Keyword: experiment
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MOD02 Status of the FLASH FEL User Facility at DESY ion, operation, electron, FEL 14
 
  • K. Honkavaara
    DESY, Hamburg, Germany
 
  The FLASH facility at DESY (Hamburg, Germany) provides high brilliance FEL radiation at XUV and soft X-ray wavelengths for user experiments. Since April 2016, the second undulator beamline, FLASH2, is in user operation. We summarize the performance of the FLASH facility during the last two years including our experience to deliver FEL radiation to two user experiments simultaneously.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOD02  
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MOD04 Status and Perspectives of the FERMI FEL Facility ion, FEL, electron, laser 19
 
  • L. Giannessi, E. Allaria, L. Badano, F. Bencivenga, C. Callegari, F. Capotondi, F. Cilento, P. Cinquegrana, M. Coreno, I. Cudin, G. D'Auria, M.B. Danailov, R. De Monte, G. De Ninno, P. Delgiusto, A.A. Demidovich, M. Di Fraia, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, W.M. Fawley, M. Ferianis, P. Furlan Radivo, G. Gaio, D. Gauthier, F. Gelmetti, F. Iazzourene, S. Krecic, M. Lonza, N. Mahne, M. Malvestuto, C. Masciovecchio, M. Milloch, N.S. Mirian, F. Parmigiani, G. Penco, A. Perucchi, L. Pivetta, O. Plekan, M. Predonzani, E. Principi, L. Raimondi, P. Rebernik Ribič, F. Rossi, E. Roussel, L. Rumiz, C. Scafuri, C. Serpico, P. Sigalotti, S. Spampinati, C. Spezzani, M. Svandrlik, M. Trovò, A. Vascotto, M. Veronese, R. Visintini, D. Zangrando, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
 
  FERMI is the seeded Free Electron Laser (FEL) user facility at the Elettra laboratory in Trieste, operating in the VUV to EUV and soft X-rays spectral range; the radiation produced by the seeded FEL is characterised by a number of desirable properties, such as wavelength stability, low temporal jitter and longitudinal coherence. In this paper, after an overview of the FELs performances, we will present the development plans under consideration for the next 3 to 5 years. These include an upgrade of the LINAC and of the existing FEL lines, the possibility to perform multi-pulse experiments in different configurations and an Echo Enabled Harmonic Generation experiment on FEL-2, the FEL line extending to 4 nm (310 eV).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOD04  
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MOP042 Status of Seeding Development at sFLASH ion, electron, laser, FEL 136
 
  • V. Grattoni, R.W. Aßmann, J. Bödewadt, I. Hartl, T. Laarmann, C. Lechner, M.M. Mohammad Kazemi, A. Przystawik
    DESY, Hamburg, Germany
  • A. Azima, M. Drescher, W. Hillert, L.L. Lazzarino, V. Miltchev, J. Roßbach
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • S. Khan, N.M. Lockmann, T. Plath
    DELTA, Dortmund, Germany
 
  The experimental seeding setup at FLASH has operated now for two years in high-gain harmonic generation mode. Using a transverse deflecting structure downstream of the seeding section allows a temporal characterization of seeded electron bunches. In addition, temporal characterization of the seeded FEL beam can be performed in a dedicated diagnostic hutch. In this contribution, we give an overview of the latest achievements and present an outlook of the planned studies.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP042  
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MOP064 An Experimental Setup for Probing the Thermal Properties of Diamond Regarding Its Use in an XFELO ion, FEL, laser, electron 200
 
  • C.P. Maag, I. Bahns, J. Roßbach, P. Thiessen
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • H. Sinn
    XFEL. EU, Hamburg, Germany
  • J. Zemella
    DESY, Hamburg, Germany
 
  Funding: Work supported by BMBF (FKZ 05K13GU4 + FKZ 05K16GU4)
This work presents an pump-probe setup for measuring the thermal evolution of diamond crystals at cryogenic temperatures under the heat load conditions of an X-ray free electron laser oscillator (XFELO). As the diamond Bragg reflectors of an XFELO are subjected to intense heat loads during operation, the correct understanding of the thermal evolution in diamond plays a major role in the correct modeling of an XFELO. Stoupin et al.* did a room temperature x-ray diffraction measurement on the nanosecond transient thermal response of diamond to an optical pulse. The measurements presented in this paper for the first time incorporate effects due to the very short penetration depth of only a few μm of an XFELO pulse in combination with the high mean free path in diamond at cryogenic temperatures. While at room temperature the heat equation based on Fourier's law accurately fits the measured results, this vastly changes due to the onset of ballistic processes at cryogenic temperatures. These changes, which are hard to predict theoretically, show the necessity of measurements of the thermal evolution in diamond with special regard to a correct mimicking of the heat load in an XFELO.
*S. Stoupin et al., Phys. Rev. B, vol. 86, p. 054301, 2012.
 
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TUB04 Recent On-Line Taper Optimization on LCLS ion, FEL, electron, undulator 229
 
  • J. Wu, X. Huang, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • A. Scheinker
    LANL, Los Alamos, New Mexico, USA
 
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
High-brightness XFELs are demanding for many users, in particular for certain types of imaging applications. Self-seeding XFELs can respond to a heavily tapered undulator more effectively, therefore seeded tapered FELs are considered as a path to high-power FELs in the terawatts level. Due to many effects, including the synchrotron motion, the optimization of the taper profile is intrinsically multi-dimensional and computationally expensive. With an operating XFEL, such as LCLS, the on-line optimization becomes more economical than numerical simulation. Here we report recent on-line taper optimization on LCLS taking full advantages of nonlinear optimizers as well as up-to-date development of artificial intelligence: deep machine learning and neural networks.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUB04  
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TUP015 Coherent Transition Radiation from Transversely Modulated Electron Beams ion, radiation, electron, detector 276
 
  • A. Halavanau, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • S.P. Antipov, W. Liu, N.R. Neveu, J.G. Power, C. Whiteford, E.E. Wisniewski
    ANL, Argonne, Illinois, USA
  • A.I. Benediktovitch
    BSU, Minsk, Belarus, Belarus
  • S.N. Galyamin, A.V. Tyukhtin
    Saint Petersburg State University, Saint Petersburg, Russia
  • D. Mihalcea, P. Piot
    Fermilab, Batavia, Illinois, USA
  • N.R. Neveu
    IIT, Chicago, Illinois, USA
 
  A transverse laser-shaping optical setup using microlens arrays (MLAs), previously developed and employed at Argonne Wakefield Accelerator (AWA), allows the formation of both highly uniform and modulated (patterned) beams. In the latter case, transverse modulation is imposed in the sub-millimeter scale. In the present study, we report the simulations of backward coherent transition radiation (CTR) emitted from a transversely modulated beam. We compare the case of a uniform round beam against different transverse modulation wavelengths by generating CTR on a steel target and measuring the autocorrelation function of the resulting radiation with an interferometer. We particularly focus on the differences between round and patterned beam distributions and discuss possible future applications of this setup in THz radiation generation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP015  
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TUP023 Recent Developments and Plans for Two Bunch Operation with up to 1 μs Separation at LCLS ion, photon, wakefield, gun 288
 
  • F.-J. Decker, K.L.F. Bane, W.S. Colocho, A.A. Lutman, J.C. Sheppard
    SLAC, Menlo Park, California, USA
 
  Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
To get two electron bunches with a separation of up to 1 microsecond at the Linac Coherent Light Source (LCLS) is important for LCLS-II developments. Two lasing bunches up to 220 ns have been demonstrated. Many issues have to be solved to get that separation increased by a factor of 5. The typical design and setup for one single bunch has to be questioned for many devices: RF pulse widths have to be widened, BPMs diagnostic can see only one bunch or a vector average, feedbacks have to be doubled up, the main Linac RF needs to run probably un-SLEDed, and special considerations have to be done for the Gun and L1X RF.
 
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TUP038 Experiments in Electron Beam Nanopatterning ion, electron, FEL, simulation 320
 
  • C. Zhang, W.S. Graves, L.E. Malin, J. Spence
    Arizona State University, Tempe, USA
  • D.B. Cesar, J.M. Maxson, P. Musumeci, A. Urbanowicz
    UCLA, Los Angeles, USA
  • R.K. Li, E.A. Nanni, X. Shen, S.P. Weathersby, J. Yang
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by NSF Accelerator Science awards 1632780 and 1415583, NSF BioXFEL STC award 1231306, and DOE contracts DE-AC02-76SF00515 and DE-SC0009914.
We report on experiments in nanopatterning electron beams from a photoinjector as a first step toward a compact XFEL (CXFEL). The nanopatterning is produced by Bragg diffraction of relativistic electron beams through a patterned Si crystal consisting of alternating thick and thin strips to produce nanometer-scale electron density modulations. Multi-slice simulations show that the target can be oriented for a two-beam condition where nearly 80% of the elastically scattered electron beam is diffracted into the 220 Bragg peak. An experiment at the two-beam condition measurement has been carried out at the SLAC UED facility showing this effect with 2.26 MeV electrons. We successfully proved a large portion of the main beam is diffracted into 220 spot by tuning the orientation of the sample. Future plans at UCLA are to observe the nanopatterned beam, and to investigate various grating periods, crystal thicknesses, and sample orientations to maximize the contrast in the pattern and explore tuning the period of the modulation. The SLAC measurement results will be presented along with design of the UCLA experiments.
 
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TUP050 Beam Driven Acceleration and RF Breakdown in Photonic Band Gap Travelling Wave Accelerator Structure ion, wakefield, electron, acceleration 333
 
  • J. Upadhyay, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
 
  We report the results of an experiment to demonstrate excitation of wakefields and wakefield acceleration in a photonic band gap (PBG) accelerating structure. The experiment was conducted at the Argonne Wakefield Accelerator (AWA) facility. For modern X-ray free electron lasers (FELs), preservation of the electron beam quality during the beam acceleration is of crucial importance. Therefore, new accelerating structures must be designed with careful attention paid to the suppression of wakefields. PBG structures are widely studied due to their ability to exclude higher order modes. A 16-cell travelling-wave normal conducting PBG structure operating at 11.700 GHz is installed at the AWA beam line. We passed a high-charge single bunch or multiple bunch train through the structure that generated wakefields and evaluated the effect of these wakefields on a low-charge witness beam. We also passed high-charge multiple bunch trains through the structure that generated up to 100 MV/m accelerating gradient and studied the RF breakdown.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP050  
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TUP053 The ACHIP Experimental Chambers at PSI ion, electron, FEL, laser 336
 
  • E. Ferrari, M. Bednarzik, S. Bettoni, S. Borrelli, H.-H. Braun, M. Calvi, Ch. David, M.M. Dehler, F. Frei, T. Garvey, V. Guzenko, N. Hiller, R. Ischebeck, C. Ozkan Loch, E. Prat, J. Raabe, S. Reiche, L. Rivkin, A. Romann, B. Sarafinov, V. Schlott, S. Susmita
    PSI, Villigen PSI, Switzerland
  • E. Ferrari, L. Rivkin
    EPFL, Lausanne, Switzerland
  • P. Hommelhoff
    University of Erlangen-Nuremberg, Erlangen, Germany
  • J.C. McNeur
    Friedrich-Alexander Universität Erlangen-Nuernberg, University Erlangen-Nuernberg LFTE, Erlangen, Germany
 
  Funding: Gordon and Betty Moore Foundation
The Accelerator on a Chip International Program (ACHIP) is an international collaboration, funded by the Gordon and Betty Moore Foundation, whose goal is to demonstrate that a laser-driven accelerator on a chip can be integrated to fully build an accelerator based on dielectric structures. PSI will provide access to the high brightness electron beam of SwissFEL to test structures, approaches and methods towards achieving the final goal of the project. In this contribution, we will describe the two interaction chambers installed on SwissFEL to perform the proof-of-principle experiments. In particular, we will present the positioning system for the samples, the magnets needed to focus the beam to sub-micrometer dimensions and the diagnostics to measure beam properties at the interaction point.
 
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TUP054 Preparations for Installation of the Double Emittance-Exchange Beamline at the Argonne Wakefield Accelerator Facility ion, emittance, wakefield, simulation 340
 
  • G. Ha
    PAL, Pohang, Republic of Korea
  • M.E. Conde, D.S. Doran, W. Gai, J.G. Power
    ANL, Argonne, Illinois, USA
 
  Funding: This work is supported by Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
Preparations to upgrade the single EEX beamline at the Argonne Wakefield Accelerator (AWA) facility to a double EEX beamline are underway. The single EEX beamline recently demonstrated exchange-based longitudinal bunch shaping (LBS) which has numerous applications including high-energy physics linear colliders, x-ray FELs, and intense radiation sources. The exchange-based method can generate arbitrary LBS in the ideal case but has limitations in the real case. The double EEX beamline was proposed as a means to overcome the limitations of single EEX due to transverse jitter and large horizontal emittance. In this paper, we present the current status of beamline design and installation and simulation results for the planned experiments: collinear wakefield acceleration with tailored beams and tunable bunch compression without the double-horn feature.
 
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TUP057 Measurement of Short-Wavelength High-Gain FEL Temporal Coherence Length by a Phase Shifter ion, FEL, electron, radiation 344
 
  • G. Zhou
    IHEP, Beijing, People's Republic of China
  • W. Liu
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • W. Qin, T.O. Raubenheimer, J. Wu, C. Yang
    SLAC, Menlo Park, California, USA
  • C.-Y. Tsai
    Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
  • B. Yang
    University of Texas at Arlington, Arlington, USA
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
 
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Short-wavelength high-gain free-electron lasers (FELs) are now well established as a source of ultra-fast, ultra-brightness, longitudinally partial coherent light. Since coherence is one of the fundamental properties of light source, so continual effort is devoted to high-gain free-electron laser coherence measurements. In this work, we propose a possible approach, employing a phase shifter to induce electron beam delay to measure the temporal coherence length. Simple analysis, numerical simulation and preliminary experimental results are presented. This approach can be robust and independent of frequency.
 
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TUP062 Electromagnetic and Mechanical Analysis of a 14 mm 10-period NbTi Superconducting Undulator ion, undulator, insertion-device, insertion 360
 
  • F. Trillaud, G.A. Barraza Montiel
    UNAM, Cuernavaca, Morelos, Mexico
  • M. Gehlot, G. Mishra
    Devi Ahilya University, Indore, India
 
  Funding: DGAPA of UNAM, fund PAPIIT TA100617 SERB, India
A 14 mm - 10 period NbTi superconducting undulator for the next generation of Free Electron Laser has been stud- ied. The optimum electromagnetic pre-design was carried out using RADIA, an extension module of the commercial software Mathematica. For this pre-design, a variable gap was considered. Additionally, a thermo-mechanical study of one eighth of the superconducting undulator was conducted. This study utilized a thermal and mechanical contact model between the pancake coils and the carbon steel core. This coupled model allowed estimating the minimum pre-loading of the coil. This pre-loading ensures that the coil would remain stuck to its pole during cooling. Numerical results are presented for both studies.
* M. Gehlot et al., Nucl. Inst. and Meth. in Phys. Res., Sec. A, Vol. 846, p. 13-17, 2017.
** B.J.A. Shepherd et al., Proceedings of IPAC2014, WEPRI095, 2014.
*** J. Grimmer, R. Kmak, PAC 2005.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP062  
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TUP067 Study on Cherenkov Laser Oscillator Using Tilted Electron Bunches ion, radiation, electron, laser 371
 
  • K. Sakaue
    Waseda University, Waseda Institute for Advanced Study, Tokyo, Japan
  • M. Brameld, Y. Tadenuma, M. Washio, R. Yanagisawa
    Waseda University, Tokyo, Japan
  • R. Kuroda, Y. Taira
    AIST, Tsukuba, Ibaraki, Japan
  • J. Urakawa
    KEK, Ibaraki, Japan
 
  Funding: This work was supported by a research granted from The Murata Science Foundation and JSPS KAKENHI 26286083.
We have been studying a coherent Cherenkov radiation by using tilted electron bunches. Bunch tilting can enhance the radiation power about 10 times due to the wavefront matching of radiations. Recently, we investigated that this technique can produce high peak power THz pulses with sufficient pulse energy. Resulting pulse energy was more than 30 nJ/pulse and peak power was about 10 kW. Introducing the oscillator cavity with two concave mirrors, it would be possible to achieve lasing using tilted electron bunches. In the calculation, 1 uJ/micro-pulse and 100 uJ/macro-pulse broadband THz pulses are expected to be achieved, which are powerful THz sources compared with the existing THz FELs. In this conference, we will report the experimental results of coherent Cherenkov radiation, calculated results toward lasing and future prospectives.
 
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TUP069 Simulating Beam Dynamics in Coherent Electron-Cooling Accelerator with WARP ion, cavity, electron, simulation 374
 
  • K. Shih
    SBU, Stony Brook, New York, USA
  • Y.C. Jing, V. Litvinenko, I. Pinayev, G. Wang
    BNL, Upton, Long Island, New York, USA
  • K. Mihara
    Stony Brook University, Stony Brook, USA
  • I. Petrushina
    SUNY SB, Stony Brook, New York, USA
 
  Funding: DoE NP office, grant DE-FOA-0000632, NSF grant PHY-1415252.
Coherent Electron Cooling (CeC) is a novel cooling technique based on amplification of interaction between hadrons and electron by an FEL. If proven, this CeC could bring a revolution in hadron and electron-hadron colliders. A dedicated CeC proof-of-principle experiment is under way at RHIC collider (BNL) using a sophisticated SRF accelerator for generating and accelerating electron beam. This paper is dedicated to studies of beam dynamics in the CeC accelerator and specifically to emittance preservation in its ballistic compressions section. Two 500-MHz RF cavities are used for generating the necessary energy chirp leading in 1.56-MeV, 0.5-nsec-long electron bunched to compress them to 25-psec duration downstream. During the commissioning of the CeC accelerator we noticed that beam emittance can be strongly degraded when electron beam passes these 500 MHz RF cavities off-axis. We used a full 3D PIC code Wrap to simulate effect of the off-axis beam propagation through these
 
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TUP070 Development of Mid-Infrared Photoacoustic Spectroscopy System for Solid Samples at Kyoto University Free Electron Laser Facility ion, FEL, laser, electron 378
 
  • J. Okumura, T. Kii, H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
 
  Photoacoustic Spectroscopy (PAS) enables IR absorption spectrum measurements of solid samples without preprocessing of samples. Its sensitivity and resolution depend on the intensity and spectral width of the infrared light, respectively. Mid-infrared free electron laser (MIR-FEL) is an intense, quasi-monochromatic and tunable laser in MIR region, so the method of PAS with FEL (FEL-PAS) was proposed.*,** However, the resolution was not so good since they used the direct FEL beam which has the spectral width of 1%. We considered that the resolution can be significantly increased by inserting a high-resolution grating monochromator before the PAS cell. Based on this consideration, a PAS system using an MIR-FEL with the monochromator is under development. We have already conducted preliminary experiments using a PAS cell which has been used in previous studies and successfully measured quite high PAS signals with this setup.*,** A demonstration of experiments to check the spectral resolution will be conducted soon. In this presentation, the progress of the development including the result of demonstration experiments will be reported.
* M. Yasumoto et al., Proceedings of the 2004 FEL Conference, 703-705 (2004).
** M. Yasumoto et al., Eur. Phys. J. Special Topics, 153, 37-40 (2008).
 
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TUP071 Study on Second Harmonic Generation in SiC Using Infrared FEL ion, FEL, scattering, detector 382
 
  • S. Tagiri
    Kyoto Univeristy, Kyoto, Japan
  • T. Kii, H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
 
  Mode-selective phonon excitation (MSPE) is an attractive method for studying the lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). In addition, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material (6H-SiC) with MIR-FEL (KU-FEL) by anti-Stokes (AS) Raman-scattering spectroscopy. Recently, we have certified that the Sum Frequency Generation (SFG) also occurs with AS Raman scattering. For distinguishing between the AS Raman scattering and SFG, we need to know the nonlinear susceptibility and transmittance. The coefficients can be measured by the Second Harmonic Generation (SHG) spectroscopy. In this paper, the outline of the measurement system and the preliminary results with a 6H-SiC sample are reported.  
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WEB03 R&D at SLAC on Nanosecond-Range Multi-MW Systems for Advanced FEL Facilities ion, kicker, FEL, linac 404
 
  • A.K. Krasnykh, A.L. Benwell, T.G. Beukers, D.F. Ratner
    SLAC, Menlo Park, California, USA
 
  Funding: Work supported by US Department of Energy contract DE-AC02-76SF00515
A nanosecond-range, multi-MW system containing TEM mode electrodynamic structures fed by controllable pulsers are needed for (1) fast injection systems in multi-bend achromat upgraded (MBA-U) storage rings and for (2) arrays of FEL beamlines powered by a superconducting linear accelerators operating with MHz-bunch repetition rate. The R&D effort covers both type (1) and (2) layouts. This report discuss the experimental results of several concepts for a generation of the nanosecond range multi MW pulsers. Compression of the initially formed electromagnetic (EM) power is employed for a generation of the nanosecond pulses in all concepts discussed here. A solid-state nonlinear media assists the EM compression. Features of the materials and components used in the design will be presented. The results will be included in the design of the kicker systems for advanced FEL facilities. For example, in the LCLS-II, the nanosecond range pulse allows for distributing closely spaced bunches to multiple undulators allowing experimenters to take advantage of combining different colored x-rays.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEB03  
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WEP010 Beam Asymmetry Studies with Quadrupole Field Errors in the PITZ Gun Section ion, quadrupole, solenoid, gun 440
 
  • Q.T. Zhao, G. Asova, P. Boonpornprasert, Y. Chen, J.D. Good, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, M. Krasilnikov, X. Li, O. Lishilin, G. Loisch, D.M. Melkumyan, A. Oppelt, H.J. Qian, Y. Renier, T. Rublack, C. Saisa-ard, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova
    INRNE, Sofia, Bulgaria
  • C. Saisa-ard
    Chiang Mai University, Chiang Mai, Thailand
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
 
  The Photo Injector Test Facility at DESY in Zeuthen (PITZ) was built to test and optimize high-brightness electron sources for free electron lasers (FELs) like FLASH and European XFEL. Although the beam emittance has been optimized and experimentally demonstrated to meet the requirements of FLASH and XFEL, transverse beam asymmetries, such as wing structures and beam tilts, were observed during many years of operation with different generations of guns. These cannot be explained by simulations with the rotationally symmetric gun cavities and symmetric solenoid fields. Based on previous RF coupler kick, solenoid field imperfection studies and coupling beam dynamics, the beam asymmetries most probably stem from rotated quadrupole field error in the gun section. A thin-lens static quadrupole model is applied in the RF gun section simulations to fit the position and intensity of quadrupole field errors by comparing the beam asymmetry directions in experiments and ASTRA simulations. Furthermore, by measuring the laser position movement at the photo cathode and the corresponding beam movement at downstream screens, the integrated quadrupole field strength can also be extracted.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP010  
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WEP015 Current Experimental Work with Diamond Field-Emitter Array Cathodes ion, cathode, electron, site 450
 
  • H.L. Andrews, R.L. Fleming, J.W. Lewellen, K.E. Nichols, D.Y. Shchegolkov, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
  • B.K. Choi
    Vanderbilt University, Nashville, USA
 
  Funding: We gratefully acknowledge the support of the U.S. Department of Energy through the LANL/LDRD Program for this work.
Diamond Field-Emitter Array (DFEA) cathodes are arrays of micron-scale diamond pyramids with nanometer-scale tips, thereby providing high emission currents with small emittance and energy spread. To date they have been demonstrated in a close-diode configuration, spaced only a few hundred microns from a solid anode, and have shown very promising results in terms of emittance, energy spread, and per-tip emission currents. We present recent results investigating DFEA performance in a large-gap configuration, such that the cathodes are a few millimeters from a solid anode, and show that performance is the same or better as the close-diode geometry previously studied. However, array performance is still limited by anode damage. We are redesigning our cathode test stand to overcome the inherent limitations of a solid anode, allow for transport of the emitted beam, and further explore real-world DFEA performance.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP015  
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WEP027 Numerical Study of Cherenkov Radiation From Thin Silica Aerogel ion, electron, radiation, diagnostics 479
 
  • H. Hama, K. Nanbu, H. Saito, Y. Saito
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
 
  Funding: This work was supported by JSPS KAKENHI Grant Numbers JP15K13394 and JP17H01070.
Cherenkov radiation (CR) emitted from low-refractive index material such as silica-aerogel is a useful tool for electron beam diagnostics because the opening angle (Cherenkov angle) is small and the CR can be transported onto a detector located far from the radiator. We have prepared a thin (1-mm thick) hydrophobic silica-aerogel with a refractive index of 1.05 that has been developed at Chiba University.* Since the intensity of CR is much stronger than that of optical transition radiation, the CR is a better light source for low-intensity beam diagnostics. In order to apply the CR to measurements of a bunch length of electron beams, we have investigated sources of finite time resolution by a numerical simulation study using the Liénard-Wiechert potentials. We will report results of simulations such as pulse duration of CR and discuss what deteriorates the time resolution.
* M. Tabata et al., Nucl. Instr. and Meth. A 668 (2012) 64.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP027  
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