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| THPD05 | Observation of High Harmonic Generation from 6H-SiC Irradiated by MIR-FEL | 555 |
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Silicon Carbide (SiC) is attractive as the next generation power devices, heat resistance material and so on. In addition, 6H-SiC is investigated as the material for high harmonic generation [1]. For verifying the possibility of high harmonic generation by 6H-SiC irradiated by MIR-FEL, we measured the emission spectrum from 6H-SiC irradiated by MIR-FEL whose center wavelength was 7.8 μm. As the result, we clearly observed the emissions at 963 nm, 861 nm and 775 nm, which correspond to harmonics of 8th, 9th and 10th wavelength respectively. In this meeting, we will present and discuss about the high harmonic generation introduced by MIR-FEL.
[1] Hiroaki Sato, Makoto Abe, Ichiro Shoji, Jun Suda, and Takashi Kondo, J. Opt. Soc. Am. B, Vol. 26, No. 10(2009), 1892-1896 |
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| THPD06 | Bio-luminescence/Scattering and its Dynamics in Enchytraeus Japonensis by Irradiation of Free Electron Laser | 559 |
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We report on the experiment results of bioluminescence from Enchytraeus Japonensis by free electron laser (FEL) irradiation, and discuss about migration of bioluminescence on Enchytraeus Japonensis body. In this experiment, we observed behaviors or dynamics of FEL irradiated Enchytraeus japonensis for a few seconds by change coupled device (CCD) camera. One shot of FEL (wavelength: 2940 nm, pulse width: 200 fsec) which resonated with hydroxyl stretching vibration was irradiated to center of the Enchytraeus Japonensis head. After FEL irradiation, head was amputated, and orange bioluminescence was generated from around the laser irradiation area. Immediately after laser amputation of the head (0.1 seconds later), yellow bioluminescence was observed, and intensity of this luminescence was increasing after 0.3 seconds. This bioluminescence migrated into living cells from the head toward the trunk of the body. 10.0 seconds later, newly blue bioluminescence was generated from Enchytraeus Japonensis head. Wavelengths of these bioluminescence were as below, orange was from 600 nm to 650 nm, yellow was from 500 nm to 600 nm, blue was from 400 nm to 450 nm.
"John. E. Wampler and B. G. M. Jamieson, Comp. Biochem. Physiol., Vol. 66B, p. 43 (1980)","R. Tadokoro, M. Sugio, J. Kutsuna, S. Tochinai and Y. Takahashi, Current Biology, Vol. 16, p. 1012 (2006)" |
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| THPD08 | Pit Formation on Dental Hard Tissues Using Two Different Free Electron Laser Sources, LEBRA-FEL and KU-FEL | 563 |
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Funding: This study was supported by a Grant for Supporting Project for Strategic Research by MEXT, Japan (S0801032) and by the ZE Research Program, IIAE, Kyoto University (A-17). According to the increased usage and demands of lasers in dentistry, research and development of the more reliable and functional lasers are needed. In the case of caries treatment, the lasers generated by commercial apparatus are not enough to dig the dental enamel and/or dentin tissues. Our previous studies showed that FEL generated at LEBRA has a potential to form pits on these dental hard tissues easily, and that the effective wavelength depends on the tissue types sensitively at about 3000 nm. To progress the FEL study on dental tissues, it is needed to spread the range of wavelengths more than that at LEBRA, between 2000 and 6000 nm. The newly established KU-FEL is able to generate the FEL of wavelength between 5000 and 13000 nm. Combining the two FEL sources, we found a new result that the dental hard tissues were easily dug by 7800 nm KU-FEL, which wavelength has not been presumed before. In the combination of LEBRA-FEL and KU-FEL, the wider knowledge on the FEL action on dental tissues will be achieved. |
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| THPD11 | The JLAB UV Undulator | 567 |
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Recently the JLAB FEL has demonstrated 150 W at 400 nm and 200 W at 700 nm* using a 33mm period undulator designed and built by STI Optronics. This paper describes the undulator design and performance. Two key requirements were low phase error, zero steering and offset end fields and small rms trajectory errors. We will describe a new genetic algorithm that allowed phase error minimization to 1.8 degrees while exceeding specifications. The mechanical design, control system and EPICS interface will also be summarized.
*S. V. Benson et al., "Beam Line Commissioning of a UV/VUV FEL at Jefferson Lab, presented at the 2011 FEL Conference, Shanghai, China, Aug. 2011 |
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| THPD12 | Design and Performance of the NLCTA-Echo 7 Undulators | 571 |
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The Echo-enabled harmonic generation (EEHG) FEL at SLAC NLCTA has shown coherent radiation in the seventh harmonic (227 nm) of the second seed laser*. Earlier experiments demonstrated 3rd and 4th EEHG**. We describe design and performance of the 33mm and 55mm period undulators built by STI Optronics and used for these experiments. Magnetic design of the 33mm period undulator was based on an earlier curved pole, two-plane focusing undulator for the UCLA seeded THz FEL***. This design used an evolutionary optimizer and custom pre/post processing FEA codes to maximize field strength with minimum magnetic material while achieving specified two-plane focusing. The 55mm undulator was identical to the JLAB IR FEL and APS UA U55 designs. A challenge for both these devices was achieving tight normal and skew trajectory excursions (<500 G-cm2), zero trajectory offset and < 10 G-cm steering without end correctors over a 5mm diameter horizontal and vertical region with a 4 month delivery requirement. We will also describe a new tuning method based on operations research linear programming that was used to help meet these goals over a 2X larger region while maintaining 1 deg phase errors.
*D. Xiang et al, Phys. Rev. Let. 108 024802 (2012) **D. Xiang et al, Phys. Rev. Let. 105 114801 (2010) *** S. Gottschalk et al, "UCLA Seeded THz FEL Undulator-Buncher Design",this conference |
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| THPD13 | Design and Performance of the Wedged Pole Hybrid Undulator for the Fritz-Haber-Institut IR FEL | 575 |
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An IR and THz FEL with a design wavelength range from 4 to 500 microns has been commissioned at the Fritz-Haber-Institut (FHI) in Berlin, Germany. Lasing at 28 MeV and a wavelength of 18 micron was achieved in Feb 2012*. We describe the performance of the undulator built and installed at FHI by STI Optronics for use in the mid-IR range (< 50 micron) and 15-50 MeV beam energy. The undulator was a high field strength wedged pole hybrid (WPH) with 40mm period, 2.0m long, minimum gap 16.5mm. A new improvement was including radiation resistance in the magnetic design. We will discuss the measured magnetic and mechanical performance; central and zero steering/offset end field magnetic designs; key features of the mechanical design and gap adjustment system; new genetic shimming algorithms and local/EPICS control systems.
*W.Schöllkopf et al., "First Lasing of the IR FEL at the Fritz-Haber-Institut Berlin", this conference |
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| THPD18 | Tuning and Testing of the Prototype Undulator for the European XFEL | 579 |
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| The European X-ray Free Electron Laser (EXFEL) uses large undulator systems with a total length of approximately 500 meters. The main part of the system is 91 5m long undulator segments. All segments are gap variable planar undulators. In the next 2 to 3 years all these 91 undulators will be manufactured and subsequently measured and tuned in order to meet the EXFEL field specifications. In order to match the tight schedule and to reach the high qualification, fast and reliable measurement methods and fine tuning algorithms must be established and be tested before the mass production starts. In this paper we report the tuning results of the undulator prototype for the EXFEL. It is shown that good quality is achieved which satisfies all specification asked by the European XFEL. It is also shown that the measurement and tuning procedures work well, fast and are straightforward to apply. | ||
| THPD19 | Technical Overview of SwissFEL Undulator Line | 583 |
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| Starting after Linac 3 at z ~ 430 m (z = 0 being the gun photocathode position), the so-called Aramis Hard-X ray undulator section extends over 170 m, from the energy collimator to the electron beam dump. Electrons enter the undulator section with a maximum energy of 5.8 GeV, a slice emittance below 0.43 μm and a peak current of 3 kA with 200 pC of charge. A prototype of the in-vacuum undulator (U15) is currently under assembly. Most of the other beamline components have been designed and for some of them prototypes are already ordered (quadrupoles, beam position monitors, phase shifters, alignment quadrupoles; mechanical supports; safety components). The paper will describe how constraints like temperature drifts, stray magnetic field, wakefields, beam losses, costs are taken into account for the design of components and building (undulators are however described in details in a companion paper). | ||
| THPD24 | Origin of Shift Dependent Multipoles in Apple-II Undulators | 587 |
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| APPLE-II insertion devices are very flexible devices for production of variably polarized photons. This devices inherently suffer from shift dependent integrated field multipoles that can reach values which can seriously deteriorate quality of the electron beam. Since there is no really effective shimming method for correction of this errors, it is important to understand where they originate. Paper presents a study of integrated field multipoles shift dependency based on deformation of magnetic array due to magnetic forces. We have modeled separately deformations of each magnet keeper in the magnetic array. Model calculations have shown that most of integrated field multipole dependency on the shift is due to mechanical deformation in combination with magnetic effects. | ||
| THPD25 | Feasibility of Diagnostics Undulator Studies at ASTA | 591 |
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Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The high-power electron beams for the Advanced Superconducting Test Accelerator (ASTA) facility involve up to 3000 micropulses with up to 3.2 nC per micropulse in a 1-ms macropulse. With beam energies projected from 45 to 800 MeV the need for non-intercepting diagnostics for beam size, position, energy, and bunch length is clear. Besides the rf BPMs, optical synchrotron radiation (OSR), and optical diffraction radiation (ODR) techniques already planned, we propose the use of undulator radiation from a dedicated device for diagnostics with a nominal period of 4-5 cm, a tunable field parameter K, and a length of several meters. We propose time resolving the e-beam properties within the macropulse by viewing the undulator radiation with standard gated ICCD's (size and position) and a streak camera coupled to an optical spectrometer (energy, bunch length, and phase). The feasibility of extending such techniques in the visible regime at a beam energy of 125 MeV into the UV and VUV regimes with beam energies of 250 and 500 MeV will be presented. |
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| THPD27 | Status of PAL-XFEL Undulator System | 595 |
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| Pohang Accelerator Laboratory (PAL) is developing 10 GeV, 0.1 nm SASE based FEL for high power, short pulse X-ray coherent photon sources named PAL-XFEL. At the first stage PAL-XFEL needs two undulator lines for photon source. PAL is developing undulator magnetic structure based on EU-XFEL design. The hard X-ray undulator features 7.2 mm min magnetic gap, and 5.0 m magnetic length with maximum effective magnetic field larger than 0.908 T to achieve 0.1nm radiation at 10 GeV electron energy. Soft X-ray undulator system has 8.3 mm undulator gap with 33.4 mm magnetic period. In this report, the status of the undulator project including mechanical design, magnetic design, phase shifter, quadrupole design are summarized. | ||
| THPD28 | Beam Diagnostic Systems for PAL-XFEL | 598 |
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Funding: Korean Ministry of Education, Science and Technology The XFEL project in Pohang Accelerator Laboratory (PAL) requires low beam-emittance (< 1 μm·rad), ultra-short bunch length (25 μm ~80 fs), high peak current(~3.5 kA), high stability of beam energy (< 0.01%), and measurement and steering of beam trajectory within micrometers (< 2 μm). Therefore, beam diagnostics for SASE XFEL should be, focused on attaining femto-second precision in the measurement of temporal beam parameters, and sub-micrometer precision in beam position measurement. Charge measurement and energy measurement are important as well. In this work, technical concepts regarding the diagnostic monitors will be summarized and present status of them will be described. |
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| THPD30 | Fast, Absolute Bunch Length Measurements in a Linac using an Improved RF-phasing Method | 602 |
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Funding: We are grateful to the US Department of Energy under contract number DE-AC02-76SF00515. There is great demand for a fast, accurate method to measure the absolute bunch length of an electron beam in a linac. Many ideas are available, with one of the most attractive based on the transverse RF deflector*. Since this specialized technology can be costly and unavailable, we introduce an alternate method using accelerating RF with the same robust characteristics (fast, accurate, and absolute). This method is based on the 'RF zero-phasing' scheme**, but includes several significant improvements based on experience with the RF deflector method. * R. Akre et al., Proc. of PAC-01, p. 2353. ** D. X. Wang et al., Proc. of PAC-97, p. 2020. |
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| THPD31 | Sub-femtosecond Hard X-Ray Pulse from Very Low Charge Beam at LCLS | 606 |
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| The Linac Coherent Light Source (LCLS) is an x-ray free-electron laser (FEL) at SLAC National Accelerator Laboratory, supporting a wide range of scientific research with an x-ray pulse length varying from a few to several hundred femtoseconds. There is also a large interest in even shorter, single-spike x-ray pulses, which will allow the investigation of matter at the atomic length (Å) and time scale (fs). In this paper, we investigate the FEL performance using 1pC and 3pC electron bunches at LCLS, based on the start-to-end simulations. With an optimization of the machine setup, simulations show that single spike, sub-femtosecond, hard x-ray pulses are achievable at this low charge. | ||
| THPD33 | Generation of Ultra-short Electron Bunches at FLASH | 610 |
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Funding: The work is supported by German Federal Ministry of Education and Research (BMBF) within Joint Project - FSP 301 under the contract number 05K10GU2. In order to produce radiation pulses of a few femtoseconds at FELs like FLASH, different concepts have been proposed. Probably the most robust method is to create an electron bunch, which is in the most extreme case as short as one longitudinal optical mode. For FLASH this translates into a bunch length of a few micrometers only. In order to mitigate space charge effects, the bunch charge needs to be about 20 pC. The technical requirements to achieve this goal are discussed. This includes beam dynamics studies to optimize the injection and compression of small charge electron bunches. A reduced photo injector laser pulse duration helps to relax the RF tolerance which scales linear with the compression factor. A new photo injector laser with sub-picosecond pulse duration in combination with a stretcher is used to optimize the initial bunch length. The commissioning of the new laser system and first experiments are described. Limitations of the presently available electron beam diagnostics at FLASH for short, low charge bunches are analyzed. Improvements of the longitudinal phase space diagnostics and the commissioning of a more sensitive beam arrival time monitor are described. |
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| THPD37 | Beam Dynamic Studies for the Generation of Short SASE Pulses at FLASH | 614 |
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Funding: The project is supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301. Many users at FLASH work on pump-probe experiments, where time resolution is determined by the duration of the SASE pulses. Therefore users have expressed the strong wish for shorter XUV pulses. The shortest possible pulse is a single longitudinal optical mode of the SASE radiation. The most direct way to realize this at FLASH would be to reduce the electron bunch length to only a few μm at the entrance of the undulator section. In the ideal case a bunch charge of 20pC is sufficient for the generation of such short bunches. A shorter bunch duration directly at the photo-cathode helps to overcome technical limitations of the bunch compression due to RF induced non-linearities and collective effects. Beam dynamic studies are being performed to optimize the parameters of the photo injector laser, of the accelerating modules, and of the bunch compression. This includes particle tracking starting from the cathode though the accelerating modules with the ASTRA code and through the dipole chicanes using CSRtrack. A comparison of the beam dynamics simulations with measurements is presented in this contribution. The expected SASE pulses are being simulated with the Genesis code. |
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| THPD38 | Laser Wavelength Tuning by Variable-gap Undulators in SACLA | 618 |
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| Wavelength tunability by variable-gap in-vacuum undulators is one of the features of SACLA. To fully utilize this advantage, it is important to suppress gap-dependent field errors down to the tolerance level, sub-microradian per undulator segment, which assures high SASE amplification gain enabling XFEL power saturation. For this purpose, we introduced a 'feed-forward correction' scheme, which is well-known technique in third-generation light sources. However, in linac-based XFELs, it was not easy to make a sufficiently accurate correction table to cancel out error fields due to shot-by-shot beam orbit and energy fluctuation propagating from the accelerator. By using cross-correlation technique based on the accelerator model, we so far succeeded in suppressing the gap-dependent orbit distortion down to a 10-micron level over the undulator section. Owing to this effort, experimental users at SACLA can quickly change the laser wavelength in a few seconds according to their demands by setting only the undulator K-value. In this conference, we will report the present status of wavelength tuning by the undulator gap in SACLA and problems to be solved towards the perfect control. | ||
| THPD40 | Femtosecond Electron Bunch Measurement using THz Cherenkov Radiation in Dielectric Materials | 622 |
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| A novel method of femtosecond electron bunch measurement has been proposed using THz Cherenkov radiation in dielectric materials. When the ultrashort electron beam moves to the dielectric materials, such as a hollow quartz tube covered by a metal, the electron induced coherent Cherenkov radiation is occurred as a frequency spectrum in THz range with discrete components (higher mode radiations). The intensities of the THz components and the width of the frequency spectrum are determined strictly by the bunch length. In the preliminary experiments, we succeeded to observe the THz Cherenkov radiation from a 200 fs electron bunch using mm-sized dielectric tubes. It was found that the radiation spectra are dependent on the bunch length. The higher mode radiations are appeared by decreasing the electron bunch length. | ||
| THPD41 | A Simple Model for the Generation of Ultra-Short Radiation Pulses | 626 |
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| A method for generating a single broadband radiation pulse from a strongly chirped electron pulse is described. The evolution of the chirped electron pulse in an undulator may generate a pulse of coherent spontaneous radiation of shorter duration than the FEL cooperation length. An analytic expression for the emitted radiation pulse is derived and compared with numerical simulation. | ||
| THPD43 | Progress on a Laser-driven Dielectric Structure for Use as a Short-period Undulator | 630 |
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| A laser-powered dielectric structure, based on theμAccelerator Platform, has been design and offers undulator periods in the micron to millimeter range. This design was shown previously to potentially support a deflection field strength of several GV/m, equivalent to a magnetic undulator with field strength of about 40 T. In this paper, we address a previous problem in the design involving the junction between half periods of the undulator. Because the structure is resonant, flipping from one deflection direction to the opposite one required controlling the phase of the incident laser and reestablishing a new resonance. One solution to this 'phase flipping' problem involves the use of two lasers at different wavelengths to excite adjacent half-periods. This new approach is explored further here along with simulations of the beam trajectory and resulting undulator radiation. We also consider parameter sets that may be possible for these extremely short period undulators. | ||
| THPD45 | Beam Dynamics and Performance of ERL-driven X-ray FEL | 634 |
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In this talk we present a self-consistent concept of ERL generated e-beam to drive an array of X-ray FELs. We use eRHIC multi-pass ERL design to explore all relevant beam dynamics. First, we study effects of incoherent and coherent synchrotron radiation on the e-beam parameters and present the set of parameters providing for the emittance preservation. Second, we present a sing bunch compressing scheme (similar to scheme described in [1]) with large compression ratio, which suppresses emittance growth caused by CSR. Finally, we present simulation result for soft- and hard-X-ray FELs driven by such electron beam. We compare projected performance of such facility with world's existing and proposed FEL facilities.
[1] Merger Designs for ERLs, V.N. Litvinenko, R.Hajima, D. Kayran, Nuclear Instruments and Methods in Physics Research A 557 (2006) 165 |
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| THPD47 | Progress on the Generation of Undulator Radiation in the UV from a Plasma-based Electron Beam | 638 |
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| Recently, at the Laboratoire d'Optique Appliquée, progresses have been made for the development of 5th generation light sources based on plasma-accelerator. Electron beams of tens of picocoulomb at about 200 MeV has been generated at the interaction of a 1 Joule, 30 fs laser focussed on a 3 mm long gas target at an electron density of 5 1018 cm-3. Then, the electron beam was refocused with a quadrupoles triplet inside a 60 cm long undulator composed of 34 periods of 18 mm with a deflection parameter equal to 1. In these conditions synchrotron radiation UV light has been measured. This constitutes a promising first step in the view of realizing FEL based on plasma acceleration in future. | ||
| THPD48 | Numerical Study of an FEL based on LWFA Electrons and a Laser-plasma Wiggler | 642 |
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Recent works* have suggested that laser-wakefield acceleration (LWFA) may be used to produce the electron beam of an FEL. However, when using conventional magnetic wigglers, the requirements on the beam quality are very stringent, and are still challenging with current LWFA beams. An interesting alternative may be to use a laser-plasma wiggler (e.g. a plasma wave or a laser beam). Compared to a conventional one, a laser-plasma wiggler has a field amplitude several orders of magnitude higher - which can place lower constraints on the beam quality. Furthermore, since laser-plasma wigglers also have a typically much shorter period, their total wiggler length is correspondingly shorter, and it may therefore not be necessary to periodically refocus the beam along the wiggler. Taking into account these effects, we evaluate the range of wiggler properties (field, period) that would make the FEL process possible. From this analysis, the counterpropagating laser wiggler** seems to be one of the most promising solutions. We therefore extend the Ming Xie formula*** to a counterpropagating laser wiggler. We use this formula to evaluate the potential use of current state-of-the-art lasers.
* Nakajima, K., Nature phys. 4, 92 (2008) ** Bacci, A. et al., Nucl. Instrum. Methods Phys. Res. A 587, 388 (2008) *** Xie, M., Nucl. Instrum. Methods Phys. Res. A 445, 59 (2000) |
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| THPD50 | Steady State Microbunching for High Brilliance and High Repetition Rate Storage Ring-based Light Sources | 646 |
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| Modern accelerator light sources are based on either linac-FELs or storage rings. The linac-FEL type has high brilliance (microbunched beam) but low repetition rate. The storage ring type has high repetition rate (rapid beam circulation) but low brilliance. We propose to explore the feasibility of a microbunched beam in a storage ring that promises high repetition rate and high brilliance. The steady-state microbunched (SSMB) beam in a storage ring could provide CW sources for THz, EUV, or soft X-rays. We review several recently proposed SSMB concepts as promising directions for high brightness, high repetition rate light sources of the future. | ||
THPD51 |
W-Band Cherenkov Maser Based on a Periodic Surface Field Structure | |
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Funding: Work supported by EPSRC Two-dimensional Bragg structures have been useful in producing distributed feedback in an FEM driven by an oversized annular electron beam [1]. The Bragg structures in this case act as frequency selective mirrors allowing the production of narrow band microwaves [2]. This structure can be observed using a hollow, copper, cylindrical waveguide with a sinusoidal grating machined into the walls where the diameter of the waveguide is much larger than λ. Localised surface fields are excited around the perturbations if the structure is radiated by an external electron beam [3]. The resultant eigenfield can be described as a superposition of a near cut-off volume field which synchronises the localised surface partial fields. A relativistic electron beam travelling close to the structure interacts with the spatial harmonics of the surface field propagating with υp< c. In this paper we demonstrate a novel high Q cavity operating at W band (75-110GHz), where there is coupling between a near cut-off TM0,6 volume field and an evanescent HE1,20 surface field, produced within the structure. Results of the numerical modelling of this device using the PIC code MAGIC will be presented. 1. N.S. Ginzburg, N. Peskov, et al, J Appl Phys, 92, pp. 1619-1629, 2002 2. I.V. Konoplev, et al, Appl Phys Lett, 92, 211501 2008 3. I.V. Konoplev, A. Maclachlan. et al, Phys Rev A, 84, 013826 2011 |
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| THPD54 | Dynamics of a Multi-beam Photonic Free Electron Laser | 650 |
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| A photonic free-electron laser (pFEL) uses free electrons streaming through a photonic crystal (PhC) to generate tunable coherent radiation. Operation in different spectral regions can be obtained by scaling the lattice period while keeping the electron velocity the same. Increasing both the transverse dimension and the number of distributed electron beams increases the output power and results in a higher quality factor Pf2. Here, we consider a pFEL driven by a set of low energy (~ 10 keV), low perveance (< 0.1 μP) electron beams. A simple and robust PhC structure is used to slow down the phase velocity (match to electron velocity) of a co-propagating electromagnetic wave. The large transverse dimensions of the PhC result in an overmoded system, allowing many transverse eigenmodes of the PhC to interact with the electron beams. Using a particle-in-cell code, we numerically study the dynamics and calculate the small-signal growth rate and output power of the various modes. We show that for an appropriate design of the PhC and selective placement of the electron beams, single-mode operation is possible. We will also present results on the scaling with the number of electron beams. | ||
| THPD56 | Two-color FEL Generation based on Emittance-spoiler Technique | 654 |
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Generation of two-pulse two-color x-ray radiation is attracting much attention within the free-electron laser (FEL) user community. Femtosecond x-ray pulses with variable durations and separation can be simply generated by the emittance-spoiler foil method* at the Linac Coherent Light Source (LCLS). In this paper, we describe three FEL schemes rely on the emittance-spoiler technique for the generation of two intense x-ray pulses with different colors. With a representative realistic set of parameters of LCLS, numerical simulations confirm that two femtosecond x-ray pulses at ten gigawatt level with different wavelengths around 1.8 nm can be generated by these schemes. The central wavelengths of the output pulses can be easily altered by changing strengths of the undulators.
*P. Emma et al., PRL 92, 074801 (2004). |
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| THPD57 | Application of laser-plasma accelerator beams to Free-Electron Lasers | 658 |
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Funding: This work was supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No.DE-AC02-05CH11231. Plasma waves excited by high-intensity, short-pulse lasers are able to generate hundreds of GV/m accelerating fields, enabling extremely compact accelerators for applications such as radiation generation. Laser-plasma accelerators (LPAs) produce ultrashort (femtosecond), 0.1-1 GeV electron bunches with high-peak (kA) currents and low (sub-micron) normalized transverse emittance, with 6D beam brightness comparable to state-of-the-art RF linac-based sources. FEL applications are presently limited by the longitudinal phase space distribution of the LPA beam. Beam phase space manipulation is considered to enable the application of LPA beams to FELs. LPA beam decompression (such that the energy spread over a coherence length is less than the FEL parameter) is examined as a path toward realizing an LPA-driven VUV FEL. The possibility of using a flat beam, with an energy correlation with transverse position, in a transverse gradient undulator is also explored. Laser-based FEL seeding options for improved coherence are considered. |
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| THPD63 | SwissFEL U15 Magnet Assembly: First Experimental Results | 662 |
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| In the framework of the SwissFEL project, an R&D activity concerning in-vacuum undulator technology is ongoing at the Paul Scherrer Institut. The magnetic field configuration of the hard X-ray SwissFEL undulators has been designed on purpose for a single pass machine. Moreover the permanent magnet material (NdFeB) is manufactured following a novel procedure (Dy diffused in the grain boundaries) to improve the coercivity versus remanence. The assembly and tests of a 44 periods hybrid magnetic structure are presented. Procedures for the magnetic field, trajectory and phase optimization are reported versus experimental results. | ||
| THPD64 | SwissFEL U15 Prototype Design and First Results | 666 |
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| The SwissFEL will have in the base line two undulator lines for the hard- and soft x-ray: U15 in-vacuum and U40 / UE40 APPLE II type undulators with 12 and 15 modules of 4m length each. All undulators are equipped with the same frame and gap drive system to profit best from the series production. The frame is built up from two identical bases and two sides made of cast mineral. In this design, the frame transfers its stiffness to the I-beam through a backlash-free wedge based gap drive system. The interfaces to the inner I-beam for the in-vacuum undulator have been rearranged and reduced significantly. Magnets and poles are carried by an extruded Aluminum block-keeper, which allows an automated tuning of the magnet structure. The prototype of the support structure has been built up during spring 2012 and measuring results will be presented. The full prototype shall be ready for the end of 2012. | ||
| THPD65 | High Dynamic Range Beam Imaging with Two Simultaneously Sampling CCDs | 670 |
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| Transverse beam profile measurement with sufficiently high dynamic range (HDR) is a key diagnostic to measure the beam halo, understand its sources and evolution. In this contribution we describe our initial experience with the HDR imaging of the electron beam at the JLab FEL. On contrary to HDR measurements made with wire scanners in counting mode, which provide only two or three 1D projections of transverse beam distribution, imaging allows to measure the distribution itself. That is especially important for non-equilibrium beams in the LINACs. The measurements were made by means of simultaneous imaging with two CCD sensors with different exposure time. Two images are combined then numerically in to one HDR image. The system works as an online tool providing HDR images at 4 Hz. An optically polished YAG:Ce crystal with the thickness of 100 um was used for the measurements. When tested with a laser beam images with the DR of about 10+5 were obtained. With the electron beam the DR was somewhat smaller due to the limitations in the time structure of the tune-up beam macro pulse. | ||
| THPD67 | Probing Transverse coherence with the Heterodyne Speckle Approach: Overview and Details | 674 |
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Spatial Coherence properties of radiation produced by accelerated relativistic electrons are far from being trivial. The correct assesment of coherence of High-Brillance X sources (Synchrotron or FEL) is of crucial importance both in machine diagnostics and in experiment planning, in the case coherent techniques are used. Classical methods (Young's interferometer) provides a mild knowledge of the spatial coherence, since probing a wide range of length scales requires long times and the engineerization of ad-hoc test plates. The Heterodyne Speckle Approach [1],[2] is a valuable alternative that exploits the statistical analysis of light scattered by spherical particles. The technique needs a very essential setup composed only by a water suspension of commercial colloidal particles and a CCD camera. Coherence information are retrieved from the Fourier analysis of the interference pattern generated by the stochastic superposition of the waves scattered by the particles and the unperturbed transmitted beam (heterodyne configuration). The technique a) provides a direct measure of transverse coherence without a-priori assumptions, b) provides full 2D coherence map with single-distance measures, c) has been proved to be capable of time-resolved measures with SR sources (ID06, ESRF), d) is potentially scalable over a wide range of walengths (tested 400nm, 0.1nm). It has been used for coherence measures both at the usage point and at the front-end of an undulator source (ID02-ESRF, Grenoble).
[1] M.D. Alaimo, M.A.C. Potenza, M. Manfredda, G. Geloni, M. Sztucki, T. Narayanan & M. Giglio, Phys. Rev. Lett. 103 (2009). [2] M. Manfredda et al., in preparation |
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