SLAC, Menlo Park, California
Prize lecture by the winner of the FEL prize 2009 for a significant contribution to the advancement of the field of Free-Electron Laser.
DESY, Hamburg
Recently the free-electron laser facility FLASH at DESY, Germany has been upgraded. An important feature of the update is the increase in electron beam energy from 1 to 1.2 GeV by adding a 7th superconducting accelerating module. Recently, FLASH met the upgrade goal and accelerated the beam just above 1.2 GeV. Shortly after, for the first time, lasing at 4.45 nm with a remarkably improved performance was obtained.
MAX-lab, Lund
The MAX-lab test FEL at MAX-lab, Lund, Sweden has during 2010 been commissioned and first results in Seeded Coherent Harmonic Generation up to the 6th harmonic (42 nm) in linear polarization and 4th harmonic (66 nm) in circular polarization of the 263 nm Ti:Sapphire seed laser achieved. The test FEL is a collaboration between MAX-lab and the Helmholtz Zentrum Berlin utilizing the 400 MeV linac injector at MAX-lab and an undulator set-up provided by HZB.
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.
JLAB, Newport News, Virginia
We report on first operation of the UV Demo Free-electron Laser at Jefferson Lab. The laser operated at the long wavelength limit of its operation at 700 nm. The average output power exceeded 165 W with 0.32 mA of beam current. The accelerator operated at 135 MeV with 67 pC bunches at 4.68 MHz. The detuning curve was more than 11 microns, indicating a gain in excess of 100%. We now plan to push the laser to higher power at 700 nm and then to push to shorter wavelengths and explore the utilization of the coherent third harmonic at 10 eV.
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.
DESY, Hamburg
In Europe, several national FEL projects are in progress, the seeded FEL FERMI@Elettra at Sincrotrone Trieste is expecting first lasing by the end of 2010, and the capacity of the FLASH facility at DESY in Hamburg will be doubled by adding a second, seeded FEL in the next few years. These national FEL centres in Europe are currently preparing the foundation of a consortium called EuroFEL in order to be more efficient and to better coordinate their activities in research and development, training and other areas. This contribution will present the main ideas of EuroFEL and the current status of its preparatory phase.
NPS, Monterey, California
Thirty-four years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.
LBNL, Berkeley, California
UCB, Berkeley, California
ANL, Argonne
The Next Generation Light Source (NGLS) is a design concept, under development at LBNL, for a 10‐beamline soft x‐ray FEL array powered by a 2.4 GeV superconducting linear accelerator, operating with a 1 MHz bunch repetition rate. The CW superconducting linear accelerator is supplied by a high-brightness, high-repetition-rate photocathode electron gun. Beam is distributed from the linac to the array of independently configurable FEL beamlines with nominal bunch rates up to 100 kHz, with even pulse spacing. Individual FELs may be configured for EEHG, HGHG, SASE, or oscillator mode of operation, and will produce high peak and average brightness x-rays with a flexible pulse format ranging from sub-femtoseconds to hundreds of femtoseconds.
BNL, Upton, Long Island, New York
In this paper, we present an analytical three-dimensional theory of free electron lasers. Under several assumptions, we arrive at an integral equation similar to earlier work carried out by Ching, Kim and Xie, but using a formulation better suited for the initial value problem of Coherent Electron Cooling. We use this model in later papers to obtain analytical results for gain guiding, as well as to develop a complete model of Coherent Electron Cooling.
BNL, Upton, Long Island, New York
We present analytical results for the one-dimensional dispersion relation for high-gain FELs. Using kappa-n distributions, we obtain analytical relations between the dispersion relations for various order kappa distributions. Since an exact solution exists for the kappa-1 (Lorentzian) distribution, this provides some insight into the number of modes on the way to the Gaussian distribution.
AUT, Tehran
Three-Dimensional simulation of Free-Electron Laser amplifiers at the presence of helical wiggler and ion-channel has been reported. The electromagnetic field is assumed to express in terms of the TE modes of a cylindrical waveguide in the absence of the electron beam. The final form of dynamical equations for the evolution of the slowly varying amplitude and wavenumber of TE mode is obtained by substitution of the vector potentials in to Maxwell’s equations. A cold, uniform, axisymmetric electron beam with a flat-top density profile has been considered for modeling the initial injection of the electron beam. The three-dimensional Lorentz force equation in the presence of a realistic helical magnetostatic wiggler, ion-channel electrostatic field and electromagnetic fields describes the electron dynamics. A set of coupled nonlinear first order differential equations is derived and solved numerically by Runge-Kutta method. The 10th-order Gussian quaderature technique is used for calculation of averages in the field equations. Finally, evolution of the radiation power and growth rate of the TE11 mode is shown.
Universita' degli Studi di Milano, Milano
INFN/LNF, Frascati (Roma)
Istituto Nazionale di Fisica Nucleare, Milano
We study both analytically and numerically the effects of a laser pulse on the longitudinal phase space of an electron beam in the stage of extraction from the cathode. We show how the interaction can produce modulations in the longitudinal momentum distribution.
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.
SLAC, Menlo Park, California
UW-Madison/SRC, Madison, Wisconsin
FEL/Duke University, Durham, North Carolina
DEEI, Trieste
A single-pass high-gain x-ray free electron laser (FEL) calls for a high quality electron bunch. In particular, for a seeded FEL amplifier and for a harmonic generation FEL, the electron bunch initial energy profile uniformity and peak current uniformity are crucial for generating an FEL with a narrow bandwidth. After the acceleration, compression, and transportation, the electron bunch energy profile entering the undulator can acquire temporal non-uniformity both in energy and local density. We study the effects of the electron bunch initial energy profile non-uniformity and local density variation on the FEL performance. Intrinsically, for a harmonic generation FEL, the harmonic generation starts with an electron bunch having energy modulation as well as density bunching at the previous stage FEL wavelength and its harmonics. Its effect on the harmonic generation FEL in the radiator is then studied.
USTRAT/SUPA, Glasgow
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
The method of Echo Enabled Harmonic Generation is a possible method of achieving coherent short wavelengths in an FEL amplifier. In this paper the effects of noise variations is some of the important parameters affecting the stability of the final harmonic bunching of the electron beam are investigated numerically.
Uni HH, Hamburg
DESY, Hamburg
The Free Electron Laser FLASH has been upgraded during winter 2009/10. Amongst other components, a third harmonic module operating at 3.9 GHz (ACC39) has been installed. Together with the energy chirp induced by off-crest operation, it allows for a linearisation of the longitudinal phase space, leading to a uniform compression of the electron bunch with final bunch lengths of 150 μm rms. In contrast to the old non-linear compression scheme, peak current and bunch length are extremely sensitive to the phases of ACC39 and ACC1 and have to be monitored continuously. The foreseen bunch length is within the resolution of electro-optic spectral decoding methods. An ytterbium fibre laser system in combination with a 175 μm thick GaP crystal is used to achieve a good match between the electric field phase velocity and the laser pulse group velocity in the electro-optic crystal. This ensures a large modulation of the polarisation of the chirped laser pulse in the EO crystal. The information on the electron bunch length carried by the laser pulse is decoded in a spectrometer and read out with an InGaAs line scan camera.
Uni HH, Hamburg
DESY, Hamburg
The free electron laser in Hamburg (FLASH) underwent major modifications during a 6 months shutdown like the installation of a 3rd harmonic module, a seeding experiment (sFLASH) and a 7th accelerating module. Also instrumentation has been improved. A new compact electro-optic (EO) bunch length monitor has been installed downstream the first bunch compressor. At this position, the bunches are expected to have a length of about 1 ps, well suited for the resolution of an EO bunch length monitor with spectral decoding of the time (EO-SD). The setup uses a commercial ytterbium fiber laser, a compact optics inside the beam pipe designed at PSI (Switzerland) and a spectrometer with fast InGaAs line scan camera. These components, together with RF synchronisation unit and readout electronics, will be installed in the accelerator tunnel. Reliability, robustness and high uptime are key features as the EO monitor is meant to serve as permanent beam diagnostics. Here we report on the commissioning of the components and first experiments with the complete system.
PAL, Pohang, Kyungbuk
Pohang Accelerator Laboratory (PAL) is proposing an X-ray free-electron laser facility that is designed to generate 0.1-nm wavelength coherent X-ray by using self-amplified spontaneous emission mechanism. A 10-GeV electron linear accelerator is required to generate high brightness electron beam with 0.2 nC charge, normalized emittance of 0.5 um-rad, and peak current of over 2.66 kA in order to reduce the required length of undulator for saturation below 60 meters. The radiation that is coherent and a few tens of femto-second long will cover the hard X-ray (0.1 ~ 1 nm) and the soft X-ray in the ranges of 2~ 5 nm. Advanced X-ray free-electron laser concepts are also being considered in the design: the self-seeded operation for narrow band spectrum as well as the attosecond X-ray pulse generation using the energy modulation of electron beam by optical laser beam. The baseline design of femtosecond X-ray generation for PAL-XFEL as well as challenges toward attosecond X-ray pulse generation will be presented.
KVI, Groningen
FOM, Utrecht
TUE, Eindhoven
RUG, Groningen
We outline our plans to construct a soft X-ray FEL facility at KVI, University of Groningen, The Netherlands. This new facility will be based on a 2.6 GeV normal-conducting electron linac followed by an undulator and will produce X-ray laser light with wavelengths downto 0.5 nm. The electron linac will be driven by a RF photo-injector and X-band acceleration structures based on CLIC developments with an acceleration gradient of 100 MeV/m. Various techniques will be implemented to also establish longitudinal coherence. The entire length of the FEL will be on the order of 100 meters. The facility is meant as a international user facility with a strong contribution of local AMO, material science and biochemistry groups. The design and construction will be a collaborative effort with contributions from different (inter)national research groups.
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).
DESY, Hamburg
Uni HH, Hamburg
The free-electron laser facility FLASH at DESY, Germany finished its very successful 2nd user period late summer 2009. Recently FLASH has been upgraded. The 3rd user period is scheduled to start late summer 2010. In many aspects the upgraded FLASH is an FEL with a new quality of performance. It can provide thousands of FEL pulses per second with wavelengths approaching the carbon 1s absorption edge and the water window. The extension of the photon wavelength range is realized by increasing the electron beam energy up to 1.2 GeV by adding a 7th superconducting accelerating module. The dynamics behavior of the electron beam is improved by installing 3rd harmonic superconducting RF cavities. In addition, an experiment for seeded FEL radiation, sFLASH, is integrated to the FLASH linac. Recently, FLASH achieved a beam energy above 1.2 GeV and lasing below 5 nm with a remarkably improved performance.
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.
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.
University of Pune, Pune
FZD, Dresden
A tapered undulator experiment was carried out at the Forschungszentrum Dresden-Rossendorf (ELBE) far-infrared FEL. The main motivation was to see whether the presence of a dispersive medium due to the partially waveguided resonator has any effect on the outcome. The FEL saturated power and the wavelength shifts have been measured as a function of both positive as well as negative undulator field amplitude tapering. In contrast to the typical high-gain FELs where positive tapering (i.e. a decrease of undulator field amplitude over the beam path) proves beneficial for the output power we observe an improvement of performance at negative taper. During the same experiments we studied the characteristics of the detuning curves. The width of the curves indicates a maximum small-signal gain for zero taper while the output peak power is highest for negative taper. Whereas the saturated power output and the detuning curve characteristics agree with the known theoretical predictions, the wavelength shifts showed deviations from the expected values. Details of the experiment are presented.
SOLEIL, Gif-sur-Yvette
PhLAM/CERCLA, Villeneuve d'Ascq Cedex
Nagoya University, Nagoya
UVSOR, Okazaki
JASRI/SPring-8, Hyogo-ken
In FEL oscillator, a desynchronisation between the electron-bunch passage frequency and the repetition rate of the laser can lead to instability, characterised by erratic longitudinal shape of the emitted light pulses. We show that this instability can be controlled using a simple feedback system which consist in re-injecting in the cavity a part of the emitted light. Analytical, numerical and experimental studies on the UVSOR-II storage ring have been performed, and show that the energy needed to achieved the control can be extremely weak, in practical higher than the noise level[1]. We also show that another important parameter is the phase of the re-injected signal with respect to the light in the cavity. Depending of the value of this phase, we can observe a shift of the emitted light wavelength, which can go with a modulation of the laser pulse envelop. Both of this two phenomenas are quantitatively analysed.
[1] C. Evain, C. Szwaj, S. Bielawski, M. Hosaka, A. Mochihashi, M. Katoh, and M.-E. Couprie, Phys. Rev. Lett. {10}2, 134501 (2009)
AIST, Tsukuba, Ibaraki
Inverse Compton X-rays were obtained during lasing of the NIJI-IV free electron laser (FEL) in the infrared range. The position of the Compton collisions between electron bunches and laser pulses inside the FEL oscillator strongly influenced the energy spectrum of the Compton X-rays. Collisions outside the undulator magnetic field led to a sharp and clear Compton edge, while collisions inside the undulator magnetic field made it quite obscure. The position of collisions can be determined by changing the bunch-filling pattern on the 16 RF successive buckets. In this experiment two or three bunches selectively remained in suitable RF buckets. The maximum X-ray energies were 0.7-2.1 MeV for the laser wavelengths of 2.6 μm - 0.88 μm with a fixed e-beam energy of 310 MeV. Relative energy width of the 1.2 MeV Compton X-rays was observed to be 11 % with a lead collimator of 10 mm in diameter. The maximum X-ray yield was of the order of 106 photons/sec in a three-bunch operation mode. The energy spectra and X-ray yields were investigated under various Compton collision conditions. The results will be discussed in the conference.
JAEA/ERL, Ibaraki
JAEA, Ibaraki-ken
Hybrid K-edge densitometer (HKED) is used for concentration measurement of U, Pu and minor actinides in liquid solution samples. In the HKED, the concentration of the most-abundant element is determined by K-edge densitometer and concentrations of other elements are derived from XRF signals. We propose a multi-turn small-size energy-recovery linac (ERL) to produce laser-Compton scattered X-rays for the HKED. The X-rays with good monochromaticity and energy tunability allow measurement of actinides with much better resolution than the existing HKED systems based on X-ray tubes. The ERL energy is 85 MeV to produce 130-keV X-rays. In the present design, we adopt a racetrack configuration, in which electrons are accelerated six times by L-band superconducting linac and decelerated six times for the energy recovery. Design and expected performance of the ERL-HKED are presented.
Mesa+, Enschede
ELETTRA, Basovizza
UT-MESA+ OS, Enschede
FERMI@Elettra is a free electron laser user facility currently under construction at Sincrotrone Trieste S.C.p.A. Its goals are to produce high-brightness, ultra-short pulses with wavelengths ranging from 100 - 20 nm (FEL1) and 40 - 4 nm (FEL2) and deliver these pulses to a wide range of user experiments. Currently, FERMI uses the HGHG technique to improve both the stability and the longitudinal and spectral coherence of the output of the laser. Direct seeding of FEL1 using a High Harmonic (HH) source is also foreseen and allows a direct comparison between the two seeding methods. For an HH source, we will use neutral atoms in a hollow waveguide in combination with coherent control of the drive laser pulse to provide wavelength tuning as well as selective enhancement of the harmonic orders. For direct seeding of FEL 2 we propose HH generation from ions in a modulated plasma waveguide. The ions allow generation of shorter wavelengths, while the modulated plasma waveguide provides a long interaction length as well as quasi-phase matching for boosting the output energy of the source. In this paper, we will present the HH source for FEL1 as well as a concept for HH seeding of FEL2.
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
It is generally accepted that harmonic-generation seeding in FELs amplifies the noise in the beam and enhances the spontaneous component of the FEL radiation. In this paper we analyze the noise dynamics caused by particle interaction in the undulators of the EEHG seeding mechanism. We develop a 1D model of the noise evolution through the system and calculate the amplification factor as a function of frequency. Our results are applied to a typical soft x-ray EEHG FEL.
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.
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.
Sokendai - Okazaki, Okazaki, Aichi
UVSOR, Okazaki
Nagoya University, Nagoya
Light source technologies based on laser seeding are under development at the UVSOR-II electron storage ring. In the last FEL conference (FEL2009), we reported spectral measurements of coherent harmonic generation (CHG) seeded by the fundamental of Ti: Sapphire laser, in the region of vacuum-ultra violet (VUV). In this conference, we will report some systematic measurements such as the undulator gap dependence and seed laser power dependence. In the laser power dependence, we have observed a saturation of CHG intensity. The result will be compared with simulations. A seeding light source based on high harmonic generation (HHG) in rare gas is under development. The status will be reported.
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.
LBNL, Berkeley, California
UCB, Berkeley, California
ANL, Argonne
A concept for a tunable soft x-ray free electron laser (FEL) oscillator is proposed and studied numerically. It is based on the idea of echo enabled harmonic generation [1] and takes advantage of the oscillator’s ability to start up from spontaneous emission, thereby eliminating the need for optical lasers. In the proposed concept, harmonic tunability is accomplished through beam manipulations using magnetic chicanes and a tunable radiator while two FEL oscillators remain at a fixed frequency. An additional advantage of the proposed technique is the possibility to utilize multilayer x-ray mirrors with a high backward reflectivity of the order of 70%, allowing the initial beam manipulation to be accomplished at a short wavelength, close to the final soft x-ray output. The high repetition rate soft x-ray output is expected to have longitudinal coherence and a narrow bandwidth.
[1] G. Stupakov, PRL, 2009
JLAB, Newport News, Virginia
ATF, Boulder
Mesa+, Enschede
We report on the design, and broadly tunable operation, of a high average power free-electron laser using edge-outcoupling. For this type of outcoupling, the cavity mode has a larger area than the mirror diameter, and the mode ‘spills” around it. While used in positive branch unstable resonators, in this case, the resonator was in a stable configuration. Using an edge-outcoupler composed of an aluminum-coated sapphire substrate, the IR Upgrade FEL at Jefferson Lab achieved a maximum power of 260W at 3.87 microns, with an output power of 20 W or higher from 0.8 to 4.2 microns. Measurements of gain, loss, and output mode are compared with our models.
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.
SOLEIL, Gif-sur-Yvette
PhLAM/CERCLA, Villeneuve d'Ascq Cedex
LAL, Orsay
University of Erlangen-Nuremberg, Erlangen-Nuremberg
We investigate a dynamical behaviors occurring in single-pass free electron lasers (FELs), depending on the electron beam, undulator and seed laser parameters. We put in evidence a complex spatiotemporal deformation of the amplified pulse, leading ultimately to a pulse splitting effect with two sub-pulses. This phenomenon has been first observed in PERSEO simulations in the case of ARC-EN-CIEL project studies, and then been analyzed more in details with the Colson-Bonifacio FEL equations. This studies reveal that slippage length as well as the seed laser pulse wings are the main ingredients of this dynamics [1]. We show that the splitting results from the nonhomogeneous saturation of the gain by the optical field copropagating with the electron beam.
M.Labat et al. “Pulse-splitting in short wavelength seeded free electron laser,” Phys. Rev. Lett. {10}3, 264801 (2009)
Uni HH, Hamburg
DESY, Hamburg
PSI, Villigen
DELTA, Dortmund
The free-electron laser facility FLASH at DESY (Hamburg) was upgraded during a five month shutdown in winter 2009. Part of this upgrade was the installation of a direct seeding experiment in the XUV spectral range. Beside all components for transport and diagnostics of the photon beam in and out of the accelerator environment, a new 10m long variable gap undulator was installed upstream of the existing FLASH undulator system. The seed pulses are generated within a noble gas jet by focusing 40 fs long Ti:Sa laser pulses into it resulting a comb of higher harmonics. In the first phase of the experiment the 21st harmonic of the 800nm drive laser will be used to seed the FEL process. The commissioning of the experiment has started in April and the first results are expected after the FLASH commissioning period mid of summer 2010. The experimental setup and the commissioning procedures as well as first result will be presented.
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.
MAX-lab, Lund
HZB, Berlin
Lund University, Division of Atomic Physics, Lund
The first generation of coherent harmonic radiation from the MAX-lab test FEL have recently been achieved. The 380 MeV electron beam has been seeded by a 263 nm Ti:Sapphire laser and coherent radiation in the harmonics 1 to 4 (263 66 nm) has been produced both in linear and circular polarization mode. The facility consists of a photo cathode RF gun, the MAX injector (two 95 MeV linacs placed in a recirculator), beam transport including compression optics and the two undulators (modulator and radiator) separated by a four magnet chicane for bunching control. The radiator undulator is of Apple type providing tunable polarization. The basic characterization of the source with dynamic studies of laser energy, undulator gap and chicane influence on the coherent harmonic signal will be reported.
ANL, Argonne
X-ray free electron lasers (FELs) are well suited to pursue a long-standing goal of studying matter in a transient state that is far from equilibrium. This state often determines the functions of materials and, thus, holds a key to understanding how to control them. The natural time scale for most of the dynamic processes involving atoms is of the order of 100 femtoseconds, and existing x-ray FELs have already surpassed this mark. The natural time scale for dynamic processes driven by electrons is of the order of 100 attoseconds, and this is the next Rubicon for FELs. In this talk I will review the state of the art in generation of femtosecond x-ray pulses using FELs and will discuss a number of new ideas en route to sub-femtosecond x-ray pulses.
SLAC, Menlo Park, California
There is a growing interest in the generation and characterization of femtosecond and sub-femtosecond pulses from linac-based free-electron lasers (FELs). In this paper we study a simple longitudinal transformation* for measuring a very short electron bunch. We show that this method can be applied in a straightforward manner at x-ray FEL facilities such as the Linac Coherent Light Source by slightly adjusting the second bunch compressor followed by running the bunch on an rf zero-crossing phase of the final linac. After taking into account the linac wakefield, we find the condition under which the final beam energy spread corresponds directly to the compressed bunch length. When used in conjunction with a high-resolution electron spectrometer, this method potentially reveals temporal information of femtosecond and sub-femtosecond electron bunches used by such FELs.
* K. Ricci and T. Smith, Phys. Rev. ST-AB 3, 032801 (2000).
ELETTRA, Basovizza
University of Nova Gorica, Nova Gorica
FERMI@Elettra will have two different seeded FELs for covering the spectral range between 80 and 4nm. The shorter wavelength FEL, namely FEL-2, will cover the spectral range between 20 and 4 nm, and will be based on a double cascade high gain harmonic generation scheme. Moreover, the system has been designed to allow the implementation of other seeding schemes, like seeding with high-order harmonics generated in gas and echo-enhanced harmonic generation (EEG). In this work, we present the studies on the possible implementation on FERMI of the EEHG, reporting about the expected performance. The number of photons per pulse and the FEL bandwidth are calculated by means of time dependent start-to- end simulations.
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.
ISIR, Osaka
Femtosecond electron beam, which is essential for pump-probe measurement, was generated with a 1.6-cell S-band photocathode rf gun. The rf gun was driven by femtosecond UV laser pulse (266 nm), which was generated with third-harmonic-generation (THG) of Ti:Sapphire femtosecond laser (800 nm). The longitudinal and transverse dynamics of the electron bunch generated by the UV laser was investigated. The bunch length was measured with the dependence of energy spread on acceleration phase in a linac, which was set at the downstream of the rf gun. Transverse emittance at the linac exit was also measured with Q-scan method.
PSI, Villigen
DESY, Hamburg
Electro Optical (EO) sampling is a promising non-destructive method for measuring ultra short (sub picosecond) electron bunches. A prototype of a compact EO bunch length monitor system for the future SwissFEL facility was designed and built at PSI. Its core components are an optical setup including the electro optically active crystal and an Ytterbium fiber laser system which emits broadband pulses at 1050nm. The new monitoring system is described in detail and first experimental results from the SLS injector are presented.
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.
JLAB, Newport News, Virginia
A sophisticated research device such as an advanced photo-cathode injector for a high energy accelerator-based X-ray light source requires drive lasers with a flat-top shape both in time and space in order to generate high-quality short electron beam bunches. There are a number of different ways to spatially shape laser beams, but the practical methods for temporal shaping, in particular in the picosecond or femtosecond regime, are quite limited. One simple way to shape laser pulses is pulse stacking by birefringent crystals. This method has been adopted for several applications. While the method itself has the great advantage of simplicity, the overall performance depends on many factors. In this paper, we will present both analysis and a recent experimental study about important pulse shaping characteristics that, to our knowledge, have not been adequately explored before. Evaluation on the pros and cons of the method and how to improve the overall performance will be discussed.
DESY Zeuthen, Zeuthen
DESY, Hamburg
YerPhI, Yerevan
Chiang Mai University, Chiang Mai
A new photocathode electron gun is about to be characterized at PITZ*. It is an L-band normal conducting 1.6 copper cell cavity with improved cooling system. It has the same design as the previously installed gun, characterized at PITZ during the run period 2008/9**. Due to the particle-free surface cleaning method utilizing dry ice, a significant reduction of the dark current was achieved in case of the previously tested cavity. This effect is also expected for the new gun. To improve the accuracy of the RF power measurement and control, a new in-vacuum directional coupler was installed between the T-combiner combining the two 5 MW arms of the RF source and the input coaxial coupler. The new in-vacuum coupler will provide much more accurate information about the RF power in the gun and will allow applying appropriate control feedback. Consequently improved stability of the gun operation is expected. Tuning and conditioning results of this new gun cavity will be presented as well as the results of the measurements of the gradient and the gun phase measurements using this new coupler.
* Photoinjector Test Facility at Zeuthen
** S. Rimjaem et al., EPAC 2008, Genoa, Italy.
DESY Zeuthen, Zeuthen
MBI, Berlin
DESY, Hamburg
UCLA, Los Angeles, California
HZB, Berlin
Uni HH, Hamburg
The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops and optimizes electron sources for Free Electron Lasers (FEL’s) such as FLASH and European XFEL. The electrons are generated by the photo effect using a cesium telluride (Cs2Te) cathode and are accelerated in an 1.6-cell L-band RF-gun cavity with about 60MV/m maximum accelerating field at the cathode. The upgraded laser system at PITZ produces flat-top and Gaussian laser pulses of different time durations. Emittance measurements have been done for short Gaussian laser temporal profile ~2ps FWHM and for 6.6 MeV electron beam energy. The transverse projected emittance was measured for various transverse laser spot sizes at the cathode and different low bunch charges to find an optimum condition for thermal emittance measurements. ASTRA simulations were performed for various measurement conditions to estimate the space charge contribution to the emittance. The comparison of emittance measurement results and simulations is presented and discussed in this contribution.
DESY Zeuthen, Zeuthen
The Photoinjector Test Stand at DESY, Zeuthen site (PITZ) was established to develop and optimize electron bunch sources for linac-based free electron lasers like FLASH or the future European XFEL. The successful operation of such FELs requires electron bunches of very low normalized transverse emittance of the order of 1 mm mrad at a charge of 1 nC. One key issue for obtaining low-emittance electron bunches is the possibility to influence the electron bunch properties by varying the photocathode laser pulse characteristics. This contribution focuses on the discussion of deviations from the optimum transverse shape of a circular flat-top. Different types of modulations are added to the flat-top and the resulting change in transverse emittance will be discussed based on beam dynamics simulations.
DESY Zeuthen, Zeuthen
DESY, Hamburg
JINR, Dubna, Moscow Region
UCLA, Los Angeles, California
HZB, Berlin
Uni HH, Hamburg
Transverse projected emittance optimization is one of the main research activities at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). The emittance measurement program in the 2009 run period concentrated on projected emittance measurements using a single sit scan technique. The photocathode laser profile has been optimized yielding small emittance. The flat-top temporal profile has been used in the standard projected emittance measurements. The small emittance values down to less than 1 mm-mrad have been measured for the nominal 1 nC bunch charge. Emittance optimizations for lower bunch charges have also been conducted using the same measurement setup and procedure as for the case of 1 nC. Numerical simulations have been carried out to compare the results with the measurements. Measurement and simulation results of the transverse emittance for the bunch charges of 0.1, 0.25, 0.5 and 1 nC will be reported and discussed in this contribution.
PSI, Villigen PSI
For high brigthness photocathode RF gun, proper laser pulses should be used to generate the photocurrent. Transverse uniformity and longitudinal laser flat top profile are predicted to improve the electron beam brigthness. Moreover the laser stability and its sub-ps synchronicity respect to accelerating field are essential for stable and reliable operation. Finally the intrinsic emittance, which is the ultimate limit for the beam emittance, could be tuned by varying the laser photon energy. For this purpose, we developed a mJ frequency tripled Ti:sapphire laser, tunable within 260-283 nm range. Dependence of the intrinsic emittence and of the quantum efficiency with the photon energy has been measured and compared to theory for various metallic photocathode. In this paper the R&D activities aiming at the photocathode laser for the future SwissFEL project are reported.
PSI, Villigen
The SwissFEL facility will produce coherent, ultra-bright, and ultra-short photon pulses covering a wavelength range from 0.1 nm to 7 nm, requiring an emittance between 0.18 to 0.43 mm mrad. It consists of an S-band rf-gun and booster and a C-band main linac, which accelerates the beam up to 5.8 GeV. Two compression chicanes will provide the required peak current of 2.7 kA. An important issue is the stability of the photon pulses leaving the undulator toward the user stations. Arrival time and peak current stability are crucial factors for the scientific return of the user experiments. Machine stability, especially the rf jitter, will directly affect these important figures. Shot-to-shot jitter is of main interest here since long term drifts can be compensated by slow feedback systems. We present a study on stability including rf tolerances for a new optimised layout of the SwissFEL.
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
University of Tokyo, Tokyo
UTNL, Ibaraki
We developed a single-shot and non-destructive 3D bunch charge distribution (BCD) monitor based on Electro-Optical (EO) sampling with a manner of spectral decoding for XFEL/SPring-8. For the transverse detection, eight EO-crystals (Pockels effect) surround the beam axis azimuthally, and a linear-chirped probe laser pulse with a hollow shape passes through the EO-crystal. We plan to use an amorphous material which has only an even-order field dependence (Kerr effect) in donut shape without assembling eight conventional EO-crystals. The polarization axis of the probe laser should be radially distributed as well as the Coulomb field of the electron bunches. Since the signal intensity encoded at each crystal depends on the strength of the Coulomb field at each point, we can detect the transverse BCD. In the longitudinal detection, we use a prove laser with a broadband square spectrum (> 400 nm @ 800 nm) so that the temporal resolution is < 30 fs, if the pulse width of probe laser is 500 fs. In order to achieve 30-fs temporal resolution, we use an organic EO material, DAST crystal, which is transparent up to 30 THz. We report the first experimental results of our 3D-BCD monitor.
HZDR, Dresden
The thermal emittance of the photocathode is an interesting physical property for the photoinjector, because it decides the minimum emittance the photoinjector can finally achieve. In this paper we will report the latest results of the thermal emittance of the Cs2Te photocathode in FZD Superconducting RF gun. The measurement is performed with solenoid scan method with very low bunch charge and relative large laser spot on cathode, in order to reduce the space charge effect as much as possible, and meanwhile to eliminate the wake fields and the effect from beam halos.
HZDR, Dresden
HZB, Berlin
MBI, Berlin
The superconducting RF photo-injector (SRF gun) at FZD is the first operating electron injector of its kind. The gun with a 3½-cell cavity and a frequency of 1.3 GHz produces an electron beam of 3 MeV with a maximum bunch charge of about 400 pC. Also the design values for the acceleration gradient could not be reached with the cavity which is in use at present the SRF gun will improve the beam quality for ELBE users. End of 2009 the beamline was installed which connects the SRF gun with the ELBE accelerator. We will report on the first test and on the progress in applying the SRF gun for user operation.
NPS, Monterey, California
Niowave, Inc., Lansing, Michigan
Boeing Company, Seattle, Washington State
Stanford University, Stanford, California
The Naval Postgraduate School Beam Physics Laboratory, Niowave, Inc., and The Boeing Company have completed construction of a superconducting 500 MHz quarter-wave gun and photocathode drive laser system. This prototype gun went from conception to initial operation in just under one calendar year. Such rapid progress is due in part to the decision to develop the gun as a prototype, deliberately omitting some features, such as tuners and cathode loadlocks, desired for a linac beam source. This will enable validation of the basic concept for the gun, including high-charge bunch dynamics, as rapidly as possible, with lessons learned applied to the next generation gun. This paper presents results from initial testing of the gun, technical challenges of the prototype design, and improvements that would enhance capabilities in future versions of this novel design.
DESY, Hamburg
The overall bunch compression in FLASH is limited on the one hand by the rf tolerances and on the other hand by linearization of the particle distribution in the longitudinal phase space. While the last one has been significantly improved after the installation of the third harmonic system during the upgrade 2009-2010, the constraint given by rf tolerances cannot be mitigated significantly. To avoid this limitation one has to operate with shorter bunches already at the injector. Since the bunch length is dominated there by the longitudinal space charge one has to go to lower bunch charges. Working points for the operation of the FLASH injector with 20-500pC bunches have been found by means of the optimization procedure based on ASTRA code. The expected bunch parameters are reported in this paper and compared with the experimental results. Further the discussion on advantages and drawbacks of the injector operation in low charge regime is given.
LBNL, Berkeley, California
LLNL, Livermore, California
POSTECH, Pohang, Kyungbuk
The fabrication and installation at the Lawrence Berkeley National Laboratory of a high-brightness high-repetition rate photo-gun, based on a normal conducting 187 MHz (VHF) RF cavity operating in CW mode, is in its final phase. The cavity will generate an electric field at the cathode plane of ~20 MV/m to accelerate the electron bunches up to ~750 keV, with peak current, energy spread and transverse emittance suitable for FEL and ERL applications. The gun vacuum system has been designed for pressures compatible with high quantum efficiency but "delicate" semiconductor cathodes to generate up to a nC bunches at MHz repetition rate with present laser technology. Several photo-cathode/laser systems are under consideration, and in particular photo-cathodes based on K2CsSb are being developed and have already achieved a QE of 8% at 532 nm wavelength, or close to 20% including the Schottky barrier lowering. The cathode will be operated by a microjoule fiber laser in conjunction with refractive optics to create a flat top transverse profile, as well as a birefringent pulse stacker to create a flat top temporal profile. The present status and the plan for future activities are presented.
ANL, Argonne
We review the development of pulse shaping techniques for high brightness beam generation. A scheme of generating a uniform ellipsoidal laser pulse for s is discussed. The scheme is based on the chromatic aberration of a dispersive lens. Fourier optics simulation reveals the interplay of group velocity delay and dispersion in the scheme, as well as diffractions. Particle tracking simulation shows that the beam generated by such a laser pulse approaches the performance of that by an ideal ellipsoidal laser pulse and represents a significant improvement from the traditionally proposed cylindrical beam geometry. The scheme is tested in an 800-nm, optical proof-of-principle experiment at lower peak power with excellent agreement between the measurement and simulation.
DESY Zeuthen, Zeuthen
DESY, Hamburg
UCLA, Los Angeles, California
HZB, Berlin
The major objectives of the Photo-Injector Test Facility at DESY in Zeuthen, PITZ, are research and development of high brightness electron sources suitable to drive FELs like FLASH and the European XFEL. In the 2008/2009 run period the facility has been operated with a new photo-cathode laser system and a dry-ice cleaned RF gun cavity. Characterization of the transverse phase space of the electron source has been performed in details using a single slit scan technique with a dedicated Emittance Measurement System. In preparation for the forthcoming run, a number of quadrupole magnets have been installed and tomography reconstruction with data from quadrupole scans with two magnets has been carried out in semi-parallel manner to the slit scans. This contribution summarizes the experience from the phase-space tomography reconstruction with nominal beam conditions. Advantages and drawbacks of the measurement procedure and the analysis are superimposed and results are compared to ones obtained with the slit scans.
DESY, Hamburg
Linac-based X-ray-free-electron lasers require very short bunches of high- brightness electron beams with peak currents of the order of kilo-Amperes and energies of the order of 10GeV. Essential components of a typical drive linac are a laser driven photo injector, the accelerator and a bunch compression system. Non linear effects from external fields (f.i. rf curvature and higher order longitudinal dispersion) as well as self effects due to space charge, wakes and coherent synchrotron radiation have to be considered for machine design. These main components will be described in principle, the layout of some drive linacs will be discussed and the magnitude of higher order effects and of self effects will be estimated.
LBNL, Berkeley, California
SLAC, Menlo Park, California
The scientific potential of femtosecond x-ray pulses at linac-driven FELs such as the LCLS is tremendous. Time-resolved pump-probe experiments require a measure of the relative arrival time of each x-ray pulse with respect to the experimental pump laser. To achieve this, precise synchronization is required between the arrival time diagnostic and the laser which are often separated by hundreds of meters. For seeded FELs, synchronization is necessary between the seed and pump laser. We describe an optical timing system based on stabilized fiber links which has been developed for the LCLS. Preliminary results show stability of the timing distribution at the sub-20 fsec level. We present details of the results measured during LCLS operation for the first pump-probe experiment in October 2009 and the present user run starting in April 2010. We conclude with a discussion of potential for development.
DESY, Hamburg
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
The Free electron LASer at Hamburg (FLASH) is a linear accelerator of 330m length. It provides laser pulses with pulse duration between 10 and hundreds fs in the soft X-ray wavelength range below 5nm produced in SASE process from electron bunches with an energy up to 1.2 GeV. FLASH works in pulse mode with repetition rate of 10 Hz where up to 800 bunches at a bunch spacing of 1 us are accelerated in one macro-pulse. The electron beam time structure is well suited for fast intra-train feedbacks using beam based measurements incorporated to the Low Level Radio Frequency (LLRF) control system of the accelerator structures to further improve the bunch compressions, bunch arrival and bunch energy stability directly impacting the quality of the FEL photon beam. In this paper, we present the beam based signal pre-processing, the implementation into LLRF system, the mandatory exception handling for robust operation and the imbedding of the real-time ~ 2us latency fast intra-train feedback with feedbacks for the removal of slow and repetitive errors. First results of the achieved intra-train bunch arrival and peak current stability will be presented together with observed limitations.
DESY, Hamburg
Uni HH, Hamburg
At FLASH, UV and soft X-Ray pulses with durations in the order of 10 fs are generated. To fully exploit the opportunities provided by these short laser pulses, an optical synchronization system provides the possibility to synchronize external lasers and stabilize the electron bunch arrival time with 10 fs precision. A seeded free-electron-laser (FEL) section, called sFLASH, is installed upstream of the existing SASE undulators. After higher-harmonic-generation, the femtosecond seed laser pulse needs to be temporarily and spatially overlapped with the electron bunch. Furthermore, for time-resolved pump-probe experiments, using an experimental laser and the FEL pulse, either of sFLASH or of the ordinary SASE process, the synchronization between pump and probe laser pulses is crucial. While the best performance for synchronizing these lasers within 10 fs will be achieved by using an optical cross-correlator, in this paper we present a precursor that relies on an RF-based locking mechanism. The setup includes a coarse and a fine phase measurement between the laser pulses of the reference and the synchronized system after their conversion to an RF signal.
MAX-lab, Lund
Lund University, Division of Atomic Physics, Lund
Electro-optical spectral decoding was used to on-line monitor the arrival time of the electron bunches relative to the seed laser pulse at the test FEL facility at MAX-lab. An infrared chirped pulse coming from the seed laser is influenced by an electron bunch induced birefringence in a ZnTe birefringent crystal and the arrival time is determined from its spectrum. The possibility of running simultaneously with the FEL allowed for a feedback scheme to be built to compensate for the long term drifts in the system. Also, the whole system (the accelerator and the lasers) were synchronized to the power grid frequency. This lock increased the stability and was monitored by the EO setup. Measurements of the bunch length were performed and their correlation with arrival time pointed towards main contributors to the jitter in the system.
LMU, Garching
University of Oxford, Clarendon Laboratory, Oxford
MPQ, Garching, Munich
LBNL, Berkeley, California
FZD, Dresden
Latest developments in the field of laser-wakefield acceleration (LWFA) have led to relatively stable electron beams in terms of peak energy, charge, pointing and divergence [13]. Electron beams with energies of up to 1 GeV have been produced from only few-centimeters long acceleration distances [4]. Driving undulators with these electron beams holds promise for producing brilliant X-ray sources on the university-laboratory scale. In this talk, we will present an experimental breakthrough on this path: our laser-driven soft-X-ray undulator source [5]. In the second part of the talk, we will discuss the physics behind the unique characteristics of laser-wakefield accelerated electron beams such as the intrinsic ltrashort pulse duration (expected to be about 10 fs) and the low normalized transverse emittances (expected to be < pi mm mrad). The properties of state-of-the-art wakefield accelerators as well as their limits will be discussed. Finally new schemes to overcome those limits and further improve the beam quality will be presented.
[1] Mangles, S. P. D. et al. in Nature 431, 535538 (2004).
[2] Geddes, C. G. R. et al. in Nature 431, 538541 (2004).
[3] Faure, J. et al. in Nature 431, 541544 (2004).
BNL, Upton, Long Island, New York
It was recently suggested[1] to use a laser beam as an undulator for an ultra compact X ray FEL. There are number of challenges in realizing this very attractive approach. This paper will discuss the one related to defining and generating an adequate laser beam. Recent development of a picosecond CO2 laser at Brookhaven ATF allows considering a practical set of laser parameters that would preserve resonant condition over the saturation length of a few mm. Electron beam parameters required for such FEL would be also discussed and will show need for further high brightness beam development. [1] Presentation by Claudio Pellegrini at 48th ICFA Advanced Beam Dynamics Workshop on Future Light Sources. March, 2010
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
A pump-probe experiment at XFEL/SPring-8 is one of the most prominent parts to extract the future of a coherent short-pulse X-ray laser. A commercial Ti:Sapphire mode-locked laser is presently used as a pump laser, while a probe laser is the XFEL. However, the time jitter of the commercial mode locked laser, as which is caused by the noise of an electrical mode-locking circuit, is around several hundred femto-seconds. This jitter value is not sufficient for a temporal resolution requirement of our pump-probe experiment with a laser pulse width of several ten femto-seconds. To improve this time jitter, the method, using a 770 nm Ti:Sapphire laser amplifiers directly triggered by a 1540 nm master optical oscillator as a time reference signal source for an XFEL accelerator, was devised. This method could eliminate the noise caused by the electrical mode-locking circuit. The basic principle of the method was proved by a preliminary experiment with laser pulse manipulation employing an E/O crystal shutter with a several ten ps response. This presentation describes a basic idea of this pumpprobe method, a preliminary experiment set-up to check its feasibility, and experiment results.
DESY, Hamburg
Electron bunches at the free electron laser FLASH at DESY have a duration of 10 fs to 150 fs and an arrival-time jitter of about 150 fs (rms). It is anticipated that the newly installed optical synchronisation system will stabilize the seed and pump-probe lasers to within ~10 fs. In order to perform reliable and stable seeding, the electron bunch timing jitter needs to be reduced. Bunch arrival-time monitors measure the arrival-time fluctuations at different locations and are used in a beam-based feedback loop to correct the amplitude of the accelerator RF. In order to provide reliable operation and high availability of the bunch arrival-time feedback, intensive efforts have been undertaken in system automation and exception handling. This will be discussed along with the latest results and limitations on the stability of the arrival-times at FLASH.
Uni HH, Hamburg
DESY, Hamburg
The optical synchronization system of the free-electron laser in Hamburg (FLASH) is based on the stabilized pulse-train distribution of a passively mode-locked laser. This master laser oscillator is based on erbium-doped fiber technology and is built in a σ-configuration, enabling passive mode-locking through nonlinear polarization evolution. Recently, a commercial laser system has been installed in addition to the existing laser. Besides maintenance-free operation, this SESAM-based laser shows an even lower timing jitter, enabling a tighter synchronization to the accelerator's RF reference. In this paper we report on the commissioning, the characterization and the long-term stabilty of the new laser system, as well as on the performance of the laser with the existing pulse-train distribution scheme and optical front-ends of the synchronization system in comparison to the old one.
DESY, Hamburg
Warsaw University of Technology, Institute of Electronic Systems, Warsaw
Bunch arrival-time monitors measure the arrival-time of each bunch in the electron bunch train at several locations at FLASH. The temporal reference for the monitors is provided by the optical synchronization system which distributes laser pulses with a repetition rate of 216 MHz and a length of around 200 fs FWHM. The pulses are delivered to the monitors with an arrival-time stability of about 10 fs. The bunch arrival-time is encoded as an amplitude modulation of a laser pulse from the optical synchronization system. These laser pulse amplitudes need to be sampled and processed together with additional input parameters. Because the arrival-time information is used in a feedback loop to adjust the accelerator fields, the signal processing, calibration and transmission of the bunch arrival-time information via a low-latency, high-speed link to an accelerator RF control station is needed. The most challenging problems of the signal processing are the synchronisation of several clock domains, regeneration and conversion of optical laser pulses, on-line calibration, and exception handling.
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)
LLNL, Livermore, California
SLAC, Menlo Park, California
UCB, Berkeley, California
Recent progress in accelerator physics and laser technology have enabled the development of a new class of tunable x-ray and gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via CPA. A precision, tunable, monochromatic (< 0.4%) source driven by a compact, high-gradient X-band linac designed in collaboration with SLAC is under construction at LLNL. High-brightness (250 pC, 3.5 ps, 0.4 mm.mrad), relativistic electron bunches will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable γ-rays in the 0.5-2.5 MeV photon energy range. This gamma-ray source will be used to excite nuclear resonance fluorescence in various isotopes. A very compact version of the accelerator (2.5 m) will also be used to generate medical x-rays in the 15-25 keV range. Fields of endeavor include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status will be discussed, along with important applications, including nuclear resonance fluorescence and high precision medical imaging.
ENEA C.R. Frascati, Frascati (Roma)
In this contribution we combine concepts from different fields to show that the stimulated annihilation of positronium could be technologically achievable in the next future, providing a source of gamma rays to to be exploited for a wealth of applications. We analyze the feasibility of such a device by developing a preliminary design of an electron-positron recombination device for the generation of a “gamma ray laser”.
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.
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
JASRI/SPring-8, Hyogo-ken
A laser-induced Schottky-effect-gated photocathode gun has been developed since 2006. This new type of gun utilizes a laser’s coherency to realize a compact laser source using Z-polarization of the IR laser on the cathode. This Z-polarization scheme reduces the laser pulse energy by reducing the cathode work function due to Schottky effect. A hollow laser incidence scheme is applied with a hollow convex lens that is focused after passing the beam through a radial polarizer. According to our calculations (convex lens: NA=0.15; 60-% hollow ratio), a Z-field of 1 GV/m needs 1.26 MW at peak power for the fundamental wavelength (792 nm). Therefore, we expect that this laser-induced Schottky emission requires just a compact femtosecond laser oscillator. We observed the first emission with a hollow laser incidence scheme (copper cathode illuminated by THG: 264 nm as a pilot experiment). The net charge of 21 pC with 100-fs laser pulse (pulse energy: 2.5 μJ; spot diameter: 200 μm). The maximum cathode surface field was 97 MV/m. This new scheme of gun will be investigated on several metal photocathode materials by comparing radial and azimuthal polarizations at 264, 396,792 nm.
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.
KYMA, Trieste
ELETTRA, Basovizza
Euromisure srl, Pieve S. Giacomo (CREMONA)
During 2009 and the first months of 2010, Kyma Srl, the spin-off company set-up by Sincrotrone Trieste, designed and realized all the insertion devices for the undulator chain at the FERMI@Elettra free-electron laser. The insertion devices manufactured and characterized so far are the following: The Laser Heater Undulator, a short, linearly polarized device, already installed in the FERMI linac. The Modulator, a 3.2 m long, linearly polarized undulator. The Radiator, comprising of six APPLE-II variable polarization undulators, each 2.4 m long. All the above devices have been characterized, both from the mechanical and the magnetic point of view. The measured parameters are in good agreement with the design values. This paper presents the most relevant results of the magnetic measurements carried out on all the above undulators, and describes the characteristics and the performance of the dedicated equipment set-up and used for this measurements.
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.
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.
SLAC, Menlo Park, California
Free Electron Lasers require a variety of beam diagnostics for tuning and feedback. This tutorial will cover radio frequency analog and digital signal processing as used in a variety of instrumentation including beam position, bunch length and arrival time monitors. It will also cover beam profile monitors including wire scanners, fluorescent screens, and optical transition radiation foils, including the issues with coherent emission from high brightness beams. In addition, it will discuss the unique requirements for X-ray instrumentation for existing and future XFELs.
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
ELETTRA, Basovizza
Technische Universität Berlin, Berlin
Physikalisches Institut Albert-Ludwig, Freiburg
Università di Roma "La Sapienza", Roma
The Low Density Matter beamline (LDM) at FERMI@Elettra is scheduled to begin operation in early 2011 as a large collaborative project for experiments on neutral matter beams, and later on trapped species and mass selected ions. FERMI@Elettra is a seeded source comprising two Free Electron Lasers(FELs) that will generate short pulses (25200fs) of VUV (FEL1:12-60eV) and XUV/soft-X-rays (FEL2:60-300eV; third harmonic: up to 900eV) with close-to-transform-limited transverse and longitudinal coherence, and full polarization control. It includes a synchronized broadly-tunable user laser for pump-probe experiments. LDM modular design seeks to exploit these unique features with a flexible choice of target system and detection method. It will supply intense beams of neutral atoms, closed-shell molecules, radicals, and pure/doped clusters (the latter ranging from ultracold helium nanodroplets, to atomic and molecular van der Waals clusters, especially water, to clusters of refractory materials such as metals and their oxides). These can be combined with a set of detectors, working in tandem when possible, for photoelectron/photoion spectroscopy, fluorescence emission, and photon scattering.