Diamond, Oxfordshire
A New Light Source project has been initiated to deliver a conceptual design for a next-generation light source facility in the UK. One option for such a light source is a free electron laser based on normal-conducting linac technology. This paper considers the different options available for waveband, gun and rf design of a normal-conducting linac FEL, and presents an overview of accelerating structure, modulator and klystron capability and availability. Particular attention is paid to the issue of the operation of a normal-conducting device at repetition rates of several hundred pulses per second. Overall capabilities and limitations of this approach are illustrated by reference to a start-to-end model of a suitable 3 GeV S-band linac design.
DESY, Hamburg
In order to compensate nonlinear distortions of the longitudinal phase space a rf section operated at three times the 1.3 GHz frequency of the existing TTF cavities is foreseen in the next phase of FLASH. Four modules of a nine-cell 3.9 GHz cavities will be installed right after the first accelerating module ACC1. These cavities could cause additional long-range wake fields which would affect the multi bunch (mb) beam dynamics leading to increase of the mb emittance. The mb emittance at the end of the linac is determined by the strength of the transverse wake fields in the rf system. These higher order modes appear after any off-crest moving bunch, which could happen either due to the cavity misalignment, or by transverse position fluctuations of the injected bunches. It is intended to damp them by means of the HOM couplers, which may reduce the damping time by factor of 105. The misalignment of the cavities offsets is expected to be by 0.5 mm rms. The paper describes the results of the simulations on the dependence of the mb emittance on cavities misalignment offsets and damping strength of the HOM couplers in the planned 3.9 GHz rf section.
DESY, Hamburg
The XFEL injector building has a length of 74.3 metres and is divided by 2.5 m long concrete shielding wall. The section upstream the shielding wall will have a length of 42.3 m and give place for the gun, accelerating module, 3rd harmonic section, laser heater and the beam diagnostics section. At its end the possibility for the beam dump is foreseen so that the tuning of the beam in the injector would become possible without any impact on the subsequent parts of the XFEL. Each of these components sets certain requirements on beam optics which may compete with each other. Downstream the shielding the beam will be vertically displaced by 2.75 m over the distance of 20 m by means of the so called dogleg - a combination of two four cell arcs (8 cell system). Since the vertical displacement takes place there it is important to optimize cells in such an order that the chromatic effects don't impact the beam quality noticeably. In this paper we describe the solution for the beam optics at the XFEL injector.
DESY, Hamburg
INFN/LASA, Segrate (MI)
Fermilab, Batavia
Ultra short bunches with high peak current are required for the creation of high brilliance coherent light in the VUV and X-ray range in undulators. At the Free Electron Laser in Hamburg (FLASH) and the European X-ray free electron laser (XFEL) they are obtained by a two stage bunch compression scheme based on acceleration off the rf field crest and transverse magnetic chicanes. The deviation of the rf field's sine shape from a straight line leads to long bunch tails and reduces the peak current. This effect can be eliminated by adding a third harmonic rf system. The paper gives an overview on the actual status of the beam dynamical examinations and as well on the development of the third harmonic sub-systems like modules, cavities and radio frequency systems for FLASH and the XFEL.
DESY Zeuthen, Zeuthen
INRNE, Sofia
DESY, Hamburg
YerPhI, Yerevan
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
INFN/LASA, Segrate (MI)
BESSY GmbH, Berlin
Uni HH, Hamburg
MEPhI, Moscow
Funding: This work was partly supported by the European Community, contracts RII3-CT-2004-506008 and 011935, and by the 'Impuls- und Vernetzungsfonds' of the Helmholtz Association, contract number VH-FZ-005.
The Photo Injector Test facility at DESY, Zeuthen site, (PITZ) was built to develop and optimize high brightness electron sources for Free Electron Lasers (FELs) like FLASH and the European XFEL. In the last shutdown a new RF gun cavity with improved water cooling was installed and conditioned. It is the first rf gun where the surface cleaning was done with dry ice technique instead of high pressure water rinsing and it showed a 10 times lower dark current emission than its precursor gun, even at cathode gradients as high as 60M V/m. In addition, a new photo cathode laser system was installed and will be available for operation in spring 2008. It will allow flat-top temporal laser shapes with 2ps rise/fall time. According to beam dynamics simulations this will further improve the beam quality reported at earlier conferences* and will lead to unprecedented low transverse projected emittance beams at a charge level of 1nC. This contribution will summarize the experimental results from the summer 2008 running period covering transverse projected emittance optimization, thermal emittance from the photocathode, longitudinal phase space and first transverse slice emittance measurements.
* L. Staykov et al., "Measurements of the Projected Normalized Transverse Emittance at PITZ", Proceedings of the FEL 2007, Novosibirsk, Russia, August 2007.
Kyoto IAE, Kyoto
An MIR-FEL facility, Kyoto University FEL (KU-FEL), has been developed for applications in "sustainable energy science", such as fundamental studies on high-efficiency solar cells. The KU-FEL, consisting of an S-band thermionic rf gun, a 3 m accelerator tube and a planer undulator, aims to generate 4-13 μmeter tunable FEL. The first lasing was achieved on March, 2008 at 12.4 μmeters by using a beamloading compensation method both in the rf gun and in the accelerator tube. *Furthermore, we introduced detuning to the rf gun and succeeded to generate an electron beam with macropulse duration of 5.1 μseconds, average current of 100 mA and energy spread of 0.5% which led to power saturation in FEL. In the conference, the improvements of the electron beam properties and power saturation of the KU-FEL will be discussed.
*H. Ohgaki et al., 'First Lasing at 12 um Mid Infrared Free Electron Laser at Kyoto University', Japanese Journal of Applied Physics, accepted for publication. (2008).
JINR, Dubna, Moscow Region
JINR/LHE, Moscow
800 MeV electron linac (LINAC-800) is under construction at JINR. It will be used as a driver for Volume FEL and as a test bench for commissioning of elements of the ILC. Presently the electron injector is commissioned and the electron beam of 50 keV of the energy at current of about 15 mA was obtained. The results of the injector operation at nominal parameters (400 keV, 300 mA) and commissioning of the first accelerating section at 20 MeV are discussed.
PSI, Villigen
In the planned PSI-XFEL facility, three FEL branches will supply coherent, ultra-bright, and ultra-short XFEL photons at wide wavelength range. FEL branch 1 will use a 6.0 GeV driving linac to generate hard X-rays from 0.1 nm to 0.3 nm, while FEL branch 2 is foreseen for X-rays from 0.3 nm to 1.0 nm. However, FEL branch 3 was designed to supply spatially as well as temporally coherent soft X-rays from 1.0 nm to 10 nm with the High-order Harmonic Generation based seeded HGHG scheme. To reach emittances of 0.2 mm.mrad and to squeeze consequently the whole facility within an 800 m long tunnel, PSI is presently developing an advanced low emittance gun (LEG) based on a 1 MV high gradient pulsed diode and field emission. The advanced LEG will be used to drive FEL branch 1 and 2, while an RF photoinjector will be used to drive the FEL branch 3. In this paper, we describe a CTF3 RF gun based injector, two bunch compressors, two diagnostic sections, and linacs for the PSI-XFEL FEL branch 3.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
The UK's new light source project was officially launched on April 11th 2007, which will be based on advanced conventional and free electron lasers, with unique and world leading capabilities. User consulation exercises have already been initiated to determine the fundamental photon output requirements for such a machine. In order to match a nominal requirement for high repetition rates (extending up to 1 MHz), a series of superconducting rf (SRF) linac options have been investigated, reflecting varied beam loading conditions and subsequent high and low power rf solutions.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Several laboratories concentrate their efforts on development of high repetition rate FEL based next generation light sources. One particular concept under development at STFC Daresbury Laboratory specifies high brightness electron bunches with a charge of 0.2-1 nC which arrive with a frequency up to 1 MHz. As emittance of the bunches should not exceed 1 um, traditional high repetition rate thermionic injectors, similar to the ones used at high micropulse repetition rate FELs like ELBE or FELIX, may not be used. We consider three options of high repetition rate injectors based on photocathode guns - a high voltage dc gun, a one and half cell superconducting rf gun and a normal conducting VHF gun, recently proposed at LBNL. We consider practical injector schemes for all three guns and provide the results of beam dynamic simulations. We also discuss the photocathodes which may be used in each gun, as this critical component defines achievable beam parameters and operational efficiency of the injectors.
ANL, Argonne
SLAC, Menlo Park, California
Funding: Work Argonne supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-06CH11357.
A Beam-Loss Monitor (BLM) system based on the detection of Cerenkov radiation is in development at the Advanced Photon Source (APS) for the Linac Coherent Light Source (LCLS) free-electron laser. The electron beam will vary in energy nominally from 4 to 14 GeV with a beam charge of 0.2 to 1.0 nC and a maximum repetition rate of 120 Hz. To limit radiation-induced demagnetization of the undulator permanent magnets, the BLM will provide beam-loss threshold detection as part of the Machine Protection System (MPS). The detector incorporates a large volume (30 cc) fused silica Cerenkov radiator coupled to a photomultiplier tube (PMT). The output of the PMT is conditioned locally by a charge amplifier circuit and then digitized at the front end of the MPS rack electronics. During commissioning, the device will be calibrated by inserting a 1-micron aluminum foil into the beam, upstream of the undulator magnets. The present design calls for five BLM detector units to be distributed throughout the 33 undulator magnets. Beam-based testing is to begin at the APS storage ring during the summer of 2008. Details and status of the detector hardware, electronics, and simulations will be discussed.
NPS, Monterey, California
Niowave, Inc., Lansing, Michigan
MIT, Middleton, Massachusetts
Stanford University, Stanford, Califormia
Funding: This research is supported by the Office of Naval Research and the Joint Technology Office.
The Naval Postgraduate School (NPS) has begun the design and assembly of the NPS Free-Electron Laser (NPS-FEL). As part of this effort, the original dc gun-based injector system is being refurbished and upgraded. As described in the accompanying paper 'Status of the NPS-FEL' (these Proceedings), the overall NPS-FEL design parameters are for 40 MeV beam energy, 1 nC bunch charge, and 1 mA average beam current, in an energy-recovery linac configuration. As we move towards this configuration, the injector system will be incrementally upgraded to add photocathode capability, have a higher final beam energy, and improve the beam brightness, to meet the demands of the overall experimental program. This paper describes the current status of the injector system, the initial set of experiments planned, and the projected upgrade path.
Fermilab, Batavia
Funding: Work supported by the Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. DOE and by Northern Illinois University under Contract No. DE-FG02-08ER41532 with the U.S. DOE
We demonstrate analytically and via numerical simulation, how a longitudinal-to-transverse phase space manipulation* can be used to produce a train of femtosecond electron bunches. The technique uses an incoming transversely-modulated electron beam obtained via destructive (e.g. using a multislits mask) or non destructive (e.g. transversely shaping the photocathode drive laser) methods. A transverse-to-longitudinal exchanger insertion is used to map this transverse modulation into a temporal modulation. Limitation of the proposed method and scalability to the femtosecond regime are analysed analytically and with the help of numerical simulation. Application of the method to generation of super-radiant far infrared (and shorter wavelength) radiation in an FEL is explored. Finally, a proof-of-principle experiment is discussed in the context of the Fermilab's A0 photoinjector.
*P. Emma, Z. Huang, K.-J. Kim, and P. Piot, Phys. Rev. ST Accel. Beams 9, 100702 (2006).
LBNL, Berkeley, California
UCB, Berkeley, California
Funding: This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
The design of the linac delivering the electron bunches into ten independent soft x-ray free electron lasers (FELs) is presented. The bunch repetition rate in the linac is 1 MHz and the bunch repetition rate in each FEL beam line is 100 kHz. Various issues regarding machine layout and lattice, bunch compression, collimation, and the beam switch yard are discussed. Particular attention is given to collective effects. A demanding goal is to preserve both a low beam slice emittance and low slice energy spread during acceleration, bunch compression and distribution of the electron bunches into the array of FEL beamlines. Detailed studies of the effect of the electron beam microbunching resulting from longitudinal space-charge forces and coherent synchrotron radiation as the beam undergoes compression have been carried out and are presented.
LANL, Los Alamos, New Mexico
Particle beams have exhibited a two-stream instability for many decades; this undesirable trait has been well-understood for many years. We propose creating a scheme that uses a beam of electrons with two distinct energies that will develop the two-stream instability as a bunching mechanism. By controlling the beam parameters and seeding them with a low-level rf signal, a gain as high as 2.5 dB per centimeter is predicted. We show the theory behind this concept and recent progress in a developing experiment.
SLAC, Menlo Park, California
The beam stability for the Linac Coherent Light Source (LCLS) Free-Electron Laser (FEL) at Stanford Linear Accelerator Center (SLAC) are critical for X-Ray power, pointing, and timing stability. Studies of the transverse, longitudinal, and intensity stability of the electron beam are presented. Identifying these sources by different methods like correlations, frequency spectrum analysis and other methods is critical for finally eliminating or reducing them.
SLAC, Menlo Park, California
UW-Madison/SRC, Madison, Wisconsin
Funding: The work of AWC and JW was supported by the US Department of Energy under contract DE-AC02-76SF00515. The work of JB was supported by National Science Foundation Award No. DMR-0537588.
A single-pass high-gain X-ray free electron laser (FEL) calls for a high quality electron bunch. In particular, for a seeded FEL, and for a cascaded harmonic generation (HG) FEL, the electron bunch initial energy profile uniformity is crucial to preserve an FEL narrow bandwidth. After the acceleration, compression, and transport, the electron bunch energy profile entering the undulator can acquire temporal non-uniformity. During the cascading stages, the electron bunch energy profile is also not uniform temporally entering the next stage. We study the effects of the electron bunch initial energy profile on the FEL performance, cascaded HG FEL or single stage FEL amplifier. Concrete examples are discussed for seeded FEL projects being studied.
SLAC, Menlo Park, California
UW-Madison/SRC, Madison, Wisconsin
Funding: The work of PE and JW was supported by the US Department of Energy under contract DE-AC02-76SF00515. The work of RAB and KJK was supported by National Science Foundation Award No. DMR-0537588.
For electron bunches driving a hard X-ray free electron laser, the electron bunch high qualities should be preserved as well as possible in the acceleration and compression. For typical configuration, the electron bunch is accelerated in rf cavity and compressed in magnetic chicane. Besides the rf curvature and high-order optics terms in a chicane, the collective effects during the bunch acceleration, transportation, and compression can further distort the phase space and even lead to instability. Among these collective effects, the coherent edge radiation dominates and governs the overall bunch property; while the longitudinal space charge is the main cause for microbunching instability. Random jitter couples to the wakefields and affect the final bunch properties. We study these effects and discuss their implication to general linac design and optimization.
SLAC, Menlo Park, California
Static magnetic field undulators are capable of producing quasi-monochromatic synchrotron radiation of very high brightness. However, it is not possible to quickly change the properties such as polarization of the radiation in a static undulator. It is possible to construct an undulator using microwaves instead of static magnets where the electron beam is undulated by both electric and magnetic fields of an rf wave. A major advantage with a microwave undulator is that the radiation properties can be changed very quickly. The biggest challenge in developing a microwave undulator is in keeping the rf losses low. We are designing a microwave undulator with the aim of achieving at least a tenth of the flux obtained by the BL13 static magnetic field Elliptical Polarized Undulator in the SPEAR ring. We have considered circular waveguide modes and hybrid HE11 mode in a corrugated waveguide as possible candidates for the microwave undulator. It is found that a corrugated waveguide has the lowest rf losses with a very desirable field profile. It is also possible to use this device for a linac driven FEL. Our analysis of the corrugated waveguide cavity for the rf undulator will be presented.
NPS, Monterey, California
Stanford University, Stanford, Califormia
Funding: This research is supported by the Office of Naval Research and the Joint Technology Office.
The Naval Postgraduate School (NPS) has begun the design and assembly of the NPS Free-Electron Laser (NPS-FEL). The basic NPS-FEL design parameters are for 40 MeV beam energy, 1 nC bunch charge, and 1 mA average beam current, in an energy-recovery linac configuration. The NPS-FEL will make use of portions of the Stanford Superconducting Accelerator (decommissioned in 2007), in particular the injector system, Stanford/Rossendorf-style cryomodules and rf system. The injector will be gradually upgraded to improve beam properties and increase the injection voltage. Each cryomodule contains two, 9-cell TESLA-type 1.3 GHz cavities, each cavity powered by an individual 10 kW cw klystron. NPS has committed to refurbishing a building for the FEL, with approximate interior vault dimensions of 7 m x 20 m x 2.5 m. The building has overall dimensions of 12 m x 49 m and will house the vault, control room, and support equipment. This paper describes the overall goals of the program, initial experimental plans, and progress to date.
BNL, Upton, Long Island, New York
The Source Development Laboratory (SDL) at the National Synchrotron Light Source (NSLS) is a laser linac facility dedicated for laser seeded FEL and beam physics R&D. The SDL consists of a RF synchronized Ti:sapphire laser, a BNL photocathode RF gun, a four-magnet chicane bunch compressor, and a 300 MeV linac. To further improve the performance of the laser seeded FEL at the NSLS SDL, we have carried out a systematic experimental characterization of the high-brightness electron beam generated by the photocathode RF gun. We will present the experimental studies of both transverse and longitudinal emittance of electron beam as a function of RF gun phase and solenoid magnet for electron beam charge ranging from 350 pC to 1 nC and their influences on FEL output.
RIKEN/SPring-8, Hyogo
The 8 GeV C-band electron linear accelerator is under construction at the SPring-8 site aiming at generating an FEL X-ray beam in 2010. C-band accelerator technology has been developed initially at KEK for the e+e- linear collider project, and employed at the XFEL project in Japan. Since C-band generates a high gradient acceleration field as high as 35 MV/m, the total length of the accelerator fits within 400 m, including the injector and three bunch compressors. C-band uses normal conducting rf technology, thus it runs in pulse mode at 60 Hz, which is well suited to XFEL operation and is less expensive. The talk will cover the current status of the XFEL project and hardware production.
SLAC, Menlo Park, California
Stanford University, Stanford, Califormia
Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Construction of the Linac Coherent Light Source (LCLS) X-ray free electron laser at the Stanford Linear Accelerator Center (SLAC) is nearing completion. A new injector and upgrades to the existing accelerator were installed in two phases in 2006 and 2007. We report on the commissioning of the injector, the two new bunch compressors at 250 MeV and 4.3 GeV, and transverse and longitudinal beam diagnostics up to the end of the existing linac at 13.6 GeV. The commissioning of the new transfer line from the end of the linac through the undulator beam line to the main dump is scheduled to start in January 2009 and for the undulator magnets in March 2009 with first light to be expected by May 2009.
DESY, Hamburg
FLASH, the FEL user facility at DESY, is operated with an electron beam energy up to 1 GeV corresponding to a photon wavelength down to 6.5 nm. The full year 2008 is dedicated to beam operation: about half of the time is scheduled for FEL users, and the rest for accelerator and FEL physics studies. Operational experience gathered at FLASH is very important not only for further improvements of the FLASH facility itself, but also for the European XFEL and for the ILC R&D effort. This talk reports our experience operating FLASH as a user facility. Failure statistics are included as well.
JASRI/SPring-8, Hyogo-ken
I developed a 3-D pulse shaping system in UV as an ideal laser for yearlong stable photoinjector. At SPring-8, the laser's pulse-energy stability has been improved to 0.7~1.4% at the UV (263 nm) under the laser environmental control included humidity. In addition, the ideal spatial and temporal profiles of an UV-laser pulse are essential to suppress emittance growth in an rf gun. I apply a deformable mirror that automatically shapes the spatial profile with a feedback routine, based on a genetic algorithm, and a pulse stacking system consisting of three birefringence Alpha-BBO crystal rods for temporal shaping at the same time. The 3D shape of the laser pulse is spatially top-hat (flattop) and temporally a square stacked chirped pulse. Using a 3D-shaped laser pulse with diameter of 0.8 mm on the cathode and pulse duration of 10 ps (FWHM), we obtain a normalized emittance of 1.4 pi mm mrad with a beam energy of 26 MeV. To keep the mirror away from beam axis, I developed a new hollow laser incidence with an axicon final focusing. Furthermore, I am developing a laser-induced Schottky-effect-gated photocathode gun using Z-polarization of the laser source with the hollow incidence.