SLAC, Menlo Park, California
Electron source and gun technology by its nature is a multi-disciplined endeavor requiring knowledge of beam dynamics with RF fields, static fields and space charge forces as well as the chemistry and surface science related to electron emission and ultra-high vacuum. The need for a broad range of disciplines results because the electrons undergo a sequence of processes involving emission, acceleration and optical matching. This talk describes the physical process of each step with the goal of estimating its lowest possible contribution to the total emittance. The physics of electron emission, space charge forces, and the electron optics of the RF and magnetic fields will be developed and the emittance growth assessed for the gun and low energy portion of the injector. The thermal emittance and other properties of metal and semi-conductor cathodes are briefly reviewed, and the affect these properties have upon the limiting emittance and the gun design will be summarized. And finally, the space charge emittance compensation technique and the Ferrario matching criteria for the booster linac are discussed and critiqued for their emittance limits.
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
ELETTRA, Basovizza
Diamond, Oxfordshire
University of Nova Gorica, Nova Gorica
JLAB, Newport News, Virginia
LBNL, Berkeley, California
ENEA C.R. Frascati, Frascati (Roma)
DEEI, Trieste
MAX-lab, Lund
Some experiences have recently been collected from the FERMI@elettra Free Electron Laser first bunch compressor area. This includes a magnetic compressor, diagnostics for the characterization of the longitudinal and transverse phase space and suitable optics for matching to the downstream part of the linac. We report on the beam dynamics investigations in comparison with the modeling as well as the high level software control that has allowed this experience.
AES, Princeton, New Jersey
EPIC Consulting, Medford, New York
Douglas Consulting, York, Virginia
FHI, Berlin
STI, Washington
Kevin Jordan PE, Newport News, Virginia
HZDR, Dresden
FZD, Dresden
The Fritz Haber Institute of the Max Planck Society in Berlin, Germany will celebrate its Centennial in 2011. Coincident with this event, they will christen a THz Free Electron Laser (FEL) that will operate from 3 to 300 microns. A linac with a gridded thermionic gun is required to operate from 15 to 50 MeV at 200 pC while delivering a transverse rms emittance of 20 mm-mrad in a 1 psec rms, 50 keV rms energy spread bunch at the wigglers. Mid-IR and far-IR wigglers enable this electron beam to deliver the required radiation spectrum. In addition to the longitudinal emittance, a key design requirement is the minimization of the micropulse and macropulse jitter to ensure radiation wavelength stability and timing consistency for pump probe experiments. We present the completed physics and engineering design that delivers the required performance for this device. Shipment is scheduled for the end of the calendar year and the status of fabrication will be summarized.
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
An unaveraged 3D model of the FEL has been developed which can model variably polarised undulators. The radiation field polarisation is self-consistently driven by the electron dynamics and is completely variable. This paper describes both physical model and computational code.
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
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.
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.
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.
DESY, Hamburg
Start-up of the amplification process in x-ray FELs from the shot noise in the electron beam defines a specific behavior of longitudinal and transverse coherence properties of the radiation. Particularly important is the case of an x-ray FEL optimized for maximum gain of the fundamental radiation mode. Applying similarity techniques to the results of numerical simulations allowed us to find universal scaling relations for the main characteristics of an optimized X-ray FEL operating in the saturation regime: efficiency, coherence time and degree of transverse coherence. We find that with an appropriate normalization of these quantities, they are functions of only the ratio of the geometrical emittance of the electron beam to the radiation wavelength. Statistical and coherence properties of the higher harmonics of the radiation are highlighted as well.
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.
JLAB, Newport News, Virginia
UW-Madison/SRC, Madison, Wisconsin
We discuss the use of multipass recirculation and energy recovery in CW SRF drivers for short wavelength FELs. Benefits include cost management (reduced system footprint, RF and SRF hardware, and associated infrastructure such as cryogenic systems), ease in radiation control (low exhaust drive beam energy), ability to accelerate and deliver multiple beams of differing energy to multiple FELs, and opportunity for seamless integration of multistage bunch length compression into the longitudinal matching scenario. Issues include those associated with ERLs, compounded by the challenge of generating and preserving the CW electron beam brightness required by short wavelength FELs. We thus consider the impact of space charge, BBU and other environmental wakes and impedances, ISR and CSR, potential for microbunching, intra-beam and beam-residual gas scattering, ion effects, RF transients, and halo, as well as the effect of traditional design, fabrication, installation and operational errors (lattice aberations, alignment, powering, field quality). Context for the discussion is provided by JLAMP, the proposed VUV/X-ray upgrade to the existing Jefferson Lab FEL.
DESY, Hamburg
The Free Electron Laser in Hamburg (FLASH) is a SASE FEL user facility and in addition serves as a prototype for the European XFEL. The recent upgrade of FLASH with a higher harmonic RF module opens a new possibility for ultra-short low charge operation. The advantage of small transverse emittance at low charges can be used only with strong, linearized bunch compression. At this report we consider simulations of the beam dynamics at low charges and estimate the expected properties of the radiation at FLASH and the European XFEL. We present first experimental results at FLASH.
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.
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.
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.
Fermilab, Batavia
It is recognized that beam manipulations such as a flat beam transformation followed by an emittance exchange (EEX) could support a high gain free-electron laser (FEL) push for shorter wavelengths. An ongoing program on demonstrating the exchange of transverse horizontal and longitudinal emittances at the Fermilab A0 photoinjector (A0PI) has benefited recently from the upgrade of several of the key diagnostics stations. The use of an array of 50-micron wide slits to sample the phase spaces to measure divergences of less than 100 microradians resulted in 20 times smaller images with positions distributed over several mm. Improvements in the screen resolution term and reduction of the system depth-of-focus impact by using YAG:Ce single crystals normal to the beam direction will be described. On the longitudinal side, the requirements to measure small energy spreads (<10 keV) in the spectrometer and bunch lengths less than 500 fs dictated specifications. Upgrades to the Hamamatsu C5680 streak camera and the addition of the Martin-Puplett interferometer addressed the short bunch lengths. An example of the EEX tables will be presented.
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.
DESY Zeuthen, Zeuthen
ThEP Center, Commission on Higher Education, Bangkok
Chiang Mai University, Chiang Mai
The Photo-Injector Test Facility at DESY, Zeuthen site (PITZ) aims to optimize high brightness electron sources for linac-based FELs. Since the performance of an FEL strongly depends on the transverse electron beam emittance, the electron source is studied in details at PITZ by measuring the emittance with the help of the Emittance Measurement Systems (EMSYs). The EMSY employs the slit scan technique which is optimized for 1nC bunch charge and, therefore, it might not be an optimal choice for low charge bunches. To extend the ability of the facility for transverse phase space measurements, a module for phase-space tomography diagnostics and its matching section are installed in 2010. The basic components of the module are four screens separated by FODO cells. It is designed for operation with high charge and low energy beams*. This work studies the performance of the tomography module when it is operated with low charge beams. The influence of different beam parameters is evaluated according to the requirement to match the envelope to the optics of the FODO lattice. Simulation results and phase space reconstructions are presented.
G. Asova et al., ‘Design considerations for phase space tomography diagnostics at the PITZ facility', proceedings of DIPAC 2007, Mestre, Italy.
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. In order to provide electrons to the soft X-ray beam line of the SwissFEL a switchyard is necessary, which will divert the electron beam, with an energy of 3.4 GeV, after the first set of accelerating structures. This switchyard has to be design in such a way to guarantee that beam properties like low emittance, high peak charge and small bunch length will not be spoiled. In this paper we present the schematics and discuss ideas and constraints on the kicker, misalignments and charge fluctuation for the SwissFEL switchyard.
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.
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.
MAX-lab, Lund
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
The MAX IV linac will be used both for injection and top up into two storage rings, and as a high brightness injector for a Short Pulse Facility (SPF) and an FEL (in phase 2). Compression is done in two double achromats with positive R56. The natural second order momentum compaction, T566, from the achromats is used together with weak sextupoles to linearise longitudinal phase space. In this proceeding we present the design of the achromat compressors and initial results from particle tracking through the MAX IV Injector in high brightness mode.
LBNL, Berkeley, California
The Advanced Photoinjector Experiment (APEX) is a part of the Next Generation Light Source (NGLS), a proposed soft x-ray FEL concept being studied at LBNL. The requirements for the beam delivered to the FELs pose restrictions on the beam parameters at the injector. In addition, different modes of operation of the machine may pose different requirements on the beam. In order to optimize the performance of the injector, a genetic multiobjective algorithm has been used. A genetic algorithm is used because of the inherent complexity of the beam dynamics at the energy range in question (0-30 MeV) and the large number of parameters available for optimization. On the other hand, the multiplicity of requirements on the beam, which include beam emittance, beam pulse length, energy chirp, as well as pulse shape and peak current, leads to a mutliobjective approach for the optimization technique. In this paper, we present the status of the optimization simulations, using the ASTRA particle-in-cell code. Different injector setups are presented and the resulting transport solutions are compared to each other and the requirements of the downstream sections of the accelerator.
ELETTRA, Basovizza
Horizontal scraping, geometric and energy collimation of the Fermi@elettra electron beam has been investigated analytically and with the elegant particle tracking code. Beam scraping in the first magnetic bunch length compressor has been characterized in terms of reduction of the transverse emittance and variation of the energy chirp induced by the succeeding linac longitudinal wake field. The locations of the geometric and energy collimators have been identified in the machine lattice. A novel definition of collimation efficiency is proposed that allowed us to identify a configuration of the collimation system that is a compromise between the collimation performance, optics design and available space.
Vanderbilt University, Nashville, TN
We report recent advances in the development of electron sources of extreme brightness approaching the quantum degenerate limit. These cathodes comprise either a diamond field emitter or carbon nanotube and an individual adsorbed atom or molecule. Both emitters are covalent carbon structures and thus have the benefits of high activation energy for atomic migration, chemical inertness, and high thermal conductivity. The single adsorbate produces surface states which result in dramatic resonant enhancement of the field emission current at the allowed energies of those states. The result is a beam with a narrow energy spread that is spatially localized to roughly the size of a single atom. Thus far, we have observed short lived (~1 sec) beams from residual gases of ~6 microamps corresponding to a normalized transverse brightness of ~3·1018 A/m2-str. Whereas conventional field emitters have a quantum degeneracy of <10-4, we estimate the degeneracy of our observed beams to be ~0.1. The use of metal adsorbates should stabilize the effect, allow higher current operation, and provide a long lived source whose brightness approaches the quantum limit.
DESY, Hamburg
Superconducting drive linacs for FEL facilities offer long rf-pulses which can accelerate thousands of electron bunches. Individual bunches are distributed to several beam lines for quasi-simultaneous operation of different user stations. We will present various schemes that fulfill this task and take the fast beam distribution of the European XFEL as an example for design choices. The main challenge is the preservation of the excellent electron beam quality, transversely and longitudinally, which leads to demanding hardware requirements to ensure beam stability and advanced electron optics to prevent emittance degradation due to self-fields.
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.
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).
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.
ELETTRA, Basovizza
University of Nova Gorica, Nova Gorica
LBNL, Berkeley, California
Two machine configurations of the electron beam dynamics in the FERMI@elettra linac have been investigated, namely the one-stage and the two-stage electron bunch compression. One of the merits of the one-stage compression is that of minimizing the impact of the microbunching instability on the slice energy spread and peak current fluctuations at the end of the linac. Special attention is given to the manipulation of the longitudinal phase space, which is strongly influenced by the linac structural wake fields. The electron bunch with a ramping peak current is used in order to obtain, at the end of the linac, an electron bunch characterized by a flat peak current profile and a flat energy distribution. Effects of various jitters on electron bunch energy, arrival time and peak current are compared and relevant tolerances are obtained.
ELETTRA, Basovizza
LBNL, Berkeley, California
Simulations of the microbunching instability through the FERMI@elettra lattice have been carried out with elegant particle tracking code. This paper focuses on the emittance growth induced by the microbunching instability in the high energy transfer line that guides the electron beam from the linac to the undulator chain. The perturbation to the transverse emittance induced by coherent synchrotron radiation and longitudinal space charge as function of the R56 transport matrix element in the transfer line have been investigated separately and in the presence of their mutual interaction. Simulation results show that the betatron phase mismatch may have a detrimental impact on the final beam emittance.
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.
ANL, Argonne
European XFEL GmbH, Hamburg
Free-electron lasers for hard x-rays can be constructed in oscillator (XFELO) configuration, providing ultra-high spectral purity and brightness [1]. The average brightness is expected to be several orders of magnitude higher than, and peak brightness comparable to that of SASE XFELs. XFELOs can enable revolutionary scientific opportunities as well as drastically improve experimental techniques developed at third-generation x-ray facilities. Low-loss x-ray crystal cavity and ultra-low-emittance electron beams are two major technical challenges in the realization of XFELOs. The requirements to x-ray cavity components are demanding: diamond crystals and curved grazing incidence mirrors must have near-perfect reflectivity, negligible wave-front distortions, and are subject to very tight tolerances on angular, spatial, and thermal stability under high heat load of the XFELO radiation. This paper gives an overview on the recent progress [2-4] and future plans in the R&D on the feasibility of x-ray cavities for XFELOs. The experimental and simulation studies results provide strong evidence for the feasibility of the x-ray cavities.
1. K-J. Kim, et al, PRL 100 (2008) 244802
2. Yu. Shvyd'ko, et al, Nature Phys. 6 (2010) 196
3. S. Stoupin, Yu. Shvyd'ko, PRL 104 (2010) 085901
4. S. Stoupin et al, Rev. Sci. Instr. 81 (2010) 055108
MAX-lab, Lund
The MAX IV project was given the green light in April 2009. The construction will begin in the near future with aim to have the first beamlines in operation during 2015. The main sources at MAX IV are two storage rings (1.5 GeV and 3 GeV) with state-of-the-art low emittance (*) for the production of soft and hard x-rays. The linac injector will also provide short pulses to a short pulse facility (**).
* S C Leemann et al, Beam dynamics for
the MAX IV 3 GeV storage ring. Phys. Rev. ST Accel. Beams,
12:120701, 2009.
** S Werin et al, Short pulse facility for MAX-lab, Nucl Instrum Methods A. 601[1-2] 98-107, 2009