FEL2014 - Table of Session: MOP (Poster Session)

Paper

Title

Page

Particle Tracking Simulations for EXFEL Complex shape Collimators

22

V.G. Khachatryan, V.H. Petrosyan, T.L. Vardanyan
CANDLE SRI, Yerevan, Armenia

The study sets the objective to investigate through numerical simulation the produced secondary radiation properties when the electron beam particles hit collimator walls. Using particle tracking simulation code FLUKA, the European XFEL electron beam as well as beam halo interaction with the collimator were simulated. The complex geometrical shape and material composition of the collimator have been taken into account. Absorbed dose spatial distribution in the material of the collimators and particle fluencies from the downstream surface of the collimator were simulated for the total secondary radiation and its main components.

MOP003

Helical Undulator Radiation in Internally Coated Metallic Pipe

26

T.L. Vardanyan, A. Grigoryan, L.V. Hovakimyan, M. Ivanyan, A.V. Tsakanian, V.M. Tsakanov
CANDLE SRI, Yerevan, Armenia

The vacuum chambers of many advanced undulator sources are coated internally in order to reduce the impedance of the vacuum chamber or improve the vacuum performance. Although the impedances and radiation properties of the internally coated metallic pipes for straightforward moving charge are well studied, the peculiarities of the particles wiggling motion on the radiation characteristics in such structure are missed. In this paper we obtain exact expressions for the fields of a particle moving along a spiral path, as in the single-layer resistive as well as in the two-layer metallic waveguides, modelling NEG coating of the waveguide walls. Based on these results, it will be possible to obtain the necessary characteristics of the radiation of helical undulators, very close to reality. The solution is obtained as a superposition of a particular solution of inhomogeneous Maxwell's equations in a waveguide with perfectly conducting walls, and the solutions of the homogeneous Maxwell equations in the single-layer and double-layer resistive waveguides. Solution in the form of the multipole expansion for inhomogeneous Maxwell's equations for a waveguide with perfectly conducting walls, are also obtained in this study.

MOP004

Optimization of APPLE-II Quasiperiodic Undulators at SOLEIL and Spectral Peformances

F. Briquez, M.-E. Couprie, N. Jaouen, O. Marcouillé, M. Valléau
SOLEIL, Gif-sur-Yvette, France

The introduction of a slight aperiodicity in an undulator enables to generate irrational harmonics, for the distinction between a one or two photon process. In the case of an APPLE-II undulator generating various types of polarizations, the aperiodicity is generally introduced by shifting vertically some magnets on arrays. The optimization of the system is not fully satisfying since different optima of magnet displacements are found for the various polarization modes, as reported in examples from SOLEIL undulators. Besides, the intensity of the first harmonics is slightly reduced. In addition, a residual photon signal appears between pseudo-harmonics. Measured spectra from built APPLE-II undulators at SOLEIL are compared to calculated ones from magnetic measurements, and confirm these observed trends, and in particular the residual structure between the pseudo-harmonics. An analytic approach is given and consequences for scientific applications are also driven.

MOP006

Coherent Accelerator-based High Field THz Radiation at FLASH II

T. Golz, V. B. Asgekar, B. Faatz, G. Geloni, N. Stojanovic, M. Tischer, P. Vagin, M. Vogt
DESY, Hamburg, Germany
M. Gensch
HZDR, Dresden, Germany
P. Vobly
BINP SB RAS, Novosibirsk, Russia

Funding: BMBF grant no. 05K10CHC + 05K10KEB + 05K12CH4
Linear accelerator based light sources with their tunable broad spectral range (THz to hard X-rays regime) and their ability to generate ultra-short pulses with peak intensities many orders of magnitude higher then synchrotron sources, gave rise to a new field of ultrafast physics. In the THz range, the ability of 4th gen. light sources to generate pulses with e-field strengths up to 1 GV/m opened the door to the field of non-linear THz spectroscopy and THz-controlled material science. The main advantage of accelerator-based THz is its scaleability. As the process is not bound to a particular medium, but occurs in the accelerator vacuum, it bypasses the limitation of table top sources. In addition, it has been demonstrated that coherent THz radiation can be generated along femtosecond X-ray pulses in 4th Generation X-ray Light sources such as FLASH [1,2,3] and LCLS [4]. This opens up the opportunity for naturally synchronized THz pump X-ray probe experiments on a few femtosecond time scale [1,2,4]. Here we present the design for the THz source at FLASH2, which takes new findings [5] and challenges into account that we face during the radiation transport to the experimental hall.

MOP007

High Accuracy Shimming Technique for the Phase Shifters of the European XFEL

29

Y. Li
DESY, Hamburg, Germany
J. Pflüger
XFEL. EU, Hamburg, Germany

For the European XFEL 91 phase shifters are needed, which have to fulfil stringent field integral specifications: There should be no observable beam deflection when the strength, i.e. the magnetic gap is changed In order to facilitate the mass production of 91 phase shifters within the tough XFEL schedule a shimming technique was developed. It is based on measured shim signatures and is straight forward and fast to apply. The method is described and results are presented demonstrating that all requirements can be fulfilled.

MOP008

Temperature Effects of the FLASH2 Undulators

34

M. Tischer, A. Schöps, P. Vagin
DESY, Hamburg, Germany

FELs are very sensitive to small changes in the resonance condition of the emitted radiation. As a consequence, permanent magnet undulators in FELs usually require extensive temperature control in order to assure stable operation conditions. In principle, the temperature dependence of permanent magnet material is well known but more things need to be considered like different thermal expansion of various mechanical parts or thermally induced deformation which do not only affect the K parameter but also the field quality. We have performed temperature dependent magnetic measurements in a range from 19 to 28 degrees Celsius and have analyzed the magnetic performance of the undulator. The results of this case study can be transferred to all FLASH2 undulators and shall allow for a simple temperature dependent gap correction in order to make the spectral properties insensitive to temperature changes of the insertion devices.

MOP009

K-Monochromator for Undulator Commissioning at the European XFEL

W. Freund, J. Grünert, A. Koch
XFEL. EU, Hamburg, Germany

Photon beam based commissioning of the European XFEL undulators requires variable 4-bounce monochromator systems equipped with Si(111) channel-cut crystals. With two different methods we will measure the K-parameters of each segment of the SASE undulators (e.g. SASE1 has 35 segments) which has to be tuned to a precision of better than 2·10^-4 in order to achieve lasing conditions. Precise magnetic K-tuning of the undulator segments is performed in the magnetic lab, but this measurement is not available after undulator installation in the tunnel. We will describe the K-monochromator system for the first undulator beamline SASE1, which is planned to be installed this year. The system consists of three main components, a chamber with filter foils, a monochromator chamber with two goniometers carrying the channel-cut crystals, and a detection chamber with an imager and a photodiode. For the imaging system we will use a highly sensitive sCMOS camera with tandem lens optics for high numerical aperture and up to three different scintillation screens.

MOP010

The Photon Beam Loss Monitors as a Part of Equipment Protection System at European XFEL

37

N. Gerasimova, H. Sinn
XFEL. EU, Hamburg, Germany
S. Dziarzhytski, R. Treusch
DESY, Hamburg, Germany

For the X-ray beam transport systems, the problem of potential damage to the equipment by mis-steered photon beam emerged with advent of powerful X-ray FELs. In particular high repetition rate machines as European XFEL, where not only focused beam can produce ablation, but even unfocused beam can melt the beamline components while machine operates in multibunch mode, demand for implementation of equipment protection. Here we report on development of photon beam loss monitors at European XFEL facility. The photon beam loss monitors will react on the mis-steered photon beam and interface the machine protection system. The prototype comprises the vacuum chamber with fluorescence crystals positioned outside the photon beampath. The fast sub-hundred ns fluorescence induced by mis-steered beam can be detected by photomultiplier tube allowing for intra-train reaction of machine protection system. First tests have been carried out at FLASH and shown the feasibility of detection based on PMT-detected fluorescence. In addition to efficient YAG:Ce crystal, the robust low-Z material as CVD microcrystalline diamonds has shown a potential to be used as fluorescence crystals.

MOP011

The SASE3 Monochromator Beamline at the European XFEL

N. Gerasimova, D. La Civita, L. Samoylova, H. Sinn, M. Vannoni
XFEL. EU, Hamburg, Germany

The photon beam transport at novel X-ray FEL machines is a challenging task. The unprecedented brilliance of European XFEL demands for optics operating close to damage limit; deterioration of spatial and temporal properties of coherent pulses should be minimized. To handle the XFEL beam, the beamlines have been designed being very long (hundreds of meters), along with very long optical elements (up to 1 m) and extremely high demands on the optical surface (50 nrad slope error, 2 nm PV residual height error). The mechanical design in terms of vibrational stability, deformations (of both mechanical and thermal origin) and movement resolution should be compliant to the optical one. Here we discuss on the optical and mechanical design of the SASE3 beamline at European XFEL. Operational in the soft X-ray regime, the SASE3 beamline comprises several reflective optical elements of specified above quality, including VLS plane grating monochromator. Expected to serve multipurpose user community, the monochromator would allow controlling temporal pulse properties and will be operational in both low and high resolution modes.

MOP012

Implementation Phase of the European XFEL Photon Diagnostics

41

J. Grünert, J. Buck, F. Dietrich, W. Freund, A. Koch, M. Planas
XFEL. EU, Hamburg, Germany

The European XFEL facility with 3 undulators and initially 6 experimental end-stations requires an extensive set of photon beam diagnostics for commissioning and user operation, capable of handling the extreme brilliance and its inherent damage potential, and the high intra bunch train repetition rate of 4.5MHz, potentially causing additional damage by high heat loads and making shot-to-shot diagnostics very demanding [1]. After extensive design [2-4] and prototype studies, in 2014 the installation of the photon beam devices starts with the equipment in the first photon tunnel XTD2 which is where the SASE1 hard X-ray undulator is located. This contribution reports on the device construction progress by focusing on the XTD2 tunnel devices and their implementation into the tunnel environment. [1] J.Grünert, Framework for X-Ray Photon Diagnostics at the European XFEL, TR-2012-003, 04/2012 [2] J.Buck, Online Photoemission Time-of-Flight Spectrometer for X-ray Photon Diagnostics, TR-2012-002, 06/2012 [3] C.Ozkan, Conceptual design report for Imaging Stations at the European XFEL, TR-2012-004, 02/2012 [4] W.Freund, The European XFEL Undulator Commissioning Spectrometer, XFEL. EU 05/2011

MOP013

Design of Invasive X-ray Beam Diagnostic Devices for the European XFEL Employing Scintillators for Imaging

A. Koch, W. Freund, J. Grünert
XFEL. EU, Hamburg, Germany

The European XFEL facility requires diagnostics of its x-ray photon beam. Imaging stations will be employed for invasive characterisations of beam properties like position, profile, and pointing. In combination with monochromators or dispersive devices, imagers can also deliver spectral information. This contribution will describe the design of different imaging stations, their expected performance and first characterisations, especially in terms of signal-to-noise properties, spatial resolution and radiation hardness. The challenge in the design is to deal with a wide range of beam properties: photon energies from 0.26 – 36 keV, beam sizes from several 100 um to mm, pulse durations of 10 fs and pulse energies up to 10 mJ which may destroy materials by single pulses. The main components of these imaging stations are: scintillators for conversion of x-rays to visible light, mirrors - both in vacuum - specialised optics and CCD / CMOS cameras for image recording.

MOP014

X-ray Photon Temporal Diagnostics for the European XFEL

45

J. Liu, J. Buck, F. Dietrich, W. Freund, J. Grünert, M. Meyer
XFEL. EU, Hamburg, Germany

European XFEL (XFEL. EU) that will commissioning in 2016 shows great features on its extremely high number of light bullets (27000 p/s) and extremely high average brilliance. The FEL pulses in XFEL. EU are produced in a 10 Hz bunch trains that contains 2700 sub-pulses within the 600 μs time intervals, corresponding to a 220 ns sub-pulse separation and 4.5 MHz repetition rate. Characterizing the temporal properties of the high repetition rate FEL pulses that implicitly different from shot to shot is important for “pump and probe” experiments and data interpretation. Here we report the concept and recent progress about temporal diagnostic for XFEL. EU. THz streaking technique and spectral encoding will be implemented considering the high repetition rate and high brilliance of XFEL. EU. Laser based THz generation, optimization and numerical simulation for streaking FEL electrons with different photon energies will be presented. High repetition rate diagnostic requirements and solutions will also be discussed.

MOP015

A Power Switching Ionization Profile Monitor (3D-IPM)

47

H.F. Breede, H.-J. Grabosch, M. Sachwitz, L.V. Vu
DESY Zeuthen, Zeuthen, Germany

FLASH at DESY in Hamburg is a linear accelerator to produce soft x-ray laser light ranging from 4.1 to 45 nm. To ensure the operation stability of FLASH, monitoring of the beam is mandatory. Two Ionization Profile Monitors (IPM) detect the lateral x and y position and profile changes of the beam. The functional principle of the IPM is based on the detection of particles, generated by interaction of the beam with the residual gas in the beam line. The newly designed IPM enables the combined evaluation of the horizontal and vertical position as well as the profile. A compact monitor, consisting of two micro-channel plates (MCP) is assembled on a conducting cage along with toggled electric fields in a rectangular vacuum chamber. The particles created by the photon beam, drift in the homogenous electrical field towards the respective MCP, which produces an image of the beam profile on an attached phosphor screen. A camera for each MCP is used for assessment. This indirect detection scheme operates over a wide dynamic range and allows the live detection of the clear position and the shape of the beam. The final design is presented.

Poster MOP015 [1.314 MB]

MOP016

Synchrotron Radiation Monitor for Beam Energy Measurements at the European XFEL

M. Sachwitz, N. Leuschner, F. Perlick
DESY Zeuthen, Zeuthen, Germany
C. Gerth, H. Huegelmann
DESY, Hamburg, Germany

Monitoring of the electron beam energies after the various accelerating sections of the European XFEL is essential for an optimal beam delivery system. Synchrotron radiation that is emitted in the dispersive section of the magnetic chicanes employed for longitudinal bunch compression can be used to determine the energy spectrum of the electron bunches. At European XFEL, vacuum chambers with an aperture of 400 mm will be installed for flexible operation of different bunch compression scenarios. Therefore, the in-vacuum mirror deflecting the visible light through a vacuum window to a camera is located on a motor driven carrier. An additional mover allows an angular adjustment of the mirror. In this paper we report on the conceptual design of the synchrotron monitor. Results obtained with a prototype setup in the laboratory are presented and several options for the synchrotron light detection are discussed.

MOP017

Measurement of the Output Power in Millimeter Wave Free Electron Laser using the Electro Optic Sampling Method

50

A. Klein
Israeli Free Electron Laser, Ariel, Israel
A. Abramovich
Ariel University Center of Samaria, Faculty of Engineering, Ariel, Israel
D. Borodin, A. Friedman
Ariel University, Ariel, Israel
H. S. Marks
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel

Funding: this work funded in part by Israel Minstry of Defence
In this experimental work an electro optic (EO) sampling method was demonstrated as a method to measure the output power of an Electrostatic Accelerator Free Electron Laser (EA-FEL). This 1.4 MeV EA-FEL was designed to operate at the millimeter wavelengths and it utilizes a corrugated waveguide and two Talbot effect quasi-optical reflectors with internal losses of ~30%. Millimeter wave radiation pulses of 10 μs at a frequency of about 100 GHz with peak power values of 1-2 kW were measured using conventional methods with an RF diode. Here we show the employment of an electro-optic sampling method using a ZnTe nonlinear crystal. A special quasi optical design directs the EA-FEL power towards the ZnTe nonlinear crystal, placed in the middle of a cross polarized configuration, coaxially with a polarized HeNe laser beam. The differences in the ZnTe optical axis due to the EA-FEL power affects the power levels of the HeNe laser transmission. This was measured using a polarizer and a balanced amplifier detector. We succeeded in obtaining a signal which corresponds to the theoretical calculation.

MOP018

Conceptual Study of a Self-seeding Scheme at FLASH2

53

T. Plath, L.L. Lazzarino
Uni HH, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355.
We present a conceptual study of a self-seeding installation at the new FEL beamline, FLASH2, at the free-electron laser at DESY, Hamburg. For self-seeding, light from a first set of undulators is filtered by a monochromator and thus acts as a seed for the gain process in the main undulator. This scheme has been tested at LCLS at SLAC with a diamond monochromator for hard X-rays and with a grating monochromator for soft X-rays covering energies between 700 and 1000 eV. For such a design to offer benefits at FLASH2, it must be modified to work with X-rays with wavelength of about 5 nm (248 eV) where the damage threshold of the monochromator in the setup and the divergence at longer wavelengths become an issue. An analysis of the potential performance and limitations of this setup is performed using GENESIS 1.3 and a method developed for the soft X-ray self-seeding experiment at the European XFEL. With a total of 9 undulators in the first stage and 8 undulators after the monochromator, a pulse energy contrast ratio of 4.5 was simulated with an initial peak current of 2.5 kA.

MOP019

Double-grating Monochromator for Ultrafast Free-electron Laser Beamlines

58

F. Frassetto, L. P. Poletto
CNR-IFN, Padova, Italy
M. Kuhlmann, E. Plönjes
DESY, Hamburg, Germany

We present the design of an ultrafast monochromator explicitly designed for extreme-ultraviolet FEL sources, in particular the upcoming FLASH II at DESY. The design originates from the variable-line-spaced (VLS) grating monochromator by adding a second grating to compensate for the pulse-front tilt given by the first grating after the diffraction. The covered spectral range is 6-60 nm, the spectral resolution is in the range 1000–2000, while the residual temporal broadening is lower than 15 fs. The proposed design minimizes the number of optical elements, since just one grating is added with respect to a standard VLS monochromator and requires simple mechanical movements, since only rotations are needed to perform the spectral scan.

MOP020

Compact Spectrometer for Single Shot X-ray Emission and Photon Diagnostics

62

F. Frassetto, P. Miotti, L. P. Poletto
CNR-IFN, Padova, Italy
M. Coreno
CNR-IMIP, Monterotondo Stazione RM, Italy
A. Di Cicco, F. Iesari
Università di Camerino, Camerino, Italy
P. Finetti, E. Giangrisostomi, R. Mincigrucci, E. Principi
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
C. Grazioli
Universita Degli Studi di Trieste, Trieste, Italy
A. Kivimaki
IOM-CNR, Trieste, Italy
S. Stagira
CNR-IFN & Dipartimento di Fisica - Politecnico di Milano, Milano, Italy
S. Stagira
Politecnico/Milano, Milano, Italy

The design and characterization of a compact spectrometer realized for photon in-photon out experiments (in particular X-Ray Emission Spectroscopy), conceived to be used at the FERMI free-electron-laser (FEL) at ELETTRA (Italy) is here presented. The instrument can be easily installed on different end stations at variable distances from the target area both at synchrotron and FEL beamlines. Different input sections can be accommodated in order to fit the experimental requests. The design is compact in order to realize a portable instrument within an overall size of less than one square meter. The spectrometer covers the 25-800 eV spectral range, with spectral resolution better than 0.2%. The characterization on Gas Phase @ ELETTRA as instrument for XES and some experimental data of the FEL emission acquired at EIS-TIMEX @ FERMI, where the instrument has been used for photon beam diagnostics, are introduced.

MOP021

Commissioning of a Dual-sweep Streak Camera with Applications to the ASTA Photoinjector Drive Laser

66

A.H. Lumpkin, D.R. Edstrom, J. Ruan, J.K. Santucci
Fermilab, Batavia, Illinois, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The high-power electron beams for the Advanced Superconducting Test Accelerator (ASTA) facility will be generated in a photoinjector based on a UV drive laser and the L-band rf photocathode (PC) gun cavity. The initial objectives of these studies were: 1) the evaluation of the amplified UV component’s bunch length and phase stability and 2) the commissioning of the laser room Hamamatsu C5680 streak camera system. We used a new readout camera based on the Prosilica GC1380 digital CCD with Gig-E readout that was compatible with our image processing tools. We observed a longer than expected UV bunch length of 4 ps σ and an unexpected peak multiplicity (with spacing of about 70 ps) in the synchronous sum of 5 UV micropulses. We have now systematically investigated the issues of whether the multiplicity was with each micropulse of the 3-MHz pulse train. We describe our extensive investigations that indicated both issues originated in the multi-pass amplifier. We have replaced the MPA with three single-pass devices, measured 3.5-ps bunch lengths without the multiplicity, and generated photoelectrons from the gun successfully.

MOP022

Pulse by Pulse Electron Beam Distribution for Multi-beamline Operation at SACLA

71

T. Hara, T. Inagaki, C. Kondo, Y. Otake, H. Takebe, H. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
K. Fukami
JASRI/SPring-8, Hyogo-ken, Japan

In order to meet the increasing demand for XFEL user operation, the second undulator beamline (BL2) will be installed during the 2014 summer shutdown at SACLA. Following the installation of BL2, a pulse by pulse electron beam distribution system composed of a kicker and a DC twin-septum magnet, which are currently under development, is planned be installed in January 2015. To distribute the electron beam on a bunch-to-bunch basis, the electron beam is deflected into 0 and ±10 mrad directions at 60 Hz by the kicker, and then the DC twin-septum magnet augments the separation angle to ±50 mrad. The kicker magnet is driven by a 60 Hz trapezoidal waveform and stability less than 30 ppm (peak-peak) has been achieved. This pulse by pulse distribution system will be also used for the beam injection to the upgraded low emittance ring of SPring-8 (SPring-8-II) in future. Since the SPring-8-II storage ring has a small dynamic aperture, low emittance is required for the injection beam. Also the beam injection in parallel with the XFEL operation enables to save the running cost of the injector during top-up operation.

MOP023

Development of a Magnetic System to Cancel the Attractive Force toward Structural Reform of Undulators

75

R. Kinjo, T. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
A. Kagamihata, T. Seike
JASRI/SPring-8, Sayo-gun, Japan
S. Yamamoto
KEK, Tsukuba, Japan

As part of a development on a compact and lightweight structure toward structural reform of undulators, cancellation of magnetic attractive force is being studied. Undulators usually require rigid mechanical components and frames to control the magnet gap precisely against the large attractive force in between. If the attractive force is canceled out near the point of load, the requirement for the undulator structure is relaxed and the cost and lead time of construction and installation are saved largely. For that purpose, we have proposed to add periodically-magnetized monolithic magnets beside the main magnets, which are expected to generate a repulsive force having the same gap-dependency as the attractive force in a cost-effective way. In the conference, the present status of the development of the force cancellation system will be presented, with a focus on the result of preliminary experiments using the periodically-magnetized magnets. Also introduced will be a development plan for the compact and lightweight undulator based on the cancellation system.

MOP026

Division-of-amplitude Photopolarimeter for Single-shot Measurement of Free Electron Laser at SDUV-FEL

L. Feng, H.X. Deng, T. Zhang
SINAP, Shanghai, People's Republic of China

Division-of-amplitude photopolarimeter (DOAP) is generally used to measure the polarization-state of the pulse beam, which divides the incident beam into four separate beams, and all four Stokes parameters can be measured simultaneously. In this paper, a home-made DOAP instrument is applied to the experiment of polarization control at Shanghai deep ultraviolet FEL test facility. The results indicate that this instrument response fast and accurately while the polarization-state of the coherent FEL are switched, and it is well verify the cross-planar undulator technique experimentally.

MOP028

Field Integral Measurement System and Optical Alignment System for HUST THz-FEL

80

B. Qin, Q.S. Chen, M. Fan, Q. Fu, T. Hu, X. Lei, K.F. Liu, X. Liu, P. Tan, Y.Q. Xiong, J. Yang, L. Yang
HUST, Wuhan, People's Republic of China
X. Liu, Z. Ouyang, Y.B. Wang
Huazhong University of Science and Technology, State Key Laboratory of Advanced Electromagnetic Engineering and Technology,, Hubei, People's Republic of China
Y.J. Pei
USTC/NSRL, Hefei, Anhui, People's Republic of China

A Free Electron Laser oscillator with radiation wavelength 50–100 μm is under construction in Huazhong University of Science and Technology (HUST). The linear polarization undulator with K=1.0-1.25 has been designed and manufactured by Kyma s.r.l., by using a pure permanent magnet scheme. Acceptance test bas been performed in Kyma factory with well controlled phase error and field integrals for all gaps. This paper introduces the development of an online field integrals measurement system for the undulator, using the stretched wire method. The design and considerations of the optical alignment system is described as well.

MOP030

Performance Analysis of Variable-Period Helical Undulator with Permanent Magnet for a KAERI THz FEL

84

J. Mun, K.H. Jang, Y.U. Jeong, K. Lee, S. H. Park, N. Vinokurov
KAERI, Daejon, Republic of Korea
M.Y. Jeon
Chungnam National University, Daejoen, Republic of Korea

Funding: This work was supported by the World Class Institute Program of the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and Future Planning.(NRF Grant Number:WCI2011-001)
We realized a variable-period permanent-magnet helical undulator with high (~1 T) field amplitude, which is almost constant over undulator periods of 23–26 mm. Each undulator period has 4 modular sections of iron poles and permanent magnets embedded in non-magnetic disks with holes along the undulator axis. Modular plates undergo a longitudinal repulsive force from the magnetic field pressure and the spring coils between modular plates. The undulator period can thus be controlled by mechanically changing of the end plate longitudinal position. This compact design is suitable for a table-top terahertz free electron lasers. The measured on-axis field is about 0.97 T with the deviation less than 1% through the whole range of the undulator period variation. The measured spread of the longitudinal coordinates of the undulator field component maxima is less than 1%, and the measured field distribution meets the requirement for our terahertz FEL. The field reproducibility was checked by six measurements of the undulator field after the period variation for the 26 mm period. The r. m. s. phase errors is 3.7 degrees.

MOP031

Progress of the PAL-XFEL Undulator System

D.E. Kim, Y.-G. Jung, H.-S. Kang, H.-G. Lee, S.B. Lee, W.W. Lee, B.G. Oh, K.-H. Park, H.S. Suh
PAL, Pohang, Kyungbuk, Republic of Korea
M.-H. Cho, I.S. Ko
POSTECH, Pohang, Kyungbuk, Republic of Korea
S. Karabekyan, J. Pflüger
XFEL. EU, Hamburg, Germany

Pohang Accelerator Laboratory (PAL) is developing 10 GeV, 0.1 nm SASE based FEL for high power, short pulse X-ray coherent photon sources named PAL-XFEL. At the first stage PAL-XFEL needs two undulator lines for photon source. PAL is developing undulator magnetic structure based on EU-XFEL design. For hard X-ray lines, we need 18 26.0 mm period hybrid type planar undulator structures, and for soft X-ray lines, 6 planar undulator with 37 mm period is planned with a couple of EPUs for polarization control. In this report we summarize the progress in the undulator system. Particular emphasis will be the results of the local-K correction, which is essential to speed-up the pole tuning process.

MOP032

PAL-XFEL Magnet Power Supply System

87

S.-H. Jeong, H.-S. Kang, D.E. Kim, I.S. Ko, H.-G. Lee, S.B. Lee, B.G. Oh, K.-H. Park, H.S. Suh, Y.G. Young-Gyu
PAL, Pohang, Kyungbuk, Republic of Korea

This paper presents an overview of the magnet power supply(MPS) for the PAL-XFEL. The number of total MPS is 628 and they will be installed along the accelerator and the undulator sections. The power capacity of the MPS was ranging from about 1 A to 300 A. These MPSs were required to meet the high stability that was subjected from the beam dynamics specifications. This paper described the overall MPS requirements, MPS assembling, test process, control scheme, installation plan and so on.

MOP033

Design, Fabrication, and Performance Tests of Dipole and Quadrupole Magnets for PAL-XFEL

90

H.S. Suh, M.-H. Cho, S.-H. Jeong, Y.-G. Jung, H.-S. Kang, D.E. Kim, I.S. Ko, H.-G. Lee, S.B. Lee, B.G. Oh, K.-H. Park
PAL, Pohang, Kyungbuk, Republic of Korea

PAL-XFEL is now being constructed in Pohang, Korea. This facility will consist of a 10 GeV linac and five undulator beamlines. As the first phase we will construct one hard X-ray and one soft X-ray beamlines which require 7 different families of dipole magnets, and 11 families of quadrupole magnets. We are designing these magnets with considering the efficient manufacturing and the proper power supplies. In this presentation, we describe the design features of the magnets, the manufacturing, and the thermal analysis with the test results.

MOP036

Estimating Effect of Undulator Field Errors using the Radiation Hodograph Method

93

N.A. Sokolov
Budker INP & NSU, Novosibirsk, Russia
N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

Spatially-periodic magnetic structures are widely used for generation of high-brilliance radiation in storage rings, sources of synchrotron radiation and free electron lasers. In 1947, V.L. Ginzburg suggested the first undulator scheme. An alternating magnetic field created by a planar undulator makes electrons oscillate in the transverse direction, with interference of radiation emitted from separate parts of the trajectory. The spectrum of the forward emitted radiation is enchanced due to constructive interference. The ondulator is made of the magnetized bars that are not perfect and their magnetization differs. Therefore, the electron trajectory is not purely sinusoidal and, as a result, the spectral intensity fades. The task was to find out if the precision of magnet manufacturing is sufficient. This paper presents modelling of electron motion in the measured magnetic field of the new (third) free electron laser at the Siberian Synchrotron Radiation Centre. We have managed to estimate the effect of the field errors through comparison of the resulting emitted field amplitude with the amplitude from ideal magnet bars using the hodograph method.

MOP037

Modeling and Design of the Variable Period and Pole Number Undulator for the Second Stage of the Novosibirsk FEL

96

I. Davidyuk
NSU, Novosibirsk, Russia
O.A. Shevchenko, V.G. Tcheskidov, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia
N. Vinokurov
KAERI, Daejon, Republic of Korea

The concept of the permanent magnet variable period undulator (VPU) has been proposed just several years ago and there are few examples of its implementation yet. The VPUs have several advantages compared to conventional undulators. One of them is wider radiation wavelength tunability range and another one is an option to increase the number of poles for shorter periods. Both these advantages will be realized in VPU which is being developed now at Budker INP. In this paper we present the 2-D and 3-D magnetic field simulation results and discuss the design features of this VPU.

MOP038

Characterization of the Undulator Magnetic Field Quality by the Angle Averaged Radiation Spectrum

100

O.A. Shevchenko, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia
N. Vinokurov
KAERI, Daejon, Republic of Korea

The real undulator magnetic field always contains errors which influence undulator performance. The effect of these errors is usually characterized by broadening of the spontaneous emission spectrum at zero angle and corresponding reduction of the spectral intensity. This approach works very well for the phase errors while it does not take into account transversal trajectory displacements. The integrated over the angles radiation spectrum contains more complete information about the undulator field quality but its calculation requires more effort. Therefore the spectral density of emitted radiation (the total number of emitted photons with given energy) can be considered as a figure of merit for an undulator. In this paper we derive analytical formula for this spectrum suitable for doing efficient numerical calculations and demonstrate its application to the case of some typical undulator field errors.

MOP039

High Stability Resonant Kicker Development for the SwissFEL Switch Yard

103

M. Paraliev, H.-H. Braun, S. Dordevic, C.H. Gough
PSI, Villigen PSI, Switzerland

The SwissFEL is a linac-based X-ray free electron laser facility under construction at the Paul Scherrer Institute. The facility will provide femtosecond, high brightness X-ray pulses for fundamental and applied science research. To increase facility efficiency, a double bunch operation is planned to serve simultaneously two experimental stations at the full linac repetition rate. The main linac will accelerate two electron bunches spaced 28 ns apart and a fast and stable deflecting system will be used to separate the two bunches into two different undulator lines. The deflecting system uses a novel concept based on resonant kicker magnets. A prototype kicker magnet and its control system were designed and built. Since stability is crucial, the stability performance of the prototype was studied. The peak to peak amplitude stability of ±11 ppm (3.5 ppm rms) was achieved, which is well within the FEL tolerance of ±80 ppm. The layout of the deflecting system and the key design parameters are also presented.

MOP040

General Strategy for the Commissioning of the ARAMIS Undulators with a 3 GeV Electron Beam

107

M. Calvi, M. Aiba, M. Brügger, S. Danner, R. Ganter, R. Ischebeck, L. Patthey, T. Schietinger, T. Schmidt
PSI, Villigen PSI, Switzerland

The commissioning of the first SwissFEL undulator line (Aramis) is planned for the beginning of 2017. Each undulator is equipped with a 5-axis camshaft system to remotely adjust its position in the micrometer range and a gap drive system to set K-values between 0.1 and 1.8. In the following paper the beam-based alignment of the undulator with respect to the golden orbit, the definition of look-up tables for the local correction strategy (minimization of undulator field errors), the fine-tuning of the K-values as well as the setting of the phase shifters are addressed. When applicable both electron beam and light based methods are presented and compared.

MOP041

Summary of the U15 Prototype Magnetic Performance

111

M. Calvi, M. Aiba, M. Brügger, S. Danner, R. Ganter, C. Ozkan, T. Schmidt
PSI, Villigen PSI, Switzerland

The first undulator prototype (U15) was assembled and magnetically tested. The instrumentation and the algorithms developed for the undulator optimization are presented and a comparison among different approaches is reviewed. The magnetic measurement results before and after the installation of the vacuum components are discussed. The summary of the undulator test with 100 MeV electron beam is presented and the impact of the radiation on the magnetics is addressed.

MOP042

Grating Interferometry Applied to X-ray Wavefront Metrology at the SACLA

Y. Kayser, Ch. David, U. Flechsig, S. Rutishauser
PSI, Villigen PSI, Switzerland
T.K. Kameshima, T. Katayama
JASRI/SPring-8, Hyogo, Japan
H. Ohashi
Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), Hyogo, Japan
M. Yabashi
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

Grating interferometry allows for spatially resolved studies of the local wavefront propagation direction with an angular sensitivity of tens of nanoradian. In this perspective the grating interferometry technique has found application in the metrology of X-ray optics at synchrotron facilities and was moreover used for the investigation of the X-ray wavefront properties at the LCLS(*). At the SACLA grating interferometry was applied to two different types of experiments. A first application was the study the wavefront preservation capabilities of the X-ray optics installed upstream of the end station of beam line 3 (two off-set mirror systems and a double crystal monochromator). The experimental results confirmed the excellent quality of the optical components and demonstrated the sensitivity of grating interferometry. In a second application the source point position was determined as the XFEL was driven into saturation. Grating interferometry permits, thus, to get a better understanding of the XFEL machine.
(*) S. Rutishauser, L. Samoylova, J. Krzywinski, et al., “Exploring the wavefront of hard X-ray free-electron laser radiation,” Nat. Commun. 3, 947 (2012).

MOP043

Magnetic Design of an Apple III Undulator for SwissFEL

116

T. Schmidt, A. Anghel, P. Boehler, M. Brügger, M. Calvi, S. Danner, P. Huber, A. Keller, M. Locher
PSI, Villigen PSI, Switzerland

In the frame of the SwissFEL project a soft x-ray line is planned in the coming years to cover the wavelength between 0.7 and 7.0nm. Based on the good experience at the SLS storage ring with Apple undulator as source of variable polarized light, Apple III type undulators are also foreseen at the SwissFEL. In this paper the design of these devices is introduced and the preliminary magnetic configuration together with the optimization strategy is presented in details.

MOP044

A Stripline Kicker Driver for the Next Generation Light Source

121

F.M. Niell, N. Butler, M.P.J. Gaudreau, M.K. Kempkes
Diversified Technologies, Inc., Bedford, Massachusetts, USA

Funding: DOE Contract DE-SC0004255
Diversified Technologies, Inc. (DTI), under an SBIR grant from the U.S. Department of Energy, assembled a prototype MOSFET-based pulse generator capable of meeting the original specifications for the Next Generation Light Source (NGLS) fast deflector. This pulse generator is also applicable to other high repetition-rate FELs with multiplexed beamlines. The unit must drive a 50 Ω load (such as a terminated TEM deflecting structure) at 10 kV, with flat-topped pulses at a 100 kHz average rate. The specification requires a 2 ns rise time (10 – 90%), a highly repeatable flattop with pulse width from 5 – 40 ns, and a fall time (90% to .01%) less than 1 μs (to allow a 1 MHz beam pulse rate). The driver must also effectively absorb high-order mode signals emerging from the deflector itself. The solid-state pulse generator is suitable for many accelerator systems with < 10 ns kicker requirements. The performance and applications of the unit will be described.

MOP045

Phase Shifter Design for iSASE

123

S.D. Chen, K. Fang, H.-D. Nuhn, C. Pellegrini, J. Wu, L. Zhu
SLAC, Menlo Park, California, USA
S.D. Chen, C.-S. Hwang
NCTU, Hsinchu, Taiwan
K. Fang
Indiana University, Bloomington, Indiana, USA
C.-S. Hwang
NSRRC, Hsinchu, Taiwan

A phase shifter to generate an additional phase advance of the spontaneous light versus the electron beam was de- signed for the iSASE scheme. The iSASE mechanism is for reducing the bandwidth further from SASE FEL process. A large phase advance about 1600*2Pi as the FEL operating at wavelength 0.8 nm was needed according to the simulation of iSASE process. Since the iSASE is thought to implement into LCLS II project, the space limitation causing by LCLS II should be considered when designing the phase shifter. An optimized three-pole electric phase shifter with 7.3 mm gap has the center field of 1.8 T . The vanadium steel was considered as pole material and the magnet physical length is 260 mm, meanwhile the water-cooling type copper coil was adopted. The temperature increment, force analysis, low field operation mode concept, and preliminary tolerance study were discussed.

MOP046

Undulator Radiation Damage Experience at LCLS

127

H.-D. Nuhn, R.C. Field, Yu.I. Levashov, X.S. Mao, M. Santana-Leitner, J.J. Welch, Z.R. Wolf
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515
The SLAC National Accelerator Laboratory has been running the Linac Coherent Light Source (LCLS), the first x-ray Free Electron Laser since 2009. Undulator magnet damage from radiation, produced by the electron beam traveling through the 133-m long straight vacuum tube, has been and is a concern. A damage measurement experiment has been performed in 2007 in order to obtain dose versus damage calibrations. Radiation reduction and detection devices have been integrated into the LCLS undulator system. The accumulated radiation dose rate was continuously monitored and recorded. In addition, undulator segments have been routinely removed from the beamline to be checked for magnetic (50 ppm, rms) and mechanic (about 0.25 μm, rms) changes. A reduction in strength of the undulator segments is being observed, at a level, which is now clearly above the noise. Recently, potential sources for the observed integrated radiation levels have been investigated. The paper discusses the results of these investigation as well as comparison between observed damage and measured dose accumulations and discusses, briefly, strategies for the new LCLS-II upgrade, which will be operating at more than 300 times larger beam rate.

MOP047

A 200 μm-period Laser-driven Undulator

131

F. Toufexis, T. Tang, S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515 and the DARPA AXiS program.
To reduce the linac energy required for a given synchrotron radiation wavelength, and hence the size of the device, a smaller undulator period with sufficient field strength is needed. In this work, a microfabricated, laser-driven undulator with 200um undulator period is proposed. A TE wave that co-propagates with the electron beam is excited between two polysilicon thin films, having a gap of 16.5um. The mode that is excited is a deflecting mode and causes the electron beam to wiggle. The device is fabricated on a silicon wafer, using conventional silicon micromachining techniques. A single polysilicon thin film is supported on a silicon chip, which has a slit from the back to allow delivery of the laser beam. Two such chips are bonded together to form a 16.5um gap, within which the electron beam passes through. The final device has dimensions 1cm x 1cm x 1.1mm and has approximately 35 undulator periods. In this paper, the model, design, fabrication, and cold measurements of the device are reported.

MOP048

Temporal Diagnostics Measurements with the Pulse Arrival and Length Monitor (PALM) at SACLA

I. Gorgisyan, C.P. Hauri
EPFL, Lausanne, Switzerland
I. Gorgisyan, C.P. Hauri, R. Ischebeck, P.N. Juranic, B. Monoszlai, B. Monoszlai, L. Patthey, C. Pradervand, M. Radovic, A.G. Stepanov
PSI, Villigen PSI, Switzerland
R. Ivanov
DESY, Hamburg, Germany
J. Liu
XFEL. EU, Hamburg, Germany
B. Monoszlai
University of Pecs, Pécs, Hungary
K. Ogawa, T. Togashi, M. Yabashi
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
S. Owada
JASRI/RIKEN, Hyogo, Japan
M. Yabashi
RIKEN/SPring-8, Hyogo, Japan

The development of FEL facilities all over the world necessitates the development of temporal diagnostics for the photon pulses these facilities provide. Photon pulse length and arrival time measurements are particularly helpful for both the operators and the users of an FEL for monitoring the operation of the facility and the experiments. The development of FEL facilities all over the world necessitates the development of temporal diagnostics for the photon pulses these facilities provide. Swiss Free Electron Laser is the upcoming X-ray FEL facility at PSI, that will provide short pulsed radiation in hard X-ray region. In order to face the challenge of measuring the temporal properties of such pulses, a pulse arrival time and length monitor (PALM) is currently being developed at PSI. The concept of THz-streak camera is used to measure the arrival time relative to a beamline laser and the length of a photon pulse. A prototype version of the device was used for measurements at SACLA in order to show the feasibility of the device for photon pulses in hard X-ray region and test the reliability of the measurements. The first results from the beamtime at SACLA will be presented. The plans for further development of the system will be discussed.

Poster MOP048 [8.009 MB]

MOP049

Oxygen Scintillation in the LCLS

137

J.L. Turner, R.C. Field
SLAC, Menlo Park, California, USA

Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Oxygen is tested as a replacement for Nitrogen in the Gas Detector system in the Linac Coherent Light Source (LCLS) x-ray Free Electron Laser (FEL) at the SLAC National Accelerator Center. The attenuation and energy monitors for LCLS use Nitrogen, but for experiments at the Nitrogen K 1S energy of about 410eV this functionality is gone due to energy fluctuations above and below the K-edge. Oxygen was tested as a scintillating gas at 400eV and 8.3keV.

MOP050

The Collimation System for LCLS-II*

J.J. Welch, E. Marín, T.O. Raubenheimer, M. Santana-Leitner, G.R. White
SLAC, Menlo Park, California, USA
C.E. Mayes
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: * Work supported by U.S. Department of Energy contract DE-AC02-76SF00515.
Minimizing beam loss is particularly important for LCLS-II because of very high average power beams, radiation sensitive undulators, and the high cost of adding shielding to existing accelerator enclosures. For example, for acceptable undulator magnet lifetime, dark current originating at the cathode must be attenuated by approximately a factor of 10^-7 in a single pass before it reaches the undulator. Multi-stage, high-efficiency collimation is necessary. The system is described in this paper. A model of beam halo and dark current is developed that includes sources due to Touschek, intra-beam, and beam-gas scattering, as well as field emission from superconducting cavities, photo-emission from stray light on the cathode, and cathode field emission. The location and gap of the collimators is optimized using tracking analysis and other tools developed and validated at Cornell. Collimator efficiency is estimated by tracking secondaries using a modified version of Lucretia which call GEANT4. Finally collimator jaw design is optimized to produce a minimum leakage using FLUKA. These topics are discussed in this paper.

MOP052

Update on FEL Performance for SwissFEL

140

E. Prat, S. Reiche
PSI, Villigen PSI, Switzerland

The SwissFEL project under construction at the Paul Scherrer Institute foresees for 2017 the realization of an X-ray FEL with a photon wavelength down to 1 Å. In this paper we present the expected SASE performance for SwissFEL based on input distributions obtained from detailed start-to-end simulation results. The effects of the longitudinal wakefields due to resistive wall and surface roughness in the undulator beamline have been taken into account. We have studied and optimized the impact on the FEL performance of different factors like the electron focusing or the undulator tapering. Results for the standard cases with 200 pC and 10 pC electron bunch charge are shown.

MOP053

SASE FEL Performance at the SwissFEL Injector Test Facility

144

S. Reiche
PSI, Villigen PSI, Switzerland

A 4 m long prototype of the SwissFEL undulator module with an undulator period length of 15 mm was installed at the SwissFEL Injector Test Facility and tested with a 200 MeV electron beam in the beginning of 2014. We observed FEL lasing in SASE mode in the wavelength range from 70 to 800 nm, tuning the wavelength by energy and gap. The measurements of the FEL performance are reported.
on behalf of the SwissFEL Team

MOP054

Harmonic Lasing Options for LCLS-II

148

G. Marcus, Y. Ding, Z. Huang, T.O. Raubenheimer
SLAC, Menlo Park, California, USA
G. Penn
LBNL, Berkeley, California, USA

Harmonic lasing can be a cheap and relatively efficient way to extend the photon energy range of a particular FEL beamline. Furthermore, in comparison to nonlinear harmonics, harmonic lasing can provide a beam that is more intense, stable, and narrow-band. This paper explores the application of the harmonic lasing concept at LCLS-II using various combinations of phase shifters and attenuators. In addition, a scheme by which individual undulator modules are tuned to amplify either the third or fifth harmonic in different configurations is presented in detail.

MOP055

Start-to-End Simulations for IR/THz Undulator Radiation at PITZ

153

P. Boonpornprasert, M. Khojoyan, M. Krasilnikov, F. Stephan
DESY Zeuthen, Zeuthen, Germany
B. Marchetti, E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany
S. Rimjaem
Chiang Mai University, Chiang Mai, Thailand

High brightness electron sources for modern linac-based Free-Electron Lasers (FELs) have been characterized and optimized at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). Since the time structure of the electron bunches at PITZ is identical to those at the European XFEL, the PITZ accelerator is being considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments planned at the European XFEL. Tunable IR/THz radiation sources using synchrotron radiation from a dipole magnet, transition radiation, high gain FELs and coherent radiation of tailored or premodulated beams are currently under consideration. This work describes start-to-end simulations for generating the FEL radiation using an APPLE-II undulator with electron beams produced by the PITZ accelerator. Analysis of the physical parameter space has been performed with tools of the FAST program code package. Electron Beam dynamics simulations were performed by using the ASTRA code, while the GENESIS 1.3 code was used to study the SASE process. The results of these studies are presented and discussed in this paper.

MOP056

SASE Characteristics from Baseline European XFEL Undulators in the Tapering Regime

159

I.V. Agapov, G. Geloni
XFEL. EU, Hamburg, Germany
G. Feng, V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov
DESY, Hamburg, Germany

The output SASE characteristics of the baseline European XFEL, recently used in the TDRs of scientific instruments and X-ray optics, have been previously optimized assuming uniform undulators without considering the potential of undulator tapering in the SASE regime. Here we demonstrate that the performance of European XFEL sources can be significantly improved without additional hardware. The procedure consists in the optimization of the undulator gap configuration for each X-ray beamline. Here we provide a comprehensive description of the X-ray photon beam properties as a function of wavelength and bunch charge. Based on nominal parameters for the electron beam, we demonstrate that undulator tapering allows one to achieve up to a tenfold increase in peak power and photon spectral density in the conventional SASE regime.

MOP057

Proposal to Generate 10 TW Level Femtosecond X-ray Pulses from a Baseline Undulator in Conventional SASE Regime at the European XFEL

164

E. Saldin, V. Kocharyan, S. Serkez, I. Zagorodnov
DESY, Hamburg, Germany
G. Geloni
XFEL. EU, Hamburg, Germany

Output characteristics of the European XFEL have been previously studied assuming an operation point at 5 kA peak current. Here we explore the possibility to go well beyond such nominal peak current level. We consider a bunch with 0.25 nC charge, compressed up to a peak current of 45 kA. An advantage of operating at such high peak current is the increase of the x-ray output peak power without any modification to the baseline design. Based on start-to-end simulations, we demonstrate that such high peak current, combined with undulator tapering, allows one to achieve up to a 100-fold increase in a peak power in the conventional SASE regime, compared to the nominal mode of operation. In particular, we find that 10 TW-power level, femtosecond x-ray pulses can be generated in the photon energy range between 3 keV and 5 keV, which is optimal for single biomolecule imaging. Our simulations are based on the exploitation of all the 21 cells foreseen for the SASE3 undulator beamline, and indicate that one can achieve diffraction to the desired resolution with 15 mJ (corresponding to about 3·10¹³ photons) in pulses of about 3 fs, in the case of a 100 nm focus at the photon energy of 3.5 keV.

MOP058

Purified SASE Undulator Configuration to Enhance the Performance of the Soft X-ray Beamline at the European XFEL

169

V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov
DESY, Hamburg, Germany
I.V. Agapov, G. Geloni
XFEL. EU, Hamburg, Germany

The purified SASE (pSASE) undulator configuration recently proposed at SLAC promises an increase in the output spectral density of XFELs. In this article we study a straightforward implementation of this configuration for the soft x-ray beamline at the European XFEL. A few undulator cells, resonant at a subharmonic of the FEL radiation, are used in the middle of the exponential regime to amplify the radiation, while simultaneously reducing the FEL bandwidth. Based on start-to-end simulations, we show that with the proposed configuration the spectral density in the photon energy range between 1.3 keV and 3 keV can be enhanced of an order of magnitude compared to the baseline mode of operation. This option can be implemented into the tunable-gap SASE3 baseline undulator without additional hardware, and it is complementary to the self-seeding option with grating monochromator proposed for the same undulator line, which can cover the photon energy range between about 0.26 keV and 1 keV.

MOP059

Beam Dynamic Simulations for Single Spike Radiation with Short-Pulse Injector Laser at FLASH

173

M. Rehders
University of Hamburg, Hamburg, Germany
J. Rönsch-Schulenburg
CFEL, Hamburg, Germany
J. Rönsch-Schulenburg, J. Roßbach
Uni HH, Hamburg, Germany
S. Schreiber
DESY, Hamburg, Germany

Funding: The project has been supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301
This paper discusses the generation of single spike SASE pulses at soft x-ray wavelength at the free-electron laser FLASH by using very short electron bunches of only a few micrometer bunch length. In order to achieve these extremely short bunch lengths, very low bunch charges (in the order of 20 pC) and short electron bunches exiting the photo-injector are required. For this, a new short-pulse injector laser with adjustable rms pulse duration in the range of 0.7 ps to 1.6 ps and bunch charges up to 200 pC was installed, extending the electron beam parameter range before bunch compression in magnetic chicanes. Beam dynamic studies have been performed to optimize the injection and compression of low-charge electron bunches by controlling the effect of coherent synchrotron radiation and space-charge induced bunch lengthening and emittance growth. Optimization includes the pulse parameters of the injector laser. The simulation codes ASTRA, CSRtrack and Genesis 1.3 were employed.

MOP060

Demonstration of SASE Suppression Through a Seeded Microbunching Instability

177

C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach
Uni HH, Hamburg, Germany
S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, E. Hass, K. Honkavaara, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov
DESY, Hamburg, Germany
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school 1355.
Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brilliance electron bunches needed for the operation of free-electron lasers. In this contribution, we demonstrate the application of a laser-induced microbunching instability to selectively suppress the SASE process. A significant decrease of photon pulse energies was observed at the free-electron laser FLASH in coincidence with overlap of 800 nm laser pulses and electron bunches within a modulator located approximately 40 meters upstream of the undulators. We discuss the underlying mechanisms based on longitudinal space charge amplification [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.

MOP061

Electron Beam Delays for Improved Temporal Coherence and Short Pulse Generation at SwissFEL

181

N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S. Reiche
PSI, Villigen PSI, Switzerland

Proposals have been made for the introduction of magnetic electron beam delays in between the undulator modules of a long sectional FEL undulator - these can be used for the generation of trains of FEL pulses which can individually be shorter than the FEL cooperation time [*] or to greatly improve the temporal coherence of the FEL output compared to the nominal SASE configuration [**,***,***]. This paper comprises a feasibility study of the application of these techniques to the SwissFEL hard X-Ray beamline. Three-dimensional simulations are used to investigate the potential photon output.
[*] N.R. Thompson and B.W.J. McNeil, PRL 100:203901, 2008.
[**] N.R. Thompson et al. In Proc IPAC2010, pages 2257–2259, 2010
[***] J. Wu, A. Marinelli, and C. Pellegrini. Proc FEL2012, 2012.

MOP062

FEL Proposal Based on CLIC X-Band Structure

186

A.A. Aksoy, Ö. Yavaş
Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey
E. Adli
University of Oslo, Oslo, Norway
D. Angal-Kalinin, J.A. Clarke
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc
SLSA, Clayton, Australia
N. Charitonidis, A. Grudiev, A. Latina, D. Schulte, I. Syratchev, W. Wuensch
CERN, Geneva, Switzerland
G. D'Auria, S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
W. Fang, Q. Gu
SINAP, Shanghai, People's Republic of China
E.N. Gazis
National Technical University of Athens, Athens, Greece
M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann
Uppsala University, Uppsala, Sweden
Z. Nergiz
Nigde University, Nigde, Turkey

A linear accelerating structure with an average loaded gradient of 100 MV/m at X-Band frequencies has been demonstrated in the CLIC study. Recently, it has been proposed to use this structure to drive an FEL linac. In contrast to CLIC the linac would be powered by klystrons not by an RF source created by a drive beam. The main advantage of this proposal is achieving the required energies in a very short distance, thus the facility would be rather compact. In this study, we present the structure choice and conceptual design parameters of a facility which could generate laser photon pulses below Angstrom. Shorter wavelengths can also be reached with slightly increasing the energy.

MOP063

A Novel Modeling Approach for Electron Beams in SASE FELs

190

P. Niknejadi, J. Madey
University of Hawaii, Honolulu,, USA

We have recently shown that the Wheeler-Feynman analysis of the interaction of a moving charge with distant absorbers [*] provides a perfect match to the energy radiated by two coherently oscillating charged particles (a heretofore unsolved problem in classical electrodynamics) [**]. Here we explain the need to include the Wheeler-Feynman coherent radiation reaction force as an integral part of the solution of the boundary value problem of free electron lasers (FELs) that radiate into “free space”. We will also discuss how the advanced field of the absorber can interact with the radiating particles at the time of emission. Finally we will introduce and explore the possibility of improving the temporal coherence in the self amplified spontaneous emission (SASE) FELs as well as the possibility of optimizing the spectrum of the emitted coherent radiation by SASE FELs via altering the structure of their targets by including the Wheeler-Feynman coherent radiation reaction force in the analysis of FEL operations.
* Wheeler, J. A.; Feynman, R. P, Rev. Mod. Phys. 17, 157, 1945.
** P. Niknejadi et al. "Energy Conservation of Coherently Oscillating Charged Particles in Classical Electrodynamics" submitted.

MOP064

Statistical Properties of the Radiation from SASE FEL Operating in a Post-saturation Regime with and without Undulator Tapering

194

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

We describe statistical and coherence properties of the radiation from x-ray free electron lasers (XFEL) operating in the post-saturation regime. We consider practical case of the SASE3 FEL at European XFEL. We perform comparison of the main characteristics of X-ray FEL operating in the post-saturation regime with and without undulator tapering: efficiency, coherence time and degree of transverse coherence.

MOP065

Optimization of a High Efficiency FEL Amplifier

199

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

The problem of an efficiency increase of an FEL amplifier is now of great practical importance. Technique of undulator tapering in the post-saturation regime is used at the existing x-ray FELs LCLS and SACLA, and is planned for use at the European XFEL, Swiss FEL, and PAL XFEL. There are also discussions on the future of high peak and average power FELs for scientific and industrial applications. In this paper we perform detailed analysis of the tapering strategies for high power seeded FEL amplifiers. Application of similarity techniques allows us to derive universal law of the undulator tapering.

MOP066

An Overview of the Radiation Properties of the European XFEL

204

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

We present an overview of the radiation properties of the European XFEL based on recently accepted strategy of operation at the fixed set of electron energies (8.5 GeV, 12 GeV, 14 GeV, and 17.5 GeV), baseline parameters if the electron beam, and new set undulator parameters. We also discuss potential extension of the parameter space which does not require new hardware and can be realized at a very early stage of the European XFEL operation.

MOP067

Prospects for CW Operation of the European XFEL in Hard X-ray Regime

210

R. Brinkmann, E. Schneidmiller, J.K. Sekutowicz, M.V. Yurkov
DESY, Hamburg, Germany

The European XFEL will operate nominally at 17.5 GeV in SP (short pulse) mode with 0.65 ms long bunch train and 10 Hz repetition rate. A possible upgrade of the linac to CW (continuous wave) or LP (long pulse) modes with a corresponding reduction of electron beam energy is under discussion since many years. Recent successes in the dedicated R&D program allow to forecast a technical feasibility of such an upgrade in the foreseeable future. One of the challenges is to provide sub-Angstroem FEL operation in CW and LP modes. In this paper we perform a preliminary analysis of a possible operation of the European XFEL in the hard X-ray regime in CW and LP modes with the energies of 7 GeV and 10 GeV, respectively. We consider lasing in the baseline XFEL undulator as well as in a new undulator with a reduced period. We show that, with reasonable requirements on electron beam quality, lasing on the fundamental will be possible in sub-Angstroem regime. As an option for generation of brilliant photon beams at short wavelengths we also consider harmonic lasing that has recently attracted a significant attention.

MOP068

Suppression of the Fundamental Frequency for a Successful Harmonic Lasing in SASE FELs

215

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

Harmonic lasing in X-ray FELs has recently attracted a significant attention and is now seriously considered as a potential method for generation of brilliant photon beams at short wavelengths. It is clear, however, that for a successful harmonic lasing one has to suppress the fundamental. In this paper we discuss different methods for such a suppression: phase shifters, intraundulator spectral filtering, switching between the 3rd and the 5th harmonics etc.

MOP070

Design Study for the PEHG Experiment at SDUV-FEL

219

C. Feng, H.X. Deng, B. Liu, D. Wang, X.T. Wang, M. Zhang, T. Zhang, W. Zhang, Z.T. Zhao
SINAP, Shanghai, People's Republic of China

Funding: This work was partially supported by National Natural Science Foundation of China (11475250, 11175240 and 11205234)
In this paper, design studies for the proof-of-principle experiment of the recently proposed phase-merging enhanced harmonic generation (PEHG) mechanism are presented. A dogleg and a new designed transverse gradient undulator should be added in the undulator system of SDUV-FEL to perform the phase-merging effect. With the help of 3D simulation codes, we show the possible performance of PEHG with the realistic parameters of SDUV-FEL.
* H. Deng, C. Feng, Phys. Rev. Lett. 111, 084801.
** C. Feng, H. Deng, D. Wang, Z. Zhao, New J. Phys.,16, 043021.
*** C. Feng, T. Zhang, H. Deng, Z. Zhao, Phys. Rev. ST Accel. Beams 17, 070701.

MOP072

Preparation for the CPA-CHG Experiment at SDUV-FEL

C. Feng, H.X. Deng, T. Lan, B. Li, B. Liu, D. Wang, X.T. Wang, Z.T. Zhao
SINAP, Shanghai, People's Republic of China

Chirped pulse amplification has been shown theoretically possible to generate ultra-short high intensity radiation pulses in a seeded FEL. To demonstrate the theoretical predictions, a CPA-CHG experiment is under preparation based on the SDUV-FEL recently. We will show the experiment layout, optical design studies and some preliminary measurement results of the optical systems in this paper.
* L. Yu, E. Johnson, D. Li, D. Umstader, Physical Review E 49 (1994) 4480
** C. Feng et al. Nuclear Instruments and Methods in Physics Research A 712 (2013) 113

MOP073

Chirped Pulse Amplification in a Seeded Free-electron Laser: Design of a Test Experiment at FERMI

G. De Ninno, E. Allaria, I. Cudin, M.B. Danailov, A.A. Demidovich, S. Di Mitri, E. Ferrari, D. Gauthier, L. Giannessi, N. Mahne, G. Penco, L. Raimondi, P. Rebernik Ribič, C. Spezzani, L. Sturari, C. Svetina, M. Zangrando
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
H. Dacasa, B. Mahieu, P. Zeitoun
LOA, Palaiseau, France
M. Fajardo
IPFN, Lisbon, Portugal
E. Ferrari
Università degli Studi di Trieste, Trieste, Italy
F. Frassetto, L. P. Poletto
LUXOR, Padova, Italy
D. Gauthier
University of Nova Gorica, Nova Gorica, Slovenia
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy

In solid-state lasers, frequency chirping is employed to stretch a short pulse prior to amplification, mitigating the problems related to high power in the active medium. After amplification, the chirp is compensated in order to recover short pulse duration and, hence, high peak power. Chirped pulse amplification (CPA) in seeded FEL’s relies on a similar principle: the seed pulse is stretched in time before interacting with the electron beam. This permits one to create bunching on a larger number of electrons, and to (approximately) linearly increase the output energy of the generated FEL pulse. In ideal conditions, the chirp carried by the phase of the seed pulse is transmitted to the output phase of the FEL pulse. Chirp compensation after the last undulator allows production of a short (ideally Fourier-transformed) pulse and, therefore, a larger peak power with respect to what obtained, for the same conditions, in standard (i.e., no-chirp-on-the-seed) operation mode. In this paper, we present the preparatory studies (i.e., numerical simulations and compressor design), which have been carried out at FERMI, in view of performing the first test experiment of CPA on a seeded FEL.

MOP075

Laser Seeding Schemes for Soft X-rays at LCLS-II

223

G. Penn
LBNL, Berkeley, California, USA
P. Emma, E. Hemsing, G. Marcus, T.O. Raubenheimer, L. Wang
SLAC, Menlo Park, California, USA

Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract Nos. DE-AC02-05CH11231 and DE-AC02-76SF00515.
The initial design for LCLS-II incorporates both SASE and self-seeded configurations. Increased stability and/or coherence than is possible with either configuration may be provided by seeding with external lasers followed by one or more stages of harmonic generation, especially in the soft x-ray regime. External seeding also allows for increased flexibility, for example the ability to quickly vary the pulse duration. Studies of schemes based on high-gain harmonic generation and echo-enabled harmonic generation are presented, including realistic electron distributions based on tracking through the injector and linac.

MOP077

Measurements of the FEL-bandwidth Scaling with Harmonic Number in a HGHG FEL

227

E. Allaria, M.B. Danailov, W.M. Fawley, E. Ferrari, L. Giannessi
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

In this work we report recent measurements done at FERMI showing the dependence of the FEL bandwidth with respect to the seed laser harmonic at which the FEL is operated. Comparison of FEL spectra for different Fourier-limit seed and chirp pulses is also reported.

MOP078

Measurements of FEL Polarization at FERMI

231

E. Allaria
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

We report detailed quantitative characterization of different polarization states of a single-pass, externally-seeded FEL operating with variable polarization undulators in the VUV spectral range. The experiment has been performed at FERMI FEL-1 operated in the 52–26 nm wavelength range. Three different, independent polarimeter setups, installed at the end of ex- perimental beamlines, have been used to characterize the four “pure” polarization states: horizontal, vertical, right-circular and left-circular. The impact of downstream transport optics upon the radia- tion polarization has been assessed; at longer wavelengths, dichroism effects lead to a non-negligible ellipticity for an originally circularly polarized state. The results from the different polarimeter setups validate each other and allow a cross-calibration of the instruments.
On behalf of the team organized for polarization measurements at FERMI.

MOP079

Generation of Multiple Coherent Pulses in a Superradiant Free-Electron Laser

233

X. Yang, S. Seletskiy
BNL, Upton, Long Island, New York, USA
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy

We analyze the structure of the tail of a superradiant pulse, which is constituted by a train of sub-pulses with decaying amplitudes. We show how a trailing pulse, with pi phase advance from the leading pulse, is generated at the falling edge of the leading superradiant pulse, where the corresponding phase space is deeply saturated and the electrons become de-trapped by the reduced ponderomotive potential. Once the trailing pulse gains enough energy, it generates a second trailing pulse, and the process takes place again. By performing detailed simulations of the resulting electron phase space distribution and the FEL pulse spectral and temporal structure with PERSEO, we confirm that the deformation and re-bunching of the longitudinal phase space create a sequence of pulses. These results are compared to 3D simulations using the FEL code GENESIS 1.3 showing a good agreement.

MOP080

Two Color Experiments at SPARC: External and Intra-bunch Seeding

D. Alesini, M.P. Anania, M. Bellaveglia, M. Castellano, E. Chiadroni, D. Di Giovenale, G. Di Pirro, M. Ferrario, A. Gallo, G. Gatti, R. Pompili, S. Romeo, V. Shpakov, C. Vaccarezza, F. Villa
INFN/LNF, Frascati (Roma), Italy
M. Artioli
ENEA-Bologna, Bologna, Italy
A. Bacci, A.R. Rossi
Istituto Nazionale di Fisica Nucleare, Milano, Italy
M.C. Carpanese, F. Ciocci, G. Dattoli, E. Di Palma, L. Giannessi, A. Petralia, E. Sabia, I.P. Spassovsky
ENEA C.R. Frascati, Frascati (Roma), Italy
A. Cianchi
INFN-Roma II, Roma, Italy
F. Filippi, A. Giribono
INFN-Roma, Roma, Italy
L. Innocenti
Università di Roma II Tor Vergata, Roma, Italy
N.S. Mirian, V. Petrillo
Universita' degli Studi di Milano & INFN, Milano, Italy
A. Mostacci
Rome University La Sapienza, Roma, Italy
J.V. Rau
ISM-CNR, Rome, Italy

The FEL-SPARC operation with two bunches at different energies has been characterized using different tools. The effect of the e-beam matching on the SASE operation has been explored by controlling the transport with an ad hoc developed control system, allowing either the transport in matching conditions and in different configurations. Since the two bunches have, at the entrance of the undulator, different phase space characteristics we used this effect as a knob to enhance or suppress one or the other FEL mode. We investigated the effect of seeding on both frequencies and observed beating waves, furthermore we observed effects of intra-bunch seeding when only one of the modes is seeded.

MOP081

Seeding Preparation at the FLASH2 Beamline

T. Tanikawa, A. Hage
DESY, Hamburg, Germany

At the FLASH Facility at DESY, Hamburg, a new undulator line, referred to as FLASH2, has been added. First electron beam in FLASH2 has reached the beam dump in May. Further commissioning, including first SASE, is foreseen for the remainder of the year. This FEL has been designed to include seeding in the future, such as a high-gain harmonic generation (HGHG) or an echo-enable harmonic generation (EEHG). The optimal choice for seeding at FLASH2 is under discussion. For seeding at FLASH2, an XUV spectrometer, a laser system based on optical parametric chirped-pulse amplification (OPCPA) as well as a system for a third harmonic generation (THG) including diagnostic tools have been prepared. We will report the current status.

MOP082

Perspectives for Imaging Single Protein Molecules with the Present Design of the European XFEL

238

G. Geloni
XFEL. EU, Hamburg, Germany
V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov
DESY, Hamburg, Germany
O. Yefanov
CFEL, Hamburg, Germany

European XFEL aims to support imaging and structure determination of biological specimens between less than 0.1 microns and 1 micron size with working photon energies between 3 keV and 16 keV. This wide operation range is a cause for challenges to the focusing optics. A long propagation distance of about 900 m between x-ray source and sample leads to a large lateral photon beam size at the optics. Due to the large divergence of nominal X-ray pulses with durations shorter than 10 fs, one suffers diffraction from mirror apertures, leading to a 100-fold decrease in fluence at photon energies around 4 keV, which seem ideal for imaging of single biomolecules. Moreover, the nominal SASE1 is very far from the level required for single particle imaging. Here we show how it may be possible to optimize the SPB instrument for single biomolecule imaging with minimal additional costs and time, achieving diffraction without destruction at near-atomic resolution with 10¹³ photons in a 4 fs pulse at 4 keV photon energy and in a 100 nm focus, corresponding to a fluence of 10²³ ph/cm². This result is exemplified using the RNA Pol II molecule as a case study.

MOP083

Start-to-End Simulation for FLASH2 HGHG Option

244

G. Feng, S. Ackermann, J. Bödewadt, W. Decking, M. Dohlus, Y.A. Kot, T. Limberg, M. Scholz, I. Zagorodnov
DESY, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany
T. Plath
Uni HH, Hamburg, Germany

The Free-electron laser in Hamburg (FLASH) is the first FEL user facility to have produced extreme ultraviolet (XUV) and soft X-ray photons. In order to increase the beam time delivered to users, a major upgrade of FLASH named FLASH II is in progress. The electron beamline of FLASH2 consists of diagnostic and matching sections, a seeding undulator section and a SASE undulator section. In this paper, results from a start-to-end simulation for a FLASH2 High-Gain Harmonic Generation (HGHG) option are presented. For the beam dynamics simulation, space charge, coherent synchrotron radiation (CSR) and longitudinal cavity wake field effects are taken into account. In order to get electron beam bunches with small correlated and uncorrelated energy spread, RF parameters of the accelerating modules have been optimized as well as the parameters of the bunch compressors. Radiation simulations for the modulator and the radiator have been done with code Genesis 1.3 by using the particle distribution generated from the beam dynamics simulation. The results show that for a single stage HGHG, 33.6 nm wavelength FEL radiation can be seeded at FLASH2 with a 235 nm seeding laser.

MOP084

Enhancing Coherent Harmonic Generation using Tilted Laser Wavefronts

248

S. Khan
DELTA, Dortmund, Germany

Funding: Work supported by BMBF (contract 05K13PE3)
Coherent Harmonic Generation (CHG) to produce ultrashort pulses of synchrotron radiation is based on the interaction of relativistic electrons in a storage ring with femtosecond laser pulses in an undulator. The resulting periodic energy modulation can be converted to a density modulation by a dispersive chicane, giving rise to coherent emission at harmonics of the laser wavelength in a second undulator. If the first undulator is in a section with non-zero dispersion, the density modulation can be enhanced using tilted laser wavefronts, thus delaying the phase-space distributions of electrons with different energy with respect to each other. The most simple way to realize the wavefront tilt would be to introduce a small crossing angle between the electron and laser beam. Details are discussed for the case of the CHG short-pulse facility at DELTA, a 1.5-GeV synchrotron light source at the TU Dortmund University, but HGHG and EEHG seeding of free-electron lasers could also be performed this way.

MOP085

Novel Seeding and Wavelength Shifting in Free Electron Lasers

N. Sipahi, S. Biedron, S.V. Milton
CSU, Fort Collins, Colorado, USA

Free Electron Lasers provide the opportunity for continuous tunability of light from the mm-wave region to hard x-rays. For example, single-pass SASE operation allows very short wavelength operation without using optical cavity structure; unfortunately, the resulting photon beam is poor in terms of longitudinal coherence and shot-to-shot stability. Seeding can greatly improved the longitudinal coherence and shot-to-shot stability but this is dependent on the availability of a suitable seed pulse and then the challenge remains of switching the wavelength quickly. Here a new concept is investigated, one called wavelength shifting where a solid seed source is utilized and then the resultant wavelength shifted to the desired result. This new idea can improve the longitudinal coherence as well as stabilize the shot-to-shot output power while permitting continuous wavelength tunability.

MOP086

Broadly Tunable THz FEL Amplifier

252

C.H. Chen, F.H. Chao, Y.C. Chiu, Y.K. Gan, K.Y. Huang, Y.-C. Huang, Y.C. Wang
NTHU, Hsinchu, Taiwan

Funding: MOST 102-2112-M-007 -002 -MY3, Taiwan
In this paper we present a broadly tunable sub-MW THz FEL amplifier driven by a photoinjector with a sub-kW seed THz source tunable between 0.7-2.0 THz. Specifically an S-band photoinjector at 2.856 GHz generate a 3.3-5.5 MeV electron bunch with 0.5 nC charge in a 4.25 ps rms bunch length, which is injected into a 2-m long undulator with a period of 18 mm and an rms undulator parameter of 0.98. The driver laser of the photoinjector is a frequency quadrupled amplified, mode-locked Nd:YVO4 laser at 1064 nm. We recycle the unconverted infrared laser at 1064 nm to pump a THz parametric amplifier using a lithium niobate crystal as its gain crystal. This THz parametric amplifier generates a transform-limited THz pulse with sub-kW power between 0.7 and 2.0 THz, which is seeded into the undulator to produce broadly tunable, transform-limited, sub-MW THz radiation through FEL amplification with a gain of about 3000. Since the pump laser of the THz OPA is derived from the driver laser of the photoinjector, the seed THz pulse is fully synchronized and overlapped with the electron bunch. Experimental progress of this work will be presented in the conference.
*Work supported by MoST under NSC 102-2112-M-007-002-MY3

Poster MOP086 [1.269 MB]

MOP087

Upgrade Plans for the Short-pulse Facility at DELTA

255

S. Hilbrich, H. Huck, M. Huck, M. Höner, S. Khan, C. Mai, A. Meyer auf der Heide, R. Molo, H. Rast, P. Ungelenk
DELTA, Dortmund, Germany

Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Land NRW.
DELTA is a 1.5-GeV synchrotron light source operated by the TU Dortmund University with a short-pulse facility based on Coherent Harmonic Generation (CHG) * to produce radiation with wavelengths in the VUV regime. Even shorter wavelengths can be generated by an upgrade based on the Echo-Enabled Harmonic Generation (EEHG) technique ** which requires additional magnetic chicanes and undulators. A new storage ring lattice provides enough free space for an EEHG setup and additionally for a femtoslicing undulator. Besides the new optics, first simulation results of EEHG will be presented.
* S. Khan et al., Sync. Rad. News 26, 3 (2013).
** G. Stupakov, Phys. Rev. Lett. 102, 074801 (2009).

MOP088

High Repetition Rate Energy Modulator System Utilizing a Laser Enhancement Cavity

260

Y. Honda
KEK, Ibaraki, Japan

A high intensity laser field can be realized at a high repetition rate using an enhancement optical cavity scheme. We propose to apply the 100GW-level laser field inside the cavity for producing a micro-bunch structure in an electron bunch. Combining this system with an ERL scheme of accelerator, it can be used for a seeded FEL at a high repetition rate of ~100MHz continuous beam. The longitudinal electric field at the center area of a higher-order transverse mode of laser can be used to modulate beam energy at a period of the laser wavelength. A 250 MeV class two-loop ERL accelerator has been proposed in KEK as a future upgrade plan of existing 35 MeV ERL test accelerator. It will be able to provide a low emittance, small energy spread, short bunch electron beam at a high repetition rate of continuous operation. We propose to apply this beam to produce a seeded VUV coherent radiation. We will discuss the feasibility of the scheme and status of the laser modulator development.

MOP089

Overview of FEL Seeding Activities at FLASH

J. Bödewadt, S. Ackermann, R.W. Aßmann, N. Ekanayake, B. Faatz, G. Feng, I. Hartl, R. Ivanov, T. Laarmann, J.M. Mueller, T. Tanikawa
DESY, Hamburg, Germany
S. Ackermann, A. Azima, M. Drescher, L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Roßbach
Uni HH, Hamburg, Germany
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany

The free-electron laser facility FLASH at DESY operates since several years in SASE mode, delivering high-intensity FEL pulses in the extreme ultra violet and soft x-ray wavelength range for users. In order to get more control of the characteristics of the FEL pulses external FEL seeding has proven to be a reliable method to do so. At FLASH, an experimental setup to test several different external seeding methods has been installed since 2010. After successful demonstration of direct seeding at 38 nm, the setup is now being commissioned to operate in HGHG and EEHG mode. Furthermore, other studies on laser induced effects on the electron beam dynamics will be performed. Beside the experimental activities, a design for the seeding option for the FLASH2 beamline is currently under investigation. The goal for that is to develop a concept which is compatible with the operation of FLASH1 and which satisfies the high demands of the future user community. In this contribution, we give an overview of the activities on FEL seeding at FLASH.

MOP090

Soft X-ray Self-seeding Simulation Methods and their Application for LCLS

264

S. Serkez
DESY, Hamburg, Germany
Y. Ding, Z. Huang, J. Krzywinski
SLAC, Menlo Park, California, USA

Self-seeding is a promising approach to significantly narrow the SASE bandwidth of XFELs to produce nearly transform-limited pulses. We study radiation propagation through the grating monochromator installed at LCLS. The monochromator design is based on a toroidal variable line spacing grating working at a fixed incidence angle mounting without an entrance slit. It covers the spectral range from 500eV to 1000eV. The optical system was studied using wave optics method to evaluate the performance of the self-seeding scheme. Our wave optics analysis takes into account the finite size of the coherent source, third-order aberrations and height error of the optical elements. Wave optics is the only method available, in combination with FEL simulations, to simulate performance of the monochromator without exit slit. Two approaches for time-dependent simulations are presented, compared and discussed. Also pulse-front tilt phenomenon effect is illustrated.

MOP091

Laser Heater and Seeded Free Electron Laser: Comments on Recent FERMI Experimental Results

G. Dattoli, E. Sabia
ENEA C.R. Frascati, Frascati (Roma), Italy
V. Petrillo
Universita' degli Studi di Milano & INFN, Milano, Italy

In this paper we consider the effect of laser heater on a seeded Free Electron Laser. We develop a model embedding the effect of the energy modulation induced by the heater with those due to the seeding. The present analysis is compatible with the experimental results obtained at FERMI displaying secondary maxima with increasing heater intensity. The problem has been considered ab-inito, by developing a numerical code based on the solution of the Liouville equation ruling the phase space evolution of the e-beam undergoing the various dynamical stages: Heating, Acceleration, Seeding. The treatment developed in the paper confirms and extends previous analyses and put in evidence further effects which can be tested in future experiments.

MOP092

X-ray Monochromators for Self-seeding XFELs in the Photon Energy Range Starting from 1.5 keV

269

Yu. Shvyd'ko
ANL, Argonne, Ilinois, USA

Self-seeding of XFELs below 1 keV can be performed using grating monochromators [1]. Forward-Bragg diffraction (wake) monochromators [2] were instrumental for achieving self-seeding in hard x-ray FELs in the photon energy range from 5 to 10 keV [3]. Large photo-absorption makes extension into the lower photon range difficult. Here alternative schemes of x-ray monochromators are introduced and discussed for achieving self-seeding in a yet inaccessible spectral range starting from 1.5 keV.
[1] J. Feldhaus, et al., Opt. Commun. 140, 341 (1997).
[2]. G. Geloni, V. Kocharyan, and E. Saldin, J. Mod. Opt. 58, 1391 (2011).
[3] J. Amann, et al., Nat. Photonics 6, 693 (2012).

MOP094

Indirect Measurements of NIR and UV Ultrashort Seed Laser Pulses using a Transverse Deflecting RF-Structure

272

N. Ekanayake, S. Ackermann
DESY, Hamburg, Germany
S. Ackermann, C. Lechner, Th. Maltezopoulos, T. Plath
Uni HH, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany

Seeding of free-electron lasers (FELs) using external coherent optical pulses recently became an area of interest as users demand spectrally and temporally coherent FEL radiation which is not achievable in traditional self-amplified spontaneous emission operation mode. Since temporal and spectral properties of the seed laser pulses are directly imprinted on the electron bunch, a proper characterization of these seed pulses is needed. However, the lack of any measurement technique capable of characterizing ultrashort seed laser pulses at the laser-electron interaction region is a primary drawback. In this paper we report indirect measurements of seed laser pulses in an undulator section using a transverse deflecting RF-structure (TDS-LOLA) at the free-electron laser FLASH at DESY. Temporally chirped and unchirped seed pulse length measurements will be compared with second-harmonic generation frequency-resolved optical gating measurements and theoretical simulations. Using this technique we will demonstrate that pulse artifacts such as pre- and post-pulses in the seed pulse in the femtosecond and picosecond timescales can be identified without any temporal ambiguity.
Authors acknowledge the support received from FLASH team and many groups at DESY in preparation and commissioning of experiments. We thank our colleagues in the FLASH seeding team for their support.

MOP095

HGHG AND EEHG MICROBUNCHES WITH CSR AND LSC

275

K.E. Hacker
DELTA, Dortmund, Germany

Funding: Work supported by BMBF (contract 05K13PE3) and DESY
Longitudinal space charge (LSC) forces in a drift and coherent synchrotron radiation (CSR) in a chicane are relevant for high gain harmonic generation (HGHG) and echo enabled harmonic generation (EEHG) seeding designs. These factors determine whether or not the modulator can be located significantly upstream of the radiator. The benefits and dangers of having a drift in between the radiator and the modulator are investigated and a measurement of the LSC enabled reduction of the energy spread of a seeded beam is presented.

MOP096

Enhancing the Harmonic Content of an HGHG Microbunch

281

K.E. Hacker
DELTA, Dortmund, Germany

Funding: BMBF grant 05K10PE1 and DESY
High Gain Harmonic Generation (HGHG) seeding has been demonstrated in the visible and ultraviolet, but it is limited in performance at high harmonics of the seed by the initial uncorrelated energy spread of the electron beam. A recent proposal from SINAP using a chirped electron beam and a canted pole undulator has suggested a new mechanism for cooling the uncorrelated energy spread of the electron beam in order to improve the performance of HGHG seeding at high harmonics. This note reviews the mechanism, the limitation of the concept and extrapolates to some new concepts using analogous mechanisms derived from transverse gradients of the laser properties. The impact of CSR wakes on the vanishingly short microbunches produced by the methods are also investigated.
[1] H. Deng and C. Feng, Phys. Rev. Lett. 111, 084801 (2013)

MOP097

A Concept for Seeding 4-40 nm FEL Radiation at FLASH2

286

K.E. Hacker
DELTA, Dortmund, Germany

Funding: Work supported by BMBF (contract 05K13PE3)
This note describes a scheme to seed the FLASH2 FEL over a range of 4-40 nm without impacting SASE capabilities. This scheme combines multiple seeding techniques, builds on current infrastructure and offers a maximized range of performance with higher pulse energies than what are available at lower-peak current facilities. The concept relies on Echo Enabled Harmonic Generation (EEHG), cascaded seeding, and Second Harmonic Afterburners (SHAB) while maintaining the possibility to operate with High Gain Harmonic Generation (HGHG) seeding at >30 nm wavelengths.