FEL2015 - Classification: FEL Technology and HW: Electron Diagnostics, Timing, Synchronization, and Controls

Paper	Title	Page
MOP033	Numerical Simulations of a Sub-THz Coherent Transition Radiation Source at PITZ	97
	P. Boonpornprasert, M. Krasilnikov, F. Stephan DESY Zeuthen, Zeuthen, Germany B. Marchetti DESY, Hamburg, Germany
	The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator can be considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments at the European XFEL. For this reason, the radiation generated by high-gain FEL and Coherent Transition Radiation (CTR) produced by the PITZ electron beam has been studied. In this paper, numerical simulations on the generation of CTR based on the PITZ accelerator are presented. The beam dynamics simulations of electron bunches compressed by velocity bunching are performed by using the ASTRA code. The characteristics of CTR are calculated numerically by using the generalized Ginzburg-Frank formula. The details and results of the simulations are described and discussed.
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MOP034	Beam Optics Measurements at FERMI by using Wire-Scanner	101
	G. Penco, A. Abrami, I. Cudin, S. Di Mitri, M. Ferianis, E. Ferrari, G. Gaio, L. Giannessi, S. Grulja, R. Sauro, L. Sturari Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy E. Ferrari Università degli Studi di Trieste, Trieste, Italy L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy G.L. Orlandi, C. Ozkan Loch PSI, Villigen PSI, Switzerland
	Measuring and controlling the electron beam optics is an important ingredient to guarantee high performance of a free-electron laser. In the FERMI linac, the Twiss parameters and the transverse emittances are routinely measured by detecting the beam spot size as a function of a scanning quadrupole placed upstream (i.e. quadrupole scan method). The beam spot size is usually measured with an OTR screen that unfortunately suffers from coherent optical transition radiation (C-OTR) that introduces spurious light and corrupts the image. Moreover, the beam size at the end of the FERMI linac is focused to a few tens of microns and this makes it difficult to precisely measure it with the OTR system, which has an estimated resolution of 20um. For this reason, a wire-scanner system has been installed at the end of the linac just in the waist of the optics channel. The wire-scanner is a SwissFEL prototype installed in FERMI in order to study the hardware and beam loss monitor performances at the GeV energy scale. The beam optics measurements performed with the wire-scanner is here presented, and the obtained results are more in agreement with the theoretical expectations. A more reliable beam optics estimation at the end of the linac has allowed to better match it to the nominal lattice and transport it up to the undulator chain, providing important benefits to the FEL performance.
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MOP036	Femtosecond Synchronization of 80-MHz Ti:Sapphire Photocathode Laser Oscillator with S-Band RF Oscillator	105
	H. Yang, C. Jeon, K. Jung, J. Kim KAIST, Daejeon, Republic of Korea H. Chung Korea University Sejong Campus, Sejong, Republic of Korea B. Han, Y.U. Jeong KAERI, Daejon, Republic of Korea
	Precision synchronization between lasers and RF sources in free-electron lasers (FELs) and ultrafast electron diffraction (UED) systems is becoming more important. There have been intense research and development toward femtosecond synchronization of lasers and RF sources in the last decade. Most of the previous approaches at large-scale FELs have used cw lasers or low-jitter mode-locked lasers at telecomm wavelength as the master oscillator and distributed the timing signals via stabilized fiber links. However, for smaller-scale FELs and UED, this approach may be a complex and high-cost method. In this work, we studied the possibility of using the commercial Ti:sapphire photocathode laser as the optical master oscillator as well. For its use in UED and FELs, we synchronized the 80-MHz Ti:sapphire photocathode laser oscillator to a 2.856-GHz RF source (used for RF-photogun) with 50-fs precision. Some interesting findings are following. First, intrinsic rms timing jitter of the used photocathode laser is 2.6 fs [10 kHz-10 MHz], which sets the fundamental limit in synchronization. Second, timing jitter in 100 Hz-1 kHz in photocathode laser is so severe (e.g., ~40 fs even feedback control is applied), so that it will require additional external-cavity control for achieving sub-10-fs precision. By addressing this issue, we are currently working toward 10-fs precision.
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MOP038	Stabilization of Magnetron Frequency for a Microtron-Driven FEL	107
	B.A. Gudkov, S. Bae, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, S.V. Miginsky, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov KAERI, Daejon, Republic of Korea S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	Under KAERI WCI program we develop a compact pulsed microtron-driven FEL. Electron bunches trains are accelerated in the microtron and transported by the beamline to the undulator. The RF cavity in the microtron is fed by a magnetron. Any accelerator driver for a FEL should provide an electron beam having very stable parameters such as electron energy, current, and especially the bunch repetition rate in a train. All mentioned parameters depend on magnetron current. It means that special attention should be paid for the shape of the current pulse, supplied to the magnetron from the modulator. We developed the modulator project with a computer control that will provide an arbitrary shape of the magnetron current. A simplified prototype was fabricated and tested. The methods of controlling of the pulse shape are considered. Simulation and experimental results are presented.
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MOP039	First Results of Commissioning of the PITZ Transverse Deflecting Structure	110
	H. Huck, P. Boonpornprasert, A. Donat, J.D. Good, M. Groß, I.I. Isaev, L. Jachmann, D.K. Kalantaryan, M. Khojoyan, W. Köhler, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, M. Pohl, Y. Renier, T. Rublack, J. Schultze, F. Stephan, G. Trowitzsch, G. Vashchenko, R.W. Wenndorff, Q.T. Zhao DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria M. A. Bakr Assiut University, Assiut, Egypt D. Churanov, L.V. Kravchuk, V.V. Paramonov, I.V. Rybakov, A.A. Zavadtsev, D.A. Zavadtsev RAS/INR, Moscow, Russia C. Gerth, M. Hoffmann, M. Hüning DESY, Hamburg, Germany C. Hernandez-Garcia JLab, Newport News, Virginia, USA M.V. Lalayan, A.Yu. Smirnov, N.P. Sobenin MEPhI, Moscow, Russia O. Lishilin, G. Pathak Uni HH, Hamburg, Germany
	For successful operation of X-ray Free Electron Lasers, one crucial parameter is the ultrashort electron bunch length yielding a high peak current and a short saturation length. In order to effectively compress the bunches during the acceleration process, a detailed understanding of the full longitudinal phase space distribution already in the injector is required. Transverse deflecting RF structures (TDS) can shear the bunch transversely, mapping the longitudinal coordinate to a transverse axis on an observation screen downstream. In addition to the bunch length, the slice emittance along the bunch as well as the full longitudinal phase space can be obtained. At the Photo Injector Test Facility at DESY, Zeuthen site (PITZ), an S-band traveling wave TDS is under commissioning since 2015. This cavity is a prototype for the TDS in the injector part of the European XFEL and has been designed and manufactured by the Institute for Nuclear Research (INR, Moscow, Russia). In this paper, first commissioning results of the system at PITZ are presented and discussed.
	Poster MOP039 [0.893 MB]
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MOP040	Implementation of MTCA.4-based Controls for the Pulsed Optical Synchronization Systems at DESY	115
	M. Felber, Ł. Butkowski, M.K. Czwalinna, M. Fenner, C. Gerth, M. Heuer, E. Janas, M. Killenberg, T. Lamb, U. Mavrič, J.M. Müller, P. Peier, K.P. Przygoda, S. Ruzin, H. Schlarb, C. Sydlo, M. Titberidze, F. Zummack DESY, Hamburg, Germany T. Kozak, P. Prędki TUL-DMCS, Łódź, Poland
	Funding: This work has partly been funded by the Helmholtz Validation Fund Project MTCA.4 for Industry (HVF-0016) With the current state of the synchronization system at FLASH (Free-electron Laser in Hamburg) the arrival time between electron bunches and optical laser pulses can be synchronized to a level of 30 fs rms, e.g. for pump-probe experiments. In the course of the development of an up-scaled system for the European XFEL and the migration of control hardware to the modern MTCA.4 (Micro Telecommunications Computing Architecture) platform, all involved components of the system will be replaced with new developments. The front-end devices are upgraded. FPGAs (Field Programmable Gate Arrays) are performing the data processing and feedback calculations. In order to facilitate the firmware development, a toolset (Rapid-X) was established which allows application engineers to develop, simulate, and generate their code without help from FPGA experts in a simple and efficient way. A software tool kit (MTCA4U) provides drivers and tools for direct register access e.g. via Matlab or Python and a control system adapter, which allows the server applications to be written control system independent. In this paper, an overview on the synchronization setups and their upgrades as well as an introduction to the new hardware is given. The Rapid-X and MTCA4U tool kits are presented followed by a status report on the implementation of the new developments.
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MOP041	Turbo-ICT Pico-Coulomb Calibration to Percent-level Accuracy	118
	F. Stulle, J.F. Bergoz BERGOZ Instrumentation, Saint Genis Pouilly, France
	We report on the calibration methods implemented for the Turbo-ICT/BCM-RF. They allow to achieve percent-level accuracy for charge and current measurements. Starting from the Turbo-ICT/BCM-RF working principle, we discuss scientific fundaments of calibration and their practical implementation in a test bench. Limits, both principle and practical, are reviewed. Achievable accuracy is estimated.
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MOP042	All-Fiber Approach to Long-Term Stable Timing Distribution System	122
	M. Xin, K. Safak, F.X. Kaernter DESY, Hamburg, Germany P.T. Callahan, M.Y. Peng MIT, Cambridge, Massachusetts, USA
	High precision timing distribution systems are critical for free-electron lasers (FELs). Real facilities such as FLASH and the European XFEL need fiber networks consisting of 20 or more timing links, which require tremendous attention to the alignment and stability of the free-space optics to minimize timing-drifts induced by beam pointing instabilities. This situation also necessitates preamplification of the master laser output to overcome excessive free-space to fiber coupling losses to provide adequate power for all timing links. Recently, we have developed integrated, fiber-coupled balanced optical cross-correlators (FC-BOC) using periodically-poled KTiOPO4 (PPKTP) waveguides. These waveguides exhibit second harmonic conversion efficiencies 20 times higher than the bulk optical devices, which will decrease the power demand from the master laser and consequently support more timing links. Furthermore, the robustness and ease of implementation of these fiber-coupled devices will eliminate alignment-related problems observed in free-space optics. In this paper, we present an all-fiber implementation of a 3.5-km timing distribution system using FC-BOCs, over 200 hours operation without interruption. The remaining drift (<1 Hz) is only 3.3 fs RMS, and the integrated jitter above 1 Hz is kept below 0.7 fs, which is more than sufficient for an efficient FEL synchronization.
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MOP043	Influence of Environment Changes on Libera Sync 3 Long-term Stability	126
	S. Zorzut, M. Cargnelutti I-Tech, Solkan, Slovenia S. Hunziker PSI, Villigen PSI, Switzerland
	Libera Sync 3 can be used as a reference clock transfer system in the latest fourth generation light sources where the long-term stability is in the range of a few tens of femtoseconds of drift per day. The system has been developed in collaboration with the Paul Scherrer Institute (PSI) and first units are already tested in SwissFEL machine. In this article we present the influence of temperature and humidity changes on the long-term phase stability of the system.
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MOP044	A Laser Heater for CLARA	129
	S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom B.D. Muratori, N. Thompson, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	CLARA is a new FEL test facility, being developed at STFC Daresbury Laboratory in UK, based on a high brightness electron linac. The electron beam of CLARA can potentially be affected by the longitudinal microbunching instability leading to a degradation of the beam quality. The inclusion of a laser heater in the linac design can allow control of the microbunching instability, the study of microbunching and deliberate increase of the final energy spread to study energy spread requirements of the FEL schemes tested at CLARA. We present the initial design and layout of the laser heater system for CLARA and its expected performance.
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TUP043	PAL-XFEL Cavity BPM Prototype Beam Test at ITF	468
	S.J. Lee, J.H. Han, H.-S. Kang, C. Kim, S.H. Kim, I.S. Ko, Y.J. Park, D.C. Shin PAL, Pohang, Kyungbuk, Republic of Korea
	To achieve sub-micrometer resolution, PAL-XFEL undulator section will use X-band Cavity beam position monitor (BPM) systems. The prototype cavity BPM pick-up was designed and fabricated to test the performance of the cavity BPM system. The fabricated prototype cavity BPM pick-up was installed at Pohang Accelerator Laboratory injector test facility (PAL ITF) for the beam test. Under 200 pC beam charge condition, the signal properties of the cavity BPM pick-up were measured. Also, the dynamic range of the cavity BPM pick-up was measured by using the corrector magnet. In this paper, the design and beam test results of the prototype cavity BPM pick-up will be discussed.
	Poster TUP043 [0.695 MB]
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TUP044	Spark EL - Single Pass BPM	471
	M. Žnidarčič I-Tech, Solkan, Slovenia
	Monitoring and subsequent optimization of the electron linacs and beam transfers requires specific instrumentation for beam position data acquisition and processing. Spark EL is the newly developed prototype intended for position monitoring in single or multi bunch operation linacs and transfer lines. The motivation, processing principles and first results are presented.
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TUP045	MTCA.4 Phase Detector for Femtosecond-Precision Laser Synchronization	474
	E. Janas, M. Felber, M. Heuer, U. Mavrič, H. Schlarb DESY, Hamburg, Germany K. Czuba Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
	For time-resolved experiments at FELs such as the European XFEL an accurate synchronization of the machine is essential. The required femtosecond- level synchronization we plan to achieve with an optical synchronization system, in which an inherent part is the master laser oscillator (MLO) locked to the electrical reference. At DESY we develop a custom rear transition module in MTCA.4 standard, which will allow for different techniques of phase detection between the optical and the electrical signal, as well as locking to an optical reference using a cross-correlator. In this paper we present the current status of the development, including two basic solutions for the detection to an RF. One of the methods incorporates an external drift free detector based on the so-called MZI setup. The other one employs the currently used downconverter scheme with subsequent improvements. The module can serve for locking a variety of lasers with different repetition rates.
	Poster TUP045 [4.010 MB]
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TUP049	Prototype of the Improved Electro-Optical Unit for the Bunch Arrival Time Monitors at FLASH and the European XFEL	478
	H. Dinter, M.K. Czwalinna, C. Gerth, K.P. Przygoda, R. Rybaniec, H. Schlarb, C. Sydlo DESY, Hamburg, Germany
	At today's free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems providing accurate timing stability for time-resolved pump-probe experiments and seeding schemes. At FLASH and the upcoming European XFEL a reliable and precise arrival time detection down to the femtosecond level has to cover a broad range of bunch charges, which may even change from 1 nC down to 20 pC within a bunch train. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultra-short laser pulses. At both facilities, the new bunch arrival time monitor has to cope with the special operation mode where the MHz repetition rate bunch train is separated into several segments for different SASE beam lines. Each of the segments will exhibit individual timing jitter characteristics since they are generated from different injector lasers and can be accelerated with individual energy gain settings. In this paper, we describe the recent improvements of the electro-optical unit developed for the bunch arrival time monitors to be installed in both facilities.
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TUP050	Extension of Existing Pulse Analysis Methods to High-Repetition Rate Operation: Studies of the "Time-Stretch Strategy"	483
	S. Bielawski PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France J.B. Brubach, L. Cassinari, M.-E. Couprie, M. Labat, L. Manceron, J.P. Ricaud, P. Roy, M.-A. Tordeux SOLEIL, Gif-sur-Yvette, France C. Evain, C. Szwaj PhLAM/CERLA, Villeneuve d'Ascq, France M. Le Parquier CERLA, Villeneuve d'Ascq, France E. Roussel Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Funding: ANR (2010-042301, DYNACO), LABEX CEMPI project (ANR-11-LABX-0007), ERC grant COXINEL (340015), GENCI TGCC/IDRIS (x2014057057,i2015057057). Many single-shot recording setups are based on the encoding of the information onto a laser pulse. This concerns in particular electro-optic sampling of bunch shapes, and VUV/X pulse monitors using transient reflectivity. The upgrade of these methods to high repetition rates presents challenging issues, that are due to the limited speed of the recording cameras. Recently [1], we demonstrated that multi-MHz repetition rates can be achieved using a relatively simple upgrade of existing setups, using the so-called "photonic time-stretch" technique. Here we present guidelines for the practical realization in the case of electro-optic sampling. We also present a performance analysis, and compare it to the spectral encoding case. The technique is potentially applicable to other cases where the information can be encoded on a chirped laser pulse, as, e.g., transient reflectivity diagnostics of XUV pulses. [1] Observing microscopic structures of a relativistic object using a time-stretch strategy, E. Roussel, C. Evain, M. Le Parquier, C. Szwaj, S. Bielawski, L. Manceron, J.-B. Brubach, M.-A. Tordeux, J.-P. Ricaud, L. Cassinari, M. Labat, M.-E Couprie, and P. Roy, Scientific Reports 5, 10330 (2015).
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TUD01	COTR Resistant Profile Monitor	554
	H. Loos SLAC, Menlo Park, California, USA
	Funding: Work supported by DOE contract DE-AC02-76SF00515 Electron beam accelerators used as drivers for short wavelength FELs need ultra-high brightness beams with small emittances and highly compressed bunch lengths. The acceleration and beam transport process of such beams leads to micro-bunching instabilities which cause the emergence of coherent optical transition radiation (COTR). The effect of COTR on profile monitors based on OTR or fluorescent screens can be quite detrimental to their intended use to measure beam sizes and profiles. This presentation will review past observations of the beam diagnostics issues due to COTR and discuss various mitigation schemes for profile monitors as well as present experience with such implementations.
	Slides TUD01 [1.536 MB]
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TUD02	Diffraction Radiation Monitor	561
	Y. Taira AIST, Tsukuba, Japan
	Non-invasive beam diagnostics using a diffraction radiation (DR) has been developed at several electron accelerator facilities. Generation process of DR is similar to that of transition radiation (TR). TR is emitted when a charged particle passes through the boundary between two media with different dielectric constants. On the other hand, DR is emitted when it passes through in the vicinity of a boundary between two media. In the generation process of DR, the charged particle doesn't intersect the medium but its electric field intersects the medium. An aperture, a slit, and an edge are used for DR target. Optical wavelength of DR is usually used for beam diagnostics. One can evaluate energy, a transverse beam size, and a divergence of an electron beam by measuring a spatial distribution of DR. Moreover, coherent diffraction radiation with the wavelength of less than millimeter range is used for a bunch length measurement. In this conference, a theoretical background of DR and experimental results carried out at several facilities will be presented.
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TUD03	First Results of the SRF Gun Test for CeC PoP Experiment	564
	I. Pinayev, Z. Altinbas, S.A. Belomestnykh, K.A. Brown, J.C. Brutus, A.J. Curcio, A. Di Lieto, C. Folz, D.M. Gassner, M. Harvey, J.P. Jamilkowski, Y.C. Jing, D. Kayran, R. Kellermann, R.F. Lambiase, V. Litvinenko, G.J. Mahler, M. Mapes, W. Meng, T.A. Miller, M.G. Minty, G. Narayan, P. Orfin, T. Rao, J. Reich, B. Sheehy, J. Skaritka, L. Smart, K.S. Smith, L. Snydstrup, V. Soria, R. Than, C. Theisen, J.E. Tuozzolo, E. Wang, G. Wang, B. P. Xiao, T. Xin, W. Xu, A. Zaltsman BNL, Upton, Long Island, New York, USA
	We have started the first tests of the equipment for the coherent electron cooling proof-of-principle experiment. After tests of the 500 MHz normal conducting cavities we proceeded with the low power beam tests of a CW SRF gun. The results of the tests with record beam parameters are presented.
	Slides TUD03 [1.201 MB]
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TUD04	Relative Bunch Length Measurements at MAX IV Linac
	F. Curbis, E. Mansten, D.F. Olsson, S. Thorin MAX-lab, Lund, Sweden
	The commission of the MAX IV linac recently started and among other features, some attention has been dedicated to the characterization of the bunch length compression. Instead of the most commonly used magnetic chicanes, in the MAX IV linac two double achromats can compress the photo-cathode beam from a few ps to hundred fs level. Since the linac is not yet equipped with dedicated diagnostics for absolute bunch measurements, we performed relative measurement of the bunch length. We take advantage of the transition radiation emitted by the bunch when crossing a ceramic gap discontinuity, which is situated after the bunch compressors. The signal is picked up by horn antennas and directed to diodes sensitive to different frequencies. In this contribution we show the first experimental results and the comparison with simulations of our specific geometry.
	Slides TUD04 [3.381 MB]
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WEP042	Commissioning and First Performance of the LINAC-based Injector Applied in the HUST THz-FEL	662
	T. Hu, Q.S. Chen, J. Li, B. Qin, P. Tan, Y.Q. Xiong HUST, Wuhan, People's Republic of China L. Cao, W. Chen Huazhong University of Science and Technology, State Key Laboratory of Advanced Electromagnetic Engineering and Technology,, Hubei, People's Republic of China Y.J. Pei, Zh. X. Tang USTC/NSRL, Hefei, Anhui, People's Republic of China
	The construction of a compact high-power THz source based on the free electron laser(FEL), which is constructed in HUST, is undergoing. Before the end of 2014, we have installed most of the key components, completed conditioning of the LINAC-based FEL injector, and performed first beam experiment. During last 5 months, we have established a high efficient beam diagnostic system with a reliable online monitor platform and precise data processing methods. At present, longitudinal properties such as the micro-pulse width and the energy spread are kept to a reasonable level, while transverse emittance compensation by adjusting focusing parameters is still undergoing. In this paper, we will give the summary on the commissioning schedule, detailed commissioning plan, the development of the commissioning and first performance of the LINAC, etc.
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WEP045	Study on Beam Modulation Technique using a Masked Chicane at FAST (Fermilab Accelerator Science and Technology) Facility	665
	Y.-M. Shin, D.R. Broemmelsiek, D.J. Crawford, A.H. Lumpkin Fermilab, Batavia, Illinois, USA A.T. Green Northern Illinois Univerity, Dekalb, Illinois, USA
	Funding: This work was supported by the DOE contract No. DEAC02-07CH11359 to the Fermi Research Alliance LLC. Longitudinal density modulations on electron beams can improve machine performance of beam-driven accelerators and FELs with resonance beam-wave coupling. The sub-ps beam modulation has been studied with a masked chicane by the analytic model and simulations with the beam parameters of the Advanced Superconducting Test Accelerator (ASTA) in Fermilab. With the chicane design parameters (bending angle of 18 degree, bending radius of 0.95 m and R56 ~ - 0.19 m) and a nominal beam of 3-ps bunch length, the analytic model showed that a slit-mask with slit period 900 microns and aperture width 300 microns generates about 100 microns modulation periodicity with 2.4% correlated energy spread. With the designed slit mask and a 3- ps bunch, particle-in-cell simulations (CST-PS), including nonlinear energy distributions, space charge force, and coherent synchrotron radiation (CSR) effect, also result in ~ 100 microns of longitudinal modulation. The beam modulation has been extensively examined with three different beam conditions, 2.25 ps (0.25 nC), 3.25 ps (1 nC), and 4.75 ps (3.2 nC), by extended 3D tracking simulations (Elegant). The modulated bunch generation will be tested by a slit-mask installed at the chicane of the ASTA 50-MeV-injector beamline for beam-driven acceleration experiments.
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WEP047	Femtosecond Timing Distribution at the European XFEL	669
	C. Sydlo, M.K. Czwalinna, M. Felber, C. Gerth, J.M. Müller, H. Schlarb, F. Zummack DESY, Hamburg, Germany S. Jabłoński Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
	Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. For time-resolved experiments and for special diagnostics it is crucial to synchronize various laser systems to the electron beam with a long-term stability of better than 10 fs. The upcoming European XFEL has raised the demands due to its large number of stabilized optical fibers and a length of 3400 m. Specifically the increased lengths for the stabilized fibers had necessitated major advancement in precision to achieve the requirement of less than 10 fs precision. This extensive rework of the active fiber stabilization has led to a system exceeding the current existing requirements and is even prepared for increasing demands in the future. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization for the European XFEL, discusses major complications, their solutions and the most recent performance results.
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WEP048	Electron Beam Diagnostics for FEL Studies at CLARA	672
	S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom D. Newton The University of Liverpool, Liverpool, United Kingdom
	CLARA (Compact Linear Accelerator for Research and Applications) is a proposed 250 MeV, 100-400 nm FEL test facility at Daresbury Laboratory [1]. The purpose of CLARA is to test and validate new FEL schemes in areas such as ultra-short pulse generation, temporal coherence and pulse-tailoring. Some of the schemes that can be tested at CLARA depend on a manipulation of the electron beam properties with characteristic scales shorter than the electron beam. In this article we describe the electron beam diagnostics required to carry on these experiments and simulations of FEL pulse and electron beam measurements. [1] J. A. Clarke et al., JINST 9, 05 (2014).
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Paper

Title

Page

Numerical Simulations of a Sub-THz Coherent Transition Radiation Source at PITZ

97

P. Boonpornprasert, M. Krasilnikov, F. Stephan
DESY Zeuthen, Zeuthen, Germany
B. Marchetti
DESY, Hamburg, Germany

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator can be considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments at the European XFEL. For this reason, the radiation generated by high-gain FEL and Coherent Transition Radiation (CTR) produced by the PITZ electron beam has been studied. In this paper, numerical simulations on the generation of CTR based on the PITZ accelerator are presented. The beam dynamics simulations of electron bunches compressed by velocity bunching are performed by using the ASTRA code. The characteristics of CTR are calculated numerically by using the generalized Ginzburg-Frank formula. The details and results of the simulations are described and discussed.

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MOP034

Beam Optics Measurements at FERMI by using Wire-Scanner

101

G. Penco, A. Abrami, I. Cudin, S. Di Mitri, M. Ferianis, E. Ferrari, G. Gaio, L. Giannessi, S. Grulja, R. Sauro, L. Sturari
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
E. Ferrari
Università degli Studi di Trieste, Trieste, Italy
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy
G.L. Orlandi, C. Ozkan Loch
PSI, Villigen PSI, Switzerland

Measuring and controlling the electron beam optics is an important ingredient to guarantee high performance of a free-electron laser. In the FERMI linac, the Twiss parameters and the transverse emittances are routinely measured by detecting the beam spot size as a function of a scanning quadrupole placed upstream (i.e. quadrupole scan method). The beam spot size is usually measured with an OTR screen that unfortunately suffers from coherent optical transition radiation (C-OTR) that introduces spurious light and corrupts the image. Moreover, the beam size at the end of the FERMI linac is focused to a few tens of microns and this makes it difficult to precisely measure it with the OTR system, which has an estimated resolution of 20um. For this reason, a wire-scanner system has been installed at the end of the linac just in the waist of the optics channel. The wire-scanner is a SwissFEL prototype installed in FERMI in order to study the hardware and beam loss monitor performances at the GeV energy scale. The beam optics measurements performed with the wire-scanner is here presented, and the obtained results are more in agreement with the theoretical expectations. A more reliable beam optics estimation at the end of the linac has allowed to better match it to the nominal lattice and transport it up to the undulator chain, providing important benefits to the FEL performance.

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MOP036

Femtosecond Synchronization of 80-MHz Ti:Sapphire Photocathode Laser Oscillator with S-Band RF Oscillator

105

H. Yang, C. Jeon, K. Jung, J. Kim
KAIST, Daejeon, Republic of Korea
H. Chung
Korea University Sejong Campus, Sejong, Republic of Korea
B. Han, Y.U. Jeong
KAERI, Daejon, Republic of Korea

Precision synchronization between lasers and RF sources in free-electron lasers (FELs) and ultrafast electron diffraction (UED) systems is becoming more important. There have been intense research and development toward femtosecond synchronization of lasers and RF sources in the last decade. Most of the previous approaches at large-scale FELs have used cw lasers or low-jitter mode-locked lasers at telecomm wavelength as the master oscillator and distributed the timing signals via stabilized fiber links. However, for smaller-scale FELs and UED, this approach may be a complex and high-cost method. In this work, we studied the possibility of using the commercial Ti:sapphire photocathode laser as the optical master oscillator as well. For its use in UED and FELs, we synchronized the 80-MHz Ti:sapphire photocathode laser oscillator to a 2.856-GHz RF source (used for RF-photogun) with 50-fs precision. Some interesting findings are following. First, intrinsic rms timing jitter of the used photocathode laser is 2.6 fs [10 kHz-10 MHz], which sets the fundamental limit in synchronization. Second, timing jitter in 100 Hz-1 kHz in photocathode laser is so severe (e.g., ~40 fs even feedback control is applied), so that it will require additional external-cavity control for achieving sub-10-fs precision. By addressing this issue, we are currently working toward 10-fs precision.

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MOP038

Stabilization of Magnetron Frequency for a Microtron-Driven FEL

107

B.A. Gudkov, S. Bae, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, S.V. Miginsky, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov
KAERI, Daejon, Republic of Korea
S.V. Miginsky, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

Under KAERI WCI program we develop a compact pulsed microtron-driven FEL. Electron bunches trains are accelerated in the microtron and transported by the beamline to the undulator. The RF cavity in the microtron is fed by a magnetron. Any accelerator driver for a FEL should provide an electron beam having very stable parameters such as electron energy, current, and especially the bunch repetition rate in a train. All mentioned parameters depend on magnetron current. It means that special attention should be paid for the shape of the current pulse, supplied to the magnetron from the modulator. We developed the modulator project with a computer control that will provide an arbitrary shape of the magnetron current. A simplified prototype was fabricated and tested. The methods of controlling of the pulse shape are considered. Simulation and experimental results are presented.

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MOP039

First Results of Commissioning of the PITZ Transverse Deflecting Structure

110

H. Huck, P. Boonpornprasert, A. Donat, J.D. Good, M. Groß, I.I. Isaev, L. Jachmann, D.K. Kalantaryan, M. Khojoyan, W. Köhler, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, M. Pohl, Y. Renier, T. Rublack, J. Schultze, F. Stephan, G. Trowitzsch, G. Vashchenko, R.W. Wenndorff, Q.T. Zhao
DESY Zeuthen, Zeuthen, Germany
G. Asova
INRNE, Sofia, Bulgaria
M. A. Bakr
Assiut University, Assiut, Egypt
D. Churanov, L.V. Kravchuk, V.V. Paramonov, I.V. Rybakov, A.A. Zavadtsev, D.A. Zavadtsev
RAS/INR, Moscow, Russia
C. Gerth, M. Hoffmann, M. Hüning
DESY, Hamburg, Germany
C. Hernandez-Garcia
JLab, Newport News, Virginia, USA
M.V. Lalayan, A.Yu. Smirnov, N.P. Sobenin
MEPhI, Moscow, Russia
O. Lishilin, G. Pathak
Uni HH, Hamburg, Germany

For successful operation of X-ray Free Electron Lasers, one crucial parameter is the ultrashort electron bunch length yielding a high peak current and a short saturation length. In order to effectively compress the bunches during the acceleration process, a detailed understanding of the full longitudinal phase space distribution already in the injector is required. Transverse deflecting RF structures (TDS) can shear the bunch transversely, mapping the longitudinal coordinate to a transverse axis on an observation screen downstream. In addition to the bunch length, the slice emittance along the bunch as well as the full longitudinal phase space can be obtained. At the Photo Injector Test Facility at DESY, Zeuthen site (PITZ), an S-band traveling wave TDS is under commissioning since 2015. This cavity is a prototype for the TDS in the injector part of the European XFEL and has been designed and manufactured by the Institute for Nuclear Research (INR, Moscow, Russia). In this paper, first commissioning results of the system at PITZ are presented and discussed.

Poster MOP039 [0.893 MB]

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MOP040

Implementation of MTCA.4-based Controls for the Pulsed Optical Synchronization Systems at DESY

115

M. Felber, Ł. Butkowski, M.K. Czwalinna, M. Fenner, C. Gerth, M. Heuer, E. Janas, M. Killenberg, T. Lamb, U. Mavrič, J.M. Müller, P. Peier, K.P. Przygoda, S. Ruzin, H. Schlarb, C. Sydlo, M. Titberidze, F. Zummack
DESY, Hamburg, Germany
T. Kozak, P. Prędki
TUL-DMCS, Łódź, Poland

Funding: This work has partly been funded by the Helmholtz Validation Fund Project MTCA.4 for Industry (HVF-0016)
With the current state of the synchronization system at FLASH (Free-electron Laser in Hamburg) the arrival time between electron bunches and optical laser pulses can be synchronized to a level of 30 fs rms, e.g. for pump-probe experiments. In the course of the development of an up-scaled system for the European XFEL and the migration of control hardware to the modern MTCA.4 (Micro Telecommunications Computing Architecture) platform, all involved components of the system will be replaced with new developments. The front-end devices are upgraded. FPGAs (Field Programmable Gate Arrays) are performing the data processing and feedback calculations. In order to facilitate the firmware development, a toolset (Rapid-X) was established which allows application engineers to develop, simulate, and generate their code without help from FPGA experts in a simple and efficient way. A software tool kit (MTCA4U) provides drivers and tools for direct register access e.g. via Matlab or Python and a control system adapter, which allows the server applications to be written control system independent. In this paper, an overview on the synchronization setups and their upgrades as well as an introduction to the new hardware is given. The Rapid-X and MTCA4U tool kits are presented followed by a status report on the implementation of the new developments.

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MOP041

Turbo-ICT Pico-Coulomb Calibration to Percent-level Accuracy

118

F. Stulle, J.F. Bergoz
BERGOZ Instrumentation, Saint Genis Pouilly, France

We report on the calibration methods implemented for the Turbo-ICT/BCM-RF. They allow to achieve percent-level accuracy for charge and current measurements. Starting from the Turbo-ICT/BCM-RF working principle, we discuss scientific fundaments of calibration and their practical implementation in a test bench. Limits, both principle and practical, are reviewed. Achievable accuracy is estimated.

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MOP042

All-Fiber Approach to Long-Term Stable Timing Distribution System

122

M. Xin, K. Safak, F.X. Kaernter
DESY, Hamburg, Germany
P.T. Callahan, M.Y. Peng
MIT, Cambridge, Massachusetts, USA

High precision timing distribution systems are critical for free-electron lasers (FELs). Real facilities such as FLASH and the European XFEL need fiber networks consisting of 20 or more timing links, which require tremendous attention to the alignment and stability of the free-space optics to minimize timing-drifts induced by beam pointing instabilities. This situation also necessitates preamplification of the master laser output to overcome excessive free-space to fiber coupling losses to provide adequate power for all timing links. Recently, we have developed integrated, fiber-coupled balanced optical cross-correlators (FC-BOC) using periodically-poled KTiOPO4 (PPKTP) waveguides. These waveguides exhibit second harmonic conversion efficiencies 20 times higher than the bulk optical devices, which will decrease the power demand from the master laser and consequently support more timing links. Furthermore, the robustness and ease of implementation of these fiber-coupled devices will eliminate alignment-related problems observed in free-space optics. In this paper, we present an all-fiber implementation of a 3.5-km timing distribution system using FC-BOCs, over 200 hours operation without interruption. The remaining drift (<1 Hz) is only 3.3 fs RMS, and the integrated jitter above 1 Hz is kept below 0.7 fs, which is more than sufficient for an efficient FEL synchronization.

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MOP043

Influence of Environment Changes on Libera Sync 3 Long-term Stability

126

S. Zorzut, M. Cargnelutti
I-Tech, Solkan, Slovenia
S. Hunziker
PSI, Villigen PSI, Switzerland

Libera Sync 3 can be used as a reference clock transfer system in the latest fourth generation light sources where the long-term stability is in the range of a few tens of femtoseconds of drift per day. The system has been developed in collaboration with the Paul Scherrer Institute (PSI) and first units are already tested in SwissFEL machine. In this article we present the influence of temperature and humidity changes on the long-term phase stability of the system.

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MOP044

A Laser Heater for CLARA

129

S. Spampinati
Cockcroft Institute, Warrington, Cheshire, United Kingdom
B.D. Muratori, N. Thompson, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

CLARA is a new FEL test facility, being developed at STFC Daresbury Laboratory in UK, based on a high brightness electron linac. The electron beam of CLARA can potentially be affected by the longitudinal microbunching instability leading to a degradation of the beam quality. The inclusion of a laser heater in the linac design can allow control of the microbunching instability, the study of microbunching and deliberate increase of the final energy spread to study energy spread requirements of the FEL schemes tested at CLARA. We present the initial design and layout of the laser heater system for CLARA and its expected performance.

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TUP043

PAL-XFEL Cavity BPM Prototype Beam Test at ITF

468

S.J. Lee, J.H. Han, H.-S. Kang, C. Kim, S.H. Kim, I.S. Ko, Y.J. Park, D.C. Shin
PAL, Pohang, Kyungbuk, Republic of Korea

To achieve sub-micrometer resolution, PAL-XFEL undulator section will use X-band Cavity beam position monitor (BPM) systems. The prototype cavity BPM pick-up was designed and fabricated to test the performance of the cavity BPM system. The fabricated prototype cavity BPM pick-up was installed at Pohang Accelerator Laboratory injector test facility (PAL ITF) for the beam test. Under 200 pC beam charge condition, the signal properties of the cavity BPM pick-up were measured. Also, the dynamic range of the cavity BPM pick-up was measured by using the corrector magnet. In this paper, the design and beam test results of the prototype cavity BPM pick-up will be discussed.

Poster TUP043 [0.695 MB]

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TUP044

Spark EL - Single Pass BPM

471

M. Žnidarčič
I-Tech, Solkan, Slovenia

Monitoring and subsequent optimization of the electron linacs and beam transfers requires specific instrumentation for beam position data acquisition and processing. Spark EL is the newly developed prototype intended for position monitoring in single or multi bunch operation linacs and transfer lines. The motivation, processing principles and first results are presented.

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TUP045

MTCA.4 Phase Detector for Femtosecond-Precision Laser Synchronization

474

E. Janas, M. Felber, M. Heuer, U. Mavrič, H. Schlarb
DESY, Hamburg, Germany
K. Czuba
Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland

For time-resolved experiments at FELs such as the European XFEL an accurate synchronization of the machine is essential. The required femtosecond- level synchronization we plan to achieve with an optical synchronization system, in which an inherent part is the master laser oscillator (MLO) locked to the electrical reference. At DESY we develop a custom rear transition module in MTCA.4 standard, which will allow for different techniques of phase detection between the optical and the electrical signal, as well as locking to an optical reference using a cross-correlator. In this paper we present the current status of the development, including two basic solutions for the detection to an RF. One of the methods incorporates an external drift free detector based on the so-called MZI setup. The other one employs the currently used downconverter scheme with subsequent improvements. The module can serve for locking a variety of lasers with different repetition rates.

Poster TUP045 [4.010 MB]

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TUP049

Prototype of the Improved Electro-Optical Unit for the Bunch Arrival Time Monitors at FLASH and the European XFEL

478

H. Dinter, M.K. Czwalinna, C. Gerth, K.P. Przygoda, R. Rybaniec, H. Schlarb, C. Sydlo
DESY, Hamburg, Germany

At today's free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems providing accurate timing stability for time-resolved pump-probe experiments and seeding schemes. At FLASH and the upcoming European XFEL a reliable and precise arrival time detection down to the femtosecond level has to cover a broad range of bunch charges, which may even change from 1 nC down to 20 pC within a bunch train. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultra-short laser pulses. At both facilities, the new bunch arrival time monitor has to cope with the special operation mode where the MHz repetition rate bunch train is separated into several segments for different SASE beam lines. Each of the segments will exhibit individual timing jitter characteristics since they are generated from different injector lasers and can be accelerated with individual energy gain settings. In this paper, we describe the recent improvements of the electro-optical unit developed for the bunch arrival time monitors to be installed in both facilities.

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TUP050

Extension of Existing Pulse Analysis Methods to High-Repetition Rate Operation: Studies of the "Time-Stretch Strategy"

483

S. Bielawski
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
J.B. Brubach, L. Cassinari, M.-E. Couprie, M. Labat, L. Manceron, J.P. Ricaud, P. Roy, M.-A. Tordeux
SOLEIL, Gif-sur-Yvette, France
C. Evain, C. Szwaj
PhLAM/CERLA, Villeneuve d'Ascq, France
M. Le Parquier
CERLA, Villeneuve d'Ascq, France
E. Roussel
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Funding: ANR (2010-042301, DYNACO), LABEX CEMPI project (ANR-11-LABX-0007), ERC grant COXINEL (340015), GENCI TGCC/IDRIS (x2014057057,i2015057057).
Many single-shot recording setups are based on the encoding of the information onto a laser pulse. This concerns in particular electro-optic sampling of bunch shapes, and VUV/X pulse monitors using transient reflectivity. The upgrade of these methods to high repetition rates presents challenging issues, that are due to the limited speed of the recording cameras. Recently [1], we demonstrated that multi-MHz repetition rates can be achieved using a relatively simple upgrade of existing setups, using the so-called "photonic time-stretch" technique. Here we present guidelines for the practical realization in the case of electro-optic sampling. We also present a performance analysis, and compare it to the spectral encoding case. The technique is potentially applicable to other cases where the information can be encoded on a chirped laser pulse, as, e.g., transient reflectivity diagnostics of XUV pulses.
[1] Observing microscopic structures of a relativistic object using a time-stretch strategy, E. Roussel, C. Evain, M. Le Parquier, C. Szwaj, S. Bielawski, L. Manceron, J.-B. Brubach, M.-A. Tordeux, J.-P. Ricaud, L. Cassinari, M. Labat, M.-E Couprie, and P. Roy, Scientific Reports 5, 10330 (2015).

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TUD01

COTR Resistant Profile Monitor

554

H. Loos
SLAC, Menlo Park, California, USA

Funding: Work supported by DOE contract DE-AC02-76SF00515
Electron beam accelerators used as drivers for short wavelength FELs need ultra-high brightness beams with small emittances and highly compressed bunch lengths. The acceleration and beam transport process of such beams leads to micro-bunching instabilities which cause the emergence of coherent optical transition radiation (COTR). The effect of COTR on profile monitors based on OTR or fluorescent screens can be quite detrimental to their intended use to measure beam sizes and profiles. This presentation will review past observations of the beam diagnostics issues due to COTR and discuss various mitigation schemes for profile monitors as well as present experience with such implementations.

Slides TUD01 [1.536 MB]

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TUD02

Diffraction Radiation Monitor

561

Y. Taira
AIST, Tsukuba, Japan

Non-invasive beam diagnostics using a diffraction radiation (DR) has been developed at several electron accelerator facilities. Generation process of DR is similar to that of transition radiation (TR). TR is emitted when a charged particle passes through the boundary between two media with different dielectric constants. On the other hand, DR is emitted when it passes through in the vicinity of a boundary between two media. In the generation process of DR, the charged particle doesn't intersect the medium but its electric field intersects the medium. An aperture, a slit, and an edge are used for DR target. Optical wavelength of DR is usually used for beam diagnostics. One can evaluate energy, a transverse beam size, and a divergence of an electron beam by measuring a spatial distribution of DR. Moreover, coherent diffraction radiation with the wavelength of less than millimeter range is used for a bunch length measurement. In this conference, a theoretical background of DR and experimental results carried out at several facilities will be presented.

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TUD03

First Results of the SRF Gun Test for CeC PoP Experiment

564

I. Pinayev, Z. Altinbas, S.A. Belomestnykh, K.A. Brown, J.C. Brutus, A.J. Curcio, A. Di Lieto, C. Folz, D.M. Gassner, M. Harvey, J.P. Jamilkowski, Y.C. Jing, D. Kayran, R. Kellermann, R.F. Lambiase, V. Litvinenko, G.J. Mahler, M. Mapes, W. Meng, T.A. Miller, M.G. Minty, G. Narayan, P. Orfin, T. Rao, J. Reich, B. Sheehy, J. Skaritka, L. Smart, K.S. Smith, L. Snydstrup, V. Soria, R. Than, C. Theisen, J.E. Tuozzolo, E. Wang, G. Wang, B. P. Xiao, T. Xin, W. Xu, A. Zaltsman
BNL, Upton, Long Island, New York, USA

We have started the first tests of the equipment for the coherent electron cooling proof-of-principle experiment. After tests of the 500 MHz normal conducting cavities we proceeded with the low power beam tests of a CW SRF gun. The results of the tests with record beam parameters are presented.

Slides TUD03 [1.201 MB]

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TUD04

Relative Bunch Length Measurements at MAX IV Linac

F. Curbis, E. Mansten, D.F. Olsson, S. Thorin
MAX-lab, Lund, Sweden

The commission of the MAX IV linac recently started and among other features, some attention has been dedicated to the characterization of the bunch length compression. Instead of the most commonly used magnetic chicanes, in the MAX IV linac two double achromats can compress the photo-cathode beam from a few ps to hundred fs level. Since the linac is not yet equipped with dedicated diagnostics for absolute bunch measurements, we performed relative measurement of the bunch length. We take advantage of the transition radiation emitted by the bunch when crossing a ceramic gap discontinuity, which is situated after the bunch compressors. The signal is picked up by horn antennas and directed to diodes sensitive to different frequencies. In this contribution we show the first experimental results and the comparison with simulations of our specific geometry.

Slides TUD04 [3.381 MB]

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WEP042

Commissioning and First Performance of the LINAC-based Injector Applied in the HUST THz-FEL

662

T. Hu, Q.S. Chen, J. Li, B. Qin, P. Tan, Y.Q. Xiong
HUST, Wuhan, People's Republic of China
L. Cao, W. Chen
Huazhong University of Science and Technology, State Key Laboratory of Advanced Electromagnetic Engineering and Technology,, Hubei, People's Republic of China
Y.J. Pei, Zh. X. Tang
USTC/NSRL, Hefei, Anhui, People's Republic of China

The construction of a compact high-power THz source based on the free electron laser(FEL), which is constructed in HUST, is undergoing. Before the end of 2014, we have installed most of the key components, completed conditioning of the LINAC-based FEL injector, and performed first beam experiment. During last 5 months, we have established a high efficient beam diagnostic system with a reliable online monitor platform and precise data processing methods. At present, longitudinal properties such as the micro-pulse width and the energy spread are kept to a reasonable level, while transverse emittance compensation by adjusting focusing parameters is still undergoing. In this paper, we will give the summary on the commissioning schedule, detailed commissioning plan, the development of the commissioning and first performance of the LINAC, etc.

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WEP045

Study on Beam Modulation Technique using a Masked Chicane at FAST (Fermilab Accelerator Science and Technology) Facility

665

Y.-M. Shin, D.R. Broemmelsiek, D.J. Crawford, A.H. Lumpkin
Fermilab, Batavia, Illinois, USA
A.T. Green
Northern Illinois Univerity, Dekalb, Illinois, USA

Funding: This work was supported by the DOE contract No. DEAC02-07CH11359 to the Fermi Research Alliance LLC.
Longitudinal density modulations on electron beams can improve machine performance of beam-driven accelerators and FELs with resonance beam-wave coupling. The sub-ps beam modulation has been studied with a masked chicane by the analytic model and simulations with the beam parameters of the Advanced Superconducting Test Accelerator (ASTA) in Fermilab. With the chicane design parameters (bending angle of 18 degree, bending radius of 0.95 m and R56 ~ - 0.19 m) and a nominal beam of 3-ps bunch length, the analytic model showed that a slit-mask with slit period 900 microns and aperture width 300 microns generates about 100 microns modulation periodicity with 2.4% correlated energy spread. With the designed slit mask and a 3- ps bunch, particle-in-cell simulations (CST-PS), including nonlinear energy distributions, space charge force, and coherent synchrotron radiation (CSR) effect, also result in ~ 100 microns of longitudinal modulation. The beam modulation has been extensively examined with three different beam conditions, 2.25 ps (0.25 nC), 3.25 ps (1 nC), and 4.75 ps (3.2 nC), by extended 3D tracking simulations (Elegant). The modulated bunch generation will be tested by a slit-mask installed at the chicane of the ASTA 50-MeV-injector beamline for beam-driven acceleration experiments.

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WEP047

Femtosecond Timing Distribution at the European XFEL

669

C. Sydlo, M.K. Czwalinna, M. Felber, C. Gerth, J.M. Müller, H. Schlarb, F. Zummack
DESY, Hamburg, Germany
S. Jabłoński
Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland

Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. For time-resolved experiments and for special diagnostics it is crucial to synchronize various laser systems to the electron beam with a long-term stability of better than 10 fs. The upcoming European XFEL has raised the demands due to its large number of stabilized optical fibers and a length of 3400 m. Specifically the increased lengths for the stabilized fibers had necessitated major advancement in precision to achieve the requirement of less than 10 fs precision. This extensive rework of the active fiber stabilization has led to a system exceeding the current existing requirements and is even prepared for increasing demands in the future. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization for the European XFEL, discusses major complications, their solutions and the most recent performance results.

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WEP048

Electron Beam Diagnostics for FEL Studies at CLARA

672

S. Spampinati
Cockcroft Institute, Warrington, Cheshire, United Kingdom
D. Newton
The University of Liverpool, Liverpool, United Kingdom

CLARA (Compact Linear Accelerator for Research and Applications) is a proposed 250 MeV, 100-400 nm FEL test facility at Daresbury Laboratory [1]. The purpose of CLARA is to test and validate new FEL schemes in areas such as ultra-short pulse generation, temporal coherence and pulse-tailoring. Some of the schemes that can be tested at CLARA depend on a manipulation of the electron beam properties with characteristic scales shorter than the electron beam. In this article we describe the electron beam diagnostics required to carry on these experiments and simulations of FEL pulse and electron beam measurements.
[1] J. A. Clarke et al., JINST 9, 05 (2014).

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