|Particle Tracking Simulations for EXFEL Complex shape Collimators
|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.
|Helical Undulator Radiation in Internally Coated Metallic Pipe
|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.
|Optimization of APPLE-II Quasiperiodic Undulators at SOLEIL and Spectral Peformances
|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.
|Coherent Accelerator-based High Field THz Radiation at FLASH II
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 . 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  and challenges into account that we face during the radiation transport to the experimental hall.
|High Accuracy Shimming Technique for the Phase Shifters of the European XFEL
|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.
|Temperature Effects of the FLASH2 Undulators
|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.
|K-Monochromator for Undulator Commissioning at the European XFEL
|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.
|The Photon Beam Loss Monitors as a Part of Equipment Protection System at European XFEL
|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.
|The SASE3 Monochromator Beamline at the European XFEL
|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.
|Implementation Phase of the European XFEL Photon Diagnostics
|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 . 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.  J.Grünert, Framework for X-Ray Photon Diagnostics at the European XFEL, TR-2012-003, 04/2012  J.Buck, Online Photoemission Time-of-Flight Spectrometer for X-ray Photon Diagnostics, TR-2012-002, 06/2012  C.Ozkan, Conceptual design report for Imaging Stations at the European XFEL, TR-2012-004, 02/2012  W.Freund, The European XFEL Undulator Commissioning Spectrometer, XFEL. EU 05/2011
|Design of Invasive X-ray Beam Diagnostic Devices for the European XFEL Employing Scintillators for Imaging
|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.
|X-ray Photon Temporal Diagnostics for the European XFEL
|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.
|A Power Switching Ionization Profile Monitor (3D-IPM)
|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]
|Synchrotron Radiation Monitor for Beam Energy Measurements at the European XFEL
|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.
|Measurement of the Output Power in Millimeter Wave Free Electron Laser using the Electro Optic Sampling Method
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.
|Double-grating Monochromator for Ultrafast Free-electron Laser Beamlines
|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.
|Compact Spectrometer for Single Shot X-ray Emission and Photon Diagnostics
|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.
|Pulse by Pulse Electron Beam Distribution for Multi-beamline Operation at SACLA
|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.
|Development of a Magnetic System to Cancel the Attractive Force toward Structural Reform of Undulators
|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.
|Division-of-amplitude Photopolarimeter for Single-shot Measurement of Free Electron Laser at SDUV-FEL
|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.
|Field Integral Measurement System and Optical Alignment System for HUST THz-FEL
|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.
|Performance Analysis of Variable-Period Helical Undulator with Permanent Magnet for a KAERI THz FEL
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.
|Progress of the PAL-XFEL Undulator System
|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.
|PAL-XFEL Magnet Power Supply System
|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.
|Design, Fabrication, and Performance Tests of Dipole and Quadrupole Magnets for PAL-XFEL
|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.
|Estimating Effect of Undulator Field Errors using the Radiation Hodograph Method
|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.
|Modeling and Design of the Variable Period and Pole Number Undulator for the Second Stage of the Novosibirsk FEL
|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.
|Characterization of the Undulator Magnetic Field Quality by the Angle Averaged Radiation Spectrum
|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.
|High Stability Resonant Kicker Development for the SwissFEL Switch Yard
|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.
|General Strategy for the Commissioning of the ARAMIS Undulators with a 3 GeV Electron Beam
|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.
|Summary of the U15 Prototype Magnetic Performance
|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.
|Grating Interferometry Applied to X-ray Wavefront Metrology at the SACLA
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).
|Magnetic Design of an Apple III Undulator for SwissFEL
|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.
|A Stripline Kicker Driver for the Next Generation Light Source
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.
|Phase Shifter Design for iSASE
|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.
|Undulator Radiation Damage Experience at LCLS
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.
|A 200 μm-period Laser-driven Undulator
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.
|Temporal Diagnostics Measurements with the Pulse Arrival and Length Monitor (PALM) at SACLA
|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]
|Oxygen Scintillation in the LCLS
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.
|The Collimation System for LCLS-II*
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.
|Measurements of FEL Polarization at FERMI
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.
|Fast, Multi-band Photon Detectors based on Quantum Well Devices for Beam-monitoring in New Generation Light Sources
|In order to monitor the photon-beam position for both diagnostics and calibration purposes, we have investigated the possibility to use InGaAs/InAlAs Quantum Well (QW) devices as position-sensitive photon detectors for Free-Electron Laser (FEL) or Synchrotron Radiation (SR). Owing to their direct, low-energy band gap and high electron mobility, such QW devices may be used also at Room Temperature (RT) as fast multi-band sensors for photons ranging from visible light to hard X-rays. Moreover, internal charge-amplification mechanism can be applied for very low signal levels, while the high carrier mobility allows the design of very fast photon detectors with sub-nanosecond response times. Segmented QW sensors have been preliminary tested with 100-fs-wide UV laser pulses and X-ray SR. The reported results indicate that these devices respond with 100-ps rise-times to ultra-fast UV laser pulses. Besides, X-ray tests have shown that these detectors are sensitive to beam position and exhibit a good efficiency in the collection of photo-generated carriers.
|THz Streak Camera for FELTemporal Diagnostics: Concepts and Considerations
|The accurate, non-destructive measurements of FEL pulse length and arrival time relative to an experimental laser are necessary for operators and users alike. The FEL operators can get a better understanding of their machine and the optics of an FEL by examining the pulse length changes of the photons coming to the user stations, and the users can use the arrival time and pulse length information to better understand their data. PSI has created the pulse arrival and length monitor (PALM) based on the THz-streak camera concept for measurement at x-ray FELs, meant to be used at the upcoming SwissFEL facility. The first results from the experimental beamtime at SACLA will be presented, showcasing the accuracy and reliability of the device. Further plans for improvement and eventual integration into SwissFEL will also be presented.
|Slides THA01 [5.798 MB]
|Experimental Characterization of FEL Polarization Control with Cross Polarized Undulators
|Polarization control of the coherent radiation is becoming an important feature of recent and future short wavelength free electron laser facilities. While polarization tuning can be achieved taking advantage of specially designed undulators, a scheme based on two consecutive undulators emitting orthogonally polarized fields has also been proposed. Developed initially in synchrotron radiation sources, crossed polarized undulator schemes could benefit from the coherent emission that characterize FELs. In this work we report the first detailed experimental characterization of the polarization properties of an FEL operated with crossed polarized undulators in the Soft-X-Rays. Aspects concerning the average degree of polarization and the shot to shot stability are investigated together with a comparison of the performance of various schemes to control and switch the polarization
|Slides THA02 [5.383 MB]
|A Plan for the Development of Superconducting Undulator Prototypes for LCLS-II and Future FELs
Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515, DE-AC02-05CH11231, and DE-AC02-06CH11357.
Undulators serve as the primary source of radiation for modern storage rings, and more recently for the advent of Free-Electron Lasers (FELs). The performance of future FELs can be greatly enhanced using the much higher magnetic fields of superconducting undulators (SCU). For example, the LCLS-II hard x-ray undulator can be shortened by up to 70 m using an SCU in place of a PMU (permanent magnet undulator), or its spectral performance can be critically improved when using a similar length. In addition, SCUs are expected to be orders of magnitude less sensitive to radiation dose; a major issue at LCLS-II with its 1-MHz electron bunch rate. We present a funded R&D collaboration between SLAC, ANL, and LBNL, which aims to demonstrate the viability of superconducting undulators for FELs by building, testing, measuring, and tuning two 1.5-m long planar SCU prototypes using two different technologies: NbTi at ANL and Nb3Sn at LBNL. Our goal is to review and reassess the LCLS-II HXR baseline plans (PMU) in July of 2015, after the development and evaluation of both prototypes, possibly in favor of an SCU for LCLS-II.
|Slides THA03 [29.468 MB]
|Optical Afterburner for Naturaly Synchronized Pump-probe Experiments at FLASH
Funding: German Federal Ministry for Education and Research, project 05K10CHC and 05K12CH4
We employ so- called Optical Afterburner [*,**] principle to generate optical replica pulses of X-ray pulse at FLASH (Free Electron LASer in Hamburg). These pulses are naturally synchronized to the FEL pulses and share the same envelope and arrival time, with accuracy down to few femtoseconds. Because of this, Optical Afterburner pulses can be used for complete temporal diagnostics for FEL pulses. Because we shift diagnostics challenge from X-ray to visible range, this significantly simplifies detection. During pulse- duration measurement campaigns at FLASH, Optical Afterburner has been demonstrated as versatile and accurate tool to measure pulse duration of X-ray FEL pulses. In the most recent development we have amplified, Optical Afterburner pulses by three orders of magnitude and will used it in the X-ray/Visible pump-probe experiments for ultimate temporal resolution. We have demonstrated amplification concept at FLASH, where we reach pulse energies above 1uJ at 1MHz repetition rate.
* E.L. Saldin, E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 030701 (2010)
* Proceedings of IPAC2011, San Sebastián, Spain. THPC084