FEL Oscillators
Paper Title Page
MOP056 Design of Apparatus for a High-Power-Density Diamond Irradiation Endurance Experiment for XFELO Applications 1
  • S.P. Kearney, K.-J. Kim, T. Kolodziej, R.R. Lindberg, D. Shu, Yu. Shvyd'ko, D. Walko, J. Wang
    ANL, Argonne, Illinois, USA
  • S. Stoupin
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
We have designed a diamond irradiation setup capable of achieving multiple kW/mm2 power density. The setup was installed at the 7-ID-B beamline at the Advanced Photon Source (APS) for a successful irradiation experiment, testing the capability of diamond to endure x-ray free electron laser oscillator (XFELO) levels of irradiation (≥ 10 kW/mm2) without degradation of Bragg reflectivity.* Focused white-beam irradiation (50 μm x 20 μm spot size at 12.5 kW/mm2 power density) of a diamond single crystal was conducted in a vacuum environment of 1x10-8 Torr for varying durations of time at different spots on the diamond, and also included one irradiation spot during a spoiled vacuum environment of 4x10-6 Torr. Here we present the apparatus used to irradiate the diamond consisting of multiple subassemblies: the fixed masks, focusing optics, gold-coated UHV irradiation chamber, water-cooled diamond holder, chamber positioning stages (with sub-micron resolution) and detector.
* T. Kolodziej et al., Free Electron Laser Conf. 2017.
Diamond Endurance to Irradiation with X-ray Beams of Multi kW/mm2 Power Densities for XFELO Application  
  • T. Kolodziej, T. Gog, S.P. Kearney, K.-J. Kim, W. Liu, A. Said, D. Shu, Yu. Shvyd'ko, D. Walko, J. Wang
    ANL, Argonne, Illinois, USA
  • M. Baldini, W. Yang
    High Pressure Synergic Consortium, Advanced Photon Source, Lemont, USA
  • V.D. Blank, S. Terentiev
    TISNCM, Troitsk, Russia
  • P. Rigg
    Dynamic Compression Sector, Washington State University, Lemont, USA
  • S. Stoupin
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  Funding: Work at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357
X-ray science has recently been considerably shaped by the advent of modern bright and powerful x-ray sources: 3rd generation synchrotron radiation storage rings and XFELs. XFELs in the oscillator configuration (XFELO) are possible future new sources, in which x-ray beams generated by the undulator circulate in an optical x-ray cavity comprised of high-reflectance (close to 100%) diamond crystal mirrors working in Bragg backscattering. XFELOs will produce stable, fully coherent hard x-rays of ultra-high (meV) spectral purity. The average power density of the x-ray beams in the XFELO cavity is however predicted to be unprecedentedly high, about ≈15 kW/mm2. Therefore, the XFELO feasibility relies on the ability of diamond to withstand such a high radiation load and preserve its high reflectivity. We are reporting on endurance studies of the highest-quality, practically flawless synthetic diamond crystals to irradiation with power density close to that expected on the XFELO crystals. Most importantly, we are studying whether the extremely high Bragg reflectivity of meV-monochromatic x-rays from the diamond crystals in backscattering is conserved after the irradiation.
High Precision Polarization Diagnostic System for Free-Electron Laser  
  • J. Yan, H. Hao, S.F. Mikhailov, V. Popov, G. Swift, Y.K. Wu
    FEL/Duke University, Durham, North Carolina, USA
  In the Duke storage ring FEL facility, an upgrade of the undulator system has created research opportunities to explore novel modes of storage ring FEL operation using as many as four helical undulators simultaneously. Recently, the generation of a linearly polarized FEL beam with the rotatable polarization direction has been realized using two sets of helical undulators of opposite helicities. To study and optimize this new FEL, high-precision polarization diagnostics are being developed to cover a wide range of wavelength from infrared (IR) to visible (VIS) to vacuum ultraviolet (VUV). In this work, we report the development of the first IR-VIS-UV polarization diagnostic system for Duke FEL operations from 1 micron to about 350 nm. This system is capable of measuring the FEL beam Stokes parameters using the extracted FEL beam. High precision measurements of FEL beam polarization have been demonstrated using a set of carefully calibrated optics.  
MOP059 Synchronized Mid-Infrared Pulses at the Fritz Haber Institute IR-FEL 1
  • R. Kiessling, S. Gewinner, A. Paarmann, W. Schöllkopf, M. Wolf
    FHI, Berlin, Germany
  The combined application of FEL radiation and femtosecond table-top lasers for two-color spectroscopy demands an accurate pulse synchronization. In order to employ the Infared FEL at the Fritz Haber Institute for non-linear and time-resolved experiments, an RF-over-fiber-based timing system has been established. Using a balanced optical cross-correlation scheme, we determined an FEL micro-pulse timing jitter of 100-200 fs (rms). The long-term timing drift was found to be well correlated to the energy fluctuations of the accelerated electron bunches. By means of the jitter-corrected cross-correlation signal, we directly measure the FEL pulse shape at different cavity detunings. For large cavity detuning, narrowband IR radiation (~ 0.3 % FWHM) can be generated and utilized for high-resolution non-linear spectroscopy. On the other hand, sub-picosecond pulses are provided at small detuning, which are well-suited for time-resolved measurements. At intermediate detuning values, we observe the build-up and dynamics of multipulses that result in the well-known limit-cycle power oscillations.  
poster icon Poster MOP059 [1.531 MB]  
Broadband THz FEL Oscillator via Resonant Coherent Diffraction Radiation at ERL Test Accelerator in KEK  
  • Y. Honda, A. Aryshev, R. Kato, T. Miyajima, T. Obina, M. Shimada, R. Takai, N. Yamamoto
    KEK, Ibaraki, Japan
  An Energy Recovery Linac can produce a low emittance and short bunch beam at a high-repetition rate. A test accelerator, compact-ERL, has been operating in KEK for development works of technologies related to ERL and CW-Superconducting accelerators. One of the promising applications of such a short bunch beam is a high-power THz radiation source produced by a coherent radiation. When a charged particle beam passes close to a conductive target, a radiation called diffraction radiation is produced. If the target mirrors form an optical cavity whose fundamental frequency matches the repetition frequency of the beam, the radiation resonates in the cavity, resulting in extracting a huge radiation power determined by the loss of the cavity. When the cavity is designed to be zero carrier envelope offset, all the longitudinal modes excite at the same time. This situation can be understood as an undulatory-less broadband FEL oscillator. We plan to perform an experiment of the resonant coherent diffraction mechanism in the return-loop of the compact-ERL. We report the design of the experimental setup to be installed in the summer of 2017.  
MOP061 X-ray Regenerative Amplifier Free-Electron Laser Concepts for LCLS-II 1
  • G. Marcus, Y. Ding, J.P. Duris, Y. Feng, Z. Huang, J. Krzywinski, T.J. Maxwell, D.F. Ratner, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • K.-J. Kim, R.R. Lindberg, Yu. Shvyd'ko
    ANL, Argonne, Illinois, USA
  • D.C. Nguyen
    LANL, Los Alamos, New Mexico, USA
  High-brightness electron beams that will drive the next generation of high-repetition rate X-ray FELs allow for the possibility of optical cavity-based feedback. One such cavity-based FEL concept is the Regenerative Amplifier Free-Electron Laser (RAFEL). This paper examines the design and performance of possible RAFEL configurations for LCLS-II. The results are primarily based on high-fidelity numerical particle simulations that show the production of high brightness, high average power, fully coherent, and stable X-ray pulses at LCLS-II using both the fundamental and harmonic FEL interactions.  
MOP062 X-ray FEL Oscillator Seeded Harmonic Amplifier for High Energy Photons 1
  • W. Qin, J. Wu
    SLAC, Menlo Park, California, USA
  • K.-J. Kim, R.R. Lindberg
    ANL, Argonne, Illinois, USA
  High-power, high-energy X-ray pulses in the range of several tens of keV have important applications for material sciences.* The unique feature of an X-ray FEL Oscillator (XFELO) makes it possible to seed a harmonic amplifier to produce such high energy photons.** In this contribution, we present simulation studies using 14.4-keV output pulses from an XFELO to generate harmonics around 40 keV (3rd harmonic) and 60 keV (4th harmonic). Techniques such as undulator tapering and fresh bunch lasing are considered to improve the amplifier performance.
* MaRIE project: http://www.lanl.gov/science-innovation/science-facilities/marie/.
** K.-J. Kim, XFELO-Seeded Amplifier, talk on MaRIE workshop, 2016.
Considerations on X-ray FEL Oscillator Operation for the Shanghai Coherent Light Facility  
  • K. Li, H.X. Deng
    SINAP, Shanghai, People's Republic of China
  Shanghai Coherent Light Facility (SCLF) is a quasi-CW hard X-ray free electron laser user facility which is recently proposed. Due to the high repetition rate and high quality electron beams, it is straightforward to consider an X-ray free electron laser oscillator (XFELO) operation for SCLF. The main parameters required for the undulator, X-ray cavity and electron beam for XFELO operation are discussed, and the performances of the expected fully coherent X-ray pulses are investigated and optimized by the combination of theoretical analysis and numerical simulation.  
MOP064 An Experimental Setup for Probing the Thermal Properties of Diamond Regarding Its Use in an XFELO 1
  • C.P. Maag, I. Bahns, J. Roßbach, P. Thiessen
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • H. Sinn
    XFEL. EU, Hamburg, Germany
  • J. Zemella
    DESY, Hamburg, Germany
  Funding: Work supported by BMBF (FKZ 05K13GU4 + FKZ 05K16GU4)
This work presents an pump-probe setup for measuring the thermal evolution of diamond crystals at cryogenic temperatures under the heat load conditions of an X-ray free electron laser oscillator (XFELO). As the diamond Bragg reflectors of an XFELO are subjected to intense heat loads during operation, the correct understanding of the thermal evolution in diamond plays a major role in the correct modeling of an XFELO. Stoupin et al.* did a room temperature x-ray diffraction measurement on the nanosecond transient thermal response of diamond to an optical pulse. The measurements presented in this paper for the first time incorporate effects due to the very short penetration depth of only a few μm of an XFELO pulse in combination with the high mean free path in diamond at cryogenic temperatures. While at room temperature the heat equation based on Fourier's law accurately fits the measured results, this vastly changes due to the onset of ballistic processes at cryogenic temperatures. These changes, which are hard to predict theoretically, show the necessity of measurements of the thermal evolution in diamond with special regard to a correct mimicking of the heat load in an XFELO.
*S. Stoupin et al., Phys. Rev. B, vol. 86, p. 054301, 2012.
poster icon Poster MOP064 [2.234 MB]  
TUC01 Polarization Control of Storage Ring FELs Using Cross Polarized Helical Undulators 1
  • J. Yan, H. Hao, S.F. Mikhailov, V. Popov, Y.K. Wu
    FEL/Duke University, Durham, North Carolina, USA
  • S. Huang
    PKU, Beijing, People's Republic of China
  • J.L. Li
    IHEP, Beijing, People's Republic of China
  • V. Litvinenko
    Stony Brook University, Stony Brook, USA
  • N.A. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  For more than two decades, accelerator researchers have been working to gain control of polarization of synchrotron radiation and FELs using non-optical means. In 2005, the first experimental demonstration of polarization control of an FEL beam was realized with the Duke storage-ring FEL. With the recent upgrade of the undulator system, the Duke FEL can be operated with up to four helical undulators simultaneously. Using two sets of helical undulators with opposite helicities, for the first time, we have demonstrated full polarization control of a storage ring FEL. First, the helicity switch of the FEL beam has been realized with good lasing up to a few Hz. Second, the linearly polarized FEL beam has been generated with a high degree of polarization (Plin>0.95). The FEL polarization direction can be fully controlled using a buncher magnet. Furthermore, the use of non-optical means to control the FEL polarization allows us to extend polarization control to gamma-ray beams generated using Compton scattering. This has been experimentally demonstrated with the production of linearly polarized Compton gamma-ray beams with rotatable polarization direction based upon helical undulators.  
slides icon Slides TUC01 [5.916 MB]  
TUC02 Thermal and Mechanical Stability of Bragg Reflectors under Pulsed XFEL Radiation 1
  • I. Bahns, C.P. Maag, J. Roßbach, P. Thiessen
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • H. Sinn, V. Sleziona
    XFEL. EU, Hamburg, Germany
  • J. Zemella
    DESY, Hamburg, Germany
  Funding: BMBF FKZ 05K16GU4
Free-electron laser(FEL) x-ray radiation can deliver pulses with a huge amount of energy in short time duration. X-ray optics like Bragg reflectors therefore must be chosen in a way that they can withstand radiation-material interaction without getting damaged so that they can maintain their technical functionality. Therefore thermal and mechanical reactions of Bragg reflectors to the radiation induced thermal strain and force (radiation pressure) have been considered in this study. The theory of thermoelasticity has been used to simulate the strain conditions at saturation of the amplifying process in an X-ray free-electron laser oscillator(XFELO). One aim of this study was to investigate, if the radiation pressure could be an effect that gives a considerable contribution to the strain propagation. The results of the simulations have shown that, if Bragg backscattering of the X-ray pulse by a diamond crystal with 99% reflectivity and 1% absorptivity is assumed, the value of the thermally induced strain is about two magnitudes higher than the radiation pressure induced strain.
High-Flux, Fully Coherent X-Ray FEL Oscillator  
  • K.-J. Kim, S.P. Kearney, T. Kolodziej, R.R. Lindberg, X. Shi, D. Shu, Yu. Shvyd'ko
    ANL, Argonne, Illinois, USA
  • K.L.F. Bane, Y. Ding, P. Emma, W.M. Fawley, J.B. Hastings, Z. Huang, J. Krzywinski, G. Marcus, T.J. Maxwell
    SLAC, Menlo Park, California, USA
  • V.D. Blank, S. Terentiev
    TISNCM, Troitsk, Russia
  • W.M. Fawley
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • C. Grizolli
    LNLS, Campinas, Brazil
  • W. Qin
    PKU, Beijing, People's Republic of China
  • S. Stoupin
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • J. Zemella
    DESY, Hamburg, Germany
  Funding: The ANL part of this work is supported by the U.S. DOE Office of Science under Contract No. DE-AC02-06CH11357 and the SLAC part under contract No. DE-AC02-76SF00515.
By optimizing the parameters of the accelerator, undulator, and the optical cavity, an XFELO driven by an 8-GeV superconducting linac is predicted to produce 10zEhNZeHn photons per pulse at the important photon energies around 14.4 keV.* This is an order of magnitude larger than that in previous designs.** With a BW of 3 meV (FWHM), rep rate of 1 MHz, and taking into account the full coherence, the spectral brightness is then 2×1026 photons per (mm2mr2 0.1\% BW), which is higher than any other source currently operating or anticipated in the future. Experiments at APS beam lines have shown that a high-quality diamond crystal can survive the power density (~15 kW/mm2) expected at the XFELO intra-cavity crystals preserving the high reflectivity.*** The compound refractive lenses can serve as the focusing element. Adding an XFELO to the suite of other FEL sources will, at a minor incremental cost but with a major scientific payoff, significantly expand the scientific capabilities at superconducting linac-based XFEL facilities, such as the European XFEL, the proposed LCLS-II High Energy upgrade and the XFEL project in Shanghai.
* W. Qin et al., this conference.
** R.R. Lindberg et al., Phys. Rev. ST Accel. Beams, vol 14, 403 (2011).
*** T. Kolodziej et al., this conference.
TUC04 Enhancement of Radiative Energy Extraction in an FEL Oscillator by Post-Saturation Beam Energy Ramping 1
  • H. S. Marks, A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • E. Dyunin, Yu. Lurie
    Ariel University, Ariel, Israel
  We present experimental results showing a greater than 50% increase in post-saturation radiation power extraction from a Free Electron Laser oscillator based on an electrostatic accelerator. Electrostatic accelerator free electron laser oscillators have the potential for CW operation. Present day operating oscillators rely on long pulses of electrons, tens of microseconds in duration; they generate correspondingly long radiation pulses, at a single longitudinal mode after a mode competition process. The presented post-saturation power extraction enhancement process is based on temporal tapering (up-ramping) of the beam energy, enabling a large synchrotron oscillation swing of the trapped electron bunches in passage along the interaction length. We further discuss the theoretical limits of the temporal tapering efficiency enhancement process.  
Start-to-End Simulations for an X-Ray FEL Oscillator at the LCLS-II and LCLS-II-HE  
  • W. Qin, K.L.F. Bane, Y. Ding, Z. Huang, G. Marcus, T.J. Maxwell
    SLAC, Menlo Park, California, USA
  • S. Huang, K.X. Liu
    PKU, Beijing, People's Republic of China
  • K.-J. Kim, R.R. Lindberg
    ANL, Argonne, Illinois, USA
  The proposed high repetition-rate electron beam from the LCLS-II and LCLS-II High Energy (LCLS-II-HE) upgrade are promising sources as drivers for an X-ray FEL Oscillator (XFELO) operating at both the harmonic and fundamental frequencies. In this contribution we present start-to-end simulations for an XFELO operating at the fifth harmonic with 4 GeV LCLS-II beam and at the fundamental with 8 GeV LCLS-II-HE beam. The electron beam longitudinal phase space is optimized by shaping the photoinjector laser and adjusting various machine parameters. The XFELO simulations show that high-flux output radiation pulses with 1010 photons and 3 meV (FWHM) spectral bandwidth can be obtained with the 8 GeV configuration.