BINP SB RAS, Novosibirsk
The first stage of Novosibirsk high power free electron laser (FEL) is in operation since 2003. Now the FEL provides average power up to 500 W in the wavelength range 120 - 240 micron. One orbit for 11-MeV energy with terahertz FEL lies in vertical plane. Other four orbits lie in the horizontal plane. The beam is directed to these orbits by switching on of two round magnets. In this case electrons pass four times through accelerating RF cavities, obtaining 40-MeV energy. Then, (at fourth orbit) the beam is used in FEL, and then is decelerated four times. At the second orbit (20 MeV) we have bypass with third FEL. When magnets of bypass are switched on, the beam passes through this FEL. The length of bypass is chosen to provide the delay, which necessary to have deceleration instead of acceleration at the third passage through accelerating cavities. Now two of four horizontal orbits are assembled and commissioned. The electron beam was accelerated twice and then decelerated down to low injection energy. Project average current 9 mA was achieved. First multi-orbit ERL operation was demonstrated successfully.
UW-Madison/SRC, Madison, Wisconsin
MIT, Cambridge, Massachusetts
Funding: Work supported by the University of Wisconsin - Madison. SRC is supported by the U.S. National Science Foundation under Award No. DMR-0537588.
The University of Wisconsin-Madison/Synchrotron Radiation Center and MIT are developing a design for a seeded VUV/soft X-ray Free Electron Laser serving multiple simultaneous users. The present design uses an L-band CW superconducting 2.2 GeV electron linac to deliver 200 pC bunches to multiple FELs operating at repetition rates from kHz to MHz. The FEL output will be fully coherent both longitudinally and transversely, with tunable pulse energy, cover the 5-900 eV photon range, and have variable polarization. We have proposed a program of R&D to address the most critical aspects of the project. The five components of the R&D program are:
- Prototyping of a CW superconducting RF photoinjector operating in the self-inflating bunch mode.
- Development of conventional laser systems for MHz seeding of the FEL, and femtosecond timing and synchronization.
- Address thermal distortion and surface contamination issues on the photon optics.
- Investigate advanced undulator concepts to help reduce facility cost and/or extend performance.
- Perform detailed modeling of all aspects of the FEL, as part of production of a Conceptual Design Report for the FEL facility.
ELETTRA, Basovizza
B.I. Stepanov Institute of Physics, Belarus
Funding: The work was supported in part by the Italian Ministry of University and Research under grant FIRB-RBAP045JF2
Particle accelerator and laser technologies are effectively combining with each other in the development of next generation light sources, with the latter being one of the key factors determining the ultimate performance of these machines. VUV and X-FEL facilities take advantage of laser technology at many strategic points: creation of the electron bunch (photo-injector laser), acceleration (laser heater), undulators (seed laser), beam diagnostics (electro-optic sampling lasers), user experiments (pump-probe lasers). The talk will discuss the main requirements and challenges (photoinjector and seed lasers in particular) for the laser systems and will illustrate proposed solutions and obtained results. Recent laser achievements that are likely to have impact on important developments like high average power injectors, different guns,tunable short wavelength FEL seeding will also be addressed.
Sigmaphi, Vannes
Vector Fields Ltd., Oxford
Oxford Instruments, Accelerator Technology Group, Oxford, Oxon
A tender for the study and construction of a large superconducting split solenoid for the C400 carbon therapy cyclotron was issued by IBA in March 2008 and awarded to Sigamphi. Although the current density is moderate, the large radius and average field imply quite a high level of hoop stress. Simple formulas range between 140 and 180 MPa and, with such large values and uncertainties, it was felt necessary to perform a finite element analysis of the structure. Average fields in a cyclotron are very well modeled using an axially symmetrical structure and the stress was therefore studied using the stress module of the Vector Fields Opera2d suite. Different models were tried with different levels of details. A comparison is made between them as well as with the analytical results.
ANL, Argonne
Illinois Institute of Technology, Chicago, Illinois
Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Future x-ray light sources such as FELs and ERLs impose requirements on emittance and bunch repetition rate that are very demanding on the electron source. Even if perfect compensation of space-charge effects could be attained, the fundamental cathode emission properties determine a lower bound on achievable source emittance. Development of ultra-low-emittance sources is a rapidly evolving area of R&D with exciting new results measured for low bunch charge, but it is very difficult to compare different results and quantify what works. The study of photocathodes, with the goal of optimizing for low emittance, is limited in scope. In this paper, we describe an R&D effort to systematically measure and design the fundamental properties of photocathodes suitable for an FEL or ERL. We plan to apply surface analysis lab techniques to characterize photoemission, and then correlate material properties with emittance. On the theory side, we plan to calculate electron band structure for crystal surfaces, correlate with lattice parameters and work function, and then estimate the transverse momentum using the three-step model. The status and results to date of this effort will be reported.
ENEA C.R. Frascati, Frascati (Roma)
INFN/LNF, Frascati (Roma)
Rome University La Sapienza, Roma
LBNL, Berkeley, California
The SPARX X-FEL accelerator will be the first FEL facility to operate with a hybrid (RF plus magnetic chicane) compression scheme. Numerical studies of propagation of beam density modulations stemming from photogun laser, through the photoinjector operating under velocity bunching conditions have been carried out. A semi-analytical model for the linear gain in a RF compressor is also being developed and some preliminary results are presented.
INFN/LNF, Frascati (Roma)
In this paper we report the status of the SPARC photocathode drive laser system. In the high brightness photoinjector the properties of the electron beam are directly related to the drive laser features. In fact the 3-D distribution of the electron beam and the time of emission are determined by the incoming laser pulse. The SPARC laser is a 10 Hz frequency-tripled TW-class Ti:Sa commercial system. A dedicated activity on the shape of the laser pulse has been performed in order to produce high energy UV flat top and multi-peaks time profile. To achieve the required flat top shape we perform a manipulation of the laser spectrum at the fundamental wavelength and directly at the third harmonic. The production of multi peaks laser pulse have been studied and tested. Finally we present the key laser performances recorded for the SPARC FEL experiment.
UMD, College Park, Maryland
NRL, Washington, DC
LANL, Los Alamos, New Mexico
Funding: This project is funded by the Joint Technology Office and the Office of Naval Research.
High performance FELs require photocathodes with quantum efficiencies of several percent at green wavelengths, kHr lifetime, kA/cm2 peak and A/cm2 average current, and ps response. Such cathodes are challenged to maintain requisite high quantum efficiency while in harsh accelerator vacuum conditions. Delicate surface coatings are often cesium-based, and therefore are reactive with contaminant gases. The dispenser photocathode architecture resupplies the cesium coating from a subsurface reservoir through a porous substrate, thereby extending lifetime*. Recesiation has been shown to rejuvenate Cs:Ag cathodes from O2, CO2, and N2O contamination**, and theory of dispenser photocathodes is advancing***. We here investigate the fabrication, contamination, and external recesiation of alkali antimonides with high quantum efficiency, in support of the dispenser photocathode design.
*Moody et al., APL90, 114108.
**Montgomery et al., Proc. AACW 2008 (submitted for publication).
***K. Jensen et al., (this conference).
PKU/IHIP, Beijing
High quality electron beam with low transverse emittance in 3.5‐cell DC‐SC photo‐injector is crucial significance for PKU‐ERL‐FEL facility. In this paper, we analyse the emittance evolution in the 3.5‐cell DC‐SC photo‐injector by simply model with consideration of DC acceleration, RF acceleration and space charge effect. The results are compared with Astra simulation. The matching condition of DC‐gun and Superconducting cavity, which is critical for the final emittance at the exit of the injector, is also presented.
Università di Roma II Tor Vergata, Roma
INFN/LNF, Frascati (Roma)
Rome University La Sapienza, Roma
INFN-Roma II, Roma
ENEA C.R. Frascati, Frascati (Roma)
The SPARC photoinjector drives a SASE FEL to perform several experiments both for the production of high brightness electron beam and for testing new scheme of SASE radiation generation. The control of the beam properties, in particular at the level of the slice dimension, is crucial in order to optimize the FEL process. We report the different measurements performed in order to characterize the slice properties of the electron beam.
Tech-X, Boulder, Colorado
Funding: Supported by the US DOE Office of Science, Office of Nuclear Physics under grants DE-FC02-07ER41499 and DE-FG02-08ER85182; used NERSC resources under grant DE-AC02-05CH11231.
Novel electron-ion collider (EIC) concepts are a high priority for the long-term plans of the international nuclear physics community. Orders of magnitude higher luminosity will be required for the relativistic ion beams in such accelerators. Electron cooling is a promising approach to achieve the necessary luminosity. The coherent electron cooling (CEC) concept proposes to combine the best features of electron cooling and stochastic cooling, via free-electron laser technology, to cool high-energy hadron beams on orders-of-magnitude shorter time scales*. In a standard electron cooler, the key physical process is dynamical friction on the ions. The modulator section of a coherent cooler would be very similar to a standard cooler, but in this case dynamical friction becomes irrelevant and the key physics is the shape of the density wake imprinted on the electron distribution by each ion. We will present results using the massively parallel VORPAL framework for both particle-in-cell (PIC) and molecular dynamics (MD) simulations of electron-ion collisions in relativistic coolers and CEC modulators.
* V.N. Litvinenko, I. Ben-Zvi, M. Blaskiewicz, Y. Hao, D. Kayran, E. Pozdeyev, G. Wang, G.I. Bell, D.L. Bruhwiler, A.V. Sobol et al., FEL Conf. Proc. (2008), in press.
Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
UNM, Albuquerque, New Mexico
SLAC, Menlo Park, California
Microbunching can cause an instability which degrades beam quality. This is a major concern for free electron lasers where very bright electron beams are required. A basic theoretical framework for understanding this instability is the 3D Vlasov-Maxwell system. However, the numerical integration of this system is computationally intensive. Investigations to date have used simplified analytical models or numerical solvers based on simple 1D models. We have developed an accurate and reliable 2D Vlasov-Maxwell solver which we believe improves existing codes. This solver has been successfully tested against the Zeuthen benchmark bunch compressors. Here we apply our self-consistent, parallel solver to study the microbunching instability in the first bunch compressor system of FERMI@Elettra.
USTRAT/SUPA, Glasgow
Cockcroft Institute, Warrington, Cheshire
Pulsar Physics, Eindhoven
Funding: The U.K. EPSRC and the European Community - New and Emerging Science and Technology Activity under the FP6 “Structuring the European Research Area” programme (project EuroLEAP, contract number 028514)
The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme* is developing laser-plasma accelerators for the production of ultra-short electron bunches as drivers of incoherent and coherent radiation sources from plasma and magnetic undulators. Focusing of ultra-short electron bunches from a laser-plasma wakefield accelerator into an undulator requires that particular attention be paid to the electron beam quality. We will discuss the design and implementation of an upgraded focusing system for the ALPHA-X beam line, which currently consists of a triplet of electromagnet quadrupoles. The upgrade will comprise the installation of additional compact permanent quadrupoles** very close to the accelerator exit. This will improve the matching of the beam into the undulator. The design has been carried out using the General Particle Tracer (GPT) code*** and TRANSPORT code, which consider space charge effects and allow a realistic estimate of electron beam properties inside the undulator to be obtained. We will present a study of the influence of beam transport on free-electron laser action in the undulator, paying particular attention to bunch dispersion.
* D. Jaroszynski et al., Phil. Trans. R. Soc. A 364, 689-710 (2006)
** T. Eichner et al., Phys. Rev. ST Accel. Beams 10, 082401 (2007)
*** S.B. Geer, M.J. Loos, Ph.D. thesis, TU/e, Eindhoven (2001)
SLAC, Menlo Park, California
Funding: Work supported by US DOE contract DE-AC02-76SF00515.
Single-pass free electron lasers require high peak currents from ultra-short electron bunches to reach saturation and an accurate measurement of bunch length and longitudinal bunch profile is necessary to control the bunch compression process from low to high beam energy. The various state-of-the-art diagnostics methods from ps to fs time scales using coherent radiation detection and RF deflection techniques are presented.
SLAC, Menlo Park, California
ANL, Argonne
Funding: Work supported by U.S. Department of Energy under Contract Nos. DE-AC02-06CH11357 and DE-AC02-76SF00515.
We present the performance of the cavity beam position monitor (BPM) system for the LCLS undulator. The construction and installation phase of 34 BPMs for the undulator and 2 for the transport line have been completed. The X-band cavity BPM employs a TM010 monopole reference cavity and a TM110 dipole cavity designed to operate at a center frequency of 11.384 GHz. The signal processing electronics features a low-noise single-stage three-channel heterodyne receiver that has selectable gain and a phase locking local oscillator. The approximately 40 MHz IF is digitized by a 120M sample/second four-channel 16-bit digitizer. System requirements include sub-micron position resolution for a single-bunch beam charge of 200 pC. We discuss the system specifications and commissioning results.
Diamond, Oxfordshire
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
STFC/DL, Daresbury, Warrington, Cheshire
STFC/RAL, Chilton, Didcot, Oxon
Imperial College of Science and Technology, Department of Physics, London
USTRAT/SUPA, Glasgow
UMAN, Manchester
The New Light Source (NLS) project was launched in April 2008 by the UK Science and Technology Facilities Council (STFC) to consider the scientific case and develop a conceptual design for a possible next generation light source based on a combination of advanced conventional laser and free-electron laser sources. Following a series of workshops and a period of scientific consultation, the science case was approved in October 2008 and the go-ahead given to continue the project to the design stage. In November the decision was taken that the facility will be based on cw superconducting technology in order to provide the best match to the scientific objectives. In this paper we present the source requirements, both for baseline operation and with possible upgrades, and the current status of the design of the accelerator driver and free-electron laser sources to meet those requirements.
LBNL, Berkeley, California
SLAC, Menlo Park, California
Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contracts No. DE-AC02-05CH11231 (LBNL) and DE-AC02-76SF00515 (SLAC).
The future directions of x-ray science and the photon beam properties required to pursue them were recently evaluated by a joint LBNL–SLAC study group*. As identified by this group, essential x-ray capabilities for light sources in the future (but not necessarily from any single source) include: 1) x-ray pulses with Fourier-transform-limit time structure from the picosecond to attosecond regime, synchronized with conventional lasers, and with control of longitudinal pulse shape, amplitude and phase; 2) full transverse coherence; 3) high average flux and brightness; 4) energy tunability in soft and hard x-ray regimes, and polarization control. Metrics characterizing source properties include not only average and peak spectral brightness but also the photons per pulse and repetition rate as a function of pulse length, and the proximity to transform-limited dimensions in six dimensional phase space. We compare the projected performance of various advanced x-ray source types, with respect to these metrics and discuss their advantages and disadvantages. We briefly discuss the technology challenges for future sources and the areas of R&D required to address them.
*R. Falcone, J. Stohr et al., “Scientific Needs for Future X-Ray Sources in the U.S. - A White Paper”, SLAC-R-910, LBNL-1090E, October 2008.
ANL, Argonne
Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
An x-ray radiation source based on a free-electron laser (FEL) oscillator was recently proposed as a complementary facility to those based on self-amplified spontaneous emission*. Such a source uses narrow-bandwidth Bragg mirrors and a low-emittance, high-brightness electron beam to produce coherent, intense pulses of hard x-ray radiation. We present a study of the FEL oscillator performance and radiation characteristics at several potential wavelengths using a variety of electron beam and undulator parameters. Our simulations include realistic complex mirror reflectivities calculated from dynamical diffraction theory, and highlight additional constraints imposed by a four-mirror cavity that can provide tunable FEL radiation. We comment on how this concept may be extended to soft x-rays using dielectric multilayer mirrors.
*K.-J. Kim, Y. Shvyd'ko, S. Reiche, Phys. Rev. Lett. 100, 244802 (2008)
BNL, Upton, Long Island, New York
Icarus Research, Inc., Bethesda, Maryland
NRL, Washington, DC
The NSLS Source Development Laboratory (SDL) has been a world leader in the development of laser seeded free electron lasers (FEL). Recently we initiated an experimental program to investigate a Self-Amplified Spontaneous Emission (SASE) FEL in both the exponential gain and the saturation regimes. We have experimentally demonstrated the saturation of a SASE FEL in the visible to near IR. The experimental characterization of the transverse and spectral properties of the SASE FEL along the undulator for a uniformed and tapered undulator will be presented. In addition, an efficiency enhancement concept for a SASE FEL, which involves a step wiggler taper in the exponential gain regime prior to trapping, will be presented. Simulations of the SASE FEL processes will employ the GENESIS FEL code.
BNL, Upton, Long Island, New York
SAIC, McLean
Funding: This work is supported in part by the Office of Naval Research (ONR), the Joint Technology Office, and U.S. Department of Energy (DOE) under contract No. DE-AC02-98CH1-886.
We report the first experimental characterization of efficiency and spectrum enhancement in a laser-seeded free-electron laser (FEL) using a tapered undulator. Output and spectra in the fundamental and 3rd harmonic were measured versus distance for uniform and tapered undulators. With a 4% field taper over 3 m, a 300% (50%) increase in the fundamental (3rd harmonic) output was observed. A significant improvement in the spectra with the elimination of side-bands was observed for the first time using a tapered undulator. The experiment is in good agreement with predictions using the MEDUSA simulation code.
CANDLE, Yerevan
PSI, Villigen
The study of radiation saturation length and saturation power sensitivity to beam main parameters (emittance, energy spread and peak current) at the entrance of the undulator section of PSI-XFEL project is presented. The comparative analysis of the SASE FEL performance with external and natural focusing in undulator section is given.
DESY, Hamburg
Uni HH, Hamburg
The free-electron laser user facility FLASH at DESY, Germany is the world-wide leading SASE-FEL operating in the VUV and the soft X-ray wavelengths range. At present, FLASH provides fully coherent femtosecond laser radiation from 47 nm down to 6.5 nm and higher harmonics. Late 2009, FLASH will be upgraded with an additional superconducting TESLA type accelerating module boosting its beam energy to 1.2 GeV. This will allow lasing with a wavelength below 5 nm. In addition, a 3rd harmonic accelerating cavity will be installed. It allows to flatten and to a certain extend shape the longitudinal phase space improving the overall performance of the facility.
Diamond, Oxfordshire
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Several new light source projects aim at the production of X-ray photons with high repetition rate (1kHz or above). We present here the results of the start-to-end simulations of a 2.2 GeV superconducting LINAC based on L-band SC Tesla-type RF cavities and the corresponding optimisation of the FEL dynamics at 1 keV photon energy.
ENEA C.R. Frascati, Frascati (Roma)
INFN/LNF, Frascati (Roma)
Rome University La Sapienza, Roma
We develop some considerations allowing the possibility of deriving the conditions under which laser heater devices may suppress the Coherent Synchrotron Instability (CSRI) without creating any prejudice to the use of the beam for FEL SASE or FEL oscillator operation. We discuss the problem using either numerical and analytical methods. The analytical part is aimed at evaluating the amount of laser power, necessary to suppress the instability. We use methods already developed within the context of FEL-storage rings beam dynamics, with particular reference to the interplay between FEL and Saw Tooth Instability. The numerical method employs a procedure based on the integration of the Liouville equation, describing the coupled interaction between e-beam and wake-fields, producing the instability, and the laser producing the heating. Particular attention is devoted to the competition between instability and heating. The comparison between numerical and analytical results is discussed too and the agreement is found to be satisfactory.
ENEA C.R. Frascati, Frascati (Roma)
We explore the possibility of using free-electron laser (FEL) triggered cathodes to produce high quality e-beams. We propose a scheme which foresees cathodes operating either as thermionic and photo-cathodes, which can be exploited in devices using the same e-beam to drive the laser and the cathode. We discuss different modes of operation, in particular we consider oscillator FELs, in which the light from higher order harmonics, generated in the oscillator cavity, is used to light the cathode. The dynamics of the system is explored along with the technical solutions, necessary for the stability of the system. The Master Oscillator Power Amplifier FEL scheme is explored too. The use of the same e-beam, driving the photocathode and the FEL, makes the system naturally free of any synchronization problem, arising when an external laser is used. The device is a kind of regenerative amplifier in which the growth of the optical power can be controlled by using a proper detuning or misalignment of the optical cavity. Specific examples are reported. The use of this technique for an ab-initio control the Coherent Radiation Synchrotron instability is finally discussed too.
FEL/Duke University, Durham, North Carolina
PKU/IHIP, Beijing
Funding: Work supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086.
The storage ring based free electron laser (FEL) oscillator serves as a photon driver for the High Intensity Gamma-Ray Source (HIGS) at Duke University. The FEL cavity consists of two concave mirrors with a large radius of curvature of more than 27 m. Both cavity mirrors see very high intensity intracavity FEL power; the downstream mirror also receives higher harmonic spontaneous UV-VUV radiation of wigglers. The large heat load by various types of radiation can deform the mirror surface, causing FEL mode distortion. The FEL mirror can also be damaged by intense UV-VUV wiggler harmonic radiation. To mitigate these problems, a pair of water-cooled, in-vacuum apertures have been installed inside the FEL cavity. These apertures are ideal for manipulating the FEL transverse profile. This paper reports our study on the FEL transverse mode shaping using these apertures, including the characterization of the transverse mode structure of the FEL beam under a variety of operation conditions. These studies allow us to minimize the diffraction loss of the fundamental mode of the FEL while effectively reducing the impact of off-axis UV-VUV wiggler radiation on the FEL mirrors.
FEL/Duke University, Durham, North Carolina
Funding: This work is supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086.
The paper presents a novel technique of measuring the gain of a storage ring based FEL oscillator. As opposed to the conventional technique of measuring the FEL gain from its macro-pulse envelope, this new technique is based upon the measurement of pass-by-pass FELμpulses. To record the growth of the optical energy in the FEL micro-pulse train, we use fast photo-diodes and photo-multiplier tubes (PMTs). PMTs are usually employed at the very beginning of the FEL lasing development, while the photodiodes are used at the latter stages when the FEL power is fully developed and saturated. This new gain measurement technique provides a powerful tool to study the details of the FEL gain process starting from spontaneous radiation to saturation. It allows us to investigate five to seven orders of magnitude of the FEL energy growth. As fast photo-detectors with a sub-nanosecond time response become available, this new technique can be adopted for many oscillator FELs, including those driven by super-conducting linacs. Special attention is paid to the dynamic non-linearity issues of the photodiodes and PMTs associated with short length of FEL pulses.
FEL/Duke University, Durham, North Carolina
PKU/IHIP, Beijing
Funding: This work was supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086.
The Madey theorem is a valuable research tool for studying Free-Electron Lasers (FELs). The theorem relates the shape of the on-axis spontaneous radiation spectrum of FEL wigglers to the FEL gain. The theorem predicts that degradation of the spontaneous spectrum, for example as a result of the increase of the electron beam energy spread, provides a direct measure of the reduction of the FEL gain. Extensive experiments have been performed to study the validity of the Madey theorem for a storage ring base optical klystron FEL. The experimental data show that the lasing wavelength of the FEL is very close to the maximum slope of spontaneous spectra as predicted by the Madey theorem with a relative wavelength discrepancy less than 0.2%. Further analysis is underway to understand this wavelength difference. In addition, we have performed direct measurements of the start up gain of the FEL and compared it with the changing slope of the spontaneous spectra. The preliminary results show a good agreement between the measured FEL gain and the prediction by Madey theorem.
FEL/Duke University, Durham, North Carolina
Funding: This work is supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086 and US Department of Energy grant DE-FG02-01ER41175.
The Duke Free-Electron Laser Laboratory (DFELL) operates several accelerators as a driver for storage ring based Free-Electron Lasers (FELs) and Compton gamma-ray source, the High Intensity Gamma-ray Source (HIGS). The HIGS is the most powerful Compton gamma-ray source in the world below 100 MeV. Since completing a major upgrade of the HIGS in 2007, the Duke storage ring FEL and HIGS gamma source have been operated extensively for user research programs. In 2008, the DFELL was merged with the Triangle Universities Nuclear Laboratory (TUNL) to become a major accelerator facility of the TUNL. The accelerator physics program at the DFELL covers a wide range of activities, from nonlinear dynamics research, to the study of beam instability with advanced feedback systems, to light source research and development, in particular, the FEL research and Compton light source development. In this paper, we will report our recent progress in accelerator physics research and light source development to meet new challenges of today's and future accelerators.
FEL/Duke University, Durham, North Carolina
Funding: This work was supported by US Department of Defense Medical FEL Program as administered by the AROSR under contract number FA9550- 04-01-0086 and US Department of Energy grant DE-FG05-91ER40665.
Accurate simultaneous measurements of storage ring free-electron laser (SRFEL) average power output and electron beam energy spread has been achieved at the Duke FEL Laboratory. It is well known that the SRFEL power is limited by the electron beam synchrotron radiation power and the induced energy spread of the electron beam. The two-wiggler spectrum of an optical klystron can be used to determine the energy spread of the electron beam. Measuring the interference pattern of the modulated spontaneous spectrum with the FEL turned on, we are able to study the FEL power output as a function of electron beam energy spread. As the energy spread increases, the modulation in the two-wiggler spectrum reduces, resulting in a smaller FEL gain. During this process, the operation of an optical klystron degrades back to that of a conventional FEL. This paper reports our recent experiment study of transition of the FEL operation from an optical klystron to a conventional FEL.
Uni HH, Hamburg
DESY, Hamburg
PSI, Villigen
DELTA, Dortmund
BESSY GmbH, Berlin
Funding: This work is supported by the Bundesministerium für Bildung und Forschung under contract 05 ES7GU1
A seeded free-electron laser operating in the soft X-ray (XUV) spectral range will be added to the SASE FEL facility FLASH. For this purpose, a 40 m long section upstream of the existing SASE undulator will be rebuilt during the shutdown in fall 2009. This includes the injection of the seed beam into a new 10 m variable-gap undulator, the out-coupling of the seeded FEL radiation and all diagnostics for photon- and electron beams. The XUV seed pulse is generated by high harmonics (HHG) from a near-infrared laser, optically synchronized with FLASH. After amplification within the undulators the XUV light will be guided towards diagnostic stations. Besides a proof-of-principle demonstration for seeding at short wavelength the purpose of this development is to provide future pump-probe experiments with a more stable FEL source in terms of spectral properties and timing.
HUST, Wuhan
A primary design of a compact THz FEL oscillator is presented, which is consisted of an independently tunable cell thermionic rf gun (ITC-RF Gun), a rf linac, a planar undulator and an near concentric optical cavity composed of symmetrical spherical mirrors with an on-axis outcouple hole. Without α-magnet and other bunch compressor, the size of this machine is decreased sharply. The effect of the electron beam parameters on THz radiation is discussed. It is found that the influence of energy spread is pronounced and the influence of emittance is neglectable. Large current is required to got saturation in several us. Then the optimized beam parameters and basic design parameters are summarized.
INFN/LNF, Frascati (Roma)
The SPARX-FEL project aims at producing ultra high peak brightness electron beams in the 1.5 - 2.4 GeV range with the goal of generating FEL radiation in the 0.6-40 nm range. The construction is planned in two steps ,starting with a 1.5 GeV Linac. The project layout includes both RF-compression and magnetic chicane techniques, in order to provide the suitable electron beam to each one of three undulator systems which will generate VUV-EUV, Soft X-Rays and Hard X-rays radiation respectively This will be distributed in dedicated beamlines suitable for applications in basic science and technology: time resolved X-ray diffraction with pump and probe experiments, nanolithography processes, biological proteins, nano-particles and clusters, coherent diffraction and holographic X-ray techniques, nano-imaging. The project was funded by the Italian Department of Research, MIUR, and by the local regional government, Regione Lazio; The associated test-facility, SPARC, located at LNF, has been successfully commissioned: the SPARX-FEL project foresees the construction of a user facility inside the Tor Vergata campus by a collaboration among CNR, ENEA, INFN and the Università di Tor Vergata itself.
INFN/LNF, Frascati (Roma)
ENEA C.R. Frascati, Frascati (Roma)
ISM-CNR, Rome
The SPARX-FEL project consists in an X-ray-FEL facility which aim is the generation of electron beams characterized by ultra-high peak brightness at the energy of 1.5 and 2.4 GeV. This facility will be built in the Tor Vergata University area in Rome. The paper describe the engineering aspects of the mechanical design of the accelerator, photo-injector, LINACs, bunch compressors, beam distribution, undulators and experimental stations. Morover the integration of accelerator with the civil infrastractures is discussed.
Kyoto IAE, Kyoto
KAERI, Daejon
UVSOR, Okazaki
The first laser amplification at a 12 micrometre mid-infrared free-electron laser (MIR-FEL) was observed at the Institute of Advanced Energy (IAE), Kyoto University in March 2008. A 25 MeV electron beam of 17 A peak current was used for the lasing experiment. FEL gain was estimated to be 16% from the exponential growth of the laser output signal. A beam loading compensation method with an RF amplitude control both in the thermionic RF gun and in the accelerator tube was used to extend the macropulse duration against the back bombardment effect in the gun. We also developed a feedforward RF phase control to stabilize the RF phase shifts which were originated with RF amplitude control. As a result FEL saturation was observed in May 2008. The estimated FEL gain was 33% with the electron beam of 5.5 microsecond macropulse duration by use of peak current of 33 A which was deduced from GENESIS simulation. A user beamline was designed and constructed. The laser characterization at the user station will be reported in the conference. Applications of the MIR-FEL at Kyoto University in the chemistry energy research will be presented as well.
FEL/Duke University, Durham, North Carolina
TUNL, Durham, North Carolina
A gamma-ray beam produced by Compton scattering of a laser beam with a relativistic electron beam has been used to determine the electron beam parameters. In the past, the electron beam energy and energy spread were directly fit from the high energy edge of a measured gamma beam spectrum using a gamma-ray detector. However, due to non-ideal response of the detector, the measured spectrum cannot represent the true energy distribution of the gamma-ray beam. Thus, the electron beam energy and energy spread could not be accurately determined from the measured gamma beam spectrum. In this paper, we will present a novel end-to-end spectrum reconstruction method to accurately extract the energy distribution of the gamma-ray beam from the measured gamma beam spectrum. Using this method we have accurately determined the energy and energy spread of the electron beam in Duke storage ring using a Compton gamma-ray beam from the High Intensity γ-ray Source (HIγS) facility.
BNL, Upton, Long Island, New York
Funding: Department Of Energy
Under certain assumptions and simplifications, we studied a few physics processes of Coherent Electron Cooling using analytical approach. In the modulation process, the effect due to merging the ion beam with the electron beam is studied under single kick approximation. In the FEL amplifier, we studied the amplification of the electron density modulation using 1D analytical approach. Both the electron charge density and the phase space density are derived in the frequency domain. The solutions are then transformed into the space domain through Fast Fourier Transformation (FFT).
ELETTRA, Basovizza
Funding: The work was supported in part by the Italian Ministry of University and Research under grant FIRB-RBAP045JF2
FERMI@Elettra is the new 4th-generation light source, based on a single-pass FEL, under construction at the Elettra Laboratory in Trieste, Italy. Some hundreds of magnets and coils need to be supplied along the accelerator sections and the undulators chains - mostly individually - with currents as low as 1.5 A up to 750 A. Starting from a successful design developed at Elettra* for the full-energy injector**, a new version of the existing 4-quadrant, 5 A PS has been studied. This new bipolar low-current PS, with full digital control, will be adopted for all 1.5 A and 5 A loads. The design of a bipolar PS for supplying the 20 A loads is in progress. This paper will describe the proposed PS system for the magnets and coils of FERMI@Elettra. The focus will be on the solutions adopted to minimize the number of different PS types. Particular stress will be laid upon the in-house design.
*D, Molaro et al. - A new bipolar power supply for Elettra booster pre-injector correctors - PCIM08
**R. Visintini et al. - Magnet power converters for the new Elettra full energy injector - EPAC08
ORNL, Oak Ridge, Tennessee
Muons, Inc, Batavia
JLAB, Newport News, Virginia
Funding: Supported in part by USDOE Contract No. DE-AC05-84-ER-40150. Supported in part by USDOE Contract DE-AC05-00OR22725
The ORNL spallation neutron source (SNS) user facility requires a reliable, intense beams of protons. The technique of H- charge exchange injection into a storage ring or synchrotron has the potential to provide the needed beam currents, but it will be limited by intrinsic limitations of carbon and diamond stripping foils. A laser in combination with magnetic stripping has been used to demonstrate a new technique for high intensity proton injection, but several problems need to be solved before a practical system can be realized. Technology developed for use in Free Electron Lasers is being used to address the remaining challenges to practical implementation of laser controlled H- charge exchange injection for the SNS. These technical challenges include (1) operation in vacuum, (2) the control of the UV laser beam to synchronize with the H- beam and to shape the proton beam, (3) the control and stabilization of the Fabry-Perot resonator, and (4) protection of the mirrors from radiation.
FEL/Duke University, Durham, North Carolina
SLAC, Menlo Park, California
Funding: *Work supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086 (YKWu).
Touschek scattering is the dominant loss mechanism for the electron beam in a low energy storage ring with a large bunch current. The Duke Free-Electron Laser (FEL) storage ring typically operates in the one-bunch or two-bunch mode with a very high bunch current and a varying electron beam energy as low as 250 MeV. The study of the Touschek lifetime is important for improving the performance of the Duke storage ring based light sources, including the storage ring FELs and a FEL driven Compton gamma source, the High Intensity Gamma-ray Source. This work reports our lifetime measurement results for few-bunch operation of the Duke storage ring. The Touschek loss rate is reduced when an electron beam is polarized in the storage ring. The change of the Touschek lifetime can be used as a method to monitor polarization of the electron beam. In this work, we will also report our preliminary results of the electron beam energy measurements using the resonant depolarization technique.
Rome University La Sapienza, Roma
RadiaBeam, Marina del Rey
UCLA, Los Angeles, California
INFN/LNF, Frascati (Roma)
We present here the design, including RF modelling, cooling, and thermal stress and frequency detuning, of an S-band RF gun capable of running near 500 Hz, for application to FEL and inverse Compton scattering sources. The RF design philosophy incorporates many elements in common with the LCLS gun, but the approach to managing cooling and mechanical stress diverges significantly. We examine the new proprietary approach of RadiaBeam Technologies for fabricating copper structures with intricate internal cooling geometries. We find that this approach may enable very high repetition rate, well in excess of the nominal project this design is directed for, the SPARX FEL.
*C.Limborg et al.,“RF Design of the LCLS Gun”,LCLS Technical Note LCLS-TN-05-3
**P. Frigola et al.,“A Novel Fabrication Technique for the Production of RF Photoinjectors”,published in EPAC08.
ELETTRA, Basovizza
Recent advances in high-stability electronic and electro-optic timing and synchronization systems are presented. These systems have been proposed for several new FEL facilities, and are in development at several labs. Several basic technical implementations are in development, some based on pulsed mode-locked laser technology, others using CW systems. There are numerous technical choices with regard to the stability, synchronizability, capability of multi-drop operation, availability of inherent diagnostic information, complexity of transmitters vs. receivers, use of commercial vs. custom-designed components, etc. This talk presents an overview of the basic timing and synchronization requirements in accelerator systems, and reviews the state of the art. Contrasts are made between the CW and pulsed optical distribution approaches. The technology in development to distribute a 38 GHz phase coherent LO at the ALMA radiotelescope is highlighted as a related technical system in development.
PSI, Villigen
INFN/LNF, Frascati (Roma)
RF deflectors are crucial diagnostic tools for bunch length and slice emittance measurements with sub-picosecond resolution. Their use is essential in commissioning and operation of VUV and X-ray FELs. The 250MeV FEL injector, under construction at PSI, will use two of them. The first one will be installed after the gun at low energy (~7MeV), the second one at the end of the Linac at high energy (250MeV). The first RF deflector consists of a single cell standing wave cavity working on the TM110 deflecting mode, and tuned at 2997.912 MHz (frequency of the linac structures). In this note we report the motivation of this measurement, beam dynamics and beam diagnostics considerations and the RF design and simulations of this cavity.
ELETTRA, Basovizza
Funding: The work was supported in part by the Italian Ministry of University and Research under grants FIRB-RBAP045JF2 and FIRB-RBAP06AWK3
FERMI@Elettra is a seeded FEL user facility under construction at Sincrotrone Trieste, Italy. The linac is based on S-band normal conducting technology. It will use the accelerating sections of the original Elettra linac injector, seven sections received from CERN after LIL decommissioning and two additional sections to be constructed for a total number of 18 S-band accelerating structures. Installation of the machine is presently being carried on. This paper will provide a summary of the requirements of the different parts of the S-band RF system and of the options for a possible upgrade path both in energy and reliability. The ongoing activities on the main subassemblies, in particular regarding the tests and the installation work, are also presented.
Muons, Inc, Batavia
JLAB, Newport News, Virginia
Funding: Supported in part by USDOE SBIR Grant DE-FG02-08ER85171
High-current RF cavities that are needed for many accelerator applications are often limited by the power transmission capability of the pressure barriers (windows) that separate the cavity from the power source. Most efforts to improve RF window design have focused on alumina ceramic, the most popular historical choice, and have not taken advantage of new materials. Alternative window materials have been investigated using a novel Merit Factor comparison and likely candidates have been tested for the material properties which will enable construction in the self-matched window configuration. Window assemblies have also been modeled and fabricated using compressed window techniques which have proven to increase the power handling capability of waveguide windows. Candidate materials have been chosen to be used in fabricating a window for high power testing at Thomas Jefferson National Accelerator Facility.
PAL, Pohang, Kyungbuk
SLAC, Menlo Park, California
In PAL, We are preparing the 3GeV Linac by upgrading the present 2.5GeV Linac and new 10GeV PxFEL project. The specification of the beam energy spread and rf phase is tighter than PLS Linac. In present PLS 2.5 GeV Linac, the specifications of the beam energy spread and rf phase are 0.6%(peak) and 3.5 degrees(peak) respectively. And the output power of klystron is 80 MW at the pulse width of 4 microseconds and the repetition rate of 10 Hz. In PxFEL, the specifications of the beam energy spread and rf phase are 0.1%(rms) and 0.1 degrees(rms) respectively. We developed the modulator DeQing system for 3GeV linac and PxFEL. And the phase amplitude detection system(PAD) and phase amplitude control(PAC) system is needed to improve the rf stability. This paper describes the microwave system for the PxFEL and the PAD and PAC system.
UVSOR, Okazaki
Nagoya University, Nagoya
Sokendai - Okazaki, Okazaki, Aichi
UVSOR, a 750 MeV synchrotron light source of 53m circumference, had been operated for more than 20 years. After a major upgrade in 2003, this machine was renamed to UVSOR-II. The ring is now routinely operated with low emittance of 27 nm-rad and with four undulators. The test run of the top up injection has been started. The latest result will be reported. By utilizing a part of the existing FEL system and an ultra-short laser system, coherent synchrotron radiation and coherent harmonic generation have been extensively studied, under international collaborations. A new program on the coherent light source developments has been started, which includes upgrades of the undulator and the laser system and a construction of dedicated beam-lines.
SLAC, Menlo Park, California
LBNL, Berkeley, California
Funding: This work was supported by U.S. DOE contracts DE-AC03-76SF00515 and under the auspices of the Office of Science, U.S. DOE under Contract No. DE-AC02-05CH11231.
Recently Stupakov* has suggested a scheme entitled echo-enabled harmonic generation (EEHG) for producing short wavelength FEL radiation that allows far higher harmonic numbers to be accessed as compared with the normal limit arising from incoherent energy spread. We have studied the feasibility of a single EEHG stage to generate coherent radiation in the "water window" (2- 4 nm wavelength) directly from a UV seed laser at ~200-nm wavelength. By adjusting the temporal overlap region of the two lasers producing energy modulation in the EEHG scheme, we find it may be possible to vary the duration of the output coherent soft x-ray pulse. We present time-dependent simulation results which explore these ideas and also examine the sensitivity of the scheme to various input electron beam parameters.
*G. Stupakov, Preprint SLAC-PUB-13445
LBNL, Berkeley, California
Funding: This work was supported under the auspices of the Office of Science, U.S. DOE under Contract No. DE-AC02-05CH11231.
Recently* it has been pointed out that numerical simulation of some systems containing charged particles with highly relativistic directed motion can by speeded up by orders of magnitude by choice of the proper Lorentz boosted frame. A particularly good example is that of short wavelength free-electron lasers (FELs) in which a high energy electron beam interacts with a static magnetic undulator. In the optimal boost frame with Lorentz factor gammaF, the red-shifted FEL radiation and blue shifted undulator have identical wavelengths and the number of required time-steps (presuming the Courant condition applies) decreases by a factor of gammaF-squared for fully electromagnetic simulation. We have adapted the WARP code** to apply this method to several FEL problems including coherent spontaneous emission (CSE) from pre-bunched e-beams, radiation in multi-wavelength undulators, and the effective lengths of undulators with entrance and exit matching ramps. We also discuss some preliminary results from applying the boosted-frame method to Coherent Synchrotron Radiation calculations.
*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).
MIT, Cambridge, Massachusetts
UW-Madison/SRC, Madison, Wisconsin
The seeded FEL performance of a number of Wisconsin FEL (WiFEL) undulator lines is described. The experimental design requirements include coverage of a broad wavelength range, rapid wavelength tuning, variable polarization, and variable pulse energy. The beam parameters allow experiments ranging from those requiring low peak power with high average spectral flux to those that need high peak power and short pulse lengths in the femtosecond range. The FELs must also be stable in timing, power, and energy while satisfying constraints on electron beam quality and fluctuations, undulator technologies, and seed laser capabilities. Modeling results are presented that illustrate the design performance over the full wavelength range of the facility.
NTHU, Hsinchu
NSRRC, Hsinchu
Funding: The authors gratefully acknowledge funding supports from National Synchrotron Radiation Research Center, National Tsinghua University, and National Science Council.
We study the generation of THz electron pulse trains from a 6 MeV photocathode electron gun driven by a beat-wave laser with a variable beat frequency [1]. We numerically inject the electrons into a single-pass FEL undulator. Owing to the prebunched electron pulse train, the quick shoot-up of the FEL power overcomes the space-charge debunching force in the 6 MeV beam. With nominal beam parameters and an initial bunching factor >5%, the FEL can reach 20-MW saturation power at 6 THz in a half meter long undulator. The length of this 20MW THz FEL, from the beginning of the electron gun to the end of the wiggler, is less than a meter. We will report our experimental progress of this work in the conference.
[1] Yen-Chieh Huang, “Laser-beat-wave bunched beam for compact superradiance sources,” International Journal of Modern Physics B, Vol. 21 Issue 3/4, p277-286 (2007).
SLAC, Menlo Park, California
UCLA, Los Angeles, California
The Linac Coherent Light Source (LCLS) is an x-ray Free-electron Laser (FEL) being commissioned at SLAC. Recent beam measurements have shown that, using the LCLS injector-linac-compressors, the beam emittance is very small at 20 pC*. A similar low charge operation mode was also suggested and studied**. In this paper we perform start-to-end simulations of the entire accelerator including the FEL undulator and study the FEL performance versus the bunch charge. At 20 pC charge, these calculations associated with the measured beam parameters suggest the possibility of generating a longitudinally coherent single x-ray spike with 2-femtosecond duration at a wavelength of 1.5 nm. At ~100 pC charge level, our simulations show an x-ray pulse with 20 femtosecond duration and up to 1012 photons at a wavelength of 1.5 Å. These results open exciting possibilities for ultrafast science and single shot molecular imaging.
*A. Brachmann et. al., to be published.
**J. Rosenzweig et al., Nuclear Instr. and Meth. A 593, 39-44 (2008); S. Reiche et al., Nucl. Instr. And Meth. A 593, 45-48 (2008).
SLAC, Menlo Park, California
ELETTRA, Basovizza
Funding: Work supported by the U.S. Dept. of Energy contract #DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) is an x-ray Free-Electron Laser (FEL) project presently in a commissioning phase at SLAC. The very bright electron beam required for the FEL is also susceptible to a micro-bunching instability* in the magnetic bunch compressors, prior to the FEL undulator. The uncorrelated electron energy spread can be increased by an order of magnitude to provide strong Landau damping against the instability without degrading the free-electron laser performance. To this end, a ‘laser-heater’ system has been installed in the LCLS injector, which modulates the energy of a 135-MeV electron bunch with an IR laser beam in a short undulator, enclosed within a four-dipole chicane. The last half of the chicane time-smears the energy modulation leaving an effective thermal energy spread increase. We present the first commissioning results of this system, its operational issues, and its impact on the micro-bunching instability.
*Z. Huang et. al., Phys. Rev. ST Accel. Beams 7, 074401 (2004).
SLAC, Menlo Park, California
USTC/NSRL, Hefei, Anhui
There is a growing interest in producing intense, coherent x-ray radiation with an adjustable and arbitrary polarization state. The crossed-planar undulator* was first proposed by Kim for rapid polarization control in synchrotron radiation and free electron laser (FEL). Recently, a statistical analysis shows a degree of polarization over 80% is obtainable for a SASE FEL near saturation**. In such a scheme, nonlinear harmonic radiation is generated in each undulator and its polarization is controllable in the same manner. In this paper, we study the degree of polarization for the nonlinear harmonic radiation. We also discuss methods to reduce the FEL power fluctuations by operating the crossed undulator in the saturation regime.
*K.-J. Kim, Nucl. Instrum. Methods A 445, 329 (2000)
**Y. Ding and Z. Huang, Phys. Rev. ST Accel. Beams 11, 030702 (2008)
SLAC, Menlo Park, California
Funding: This work was supported by US DOE contracts DE-AC03-76SF00515
The echo-enabled harmonic generation free electron laser (EEHG FEL) holds great promise in generation of coherent soft x-ray directly from a UV seed laser within one stage. The density modulation in the harmonic generation process is affected by the smearing effect caused by the fluctuations of energy and current along the beam, as well as the field error of the dispersive elements. In this paper we study the tolerance of the EEHG FEL on beam quality and field quality.
SLAC, Menlo Park, California
Microbunching instability is one of the most challenging threats to FEL performances. The most effective way to suppress microbunching instability is to increase the relative slice energy spread of the beam. In this paper we show that the velocity bunching inherently mitigates the microbunching instability. PARMELA simulation indicates that the initial current modulations are suppressed in velocity bunching process, which may be attributed to the strong Landau damping from the relatively large relative slice energy spread.
SLAC, Menlo Park, California
ASCo, Clayton, Victoria
Funding: Work supported by Department of Energy contract DE-AC02-76SF00515. This work was performed in support of the LCLS project at SLAC
The Linac Coherent Light Source is an x-ray Free-Electron Laser (FEL) project being commissioned at SLAC. The very bright electron beam required for the FEL is subjected to various sources of jitter along the accelerator. The peak current, centroid energy, and trajectory of the electron bunch are controlled precisely at the highest repetition rate possible with feedback systems. We report commissioning experience for these systems. In particular, there is high frequency content in the electron bunch current spectrum, and we report its impact on the systems. Due to the coupling of the betatron motion and the dispersion component of the electron trajectory, a fast in-line model* is incorporated. For the longitudinal feedback, we report the performance of two different configurations: one with RF system as direct actuators, which are nonlinear, and the other with artificially formed linear energy and energy-chirp actuators. Since the electron bunch is compressed to a final peak current of 2 to 3 kA, coherent synchrotron radiation and other wakefields are included for precise control of the electron bunch parameters. Machine performance is compared to start-to-end simulations.
*P. Chu et al., these PAC09 proceedings
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
JAI, Oxford
Diamond, Oxfordshire
UMAN, Manchester
Cockcroft Institute, Warrington, Cheshire
A design for a free electron laser driver which utilises 1.3 GHz superconducting CW accelerating structures is studied. The machine will deliver longitudinally compressed electron bunches with repetition rates of 1 kHz with a possibility to increase up to 1 MHz. Tracking is performed from an NC RF photocathode gun, accelerating and compressing in three stages to obtain peak current greater than 1 kA at 2.2 GeV. This is achieved through injection at 200 MeV, then recirculating twice in a 1 GeV main linac. The optics design, optimisation procedures and start to end modelling of this system are presented.
ELETTRA, Basovizza
University of Nova Gorica, Nova Gorica
In single-pass FELs, for the amplification process to be effective, it is necessary to compensate the phase advance of photons with respect to electrons in the break region between undulators. In fact, most of the FELs are based on the use of phase shifters between different undulator sections in order to allow the control of the relative phase advance. In this work we present different methods in which the use of phase shifters can be useful for a further improvement of the FEL performance.
ELETTRA, Basovizza
University of Nova Gorica, Nova Gorica
The second FEL line of the FERMI project was originally designed for providing long optical pulses (about 1ps) in the spectral range between 40 and 10 nm. Recent developments of both the FERMI scientific case and of new possible configurations of the FERMI linac stimulated a revision of the original setup in order to exploit new possibilities and fulfill requirements. In this work we deeply investigated the most relevant FEL configurations that may be implemented for the FERMI FEL2, showing that a revision of the original double-cascade high-gain harmonic generation is the most promising. According to numerical simulations, using the electron-beam parameters expected from the FERMI linac, the spectral range for FEL2 can now be extended down to 5 nm, and a significant amount of power can be produced also in the 1-nm spectral range. Moreover, the proposed setup is flexible enough for exploiting future developments of new seeding sources like HHG in gases.
Tohoku University, School of Scinece, Sendai
To develop a coherent Terahertz (THz) light sources, producing very short electron bunch has been progressed at Laboratory of Nuclear Science, Tohoku University. We have developed an independently-tunable-cells (ITC) RF gun consisted with two cavities and thermionic cathode in order to produce bunch length around a hundred femto-second. Possibility of pre-bunched FEL is investigated by numerical simulations. In case of the bunch length shorter than wavelength, the FEL interaction seems to be different from conventional way. High intensity and short FEL pulse is possibly obtained *. In a broad band regime, coherent spontaneous THz radiation has been developed. A ring type source consisted with isochronous arcs can provide the coherent THz pulses from every bending magnets. The project has aimed multi-user facility **. In addition, a compact DC gun is also under development. Measured normalized emittance is less than 1μrad for a beam energy of 50 keV and a beam current of 300 mA. This low emittance beam is quite suitable for driving Smith-Purcell Backward Wave Oscillator FEL in THz region. Detail of the DC gun and prospect will be presented ***.
*M. Yasuda et al., Proc. FEL08, (2008) in press.
**H. Hama et al., New J. Phys. 8 (2006) 292.
***K. Kasamsook et al., Proc. FEL07, (2007) 417 - 420.
Universita' degli Studi di Milano, Milano
Istituto Nazionale di Fisica Nucleare, Milano
INFN/LNF, Frascati (Roma)
ENEA C.R. Frascati, Frascati (Roma)
INFN-Roma, Roma
In this paper a possible experiment with the existing SPARC photoinjector is described to generate sub-picosecond high brightness electron bunches able to produce single spike radiation pulses at 500 nm with the SPARC self-amplified spontaneous emission free-electron laser (SASE-FEL). The main purpose of the experiment will be the production of short electron bunches as long as few SASE cooperation lengths, the determination of the shape of the radiation pulse and the validation of the single spike scaling law, in order to foresee operation at shorter wavelength in the future operation with SPARX. We present in this paper start to end simulations regarding the beam production and FEL performance, and discuss the layout of the machine. The experience, gained from this experiment, will help in the configuration of the VUV and X-ray FEL SPARX to obtain FEL pulses below 10 fs.
UW-Madison/SRC, Madison, Wisconsin
SLAC, Menlo Park, California
The microbunching gain of a free-electron laser (FEL) driver is affected by the beam spreader that distributes bunches to the FEL beam lines. For the Wisconsin FEL (WiFEL), analytic formulas and tracking simulations indicate that a beam spreader design with a low value of R56 has little effect upon the gain.
UW-Madison/SRC, Madison, Wisconsin
SLAC, Menlo Park, California
The microbunching gain of the driver for the Wisconsin FEL (WiFEL) is reduced by more than an order of magnitude by using a single-stage bunch compressor rather than a two-stage design. This allows compression of a bunch with lower energy spread for improved FEL performance.
ANL, Argonne
Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava
Funding: * Work at Argonne supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357.
Hall probe is the best way to do tuning and measurements of insertion devices. Horizontal Hall probe magnetic field measurements in the presence of a strong vertical magnetic field were tested in 1997. The next step of this investigation was reported at the 2004 FEL Conference. Hall probe horizontal field measurements in the presence of a vertical magnetic field are complicated due to the influence of the Planar Hall probe effect on the resulting Hall voltage. 2-axis Sentron Hall probe was used for the Linear Coherent Light Source devices. By positioning the Hall probe accurately in the vertical direction, the probe could be used for fast measurements and tuning of FEL devices. To eliminate the high sensitivity to the positioning of the probe, a new type of Hall probe, consisting of two sensors combined so as to cancel the influence of the PHE, was developed at the Institute of Electrical Engineering, Slovak Academy of Sciences. The results of tests done at the APS showed that it is not sensitive to vertical position and is 60 times less sensitive than a Bell probe to the angle between the Hall sensor current and the in-plane component of the field direction.
Uni HH, Hamburg
DESY, Hamburg
A seeded free-electron laser experiment at VUV wavelengths, called sFLASH, is being prepared at the existing SASE FEL user facility FLASH. Seed pulses at wavelengths around 30 nm from high harmonic generation will interact with the electron beam in sFLASH undulators upstream of the existing SASE undulator section. In this paper, sFLASH undulators are described.
HUST, Wuhan
The design of compact terahertz (THz) radiation source based on free electron laser (FEL) has been implemented, whose concept machine is consisting of a thermionic RF gun (ITC-RF Gun), a LINAC, a hybrid undulator combined with an optical resonance cavity of hole-coupling mode. The aim of the project is to provide a stable coherent THz (1~3THz) source. The hybrid undulator system is the critical component for compact terahertz FEL. Emission wavelength is related to the period and the peak magnetic field of the hybrid undulator. In particular, the magnetic structure by adding side magnet blocks to each pole will increase the field strength, avoid too small gap, and make the system more compact. Simulations using RADIA are presented. The feature of designs, optimization of the magnetic parameters and field analysis will be discussed.
LBNL, Berkeley, California
Funding: This work was supported by the Director, Office of Science, U.S. Department of Energy, under contract No. DE-AC02-05CH11231.
Superconducting undulators are currently under development at a number of light sources to serve as the next generation of insertion devices, with higher fields providing enhanced spectral range for users. Most of these devices are designed with wire-based technologies appropriate for periods greater than ~10mm. New undulator concepts yielding very short-period, high-field devices with periods of a few millimeters and a K~1 have the potential to significantly reduce the cost and enhance the performance of FEL's. Here we describe a design using high temperature superconductor tapes that are commercially available, and that promise a cost-effective fabrication process using micromachining or lithography. Detailed magnetic and spectral performance analysis will be provided.
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
The SuperB collider project aims at the construction of an asymmetric high luminosity B-Factory in the Tor Vergata University campus in Rome (Italy). The engineering aspects of the SuperB design and construction with the aim to reuse at maximum the PEP II components will be presented. Sinergies with the Italian FEL project SPARX, which will start civil construction this year, will be discussed. The two projects can share the Linac tunnel and other facilities. A study of ground motion will also be presented.
CLASSE, Ithaca, New York
N.U, Nigde
We consider a scheme for gamma-gamma collisions at ILC. In our scheme the electron beam from 5 GeV injector-Linacs, present in ILC scheme, used in FEL amplifier. The laser radiation from solid-state laser amplified in this FEL and directed to nearby IP point for further Compton back scattering. Two additional ~50 m helical undulators and master laser system of intermediate power required for this scheme at ILC.
DESY, Hamburg
SLAC, Menlo Park, California
Funding: Work supported in part by the DOE under contract DE-AC02-76SF00515.
Different scenario of a start-up with international linear collider (ILC) are under discussion at the moment in the framework of the Global Design Effort (GDE). One of them assumes construction of the ILC in stages from some minimum CM energy up to final target of 500 GeV CM energy. Gamma-gamma collider with CM energy of 180GeV is considered as a candidate for the first stage of the facility. In this report we present conceptual design of a free electron laser as a source of primary photons for the first stage of ILC.
ELETTRA, Basovizza
Funding: The work was supported in part by the Italian Ministry of University and Research under grant FIRB-RBAP045JF2.
The FERMI@elettra electron beam dump is designed for a 1nC, 1.8 GeV, 50Hz repetition rate beam. Using GEANT simulations, materials are chosen to absorb 99% of the beam energy and to limit the radio-isotope production. In addition, from the energy deposition distribution inside the dump, the thermal load is estimated. The necessary requirements, the design and the expected performance are presented and discussed.
LBNL, Berkeley, California
Funding: US Department of Energy contract No. DE-AC02-05CH11231, and NSF Grant 0614001
We discuss the design and current status of experiments to couple the THUNDER undulator to the Lawrence Berkeley National Laboratory (LBNL) laser wakefield accelerator (LWFA). Currently the LWFA has achieved quasi-monoenergetic electron beams with energies up to 1 GeV*. These ultra-short, high-peak-current, electron beams are ideal for driving a compact XUV free electron laser (FEL)**. Understanding the electron beam properties such as the energy spread and emittance is critical for achieving high quality light sources with high brightness. By using an insertion device such as an undulator and observing changes in the spontaneous emission spectrum, the electron beam energy spread and emittance can be measured with high precision. The initial experiments will use spontaneous emission from 1.5 m of undulator. Later experiments will use up to 5 m of undulator with a goal of a high gain, XUV FEL.
*W.P. Leemans et al., Nature Physics, Volume 2, Issue 10, pp. 696-699 (2006).
**C.B. Schroeder et al., Proceedings AAC08 Conference (2008).
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Dept. of Energy contract #DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) is a SASE 1.5-15 Å x-ray Free-Electron Laser (FEL) facility under construction at SLAC, and presently in an advanced phase of commissioning. The injector, linac, and new bunch compressors were commissioned in 2007 and 2008, establishing the necessary electron beam brightness at 14 GeV. The final phase of commissioning, including the FEL undulator and the long transport line from the linac, began in November 2008, with first 1.5-Å FEL light and saturation observed in mid-April 2009. We report on the accelerator, undulator, and FEL operations, although prior to the availability of the full x-ray diagnostics suite, which will not be ready until June 2009.
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
The SPring-8 compact SASE source (SCSS) test accelerator was constructed in FY2005 to demonstrate a new concept for X-ray free electron lasers composed of a low-emittance thermionic electron injector, a high-gradient normal conducting C-band accelerator, and a short-period in-vacuum undulator. With a 250 MeV electron beam, continuous SASE saturation can generate intense and stable FEL beams at the wavelength range from 50 to 60 nm with the maximum pulse energy of 30 micro-J and the intensity fluctuation of ~10%. Analysis of the SASE saturation data with a 3D-FEL simulation code suggests negligible degradation of the electron beam emittance during the high bunch compression process. We also succeeded in operating the C-band accelerator with a high accelerating gradient of 37 MV/m and a repetition rate of 60 pps. Now, the FEL beam is routinely delivered for user experiments. At this conference we will present the machine performance and recent progress of the SCSS test accelerator together with the anticipated performance of the 8 GeV XFEL under construction.
JLAB, Newport News, Virginia
Funding: Work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Air Force Research Laboratory, and by the DOE Contract DEAC05-84ER40150.
As the only currently operating free electron laser (FEL) based on a CW superconducting energy recovering linac (ERL), the Jefferson Laboratory FEL Upgrade remains unique as an FEL driver. The present system represents the culmination of years of effort in the areas of SRF technology, ERL operation, lattice design, high power optics and DC photocathode gun technology. In 2001 the FEL Demo generated 2.1 kW of laser power. Following extensive upgrades, in 2006 the FEL Upgrade generated 14.3 kW of laser power breaking the previous world record. The FEL Upgrade remains a valuable testbed for studying a variety of collective effects, such as the beam breakup instability, longitudinal space charge and coherent synchrotron radiation. Additionally, there has been exploration of operation with lower injection energy and higher bunch charge. Recent progress and achievements in these areas will be presented, and two recent milestones – installation of a UV FEL and establishment of a DC gun test stand – will be discussed. Additionally, a review of the longitudinal matching scheme and the use of incomplete energy and its implications will be presented.
DESY, Hamburg
The free-electron laser facility FLASH at DESY, Germany is the world-wide unique SASE-FEL operating in the VUV and the soft X-ray wavelengths range. Since Summer 2005, FLASH operates as a user facility providing fully coherent 10 to 50 femtosecond long laser radiation in the wavelength range from 47 nm to 6.5 nm and with an unprecedented brilliance - many orders of magnitude higher than any other facility. The SASE radiation contains also higher harmonics. Several experiments have successfully used the third and fifth harmonics, in the latter case with a wavelength down to 1.59 nm. In addition, FLASH serves as a pilot facility for the European XFEL. Part of the beam time is reserved for general accelerator studies which also includes ILC related studies.
UCLA, Los Angeles, California
Funding: This work was supported by DOE grants DE-FG03-92ER40727 and DE-FG03-92ER40693
Many proposals and ongoing national projects exist worldwide to build a single-pass X-ray FEL amplifier in which a high-brightness, multi-GeV electron beam has a resonant energy exchange with radiation in an undulator. Because of the practical limit on the undulator period, the electron beam energy represents one of constraints on the shortest reachable wavelength. Recently the high-order harmonic FEL/IFEL interactions were considered theoretically as a technique that would allow the reduction of the beam energy without corresponding decrease in the undulator period and the magnetic field strength. We demonstrate microbunching of the 12.3 MeV electrons in a 7th order IFEL interaction, where the seed radiation frequency is seven times higher then the fundamental frequency. Strong longitudinal modulation of the beam is inferred from the observation of the first, second and third harmonics of the seed radiation in a Coherent Transition Radiation spectrum. The level of seed power is comparable to that required for microbunching at the fundamental frequency of the ten-period-long undulator. The implications of these results for the next generation of FELs will be explored.
USTRAT/SUPA, Glasgow
University of Dundee, Nethergate, Dundee, Scotland
UAD, Dundee
Funding: The U.K. EPSRC and the European Community - New and Emerging Science and Technology Activity under the FP6 “Structuring the European Research Area” programme (project EuroLEAP, contract number 028514)
The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme* is developing laser-plasma accelerators for the production of ultra-short electron beams as drivers of incoherent and coherent radiation sources from plasma and magnetic undulators**. Initial quantitative measurements of the electron beam properties have been made. A high power (20 TW) femtosecond laser pulse is focused into a gas jet (length 2 mm) and electrons from the laser-induced plasma are self-injected into the accelerating potential of the plasma density wake behind the laser pulse. The electron beam pointing as it exits the gas jet is as large as 10 mrad. Understanding the pointing stability is an essential step for reproducible beam transport and we present a theoretical model to account for this behaviour. The beam divergence is as low as 2 mrad, which is consistent with a normalised emittance of the order of 1 pi mm mrad. The maximum central energy of the beam is ~90 MeV with r.m.s. relative energy spread as low as 0.8%. An analysis of this unexpectedly high beam quality is presented and its impact on the viability of a free-electron laser*** driven by such a beam is examined.
* D. A. Jaroszynski et al., Phil. Trans. R. Soc. A 364, 689 (2006).
** H.-P. Schlenvoigt et al., Nature Phys. 4, 130 (2008).
*** B. Shepherd and J. Clarke, Proc. EPAC 2006, 3580 (2006).
INFN/LNF, Frascati (Roma)
Istituto Nazionale di Fisica Nucleare, Milano
CEA, Gif-sur-Yvette
INFN-Roma II, Roma
ENEA C.R. Frascati, Frascati (Roma)
SOLEIL, Gif-sur-Yvette
INFN-Roma, Roma
University of Tehran, Tehran
UCLA, Los Angeles, California
The SPARC project foresees the realization of a high brightness photo-injector to produce a 150-200 MeV electron beam to drive 500 nm FEL experiments in SASE, Seeding and Single Spike configurations. The SPARC photoinjector is also the test facility for the recently approved VUV FEL project named SPARX. The second stage of the commissioning, that is currently underway, foresees a detailed analysis of the beam matching with the linac in order to confirm the theoretically prediction of emittance compensation based on the “invariant envelope” matching , the demonstration of the “velocity bunching” technique in the linac and the characterisation of the spontaneous and stimulated radiation in the SPARC undulators. In this paper we report the experimental results obtained so far. The possible future energy upgrade of the SPARC facility to produce UV radiation and its possible applications will also be discussed.
FEL/Duke University, Durham, North Carolina
TUNL, Durham, North Carolina
Funding: This work is supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086 and by US Department of Energy grant DE-FG02-01ER41175.
Since 2008, the upgraded High Intensity Gamma-ray Source (HIGS) at the Duke FEL Lab has provided users with gamma beams of unprecedented quality for scientific research. The recently completed accelerator upgrades include a HOM-damped RF cavity, a full-energy top-off booster injector, redesigned storage ring straight sections, and two new FELs. The HIGS facility is now capable of producing a high intensity gamma beam in a wide energy range (1 - 100 MeV) using commercial FEL mirrors. It has achieved an exceptionally high flux, up to ~1010 g/s total (< 20 MeV), making it the world's most powerful Compton gamma source. It produces almost 100% polarized gammas, either linear or circular. At the HIGS, the gamma energy can be changed rapidly within a factor of three in minutes. Operated by Triangle Universities Nuclear Laboratory since summer 2008, the HIGS is a dedicated Compton gamma source, capable of producing more than 2,000 h of gamma beam time per year with a five-day, two-shift schedule. Future development at the HIGS includes higher energy gamma beams toward the pion threshold and a rapid switch of circular polarization.
LANL, Los Alamos, New Mexico
At Los Alamos National Laboratory we are actively exploring the feasibility of constructing a 50-keV x-ray free-electron laser. For such a machine to be feasible, we need to limit the cost and size of the accelerator and, as this is intended as a user facility, we would prefer to use proven, conventional accelerator technology. Using recent developments in transverse-to-transverse and transverse-to-longitudinal emittance exchange optics *, **, we present a conceptual 20-GeV conventional electron accelerator design capable of producing an electron beam with a normalized transverse emittance as low as 0.2 mm-mrad, a root-mean-square (RMS) beam length of 74 fs, and an RMS energy spread of 0.01%. We also explore the possibility of introducing a crystallographic mask into the beam line. Combined with a transverse-to-longitudinal emittance exchange optic, we show that such a mask can be used to modulate the electron beam longitudinally to match the x-ray wavelength. This modulation, combined with the very low transverse beam emittance, allows us to not only generate 50-keV x-rays with a 20-GeV electron beam, but also drastically decrease the length of the required undulator.
*P. Emma, Z. Huang, K. -J. Kim, and P. Piot, Phys. Rev. ST Accel. Beams 9, 100702 (2006).
**B. E. Carlsten and K. A. Bishofberger, New J. Phys. 8, 286 (2006).
Fermilab, Batavia
KAERI, Daejon
BINP SB RAS, Novosibirsk
Funding: Work supported by the U.S. Department of Energy under contract No. DE-AC02-07CH11359.
Noninvasive bunch duration monitoring has a crucial importance for modern accelerators intended for short wavelength FEL’s, colliders and in some beam dynamics experiments. Monitoring of the bunch compression in the Emittance Exchange Experiment at the A0 Photoinjector was done using a parametric presentation of the bunch duration via Coherent Synchrotron Radiation (CSR) emitted in a dipole magnet and measured with a wide-band quasi-optical Schottky Barrier Detector (SBD). The monitoring resulted in a mapping of the quadrupole parameters allowing a determination of the region of highest compression of the bunch in the sub-picosecond range. The obtained data were compared with those measured using the streak camera. A description of the technique and the results of simulations and measurements are presented and discussed in this report.
FEL/Duke University, Durham, North Carolina
TUNL, Durham, North Carolina
A gamma-ray beam produced by Compton scattering of a laser beam and a relativistic electron beam has been used to determine electron beam parameters. In order to accurately measure the electron beam energy, a fitting model based upon Compton scattering cross section is introduced in this paper. With this model, we have successfully determined the energy of the electron beam in Duke storage ring with a relative uncertainty of 3× 10-5 using a Compton gamma beam from the High Intensity γ-ray Source (HIγS) facility at Duke University.
Ankara University, Faculty of Engineering, Tandogan, Ankara
FZD, Dresden
SDU, Isparta
Funding: State Planning Organization of Turkey
Turkish Accelerator Center (TAC) Infrared (IR) Free Electron Laser facility (FEL) supported by State Planning Organization (SPO) of Turkey will be based on 15-40 MeV energy range electron linac and two different undulators with 2.5 cm and 9 cm period lengths in order to obtain FEL in 2-250 micron wavelength range. The electron linac will consist of two superconducting ELBE modules which houses two 9-cell TESLA cavity in one module and can operate in cw mode. The electron bunches in cw mode which are compatible with the main linac will be provided by a thermionic gun and an injector system which is totally based on normal conducting technology. In this study the injector design for TAC IR FEL is represented and beam dynamics issues were discussed for suitable injection to first accelerating module.
IHEP Beijing, Beijing
SINAP, Shanghai
RF deflectors can be used for bunch length measurement with high resolution. This paper describes the completed S-band travelling wave RF deflector and the bunch length measurement of the electron beam produced by the photocathode RF gun of Shanghai DUV-FEL facility. The deflector’s VSWR is 1.06, the whole attenuation 0.5dB, and the bandwidth 4.77MHz for VSWR less than 1.1. With laser pulse width of 8.5ps, beam energy of 4.2 MeV, bunch charge of 0.64 nC, the bunch lengths for different RF input power into the deflector were measured, and the averaged rms bunch length of 5.25 ps was obtained. A YAG crystal is used as a screen downstream of the deflector, with the calibrated value of 1pix =136um.
RadiaBeam, Marina del Rey
Spectrum Detector, Lake Oswego, Oregon
UGA, Athens, Georgia
UCLA, Los Angeles, California
Funding: Work supported by U.S. DOE Grant Number DE-FG02-07ER84814.
The generation of high peak current, high brightness beams routinely requires compression methods (e.g. four-bend chicane), which produce coherent radiation as a by-product. The sensing of this radiation, coupled with interferometric methods, yields crucial longitudinal bunch length and bunch profile information. This paper discusses the progress of the development of a real-time terahertz interferometer used for longitudinal beam profile diagnosis.
RadiaBeam, Marina del Rey
UCLA, Los Angeles, California
A Coherent Optical Transition Radiation (COTR) arising from the photo-injector electron beams spontaneous microbunching at optical frequencies has been recently observed in a number of experiments. This effect can lead to an undesirable optical background for OTR beam profile measurements at these facilities. A method to resolve this problem is proposed, based on selectively suppressing the back-scattered COTR using multiple scattering in the insertion foil. An analytical treatment of COTR dependence on the angular divergence in the radiating beam is presented, and the efficacy of the approach is illustrated with the numerical examples.
RIKEN Spring-8 Harima, Hyogo
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
In XFEL/SPring-8, it is very important to generate an electron beam, having a low slice emittance of 0.7 pimm-mrad, a pulse width of 30 fs, and a peak current of 3 kA at an X ray lasing part. For tuning such beam to guarantee stable X ray laser generation, beam and laser monitors to diagnose the temporal structure of them are an indispensable function. The monitors, such as a beam position monitor (BPM), a TM11-mode rf beam deflector and a screen monitor (SCM), have been developed to satisfy the function. The BPM has a position resolution of less than 1 um. The SCM to observe the beam deflecting image has a position resolution of 2.5 um. The design of a longitudinal beam diagnosis system using the monitors showed that it can measure a temporal structure with a resolution of 0.5 fs along the beam pulse. The experiment to check feasibility of the BPM showed that it can work as a beam arrival timing monitor with a temporal resolution of 46 fs. A monitor system using an in-vacuum photo diode was also developed to measure the laser arrival timing, and showed ability to resolve a 2 ps time jitter. These temporal resolutions allow us fine beam tuning required for the XFEL.
The University of Tokyo, Nuclear Professional School, Ibaraki-ken
JASRI/SPring-8, Hyogo-ken
In XFEL/SPring-8, it requires ultra high-brightness electron bunches with ultralow slice emittance and bunch duration of 30 fs (FWHM) in a lasing part. In order to measure such bunches, we are developing a single-shot, non-destructive, real-time 3-D bunch shape monitor based on EO sampling with a manner of spectral decoding. It consists of a radially polarized probe laser and 8 EO-crystals, which surround a beam axis azimuthally and their crystal-axes are radially distributed as well as Coulomb fields of electron bunches. The probe laser has a linear-chirped broad bandwidth (> 400 nm at 800 nm of a central wavelength) for higher temporal resolution, and a hollow shape to avoid interacting with electron bunches. As an EO crystal, we investigate the feasibility of an organic crystal such as a DAST for 20-fs temporal response. This monitor can measure not only longitudinal but also transverse charge distribution at the same time. These real-time 3-D bunch shape measurements are very important to optimize electron bunches for XFEL operation. We present the scheme of this monitor with its estimation in detail and report the developing status for probe laser and organic-EO-crystals.
UCLA, Los Angeles, California
INFN/LNF, Frascati (Roma)
ENEA C.R. Frascati, Frascati (Roma)
It has been suggested that an ultra-short, very low charge beam be used to drive short wavelength single-spike operation at the SPARC FEL. This paper explores the development and construction of a longitudinal diagnostic capable of completely characterizing the radiation based on the Frequency-Resolved Optical Gating (FROG) technique. In particular, this paper explores a new geometry based on a Transient-Grating (TG) nonlinear interaction and includes studies of start to end simulations for pulses at the SPARC facility using GENESIS and reconstructed using the FROG algorithm. The experimental design, construction and initial testing of the diagnostic are also discussed.
ELETTRA, Basovizza
DEEI, Trieste
Funding: The work was supported in part by the Italian Ministry of University and Research under grant FIRB-RBAP045JF2.
Travelling wave and standing wave deflectors are well known RF devices that nowadays are used in particle accelerators as a beam diagnostic tool. They will also be implemented in FERMI@Elettra project, a soft X-ray fourth-generation light source under development at the ELETTRA laboratory, and used to completely characterize the beam phase space by means of measurements of bunch length and transverse slices emittance. In particular, one deflector will be placed at low energy (250MeV) and another at high energy (1.2GeV), just before the FEL process starts. In this note we collect our experience and simulation on this last device, making a comparison between the most relevant options we have considered to satisfy our RF and space constraints. Basic cell design is discussed for both the travelling and standing wave choice. In particular, two different modes, the 2/3π and the 5/6π, are analyzed for the travelling wave option while an 11 cells design in π mode is presented for the standing wave case. For both cases sensitivity analysis and other relevant RF parameters are given.
DESY, Hamburg
Uni HH, Hamburg
Next generation FEL light sources like the European XFEL require timing stability between different subsystems of 10-20 fs. In optical synchronization systems, the timing information is distributed across the facilities via sub-ps laser pulses travelling on length stabilized optical fibers. Different methods are available for RF extraction from the pulse train. In this paper, we characterize the long-term phase stability of a 1.3 GHz signal gained from the direct conversion of a higher harmonic of the pulse repetition frequency, and from a voltage controlled oscillator locked with a PLL that uses a Sagnac-Loop as balanced optical-microwave phase detector.
Uni HH, Hamburg
PSI, Villigen
DESY, Hamburg
CLASSE, Ithaca, New York
ITER, St Paul lez Durance
The free-electron laser FLASH and the planned European XFEL generate X-ray light pulses on the femtosecond time-scale. The feasibility of time-resolved pump-probe experiments, special diagnostic measurements and future operation modes by means of laser seeding crucially depend on the long-term stability of the synchronization of various laser systems across the facility. For this purpose an optical synchronization system is being installed and tested at FLASH. In this paper, we report on the development and the performance of a background-free optical cross-correlation scheme to synchronize two individual mode-locked lasers of different center wavelengths and repetition rates with an accuracy of better than 10 fs. The scheme can be tested by linking a Ti:sapphire oscillator, used for electro-optical diagnostics at FLASH, to both a locally installed erbium-doped fiber laser and the end-point of an actively length-stabilized fiber link distributing the pulses from a master laser oscillator. After the commissioning of this fiber link, the diagnostics laser can be synchronized to the electron beam and first accelerator based measurements on the performance of the system will be carried out.
BNL, Upton, Long Island, New York
Cooling intense high-energy hadron beams remains a major challenge in modern accelerator physics. Synchrotron radiation is still too feeble, while the efficiency of two other cooling methods, stochastic and electron, falls rapidly either at high bunch intensities (i.e. stochastic of protons) or at high energies (e-cooling). In this talk a specific scheme of a unique cooling technique, Coherent Electron Cooling, will be discussed. The idea of coherent electron cooling using electron beam instabilities was suggested by Derbenev in the early 1980s, but the scheme presented in this talk, with cooling times under an hour for 7 TeV protons in the LHC, would be possible only with present-day accelerator technology. This talk will discuss the principles and the main limitations of the Coherent Electron Cooling process. The talk will describe the main system components, based on a high-gain free electron laser driven by an energy recovery linac, and will present some numerical examples for ions and protons in RHIC and the LHC and for electron-hadron options for these colliders. BNL plans a demonstration of the idea in the near future.
SLAC, Menlo Park, California
Funding: Work supported by US DOE contracts DE-AC03-76SF00515.
A remarkable progress over the last decade in development of computer codes significantly advanced our capabilities in calculation of wakefields and impedances for accelerators. There are however a number of practical problems that, when approached numerically, require a huge mesh, and hence memory, or an extraordinary CPU power, or both. One class of such problems is related to wakes of ultra short bunches, typical for many next generation electron/positron accelerators and photon sources. Another class is represented by long shallow collimators and tapers, often with non round cross sections. The numerical difficulties with these problems can be traced to a small parameter in the system, such as, e.g., a ratio of the bunch length to the length of a taper. It is remarkably, however, that the same small parameter often allows developing approximate analytical methods that provide a simplified solution to the impedance problem. In this paper, we review recent results in the analytical theory of wakefields, which include calculation of the wakes of very short bunches, long transitions and some special cases of the resistive wall impedance.
SLAC, Menlo Park, California
DESY, Hamburg
LLNL, Livermore, California
Uppsala University, Biomedical Centre, Uppsala
LBNL, Berkeley, California
Tofwerk, Thun
Radiation damage limits the resolution of structural information obtained by X-ray diffraction. We are developing coherent diffractive imaging of biological specimens beyond conventional radiation damage resolution limits. The soft X-ray free-electron-laser (FEL) in Hamburg, FLASH*, was used to generate high-resolution low-noise coherent diffraction patterns from nanostructured nonperiodic objects before they turned into a plasma and exploded during single {10}-30 fs long X-ray pulses**,***. Iterative phase retrieval algorithms were used to reconstruct images of the objects****. Recent single particle diffraction experiments at FLASH, achieved in part due to the bunch train time pattern available from this superconducting linear accelerator, will be described. Data from single nanoparticles, their clusters and single cells will be discussed. Extending this approach to hard X-ray FELs, such as the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory, is anticipated to facilitate near atomic resolution imaging of nm-to-um-sized objects without the need for crystallization*****.
* Ayvazyan et al Eur Phys J D 2006 37 297
** Chapman et al Nat Phys 2006 2 839
*** Bogan et al Nano Lett 2008 8 310
**** Marchesini Rev Sci Instr 2007 78 011301
***** Neutze et al Nature 2000 406 752
SLAC, Menlo Park, California
Funding: work supported by the Department of Energy under contract number DE-AC03-76SF00515
Shorter and shorter electron bunches are now used in the FEL designs. The fine structure of the wall of a beam vacuum pipe plays more noticeable role in the wake field generation. Additionally to the resistance and roughness, the wall may have an oxide layer, which is usually a dielectric. It is important for aluminum pipe, which have Al2O3 layer. The thickness of this layer may vary in a large range: 1-100 nm. We study this effect for the very short (20-1000 nm) ultra relativistic bunches in an infinite round pipe. We solved numerically the Maxwell equations for the fields in the metal and ceramics. Results showed that the oxide layer may considerably increase the wavelength and the decay time of the resistive-wall wake fields, however the loss factor of the very short bunches does not change much.
SLAC, Menlo Park, California
Funding: Work supported in part by Department of Energy contract DE-AC02-76SF00515.
An x-ray Free-Electron Laser (FEL) calls for a high brightness electron beam. Generically, such a beam needs to be accelerated to high energy on the GeV level and compressed down to tens of microns, if not a few microns. The very bright electron beam required for the FEL has to be stable and the high quality of the electron beam has to be preserved during the acceleration and bunch compression. With a newly developed model independent global optimizer*, here we report study for the control and error diagnostics of such a generic machine: magnetic elements, and RF cavities, and the electron beam parameters: the peak current, centroid energy, and trajectory. Collective effects, such as coherent synchrotron radiation, space charge, and various wakefields are incorporated in a parametric approach. Applicability and verification are detailed for the LINAC Coherent Light Source, an x-ray FEL project being commissioned at SLAC.
*M.J. Lee, SLAC Report in press (2009).
BNL, Upton, Long Island, New York
In this paper we report the current status of the studies of a phenomenon of microbunching at NSLS Source Development Laboratory (SDL). We observed the microbunching inside 70MeV electron bunches even for subpicosecond beams of 10pC charge. Additional microbunching is formed when the beam is compressed in the bunch compressor utilizing the 4-magnet chicane. We study the mechanisms of microbunching in an electron beam generated by a 100fs laser pulse. It allows reducing the possibility of having beam structures induced by photo-injector laser, eliminating effects of RF curvature, and enhancing the longitudinal space charge (LSC) and the coherent synchrotron radiation (CSR) effects.
Imperial College of Science and Technology, Department of Physics, London
STFC/RAL, Chilton, Didcot, Oxon
A 4m-long, 324MHz four-vane RFQ, consisting of four coupled sections, is currently being designed for the Front End Test Stand (FETS) at RAL in the UK. Previous beam dynamics simulations, based on field maps produced with a field approximation code, provide a baseline for the new design. A novel design method is presented that combines the CAD and electromagnetic modelling of both the RFQ tank and the vane modulations with more sophisticated beam dynamics simulations using the General Particle Tracer code (GPT). This approach allows the full integration of the optimisation of the RFQ, based on beam dynamics simulations using a 3D EM-field map of the CAD model, with the design and manufacture of the RFQ vane modulations and RFQ tank. The design process within the Autodesk Inventor CAD software is outlined and details of the EM modelling of the RFQ in CST EM Studio are given. Results of beam dynamics simulations in GPT are presented and compared to previous results with field approximation codes. Finally, possible methods of manufacture based on this design process are discussed.