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.
SLAC, Menlo Park, California
LLNL, Livermore, California
The Linac Coherent Light Source (LCLS) is a Free Electron Laser (FEL) operating with a fundamental wavelength ranging from 1.5-0.15 nm. Characterization of the higher harmonics present in the beam is important to users, for whom harder X-rays can either extend the useful operating wavelength range or represent a background to measurements. We present here measurements of the power in both the second and third harmonics.
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.
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.
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.
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.
PSI, Villigen
DESY, Hamburg
The spectral and angular distribution of the radiation intensity by a single and individually radiating electron is in principle different from what expected from a high density electron beam. For a given wavelength, the beam particle density modifies via a charge form factor the angular and spectral distributions characterizing the radiation emission by a single electron. In particular, under high energy and high particle density conditions, the Transition Radiation (TR) energy spectrum by an electron beam is expected to be affected by the electron-transverse-density that, at very short wavelength even in the visible, in principle - can influence the number of photons emitted at a given wavelength and their angular distribution (brightness increase with density). The investigation of such a phenomenon is relevant to beam diagnostics and to understand the bunch collective effects influencing TR emission. The status of the experimental investigation of the beam-transverse-size effects in the Optical Transition Radiation (OTR) at SLS and, in perspective, at the SwissFEL will be presented and the main formal aspects of the model predicting them will be described.
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.
Tohoku University, School of Scinece, Sendai
The t-ACTS (test Accelerator as Coherent THz Source) at Tohoku University will provide intense terahertz radiation employing novel sources such as an isochronous accumulator ring and a pre-bunched free electron laser. Stable production of the very short electron pulse is a key issue for the t-ACTS accelerator system, in which a thermionic RF gun is being used. Particularly observation of the longitudinal phase space of the beam extracted the gun is crucial for efficient bunch compression. Because of space charge effect, the beam has to be diagnosed within a short drift space. We have studied a novel energy spectrometer using Cherenkov radiation (Linear Focal Cherenkov ring camera, LFC-camera). Though the method is valid for the lower energy less than 3 MeV, the energy distribution can be measured immediately at the gun exit. In addition to the present status of the t-ACTS project, we describe the principle of LFC camera and discuss energy resolution, prospect of the direct measurement of the particle distribution in the longitudinal phase space as well.
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.
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.
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.
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.
ELETTRA, Basovizza
The advent of FEL sources has brought new possibilities for experimentalists performing measurements that are challenging in terms of time resolution, flux, coherence, and so on. One of the most important points, however, is the capability of characterizing the FEL photon beam so to determine the different parameters of each pulse hitting the system under investigation. For this reason it is mandatory to realize diagnostics sections along FEL user facilities recording beam pulse-resolved features such as the absolute intensity, the energy spectrum, the beam position, the time arrival, and the wavefront. For other parameters like the coherence and the pulse length, on the other side, a direct and online detection is not possible. At FERMI@Elettra, the Italian FEL facility, a dedicated diagnostic section called PADReS (Photon Analysis Delivery and Reduction System) will be installed after the undulatory' exit, and it will serve as a source of pulse-resolved informations for end-users. In this talk the instruments that are part of typical FEL diagnostic sections will be described using PADReS as a real example to see the roles of the different diagnostic tools.