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.
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.
RIKEN/SPring-8, Hyogo
XFEL/SPring-8 construction was started in 2006, aiming at generating X-ray laser at 1 Angstrom. The building construction was completed in April 2009, followed by installation of accelerator components. In March 2010, we completed all accelerating structure installation. The klystron modulator and LLRF systems are under installation. We use 19 undulator of in-vacuum type (5 m each). At this moment 10 undulators have been installed and careful qualification of undulator field is carried out. We will start high power processing in this October, and we will send the first electron beam into beam dump before April 2011, followed by beam commissioning for X-ray lasing.
PSI, Villigen
The Paul Scherrer Institut is planning to construct a free electron laser covering the wavelength range of 1-70 Å. This project, “SwissFEL” will use a C-band radio-frequency linac of variable energy, 2.1 GeV to 5.8 GeV. The laser will be equipped with two undulator lines. A short period (15 mm) in-vacuum undulator, ‘Aramis’ will provide hard X-ray radiation in the range 1 Å to 7 Å. A 40 mm period APPLE-type undulator ‘Athos’ will provide wavelengths from 7 Å to 7 nm. The accelerator will employ an S-band RF photo-gun and an S-band injector providing a low normalized slice emittance (~ 0.3 mm-mrad @ 200 pC) beam of 450 MeV. The initial photo-current of 22 Amperes is increased to 2.7 kA through the use of two magnetic chicane bunch compressors. Acceleration to full energy is provided by twenty-six C-band RF “modules” each consisting of four, 2 m long, C-band structures. We will describe the status of the project and in particular the design of the accelerator. The beam dynamics simulations which have led us to our base-line design will be discussed and a description of the basic RF module will be given. A schedule for the project realization will also be presented.
* Submitted by T. Garvey on behalf of the SwissFEL project group
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.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
STFC/DL/SRD, Daresbury, Warrington, Cheshire
An infra-red oscillator FEL was installed into the accelerator test facility, ALICE, at Daresbury Laboratory at the end of 2009. The FEL will be used to study energy recovery performance with a disrupted, large energy spread, beam and also to test novel FEL concepts. This paper will describe the installed hardware, the pre-alignment techniques that have been employed, the diagnostics that are being used to detect the infra-red output, and the progress with commissioning of the FEL itself.
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.
NASU/IRE, Kharkov
Using a time-dependent approach the analysis and optimization of a planar FEL-amplifier with an axial magnetic field and an irregular waveguide is performed. By applying methods of nonlinear dynamics three-dimensional equations of motion and the excitation equation are partly integrated in an analytical way. As a result, a self-consistent reduced model of the FEL is built in special phase space. The reduced model is the generalization of the Colson-Bonifacio model and takes into account the electrons’ intricate dynamics and intramode scattering. The reduced model and concepts of evolutionary computation are used to find optimal waveguide profiles. The numerical simulation of the original non-simplified model is performed to check the effectiveness of found optimal profiles. The FEL parameters are chosen to be close to the parameters of the experiment*, in which a sheet electron beam with the moderate thickness interacts with the TE01 mode of a rectangular waveguide. The results strongly indicate that one can improve the efficiency by a factor of five or six if the FEL operates in the magnetoresonance regime and if the irregular waveguide with the optimized profile is used.
*S. Cheng et al. IEEE Trans. Plasma Sci. 1996, vol. 24, p. 750
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.
SLAC, Menlo Park, California
Frequency-chirped FELs are useful to generate a large photon bandwidth or a shorter x-ray pulse duration. In this paper, we present a three-dimensional analysis of a high-gain FEL driven by the energy-chirped electron beam. We show that the FEL eigenmode equation is the same for a frequency-chirped FEL as for an undulator-tapered FEL. We study the transverse effects of such FELs including mode properties and transverse coherence. Comparison with numerical simulations are also discussed.
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.
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.
RIKEN/SPring-8, Hyogo
The commissioning of the XFEL/SPring-8 facility is scheduled in the spring of 2011. Since the accelerator of XFEL/SPring-8 uses a thermionic gun with an 1 A initial beam current, the total bunch compression ratio reaches about 3000, which is one order higher than a photocathode system. For nonlinearity compensation in the bunch compression, two correction cavities are installed, which are operated at the same frequency as the linac and not at its higher-harmonic. A large compression ratio, particularly at the velocity bunching, results in larger projected parameters of the electron bunch compared to its slice values. The transverse optics of the accelerator is designed for the projected parameters using newly introduced linear formulation of the beam envelope including acceleration effects. The beam optics of the main linac and undulator sections are based on a FODO-like lattice and additional quadrupole magnets are installed at each chicane for dispersion correction. In this presentation, the XFEL/SPring-8 accelerator layout and its expected beam parameters are shown to achieve the 0.1 nm X-ray FEL.
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
With bright electron beams the full length of gap-tunable X-ray FEL undulators can be efficiently used to generate multiple x-ray beams with different independent wavelengths for simultaneous multi-user operation. We propose a betatron switcher and show that one only needs to install a compact fast kicker in front of an undulator without any modifications of the undulator itself. Different groups of bunches get different angular kicks, and for every group a kick is compensated statically (by corrections coils or moving quadrupoles) in a part of the undulator, tuned to the wavelength designated to the given group. As a generalization of the method of the betatron switcher, we briefly describe a scheme for pump-probe experiments.
Fermilab, Batavia
A superconducting (SC) RF Test Accelerator at the New Muon Lab (NML) is currently under construction at Fermilab. Its design goals include the replication of the pulse train proscribed for the International Linear Collider (ILC) and operations with the prototypic beam of the base RF unit. At 3 nC per micropulse and with 3000 micropulses per macropulse at a 5-Hz rate and at 750 MeV, a 40-kW beam would be generated. An RF photoelectric gun based on the PITZ-Zeuthen design will generate the beam which has a lower emittance of about 1-2 pi mm mrad when run at 1 nC or less per micropulse based on tests at Zeuthen. This beam quality is sufficient, when properly bunch compressed, to provide the driving beam for an extreme ultraviolet (EUV) and soft x-ray (SXR) self-amplified spontaneous emission (SASE) free-electron laser (FEL) or seeded FEL. Estimates for the gain length and output power have been calculated for wavelengths from 80 to 12 nm (at 1.5 GeV) using the simple scaling formula of M. Xie. This wavelength regime with 200-fs bunch lengths would complement the hard x-ray SASE FEL project at SLAC in the USA.
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.
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.
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.
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.
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.
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.
JASRI/SPring-8, Hyogo-ken
In recent years ultimate storage ring has been studied aiming at ultra-small emittances and ultra-bright synchrotron radiation. Z. Hung et al.* studied an FEL in the EUV and soft x-ray regions in one of such rings as PEPX 4.5 GeV storage ring and showed that the three orders of magnitude improvement in the average brightness is possible at these radiation wavelengths. We studied an ultimate storage ring that has 0.034 nm-rad natural emittance and 5.4 MeV energy spread at 6 GeV**. The normalized emittance is 0.2 μm-rad with full coupling and the relative energy spread is 0.089 %. As smaller beam emittances and higher beam energy have possibilities of shorter wavelength FELs, we studied the feasibility of high-gain FELs in the range of x-ray regions as well as soft x-ray regions. In this paper we present the results of analysis and simulation of high-gain FEL in the ultimate storage ring.
*Z. Hung, et al., Nucl. Instr. Meth. A 593 (2008) 120.
** K. Tsumaki, N. Kumagai, Nucl. Instr. Meth. A 565 (2006) 394.
SLAC, Menlo Park, California
The success of LCLS [1] generates strong motivation and solid technical basis to extend its capabilities. The upgrade will extend x-rays wavelength range down to 0.06 nm. A new soft x‐ray adjustable‐gap undulator line will produce FEL with wavelengths up to 6 nm. To allow full electron beam rate and independent electron beam parameters in each line, a new injector and pair of bunch compressors will be added to the second kilometer of SLAC linac. The electron from this linac part will bypass the LCLS accelerator into the soft x‐ray undulators which can provide two FEL pulses with variable delay and photon energy and may be configured for narrow bandwidth pulse via self‐seeding. External seeding with the echo‐enabled harmonic generation can improve temporal coherence. The new bypass line can add multiple electron bunches within each RF pulse. LCLS‐II will provide polarization control and can incorporate the low‐charge, few‐femtosecond pulse duration operating mode. A THz radiation source will be included to provide x‐ray/THz pump‐probe capabilities. The schemes and parameters are based on measurements and experience at LCLS.
1. P. Emma et al., Nature Photonics (accepted, 2010).
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.
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.
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
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.
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.
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
UCLA, Los Angeles, California
Success of the world's first x-ray (0.15-1.5 nm) free electron laser (FEL) - LCLS - at SLAC opens the gate for new science. In this paper, we study the FEL performance for a two-stage self-seeding scheme by introducing a photon monochromator and an electron by-pass in the undulator system. The FEL generated in the first part of the undulator system is purified in spectrum, recombines with the electron bunch, and is amplified in the second part of the undulator system to saturation. Such modifications will improve the FEL longitudinal coherence, reducing the FEL band-width by two-orders of magnitude, but with similar peak power; hence improving the peak brightness by two-orders of magnitude. Such a self-seeding scheme is studied for both soft x-ray (200 eV to 2 keV) and hard x-ray (800 eV to 8 keV) cases with single electron bunch. The photon monochromator system is configurated as variable line spacing gratings for soft x-ray and single crystal for hard x-ray. Harmonic Generation and Chirped FEL are also considered aiming at reaching even shorter wavelength x-ray photons and at generating FEL pulse with even shorter temporal duration, respectively.
SLAC, Menlo Park, California
LBNL, Berkeley, California
A complete optical system including grating monochromator and mirrors was designed to provide self-seeding of the soft X-ray undulators to be possibly built as part of the LCLS-II project. The grating monochromator consisted of a cylindrical horizontally focusing mirror, a plane vertically deflecting pre-mirror, a variable-line-spacing plane vertically deflecting grating, a horizontal exit slits, and a spherical vertically collimating mirror. The grating monochromator was designed to operate in the fixed-focus mode and tuning of the energy was designed to be achieved by rotations of only the pre-mirror and the grating. Only one ruling of 2200 l/mm was needed to cover the energy range from 200 to 2000 eV with an almost constant resolving power of greater than 22700. The monochromator would produce fully transform-limited pulses of 12 fs (rms) long at 2000 eV or 120 fs (rms) long at 200 eV with sufficient power to allow seeding. The optical system produced a slightly energy-dependent time delay of about 10 ps. The transverse size of the input beam was preserved in the horizontal direction, but was reduced in the vertical direction depending on the tuning energy.
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.
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.
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.
FOM Rijnhuizen, Nieuwegein
Several of the short-pulse FELs that are operated in a wavelength range starting well below and ending well above 100 microns make use of a partial waveguide in the resonator and a central hole in one of the mirrors for outcoupling. The purpose of the waveguide is to confine the optical mode, in particular within the gap of the undulator. Experimentally, it was found that these FELs suffer from one or a number of tuning 'gaps': narrow wavelength windows within the tuning range where the output is strongly reduced or where the laser even does not turn on. Recently, Prazeres et al.[1] , using a simulation model, were able to reproduce some of the main features of the tuning curve and showed that the cavity outcoupling and losses change abruptly across a tuning gap. In this contribution we will present experimental results for the gain, cavity loss, saturated power and spectral intensity across one of the most prominent gaps in the tuning curve of the FELIX long-wavelength FEL. Both for the normal case and for the case where a slit is used to limit the optical mode extent on the free-space mirror.
[1]. R. Prazeres, F. Glotin, and J.-M. Ortega, PRST-AB, 12 (2009) 010701
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.
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.
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.
UCLA, Los Angeles, California
SLAC, Menlo Park, California
Success in commissioning the world's first x-ray (0.15-1.5 nm) free electron laser (FEL) - the LINAC Coherent Light Source (LCLS) - at SLAC National Accelerator Laboratory opens the gate for new science. Further improving the FEL spectrum bandwidth, shortening the FEL pulse temporal duration, and generating even higher energy x-ray photons are urged by various potential users. In this paper, we study the possibility of generating femtosecond duration X-ray pulses with a variable photon energy from 1.5 to 48 keV, using an electron beam with the same characteristics of the LCLS beam, and a planar undulator with additional focusing. We assume that the beam energy can be changed, and the undulator has a variable gap, allowing the undulator parameter to be changed from zero to a maximum value. It is assumed to be operated in an ultra-low charge and ultra-short pulse regime.
MAX-lab, Lund
The MAX IV injector is funded and under construction. It is designed to drive a Short Pulse Facility generating spontaneous incoherent photon pulses in the keV range with pulse lengths below 100 fs in the first phase of the project. This source will with minor modifications be able to drive a Free Electron Laser down into the soft X-ray region and with an extended energy a full X-ray FEL at 1-2 Å. The key feature of the system is the availability of a 3-3.5 GeV linac, a low emittance photo cathode RF-gun and two bunch compressors including sextupoles for linearization. By extracting pulses of 0.1-0.2 nC charge, normalized emittances below 1 mm mRad and peak currents above 3 kA can be achieved. Such pulses are very well suited for a FEL facility. We describe the MAX IV injector system and discuss the options and perspectives for an X-ray FEL at the MAX IV facility.
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.
PSI, Villigen
This paper introduces the architecture and first beam commissioning results of the standard BPM system for the SwissFEL test injector, a 250MeV linac that is progressively being commissioned in order to perform R&D for the "SwissFEL" 5.8GeV hard-X-ray FEL facility proposed at PSI. Since the SwissFEL has a nominal bunch charge range of 10-200pC, the test injector is equipped with 500MHz resonant stripline BPMs that are optimized for high dynamic range and sensitivity, to support machine operation well below 10pC. Beam tests with a 5 GSa/s direct sampling electronics designed at PSI showed a single-bunch resolution of <20um RMS at 2pC and typically 7um RMS for charges >10pC. The BPMs also measure bunch charge, insensitively to dark current, with <30fC RMS resolution at 2pC.
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.
SLAC, Menlo Park, California
The Linac Coherent Light Source at SLAC is a hard X-ray FEL which was designed for single electron bunch operation. Although most user experiments are not interested in multiple bunches from an S-band linac due to their short (ns) separation, there are some advantages with multi-bunch operation. Starting with two bunches where the delayed light of one bunch is used to seed the light of a second bunch, to many more bunches to increase the likelihood of rare target collisions, multi-bunch operation would open more options for the LCLS. In the past the SLAC Linac has operated with a few dedicated bunches for the SLC (Stanford Linear Collider), and up to 1400 bunches for some fixed target experiments, so a few bunches for the LCLS seems possible even with the original single bunch design. This paper will describe how the current RF implementation supports multi-bunch operation. Initial experimental tests with two bunches are presented.
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
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.
PSI, Villigen
Transverse beam trajectory control is of great importance for SwissFEL as the lasing strategy is based on a relatively low energy and low emittance beam compared with other X-FEL facilities, thus aiming at a reasonable construction cost and size of the facility. A study of beam based alignment and orbit feedback has been performed, and a trajectory correction scenario, which would fulfill the beam requirements as well as the hardware constraints, has been set up. The beam based alignment will be discussed for the linac and the undulator section separately because of the much tighter tolerance in the latter. Several correction algorithms are examined using numerical simulations. BPM requirements and orbit feedback concept will be discussed, with reference to some available data on dynamic disturbances such as ground motion at the PSI site, e.g. at the SwissFEL injector test facility currently under commissioning.
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”.
SINAP, Shanghai
A compact hard X-ray FEL facility is proposed based on self-amplified spontaneous emission (SASE) scheme, which is aiming at generating 0.1nm coherent intense hard X-ray laser with the total facility length less than 600m. To reach this goal, low emittance S-band photo cathode injector, high gradient C-band linear accelerator and short period cryogenic undulator are used. Simulation results show that 0.1nm coherent hard X-ray FEL with peak power up to 10GW can be generated from a 50-m-long undulator when the slice emittance of the electron beam is about 0.4mm-mrad. The energy of the electron beam is only 6.4GeV which is available in accelerator length of 230m with the help of 40MV/m C-band rf system. This paper describes the physic design of this ultra-compact hard X-ray FEL facility.
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).
Kyoto IAE, Kyoto
The bulk high temperature superconductor staggered array undulator (Bulk HTSC SAU) has potential to generate strong periodic magnetic field in short period and to control K value without a mechanical gap control structure.* However, availability of the bulk HTSC magnets having matched performance of critical current density is a problem to be solved. In this study, we have numerically and experimentally estimated influence of variation of critical density upon field error. It was numerically found that the field error was naturally compressed, because the difference in critical current density was compensated by natural variation of the region where the supercurrent flows. In the conference, the experimental results of the field error compression and principle of the compression will be discussed.
* R. Kinjo, et al., “BULK HIGH-TC SUPERCONDUCTOR STAGGERED ARRAY UNDULATOR”, Proceedings of FEL 2008, 473 (2009).
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.
BNG, Würzburg
Karlsruhe Institute of Technology (KIT), Karlsruhe
Superconducting undulators show, with respect to permanent magnet undulators, a larger magnetic field strength for the same gap and period length, being able to generate a harder X-ray spectrum and higher brilliance X-ray beams. The worldwide first short period length superconducting undulator is in operation since 2005 at the synchrotron light source ANKA in Karlsruhe. To further drive the development in this field a research and development program has been defined. A 1.5 m long superconducting undulator with a period length of 15 mm is planned to be installed in ANKA at the end of 2010 to be the light source of the new beamline NANO for high resolution X-ray diffraction. The key specifications of the system are an undulator parameter K higher than 2 and a phase error smaller than 3.5 degrees. The coils will be cooled using cryocoolers and should have a capability of withstanding a 4 W beam heat load at 4 K. Here we describe the main features of the 1.5 m long superconducting undulator, the test results of the coils in liquid helium and the test results of a prototype switchable period length device.
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.
MSL, Stockholm
DESY, Hamburg
European XFEL GmbH, Hamburg
The Manne Siegbahn Laboratory at Stockholm University is currently involved in two separate projects at the European XFEL. The first concerns the fiducialization and characterization of the quadrupole magnets in the undulator sections. A recently upgraded rotating coil system measures the magnetic centre stability during magnet excitation, magnet gradient and field error components. In connection, a coordinate measuring machine is used to fiducialize the quadrupole magnetic centre to better than 0.050 mm. The second project concerns high precision measurements of the undulator temperature. The SASE radiation intensity depends strongly on the undulator period and the magnetic field strength, which are both sensitive to temperature. Instead of keeping the temperature within 0.1 degrees along the undulator tunnel, a temperature compensation scheme can be applied. Here, a change in temperature initiates adjustment of the undulator gap to compensate for changes in magnetic field. A system for undulator segment temperature measurement, with resolution of 0.03 degrees, necessary for the compensation scheme, is presented together with a brief overview of the upgraded rotating coil system.
Kyoto IAE, Kyoto
The bulk high temperature superconductor staggered array undulator (Bulk HTSC SAU) has several advantages: such as strong magnetic field, potential of short period undulator, K value variability without gap control. In addition to these advantages, the Bulk HTSC SAU can be used near the electron beam because the undulator is expected to show good performance at 20 30 K. In the conference, we will report the expected performance of the undulator at low temperature through magnetic measurement by using a superconducting quantum interference device (SQUID) magnetometer. Also we will report the results of the first operation at 4 77 K of new prototype undulator consisting of a helium cooling system and a 2 T superconducting solenoid.
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.
SINAP, Shanghai
Abstract: The Shanghai deep ultraviolet FEL (SDUV-FEL) with single-stage to higher harmonics is designed and most equipment of accelerator is performed and operating. In this paper, we present the instrumentations on the proof-of principle experiment of FEL physics study. We discuss diagnostic techniques for testing photo cathode RF gun and magnetic bunch compressors, and undulator sections including a modulator undulator. The multiple alignment-laser station is used for pop-in equipments alignment in the undulators. We also investigated the observed e-beam size using OTR and YAG in the cameras using the near-field focus. Network camera and network techniques are used on monitor components. It will be described in this report also.
* SDUV-FEL is at SINAP in Shanghai.