ENEA C.R. Frascati, Frascati (Roma)
SPARC is a single pass free electron laser test facility realized in collaboration between the main Italian research institutions and devoted to experiments of light amplification in different beam conditions. We have reached full saturation at 540nm by operating the FEL with a compressed beam obtained with "velocity bunching". The strongly chirped longitudinal phase space resulting from the compression process has been compensated by accordingly tapering the undulator gaps. Spectra with and without taper have been collected and an increase of about a factor 5 of the pulse energy in combination with spectra with a single coherence region have been detected in presence of the taper. The FEL has been operated as an amplifier and as a two stages cascade seeded with the second harmonic of the Ti:Sa driver laser generated in a crystal and with higher order harmonics generated in a gas cell. In seeded mode the cascade has been operated in saturated conditions with the observation of the third harmonic in the radiator at 67nm. High order harmonics up to th 11th at 37 nm have been observed from the seeded amplifier in deeply saturated conditions.
JASRI/SPring-8, Hyogo-ken
JAEA/Kansai, Kyoto
SOLEIL, Gif-sur-Yvette
RIKEN/SPring-8, Hyogo
The University of Tokyo, Tokyo
Keio University, Kanagawa-ken
RIKEN, Saitama
NTT Corp., Kanagawa-ken
KEK, Tsukuba
A seeded FEL is the most promised way to generate fully coherent radiation in a short-wavelength region. After the improvement of the laser and HHG system at the SCSS test accelerator, we have succeeded the amplification of the seed, for the first time, in the plateau region. The wavelength of the seed is 61.5 nm, which is the 13th harmonic of a Ti:Sa laser, and clear intensity increase and spectral narrowing by the FEL was observed. Although there still remains room for optimization of the transverse matching and synchronization of the seed, this result leads to realization of a fully coherent light source to users in VUV and soft x-ray regions.
SINAP, Shanghai
As the solid development steps towards constructing a hard X-Ray FEL in China, the SDUV-FEL was integrated at SINAP to test the FEL key technologies, and the Shanghai Soft X-ray FEL test facility (SXFEL) was proposed and will be constructed to generate 9nm FEL radiation with two-stage cascaded HGHG scheme. Recently a design study on a compact hard X-ray FEL was initiated aiming at constructing this XFEL facility within the SSRF campus. In this paper, the progress in SDUV-FEL, including the recent results of SASE, HGHG and ECHO experiments, is presented and the preliminary design of the SXFEL test facility and the design consideration of a compact X-Ray FEL based on a C-band linac are described.
ELETTRA, Basovizza
Diamond, Oxfordshire
University of Nova Gorica, Nova Gorica
JLAB, Newport News, Virginia
LBNL, Berkeley, California
ENEA C.R. Frascati, Frascati (Roma)
DEEI, Trieste
MAX-lab, Lund
Some experiences have recently been collected from the FERMI@elettra Free Electron Laser first bunch compressor area. This includes a magnetic compressor, diagnostics for the characterization of the longitudinal and transverse phase space and suitable optics for matching to the downstream part of the linac. We report on the beam dynamics investigations in comparison with the modeling as well as the high level software control that has allowed this experience.
LBNL, Berkeley, California
Numerical electromagnetic simulation of some systems containing charged particles with highly relativistic directed motion can by sped up by orders of magnitude by choice of the proper Lorentz-boosted frame*. A particularly good application for boosted frame calculation is short wavelength FEL simulation. In the optimal boost frame (i.e., the ponderomotive rest frame), the red-shifted FEL radiation and blue-shifted undulator field have identical wavelengths and the number of required time-steps for fully electromagnetic simulation (relative to the laboratory frame) decreases by a factor of gamma squared. We have adapted the WARP code** to apply this method to several FEL problems including coherent spontaneous emission from prebunched e-beams, strong exponential gain in a single pass amplifier configuration, and FEL emission from e- beams in undulators with multiple harmonic components. We discuss our results and compare with those obtained using the "standard" FEL simulation approach which applies the eikonal and wiggler-period-averaging approximations.
* J.-L. Vay, Phys. Rev. Lett. 98, 130405 (2007).
** D.P. Grote, A. Friedman, J.-L. Vay, and I. Haber, AIP Conf. Proc. 749, 55 (2005).
BNL, Upton, Long Island, New York
Stony Brook University, Stony Brook
We solve linearized Vlasov-Maxwell FEL equations for a 3-D perturbation in an infinite electron beam with Lorentzian energy distributions using paraxial approximation. We present analytical solutions for various initial perturbations and discuss the effect of optical guiding in such system.
Universita' degli Studi di Milano, Milano
INFN/LNF, Frascati (Roma)
ENEA C.R. Frascati, Frascati (Roma)
We have written and numerically solved a set of 1-d FEL equations for electrons and radiation without the need of the slowly varying envelope approximation (SVEA). The equations, which take into account both forward and backward waves, have been applied to the case of a very short beam, as long as few wavelenghts, and to the case of long beams with short density modulations.
CENBG, Gradignan
CESTA, Le Barp
Several years ago Andrews and Brau * presented a two-dimensional (2-D) theory for the production of coherent Smith-Purcell radiation by an initially continuous beam. An essential component of their analysis was the dispersion relation for a lamellar grating (i.e., rectangular profile) relating frequency and axial wave number k. Both simulations and an experiment performed at CESTA ** using a wide beam have confirmed the validity of their approach. However, all gratings are three-dimensional objects, and one may ask what modifications of the theory might be necessary. We present here our solution to the problem, which assumes a progressive wave in the direction of the grooves, with wave number q. A surprisingly simple modification of the Andrews and Brau 2-D dispersion relation is found. We have extensively tested our theory, both with simulations using the 3-D PIC code "MAGIC", and with measurements of the properties of the surface wave on the CESTA grating made using a network analyzer. Extremely good agreement is found, both with and without sidewalls on the grating.
* H. L. Andrews and C. A. Brau, Phys. Rev. ST Accel. Beams 7, 070701 (2004).
** J. Gardelle, L. Courtois, P. Modin and J.T. Donohue, Phys. Rev. ST Accel. Beams 12, 110701 (2009).
USTRAT/SUPA, Glasgow
An unaveraged 3D model of the FEL has been developed which can model variably polarised undulators. The radiation field polarisation is self-consistently driven by the electron dynamics and is completely variable. This paper describes both physical model and computational code.
BINP SB RAS, Novosibirsk
The new approach for the SASE radiation properties calculation was proposed recently. It is based on the use of BBGKY chain of equations, adapted for FEL. In fact, it is the only known logically correct way to describe the SASE phenomenon. The two-time correlation function is necessary for calculation of averaged SASE spectrum. The solution of the correlation function equation for linear stage of SASE process is obtained.
DESY, Hamburg
With the present undulator (planar, period 2.73 cm, peak field 0.486 T) the minimum wavelength of 4.5 nm at FLASH is determined by the maximum electron beam energy of approximately 1.2 GeV. On the other hand, many perspective user applications require shorter wavelength radiation and circular polarization. In this paper we perform analysis of a helical afterburner for generation of short wavelength, helically polarized radiation. We consider two options, operation of the afterburner at the second (frequency doubler), and the fourth (frequency quadrupler) harmonics. Since even harmonic of the SASE FEL radiation are suppressed, there is no linearly polarized background radiation from the main undulator. Our simulations show that relatively high level of the radiation power can be achieved in the afterburner, about 60 MW in the frequency doubler, and about 5 MW in the frequency quadrupler.
DESY, Hamburg
This report deals with the analysis of the parameter space of the European XFEL. An impact of two potential changes is analyzed: consequences of the operation with low-emittance beams, and decrease of the driving energy of the accelerator from 17.5 to 14 GeV.
DESY, Hamburg
Wavelength range of high scientific interest refers to K- and L- absorption edges of magnetic elements which spans from 2.5 nm to 1.4 nm (500 - 900 eV). This wavelength range can be partially covered by SASE3 at the European XFEL, from 1.6 nm and down when operating at the nominal energy of 17.5 GeV. Operation at the reduced energy would allow to cover complete wavelength range of interest. Currently SASE3 is a planar device producing linearly polarized radiation. On the other hand, it is important to have circular polarization for experiments with magnetic samples. Solution of the problem of polarization is installation of an afterburner generating circularly polarized radiation. This can be helical afterburner or crossed-planar afterburner operating at the fundamental or double frequency. Here we present the results for a helical afterburner operating at the double frequency.
DESY, Hamburg
The capability of the free-electron laser (FEL) user facility FLASH at DESY was expanded by several upgrades during the shutdown in 2009/2010. A key extension is the installation of a third-harmonic (3.9 GHz) RF system for the linearization of the longitudinal phase space in front of the bunch compressors. In order to control the bunch compression and make full use of the third-harmonic RF system, a new diagnostic section for the measurements of sliced bunch parameters directly in front of the undulators was designed and commissioned. In this paper, we describe the beam imaging systems and their optical performance. The achievable resolution of both time and energy is shown and compared to the design values. First measurements of the linearized longitudinal phase space with high resolution are presented.
SLAC, Menlo Park, California
DESY, Hamburg
For a SASE-FEL, the FEL pulse energy fluctuates from shot to shot, because the lasing process starts up from shot noise. When operating in the exponential growth regime, the radiation exhibits the properties of completely chaotic polarized light. Hence, the probability distribution of the FEL pulse energy follows a gamma distribution. Based on the measurement of such a distribution function, one can calculate the average number of ‘degrees of freedom’ or ‘modes’ in the radiation pulse. Thus, one can measure the FEL pulse temporal duration. In this paper, we report experimental results at LCLS. Measurements are conducted for both nominal charge (250 pC) and low charge (20 pC) cases. For both cases, results are obtained for different undulator lengths and various electron peak current settings.
SLAC, Menlo Park, California
MIT, Cambridge, Massachusetts
The Linac Coherent Light Source has achieved stable operation at x-ray wavelengths of 20-1.2 Angstrom with peak brightness many orders of magnitude beyond conventional synchrotron sources. Understanding transverse coherence properties of such a SASE source is of great practical importance for user experiments. Based on a fast Monte Carlo algorithm, we present numerical analysis of the LCLS coherence properties for the simulated radiation fields at different wavelengths and bunch charges.
PSI, Villigen
The proposed SwissFEL project is an X-ray Free-Electron Laser, which operates down to a wavelength of 1 Ångstrom. In comparison to other XFELs (LCLS, SCSS and European XFEL) SwissFEL has the lowest beam energy of 5.8 GeV. Therefore a short period in vacuum undulator (15 mm) and a low beam emittance is required for maximum overlap between the electron beam and the fundamental FEL mode and a sufficient degree of transverse coherence at the saturation point. We present the numerical analysis of the radiation field properties along the undulator with an emphasis on the degree of coherence at saturation and undulator exit.
PSI, Villigen
The coupled system of radiation interacting with a co-propagating electron beam within an undulator of an FEL exhibits many degrees of freedom. Only in an idealized and simplified model can the FEL equations be solved analytically and a more complete description requires numerical methods. Therefore numerical codes have been developed along with the advances in FEL theory, starting from a simple 1 D model to today's fully time-dependent 3D simulations, utilizing large scale parallel computers. This presentation gives a brief history of FEL simulation and addresses the remaining challenges in FEL modeling which we hope to solve in the near future.
DESY, Hamburg
Start-up of the amplification process in x-ray FELs from the shot noise in the electron beam defines a specific behavior of longitudinal and transverse coherence properties of the radiation. Particularly important is the case of an x-ray FEL optimized for maximum gain of the fundamental radiation mode. Applying similarity techniques to the results of numerical simulations allowed us to find universal scaling relations for the main characteristics of an optimized X-ray FEL operating in the saturation regime: efficiency, coherence time and degree of transverse coherence. We find that with an appropriate normalization of these quantities, they are functions of only the ratio of the geometrical emittance of the electron beam to the radiation wavelength. Statistical and coherence properties of the higher harmonics of the radiation are highlighted as well.
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
The cooperative spontaneous emission from a bunch of particulate dipole radiators (e.g. excited atoms) can be enhanced (super-radiance) or suppressed (sub-radiance) by proper phasing of the radiators[1] Analysis and 3-D simulation of collective interaction micro-dynamics in a drifting e-beam, reveal a process of homogenization of the particles distribution and suppression of the beam current shot-noise[2]. Consequently, such a beam would exhibit Dicke’s kind of spontaneous emission sub-radiance when injected into a FEL. With present state of the art technology, suppression and control of FEL SASE power can be attained at optical frequencies up to the UV. A theory will be presented on the implications of this beam noise control on the attainable coherence level of seed injected FELs. It is shown that when the beam current shot-noise is suppressed, the coherence of the FEL is limited by the beam energy spread. The fundamental theoretical limit of FEL coherence, analogously to conventional lasers[3], is found to be, the quantum noise limit. This would be attainable only if the beam energy spread can be reduced below the level of the photon emission energy.
[1] R. H. Dicke, Phys. Rev. 93, 99 (1954).
[2] A.Gover, E.Dyunin, Phys. Rev.Lett., {10}2, 154801, (2009).
[3] A.L.Schawlow and C.H.Townes, Phys. Rev., 112, 1940
USTC/NSRL, Hefei, Anhui
The harmonics field effect of planar undulator on Free-Electron Laser (FEL) harmonic generation has been analyzed. For both the linear and the nonlinear harmonic generation, the harmonic generation fraction can be charactered by the coupling coefficients. The modification of coupling coefficients is given when third harmonics field component exist, thus the enhancement of the harmonic radiation can be predicted. With the third harmonics magnet field being 30 percent of the fundament, for both the small signal gain and the nonlinear harmonic generation in high gain, the intensity of third-harmonic radiation can maximally be doubled.
UVSOR, Okazaki
Coherent synchrotron radiation (CSR) has been intensively investigated because of its potential ultrahigh power in the terahertz (THz) region. CSR is emitted not only from short electron bunches but also from bunches with longitudinal microstructure of radiation wavelength scale. Laser slicing is a technique for creating sub-mm dip structure on electron bunches circulating in a storage ring. Such a bunch emits broadband CSR of sub-ps duration. More generally, in principle, one can produce arbitrary density structures by the laser electron interaction. As a useful example, periodic density structures can be produced by using amplitude-modulated laser pulses. The period of the structure can be varied by changing the period of the amplitude modulation. The first successful demonstration was conducted at UVSOR-II. The electron bunch with the periodic density modulation emitted monochromatic and tunable THz-CSR in a bending magnet. In this talk, some latest results from the THz CSR experiments with laser modulation technique at UVSOR-II will be presented, including the direct measurement of the CSR electric field and beam dynamics of the micro-density structures on electron bunches.
Some results are from joint researches by UVSOR, PhLAM, Nagoya U., Kyoto U. and Osaka U
ELETTRA, Basovizza
CNR - IMIP, Trieste
University of Nova Gorica, Nova Gorica
Università degli Studi di Trieste, Trieste
European XFEL GmbH, Hamburg
The paper will report about the last achievements of the Elettra storage-ring FEL. The latter include: a) a noticeable improvement of the source performance (generation of coherent radiation at 87 nm, attainment of a very good shot-to-shot stability); b) general FEL studies, relevant to single-pass devices (characterization of the angular distribution of harmonic emission, analysis of the frequency pulling effect), and c) first user experiments (pump-probe on gas phase and solid-state samples).
SINAP, Shanghai
The echo-enabled harmonic generation (EEHG) scheme has remarkable efficiency for generating high harmonic microbunching with a relatively small energy modulation. A proof of principle experiment of EEHG scheme is under commissioning at Shanghai deep ultraviolet (SDUV) free electron laser (FEL) facility, where the third harmonic of the 1047nm seed laser is expected to be amplified in the 9m long radiator. Recently, to explore the advantage of EEHG scheme, higher order harmonics are under consideration seriously in SDUV-FEL. In this paper, several methods for measuring 9~15th order harmonic microbunching are comparatively analyzed. Study shows that, in comparison with the coherent transition radiation (CTR) and coherent synchrotron radiation (CSR) based diagnostics, the coherent harmonic radiation (CHR) of the radiator undulator would be a more feasible way to characterize the high order harmonic microbunching in EEHG operation of SDUV-FEL.
SLAC, Menlo Park, California
LLNL, Livermore, California
The Linac Coherent Light Source (LCLS) is a Free Electron Laser (FEL) operating with a fundamental wavelength ranging from 1.5-0.15 nm. Characterization of the higher harmonics present in the beam is important to users, for whom harder X-rays can either extend the useful operating wavelength range or represent a background to measurements. We present here measurements of the power in both the second and third harmonics.
FZD, Dresden
In order to decrease the average radiation power of the Rossendorf free-electron laser FELBE, as required for certain experiments (high pulse energies but moderate or low average power), the FEL repetition rate can be reduced from 13 MHz to 1 kHz. To this end, plasma switching of FEL radiation pulses was demonstrated for cw operation. The plasma switch is based on the principle of photo-induced reflectivity by an optically excited electron-hole plasma. Germanium or silicon serves as semiconductor material for the switch. The semiconductor was illuminated by a Nd:YAG laser amplifier system (1 kHz, wavelength {10}64 nm, pulse duration16 ps, 1Watt), generating an electron-hole plasma on the front surface of the semiconductor. To integrate this plasma-switch into the existing experimental set-up we build an additional by-pass to the Germanium or Silicon slab which is under Brewster’s angle. To get a high contrast in the switched beam we adjust the polarization plane of the incoming beam to the right direction by using an additional polarization rotator. We will report on first results at different wavelength. Submitted as a poster to the FEL 2010 conference.
SLAC, Menlo Park, California
USTC/NSRL, Hefei, Anhui
Lots of applications with mm wave need very high power (from tens of kW to MW), such as surface processing of metals and ceramics, heating magnetically confined plasma in thermonuclear fusion reactors, isotope separation and so on. Recently developed gyrotrons can provide up to 1 MW CW mm-wave source, however there are a number of limitations, needs of supper conducting magnet, cathode lifetime degradation because of very high current, almost approaching the upper limit of their power and frequency capabilities, and so on. It is thought that the electrostatic accelerator FEL (EA-FEL) will be a promising high power IR-mm source, because of its high average power generation, high-energy conversion efficiency and high spectral purity. The property of an EA as a high quality e-beam source for a FEL is crucial for attaining high brightness spontaneous emission radiation. The unique features of EA-FELs make them naturally fitting for a variety of applications in the present and in the near future. And few high power mm-IR EA FEL facilities have been successfully built around world. Here an EA of 3 MeV with beam current of 2 A is studied for a high average power (kWs) mm-THz source
CENBG, Gradignan
CESTA, Le Barp
At FEL 2009, we presented experimental results on coherent Smith-Purcell obtained at CESTA in the microwave frequency domain * . Those results strongly supported the two-dimensional theory proposed by Andrews and Brau some years ago ** , and were consistent with simulations performed with the PIC code "MAGIC". That experiment used a large current, 200 A, for a grating of width 10 cm. In a follow-up experiment, emittance slits were used to reduce the current to as low as 2 A, with a quite thin, flat, and wide beam. The gain as a function of current and also of vertical beam position was measured in detail. In particular, the start current for our set-up was found. In parallel, 2-D simulations of the experiment with "MAGIC" were extensively compared with the experimental results. Very good agreement between simulations and experiment is obtained. This lends confidence that simulations of a scaled-down version of our experiment will be a reliable guide for Terahertz frequency coherent Smith Purcell experiments. Such simulations suggest that radiation in the range 100-200GHz should be feasible.
* J. T. Donohue, J. Gardelle, L. Courtois and P Modin, Proceeedings of FEL 2009.
** H. L. Andrews and C. A. Brau, Phys. Rev. ST Accel. Beams 7, 070701 (2004).
Vanderbilt University, Nashville, TN
LANL, Los Alamos, New Mexico
Recently, the theory of the Smith-Purcell free-electron laser has been confirmed by the experiments of Andrews, et al. [1], and of Gardelle, et al. [2] In addition, high-brightness cathodes have been developed using field-emission from arrays of diamond pyramids [3]. By combining these developments we have designed an ultracompact (“shirt-pocket”) free-electron laser and we have begun constructing the device. The electron beam comprises an array of 2-micron diamond-pyramid field emitters that overfills an einzel lens 200-microns wide and 1-mm long, fabricated using ps-laser machining. The beam is accelerated to 10 keV and focused in the short dimension over a lamellar metal grating with a period of 150 microns and a length of 10 mm. The predicted start current at a wavelength of {10}84 microns is 11 mA, which corresponds to 9 A/cm2 at the cathode, before focusing. We have tested cathodes at 30 A/cm2 and 600 mA total current; higher current density should be possible.
[1] Andrews, et al, JAP {10}5, 024904 (2009)
[2] Andrews, et al, PRST-AB 12, 080703 (2009)
[3] Gardelle, et al, PRST-AB 12, 110701 (2009)
[4] Jarvis, et al, JVSTB 27, 2264 (2009)
[5] Jarvis, Thesis, 2009
LBNL, Berkeley, California
ANL, Argonne
The oscillator package within the GINGER FEL simulation code has now been extended to include angle-dependent reflectivity properties of Bragg crystals. Previously, the package was modified to include frequency-dependent reflectivity in order to model x-ray FEL oscillators[*] from start up from shot noise to saturation. We will present a summary of the algorithms used for modeling the crystal reflectivity and radiation propagation outside the undulator, discussing various numerical issues relevant to the domain of high Fresnel number and efficient Hankel transforms. We give some sample XFEL-O simulation results obtained with the angle-dependent reflectivity model, with particular attention directed to the longitudinal and transverse coherence of the radiation output.
[*] R.R. Lindberg et al., submitted to PRST-AB, 2010.
IAP/RAS, Nizhny Novgorod
Periodical Bragg structures can be considered as an effective way of controlling the electromagnetic energy fluxes and provision of spatial coherence of radiation in the electron devices with oversized interaction space. Advance of FEL with 2D distributed feedback [*] into the terahertz waveband can be achieved basing on a two-mirror hybrid scheme in which a new modification of Bragg reflector exploiting the coupling between the two counter-propagating waves and a cutoff mode is used as an upstream mirror. This reflector provides effective mode selection over the "narrow" transverse coordinate directed between the plates forming planar waveguide. Synchronization of radiation from a sheet electron beam over the "wide" coordinate can be obtained by 2D Bragg structures providing 2D distributed feedback used as a downstream mirror. Both upstream and downstream Bragg reflectors are compatible with intense beam transport. Thus the advantage of suggested scheme against traditional THz band FEL [**] is the possibility of realization of long-pulse (microsecond) generation regimes with high (mulimegawatt) output power level.
*Ginzburg N.S., Peskov N.Yu., Sergeev A.S. // Optics Сommun. 1994. V.112. P.151.
**G.R.Neil, C.L.Bohn, S.V.Benson, et al. // Phys. Rev. Lett.2000. V.84. P.662.
Falcon Analytics, Netanya
BINP SB RAS, Novosibirsk
HZB, Berlin
Lithography over the last years has been actively used to produce more compact and powerful computers. The dimensions of the microchips still require shorter wavelengths of light to enhance future ‘nano’ scale production. It is envisaged that 193 nm lithography is beginning to reach its limit. Extreme Ultraviolet (EUV) lithography of 13.5 nm wavelength could provide a solution for the next step of miniaturization, however presently no light source exists with sufficient average power. We report here results of a study, showing the feasibility of a FEL EUV source driven by a multi-turn superconducting energy-recovery linac (ERL). The proposed 40x20 m2 facility will be located underground for radiation safety purposes. With MW-scale consumption from the power grid it is estimated to provide 5 kW of average EUV power. We elaborate in some detail the SASE option, which is presently technically feasible, however regenerative-amplifier option should be also kept in mind. The proposed design is based on a short-period (2-3 cm) undulator. The corresponding electron beam energy is about 0.6-0.8 GeV. The proposed accelerator consists of photoinjector, booster, and a multi-turn ERL.
European XFEL GmbH, Hamburg
DESY, Hamburg
We describe a novel single-bunch self-seeding scheme to obtain highly monochromatic X-rays from a baseline XFEL undulator. For a single-bunch self-seeding scheme a long electron beam bypass is required, implying modifications of the baseline undulator configuration. We avoid such requirement exploiting a single crystal in the transmission direction. The method can be realized using a temporal windowing technique, requiring a magnetic delay for the electron bunch only. The proposed setup is extremely simple and composed of as few as two simple elements: the crystal and the short magnetic chicane, which accomplishes three tasks by itself. It creates an offset for crystal installation, removes the electron micro-bunching from the first undulator, and acts as a delay line for temporal windowing. Using a single crystal installed within a short magnetic chicane in the baseline undulator, it is possible to decrease the bandwidth of the radiation well beyond the XFEL design down to 10-5. The installation of the magnetic chicane does not perturb the undulator focusing system and does not interfere with the baseline mode of operation.
SLAC, Menlo Park, California
It is well known that harmonic generation in HGHG amplifies the shot noise in the beam. In this work, we introduce a framework for theoretical description of the noise dynamics in such a device consisting from un undulator-modulator and a chicane. We propose to consider the interaction of particles in the modulator-undulator through the radiation field as a source which modifies the noise level in the beam. The coherent part of this interaction is responsible for the FEL process while the random part introduces correlations in the particle's positions and modifies the noise properties of the beam. We develop a 1D version of the method and apply it to the HGHG seeding mechanism.
SLAC, Menlo Park, California
The success of LCLS has opened up a new era of x-ray sciences. An upgrade to LCLS is currently being planned to enhance its capabilities. In this paper we study the feasibility of using the echo-enabled harmonic generation (EEHG) technique to generate narrow bandwidth soft x-ray radiation in the proposed LCLS-II soft x-ray beam line. We focus on the conceptual design, the technical implementation and the expected performances of the echo-seeding scheme. We will also show how the echo-seeding scheme allows one to generate two color x-ray pulses with the higher energy photons leading the lower energy ones as is favored by the x-ray pump-probe experiments.
UVSOR, Okazaki
Nagoya University, Nagoya
Sokendai - Okazaki, Okazaki, Aichi
Coherent Harmonic Generation Free Electron Laser (CHG-FEL)* ** is a short pulse and coherent radiation source in vacuum ultra-violet regime. A measurement of CHG-FEL spectrum*** has been done and sidebands in spectrum were observed under an over-bunching condition. The measurement was done with chirped seed laser to avoid strong over-bunching of electron beam and to obtain larger pulse energy for high signal to noise ratio. In the paper ***, however, the seed laser chirping was not taken into account in the numerical analysis and the numerical results qualitatively agreed with experimental results but quantitatively not. We consider that the discrepancy was caused by the chirping property of the seed laser, and thus we have developed a time dependent simulation code which can deal the effect of seed laser chirping. Results of the code qualitatively agreed well with the shape of measured spectrum, not only bandwidth but also the sideband structure. And the code was used to evaluate the temporal and spectral property of CHG-FEL seeded by a chirped laser. The code revealed the spectral widening and chirped property of CHG-FEL pulse when the CHG-FEL is driven by a chirped seed laser.
* L. H. Yu et al., Phys. Rev. A 44, 5178 (1991).
** G. D. Ninno et al., Phys. Rev. Lett. {10}1, 053902 (2008).
***M. Labat et al., Phys. Rev. Lett. {10}2, 014801 (2009).
LBNL, Berkeley, California
SLAC, Menlo Park, California
In this paper, we propose a scheme to generate atto-second to femto-second tunable water window (~2-4 nm) coherent X-ray radiation for future light source applications. This scheme improves the previously proposed modulation compression method [1] by using a 10 pC, 100 μm electron beam at 2 GeV energy, a 200 nm seeding laser, an X-band linac, two opposite sign bunch compressors, and a long wavelength laser to generate a prebunched, kilo-Amper current beam with a modulation wavelength within the water window. Such a beam will be sent into an undulator to generate a short pulse transverse and temporal coherent soft X-ray radiation. The requirement of initial seeding laser power is small. The electron beam at the entrance of undulator can have sub micron normalized emittance.
[1] J. Qiang, "Short wavelength seeding through compression for free electron lasers," NIM-A,10.{10}16/j.nima.2010.04.053, 2010.
ENEA C.R. Frascati, Frascati (Roma)
INFN/LNF, Frascati (Roma)
Istituto Nazionale di Fisica Nucleare, Milano
CEA, Gif-sur-Yvette
SOLEIL, Gif-sur-Yvette
Università di Roma II Tor Vergata, Roma
LUXOR, Padova
LOA, Palaiseau
UCLA, Los Angeles, California
INFN-Roma, Roma
Rome University La Sapienza, Roma
ISM-CNR, Rome
SPARC is a single pass free electron laser test facility realized in collaboration between the main Italian research institutions and devoted to experiments of light amplification in different beam conditions. While the laser was commissioned in self amplified spontaneous emission (SASE) mode during the last year, the operation in seeded mode has been recently demonstrated. The amplifier has been seeded with the second harmonic of the Ti:Sa driver laser generated in a crystal and with higher order VUV harmonics generated in a gas cell. The comparison between seeded and unseeded FEL emission will be discussed. The laser has been also operated in a new SASE configuration with a strongly chirped longitudinal e-beam phase space resulting from the RF compression. The chirp has been compensated by accordingly tapering the undulator gaps. Spectra with and without taper have been collected. An increase of about a factor 5 of the pulse energy in combination with spectra with a single longitudinal coherence region have been detected in presence of the taper. The combination of the chirp with the input seed is under study.
Uni HH, Hamburg
DESY, Hamburg
Since 2004, the free-electron laser FLASH at DESY has operated in the Self-Amplified Stimulated Emission mode (SASE), delivering gigawatt pulses with wavelengths between 6.5 nm and 40 nm in the femtosecond domain. In 2009, DESY installed an additional radiofrequency module for controlling the phase space of the electron bunches that gives the possibility to generate bunches with high peak currents (~kA), but ten times larger pulse durations (~250 fs) compared to the previous configuration. The relaxed timing requirements of the new configuration make it possible to externally seed FLASH with high-order harmonics of an optical laser below 40nm generated in a gas target (sFLASH). Because in this case amplification is triggered within the seed pulse length instead of starting from shot-noise as in the SASE process, spikes in the temporal/spectral pulse profiles should be absent and the temporal jitter should be eliminated. In this contribution the present status of the sFLASH photon diagnostics including first commissioning will be discussed.
BNL, Upton, Long Island, New York
We report the first experimental characterization of the wideband tunability of an ultrafast laser seeded FEL using a short seed laser pulse (140 fs in FWHM) and a variable energy electron beam. The experiments were conducted at the NSLS SDL and the FEL output spectrum and pulse energy were measured versus the electron beam energy. A significant spectral tuning range (8%) was observed. The experiment is in good agreement with predictions using the Perseo simulation code.
DELTA, Dortmund
The storage-ring FEL at DELTA has been successfully operated with different filling patterns and temporal structures following the installation of new mirror chambers three years ago. The modulation depth of the optical-klystron spectrum was used to measure the electron energy spread. The measured FEL output power at high beam currents strongly exceeded the predictions of the low-gain model. This could be explained by the microwave instability being damped significantly by the onset of the FEL interaction. In the near future, the optical klystron will be seeded by external ultrashort laser pulses in order to produce highly coherent, intense and ultrashort VUV pulses by coherent harmonic generation (CHG). Additionally, coherent ultrashort THz pulses will be generated several meters downstream of the optical klystron by the laser-induced gap in the electron bunch.
FZD, Dresden
Two free-electron lasers (FELBE; 4-21 μm and 18-250 μm, respectively) have been in routine user operation for a wide range of IR experiments at the radiation source ELBE in the Forschungszentrum Dresden-Rossendorf for several years. The lasers are driven by a superconducting RF linac that permits the generation of a cw-beam with a repetition rate of 13 MHz and a high average beam power. In addition, operation in a macropulse modus (pulse duration >100 μs, repetition rate ≤ 25 Hz) is possible. A few important experiments using the cw-operation are discussed. Furthermore, an outlook is given on the experiments which use the beam of FELBE in the High Magnetic Field Laboratory Dresden (HLD). The HLD provides pulsed magnetic fields up to 60 T. It operates as a user facility since 2007.
Lund University, Division of Atomic Physics, Lund
When an intense laser field interacts with an atomic gas, nonlinear processes take place, leading to the emission of high-order harmonics of the laser radiation. In the spectral domain, a comb of odd-order harmonics is obtained,while in the temporal domain, the emission consists of a sequence of extremely short pulses of light, in the attosecond range. This talk will review the basic physics of high- order harmonic generation, the performances that can be obtained as well as some of the applications.
SLAC, Menlo Park, California
EPFL, Lausanne
ECHO-7 is a proof-of-principle echo-enabled harmonic generation FEL experiment in the Next Linear Collider Test Accelerator (NLCTA) at SLAC. The experiment aims to generate coherent radiation at 318 nm and 227 nm, which are the 5th and 7th harmonic of the infrared seed laser. In this paper we present the experimental results from the commissioning run of the completed experimental setup which started in April 2010.
DESY, Hamburg
The Free Electron Laser in Hamburg (FLASH) is a SASE FEL user facility and in addition serves as a prototype for the European XFEL. The recent upgrade of FLASH with a higher harmonic RF module opens a new possibility for ultra-short low charge operation. The advantage of small transverse emittance at low charges can be used only with strong, linearized bunch compression. At this report we consider simulations of the beam dynamics at low charges and estimate the expected properties of the radiation at FLASH and the European XFEL. We present first experimental results at FLASH.
Diamond, Oxfordshire
JAI, Oxford
The production of short pulse radiation of 1fs or below would open up many new areas of research. Saldin et al recently proposed a scheme to generate such pulses, in which a laser pulse consisting of only a few optical cycles is used to give a short energy chirp to the electron bunch and uses a tapered undulator to compensate the chirped region. In this paper we study the application of this scheme to a soft x-ray free electron laser, including the results of fully start to end simulations and an assessment of the sensitivity to jitter.
SINAP, Shanghai
A SASE experiment has been done at SDUV-FEL(SINAP), the spontaneous radiation and exponential growth regime are observated. The results are compared with the SASE theory.
DESY, Hamburg
PSI, Villigen
Electro Optical (EO) sampling is a promising non-destructive method for measuring ultra short (sub-ps) electron bunches. The FEMTO slicing experiment at the Swiss Light Source modulates about 3 pC of the 5 nC electron bunch longitudinally. The coherent synchrotron radiation (CSR) emitted by this substructure was measured in a single shot EO technique in gallium phosphide (GaP) using pulses from an Yb fiber laser. The arrival time jitter and the broadening of this ps long structure over several turns of the synchrotron could be measured with sub-ps resolution.
European XFEL GmbH, Hamburg
DESY, Hamburg
In this paper we describe a measurement technique capable of resolving femtosecond X-ray pulses from XFEL facilities. Since these ultrashort pulses are themselves the shortest event available, our measurement strategy is to let the X-ray pulse sample itself. Our method relies on the application of a "fresh" bunch technique, which allows for the production of a seeded X-ray pulse with a variable delay between seed and electron bunch. The shot-to-shot averaged energy per pulse is recorded. It turns out that one actually measures the autocorrelation function of the X-ray pulse, which is related in a simple way to the actual pulse width. For implementation of the proposed technique, it is sufficient to substitute a single undulator segment with a short magnetic chicane. The focusing system of the undulator remains untouched, and the installation does not perturb the baseline mode of operation. We present a feasibility study and we make exemplifications with typical parameters of an X-ray FEL.
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
To measure the femtosecond bunch length (10 - {10}00 fs) of the XFEL facility at SPring-8, we developed a coherent synchrotron radiation (CSR) monitor and a streak camera system. A pyro-electric detector was employed to measure the CSR intensity, since the CSR frequency region is THz or far infra-red. The CSR source is a dipole magnet of a chicane section. For the streak camera, we used Hamamatsu FESCA200, which has 200 fs resolution. The temporal structure of the optical transition radiation (OTR) from a metal mirror is observed by this camera. By using these monitors, the bunch length dependence was measured as a function of the rf phase of an S-band accelerator upstream of the bunch compressor at the SCSS test accelerator. A strong correlation between the CSR intensity and the S-band phase was observed. The CSR intensity was small at a debunching phase and the intensity increased as the rf phase was shifted to the bunching direction. Finally, it decreased in the over-bunching region. The bunch length data from the streak camera also had the same tendency. Thus, the bunch compression characteristics were appropriately measured and were consistent with our simulation results.
PSI, Villigen
DESY, Hamburg
The spectral and angular distribution of the radiation intensity by a single and individually radiating electron is in principle different from what expected from a high density electron beam. For a given wavelength, the beam particle density modifies via a charge form factor the angular and spectral distributions characterizing the radiation emission by a single electron. In particular, under high energy and high particle density conditions, the Transition Radiation (TR) energy spectrum by an electron beam is expected to be affected by the electron-transverse-density that, at very short wavelength even in the visible, in principle - can influence the number of photons emitted at a given wavelength and their angular distribution (brightness increase with density). The investigation of such a phenomenon is relevant to beam diagnostics and to understand the bunch collective effects influencing TR emission. The status of the experimental investigation of the beam-transverse-size effects in the Optical Transition Radiation (OTR) at SLS and, in perspective, at the SwissFEL will be presented and the main formal aspects of the model predicting them will be described.
ELETTRA, Basovizza
Both absolute and relative bunch length measurement are key information for FERMI@Elettra commissioning and operation. In this paper we present the relative Bunch Length Monitor (BLM) system that has been designed and implemented at Sincrotrone Trieste. The first BLM station has been installed downstream the first bunch magnetic compressor (BC1) of FERMI@Elettra. In this paper we report about the first operation of the BLM system; it is based on the power measurement of the coherent radiations. To allow for efficient performances in the extended range of the foreseen bunch lengths for FERMI@Elettra, the system has adopted a pyro detector for coherent edge radiation from the last dipole. Also, the coherent diffraction radiation generated in a ceramic gap located downstream of BC1 is detected by a set of mm-wave diodes. The design of the system, along with its layout, is presented as well as the first measurement results obtained from the FERMI@Elettra compressed bunches.
Tohoku University, School of Scinece, Sendai
The t-ACTS (test Accelerator as Coherent THz Source) at Tohoku University will provide intense terahertz radiation employing novel sources such as an isochronous accumulator ring and a pre-bunched free electron laser. Stable production of the very short electron pulse is a key issue for the t-ACTS accelerator system, in which a thermionic RF gun is being used. Particularly observation of the longitudinal phase space of the beam extracted the gun is crucial for efficient bunch compression. Because of space charge effect, the beam has to be diagnosed within a short drift space. We have studied a novel energy spectrometer using Cherenkov radiation (Linear Focal Cherenkov ring camera, LFC-camera). Though the method is valid for the lower energy less than 3 MeV, the energy distribution can be measured immediately at the gun exit. In addition to the present status of the t-ACTS project, we describe the principle of LFC camera and discuss energy resolution, prospect of the direct measurement of the particle distribution in the longitudinal phase space as well.
BNL, Upton, Long Island, New York
OFFELO (optics-free FEL oscillator) is a brand new idea for obtaining hard X-ray wavelength radiation using an oscillator without concerning the damage to the mirror. By using an extra electron beam to transport the radiation information, OFFELO also provide pleasant flexibility compared with traditional oscillator scheme. We simulated the lasing process and carry out the saturation condition and explore other properties of this scheme.
USTRAT/SUPA, Glasgow
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Chicanes placed between undulator modules in a high-gain FEL amplifier have been shown to generate a set of axial modes that may be locked to generate attosecond pulse trains in the x-ray [1]. Using numerical simulations, it is shown in this paper that a similar system of undulator/chicane modules may be used in a low-gain FEL cavity resonator to generate a equally spaced set of frequency modes with a spacing much greater than those of the cavity. As with the high-gain FEL amplifier case, these mode can lock to generate a pulse train.
[1] N.R. Thompson & B.W.J. McNeil, Phys. Rev. Lett. 100, 203901 (2008)
DESY, Hamburg
Longitudinal space charge (LSC) driven microbunching instability in electron beam formation systems of X-ray FELs is a recently discovered effect hampering beam instrumentation and FEL operation. The instability was observed in different facilities in infrared and visible wavelength ranges. In this paper we propose to use such an instability for generation of VUV and X-ray radiation. A typical longitudinal space charge amplifier (LSCA) consists of few amplification cascades (drift space plus chicane) with a short undulator behind the last cascade. A wavelength compression could be an attractive option for LSCA since the process is broadband, and a high compression stability is not required. LSCA can be used as a cheap addition to the existing or planned short-wavelength FELs. In particular, it can produce the second color for a pump-probe experiment. It is also possible to generate attosecond pulses in the VUV and X-ray regimes. Finally, since the amplification mechanism is broadband and robust, LSCA can be an interesting alternative to self-amplified spontaneous emission free electron laser (SASE FEL) in the case of using laser-plasma accelerators as drivers of light sources.
Report DESY 10-048, March 2010
European XFEL GmbH, Hamburg
DESY, Hamburg
The magnetic gap of the baseline XFEL undulators can be varied mechanically for wavelength tuning. In particular, the wavelength range 0.1 nm - 0.4 nm can be covered by operating the European XFEL with the SASE2 undulator. The length of the SASE2 undulator (256.2 m) is sufficient to independently generate three pulses of different radiation wavelengths at saturation. Normally, if a SASE FEL operates in saturation, the quality of the electron beam is too bad for generation of SASE radiation in the subsequent part of undulator which is resonant at a few times longer wavelength. The new method of SASE undulator-switching based on the rapid switching of the FEL amplification process proposed in this paper is an attempt to get around this obstacle. Using mechanical SASE shutters installed within short magnetic chicanes in the baseline undulator, it is possible to rapidly switch the FEL photon beam from one wavelength to another, providing simultaneous multi-color capability. Combining this method with a photon-beam distribution system can provide an efficient way to generate a multi-user facility.
European XFEL GmbH, Hamburg
DESY, Hamburg
This paper describes a scheme for pump-probe experiments that can be performed at LCLS and at the European XFEL and determines what additional hardware development will be required to bring these experiments to fruition. It is proposed to derive both pump and probe pulses from the same electron bunch, but from different parts of the tunable-gap baseline undulator. This eliminates the need for synchronization and cancels jitter problems. The method has the further advantage to make a wide frequency range accessible at high peak-power and high repetition-rate. An important feature of the proposed scheme is that the hardware requirement is minimal. Our technique is based in essence on the "fresh" bunch technique. For its implementation it is sufficient to substitute a single undulator module with short magnetic delay line, i.e. a weak magnetic chicane, which delays the electron bunch with respect to the SASE pulse of half of the bunch length in the linear stage of amplification. This installation does not perturb the baseline mode of operation. We present a feasibility study and we make exemplifications with the parameters of the SASE2 line of the European XFEL.
Monash University, Faculty of Science, Victoria
ASCo, Clayton, Victoria
From a detection perspective, short wavelength phase information is lost when event sizes exceed radiation wavelengths, making conventional holography impossible above a material-dependent quantum energy limit. Despite this, and prior to the invention of lasers or holography, Bragg's X-ray microscope* opened the door to optical computation in short-wavelength studies using spatially coherent visible light, including phase retrieval methods. This optical approach lost ground to semiconductor detection and digital computing in the 1960s. Since then, visible optics such as spatial light modulators, array detectors and femtosecond lasers have become widely available, routinely allowing versatile and computer-interfaced imposition of optical phase, detection, and molecular coherent control in pump-probe studies. Today, FELs begin to offer opportunities for atomic resolution and ultrafast studies. Thus we investigate an overlooked aspect of Bragg's X-ray microscope: the short-wavelength to visible-wavelength, incoherent to coherent conversion that is a necessary prerequisite for coherent optical computations. Some potential approaches, techniques and opportunities are outlined.
* W.L. Bragg, A new type of 'X-Ray microscope', Nature 143, 678 (1939)
AUT, Tehran
The dynamical stability of electron trajectories in a free-electron laser with planar wiggler is studied. The analysis is based on the numerical simulation of Kolmogorov entropy to investigate how the separation of the trajectories of two neighboring electrons in the six-dimensional phase space evolves along the undulator. Self-electric and self-magnetic fields are taken into account and an adiabatically tapered wiggler magnetic field is used in order to inject the electrons into the wiggler. A considerable decrease in the dynamical stability of electron trajectories was found near the resonance region. It was found that self-fields decrease the dynamical stability of electron trajectories in group I orbits and increase it in group II orbits. Furthermore, the electromagnetic radiation weakens the dynamical stability of electrons as it grows exponentially and become very intense near the saturation point.
KAIST, Daejeon
KAERI, Daejon
Hanyang University, Seoul
Korea University, Seoul
Laser accelerated electron beam can be a compact source for high energetic photon generation for nuclear application. A simulation code using GEANT4 has been developed for the estimation of Bremsstrahlung radiation from laser accelerated electron beams impinging on a metalic target and the photonuclear reaction of a sample target. It includes ElectroMagnetic physics , Photonuclear reaction and Radio Active Decay physics, so that the calculation from Bremsstrahlung radiation to decay process can be conveyed in series. The energy and angular distribution of Bremsstrahlung radiation depending on different target thickness and electron parameters as well as the emission spectrum by radioactive decay due to photonuclear reaction can give us an idea of optimal condition for the desired nuclear applications. We discussed the critical issues of high energy photon generation for photonuclear reaction experiments.
USTRAT/SUPA, Glasgow
DESY, Hamburg
So far, short wavelength Free Electron Laser amplifiers have produced linearly polarised radiation. For several important classes of experiment, variable polarisation is required. For example, in the wavelength range from 1.5 to 2.5 nm, light polarisation is important in characterising magnetic materials where measurements depend critically upon the handedness of the polarisation. It is therefore important that the polarisation does not fluctuate between measurements. In this paper, we study possible methods to generate variably polarised light and consider its shot-to-shot stability.
SINAP, Shanghai
The high-gain seeded free-electron laser (FEL) schemes are capable of producing fully coherent radiation in the short wavelength regions. In this paper, we introduce the pre-density modulation (PDM) scheme to enhance the performance of the echo-enabled harmonic generation (EEHG) scheme and to significantly extend the short-wavelength range. The PDM is used to enhance the microbunching and reduce the electron energy spread of seeded FEL schemes by gathering most of the electron into the phase range which makes a contribution to the microbunching.
Belarussian State University, Scientific Research Institute of Nuclear Problems, Minsk
Volume Free Electron Laser (VFEL) is a peculiar kind of radiation generators using volume multi-wave distributed feedback*. Recent years applications of a “grid” photonic crystal (crystal-like artificial periodic structure) as a volume resonator for VFEL operation are intensively studied. Theoretical analysis** shows that a periodic metal grid does not absorb electromagnetic radiation and the ''grid'' photonic crystal, made of metal threads, is almost transparent for electromagnetic waves within the frequency range from GHz to THz. Operation of Volume Free Electron Laser with a photonic crystal formed by thin metallic threads periodically strained inside a waveguide*** confirmed the above conclusions. In the present paper operation of Volume Free Electron Laser with the photonic crystal built from brass foils strained inside a cylindrical waveguide is discussed. Dependence of radiation yield on the crystal length is studied in the range up to 8 GHz. Experimental results are compared with those obtained for the photonic crystal formed by threads.
* V.Baryshevsky, NIM A445 (2000) 281; LANL e-print archive physics/9806039.
** V.Baryshevsky, A.Gurinovich, NIM B252(2006)92.
*** V.Baryshevsky, N.Belous, A.Gurinovich et al,FEL'06,TUPPH012,p.331
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
USTRAT/SUPA, Glasgow
The effects of pre-conditioned electron beams on free electron laser (FEL) behaviour are considered in simulations. Under consideration is modulation of the electron beam energy, using long-scale modulation period relative to the resonant FEL wavelength. Structure can be generated in the radiation field and electron beam with extent of significantly less than the FEL co-operation length, without applying spatio-temporal shifts between the radiation and electron beam*.
* N.R. Thompson and B.W.J. McNeil, Phys. Rev. Lett. 100, 203901 (2008).
Mesa+, Enschede
Compact, slow-wave, low energy electron beam radiation sources, like Cerenkov free-electron lasers (FELs), emit high power microwaves. However, they seriously degrade in output power, when scaled towards the THz range (0.1-10 THz). This prevents industry from applying THz radiation, although it would allow many new applications, like chemical selective security surveillance. The photonic free-electron laser (pFEL) is a promising concept for a handheld, tunable and Watt-level THz laser. In a pFEL several electron beams stream through a photonic crystal (PhC) leading to the emission of coherent Cerenkov radiation. The beams emit phase-locked due to the transverse scattering inside the PhC, which allows increasing the output power by increasing the number of beams streaming through the PhC. Therefore, scaling the pFEL’s operating frequency towards THz frequencies can be done without loss in output power. Furthermore, compact, low energy electron sources (< 15 keV) can drive the laser, due to the strong deceleration of the light by PhC’s. As a proof of principle, we developed the setup for a pFEL operating at 20 GHz to study the interaction between a single electron beam and the PhC.
European XFEL GmbH, Hamburg
In the European XFEL permanent magnet phase shifters are routinely between two undulator segments. Its main purpose is to control the phase of the electrons with respect to the emitted radiation. In addition the path length is dependent on the electron energy, which corresponds to a small R56 . In this paper we investigate the R56 of a permanent magnet phase shifter and propose to use it to fine tune R56 by adjusting the phase shifter gap.
FZD, Dresden
Ankara University, Faculty of Engineering, Tandogan, Ankara
To extend the wavelength range of possible experiments from the FIR into the THz region a dedicated beamline is planned at the ELBE Radiation Source. The beamline will deliver coherent transition radiation and coherent synchrotron radiation as broad-band (essentially single-cycle) radiation. Superradiant undulator radiation will be produced for a tunable narrow-band radiation source in the 100GHz to 3THz range. This requires a compression of the ELBE electron beam down to 150fs bunchlength. The beam transport and bunch compression scheme as well as the properties of the produced radiation are presented in detail.
ELETTRA, Basovizza
INFN-Roma II, Roma
FERMI@Elettra is a linac-driven free-electron laser currently under construction at the synchrotron radiation facility Elettra in Trieste, Italy. In order to prevent damage to accelerator components, an active machine protection system (MPS) monitors beam losses along the linac and, if necessary, inhibits the beam production in the injector. Special attention is paid to the protection of permanent undulator magnets from demagnetization by the excessive absorption of radiation. This paper discusses the system architecture and gives an overview of the major diagnostic subsystems: A beam loss position monitor based on the detection of Cherenkov light induced in quartz fibers, an array of discrete ionization chambers, and a system for differential charge loss measurements. The dose deposition in the undulator magnets will be monitored with electronic RadFET dosimeters; first details of the readout system are presented.
European XFEL GmbH, Hamburg
The European XFEL will provide up to 2700 X-ray pulses during 600 microsecond long pulse trains with a repetition rate of 10 Hz. This leads to a short time heat load of FEL radiation of more than 10 kW in a sub-mm spot on the optical elements averaged over a pulse train and a less collimated high energy spontaneous radiation of similar magnitude. On the other hand, the conservation of coherence properties requires a stability of X-ray optics on the nanometer scale. Cooling concepts for mirrors and monochromators as well as photon damage aspects will be discussed. The conceptual design of photon beamlines and photon distribution schemes to different experimental stations will be presented.
SLAC, Menlo Park, California
During undulator commissioning of the Linac Coherent Light Source (LCLS) x-ray Free Electron Laser (FEL) at the SLAC National Accelerator Laboratory it was shown that saturation lengths much shorter than the installed length of the undulator line can routinely be achieved. This frees undulator segments that can be used to provide enhanced spectral properties and at the same time, test the concept of FEL Afterburners. In December 2009 a project was initiated to convert undulator segments at the down-beam end of the undulator line into Second Harmonic Afterburners (SHAB) to enhance LCLS radiation levels in the 10 20 keV energy range. This is being accomplished by replacement of gap-shims increasing the fixed gaps from 6.8 mm to 9.9 mm, which reduces their K values from 3.50 to 2.25 and makes the segments resonant at the second harmonic of the upstream unmodified undulators. The paper reports experimental results of the commissioning of the SHAB extension to LCLS.
BINP SB RAS, Novosibirsk
To change the wavelength of undulator radiation people frequently use the variation of undulator magnetic field amplitude. Another option is to change the undulator period. The scheme for such undulator is described. It provides possibility to change both period and number of periods. For the set of undulator sections (like in x-ray FELs) mechanical motion of periods eliminates the necessity of phase shifters between the undulator sections. Magnetic field calculations for some interesting undulator parameters were performed. Numerous advantages of new undulators (fixed gap, strong dependence of undulator radiation wavelength on period, relatively low field amplitude variation and variable number of periods) look very attractive. Prospects for this new type of undulators are discussed.
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
An interlock sensor is indispensable to protect the undulator magnets against radiation damage. The beam halo monitor using diamond detectors, which are operated in photoconductive mode, has been developed for the X-ray free electron laser facility at SPring-8 (XFEL/SPring-8). Pulse-by-pulse measurements are adopted to suppress the background noise efficiently, and to improve the detective sensitivity. The feasibility tests of this monitor have been demonstrated at the SPring-8 compact SASE source (SCSS) test accelerator for SPring-8 XFEL. As the next step, we are trying to improve the high-frequency properties: (a) dimension of diamond detectors was newly designed to optimize the beam halo monitor for SPring-8 XFEL, (b) the microstripline structure is applied in the vacuum chamber to improve the high-frequency property, (c) RF fingers are also applied to suppress the effect of the wake field from intense electron beam. Details of these devices and experimental results are presented.
ELETTRA, Basovizza
The advent of FEL sources has brought new possibilities for experimentalists performing measurements that are challenging in terms of time resolution, flux, coherence, and so on. One of the most important points, however, is the capability of characterizing the FEL photon beam so to determine the different parameters of each pulse hitting the system under investigation. For this reason it is mandatory to realize diagnostics sections along FEL user facilities recording beam pulse-resolved features such as the absolute intensity, the energy spectrum, the beam position, the time arrival, and the wavefront. For other parameters like the coherence and the pulse length, on the other side, a direct and online detection is not possible. At FERMI@Elettra, the Italian FEL facility, a dedicated diagnostic section called PADReS (Photon Analysis Delivery and Reduction System) will be installed after the undulatory' exit, and it will serve as a source of pulse-resolved informations for end-users. In this talk the instruments that are part of typical FEL diagnostic sections will be described using PADReS as a real example to see the roles of the different diagnostic tools.
CFEL, Hamburg
The ultrafast, ultrabright, coherent X-ray pulses offered by X-ray FELs open the doors to a range of new capabilities in X-ray science. The ultrafast pulses from X-ray FELs enable X-ray imaging beyond conventional radiation damage limits enabling the ultrafast single-shot images of transient phenomena and material structure to be captured. Although sufficient dose is deposited in a single pulse to completely destroy the sample, it is nevertheless possible to collect meaningful diffraction patterns from the undamaged sample before it is destroyed using ultra-short X-ray pulses that terminate pulse before the effects of sample damage are manifested. Experiments in recent years at the first operational FELs in the X-ray regime FLASH and LCLS - have demonstrated the feasibility of flash imaging using soft X-ray FELs. In particular it has been shown that measurements can be made before sample damage occurs. Single-pulse X-ray imaging has been used to study the time evolution of non-cyclic phenomena such as laser-induced ablation with nanoscale resolution and a shutter speed measured in femtoseconds.
This work was carried out as part of a large collaboration consisting of CFEL DESY, Arizona State University, SLAC, Uppsala University, LLNL, The University of Melbourne, LBNL, the Max Planck