|Simultaneous Measurement of Electron and Photon Pulse Duration at FLASH
|One of the most challenging tasks for extreme ultraviolet, soft and hard X-ray free-electron laser photon diagnostics is the precise determination of the photon pulse duration, which is typically in the sub 100 fs range. In a larger campaign nine different methods, which are able to determine such ultrashort photon pulse durations were compared at FLASH. Radiation pulses at a wavelength of 13.5 nm and 24.0 nm together with the corresponding electron bunch duration were measured by indirect methods like analyzing spectral correlations, statistical fluctuations and energy modulations of the electron bunch, and also direct methods like autocorrelation techniques, THz streaking or reflectivity changes of solid state samples.
|Slides THB01 [4.520 MB]
|Experimental Results of Diagnostics Response for Longitudinal Phase Space
|At SwissFEL, electron bunches will be accelerated, shaped, and longitudinally compressed by different radio frequency (RF) structures (S-, C-, and X-band) in combination with magnetic chicanes. In order to meet the envisaged performance, it is planned to regulate the different RF parameters based on the signals from numerous electron beam diagnostics. Here we will present experimental results of the diagnostics response on RF phase and field amplitude variations that were obtained at the SwissFEL Injector Test Facility.
|Slides THB02 [6.110 MB]
|Femtosecond-Stability Delivery of Synchronized RF-Signals to the Klystron Gallery over 1-km Optical Fibers
Funding: This work was supported by the PAL-XFEL Project and the National Research Foundation (Grant number 2012R1A2A2A01005544) of South Korea.
We present our recent progress in optical frequency comb-based remote optical and RF distribution system at PAL-XFEL. A 238 MHz mode-locked Er-laser is used as an optical master oscillator (OMO), which is stabilized to a 2.856 GHz RF master oscillator (RMO) using a fiber- loop optical-microwave phase detector (FLOM-PD). We partly installed a pair of 1.15 km long fiber links through a cable duct to connect and OMO room to a klystron gallery in the PAL-XFEL Injector Test Facility (ITF). The fiber links are stabilized using balanced optical cross- correlators (BOC). A voltage controlled RF oscillator (VCO) is locked to the delivered optical pulse train using the second FLOM-PD. Residual timing jitter and drift between the two independently distributed optical pulse train and RF signal is measured at the klystron gallery. The results are 6.6 fs rms and 31 fs rms over 7 hours and 62 hours, respectively. This is the first comb-based optical/RF distribution and phase comparison in the klystron gallery environment.
|Slides THB03 [7.478 MB]
|Electron Beam Diagnostics and Feedback for the LCLS-II
Funding: work supported by DOE contract DE-AC02-76-SF00515
The LCLSII is a CW superconducting accelerator driven, hard and soft X-ray Free Electron Laser which is planned to be constructed at SLAC. It will operate with a variety of beam modes from single shot to approximately 1 MHz CW at bunch charges from 10pc to 300pC with average beam powers up to 1.2 MW. A variety of types of beam instrumentation will be used, including stripline and cavity BPMS, fluorescent and OTR based beam profile monitors, fast wire scanners and transverse deflection cavities. The beam diagnostics system is designed to allow tuning and continuous measurement of beam parameters, and to provide signals for fast beam feedbacks.
|Slides THB04 [1.501 MB]
|Towards a Novel THz-based Monitor for Subpicosecond Electron Bunches Working at MHz Repetition Rates and Low Bunch Charges
|The control and measurement of electron bunch properties at the femtosecond (fs) level has become an important field in modern accelerator physics, in particular since these became crucial parameters for the operation of 4th Generation X-ray Light-sources. In order to operate modern-day photon factories such as LCLS and the future European X-FEL reliably, a number of novel approaches have been developed that allow the noninvasive measurement of electron bunch form and arrival time. Some of those are based on the electro-optic detection of the coulomb field of the electron bunches in the electron beamline; some detect the super-radiant THz pulses from the electron bunch. However, none of these concepts allows for pulse-to-pulse detection on a quasi-CW accelerator operating at the MHz repetition rates planned for the next generation of X-ray free electron lasers. In this contribution we present first results from a new monitor concept, based on the single-shot electro-optic detection of super-radiant THz pulses, that has the potential to operate at MHz repetition rates.
|Poster THP065 [1.966 MB]
|Recent Developments for the Improved Bunch Arrival Time Monitors at FLASH and for the European XFEL
|At today's free-electron lasers, pump-probe experiments and seeding schemes put high demands on the timing stability of electron bunches. At FLASH and the upcoming European XFEL a reliable and precise arrival time detection down to the femtosecond level has to cover a broad range of bunch charges, which may even change from 1 nC down to 20 pC within a bunch train. At FLASH, the new bunch arrival time monitor has to cope with the special operation mode where the MHz repetition rate bunch train is separated into two segments for FLASH1 and FLASH2 beam lines. Each of the two segments will exhibit individual timing jitter characteristics since they are generated from two different injector lasers and can be accelerated with individual energy gain settings. This operation mode places high demands on both, the hardware and the required servers for the bunch arrival time monitor, with regard to automated control and exception handling. In this paper, we describe the adapted electro-optical subsystem and show latest results from the newly implemented read-out electronics based on the MTCA.4 platform.
|Performance Study of High Bandwidth Pickups Installed at FLASH and ELBE for Femtosecond-Precision Arrival Time Monitors
|At today's free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems for a timing jitter reduction down to the femtosecond level as well as for time-resolved pump-probe experiments. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultrashort laser pulses. Even more, at FLASH and the European XFEL the measurement has to cover a wide range of bunch charges from 1 nC down to 20 pC with equally sub-10 fs resolution. To meet these requirements, recently a high bandwidth pickup electrode with a cut-off frequency above 40 GHz has been developed. These pickups are installed at the macro-pulsed SRF accelerator of the free-electron laser FLASH and at the macro-pulsed continuous wave SRF accelerator ELBE. In this paper we present an evaluation of the pickup performance by direct signal measurements with high bandwidth oscilloscopes and by use of the electro-optical arrival time monitor.
|A Tool for Real Time Acquisitions and Correlation Studies at FERMI
|In this work we report the recent implementation of a Matlab based acquisition program that, exploiting the real time capabilities of TANGO, can be used at FERMI for acquiring various machine parameter and electron beam properties together with most FEL signals. Analysis of the saved datafiles is performed with a second code that allows to retrieve correlations and to study dependence of FEL properties on machine parameters. An overview of the two codes is reported.
|Installation and First Measurements of an Electron Beam Detector at the FLASH II Beam Dump
|For the electron absorber at FLASH II a detector has been developed to control the position, dimensions and profile of the electron beam. Scintillation light, emitted from a luminescent screen in front of the dump window, is reflected by a mirror, located in two meter distance from the screen, and passes through a vacuum window. For optical analysis, the beam image is then transferred by an optical fibre bundle to a CCD camera, which is located in one meter distance from the beam line. To test the survivability of the fibre bundle in such a highly radioactive environment, an irradiation test was performed by installing a similar fibre bundle onto a radioactive hot spot at FLASH. The test revealed that the fibre’s optical qualities after irradiation of approximately one megagray degraded by less than ten percent. After the optical system had been simulated in an experimental setup in the lab, showing satisfactory results, the monitor has recently been installed and adjusted at FLASH II. The results of the first measurements will be presented in the paper.
|Optics Measurements at FLASH2
|FLASH2 is a newly build second beam line at FLASH, the soft X-ray FEL at DESY, Hamburg. Unlike the existing beam line FLASH1, it is equipped with variable gap undulators. This beam line is currently being commissioned. Both undulator beam lines of FLASH are driven by a common linear accelerator. Fast kickers and a septum are installed at the end of the linac to distribute the electron bunches of every train between FLASH1 and FLASH2. A specific beam optic in the extraction arc with horizontal beam waists in the bending magnets is mandatory in order to mitigate CSR effects. Here we will show first results of measurements and compare to simulations.
|Infrared Diagnostics Instrumentation Design for the Coherent Electron Cooling Proof of Principle Experiment
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy
The Coherent Electron Cooling Proof-of-Principle experiment [*] based on an FEL is currently under construction in the RHIC tunnel at BNL. Diagnostics for the experimental machine [**] are currently being designed, built and installed. This paper focuses on the design of the infrared diagnostic instrumentation downstream of the three tandem 2.8m long helical wiggler sections that will act on a 22MeV 68uA electron beam co-propagating with the 40GeV/u RHIC gold beam. The 14 um FEL radiation, or wiggler light, will be extracted from RHIC via a viewport in a downstream DX magnet cryostat and analysed by instrumentation on a nearby optics bench. Instruments concentrating on three parameters, namely intensity, spectral content, and transverse profile, will extract information from the wiggler light in an attempt to quantify the overlap of the electron and ion beams and act as an indicator of coherent cooling.
* V. Litvinkenko, et al THOBN3, PAC2011, New York, NY
** D. M. Gassner, et al WEAP01, BIW2012, Newport News, VA
|Design of TDS-based Multi-screen Electron Beam Diagnostics for the European XFEL
|Dedicated longitudinal electron beam diagnostics is essential for successful operation of modern free-electron lasers. Demand for diagnostic data includes the longitudinal bunch profile, bunch length and slice emittance of the electron bunches. Experimental setups based on transverse deflecting structures (TDS) are excellent candidates for this purpose. At the Free-Electron Laser in Hamburg (FLASH), such a longitudinal bunch profile monitor utilizing a TDS, a fast kicker magnet and an off-axis imaging screen, has been put into operation. It enables the measurement of a single bunch out of a bunch train without affecting the remaining bunches. At the European X-ray Free-Electron Laser (XFEL) multiscreen stations in combination with TDS are planned to be installed. In order to allow for flexible measurements of longitudinal bunch profile and slice emittance, a configurable timing and trigger distribution to the fast kicker magnets and screen stations is required. In this paper, we discuss various operation patterns and the corresponding realization based on MTCA.4 technology.
|Measurements of the Timing Stability at the FLASH1 Seeding Experiment
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.
For seeding of a free-electron laser, the spatial and temporal overlap of the seed laser pulse and the electron bunch in the modulator is critical. To establish the temporal overlap, the time difference between pulses from the seed laser and spontaneous undulator radiation is reduced to a few pico-seconds with a combination of a photomultiplier tube and a streak camera. Finally, for the precise overlap the impact of the seed laser pulses on the electron bunches is observed. In this contribution, we describe the current experimental setup, discuss the techniques applied to establish the temporal overlap and analyze its stability.
|A High Repetition Rate, Single-Shot Recording Scheme for Short Pulses
|We demonstrate high repetition rate (up to 88 MHz) single shot recordings of pulses shapes, using a novel opto-electronic strategy. The technique is based on the classical spectral encoding technique, but at a much higher repetition rate than with the state-of-art strategy (which is limited by camera speed). In the present demonstration, the signals are coherent THz pulses emitted at SOLEIL, and the resolution is in the ps range. However the technique is not specific to THz pulses and can be potentially adapted to other wavelengths and situations, provided it is possible to imprint the ultrafast signal on chirped laser pulses (through electro-optic sampling, frequency mixing, transient reflectivity, etc.).
|Observation of Laser-Sliced Electron Bunch using a YBCO Detector at UVSOR-III
When the current of a storage ring is near the microbunching instability threshold, a strong burst of CSR instability may be seeded by an external laser pulse*. Here we present real time recordings of the coherent synchrotron radation (CSR) pulse shapes emitted by sliced electron bunch using a new technology based on YBCO thin film detector combined with the state-of-the-art oscilloscope. This allows to make measurements in real time of the sliced electron bunch dynamics over several turns. These experimental observations open a new way to make severe comparisons with existing and future models of the microbunching instability. Tests of a Vlasov-Fokker-Planck model are presented.
* Byrd et al. Phys. Rev. Lett. 97, 074802 (2006)
|A Low-Cost, High-Reliability Femtosecond Laser Timing System for LCLS
Funding: Work supported by DOE Contract DE-AC02-76-SF00515
LCLS has developed a low-cost, high-reliability radio-frequency-based locking system which provides phase locking with sub-25-femtosecond jitter for the injector and experiment laser systems. This system does not add significantly to the X-ray timing jitter from the accelerator RF distribution. The system uses heterodyne RF locking at 3808 MHz with an I/Q vector phase shifter and variable event receiver triggers to control the timing of the emission of the amplified laser pulse. Controls software provides full automation with a single process variable to control the laser timing over a 600 microsecond range with up to 4 femtosecond resolution, as well as online diagnostics and automatic error correction and recovery. The performance of this new locking system is sufficient for experiments with higher-precision timing needs that use an X-ray/optical cross-correlator to record relative photon arrival times.
|Beam Loss Monitors for the SwissFEL
|There are currently three types of monitors planned for tracking and minimizing beam losses at the SwissFEL. Fiber-based loss monitors will provide information on the longitudinal loss location, help reduce losses at undulators and measure losses due to insertion of wire scanners for transverse beam profile measurements. They shall be integrated to the Machine Protection System due to their fast response capabilities. The dose deposited over time at the undulators shall be measured with RadFETs and readout using the DOSFET L-02 reader. Characterization of all three types of loss monitors have been carried out at the SwissFEL Injector Test Facility. This contribution shall provide in-depth description of the monitors along with their complete readout chain and results from the characterization studies.
|Measurements of Compressed Bunch Temporal Profile using Electro-Optic Monitor at SITF
Funding: The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n.°290605 (PSI-FELLOW/COFUND)
The SwissFEL Injector Test Facility (SITF) is an electron linear accelerator with a single bunch compression stage at Paul Scherrer Institute (PSI) in Switzerland. Electro-optic monitors (EOMs) are available for bunch temporal profile measurements before and after the bunch compressor. The profile reconstruction is based upon spectral decoding technique. This diagnostic method is non-invasive, compact and cost-effective. It does not have high resolution and wide dynamic range of an RF transverse deflecting structure (TDS), but it is free of transverse beam size influence, what makes it a perfect tool for fast compression tuning. We present results of EOM and TDS measurements with down to 150 fs long bunches after the compression stage at SITF.
|Coherent Radiation Diagnostics for Longitudinal Bunch Characterization at European XFEL
|European XFEL comprises a 17.5 GeV linear accelerator for the generation of hard X-rays. Electron bunches from 20 pC to 1 nC will be produced with a length of a few ps in the RF gun and compressed by three orders of magnitude in three bunch compressor (BC) stages. European XFEL is designed to operate at 10 Hz delivering bunch trains with up to 2700 bunches separated by 222 ns. The high intra-bunch train repetition rate offers the unique possibility of stabilizing the machine with an intra-bunch train feedback, which puts in turn very high demand on fast longitudinal diagnostics. Two different systems will be installed in several positions of the machine. Five bunch compression monitors (BCM) will monitor the compression factor of each BC stage and used for intra-bunch train feedbacks. A THz spectrometer will be used to measure parasitically the longitudinal bunch profile after the energy collimator at 17.5 GeV beam energy. We will present concepts for fast longitudinal diagnostic for European XFEL based on coherent radiation, newest developments for high repetition rate measurements and simulations for the feedback capability of the system.
|Longitudinal Diagnostics of RF Electron Gun using a 2-cell RF Deflector
Funding: This work was supported by JSPS Grant-in-Aid for Scientific Research (A) 10001690 and the Quantum Beam Technology Program of MEXT.
We have been studying a compact electron accelerator based on an S-band Cs-Te photocathode rf electron gun at Waseda University. We are using this high quality electron bunch for many application researches. It is necessary to measure the bunch length and temporal distribution for evaluating application researches and for improving an rf gun itself. Thus we adopted the rf deflector system. It kicks the electron bunch with resonated rf electromagnetic field. Using this technique, the longitudinal distribution is mapped into the transverse space. The rf deflector has a 2-cell standing wave π-mode structure, operating in TM120 dipole mode at 2856 MHz. It provides a maximum vertical kick of 1.00MV with 750 kW input rf-power which is equivalent to the temporal resolution of around 58 femtoseconds bunch length. In this conference, we report the details of our rf deflector, the latest progress of longitudinal phase space diagnostics and future prospective.
|Commissioning and Results from the Bunch Arrival-time Monitor Downstream the Bunch Compressor at the SwissFEL Test Injector
|A high bandwidth Bunch Arrival-Time Monitor has been commissioned at the Swiss FEL test injector. A new acquisition front end allowing utilization of the ADC full dynamic range has been implemented. The resolution is measured as a function of the charge for different EOM front-ends. Downstream the magnetic chicane the bunch arrival time is sensitive to the amplitude and phases of the RF structures, responsible for creation of an energy chirp, used for bunch compression, as well as the ones of the harmonic cavity, used for phase space linearization. The time of flight as a function of the angle of the magnetic chicane has also been measured.
|A Novel ‘Metamaterial’ for Electro-Optic Electron Bunch Profile Monitors
Current techniques for ultra-short electron bunch profiles allow the measurement of ~60-fs (rms) electron bunches. Future electron and photon sources will generate bunches in the 1-5 fs regime and even shorter, and therefore new methods need to be devised to characterise such ultra-short bunches with good precision. We present a novel electro-optic (EO) material in the form of metallic nanoparticles embedded in glass substrates (metal-glass nanocomposites – MGNs) for future use in EO monitors. Uniform shape modification of the nanoparticles from spherical to spheroidal shapes led to changes in the surface plasmon resonance (SPR) band of the nanoparticles. Second harmonic generation (SHG) - as an indicator of a first-order EO effect – in both transmission and reflection geometries has been observed on excitation by a polarised 10 ps pulsed laser beam at 1064 nm with a repetition rate of 200 kHz. This new ‘metamaterial’ shows promising results for future measurements of ultra-short electron bunches, due to the SPR enhancement of the electro-optical coefficients.
S.P. Jamison et al., Nuclear Instruments and Methods A 557, 305-308 (2006).
A. Podlipensky et al., Optics Letters 28, 9 (2003)
|Electron Beam Diagnostics for COXINEL
|On the path towards more compact free electron lasers (FELs), the project COXINEL was recently funded: a transfer line will be installed to adapt a plasma accelerated beam (from LOA) into an in-vacuum undulator built by SOLEIL. This experiment should enable to demonstrate the first FEL based on a plasma accelerator. Because plasma beams are intrinsically very different from RF acceletor beams (much shorter, divergent and smaller with a higher energy spread and energy jitter), their transport and matching in the undulator is critical if willing to obtain a significant amplification. This is why special care has to be taken in the design of the beam diagnostics to be able to measure the transverse beam sizes, energy spread and jitter, emittance and bunch length. For these purposes, several diagnostics will be implemented from the plasma accelerator exit down to the undulator exit. In each station, several screen types will be available and associated to high resolution imaging screens. In this paper, we present the experimental layout and associated simulation of the diagnostics performances.
|Comparison of Quadrupole Scan and Multi-screen Method for the Measurement of Projected and Slice Emittance at the SwissFEL Injector Test Facility
|High-brightness electron bunches with small transverse emittance are required to drive X-ray free-electron lasers (FELs). For the measurement of the transverse emittance, the quadrupole scan and multi-screen methods are the two most common procedures. By employing a transverse deflecting structure, the measurement of the slice emittance becomes feasible. The quadrupole scan is more flexible in freely choosing the data points during the scan, while the multi-screen method allows on-line emittance measurements utilising off-axis screens in combination with fast kicker magnets. The latter is especially the case for high-repetition multi-bunch FELs, such as the European XFEL, which offer the possibility of on-line diagnostics. In this paper, we present comparative measurements of projected and slice emittance applying these two methods at the SwissFEL Injector Test Facility and discuss the implementation of on-line diagnostics at the European XFEL.
|Compact Synchronization of Optical Lasers to the Accelerator RF based on MTCA.4
|X-ray free-electron laser facilities utilize a variety of optical short-pulse lasers to fully exploit the femtosecond time structure of the electron bunches and photon pulses. For temporal overlap, a precision synchronization of the optical lasers to the radio-frequency (RF) system of the FEL accelerator is required. A compact scheme for laser to external RF synchronization has been developed based on a digital controller implemented in MTCA.4 technology. An RF section is employed for the generation of electrical signals from the laser pulses. Further processing of the RF signals and phase locking to the reference is realized with commercially available MTCA.4 compliant modules. In this paper, we present a performance evaluation of the newly designed RF section, which consists of three printed circuit boards, as well as results from the synchronization of an Yb-fiber (1030 nm) and Er-fiber (1550 nm) laser to an RF reference source.
|Femtosecond Timing Distribution for the European XFEL
|Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. Albeit its maturity and proven performance this system had to undergo a major redesign for the upcoming European XFEL due to the enlarged number of stabilized optical fibers and an increase by a factor of up to 10 in length. The experience and knowledge gathered from the operation of the optical synchronization system at FLASH has led to an elaborate and modular precision instrument which can stabilize polarization maintaining fibers for highest accuracy as well as economic single mode fibers for shorter lengths. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization units for the European XFEL, discusses major complications, their solutions and and the most recent performance results.
|Design and Test of Wire-Scanners for SwissFEL
|The SwissFEL light-facility will provide coherent X-rays in the wavelength region 7-0.7 nm and 0.7-0.1 nm. In SwissFEL, view-screens and wire-scanners will be used to monitor the transverse profile of a 200/10pC electron beam with a normalized emittance of 0.4/0.2 mm.mrad and a final energy of 5.7 GeV. Compared to view screens, wire-scanners offer a quasi-non-destructive monitoring of the beam transverse profile without suffering from possible micro-bunching of the electron beam. The main aspects of the design, laboratory characterization and beam-test of the SwissFEL wire-scanner prototype will be presented.
|Transition Radiation of an Electron Bunch and Imprint of Lorentz-Covariance and Temporal-Causality
|The study of Transition Radiation (TR) of a bunch of N electrons offers a precious insight into the role that Lorentz-covariance and temporal-causality play in an electromagnetic radiative mechanism of a relativistic beam. The contributions of the N single electrons to the radiation field are indeed characterized by emission phases from the metallic surface which are in a causality relation with the temporal sequence of the N particle collisions onto the radiating screen. The Lorentz-covariance characterizing the virtual quanta field of the relativistic charge is also expected to imprint the radiation field and the related energy spectrum. The main aspects of a Lorentz-covariance and temporal-causality consistent formulation of the TR energy spectrum of an electron bunch will be described.
|Coherent Electron Cooling Proof of Principle Phase 1 Instrumentation Status
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy
The purpose of the Coherent electron Cooling Proof-of- Principle (CeC PoP)  experiment being designed at RHIC is to demonstrate longitudinal (energy spread) cooling before the expected CD-2 for eRHIC. The scope of the experiment is to longitudinally cool a single bunch of 40 GeV/u gold ions in RHIC. The cooling facility will be installed inside the RHIC tunnel in 3 phases. The status of the instrumentation systems planned for phase 1 commissioning efforts will be described. This paper will also describe updates to the instrumentation systems proposed to meet the diagnostics challenges during the final phase of cooling commissioning . These include measurements of beam intensity, emittance, energy spread, bunch length, position, and transverse alignment of electron and ion beams.
|Evolvement of the Laser and Synchronization System for the Shanghai DUV-FEL Test Facility
Funding: supported by the National Natural Science Foundation of China (Grant No. 11175241)
Many attractive experiments including HGHG, EEHG, cascaded HGHG, chirped pulse amplification etc. are carried out or planned on the Shanghai Deep Ultra-Violet Free Electron Laser test facility. These experiments are all utilizing a laser as seed, and need precise synchronization between the electron beam and the laser pulse. We will describe the history and current status of the seeding and synchronization scheme for the SDUV-FEL together with some related experiment results in this paper.
|Development of an S-band Cavity-type Beam Position Monitor for a Table-top Terahertz Free-electron Laser
|A cavity-type beam position monitor (BPM) has been developed for a compact terahertz (THz) free-electron laser (FEL) system and ultrashort-pulsed electron linac system at the Korea Atomic Energy research Institute (KAERI). The cavity-type BPM has higher sensitivity and faster response time even at low charges, comparing with other types of BPMs. The designed position resolution of the cavity BPM is less than 10 μm. The material of the BPM is aluminium and the vacuum could be kept by indium sealing without brazing process, which result in easy modification and saving cost. The resonance frequency of the cavity BPM is 2.801 GHz and has a dimension of 200 x 220 mm (length x height) with a pipe radius of 38 mm. When electron beam passing through the cavity BPM with an offset, the amplitude of a dipole mode which depends linearly on the beam offset inside the cavity BPM is excited. With the KAERI THz FEL, signals from the BPM was measured by using an oscilloscope as a function of the beam offset. The position sensitivity was calculated to be 6.19 mV/mm/mA. By measuring the thermal noise of the system, position resolution of the cavity BPM was estimated to be less than 1 μm.
|Longitudinal Response Matrix Simulations for the SwissFEL Injector Test Facility
|The Singular Value Decomposition (SVD) method has been applied to the SwissFEL Injector Test Facility to identify and better expose the various relationships among the possible jitter sources affecting the longitudinal phase space distribution and the longitudinal diagnostic elements that measure them. To this end, several longitudinal tracking simulations have been run using the Litrack code. In these simulations the RF and laser jitter sources are varied one-by-one within a range spanning twice their expected stability. The particle distributions have been dumped at the diagnostic locations and the measured quantities analyzed. A matrix has been built by linearly fitting the response of each measured quantity to each jitter source. This response matrix is normalized to the jitter source stability and the instrumentation accuracy, and it is inverted and analyzed using SVD. From the eigenvalues and eigenvectors the sensitivity of the diagnostics to the jitters can be evaluated and their specifications and locations optimized.
|CameraLink High-Speed Camera for Bunch Profiling
|In the context of upcoming SwissFEL linear accelerator, we are working on a high-speed high-resolution instrument capable of delivering good sensitivity even in dark conditions. The camera selected is a PCO. Edge with SCMOS technology and an ultra-low noise sensor with 2560x2160 pixel resolution working at 100Hz. This allows for single bunch monitoring in SwissFEL, allowing eventually for on-the-fly inter-bunch image processing. The communication between the PCO. Edge camera and a last-generation Kintex7 FPGA has been demonstrated using a prototyping evaluation board and an 850-nm optical link connected to a 10Gbit SFP+ transceiver. Rudimentary packet processing has been implemented to confirm the satisfactory operation of the new link-layer protocol X-CameraLinkHS, specifically development for high-speed image transmission. We aim for online image processing and investigating the feasibility of achieving inter-bunch feedback (< 10 ms).
|Progress Towards Transverse Beam Profile Measurements with Dynamic Range of 10+6
Funding: Work supported by US DOE office of Basic Energy Sciences under the early career program; DOE award number FWP#JLAB-BES11-05
Future high average brightness FELs, operated with CW electron beams, and other high average current LINACs will require extremely good control of beam halo. Based on JLab FEL experience of operating IR FEL with average beam current of 9 mA, it was suggested that, beam diagnostics with large dynamic range (LDR) of 10+6 or higher, are necessary to improve understanding of beam halo formation, its sources and evolution. In this contribution we describe status of two LDR transverse beam profile diagnostics, which are under development at Jefferson Lab. First is beam imaging, where diffraction usually causes a strong limitation of the dynamic range. It was suggested that amplitude apodization of the imaging optics will allows to achieve much higher dynamic range. We present results of such apodized optics evaluation on an optical test bench. Wire-scanners are also capable of LDR measurements. We argue that the best dynamic range (DR) will be given by PMT based detection scheme, when a combination of counting and analog mode for PMT signal processing is used. We present designs of several PMT current measurements techniques with DR larger than 10+6 and results of their laboratory tests.