FEL Technology
Paper Title Page
TUOCI1 Latest Developments for Photoinjector, Seeding and THz Laser Systems 173
 
  • C.P. Hauri, A. Trisorio, C. Vicario
    Paul Scherrer Institut, Villigen, Switzerland
  • C. Ruchert
    PSI, Villigen PSI, Switzerland
  
  For driving compact FEL facilities cutting edge laser technology is required. We present the latest laser developments and concepts for ultrastable and versatile electron gun lasers, seed lasers and high-power laser-based THz sources taking place at the Paul Scherrer Institute and at other Free Electron Laser facilities. Such developments are of fundamental interest for next generation FEL pump-probe experiments requiring a temporal resolution beyond state of the art.  
slides icon Slides TUOCI1 [5.159 MB]  
 
TUOC3 High QE, Low Emittance, Green Sensitive FEL Photocathodes Using K2CsSb 179
 
  • H.A. Padmore, D. Dowell, J. Feng, T. Vecchione, W. Wan
    LBNL, Berkeley, California, USA
  • I. Ben-Zvi
    Stony Brook University, Stony Brook, USA
  • T. Rao, J. Smedley
    BNL, Upton, Long Island, New York, USA
  
  Funding: Work was supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231, KC0407-ALSJNT-I0013, and DE-SC0005713.
We describe the development of photocathodes based on Potassium-Cesium-Antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light and low transverse emittance. We have demonstrated QE of 7% at 532 nm, a normalized transverse emittance of 0.36 μm at 543 nm and 3 MV/m field gradient[1]. We have also shown that the material can be relatively robust to residual water contamination and we have extracted current densities of 1 mA/mm2 with very long lifetime. We believe that this work is an important step forward in FEL development where high repetition rate is required.
[1] Applied Physics Letters (submitted) 		 
slides icon Slides TUOC3 [4.825 MB]  
 
TUOC4 Design and First Experience with the FERMI Seed Laser 183
 
  • M.B. Danailov, P. Cinquegrana, A.A. Demidovich, R. Ivanov, I. Nikolov, P. Sigalotti
    ELETTRA, Basovizza, Italy
  
  Fermi@Elettra is the first fully seeding-based FEL. Laser operation was first demonstrated in December 2010 and later consistently studied during the runs in 2011. It is known that seeded operation puts heavy demands on the seed laser performance. This paper describes the design of the FERMI seed laser system, including the main laser as well as the most important subsystems and the issues that were solved to easily reach seeded operation. The main requirements to the seed were set by the use of High Gain Harmonic Generation FEL scheme and can be found in details in the FERMI CDR. Here we only recall that the seed needs to be broadly tunable in UV (down to 200 nm) with a peak power above 100 MW all over the tunability range. Obviously, such a tunability imposed the use of a parametric amplifier. For the first seeding comissioning, a fixed wavelength scheme was used, allowing much higher peak power. Here we present both solutions, showing the obtained performance and the limitations. The synchronization of the laser to the timing signals was of crucial importance for the successful seeded operation so the last part of the paper to the laser synchronization setup developed for FERMI.  
slides icon Slides TUOC4 [1.360 MB]  
 
WEPA01 Commissioning of a Photoinjector in HLS 331
 
  • Z.G. He, Q.K. Jia, B.G. Sun, X.H. Wang
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  
  A BNL type photoinjector was installed in HLS (Hefei Light Source) and commissioning work was carrying out in last months. The dark current was measured when the high power testing of the gun was processed. The quantum efficiency (QE) of the photocathode was measured and studied, the main parameters of beam quality such as electric charge, transverse emittance and energy were measured and presented in this paper.  
 
WEPA02 Thermal Acoustic Sensor for High Pulse Energy X-ray FEL Beams 334
 
  • T.J. Smith, J.C. Frisch, E.M. Kraft, J. Loos
    SLAC, Menlo Park, California, USA
  • G.S. Bentsen
    Rochester University, Rochester, New York, USA
  
  Funding: Work supported by Department of Energy Contract DE AC03 76SF00515
The pulse energy density of X-ray FELs will saturate or destroy conventional X-ray diagnostics, and the use of large beam attenuation will result in a beam that is dominated by harmonics. We present results at the LCLS from using a pulse energy detector based on the thermal acoustic effect. In this type of detector an X-ray resistant material (Boron Carbide for this system) intercepts the beam. The pulse heating of this material produces an acoustic pulse that can be detected with high frequency microphones to produce a signal that is linear in the absorbed energy. 		 
 
WEPA04 Design Study for a Hard X-ray Generation by Using High Harmonic Generation Free Electron Laser 337
 
  • E.-S. Kim, J.G. Hwang, H.J. Kim
    Kyungpook National University, Daegu, Republic of Korea
  
  A high harmonic-generation (HHG) FEL scheme was investigated to produce a hard X-ray light of amplified, longitudinally coherent and short wavelength. For more realistic study, S2E simulation in an accelerator with a beam energy of 6.4 GeV was performed. For the intense output of HHG FEL, we optimized a system that consists of 2 modulators, 2 chicanes and 1 radiator. We show the results on steady-state and time-dependent simulations which can produce a wavelength of 0.1 nm and output power of 4 GW in a HHG system of 70 m long.  
 
WEPA06 Experimental Studies with Spatial Gaussian-cut Laser for the LCLS Photocathode Gun 341
 
  • F. Zhou, A. Brachmann, P. Emma, A. Gilevich, Z. Huang
    SLAC, Menlo Park, California, USA
  
  Funding: U.S. Department of Energy under contract DE-AC02-76SF00515
To further enhance the LCLS injector performances or simplify its operating conditions, we are evaluating the various parameters including the photocathode drive laser. Simulations show that both the projected and time-sliced emittances with spatial Gaussian profiles having reasonable tail-cutoff are better than those with uniform one. The simulated results are also supported by theoretical analyses. In the LCLS, the spatial uniform or quasi-Gaussian laser profiles are conveniently obtained by adjusting the optics of telescope upstream of an iris, used to define laser size on the cathode. Preliminary beam studies at the LCLS show that both the projected and time-sliced emittances with spatial quasi-Gaussian laser are almost as good as, although not better than, those with uniform one, and also laser transmission through the iris with the quasi-Gaussian is twice that with uniform one, which is to ease copper cathode operations and thus improve the LCLS operation efficiency. More beam studies are planned in the coming summer to measure FEL performances with the quasi-Gaussian in comparison with the uniform one. All simulations and measurements are presented. 		 
 
WEPA11 Longitudinal Stability of ERL with Two Accelerating RF Structures 345
 
  • Ya.V. Getmanov, O.A. Shevchenko
    BINP SB RAS, Novosibirsk, Russia
  • N. Vinokurov
    NSU, Novosibirsk, Russia
  
  Modern ERL projects use superconductive accelerating RF structures. Their RF quality is typically very high. Therefore, the RF voltage induced by electron beam is also high. In ERL the RF voltage induced by the accelerating beam is almost cancelled by the RF voltage induced by the decelerating beam. But, a small variation of the RF voltage may cause the deviations of the accelerating phases. These deviations then may cause further voltage variation. Thus the system may be unstable. The stability conditions for ERL with one accelerating structure are well known [1, 2]. The ERL with split RF structure was discussed recently [3, 4]. The stability conditions for such ERLs are discussed in this paper.
[1] L. Merminga et al., Annu. Rev. Nucl. Part. Sci. 53(2003) 387.
[2] N.A. Vinokurov et al., Proc. SPIE 2988 (1997) 221.
[3] D. Douglas, ICFA BD-Nl 26 (2001)40.
[4] N.A. Vinokurov et al., Proc. IPAC’10. 		 
 
WEPA12 The Driving Laser for FEL-THz 349
 
  • Y. Chen, M. Li, H.B. Wang, D. Wu, X. Yang
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  
  A solid-state driving laser system have been developed to meet the requirements of the FEL-THz research. The design specifications, configuration and diode-pumped amplifier of the drive-laser system are also described. The laser system can generate continuous or 10μs-20μs pulses light with wavelength 1064 nm, 532nm, 266nm at a repetition rate 54.167MHz. The average power of the driving laser system is more than 25W, 8W, 1W at wavelength 1064nm, 532nm, 266nm respectively. The cathode material is GaAs. The second harmonic is used, of which average power is 8.55W, pulse width is about 12ps, power stability is 0.72% and pointing stability is 46urad.  
 
WEPA14 Effect of a Quasiperiodic Undulator on FEL Radiation 352
 
  • F. Briquez, C. Benabderrahmane, M.-E. Couprie, C. Evain, M. Labat
    SOLEIL, Gif-sur-Yvette, France
  
  The operation of conventional undulators results from an interference scheme in order to generate radiation of a fundamental wavelength and its harmonics. Whereas these harmonics are in most of the cases useful to reach higher energies, it is profitable in specific configurations to shift or reduce them, for instance to limit power on optics or to distinguish between one or two photon process in user experiments. This can be performed by so-called quasi-periodic undulators in which the periodicity of the magnetic field is destructed. In this case, the field amplitude is reduced on a few positions among the axis, inducing a destruction of the interference scheme. Such undulators are commonly used to generate spontaneous emission in synchrotron radiation facilities but could also be installed in Free Electron Lasers. The emitted radiation of the quasi-periodic undulator is compared with the usual configuration one, in the case of LUNEX5. Simulations using GENESIS code are described and results are discussed.  
 
WEPA15 S-band High Gradient Linac for a Compact XFEL 356
 
  • F. Wang
    SLAC, Menlo Park, California, USA
  
  With the successful operation of the first hard X-ray FEl, LCLS, other XFEL facilities are being developed worldwide. Due to the limited site size, many proposed XFELs are based on C-band technology. Switching from S-band to C-band enables a higher acceleration gradient (>35 MV/m) that is nearly double that of the SLAC S-band Linac. Based on the high gradient research, it found that the actually operational gradient is scaled as 1/6 power of the required rf pulse length at constant rf breakdown rate. Therefore, it is possible to have a S-band linac at higher gradient (>35MV/m) operated at very short rf pulse length, such like the single/two bunch operating XFEL.  
 
WEPA16 Quasi-cw Normal Conducting Linac for Soft XFEL 359
 
  • F. Wang, C. Adolphsen
    SLAC, Menlo Park, California, USA
  
  The CW operating soft XFELs have been proposed worldwide to serve large user community simultaneous. In principle, the superconducting linac technology is the only solution to realize such a cw light source. However, large amount of R&D efforts are still needed to build such a linac, which could delay such facility for a significant long period. Therefore, it will be very important to explore the other technology based such XFEL, like the normal conducting based quasi-cw (10s kHz) linac. With the initial study, it turns out that such a quasi-cw linac could be built with L-band (1.3 GHz) or X-band (11.4 GHz) technology. And the L-band devices for such a linac have been developed in the frame work of ILC.  
 
WEPA17 Technical Developments for Injecting External Laser to a Storage Ring FEL in CW and Q-switched Operation 362
 
  • H. Zen
    UVSOR, Okazaki, Japan
  • M. Adachi, M. Katoh
    Sokendai - Okazaki, Okazaki, Aichi, Japan
  • S. Bielawski, C. Szwaj
    PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
  • M. Hosaka
    Nagoya University, Nagoya, Japan
  
  For controlling the dynamics of a storage ring FEL, we propose to inject the FEL oscillator with an external laser [1]. Another purpose is generation of long sustain and intense coherent synchrotron radiation with combining Q-switched and injected FEL [2]. In this presentation, we will report on technical developments for injecting the external laser to FEL oscillator, which works both in CW and Q-switched operation. Optical system for injecting external laser and RF modulation system for Q-switching are newly developed. Practical problems and way to overcome them will be discussed.
[1] C. Szwaj et al., FEL2011, TUPB05, in this conference.
[2] M. Hosaka et al., FEL2011, WEOC4, in this conference. 		 
 
WEPA18 Chirped Pulse Generation by CHG-FEL 366
 
  • H. Zen, T. Tanikawa
    UVSOR, Okazaki, Japan
  • M. Adachi, M. Katoh
    Sokendai - Okazaki, Okazaki, Aichi, Japan
  • M. Hosaka, N. Yamamoto
    Nagoya University, Nagoya, Japan
  
  Funding: Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists (B), 23760067 (Japan)
Coherent Harmonic Generation Free Electron Laser (CHG-FEL)* is one of the promising ways to generate coherent, femtosecond and short-wavelength optical pulses from electron bunches circulating in an electron storage ring. However, the CHG pulse energy becomes smaller as the shorter pulse of laser is used for driving CHG-FEL because the number of electrons which contribute to the CHG production is limited by the pulse duration of driving laser. We proposed “chirped pulse generation and compression of CHG-FEL” to overcome such trade-off relationship, and got a small budget for proof-of-principle experiments in DUV region. In the experiment, chirped DUV pulses will be generated by CHG-FEL driving with chirped laser, and the DUV pulses will be compressed by a pulse compressor. The pulse duration of CHG-FEL before and after the compressor will be measured by a crosscorrelator. The principle, strategy, present status, and future prospects will be presented in the conference.
*R. Coisson and F De Martini, Physics of Quantum Electronics (Addison−Wesley, 1982) vol. 9. chap. 42. 		 
 
WEPA19 Report on the Redesign of the Fibre Link Stabilisation Units at FLASH 370
 
  • M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, H. Schlarb, B. Schmidt, S. Schulz
    DESY, Hamburg, Germany
  • M. Kuntzsch
    HZDR, Dresden, Germany
  
  Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285)
Recently, the fibre link stabilisation unit of the optical synchronisation system at FLASH has been subject to several design changes involving some major issues. Enhancements of the optical design have led to improvements in the efficiency of the free space optics and a new optical delay line allows for a more than two times longer adjustment range. The amplitude noise, encountered previously at the remote station of the links, was drastically decreased by a new beam splitting configuration. In future, this new link design will not only be used for the planned additional fibre links at FLASH, but it will also replace the already installed ones. In this paper we report on the changes of opto-mechanical design and we present first results from the recently commissioned links. 		 
 
WEPA20 Designing a Pulse-resolved Photon Diagnostic System for Shanghai SXFEL 374
 
  • Y.Q. Wu, J.H. Chen, J.N. Liu, R.Z. Tai, D. Wang, R. Wang, C.F. Xue, G.F. Zhao
    SINAP, Shanghai, People's Republic of China
  
  It is presented the design of photon diagnostic system for SSRF-XFEL, the X-ray Free Electron Laser facility in Shanghai Synchrotron Radiation Facility. The system mainly includes a diagnostic beamline with two branches and some diagnostic devices. In the direct passing branch, the intensity distribution of the spot is measured. A set of multi-slit plates are applied for measuring the spatial coherence of a single FEL pulse; In the deflecting branch, a high-resolution VLS-PGM type monochromator, with a simple manual adjusting system, is set up for detecting spectrum of single FEL pulse. The measuring range of wavelength is 45nm-3nm. A fast responding EUV CCD ensures a high pulse resolution to 100Hz.  
 
WEPA21 Research of Emittance Compensation of CAEP CW DC-Gun Photoinjector 377
 
  • P. Li, M. Li, D. Wu, Z. Xu, X. Yang
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  
  Emittance growth is very import for photo-cathode injector due to space charge effect. The emittance compensation technology will be used on the 350 kV photo-cathode DC gun for the CAEP CW FEL, where the energy of electron beam is extremely low and Emittance growth is great severity. In this paper, the space charge force and its effect on electron beam transverse emittance is discussed, the principle of emittance compensation in phase space is analyzed. And a solenoid for emittance compensation is designed. Its beam dynamics has been studied by the PARMELA code. Simulation results indicate that the normalized transverse RMS emittance for electron beam of 80 pC is 1.267 mm•mrad with σr=1.5 mm, σz=4.25 pS.  
 
WEPA22 Development of Insertion Devices Measurement System at IHEP 381
 
  • W. Chen, X. Feng, H.H. Lu, C. Shi, Y. Yang, J.C. Zhang
    IHEP, Beijing, People's Republic of China
  
  In the cooperation between IHEP and EXFEL, prototype undulator U48 for EXFEL is developed by IHEP. In order to meet, maintain and verify the ID’s magnetic performance, a magnetic measurement system has been developed. The development status of the system at IHEP is described in this paper. A 6.5 m long measurement bench with hall probe and small coil is used to measure the vertical and horizontal components of the Insertion Device magnetic field. The measurement system includes a precise granite bench to position and move the magnetic sensors, motion control part and data acquisition part. The characteristics and performances of the magnetic measurement system are presented.  
 
WEPA23 DEVELOPMENT OF AN ITC-RF GUN FOR COMPACT THz FEL 385
 
  • W. Bai, Y. Chen, M. Li, L.J. Shan, X.M. Shen, H.B. Wang
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  
  An independent tunable cells thermionic rf gun (ITC-RF Gun) used for compact Tera-hertz (THz) free electron laser(FEL) is developed at Institute of Applied Electronics, China Academy of Engineering Physics (CAEP). This RF-gun consists of a single cell and a 3-cells accelerating cavity which are excited independently, so the amplitude and phase of the two parts can be adjusted easily. The paper introduces some results of the simulation, cold test and preliminary hot test. The test results agree well with the theoretical design.  
 
WEPA24 Error Analysis for Hybrid Undulators 387
 
  • D. Arbelaez, A. Madur, S. Marks, S. Prestemon, D. Schlueter
    LBNL, Berkeley, California, USA
  • H.-D. Nuhn
    SLAC, Menlo Park, California, USA
  
  Funding: This work was supported by the Director, Office of Science, of the US Department of Energy under Contract No. DE-AC02-05CH11231.
An analysis is performed on various possible errors that may occur throughout a hybrid undulator. Of particular significance is the scaling of the various errors with variations in the gap of the device. Tuning strategies are considered for the mitigation of these errors for the entire range of usable gap. Sorting strategies for the reduction of the initial errors in the undulator are also considered. Specifically, the effectiveness of the sorting algorithm is evaluated with respect to the number of permanent magnet blocks used per pole as well as the size and distribution of the block population. The results of this analysis are applied to the LCLS-II undulators to determine the required machining and positioning tolerances and viable tuning strategies in order to meet the design requirements. 		 
 
WEPB02 Study of Highly Isochronous Beamlines for FEL Seeding 391
 
  • C. Sun, H. Nishimura, G. Penn, M.W. Reinsch, D. Robin, F. Sannibale, C. Steier, W. Wan
    LBNL, Berkeley, California, USA
  
  Recently seeding schemes, such as ECHO for short (nm) wavelength FELs, have been proposed. These schemes require that the nm level longitudinal bunch structure be preserved over distance of several meters. This poses a challenge for the beamline design. In this paper we present our studies of several solutions for beamlines that are nearly isochronous.  
 
WEPB03 LCLS-II Undulator Tolerance Analysis 394
 
  • H.-D. Nuhn, J. Wu
    SLAC, Menlo Park, California, USA
  • S. Marks
    LBNL, Berkeley, California, USA
  
  Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
The SLAC National Accelerator Laboratory is constructing the new FEL user facility LCLS-II, as a major upgrade to the Linear Coherent Light Source (LCLS). The upgrade will include two new Free Electron Lasers, to generate soft (SXR) and hard X-ray (HXR) SASE FEL radiation, based on planar, variable gap hybrid undulators with two different undulator periods (SXR 55 mm, HXR 32 mm). An systematic FEL tolerance analysis for the undulator lines, including tuning, alignment, yaw deformation, and phase correction tolerances has been performed. The methods and results are presented in this work. 		 
 
WEPB04 Position Stability Monitoring of the LCLS Undulator Quadrupoles 398
 
  • H.-D. Nuhn, G.L. Gassner, F. Peters
    SLAC, Menlo Park, California, USA
  
  Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
In the era of SASE FELs, the demand for position stability of undulator components scales down to the range of sub-micrometers per day. Simultaneously, the undulator length increases significantly, in order to reach X-ray wavelengths. To minimize the impact of the outside environment, the LCLS undulator is placed underground, but reliable data about ground motion inside such a tunnel were not available in the required stability range. Therefore, a new position monitor system has been developed and installed for the LCLS undulator. That system is capable to measure X-, Y- and Roll positions of each of the 33 undulator quadrupoles, with respect to stretched wires. Instrument resolution is about 20 nm and instrument drift is negligible small. Position data of individual quadrupoles can be correlated along the entire undulator, which has a length of 132 m. The system is under continuous operation since 2009. The report describes long term experience with the running system and the observed position stability of the undulator quadrupoles. 		 
 
WEPB05 Experiments on Femtosecond Stabilization of Fiber Link for Shanghai Soft-XFEL 402
 
  • X.P. Ma
    IHEP, Beijing, People's Republic of China
  • B. Liu
    SINAP, Shanghai, People's Republic of China
  
  The Shanghai Soft X-ray Free Electron Laser (SXFEL) facility will be constructed in the Shanghai Synchrotron Radiation Facility (SSRF) campus. SXFEL will operate in the HGHG and/or EEHG mode and require a femtosecond timing distribution system as well as the synchronization between femtosecond pulsed lasers, femtosecond pulsed X-rays, CW microwave signals and electron bunches with 10 fs precision. The pulsed fiber laser based femtosecond T&S system which has been proposed by the MIT/DESY team is adopted. In this paper the status of the femtosecond T&S system for SXFEL is introduced. Some initial progress of the phase stabilization by electronics control when laser pulses transport though long optical fibers is presented.  
 
WEPB14 Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflector 405
 
  • C. Behrens
    DESY, Hamburg, Germany
  • Y.T. Ding, P. Emma, J.C. Frisch, Z. Huang, P. Krejcik, H. Loos, M.-H. Wang
    SLAC, Menlo Park, California, USA
  
  The measurement of ultra-short electron bunches on the femtosecond time scale constitutes a very challenging problem. In X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of sub-ten femtosecond X-ray pulses is possible, and some efforts have been put into both ultra-short electron and X-ray beam diagnostics. Here we propose a single-shot method using a transverse deflector (X-band) after the undulator to reconstruct both the electron bunch and X-ray temporal profiles. Simulation studies show that about 1 fs (rms) time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and pulse lengths. The jitter, resolution and other related issues will be discussed.  
 
WEPB15 Reversible Electron Beam Heater for Suppression of Microbunching Instabilities Based on Transverse Deflecting Cavities 409
 
  • C. Behrens
    DESY, Hamburg, Germany
  • Z. Huang, D. Xiang
    SLAC, Menlo Park, California, USA
  
  The presence of the microbunching instability due to the compression of high-brightness electron beams at existing and future X-ray free-electron lasers (FEL) results in restrictions on the attainable lasing performance and renders diagnostics like beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e. heating the beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of seeded FELs. In this paper, we present a reversible electron beam heating system based on two transverse deflecting cavities (TCAV) in front and behind a bunch compressor chicane. The additional energy spread will be introduced in the first TCAV, which suppresses the microbunching instability, and then will be eliminated in the second TCAV. We show the feasibility of the suppression of microbunching instabilities based on calculations and simulations, and set limits to the acceptable jitter tolerances.  
 
WEPB16 Study for Evaluation of Undulator Magnetic Field Using Vibrating Wire Method 413
 
  • Y. Tanaka
    Tohoku University, School of Science, Sendai, Japan
  • H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  
  A test accelerator for a terahertz source project (t-ACTS) has been progressed at the Electron Light Science Centre, Tohoku University, in which a generation of intense coherent terahertz radiation from the very short electron bunch will be demonstrated. A narrow-band coherent terahertz radiation using an undulator has been considered to be implemented. We have constructed a planer undulator that is basically a Halbach type composed of permanent magnet blocks. The period length of the undulator and the number of periods are 100 mm and 25, respectively. The vibrating wire method is studied to measure the periodic magnetic field of the undulator. A thin copper-beryllium wire is placed on beam axis in the undulator, and an AC current flow is applied in the wire. By measuring amplitudes and phases of standing waves excited on the wire by the Lorentz force between AC current and magnetic field, we can reconstruct the magnetic field distribution along the wire. We discuss relations between reproducibility of the undulator field and the mode harmonics number used for the reconstruction. The results of preliminary measurement using the vibrating wire will be shown in this conference.  
 
WEPB17 Evaluation of Lasing Range with a 1.8 m Undulator in KU-FEL 417
 
  • K. Ishida, M. A. Bakr, Y.W. Choi, H. Imon, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen
    Kyoto University, Institute for Advanced Energy, Kyoto, Japan
  
  In KU-FEL (Kyoto University FEL) 12-14 μm FEL has been available by using a 40 MeV S-bend linac and 1.6 m undulator. We are going to install 1.8 m undulator which was used in JAEA to extend the lasing range of KU-FEL. Numerical evaluation of the lasing range has been carried out by using GENESIS1.3. However, this work used an ideal undulator field data which was measured by JAEA in several years before. Therefore we re-measured the undulator field for different gaps. Then we evaluated the FEL gain and possible lasing range with 1.8 m undulator using measured undulator field. The undulator field measurement, FEL gain calculations and evaluation of lasing range in KU-FEL will be presented in the conference.  
 
WEPB18 Development of the First U48 Undulator Prototype for the European X-ray Free Electron Laser 420
 
  • H.H. Lu, W. Chen, X. Feng, X.M. Jiang, C. Shi, S.C. Sun, M.T. Wang, Z.X. Wang, Y.F. Yang
    IHEP, Beijing, People's Republic of China
  • Y. Li, J. Pflüger
    European XFEL GmbH, Hamburg, Germany
  
  Funding: MOST973 Program
The European XFEL will be a user facility consisting of three beamlines named SASE1/2/3 at the first stage. The first undulator prototype U48 for the European XFEL SASE2 beamline has been developed and tested by IHEP, China. Its magnetic design and specifications are briefly given. Development of U48, including magnetic material, mechanical structure, control system and assembly, are introduced. Magnetic tuning and test results are presented and discussed. 		 
 
WEPB19 Enhancement of Undulator Field in Bulk HTSC Staggered Array Undulator with Hybrid Configuration 424
 
  • R. Kinjo, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, K. Komai, K. Masuda, K. Nagasaki, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen
    Kyoto University, Institute for Advanced Energy, Kyoto, Japan
  
  Funding: This work was supported by the Grant-in-Aid for Scientific Research B and JSPS Fellows by the Ministry of Education, Culture, Sports, Science and Technology of Japan
The purpose of this study is enhancement of the undulator field and it's stability in bulk high temperature superconductor staggered array undulator by introducing hybrid configuration. The authors made the magnetic field calculations with some hybrid configurations consists of bulk HTSCs, ferromagnetic pieces and permanent magnets. We also made prototype measurements. The results shows the hybrid configuration can generates stronger and more uniform magnetic field than bulk-HTSCs-only configuration. In this conference, numerical and experimental results of the hybrid configuration will be presented. 		 
 
WEPB20 The Design Of A Multi-Beam Electron Gun For A Photonic Free-Electron Laser 427
 
  • J.H.H. Lee, K.-J. Boller, T. Denis, P.J.M. van der Slot
    Mesa+, Enschede, The Netherlands
  
  Funding: This research is supported by the Dutch Technology Foundation STW, applied science division of NWO and the Technology Program of the Ministry of Economic Affairs.
The photonic Free-Electron Laser (pFEL) is a novel slow-wave device which relies on a photonic crystal (PhC) to synchronize the Cherenkov electromagnetic radiation generated from the co-propagating electron beams. The advantage of pFEL is in its frequency- and power-scaling properties. The scale invariance of Maxwell’s equations allows the use of the same beam energy to operate at higher frequencies when the PhC is correspondingly scaled. On the other hand, power-scaling is achieved by varying the number of electron beams propagating in parallel through the PhC. To produce a set of parallel beams, we have designed a multi-beam electron gun using flat cathodes, which produces a total current of 1 A at a beam voltage of 14 kV. We will present the design of this gun together with the expected performance. In addition, we have investigated the beam transport system and will discuss the options for guiding the beams through the PhC. 		 
 
WEPB22 An Optical Streaking Method for Measuring Femtosecond Electron Bunches 431
 
  • Y.T. Ding, K.L.F. Bane, Z. Huang
    SLAC, Menlo Park, California, USA
  
  The measurement of the ultra-short electron bunch on the femotosecond time scale constitutes a very challenging problem. In the X-ray free electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of a sub-ten femtoseconds electron beam at low charge operation mode is possible, based on indirect measurements and computer simulations. Direct measurements are not available due to the resolution limit of the present diagnostics. We propose a new method based on the energy modulation of the ultra-short electron bunch by interacting with an optical laser in a short wiggler. Compared with a laser-based transverse deflector, which requires the laser wavelength much longer than the electron bunch length, here we propose a scheme to use a laser with its wavelength shorter than the electron bunch length, where the slope on the laser intensity envelope has been used to help distinguish the different periods. The calibration is simple and it is possible to reconstruct the bunch longitudinal profile from a single shot measurement.  
 
THOAI1 Pushing the Limits of Short Period Permanent Magnet Undulators 435
 
  • J. Bahrdt
    HZB, Berlin, Germany
  
  Short period undulators to be used as FEL radiators permit lower electron energies and, thus, reduce linac and undulator lengths. The first X-ray FEL facility based on in-vacuum undulators goes into operation soon (SPRING-8 XFEL). Other in-vacuum undulator based FELs are under construction (SWISS-FEL) or are planned. The in-vacuum undulators have period lengths between 18mm (SPRING-8-X-FEL) and 15mm (SWISS-FEL). In the future the period length will be pushed further into the sub-cm regime. The technical implications of these devices will be discussed: New materials such as PrFeB-magnets are employed. They show their superior characteristics at cryogenic temperatures. Geometric and magnetic tolerances will be tighter and the construction and shimming concepts have to be revised. New magnetic measurement systems are required as well. Recently, a 9mm period length 20 period prototype undulator has been built in collaboration between Ludwig-Maximilian-University Munich and Helmholtz-Zentrum Berlin. The potential and the challenges of sub-cm undulators will be illustrated based on first results from this prototype.  
slides icon Slides THOAI1 [3.344 MB]  
 
THOAI2
 Development of Superconducting Undulators  
 
  • S. Prestemon, D. Arbelaez, T. Koettig, A. Madur, S. Marks, D. Schlueter
    LBNL, Berkeley, California, USA
  
  Funding: This work was supported by the Director of the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Undulator technology plays a critical role in FEL performance. The desire to provide a specific range of photon wavelengths for science applications constrains the design space of electron beam energy and undulator tuning capabilities. In particular, the coupling between photon wavelength, beam energy, and undulator period and strength indicates that undulator technology is a major cost driver in the design of FEL facilities. Superconducting undulators have the potential to significantly improve upon performance of current state-of-the-art undulator technologies being implemented in the first FEL facilities. Here we review the status of superconducting undulator technology, including developments in the areas of helical, planar, and variable polarizing superconducting undulator concepts at a variety of laboratories around the world. Implications of superconducting undulator performance for FEL applications are described. Finally, the major technological hurdles that remain to be addressed prior to implementation in FEL facilities are outlined, together with a summary of current R&D efforts. 		 
slides icon Slides THOAI2 [3.891 MB]  
 
THOB4 Transverse Coherence and Polarization Measurement of Coherent Femtosecond Pulses from a Seeded FEL 458
 
  • J. Schwenke, N. Čutić, F. Lindau, S. Werin
    MAX-lab, Lund, Sweden
  • E. Mansten
    Lund University, Division of Atomic Physics, Lund, Sweden
  
  We report on measurements of the transverse coherence and polarization of light pulses at 131 nm generated by a seeded free-electron laser. Our setup consists of two undulators. The first undulator is used to energy modulate relativistic electron bunches (375 MeV) with the help of an ultraviolet seed laser pulse at 263 nm. The electron bunches subsequently pass through a dispersive section, where the energy modulation is converted into microbunching, and then enter the radiator undulator. The radiator is an APPLE-II type undulator set to be in resonance for 131 nm radiation. The radiator emits coherent femtosecond pulses up to the 6th harmonic of the seed laser [1]. The state of polarization of the pulses can be tuned from planar to helical polarization by shifting the undulator magnets. The emitted pulses are analyzed with a grating spectrometer. A double slit aperture is positioned in the beam in order to determine the transverse coherence of the light pulses by analyzing the fringe visibility. Furthermore, the generation of circular polarized light is demonstrated. The polarization state of the light pulses is measured with a Rochon prism polarizer.
[1] Cutic et al, Phys. Rev. Spec. Top-AC 14, 030706 (2011) 		 
slides icon Slides THOB4 [1.173 MB]  
 
THOCI1
 Measurement and Control of the Longitudinal Phase Space at High-Gain Free-electron Lasers  
 
  • C. Behrens, C. Gerth
    DESY, Hamburg, Germany
  
  Free-electron lasers provide a high degree of flexibility in terms of pulse intensity and wavelength range. In the case of high-gain FELs with a two-frequency accelerator in front of the bunch compressors, the flexibility is extended with electron bunch shape and length tunability. The final goal is to get control of the FEL photon pulses which might be achieved by controlling the longitudinal phase space (LPS) of the driving electron bunch. This can be achieved by using transverse deflecting structures/cavities (TDS/C) in combination with energy spectrometers which provide a direct measurement method with high resolutions in both energy and time. In this talk, the basic concepts of longitudinal phase space diagnostics, using transverse deflecting structures/cavities in combination with energy spectrometers, will be discussed with examples from FLASH at DESY and LCLS at SLAC. The obtainable resolutions and limitations due to the accelerator optics, induced energy spread by the TDS/C itself, and coherent synchrotron radiation will be shown by simulations and measurements. Finally, an overview of planned LPS diagnostics at other facilities, like the European XFEL, will be presented.  
slides icon Slides THOCI1 [3.849 MB]  
 
THOCI2
 Measurement of Ultrashort Electron and X-ray Beams for X-ray FELs  
 
  • Y.T. Ding
    SLAC, Menlo Park, California, USA
  
  Measurement of ultrashort electron and X-ray pulses is a challenging but important subject for X-ray free electron lasers. After a brief overview of the common temporal diagnostics for X-ray FEL facilities, we discuss new techniques developed recently to push the temporal resolution to the femtosecond level and below. One of them is the longitudinal transformation method that directly maps time to energy by adjusting the accelerator settings [1]. Experiments at LCLS using a high-resolution spectrometer demonstrate that the bunch profile can be measured with a temporal resolution approaching 1 fs rms [2]. Another single-shot method is to use an X-band transverse cavity, not yet installed, after the FEL undulator to reconstruct both the electron and X-ray temporal profiles by measuring electron beam longitudinal phase space. Simulation studies show that about 1 fs rms time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and operating facilities. Other techniques including optical streaking methods will also be discussed.
[1] Z. Huang, K. Bane, Y. Ding and P. Emma, Phys. Rev. ST Accel. Beams, 13, 092801 (2010);
[2] Z. Huang et al, PAC11, THP183. 		 
slides icon Slides THOCI2 [3.321 MB]  
 
FROA3 Sub-100-attosecond Timing Jitter Ultrafast Fiber Lasers for FEL Optical Master Oscillators 648
 
  • J. Kim, K. Jung, C. Kim, H. Kim, T.K. Kim, S. Park, Y. Song, H. Yang
    KAIST, Daejeon, Republic of Korea
  
  Funding: Pohang Accelerator Laboratory and NRF of Korea (2010-0003974)
Future FELs require femtosecond and even sub-femtosecond timing precision over the entire facility. To meet this timing demand, optical techniques based on modulated cw lasers or ultrafast pulsed lasers have been investigated intensively. It has recently been shown that the timing system based on ultrafast fiber lasers and timing-stabilized fiber links enables long-term stable, sub-10-femtosecond level synchronization [*]. In order to achieve sub-femtosecond level synchronization, the optimization of timing jitter in ultrafast fiber lasers is required. In this work, by operating the fiber lasers at close-to-zero intracavity dispersion, we optimize the timing jitter of ultrafast fiber lasers toward sub-femtosecond level for the first time. The measured timing jitter of 80 MHz Er-fiber and Yb-fiber lasers is 100 attosecond and 185 attosecond, respectively, when integrated from 10 kHz to 40 MHz (Nyquist frequency) offset frequency. To our knowledge, this is the lowest high-frequency timing jitter from ultrafast fiber lasers so far. The sub-100-attosecond timing jitter from optical master oscillators is the first step toward attosecond-precision FEL timing systems.
[1] J. Kim et al, "Drift-free femtosecond timing synchronization of remote optical and microwave sources," Nature Photonics 2, 733-736 (2008).