  • D.W. Rule
    Private Address, Silver Spring, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
The periodic longitudinal density modulation of relativistic electrons at the resonant wavelength (microbunching) is a fundamental aspect of free-electron lasers (FELs). In one case, microbunching fractions reached 20% at saturation of a self-amplified spontaneous emission (SASE) FEL resulting in gains of 1 million at 530 nm [1]. In that experiment the z-dependent gain of coherent optical transition radiation (COTR) was also measured. In laser-driven plasma accelerators (LPAs), microbunching at visible wavelengths has also been recently reported as evidenced by significant COTR enhancements measured in near-field and far-field images on a single shot for the first time [2]. An analytical model for COTR interferometry (COTRI) addresses both cases. In the FEL, one identified microbunched transverse cores of 25-100 microns while in the LPA the reported transverse sizes at the exit of the LPA were a few microns. In the latter case, signal enhancements of nearly 100, 000 and extensive fringes out to 30 mrad in angle space were recorded. The broadband microbunching observed in the LPA case could act as a seed for a SASE FEL experiment with tunability in principle over the visible regime.
[1] A.H. Lumpkin et al., Phys. Rev. Lett. 88, No.23, 234801 (2002).
[2] A.H. Lumpkin, M. LaBerge, D.W. Rule et al., Proceedings of AAC18, (IEEE), (2019).
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP069  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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THP071 Progress in High Power High Brightness Double Bunch Self-Seeding at LCLS-II 726
 
  • A. Halavanau, F.-J. Decker, Y. Ding, C. Emma, Z. Huang, A.K. Krasnykh, J. Krzywiński, A.A. Lutman, G. Marcus, A. Marinelli, A. Ratti, D. Zhu
    SLAC, Menlo Park, California, USA
  • C. Pellegrini
    UCLA, Los Angeles, California, USA
 
  Funding: Work supported by the U.S. Department of Energy Contract No. DE-AC02-76SF00515.
We have previosuly shown that we can generate near TW, 15 fs duration, near transform limited X-ray pulses in the 4 to 8 keV photon energy range using the LCLS-II copper linac, two electron bunches, a 4-crystal monochromator/delay line and a fast transverse bunch kicker. The first bunch generates a strong seeding X-ray signal, and the second bunch, initially propagating off-axis, interacts with the seed in a tapered amplifier undulator, where it propagates on axis. In this paper, we investigate the design of the 4-crystal monochromator, acting also as an X-ray delay system, and of the fast kicker, in preparation of the implementation of the system in LCLS-II.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP071  
About • paper received ※ 20 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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THP073 Status Update for the High Gain High Efficiency TESSA-266 Experiment 730
 
  • Y. Park, D.K. Dang, P.E. Denham, P. Musumeci, N.S. Sudar
    UCLA, Los Angeles, USA
  • R.B. Agustsson, T.J. Campese, I.I. Gadjev, A.Y. Murokh
    RadiaBeam, Los Angeles, California, USA
  • C.C. Hall, S.D. Webb
    RadiaSoft LLC, Boulder, Colorado, USA
  • Y. Sun, A. Zholents
    ANL, Lemont, Illinois, USA
 
  Funding: DOE grant No. DE-SC0009914 and DE-SC0018559
Tapering Enhanced Stimulated Superradiant Amplification (TESSA) allows to increase the efficiency of Free Electron Laser (FEL) based radiation generation from ~0.1% to 10% by using intense seed laser pulses, strongly tapered undulators and prebunched electron beams [1]. Initial results validating this method have already been obtained at 10 µm wavelength at Brookhaven National Laboratory [2]. We will present the design of an experiment to demonstrate the TESSA scheme at high gain and shorter wavelength (266 nm) using the APS injector linac at Argonne National Labor-atory (ANL) to obtain conversion efficiency of up to 10%. Undulator and focusing lattice design, as well as beam dynamics and diagnostics for this experiment will be discussed. An extension of the experiment to include the possibility of multi-bunch linac operation and an optical cavity around the undulator to operate in the TESSO regime will also be presented [3].
[1] J. Duris et al., New J. Phys. 17 063036 (2015)
[2] N Sudar et al., Physical review letters, 117, 174801 (2016)
[3] J. Duris et al., Physical Review Accelerators and Beams 21, 080705 (2018)
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP073  
About • paper received ※ 20 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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THD01
From Femtosecond to Attosecond Coherent Undulator Pulses  
 
  • V.A. Goryashko, P.M. Salén, G.K. Shamuilov
    Uppsala University, Uppsala, Sweden
 
  Funding: Swedish Research Council (VetenskapsrÃ¥det) (grant no. 2016-04593); Stockholm-Uppsala Centre for Free-Electron Laser Research (SUFEL).
In Bohr’s model of the hydrogen atom, the ground-state electron completes one cycle of revolution in 150 attoseconds. Some other processes in atoms and molecules can be even faster. Femtosecond and attosecond pulses of light can provide the resolution needed for studying and ultimately controlling the dynamics of electrons in solids, molecules and atoms. Therefore, there is a strong scientific demand for the development of sources of high-energy, ultrashort, coherent, X-ray pulses. In this talk, we (i) review the characteristic time and length scales in atoms, molecules and nanostructures, (ii) outline the progress on short-pulse generation over time and the state-of-the-art of production of high-energy, ultrashort pulses; (iii) examine the demonstrated and proposed schemes of the generation of femtosecond and sub-femtosecond pulses with FELs, (iv) discuss recent concepts [1] for the production of 100-attosecond pulses.
[1] A. Mak et al., "Attosecond single-cycle undulator light: a review," Reports on Progress in Physics, Vol. 82, 02590 (2019).
 
slides icon Slides THD01 [9.690 MB]  
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THD02
Attosecond Pulses from Enhanced SASE at LCLS  
 
  • A. Marinelli, P.H. Bucksbaum, E. Champenois, J. Cryan, T.D.C. Driver, J.P. Duris, Z. Huang, A.A. Lutman, J.P. MacArthur, Z. Zhang
    SLAC, Menlo Park, California, USA
  • Z. Huang, S. Li, J.P. MacArthur
    Stanford University, Stanford, California, USA
  • M. Kling, P. Rosenberger
    LMU, Garching, Germany
  • A. Zholents
    ANL, Lemont, Illinois, USA
 
  In my talk I will report the generation and diagnostic of GW-scale soft X-ray attosecond pulses with a current-enhanced X-ray free-electron laser. Our method is based on the enhaced SASE scheme, where an electron bunch with high-current spike is generated by the interaction of the relativistic electrons with a high-power infrared pulse. The X-ray pulses generated by the compressed electron beam are diagnosed with angular photoelectron streaking, and have a mean pulse duration of 350 attoseconds. Our source has a peak brightness that is 6 orders of magnitude larger than any other source of isolated attosecond pulses in the soft X-ray spectral region. This unique combination of high intensity, high photon energy and pulse duration enables the investigation of valence electron dynamics with non-linear spectroscopy and single-shot imaging. I will also discuss the generation of two-color attosecond pulses and our future plans for attosecond science at LCLS-II.  
slides icon Slides THD02 [0.260 MB]  
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THD03 FEL Optimization: From Model-Free to Model-Dependent Approaches and ML Prospects 762
 
  • S. Tomin, G. Geloni
    EuXFEL, Schenefeld, Germany
  • M. Scholz
    DESY, Hamburg, Germany
 
  Users beam-time at modern FEL sources is an extremely valuable commodity. Moreover, maximization of FEL up-time must always be performed accounting for stringent requirements on the photon pulse characteristics. These may vary widely depending on the users requests, which poses issues to parallel operation of high-repetition rate facilities like the European XFEL. Therefore, both model-free or model-dependent optimization schemes, where the model might be given, or provided by machine-learning approaches, are of high importance for the overall efficiency of FEL facilities. In this contribution, we review our previous activities and we report on current efforts and progress in FEL optimization schemes at the European XFEL. Finally, we provide an outlook on future developments.  
slides icon Slides THD03 [13.636 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THD03  
About • paper received ※ 21 August 2019       paper accepted ※ 12 September 2019       issue date ※ 05 November 2019  
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THD04
A Novel Optical Undulator Using Array of Pulse-Front Tilted Laser Beams  
 
  • W. Liu
    USTC/NSRL, Hefei, Anhui, People’s Republic of China
 
  Funding: This work is supported by Natural Science Foundation of China (U1632150, 51627901, 61471332, 11675178-11611140102) and Chinese Universities Scientific Fund (WK2310000059).
We report a laser-driven undulator for developing compact ultraviolet-to-X free-electron lasers (FELs), which overcomes the main disadvantages of previous optical and magnetic undulators. It uses an array of transverse-polarized laser beams with alternated phases to provide the periodic deflecting fields. The pulse-front tilt is applied to free the undulating period from the laser wavelength. The transverse electric field of laser is to deflect the electrons in the vacuum, which greatly increases the efficiency and the achievable deflecting forces since it avoids the breakdown of medium. The ultraviolet-to-X FEL with a desirable undulator strength can be achieved by lasers with intensities being orders of magnitude less than that in previous optical undulator, and by electrons with energies being remarkably less than that of magnetic undulator. Thus, it affords a promising way for developing the ultra-compact and powerful FELs.
 
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