FEL2017 - Classification: Undulators, Photon Diagnostics, Beamline

Paper	Title	Page
WEC01	Photon Beam Transport and Diagnostics Systems at an EUV FEL Facility: General Considerations, and Specific Challenges, Solutions and Developments at the FERMI Seeded FEL
	M. Zangrando Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	After the start of FLASH user operations in 2005, the possibility of performing user experiments at an EUV free electron laser source became reality. This kind of opportunity was extended in 2012 when the Italian FERMI seeded-FEL user facility started its user program. As a consequence, for such light sources new photon transport and diagnostic solutions were designed, developed, and implemented. A brief general overview about these issues will be introduced, together with a more detailed presentation of challenges faced and solutions found at the FERMI FEL. In particular, different instruments were developed in order to meet machine and endstation users' requirements concerning online non-invasive spectral content determination, pulse length and intensity characterization/control, active modification of the focusing properties, etc. Some examples and results will be presented, possibly comparing them to what was done elsewhere. Possible future implementations in photon-beam manipulation and characterisation will also be discussed.
	Slides WEC01 [45.346 MB]
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WEC02	Optimization of Superconducting Undulators for Low Repetition Rate FELs	411
	J.A. Clarke, K.B. Marinov, B.J.A. Shepherd, N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom V. Bayliss, J. Boehm, T.W. Bradshaw, A.J. Brummitt, S.J. Canfer, M.J.D. Courthold, B. Green, T. Hayler, P. Jeffery, C. Lockett, D.S. Wilsher STFC/RAL, Chilton, Didcot, Oxon, United Kingdom S. Milward, E.C.M. Rial DLS, Oxfordshire, United Kingdom
	Superconducting undulators (SCUs) optimized for storage rings and MHz-level FELs require an intermediate beam screen to intercept the power deposited by the electron beam, due to resistive wall wakefields, to prevent magnet quenching. This beam screen increases the magnet gap by around 2 mm which is a significant increase when compared to the typical electron beam aperture of around 5 mm. However, lower repetition rate FELs only deposit of the order of tens of mW/m and so the beam screen is no longer needed resulting in a significant reduction in undulator magnet gap. We have investigated the impact of this reduced magnet gap and found that the magnetic field level increases greatly. For example, an SCU with a 15 mm period and 5 mm aperture optimized for a low repetition rate FEL instead of a storage ring will generate a field of 2.1 T compared to 1.4 T. Such a major increase in undulator performance could have a significant impact on the optimization of FELs. This paper describes how an SCU optimized for application in a FEL will be able to generate magnetic field levels far beyond those currently foreseen for any other magnet technology.
	Slides WEC02 [6.234 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEC02
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WEC03	Wavefront Preserving Optics for the LCLS Photon Transport System
	D. Cocco, C.L. Hardin, D.S. Morton, P. Stefan SLAC, Menlo Park, California, USA J. Nicolás ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
	The Linac Coherent Light Source (LCLS) is upgrading to a High Repetition Rate mode and to a higher quality of the wavefront. This poses extreme challenges to the optical components. A new approach to beamline design is needed, starting from a new way to assess the effect of slope and shape errors, to taking into account any potential source of distortion. Among the technical novelties the LCLS optics team is introducing, the most important are: a novel cooling scheme to maintain the mirror shape within 0.5 nm rms under heat load, the study of the effect of the cooling interface to the mirror surface, and new diagnostic systems. Ultra-flat mirrors with novel holder mechanisms have been recently installed. First results, showing the improvement of the beam quality, are expected in mid-June 2017. A controlled cleaning process to remove, in situ, carbonaceous contamination from carbon-based coatings will also be presented. It has been successfully implemented in the SXR mirrors. All the above tests and studies will be presented, as well as the effect seen on a six-year old mirror exposed to FEL for its entire lifetime.
	Slides WEC03 [32.902 MB]
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WEC04	Progress of PAL-XFEL Undulator Program
	D.E. Kim, H.-S. Kang, K.-H. Park PAL, Pohang, Kyungbuk, Republic of Korea I.S. Ko POSTECH, Pohang, Kyungbuk, Republic of Korea
	Pohang Accelerator Laboratory (PAL) recently commissioned and started early user service of 0.1 nm SASE-based FEL based on the 10 GeV S-band linear accelerator named PAL-XFEL. One of the key components of the PAL-XFEL is the undulator system which consists of 20 units of Hard X-ray undulators, and 7 units Soft X-ray FELs. The basic design concept is based on the EU-XFEL undulator, but it also requires modification reflecting PAL-XFEL requirements. In this report, PAL efforts to modify, re-design, manufacture, take measurements, tune, install, and commission the undulator system will be summarized.
	Slides WEC04 [2.697 MB]
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WEC05	Radiation-Induced Magnetization Reversal Causing a Large Flux Loss in Undulator Permanent Magnets
	R. Kinjo, Y. Asano, T. Hara, T. Hasegawa, Y. Kida, T. Tanaka RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan T. Bizen, T. Itoga, A. Kagamihata, T. Seike, T. Watanabe JASRI/SPring-8, Hyogo, Japan
	A large degradation of undulator field up to 35 percent was observed at the entrance of the in-vacuum undulators in SACLA;　although this may be because of the radiation-induced demagnetization, it is much larger than what is expected from the former irradiation experiments. From the measurement of the surface field profile of individual permanent magnets (PMs) and the numerical calculations, we found that not the demagnetization but the magnetization reversal in small areas of the magnets is the reason of the large degradation of the undulator field. Numerical and experimental studies suggest that the magnetization reversal is a highly nonlinear process with respect to the reverse field in the PM, which is applied to the PM in the hybrid array. The experimental study also shows that a　10-cm stainless steel block placed just in front of the PMs significantly impedes the progress of the magnetization reversal, which suggests a simple and effective method to improve the lifetime of in-vacuum undulators.* * T. Bizen et al., Scientific Reports 6, 37937 (2016).
	Slides WEC05 [1.950 MB]
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WEP051	Helical Undulators for Coherent Electron Cooling System	519
	I. Pinayev, Y.C. Jing, R. Kellermann, V. Litvinenko, J. Skaritka, G. Wang BNL, Upton, Long Island, New York, USA I.V. Ilyin, Y. Kolokolnikov, P. Vobly BINP SB RAS, Novosibirsk, Russia
	Funding: DoE NP office, grant DE-FOA-0000632 In this paper we present the description and results of the magnetic measurements and tuning of helical undulators for the Coherent electron Cooling system (CeC). The FEL section of the CeC comprises three 2.5-m long undulators separated by 40-cm drift sections, where BPMs and phase-adjusting 3-pole wigglers are located. We present design, tuning techniques and achieved parameters of this system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP051
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WEP054	The Magnetic Field Integral Hysteresis on the European XFEL Gap Movable Undulator Systems	522
	F. Wolff-Fabris, Y. Li, J. Pflüger XFEL. EU, Schenefeld, Germany
	The European XFEL GmbH is a new X-ray FEL facility expected to be lasing to users at the end of 2017. Three gap-movable SASE Undulator Systems are designed to produce FELs with tunable wavelengths from 0.05 to 5.2nm.,* A total of 91 5m long undulator segments and phase shifters were magnetically tuned respecting tight specifications. Magnetic field hysteresis effects due to the gap shift of the Undulator System while changing the FEL radiation wavelength may impact the machine's operational mode. We report on these effects by either opening or closing the gap while performing field integrals measurements with moving wire technique. The undulator segments show negligible magnetic hysteresis and are expected to be operated with no influence to the FEL and beam trajectories in either feed forward or feed backward mode. The phase shifters show first field integrals hysteretic behavior of few G.cm which is comparable in magnitude to the allowed total field integrals and can be associated to the magnetization of the yoke structure. Phase shifters are magnetically tuned for that the feed forward mode (opening gap) fully satisfies the XFEL. EU magnetic specifications for beam operation. * M. Altarelli et al., Technical Design Rep. DESY 2006-097, July 2007. ** E. Schneidmiller et al., European XFEL Technical Rep. TR-2011-006, Sep. 2011.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP054
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WEP055	Tapered Flying Radiofrequency Undulator	525
	S.V. Kuzikov, A.V. Savilov, A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia S.P. Antipov, A. Liu Euclid TechLabs, LLC, Solon, Ohio, USA A.V. Savilov UNN, Nizhny Novgorod, Russia
	Funding: This project is supported by DoE Small Business Innovative Research phase I grant #DE-SC0017145. We propose an efficient XFEL consisting of sequential RF undulator sections using: 1) tapered flying RF undulators, 2) short pulse, high peak-power RF and 3) driving undulator sections by spent electron beam. In a flying RF undulator, an electron bunch propagates through a high-power, nanosecond, co-propagating RF pulse. Helical waveguide corrugation supports a space harmonic with a negative propagation constant, providing a large Doppler up-shift. The undulator tapering technique improves FEL efficiency by 1-2 orders of magnitude in comparison with other facilities by decreasing the undulator period so that particles are trapped in the combined field of the incident x-ray and undulator field. We develop a so-called non-resonant trapping regime not requiring phase locking for feeding RF sources. Simulations show that by decreasing the corrugation periodicity one can vary an equivalent undulator period by 15%. The spent electron beam can be used to produce wakefields that will drive the RF undulator sections for interaction with the following beam. We have already manufactured and tested the 30 GHz simplified version of the 50 cm long undulator section for cold measurements.
	Poster WEP055 [1.565 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP055
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WEP056	Effect of Beam Transverse Angle Deflection in TGU on FEL Power	529
	G. Zhou, J.Q. Wang IHEP, Beijing, People's Republic of China J. Wu SLAC, Menlo Park, California, 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. Recent study shows that electron beams with constant dispersion together with the transverse-gradient undulator (TGU) can reduce the sensitivity to energy spread for free-electron laser (FEL). By inducing dispersion function, electrons with different energy are placed at different positions corresponding to proper magnetic fields. Thus, FEL resonant condition can be kept for electrons with different energy. In this paper, we mainly studied: 1.The effects of electron beam angle deflection at the entrance of the TGU on the radiation power. 2. The utility of a kicker to introduce an angle deflection of electron beam to improve the FEL radiation power.
	Poster WEP056 [0.638 MB]
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WEP057	Design of a Compact Hybrid Undulator for the THz Radiation Facility of Delhi Light Source (DLS)	532
	S. Tripathi, R.K. Bhandari, S. Ghosh, D. Kanjilal IUAC, New Delhi, India U. Lehnert HZDR, Dresden, Germany M. Tischer DESY, Hamburg, Germany
	Funding: One author, Sumit Tripathi (PH/16-17/0029), would like to acknowledge University Grant Commission (UGC), New Delhi, India for financial support as D.S.Kothari Postdoctoral fellowship. A compact Free Electron Laser (FEL) facility to produce coherent THz radiation is in the development stage at Inter-University Accelerator Centre (IUAC), New Delhi, India.,* The name of this facility is Delhi Light Source (DLS) in which a low-emittance electron beam from a photocathode RF gun with a maximum energy of 8 MeV will be injected into a compact undulator magnet to generate THz radiation. To produce the THz radiation in the range of 0.15 to 3.0 THz, the electron beam energy and the undulator gap need to be varied from 4 to 8 MeV and 20 to 45 mm, respectively. The variable gap undulator of 1.5-m length will consist of NdFeB magnets with vanadium permendur poles. The magnet design and dimensions are optimised by using code 3D RADIA.*** The detailed design of the compact hybrid undulator will be presented in this paper. * S.Ghosh et al., presented at this conference. S.Ghosh et al., NIMB-2017 (in press). * RADIA. Available at http://www.esrf.eu/Accelerators/ groups/ Insertion Devices/ Software/ Radia.
	Poster WEP057 [1.117 MB]
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WEP060	Characterizing Sub-Femtosecond X-ray Pulses from the Linac Coherent Light Source	535
	S. Li, R.N. Coffee, J. Cryan, K.H. Hegazy, Z. Huang, A. Marinelli, A. Natan, T. Osipov, D. Ray SLAC, Menlo Park, California, USA G. Guo Stanford University, Stanford, California, USA
	The development of sub-femtosecond x-ray capabilities at the Linac Coherent Light Source requires the implementation of time-domain diagnostics with attosecond (as) time resolution. Photoelectrons created by attosecond duration x-ray pulses in the presence of a strong-laser field are known to suffer an energy spread which depends on the relative phase of the strong-laser field at the time of ionization. This phenomenon can be exploited to measure the duration of these ultrashort x-ray pulses. We present an implementation which employs a circularly polarized infrared laser pulse and novel velocity map imaging design which maps the phase dependent momentum of the photoelectron onto a 2-D detector. In this paper, we present the novel co-linear VMI design, simulation of the photoelectron momentum distribution, and the reconstruction algorithm.
	Poster WEP060 [1.260 MB]
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WEP061	Thermal Stress Analysis of a Thin Diamond Crystal Under Repeated Free Electron Laser Heat Load	539
	J. Wu SLAC, Menlo Park, California, USA B. Yang University of Texas at Arlington, Arlington, 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. Thin crystals are used in many important optical elements, such as monochromator and spectrometer, in XFELs. To function properly, they must survive the ever-increasing heat load under repeated pulses. Here, we conduct a thermal stress analysis to examine the crystal lattice distortion due to the thermal load under various rep rates from 0.1 to 1 MHz. The thermal field is obtained by solving the transient heat transfer equations. The temperature-dependent material properties are used. It is shown that for pulse adsorption energy around tens of microjoule over a spot size of 10 micrometer, the thermal response of diamond is sensitive to rep rate. The thermal strain components are very different in the in- and out-of-plane directions, due to different constraint conditions. It suggests complicated strain effects in the Bragg and Laue diffraction cases.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP061
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WEP062	Optical Beam Quality Analysis of the Clara Test Facility Using Second Moment Analysis	543
	H.M. Castaneda Cortes, D.J. Dunning, M.D. Roper, N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	We studied and characterised the FEL optical radiation in simulations of the CLARA FEL test facility under development at Daresbury Laboratory in the UK. In particular, we determined the optical beam quality coefficient, waist position and other source properties corresponding to different potential FEL operating modes via wavefront propagation in free space using OPC (Optical Propagation Code) and Second Moment Analysis. We were able to find the operation mode and undulator design for which the optical beam has the optimum quality at highest brightness. Furthermore, we studied the way that different properties of the electron bunches (emittance, peak current, bunch length) affect the optical beam. We are now able to understand how the optical beam will propagate from the end of the undulator and through the photon transport system to the experimental stations. This knowledge is necessary for the correct design of the photon transport and diagnostic systems.
	Poster WEP062 [0.495 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP062
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WEP063	A Two-in-One Type Undulator	547
	D. Wang, H.X. Deng, Z. Jiang SINAP, Shanghai, People's Republic of China
	Funding: This work is supported by the Ministry of Science and Technology of China. The typical X-ray free electron lasers have long tunnels to accommodate high energy electron linear accelerator and long undulator line to produce intense coherent radiations at very short wavelengths. The number of undulator lines is limited by the available space in the tunnel. This is especially true for those facilities that adopt underground tunnels or utilize the existing tunnels originally built for other purpose. This work explored the possibility to better use the tunnel space for accommodating more FEL undulator lines by designing a new type of undulator structure.
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WEP064	Tunable High-Gradient Quadrupoles for a Laser-Plasma Acceleration-Based FEL	550
	A. Ghaith, F. Blache, M.-E. Couprie, C.A. Kitegi, F. Marteau, P. N'gotta, M. Valléau, J. Vétéran SOLEIL, Gif-sur-Yvette, France C. Benabderrahmane ESRF, Grenoble, France O. Cosson, F. Forest, P. Jivkov, J.L. Lancelot Sigmaphi, Vannes, France
	The magnetic design and characterization of tunable high gradient permanent magnet based quadrupole, are presented. To achieve a high gradient field with a compact structure, permanent magnets are chosen rather than usual electro-magnets due to their small aperture. The quadrupole structure consists of two quadrupoles superimposed capable of generating a gradient of 210 T/m. The first quadrupole is composed of permanent magnets following a Halbach configuration shaped as a ring attaining a constant gradient of 160T/m, and the second of four permanent magnet cylinders surrounding the ring and capable of rotating around their axis to achieve a gradient tunability of ±50 T/m. Each tuning magnet is connected to a motor and is controlled independently, enabling the gradient to be tuned with a rather good magnetic center stability (±20 μm) and without any field asymmetry. Seven quadrupoles have been built with different magnetic lengths in order to fulfil the integrated gradient required. A set of QUAPEVA triplet are now in use, to focus a high divergent electron beam with large energy spread generated by a laser plasma acceleration source for a free electron laser application.
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WEP065	Cryogenic Permanent Magnet Undulator for an FEL Application	554
	A. Ghaith, T. André, I.A. Andriyash, P. Berteaud, F. Briquez, N. Béchu, M.-E. Couprie, C. Herbeaux, M. Labat, O. Marcouillé, F. Marteau, E. Roussel, M. Sebdaoui, K.T. Tavakoli, M. Tilmont, M. Valléau SOLEIL, Gif-sur-Yvette, France
	A Cryogenic Permanent Magnet Undulator (CMPU) is capable of achieving high brightness radiation at short wavelengths, by taking advantage of the permanent magnets' enhanced performance at low temperature. A CPMU of period 18 mm (U18) that has been built at Synchrotron SOLEIL is used for the COXINEL project to demonstrate Free Electron Laser (FEL) at 200 nm using a laser plasma acceleration source. Another undulator of period 15 mm (U15) is currently being built to replace U18 undulator for FEL demonstration at 40 nm. A new method is also introduced, using SRWE code, to compute the spectra of the large energy spread beam (few percent) taking into account the variation of the Twiss parameters for each energy slice. The construction of U18 undulator and the magnetic measurements needed for optimization, as well as the mechanical design of U15, are presented.
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Paper

Title

Page

WEC01

Photon Beam Transport and Diagnostics Systems at an EUV FEL Facility: General Considerations, and Specific Challenges, Solutions and Developments at the FERMI Seeded FEL

M. Zangrando
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

After the start of FLASH user operations in 2005, the possibility of performing user experiments at an EUV free electron laser source became reality. This kind of opportunity was extended in 2012 when the Italian FERMI seeded-FEL user facility started its user program. As a consequence, for such light sources new photon transport and diagnostic solutions were designed, developed, and implemented. A brief general overview about these issues will be introduced, together with a more detailed presentation of challenges faced and solutions found at the FERMI FEL. In particular, different instruments were developed in order to meet machine and endstation users' requirements concerning online non-invasive spectral content determination, pulse length and intensity characterization/control, active modification of the focusing properties, etc. Some examples and results will be presented, possibly comparing them to what was done elsewhere. Possible future implementations in photon-beam manipulation and characterisation will also be discussed.

Slides WEC01 [45.346 MB]

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WEC02

Optimization of Superconducting Undulators for Low Repetition Rate FELs

411

J.A. Clarke, K.B. Marinov, B.J.A. Shepherd, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
V. Bayliss, J. Boehm, T.W. Bradshaw, A.J. Brummitt, S.J. Canfer, M.J.D. Courthold, B. Green, T. Hayler, P. Jeffery, C. Lockett, D.S. Wilsher
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
S. Milward, E.C.M. Rial
DLS, Oxfordshire, United Kingdom

Superconducting undulators (SCUs) optimized for storage rings and MHz-level FELs require an intermediate beam screen to intercept the power deposited by the electron beam, due to resistive wall wakefields, to prevent magnet quenching. This beam screen increases the magnet gap by around 2 mm which is a significant increase when compared to the typical electron beam aperture of around 5 mm. However, lower repetition rate FELs only deposit of the order of tens of mW/m and so the beam screen is no longer needed resulting in a significant reduction in undulator magnet gap. We have investigated the impact of this reduced magnet gap and found that the magnetic field level increases greatly. For example, an SCU with a 15 mm period and 5 mm aperture optimized for a low repetition rate FEL instead of a storage ring will generate a field of 2.1 T compared to 1.4 T. Such a major increase in undulator performance could have a significant impact on the optimization of FELs. This paper describes how an SCU optimized for application in a FEL will be able to generate magnetic field levels far beyond those currently foreseen for any other magnet technology.

Slides WEC02 [6.234 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEC02

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WEC03

Wavefront Preserving Optics for the LCLS Photon Transport System

D. Cocco, C.L. Hardin, D.S. Morton, P. Stefan
SLAC, Menlo Park, California, USA
J. Nicolás
ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain

The Linac Coherent Light Source (LCLS) is upgrading to a High Repetition Rate mode and to a higher quality of the wavefront. This poses extreme challenges to the optical components. A new approach to beamline design is needed, starting from a new way to assess the effect of slope and shape errors, to taking into account any potential source of distortion. Among the technical novelties the LCLS optics team is introducing, the most important are: a novel cooling scheme to maintain the mirror shape within 0.5 nm rms under heat load, the study of the effect of the cooling interface to the mirror surface, and new diagnostic systems. Ultra-flat mirrors with novel holder mechanisms have been recently installed. First results, showing the improvement of the beam quality, are expected in mid-June 2017. A controlled cleaning process to remove, in situ, carbonaceous contamination from carbon-based coatings will also be presented. It has been successfully implemented in the SXR mirrors. All the above tests and studies will be presented, as well as the effect seen on a six-year old mirror exposed to FEL for its entire lifetime.

Slides WEC03 [32.902 MB]

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WEC04

Progress of PAL-XFEL Undulator Program

D.E. Kim, H.-S. Kang, K.-H. Park
PAL, Pohang, Kyungbuk, Republic of Korea
I.S. Ko
POSTECH, Pohang, Kyungbuk, Republic of Korea

Pohang Accelerator Laboratory (PAL) recently commissioned and started early user service of 0.1 nm SASE-based FEL based on the 10 GeV S-band linear accelerator named PAL-XFEL. One of the key components of the PAL-XFEL is the undulator system which consists of 20 units of Hard X-ray undulators, and 7 units Soft X-ray FELs. The basic design concept is based on the EU-XFEL undulator, but it also requires modification reflecting PAL-XFEL requirements. In this report, PAL efforts to modify, re-design, manufacture, take measurements, tune, install, and commission the undulator system will be summarized.

Slides WEC04 [2.697 MB]

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WEC05

Radiation-Induced Magnetization Reversal Causing a Large Flux Loss in Undulator Permanent Magnets

R. Kinjo, Y. Asano, T. Hara, T. Hasegawa, Y. Kida, T. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
T. Bizen, T. Itoga, A. Kagamihata, T. Seike, T. Watanabe
JASRI/SPring-8, Hyogo, Japan

A large degradation of undulator field up to 35 percent was observed at the entrance of the in-vacuum undulators in SACLA;　although this may be because of the radiation-induced demagnetization, it is much larger than what is expected from the former irradiation experiments. From the measurement of the surface field profile of individual permanent magnets (PMs) and the numerical calculations, we found that not the demagnetization but the magnetization reversal in small areas of the magnets is the reason of the large degradation of the undulator field. Numerical and experimental studies suggest that the magnetization reversal is a highly nonlinear process with respect to the reverse field in the PM, which is applied to the PM in the hybrid array. The experimental study also shows that a　10-cm stainless steel block placed just in front of the PMs significantly impedes the progress of the magnetization reversal, which suggests a simple and effective method to improve the lifetime of in-vacuum undulators.*
* T. Bizen et al., Scientific Reports 6, 37937 (2016).

Slides WEC05 [1.950 MB]

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WEP051

Helical Undulators for Coherent Electron Cooling System

519

I. Pinayev, Y.C. Jing, R. Kellermann, V. Litvinenko, J. Skaritka, G. Wang
BNL, Upton, Long Island, New York, USA
I.V. Ilyin, Y. Kolokolnikov, P. Vobly
BINP SB RAS, Novosibirsk, Russia

Funding: DoE NP office, grant DE-FOA-0000632
In this paper we present the description and results of the magnetic measurements and tuning of helical undulators for the Coherent electron Cooling system (CeC). The FEL section of the CeC comprises three 2.5-m long undulators separated by 40-cm drift sections, where BPMs and phase-adjusting 3-pole wigglers are located. We present design, tuning techniques and achieved parameters of this system.

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WEP054

The Magnetic Field Integral Hysteresis on the European XFEL Gap Movable Undulator Systems

522

F. Wolff-Fabris, Y. Li, J. Pflüger
XFEL. EU, Schenefeld, Germany

The European XFEL GmbH is a new X-ray FEL facility expected to be lasing to users at the end of 2017. Three gap-movable SASE Undulator Systems are designed to produce FELs with tunable wavelengths from 0.05 to 5.2nm.*,** A total of 91 5m long undulator segments and phase shifters were magnetically tuned respecting tight specifications. Magnetic field hysteresis effects due to the gap shift of the Undulator System while changing the FEL radiation wavelength may impact the machine's operational mode. We report on these effects by either opening or closing the gap while performing field integrals measurements with moving wire technique. The undulator segments show negligible magnetic hysteresis and are expected to be operated with no influence to the FEL and beam trajectories in either feed forward or feed backward mode. The phase shifters show first field integrals hysteretic behavior of few G.cm which is comparable in magnitude to the allowed total field integrals and can be associated to the magnetization of the yoke structure. Phase shifters are magnetically tuned for that the feed forward mode (opening gap) fully satisfies the XFEL. EU magnetic specifications for beam operation.
* M. Altarelli et al., Technical Design Rep. DESY 2006-097, July 2007.
** E. Schneidmiller et al., European XFEL Technical Rep. TR-2011-006, Sep. 2011.

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WEP055

Tapered Flying Radiofrequency Undulator

525

S.V. Kuzikov, A.V. Savilov, A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia
S.P. Antipov, A. Liu
Euclid TechLabs, LLC, Solon, Ohio, USA
A.V. Savilov
UNN, Nizhny Novgorod, Russia

Funding: This project is supported by DoE Small Business Innovative Research phase I grant #DE-SC0017145.
We propose an efficient XFEL consisting of sequential RF undulator sections using: 1) tapered flying RF undulators, 2) short pulse, high peak-power RF and 3) driving undulator sections by spent electron beam. In a flying RF undulator, an electron bunch propagates through a high-power, nanosecond, co-propagating RF pulse. Helical waveguide corrugation supports a space harmonic with a negative propagation constant, providing a large Doppler up-shift. The undulator tapering technique improves FEL efficiency by 1-2 orders of magnitude in comparison with other facilities by decreasing the undulator period so that particles are trapped in the combined field of the incident x-ray and undulator field. We develop a so-called non-resonant trapping regime not requiring phase locking for feeding RF sources. Simulations show that by decreasing the corrugation periodicity one can vary an equivalent undulator period by 15%. The spent electron beam can be used to produce wakefields that will drive the RF undulator sections for interaction with the following beam. We have already manufactured and tested the 30 GHz simplified version of the 50 cm long undulator section for cold measurements.

Poster WEP055 [1.565 MB]

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WEP056

Effect of Beam Transverse Angle Deflection in TGU on FEL Power

529

G. Zhou, J.Q. Wang
IHEP, Beijing, People's Republic of China
J. Wu
SLAC, Menlo Park, California, 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.
Recent study shows that electron beams with constant dispersion together with the transverse-gradient undulator (TGU) can reduce the sensitivity to energy spread for free-electron laser (FEL). By inducing dispersion function, electrons with different energy are placed at different positions corresponding to proper magnetic fields. Thus, FEL resonant condition can be kept for electrons with different energy. In this paper, we mainly studied: 1.The effects of electron beam angle deflection at the entrance of the TGU on the radiation power. 2. The utility of a kicker to introduce an angle deflection of electron beam to improve the FEL radiation power.

Poster WEP056 [0.638 MB]

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WEP057

Design of a Compact Hybrid Undulator for the THz Radiation Facility of Delhi Light Source (DLS)

532

S. Tripathi, R.K. Bhandari, S. Ghosh, D. Kanjilal
IUAC, New Delhi, India
U. Lehnert
HZDR, Dresden, Germany
M. Tischer
DESY, Hamburg, Germany

Funding: One author, Sumit Tripathi (PH/16-17/0029), would like to acknowledge University Grant Commission (UGC), New Delhi, India for financial support as D.S.Kothari Postdoctoral fellowship.
A compact Free Electron Laser (FEL) facility to produce coherent THz radiation is in the development stage at Inter-University Accelerator Centre (IUAC), New Delhi, India.*,** The name of this facility is Delhi Light Source (DLS) in which a low-emittance electron beam from a photocathode RF gun with a maximum energy of 8 MeV will be injected into a compact undulator magnet to generate THz radiation. To produce the THz radiation in the range of 0.15 to 3.0 THz, the electron beam energy and the undulator gap need to be varied from 4 to 8 MeV and 20 to 45 mm, respectively. The variable gap undulator of 1.5-m length will consist of NdFeB magnets with vanadium permendur poles. The magnet design and dimensions are optimised by using code 3D RADIA.*** The detailed design of the compact hybrid undulator will be presented in this paper.
* S.Ghosh et al., presented at this conference.
** S.Ghosh et al., NIMB-2017 (in press).
*** RADIA. Available at http://www.esrf.eu/Accelerators/ groups/
Insertion Devices/ Software/ Radia.

Poster WEP057 [1.117 MB]

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WEP060

Characterizing Sub-Femtosecond X-ray Pulses from the Linac Coherent Light Source

535

S. Li, R.N. Coffee, J. Cryan, K.H. Hegazy, Z. Huang, A. Marinelli, A. Natan, T. Osipov, D. Ray
SLAC, Menlo Park, California, USA
G. Guo
Stanford University, Stanford, California, USA

The development of sub-femtosecond x-ray capabilities at the Linac Coherent Light Source requires the implementation of time-domain diagnostics with attosecond (as) time resolution. Photoelectrons created by attosecond duration x-ray pulses in the presence of a strong-laser field are known to suffer an energy spread which depends on the relative phase of the strong-laser field at the time of ionization. This phenomenon can be exploited to measure the duration of these ultrashort x-ray pulses. We present an implementation which employs a circularly polarized infrared laser pulse and novel velocity map imaging design which maps the phase dependent momentum of the photoelectron onto a 2-D detector. In this paper, we present the novel co-linear VMI design, simulation of the photoelectron momentum distribution, and the reconstruction algorithm.

Poster WEP060 [1.260 MB]

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WEP061

Thermal Stress Analysis of a Thin Diamond Crystal Under Repeated Free Electron Laser Heat Load

539

J. Wu
SLAC, Menlo Park, California, USA
B. Yang
University of Texas at Arlington, Arlington, 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.
Thin crystals are used in many important optical elements, such as monochromator and spectrometer, in XFELs. To function properly, they must survive the ever-increasing heat load under repeated pulses. Here, we conduct a thermal stress analysis to examine the crystal lattice distortion due to the thermal load under various rep rates from 0.1 to 1 MHz. The thermal field is obtained by solving the transient heat transfer equations. The temperature-dependent material properties are used. It is shown that for pulse adsorption energy around tens of microjoule over a spot size of 10 micrometer, the thermal response of diamond is sensitive to rep rate. The thermal strain components are very different in the in- and out-of-plane directions, due to different constraint conditions. It suggests complicated strain effects in the Bragg and Laue diffraction cases.

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WEP062

Optical Beam Quality Analysis of the Clara Test Facility Using Second Moment Analysis

543

H.M. Castaneda Cortes, D.J. Dunning, M.D. Roper, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

We studied and characterised the FEL optical radiation in simulations of the CLARA FEL test facility under development at Daresbury Laboratory in the UK. In particular, we determined the optical beam quality coefficient, waist position and other source properties corresponding to different potential FEL operating modes via wavefront propagation in free space using OPC (Optical Propagation Code) and Second Moment Analysis. We were able to find the operation mode and undulator design for which the optical beam has the optimum quality at highest brightness. Furthermore, we studied the way that different properties of the electron bunches (emittance, peak current, bunch length) affect the optical beam. We are now able to understand how the optical beam will propagate from the end of the undulator and through the photon transport system to the experimental stations. This knowledge is necessary for the correct design of the photon transport and diagnostic systems.

Poster WEP062 [0.495 MB]

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WEP063

A Two-in-One Type Undulator

547

D. Wang, H.X. Deng, Z. Jiang
SINAP, Shanghai, People's Republic of China

Funding: This work is supported by the Ministry of Science and Technology of China.
The typical X-ray free electron lasers have long tunnels to accommodate high energy electron linear accelerator and long undulator line to produce intense coherent radiations at very short wavelengths. The number of undulator lines is limited by the available space in the tunnel. This is especially true for those facilities that adopt underground tunnels or utilize the existing tunnels originally built for other purpose. This work explored the possibility to better use the tunnel space for accommodating more FEL undulator lines by designing a new type of undulator structure.

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WEP064

Tunable High-Gradient Quadrupoles for a Laser-Plasma Acceleration-Based FEL

550

A. Ghaith, F. Blache, M.-E. Couprie, C.A. Kitegi, F. Marteau, P. N'gotta, M. Valléau, J. Vétéran
SOLEIL, Gif-sur-Yvette, France
C. Benabderrahmane
ESRF, Grenoble, France
O. Cosson, F. Forest, P. Jivkov, J.L. Lancelot
Sigmaphi, Vannes, France

The magnetic design and characterization of tunable high gradient permanent magnet based quadrupole, are presented. To achieve a high gradient field with a compact structure, permanent magnets are chosen rather than usual electro-magnets due to their small aperture. The quadrupole structure consists of two quadrupoles superimposed capable of generating a gradient of 210 T/m. The first quadrupole is composed of permanent magnets following a Halbach configuration shaped as a ring attaining a constant gradient of 160T/m, and the second of four permanent magnet cylinders surrounding the ring and capable of rotating around their axis to achieve a gradient tunability of ±50 T/m. Each tuning magnet is connected to a motor and is controlled independently, enabling the gradient to be tuned with a rather good magnetic center stability (±20 μm) and without any field asymmetry. Seven quadrupoles have been built with different magnetic lengths in order to fulfil the integrated gradient required. A set of QUAPEVA triplet are now in use, to focus a high divergent electron beam with large energy spread generated by a laser plasma acceleration source for a free electron laser application.

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WEP065

Cryogenic Permanent Magnet Undulator for an FEL Application

554

A. Ghaith, T. André, I.A. Andriyash, P. Berteaud, F. Briquez, N. Béchu, M.-E. Couprie, C. Herbeaux, M. Labat, O. Marcouillé, F. Marteau, E. Roussel, M. Sebdaoui, K.T. Tavakoli, M. Tilmont, M. Valléau
SOLEIL, Gif-sur-Yvette, France

A Cryogenic Permanent Magnet Undulator (CMPU) is capable of achieving high brightness radiation at short wavelengths, by taking advantage of the permanent magnets' enhanced performance at low temperature. A CPMU of period 18 mm (U18) that has been built at Synchrotron SOLEIL is used for the COXINEL project to demonstrate Free Electron Laser (FEL) at 200 nm using a laser plasma acceleration source. Another undulator of period 15 mm (U15) is currently being built to replace U18 undulator for FEL demonstration at 40 nm. A new method is also introduced, using SRWE code, to compute the spectra of the large energy spread beam (few percent) taking into account the variation of the Twiss parameters for each energy slice. The construction of U18 undulator and the magnetic measurements needed for optimization, as well as the mechanical design of U15, are presented.

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