M E Couprie

SOLEIL synchrotron, Gif, Île-de-France, France

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Publications (253)356.31 Total impact

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    ABSTRACT: Relativistic electron bunches are powerful light sources, which are largely exploited in synchrotron radiation facilities, and are crucial for most sciences. However, electrons bunches suffer from instabilities, leading to spontaneous spatial structure formation. This effect --recalling fluid turbulence issues-- represents a fundamental limitation for light sources, and simultaneously an opportunity because the structures emit high powers of terahertz radiation ($>$10000 times normal synchrotron radiation). Up to now, though crucial for understanding and mastering synchrotron sources, observations of the structures remained a largely open problem, because of their extreme evolution speed. Here we demonstrate the possibility of direct observation by adapting a technique from photonics, {\it time-strech}, consisting in "slowing-down" the phenomena prior to recording. As a main result, we present the first recording of electron bunch microstructures versus time, with submillimeter resolution, in a storage ring. This opens the way to unpreceeded possibilities for analyzing and mastering new generation light sources.
    10/2014;
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    ABSTRACT: Microbunching instability arises in storage rings when the number of electrons in a bunch exceeds a threshold value [1, 2, 3]. Its signature, i.e. a strong and irreg-ular emission of Coherent Synchrotron Radiation (CSR) in the Terahertz (THz) domain, is studied at SOLEIL on the AILES infrared beamline [4], with the storage ring tuned in a low-alpha configuration (used to get shorter elec-tron bunch) [5, 6]. The comparison of this observed THz CSR with numerical simulations of the longitudinal elec-tron bunch dynamics permits to put in evidence that during the instability a modulation appears and drifts in the lon-gitudinal profile of the electron bunch. The understanding of this instability is important as it limits some operation of the storage rings. Indeed the induced fluctuations prevent the use of THz on the far IR beamline at high current per bunch. In addition, in normal alpha operation this instabil-ity may spoil the electron/laser interaction effects required to get femtosecond and/or coherent pulse in storage rings (with slicing [7], Coherent Harmonic Generation or Echo-Enabled Harmonic Generation schemes on storage ring).
    IPAC 2011; 10/2014
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    ABSTRACT: The microbunching instability is an ubiquitous problem in storage rings at high current density. However, the in-volved fast time-scales hampered the possibility to make direct real-time recordings of theses structures. When the structures occur at a cm scale, recent works at UVSOR [1], revealed that direct recording of the coherent synchrotron radiation (CSR) electric field with ultra-high speed elec-tronics (17 ps) provides extremely precious informations on the microbunching dynamics. However, when CSR occurs at THz frequencies (and is thus out of reach of electron-ics), the problem remained largely open. Here we present a new opto-electronic strategy that enabled to record series of successive electric field pulses shapes with picosecond res-olution (including carrier and envelope), every 12 ns, over a total duration of several milliseconds. We also present the first experimental results obtained with this method at Synchrotron SOLEIL, above the microbunching instability threshold. The method can be applied to the detection of ps electric fields in other situations where high repetition rate is also an issue.
    Proceedings of the 5th International Particle Accelerator Conference, At Dresden, Germany; 06/2014
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    M.E. Couprie
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    ABSTRACT: Spectroscopy and imaging in the VUV–X-ray domain are very sensitive tools for the investigation of the properties of matter [1], [2] and [3]. Time-resolved studies enable to follow the movies of ultra-fast reactions. More than fifty years after the laser discovery [4], VUVX light sources are actively developed around the world. Among them, High order Harmonics generated in Gas, X-ray lasers, synchrotron radiation, Free electron lasers are providing a wide offer, from laboratory size sources to large scale facilities, with various features, suitable for different types of experiments. The properties of these sources are here reviewed. Quest of new performances and flexibility is also discussed.
    Journal of Electron Spectroscopy and Related Phenomena 12/2013; · 1.71 Impact Factor
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    ABSTRACT: The LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) in France aims at investigating the generation of short, intense, and coherent pulses in the soft x-ray region (with two particular targeted wavelengths of 20 and 13 nm). It consists in a single Free Electron Laser (FEL) line with cryo-ready in-vacuum undulators using a Conventional Linear Accelerator (CLA) using the superconducting technology of 400 MeV or a Laser Wake Field Accelerator (LWFA) ranging from 0.4 to 1 GeV with multi-TW or PW lasers. The FEL line can be operated in the seeded (High order Harmonic in Gas seeding) and Echo Enable Harmonic Generation configurations, which performances will be compared. Two pilot user experiments for time-resolved studies of isolated species and magnetization dynamics will take benefit of LUNEX5 FEL radiation.
    11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012); 05/2013
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    ABSTRACT: A new concept of wiggler has been designed and realized at SOLEIL to produce high energy photons in low/intermediate electron storage rings. Instead of using the superconducting technology which requires new equipment and instrumentation, heavy maintenance, and additional running costs, we have proposed to build a compact in-vacuum small gap short period wiggler that operates rather at moderate field than at high field. The wiggler composed of 38 periods of 50 mm produces 2.1 T at a gap of 5.5 mm. The moderate value of the magnetic field enables one to limit the effects on the beam dynamics and to avoid excessive power and magnetic forces. In this purpose, the narrow magnetic system has been equipped with a counterforce device made of nonmagnetic springs. The roll-off resulting from the small size of poles has been compensated in situ by permanent magnet magic fingers. This paper reports the phases of design, construction, magnetic measurements, and on-beam tests of the in-vacuum wiggler WSV50.
    Review of Modern Physics 05/2013; · 44.98 Impact Factor
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    M E Couprie
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    ABSTRACT: On intermediate energy synchrotron radiation light sources, a broad spectral range can be covered by a wide panoply of insertion devices, from long period electromagnetic systems to short period in vacuum undulators. Furthermore, in-vacuum wiggler can be developed as an alternative to superconduting ones. The effects on the electron beam, also more critical at low electron beam energies, require specific care on the magnetic field multipolar terms and can include direct compensation of the dynamical integral. In addition, for field enhancement at short period, cryogenic undulators are now currently developed, with a recently installed PrFeB based undulator at SOLEIL. Besides, variable polarisation can be provided with APPLE-II type undulators, with possible aperiodicity. Rapid switching can be achieved with electromagnet/permanent magnet undulator using copper sheets coils.
    Journal of Physics Conference Series 03/2013; 425(3):032012.
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    ABSTRACT: Now that the machine and beamlines are in operation, new requirements have been identified. On the machine, a significant effort is under way to improve beam orbit stability. Among the sources of noise which perturb the electron beam, the effect of the undulators' transient electromagnetic fields has been identified. On beamlines using electromagnetic insertion devices, fast variation of the electromagnetic field is required. In order to improve this performance, a new implementation of the control system for the electromagnetic insertion devices (HU256, HU640 and EMPHU) was designed. This new control is based on a set of boards developed at SOLEIL, called "SPI BOARD PACKAGE".
    Journal of Physics Conference Series 03/2013; 425(3):032022.
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    ABSTRACT: A 2 m long 18 mm period Cryogenic Permanent Magnet Undulator (CPMU) has been constructed at SOLEIL. Praseodymium was chosen instead of Neodymium magnetic material, because of the absence of the Spin Reorientation Transition phenomenon. The use of Pr2Fe14B with a remnence Br of 1.35 T at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. The magnetic field reaches 1.91 T at a gap of 3 mm in case of FELs applications. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. A dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature has been designed and assembled inside the vacuum chamber. The results of the magnetic measurements at low temperature and at room temperature are compared. The CPMU has been installed and commissioned in the storage ring.
    Journal of Physics Conference Series 03/2013; 425(3):032019.
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    ABSTRACT: The aim of the Femto-Slicing project at SOLEIL is to generate 100 fs X-rays pulses on two beamlines, CRISTAL and TEMPO, for pump-probe experiments in the hard and soft X-rays regions. Two fs lasers are currently in operation on TEMPO and CRISTAL for pump-probe experiments on the ps time scale enabling time resolved photoemission and photodiffraction studies. The Femto-Slicing project is based on the fs laser of the CRISTAL beamline, which can be adjusted to deliver 3 mJ pulses of 30 fs duration at 2.5 kHz. The laser beam will be separated in three branches: one delivering about 2 mJ to the modulator Wiggler and the other ones delivering the remaining energy to the TEMPO and CRISTAL experiments. This layout will yield natural synchronization between IR laser pump and X-ray probe pulses, only affected by jitter associated with beam transport. In this paper, we present the current status of the Femto-Slicing project at SOLEIL, with particular emphasis on the expected performance, and the design and construction of the laser beam transport and the diagnostics implementation.
    Journal of Physics Conference Series 03/2013; 425(7):072022.
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    ABSTRACT: We report measurements demonstrating the concept of the free-electron laser (FEL) superradiant cascade. Radiation (lambda_rad = 200 nm) at the second harmonic of a short, intense seed laser pulse (lambda_seed = 400 nm) was generated by the cascaded FEL scheme at the transition between the modulator and radiator undulator sections. The superradiance of the ultrashort pulse is confirmed by detailed measurements of the resulting spectral structure, the intensity level of the produced harmonics, and the trend of the energy growth along the undulator. These results are compared to numerical particle simulations using the FEL code GENESIS 1.3 and show a satisfactory agreement.
    Physical Review Letters 01/2013; 110:044801. · 7.73 Impact Factor
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    ABSTRACT: At SOLEIL, Insertion Devices (IDs) performances are first evaluated with the electron beam commissioning then by the study of the radiation properties with the beamline. Spectra calculated from magnetic measurements with Synchrotron Radiation Workshop code and the ones measured on the beamline are compared. Even and odd harmonics width are measured and spatial distributions at a fixed energy are checked for several gap and phase values. Radiation properties are detailed in the cases of a 20 mm period planar in-vacuum undulator (U20), a 42 mm period APPLE II device (HU42) and a 80 mm period APPLE II device (HU80) generating non periodic magnetic fields components.
    Journal of Physics Conference Series 01/2013; 425(3):032015.
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    ABSTRACT: SOLEIL, a 2.75 GeV third-generation synchrotron light source [1], is presently delivering photons to 24 beamlines for users in five different filling patterns with top-up injection. The 430 mA multibunch (with three successive quarters filled; i.e., 312 out of 416 bunches) is complemented with time-resolved (hybrid multibunch, eight bunches and single bunch) and 4-2 ps bunch-length low-alpha modes. Even shorter bunches will be available at the end of 2013 with the forthcoming Femto-slicing project. With the continuous improvements of transverse beam position (200 nm RMS in the vertical plane) and the understanding of collective effects, the beam current and the stability provided to the beamlines have been steadily increased. New exotic modes of operation and upgrades of the optics to reduce the 3.9 nm.rad horizontal emittance are being studied.
    Synchrotron Radiation News 01/2013; 26(3).
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    ABSTRACT: In storage rings, short electron bunches can produce an intense THz radiation called Coherent Synchrotron Radiation (CSR). The flux of this emission between 250 and 750 GHz is very advantageous for spectroscopy, but intensity fluctuations lead to artifacts in the FTIR spectra and, until now, prevented the use of CSR for high-resolution measurements. At SOLEIL, we found stable CSR conditions for which the signal-to-noise ratio (S/N) allows for measurements at high resolution. Moreover, we developed an artifact correction system, based on a simultaneous detection of the input and the output signals of the interferometer, which allows improving further the signal-to-noise ratio. The stable CSR combined with this ingenious technique allowed us to record for the first time high-resolution FTIR spectra in the sub-THz range, with an exceptional S/N of 100 in a few hours.
    Proc SPIE 10/2012;
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    ABSTRACT: Instead of seeding a free electron laser in the UV-VUV with a frequency doubled or tripled laser or high order harmonics, here we investigate and present the first results on seeding the SPARC-FEL with a fibre-based tunable ultraviolet source. The seed generation system consists of a kagome hollow-core photonic crystal fibre filled with noble gas. Diffraction-limited DUV pulses of >50 nJ and fs-duration which are continuously tunable from below 200 nm to above 300 nm are generated. The process is based on soliton-effect self-compression of the pump pulse down to a few optical cycles, accompanied by the emission of a resonant dispersive wave in the DUV spectral region. The quality of the compression highly depends on the pump pulse duration, and ideally, pulses <60 fs should be used. Our experimental set-up and associated GENESIS simulations enable us to study the utility of the seed tunability, and the influence of the seed quality, on the performance of the SPARC-FEL in the 200-300 nm range.
    34th Intern. Free-Electron Laser Conference; 08/2012
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    ABSTRACT: A new Electromagnetic/Permanent Magnets Helical Undulator (EMPHU), with a 65 mm magnetic period is under construction at SOLEIL for providing a rapid switching at 5 Hz of the photon polarization required to perform dichroism experiments. The vertical field is produced by coils fed by a fast switching power supply, with a maximum current of 350 A and a polarity switching time shorter than 100 ms. The coils consist of copper sheets shaped by water jet cutting. 25 layers of copper are stacked together. The current flows in 16 layers and nine of them are cooled with thermal drain to a water piping. The current-regulated power supply, in-house developed , should be able to operate in the 4 quadrant with a 50 ppm current resolution over the full scale. It is complemented by eight power supplies for the correction coils required to provide dynamics correction of the field integrals. The horizontal field is generated by NdFeB permanent magnets. The designed vertical and horizontal first harmonic field values in the helical configuration reach 0.24 T at the minimum 14.7 mm gap. The magnetic design, the magnetic measurements (DC and AC) and the correction schemes are described.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):4102004-4102004. · 1.20 Impact Factor
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    ABSTRACT: The intense Coherent Synchrotron Radiation emitted in the Terahertz range by relativistic electron bunches circulating in a storage ring is an attractive source for spectroscopy. Its stability is related to the electron bunch dynamics, and can exhibit a bursting behavior resulting from the irregular presence of micro-structures in the bunch. We evidence here the existence of two thresholds in the electron bunch spatio-temporal dynamics, associated with different levels of Terahertz signal fluctuations, with increasing number of electrons. The first threshold indicates the presence of micro-structures drifting in the bunch profile, and the second one appears when those micro-structures are strong enough to persist after about half a revolution period of the electron-bunch in the phase-space. Their prediction thanks to numerical simulations are confirmed by experiments at the synchrotron SOLEIL.
    EPL (Europhysics Letters) 05/2012; 98(4):40006. · 2.26 Impact Factor
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    ABSTRACT: Higher order harmonic generation in a free-electron laser amplifier operating in the superradiant regime [R. H. Dicke, Phys. Rev. 93, 99 (1954).] has been observed. Superradiance has been induced by seeding a single-pass amplifier with the second harmonic of a Ti:sapphire laser, generated in a β-Barium borate crystal, at seed intensities comparable to the free-electron laser saturation intensity. Pulse energy and spectral distributions of the harmonics up to the 11th order have been measured and compared with simulations.
    Physical Review Letters 04/2012; 108(16):164801. · 7.73 Impact Factor
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    ABSTRACT: We show that the macropulse instability affecting storage ring free-electron laser (FEL) oscillators can be suppressed using a delayed optical feedback. The principle, known as coherent photon seeding, consists in reinjecting a very small part of the laser output in the laser cavity in order to create a new deterministic solution. The feedback is shown to be efficient over a large range of the detuning parameter of the FEL cavity, even with very small fractions of reinjected power (<10-8 here from inside to inside the cavity). The experiments have been performed on the UVSOR-II storage ring free-electron laser.
    Physical Review Special Topics - Accelerators and Beams 04/2012; 15(4). · 1.57 Impact Factor

Publication Stats

900 Citations
356.31 Total Impact Points

Institutions

  • 2006–2014
    • SOLEIL synchrotron
      Gif, Île-de-France, France
  • 2009–2012
    • ENEA
      Roma, Latium, Italy
  • 2003–2006
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 1988–2006
    • Université Paris-Sud 11
      • Laboratoire de Photophysique Moléculaire
      Orsay, Île-de-France, France
  • 2004–2005
    • Université des Sciences et Technologies de Lille 1
      • Laboratoire de Physique des Lasers, Atomes et Molécules (PhLAM)
      Lille, Nord-Pas-de-Calais, France
  • 1996
    • The Graduate University for Advanced Studies
      Миура, Kanagawa, Japan