DIPAC2011 - List of Keywords (FEL)

Paper	Title	Other Keywords	Page
MOOA02	Beam Instrumentation for X-ray FELs	cavity, feedback, undulator, diagnostics	1
	H. Loos SLAC, Menlo Park, California, USA
	Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC03-76SF00515. The performance of X-ray Free-electron lasers depends strongly on the achieved quality of the high brightness electron beam and its shot by shot stability. The requirements and challenges of the instrumentation needed to tune and optimize such electron beams will be discussed. Of particular interest are measurements of the beam orbit, emittance, energy, and bunch length and the different measurement techniques for these transverse and longitudinal beam parameters and their implementation for routine operation will be addressed in detail, particularly the necessary instrumentation to fulfill different user requirements in terms of beam energy and bunch length. Specific requirements for the initial commissioning, routine optimization and feedback applications will be presented as well.
	Slides MOOA02 [2.114 MB]

MOOB04	Bunch Compression, RF Curvature Correction and R₅₅, T₅₅₅ and U₅₅₅₅ Measurements at JLab FEL	linac, cavity, SRF, sextupole	15
	P. Evtushenko, S.V. Benson, D. Douglas JLAB, Newport News, Virginia, USA
	The JLab IR/UV FEL Upgrade operates with the bunch length compressed down to 100-150 fs RMS. An indispensible part of the bunch compression scheme is the correction of the so-called LINAC RF curvature. Unlike other systems – where the RF curvature gets corrected using higher a harmonic LINAC – our system utilizes magnetic elements of the beam transport system to correct and adjust the second and third order correlation terms. These are expressed in terms of the transport matrix elements T₅₆₆ and U₅₆₆₆. The linear correlation term described by M₅₅ is adjusted using the magnetic system as well. The large energy spread induced on the beam by the FEL operation is compressed as a part of the energy recovery process. As in the case of bunch length compression, this energy compression is optimized by properly adjusting high order transport matrix elements. In this contribution we describe the system used for direct measurements of the transport matrix elements M₅₅, T₅₆₆ and U₅₆₆₆ and its impact on the operation and bunch compression. Results of the measurements are presented together with the bunch length measurements including the data showing resolution and accuracy of the system.
	Slides MOOB04 [0.999 MB]

MOOC03	The Fermi@Elettra Cavity BPM System: Description and Commissioning Results	cavity, pick-up, controls, undulator	26
	M. Ferianis, A.O. Borga, P. Craievich, R. De Monte, G. Gaio, M. Predonzani ELETTRA, Basovizza, Italy M. Dal Forno DIEIT, Trieste, Italy
	The Fermi@elettra cavity BPM (C-BPM) system is based on an original implementation of the C-BPM scheme as the pick-up, operating at 6.5GHz, is coupled to a dedicated, self-calibrating electronics based on a novel concept. The system has been developed in-house; both the E-M and the mechanical design of the pick-up have been carried out, including an original frequency tuning scheme. The detector electronics directly obtains the envelope of the sum and difference signals by means of an RF 180° hybrid; no mixer for the RF signal down conversion is used. The detector is based on 3 blocks: an RF front-end, a baseband analogue transmission module and a digital back-end unit, based on a micro-TCA platform. The digital back-end is equipped with a powerful Virtex 5 FPGA and several real-time tasks have been implemented on it, including intra-pulse calibration. Ten C-BPM stations have been installed so far, fully integrated in the FERMI control System, enabling a real-time control of this key FEL diagnostics. Results on performances with beam are also presented; the scale factor of C-BPMs is obtained with beam, as two-axis micrometer translation stages have been installed.
	Slides MOOC03 [2.733 MB]

MOPD12	Expressing Properties of BPM Measurement System in Terms of Error Emittance and Error Twiss Parameters	emittance, betatron, beam-transport, focusing	62
	V. Balandin, W. Decking, N. Golubeva DESY, Hamburg, Germany
	The determination of variations in the beam position and in the beam energy using BPM readings is one of the standard problems of accelerator physics. If the optical model of the beam line and BPM resolutions are known, the typical choice is to let jitter parameters be a solution of the weighted linear least squares problem. For transversely uncoupled motion this least squares problem can be solved analytically, but the direct usage of the obtained solution as a tool for designing a BPM measurement system is not straightforward. A better understanding of the nature of the problem is needed. In this paper we show that properties of the BPM measurement system can be described in terms of the usual accelerator physics concepts of emittance, energy spread, dispersions and betatron functions. In this way one can compare two BPM systems comparing their so-called error emittances and error energy spreads, or, for a given measurement system, one can achieve a balance between coordinate and momentum reconstruction errors by matching the error betatron functions in the point of interest to the desired values.

MOPD54	Commissioning Results of the Photon-Electron Diagnostic Unit at sFLASH	laser, electron, undulator, diagnostics	173
	J. Bödewadt, E. Hass, J. Roßbach Uni HH, Hamburg, Germany
	Funding: Supported by the Federal Ministry of Education and Research of Germany under contract 05 ES7GU1 Recently a seeded free-electron laser operating in the extreme ultra-violet (XUV) spectral range was installed and commissioned at the free-electron laser FLASH. The seed beam is generated by higher harmonics of near infrared laser pulses. A dedicated transport system guides the radiation into the electron accelerator environment. Within the seed undulator section compact diagnostic units were installed to control the transverse overlap of the photon and the electron beam. These units contain a BPM, horizontal and vertical wire scanners and an OTR screen for the electron diagnostic. A Ce:YAG screen and a MCP readout for the wire scanner are used to measure the photon beam position. This paper presents the commissioning results and the performance of the diagnostic units.

TUOA04	Instrumentation for Machine Protection at FERMI@Elettra	undulator, radiation, diagnostics, electron	286
	L. Fröhlich, A.I. Bogani, K. Casarin, G. Cautero, G. Gaio, D. Giuressi, A. Gubertini, R.H. Menk, E. Quai, G. Scalamera, A. Vascotto ELETTRA, Basovizza, Italy L. Catani, D. Di Giovenale INFN-Roma II, Roma, Italy
	FERMI@Elettra is a linac-driven free-electron laser currently under commissioning at Sincrotrone Trieste, Italy. In order to protect the facility's permanent undulator magnets from radiation-induced demagnetization,beam losses and radiation doses are monitored closely by an active machine protection system. The talk focuses on the design and performance of its main diagnostic subsystems: Beam loss position monitors based on the detection of Cherenkov light in quartz fibers with multi-pixel photon counters, conventional ionization chambers with a new frontend electronics package, and solid-state RadFET dosimeters providing an online measurement of the absorbed dose in the undulator magnets.
	Slides TUOA04 [2.559 MB]

TUPD14	Commissioning of the Cavity BPM for the FERMI@Elettra FEL Project	cavity, electron, undulator, polarization	329
	P. Craievich, T. Borden, A.O. Borga, R. De Monte, M. Ferianis, M. Predonzani ELETTRA, Basovizza, Italy M. Dal Forno, R. Vescovo DIEIT, Trieste, Italy
	The cavity Beam Position Monitor (BPM) is a fundamental beam diagnostic device that allows the measurements of the electron beam trajectory in a non-destructively way and with sub-micron resolution. Ten cavity BPM systems have been installed along the undulators chain in the FERMI@Elettra FEL1 project. In this paper we discuss the installation, commissioning and performance of these cavity BPM systems. We have carried out preliminary operations during a pre-beam period, such as the alignment and fine tuning of the RF cavities under vacuum. During the commissioning each BPM has been calibrated by mechanically moving the support on which the BPM is mounted. We have estimated the single shot resolution in presence of beam jitter by reading the beam position synchronously over many electron bunches from three or more BPMs. The algorithms have been subsequently improved, and the results are described.
	Poster TUPD14 [0.460 MB]

TUPD28	Benchmarking the Performance of the Present Bunch Arrival Time Monitors at FLASH	pick-up, feedback, laser, electron	365
	M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz DESY, Hamburg, Germany
	Funding: This work is partly supported by IRUVX-PP, an EU co-funded project under FP7 (Grant Agreement 211285) Presently, at FLASH four bunch arrival time monitors (BAM) are installed and in permanent operation. Moreover, they are incorporated in a longitudinal intra-bunch train feedback. In this paper, we present a review of the performance and the limitations of the current BAM design, based on the most recent machine studies. The detection principle of the monitor implements the electro-optical modulation of synchronised laser pulses. The RF and electro-optical front-ends are designed to be operated in a frequency band from DC up to 10 GHz. This allows for measuring the arrival time of each individual electron bunch at femtosecond resolution. The current design of the BAMs has been tested under the influence of disturbances on the arrival time measurement, such as variation of the bunch charge as well as deviation from the reference transverse bunch position. Those results will be incorporated in an upcoming design revision to upgrade the application and robustness of the BAMs.

TUPD31	Measurement of the Slice Energy Spread Induced by a Transverse Deflecting RF Structure at FLASH	electron, RF-structure, emittance, free-electron-laser	371
	C. Gerth, C. Behrens DESY, Hamburg, Germany
	Operation of a high-gain free-electron laser requires a high-brightness electron beam with high peak current and small slice energy spread. The slice energy spread can be measured with high longitudinal resolution by using a transverse deflecting structure in combination with viewing screen in a dispersive section. However, off-axis accelerating fields induce a correlated energy spread that depends inversely proportional on the longitudinal resolution. As a consequence, short bunches, which intrinsically require a high longitudinal resolution in order to be diagnosed, suffer from a large induced energy spread which limits the energy resolution. To be able to measure the impact of the transverse deflecting structure on the slice energy spread without distortions by space charge or coherent synchrotron radiation effects, we tailored short electron bunches with low peak currents by clipping low energy electrons in the collimator of the first bunch compressor at FLASH. In this paper, we present first systematic measurements of the correlated energy spread induced by a transverse deflecting structure. The results are compared with analytical calculations.

TUPD32	THz Radiation Diagnostics for Monitoring the Bunch Compression at the SwissFEL Injector Test Facility	radiation, electron, vacuum, simulation	374
	C. Gerth, B. Schmidt, S. Wesch DESY, Hamburg, Germany R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott PSI, Villigen, Switzerland
	At the SwissFEL Injector Test Facility, installation of a magnetic chicane for longitudinal bunch compression is foreseen for the first half of 2011. Bunch compression will be accomplished by operating two S-band accelerating structures on-crest and two S-band structures at off-crest RF phases. An X-band structure for the linearization of the longitudinal phase space will be installed at a later stage. The detection of coherent synchrotron radiation or coherent diffraction radiation in the THz range can be used to monitor the bunch compression process and stabilize the RF phases by a beam-based feedback. In this paper, we study the source characteristics of the edge radiation emitted at the 4th dipole of the bunch compressor as well as the diffraction radiation generated by a metallic foil with a hole. Particle tracking simulations were used to model the bunch compression process for different operation modes. The performance of a bunch compression monitor consisting of focusing mirrors and band pass filters has been evaluated by simulating the THz radiation transport of the optical components.

TUPD35	Development of an Alternative, Photodiode-Based, Femtosecond Stable Detection Principle for the Link Stabilization in the Optical Synchronization Systems at FLASH and XFEL	laser, controls, feedback, status	380
	T. Lamb, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz DESY, Hamburg, Germany
	Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285). The fs-stable timing information in the optical synchronization system at FLASH and the upcoming European XFEL is based on the distribution of laser pulses in optical fibers. The optical length of the fibers is continuously monitored and drifts in signal propagation time are actively compensated in order to provide a phase stable pulse train at the end of the fiber link. At present, optical cross-correlation is used to measure the optical length changes. To overcome some of the disadvantages of the current scheme, a different approach for the detection of the optical fiber link length variation was developed. This new scheme uses 10GHz photodiodes to measure the amplitude modulation of harmonics created by overlapping two pulse trains. The long-term stability of the prototype of this detector over 33h was demonstrated to be below 5fs (peak-to-peak) with a rms jitter of about 0.86fs. The detection principle itself is practically insensitive to environmental influences and needs only about 10% of the optical power, compared to the optical cross-correlator.

TUPD36	Progress and Status of the Laser-based Synchronization System at FLASH	laser, feedback, electron, status	383
	S. Schulz, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt DESY, Hamburg, Germany
	Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285). The free-electron lasers FLASH and European XFEL demand a high timing accuracy between the electron bunches and external laser systems for both exploitation of the short VUV and X-ray pulses in time-resolved pump-probe experiments and seeded operation modes. The required precision can only be achieved with laser-based synchronization schemes. The prototype system installed at FLASH is continuously evolving and subject to improvements. In this paper, we give an overview on the present status, report on the latest developments and extensions, and discuss future challenges. Particularly, the recent move to a new type of master laser oscillator led to a significant enhancement of the robustness and reliability. Consequently, research can focus on the implementation of the electron bunch arrival time feedback, new technologies for timing distribution and integration of Ti:sapphire lasers into the optical synchronization system.

TUPD48	Transition Radiation from a Cylindrical Target and Transverse Beam Size Diagnostics	target, electron, radiation, optics	410
	A. Potylitsyn TPU, Tomsk, Russia L.G. Sukhikh DESY, Hamburg, Germany
	For modern X-ray FELs like LCLS in SLAC, FLASH in DESY and constructed ones like European X-FEL the transverse beam profile diagnostics using well-known optical Transition Radiation (TR) is not a trivial task because of a short bunch length and instabilities. Due to these reasons a bunch emits any kind of radiation coherently that makes it impossible to determine transverse profile of such bunch. One may use radiation with wavelengths shorter than bunch length (e.g. EUV) to avoid the problem of radiation coherence. Because of a high quality of mirrors in that region needed to construct proper optical line we propose to use a cylindrical target instead of flat one. TR generated by the cylindrical target is wider than the one from the flat target. But in this case the radiation generated by particles with different impact-parameters relative to a cylinder axes depends on the point of interaction. Proper choice of cylinder parameters allows to obtain beam profile image without any additional optics. In this report we present the simulation results and show how the radiation from the cylindrical target may be used for the bunch transverse profile diagnostics with good space resolution.

TUPD54	Comparison of Different Radiators used to Measure the Transverse Characteristics of Low Energy Electron Beams at PITZ	electron, cathode, laser, radiation	428
	S. Rimjaem, G. Asova, J.W. Bähr, H.-J. Grabosch, M. Gross, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger DESY Zeuthen, Zeuthen, Germany D. Richter HZB, Berlin, Germany
	The photoinjector test facility at DESY, Zeuthen site (PITZ), has been established for developing and optimizing electron sources for linac based Free Electron Lasers (FELs). Characterizations of electron beams with maximum energies of about 25 MeV are carried out at PITZ. In order to study properties of electron beams, several diagnostic systems are applied. One of the important investigations is the study of transverse beam profiles at different beam conditions. Three screen types -YAG powder coated, optical transition radiation (OTR), and CVD-diamond screen- are used as beam profile monitors and are installed in screen stations at different locations along the beam transport line. In addition, wire scanner systems are available in the beamline for the same purpose. In this contribution a comparison of measurement results from all three screen types and the wire scanner used to characterize long pulse trains will be presented and discussed.
	Poster TUPD54 [0.193 MB]

TUPD59	Suppression of Coherent Optical Transition Radiation in Transverse Beam Diagnostics by Utilising a Scintillation Screen with a Fast Gated CCD Camera	electron, simulation, laser, linac	440
	M. Yan Uni HH, Hamburg, Germany C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch DESY, Hamburg, Germany
	Micro-bunching instabilities in high-brightness beams of linac-driven FELs can lead to coherence effects in the emission of optical transition radiation (OTR) used for standard transverse profile diagnostics, thus rendering it impossible to observe a direct image of the particle beam. By using a scintillation screen in combination with a fast gated CCD camera, coherence effects can be suppressed as OTR is created in an instantaneous process while scintillation light has a certain decay time. In addition, the emission of the scintillation light is a statistical process from many atoms which is completely insensitive to the longitudinal bunch structure and does not produce coherence effects. Gating the camera during the passage of the electron bunch should eliminate any influence of the coherent OTR (COTR). First experiments using this method have been performed successfully at FLASH as a proof-of-principle. In this paper, we study the applicability of scintillation screens for high-energy electron beams under operation conditions for which COTR is emitted. Experimental results together with simulations are presented and discussed in view of COTR suppression and spatial resolution.

TUPD91	Comparative Studies of Reconstruction Methods to Achieve Multi-Dimensional Phase Space Information	emittance, diagnostics, proton, ion	521
	C. Gabor STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom A.P. Letchford STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom D. Reggiani, M. Seidel PSI, Villigen, Switzerland
	High Intensity Proton Accelerators like SNS, PSI or future machines like ESS or Isis upgrade cannot tolerate high losses due to activation. Standard beam diagnostics may not provide enough information about potential loss sources like beam filamentation or halo. Moreover, the application of interceptive methods like slits or pepperpot can be seriously discouraged by either high power deposition or explicit requirements for non-destructive methods like on-line diagnostics near superconducting cavities. Reconstruction of the beam distribution with a tomography method based on Maximum Entropy could help to overcome those problems and is easily to integrate in already existing facilities because the algorithm does not depend on the experimental profile measurement technique. Furthermore beam tomography can be employed on both spatial and phase-space reconstruction. The paper compares results from two different software packages from PSI (Maximum Entropy Tomography MENT) with the code used at RAL (MemSys 5).

TUPD97	Diagnostic System of TAC IR FEL Facility	electron, emittance, linac, diagnostics	536
	Z. Nergiz N.U, Nigde, Turkey A. Aksoy Ankara University, Faculty of Engineering, Tandogan, Ankara, Turkey S. Ceylan, S. Özkorucuklu SDU, Isparta, Turkey C. Kaya HZDR, Dresden, Germany
	The TAC (Turkish Accelerator Center) IR FEL facility which is named as Turkish Accelerator and Radiation Laboratory at Ankara, TARLA will be based on a 15-40 MeV electron linac accompanying two different undulators with 2.5 cm and 9 cm periods in order to obtain IR FEL ranging between 2-250 microns. The electron linac will consist of two sequenced modules, each housing two 9-cell superconducting TESLA cavities for cw operation. It is planned that the TARLA facility will be completed in 2013 at Golbasi campus of Ankara University. This facility will give an opportunity to the scientists and industry to use FEL in research and development in Turkey and our region. In this study, the main structure of the facility and planned electron beam diagnostics system is given in detail.
	Poster TUPD97 [0.514 MB]

WEOA01	Summary of COTR Effects	radiation, emittance, diagnostics, electron	539
	S. Wesch, B. Schmidt DESY, Hamburg, Germany
	Coherent transition radiation in the visible regime (COTR) has become a serious issue in FEL - Linacs disturbing the measurement of beam profiles by OTR screens up to a level, where this diagnostics becomes totally impossible. The talk will summarize the measured COTR effects from LCLS, FLASH and other machines and the investigations done so far into the dependence of the effect on beam and machine parameters. The status of the theoretical background and understanding of its origin will be discussed as well as proposals and experiences with possible remedies.
	Slides WEOA01 [2.520 MB]

WEOA02	Experimental Investigations of Backward Transition Radiation from Flat Target in Extreme Ultraviolet Region	radiation, target, diagnostics, electron	544
	L.G. Sukhikh, G. Kube DESY, Hamburg, Germany D. Krambrich, W. Lauth IKP, Mainz, Germany Yu.A. Popov, A. Potylitsyn Tomsk Polytechnic University, Tomsk, Russia
	Forward transition radiation in X-ray range and backward transition radiation (BTR) in optical spectral region are investigated in details due to their use for purposes of particle and beam diagnostics. In order to improve diagnostics tools we proposed to use BTR in extreme ultraviolet (EUV) region [,], where theoretical models are existing only. We performed experimental investigations of BTR characteristics in EUV spectral region generated by a molybdenum target at 855 MeV electron beam of the MAMI-B (Mainz, Germany). Angular patterns and intensities of BTR both in optical and EUV regions for different observation angles were investigated. The measured intensity of optical BTR agrees with a theory with reasonable accuracy but one in EUV region is more intense than theoretically predicted. Our experimental estimation of the experimental BTR yield in EUV region is (2.4/3.6)•10⁻⁴ photons/electron and this is more than 4 / 6 times higher than the theoretical value. L.G. Sukhikh, S.Yu.Gogolev and A.P.Potylitsyn, Nucl. Instrum. Methods Phys. Res., Sect. A 623, 567 (2010) ** L.G. Sukhikh, S.Yu.Gogolev and A.P.Potylitsyn, J. Phys.: Conf. Ser. 236, 012011 (2010).
	Slides WEOA02 [6.967 MB]

WEOC03	Dark Current Monitor for the European XFEL	simulation, solenoid, controls, impedance	572
	D. Lipka, W. Kleen, J. Lund-Nielsen, D. Nölle, S. Vilcins, V. Vogel DESY, Hamburg, Germany
	Dark current is produced due from field emission in the accelerator. This generates a radiation background in the tunnel which damages the electronics and activates components. To decrease the dark current different methods like kickers and collimators are used. To control the dark current level and measure and optimize the efficiency of dark current reduction dark current monitors are required. To measure the dark current a cavity was designed and built with the operation frequency of the accelerator. Here the small charge of the dark current present in every RF bucket induces and superimposes a field up to a measurable level. The cavity is proven at the PITZ facility. In addition to dark current levels down to 50 nA, the monitor allows for charge measurements resolution below pC, better than the Faraday cup. In addition the ratio of amplitudes from higher order monopole modes is a function of the bunch length. Measurements show the same trend of bunch length compared with a destructive streak camera method with comparable resolution. Therefore this monitor is able to measure bunch charge, dark current and bunch length in a non-destructive manner.
	Slides WEOC03 [0.935 MB]

Paper

Title

Other Keywords

Page

MOOA02

Beam Instrumentation for X-ray FELs

cavity, feedback, undulator, diagnostics

1

H. Loos
SLAC, Menlo Park, California, USA

Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC03-76SF00515.
The performance of X-ray Free-electron lasers depends strongly on the achieved quality of the high brightness electron beam and its shot by shot stability. The requirements and challenges of the instrumentation needed to tune and optimize such electron beams will be discussed. Of particular interest are measurements of the beam orbit, emittance, energy, and bunch length and the different measurement techniques for these transverse and longitudinal beam parameters and their implementation for routine operation will be addressed in detail, particularly the necessary instrumentation to fulfill different user requirements in terms of beam energy and bunch length. Specific requirements for the initial commissioning, routine optimization and feedback applications will be presented as well.

Slides MOOA02 [2.114 MB]

MOOB04

Bunch Compression, RF Curvature Correction and R₅₅, T₅₅₅ and U₅₅₅₅ Measurements at JLab FEL

linac, cavity, SRF, sextupole

15

P. Evtushenko, S.V. Benson, D. Douglas
JLAB, Newport News, Virginia, USA

The JLab IR/UV FEL Upgrade operates with the bunch length compressed down to 100-150 fs RMS. An indispensible part of the bunch compression scheme is the correction of the so-called LINAC RF curvature. Unlike other systems – where the RF curvature gets corrected using higher a harmonic LINAC – our system utilizes magnetic elements of the beam transport system to correct and adjust the second and third order correlation terms. These are expressed in terms of the transport matrix elements T₅₆₆ and U₅₆₆₆. The linear correlation term described by M₅₅ is adjusted using the magnetic system as well. The large energy spread induced on the beam by the FEL operation is compressed as a part of the energy recovery process. As in the case of bunch length compression, this energy compression is optimized by properly adjusting high order transport matrix elements. In this contribution we describe the system used for direct measurements of the transport matrix elements M₅₅, T₅₆₆ and U₅₆₆₆ and its impact on the operation and bunch compression. Results of the measurements are presented together with the bunch length measurements including the data showing resolution and accuracy of the system.

Slides MOOB04 [0.999 MB]

MOOC03

The Fermi@Elettra Cavity BPM System: Description and Commissioning Results

cavity, pick-up, controls, undulator

26

M. Ferianis, A.O. Borga, P. Craievich, R. De Monte, G. Gaio, M. Predonzani
ELETTRA, Basovizza, Italy
M. Dal Forno
DIEIT, Trieste, Italy

The Fermi@elettra cavity BPM (C-BPM) system is based on an original implementation of the C-BPM scheme as the pick-up, operating at 6.5GHz, is coupled to a dedicated, self-calibrating electronics based on a novel concept. The system has been developed in-house; both the E-M and the mechanical design of the pick-up have been carried out, including an original frequency tuning scheme. The detector electronics directly obtains the envelope of the sum and difference signals by means of an RF 180° hybrid; no mixer for the RF signal down conversion is used. The detector is based on 3 blocks: an RF front-end, a baseband analogue transmission module and a digital back-end unit, based on a micro-TCA platform. The digital back-end is equipped with a powerful Virtex 5 FPGA and several real-time tasks have been implemented on it, including intra-pulse calibration. Ten C-BPM stations have been installed so far, fully integrated in the FERMI control System, enabling a real-time control of this key FEL diagnostics. Results on performances with beam are also presented; the scale factor of C-BPMs is obtained with beam, as two-axis micrometer translation stages have been installed.

Slides MOOC03 [2.733 MB]

MOPD12

Expressing Properties of BPM Measurement System in Terms of Error Emittance and Error Twiss Parameters

emittance, betatron, beam-transport, focusing

62

V. Balandin, W. Decking, N. Golubeva
DESY, Hamburg, Germany

The determination of variations in the beam position and in the beam energy using BPM readings is one of the standard problems of accelerator physics. If the optical model of the beam line and BPM resolutions are known, the typical choice is to let jitter parameters be a solution of the weighted linear least squares problem. For transversely uncoupled motion this least squares problem can be solved analytically, but the direct usage of the obtained solution as a tool for designing a BPM measurement system is not straightforward. A better understanding of the nature of the problem is needed. In this paper we show that properties of the BPM measurement system can be described in terms of the usual accelerator physics concepts of emittance, energy spread, dispersions and betatron functions. In this way one can compare two BPM systems comparing their so-called error emittances and error energy spreads, or, for a given measurement system, one can achieve a balance between coordinate and momentum reconstruction errors by matching the error betatron functions in the point of interest to the desired values.

MOPD54

Commissioning Results of the Photon-Electron Diagnostic Unit at sFLASH

laser, electron, undulator, diagnostics

173

J. Bödewadt, E. Hass, J. Roßbach
Uni HH, Hamburg, Germany

Funding: Supported by the Federal Ministry of Education and Research of Germany under contract 05 ES7GU1
Recently a seeded free-electron laser operating in the extreme ultra-violet (XUV) spectral range was installed and commissioned at the free-electron laser FLASH. The seed beam is generated by higher harmonics of near infrared laser pulses. A dedicated transport system guides the radiation into the electron accelerator environment. Within the seed undulator section compact diagnostic units were installed to control the transverse overlap of the photon and the electron beam. These units contain a BPM, horizontal and vertical wire scanners and an OTR screen for the electron diagnostic. A Ce:YAG screen and a MCP readout for the wire scanner are used to measure the photon beam position. This paper presents the commissioning results and the performance of the diagnostic units.

TUOA04

Instrumentation for Machine Protection at FERMI@Elettra

undulator, radiation, diagnostics, electron

286

L. Fröhlich, A.I. Bogani, K. Casarin, G. Cautero, G. Gaio, D. Giuressi, A. Gubertini, R.H. Menk, E. Quai, G. Scalamera, A. Vascotto
ELETTRA, Basovizza, Italy
L. Catani, D. Di Giovenale
INFN-Roma II, Roma, Italy

FERMI@Elettra is a linac-driven free-electron laser currently under commissioning at Sincrotrone Trieste, Italy. In order to protect the facility's permanent undulator magnets from radiation-induced demagnetization,beam losses and radiation doses are monitored closely by an active machine protection system. The talk focuses on the design and performance of its main diagnostic subsystems: Beam loss position monitors based on the detection of Cherenkov light in quartz fibers with multi-pixel photon counters, conventional ionization chambers with a new frontend electronics package, and solid-state RadFET dosimeters providing an online measurement of the absorbed dose in the undulator magnets.

Slides TUOA04 [2.559 MB]

TUPD14

Commissioning of the Cavity BPM for the FERMI@Elettra FEL Project

cavity, electron, undulator, polarization

329

P. Craievich, T. Borden, A.O. Borga, R. De Monte, M. Ferianis, M. Predonzani
ELETTRA, Basovizza, Italy
M. Dal Forno, R. Vescovo
DIEIT, Trieste, Italy

The cavity Beam Position Monitor (BPM) is a fundamental beam diagnostic device that allows the measurements of the electron beam trajectory in a non-destructively way and with sub-micron resolution. Ten cavity BPM systems have been installed along the undulators chain in the FERMI@Elettra FEL1 project. In this paper we discuss the installation, commissioning and performance of these cavity BPM systems. We have carried out preliminary operations during a pre-beam period, such as the alignment and fine tuning of the RF cavities under vacuum. During the commissioning each BPM has been calibrated by mechanically moving the support on which the BPM is mounted. We have estimated the single shot resolution in presence of beam jitter by reading the beam position synchronously over many electron bunches from three or more BPMs. The algorithms have been subsequently improved, and the results are described.

Poster TUPD14 [0.460 MB]

TUPD28

Benchmarking the Performance of the Present Bunch Arrival Time Monitors at FLASH

pick-up, feedback, laser, electron

365

M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz
DESY, Hamburg, Germany

Funding: This work is partly supported by IRUVX-PP, an EU co-funded project under FP7 (Grant Agreement 211285)
Presently, at FLASH four bunch arrival time monitors (BAM) are installed and in permanent operation. Moreover, they are incorporated in a longitudinal intra-bunch train feedback. In this paper, we present a review of the performance and the limitations of the current BAM design, based on the most recent machine studies. The detection principle of the monitor implements the electro-optical modulation of synchronised laser pulses. The RF and electro-optical front-ends are designed to be operated in a frequency band from DC up to 10 GHz. This allows for measuring the arrival time of each individual electron bunch at femtosecond resolution. The current design of the BAMs has been tested under the influence of disturbances on the arrival time measurement, such as variation of the bunch charge as well as deviation from the reference transverse bunch position. Those results will be incorporated in an upcoming design revision to upgrade the application and robustness of the BAMs.

TUPD31

Measurement of the Slice Energy Spread Induced by a Transverse Deflecting RF Structure at FLASH

electron, RF-structure, emittance, free-electron-laser

371

C. Gerth, C. Behrens
DESY, Hamburg, Germany

Operation of a high-gain free-electron laser requires a high-brightness electron beam with high peak current and small slice energy spread. The slice energy spread can be measured with high longitudinal resolution by using a transverse deflecting structure in combination with viewing screen in a dispersive section. However, off-axis accelerating fields induce a correlated energy spread that depends inversely proportional on the longitudinal resolution. As a consequence, short bunches, which intrinsically require a high longitudinal resolution in order to be diagnosed, suffer from a large induced energy spread which limits the energy resolution. To be able to measure the impact of the transverse deflecting structure on the slice energy spread without distortions by space charge or coherent synchrotron radiation effects, we tailored short electron bunches with low peak currents by clipping low energy electrons in the collimator of the first bunch compressor at FLASH. In this paper, we present first systematic measurements of the correlated energy spread induced by a transverse deflecting structure. The results are compared with analytical calculations.

TUPD32

THz Radiation Diagnostics for Monitoring the Bunch Compression at the SwissFEL Injector Test Facility

radiation, electron, vacuum, simulation

374

C. Gerth, B. Schmidt, S. Wesch
DESY, Hamburg, Germany
R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott
PSI, Villigen, Switzerland

At the SwissFEL Injector Test Facility, installation of a magnetic chicane for longitudinal bunch compression is foreseen for the first half of 2011. Bunch compression will be accomplished by operating two S-band accelerating structures on-crest and two S-band structures at off-crest RF phases. An X-band structure for the linearization of the longitudinal phase space will be installed at a later stage. The detection of coherent synchrotron radiation or coherent diffraction radiation in the THz range can be used to monitor the bunch compression process and stabilize the RF phases by a beam-based feedback. In this paper, we study the source characteristics of the edge radiation emitted at the 4th dipole of the bunch compressor as well as the diffraction radiation generated by a metallic foil with a hole. Particle tracking simulations were used to model the bunch compression process for different operation modes. The performance of a bunch compression monitor consisting of focusing mirrors and band pass filters has been evaluated by simulating the THz radiation transport of the optical components.

TUPD35

Development of an Alternative, Photodiode-Based, Femtosecond Stable Detection Principle for the Link Stabilization in the Optical Synchronization Systems at FLASH and XFEL

laser, controls, feedback, status

380

T. Lamb, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz
DESY, Hamburg, Germany

Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285).
The fs-stable timing information in the optical synchronization system at FLASH and the upcoming European XFEL is based on the distribution of laser pulses in optical fibers. The optical length of the fibers is continuously monitored and drifts in signal propagation time are actively compensated in order to provide a phase stable pulse train at the end of the fiber link. At present, optical cross-correlation is used to measure the optical length changes. To overcome some of the disadvantages of the current scheme, a different approach for the detection of the optical fiber link length variation was developed. This new scheme uses 10GHz photodiodes to measure the amplitude modulation of harmonics created by overlapping two pulse trains. The long-term stability of the prototype of this detector over 33h was demonstrated to be below 5fs (peak-to-peak) with a rms jitter of about 0.86fs. The detection principle itself is practically insensitive to environmental influences and needs only about 10% of the optical power, compared to the optical cross-correlator.

TUPD36

Progress and Status of the Laser-based Synchronization System at FLASH

laser, feedback, electron, status

383

S. Schulz, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt
DESY, Hamburg, Germany

Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285).
The free-electron lasers FLASH and European XFEL demand a high timing accuracy between the electron bunches and external laser systems for both exploitation of the short VUV and X-ray pulses in time-resolved pump-probe experiments and seeded operation modes. The required precision can only be achieved with laser-based synchronization schemes. The prototype system installed at FLASH is continuously evolving and subject to improvements. In this paper, we give an overview on the present status, report on the latest developments and extensions, and discuss future challenges. Particularly, the recent move to a new type of master laser oscillator led to a significant enhancement of the robustness and reliability. Consequently, research can focus on the implementation of the electron bunch arrival time feedback, new technologies for timing distribution and integration of Ti:sapphire lasers into the optical synchronization system.

TUPD48

Transition Radiation from a Cylindrical Target and Transverse Beam Size Diagnostics

target, electron, radiation, optics

410

A. Potylitsyn
TPU, Tomsk, Russia
L.G. Sukhikh
DESY, Hamburg, Germany

For modern X-ray FELs like LCLS in SLAC, FLASH in DESY and constructed ones like European X-FEL the transverse beam profile diagnostics using well-known optical Transition Radiation (TR) is not a trivial task because of a short bunch length and instabilities. Due to these reasons a bunch emits any kind of radiation coherently that makes it impossible to determine transverse profile of such bunch. One may use radiation with wavelengths shorter than bunch length (e.g. EUV) to avoid the problem of radiation coherence. Because of a high quality of mirrors in that region needed to construct proper optical line we propose to use a cylindrical target instead of flat one. TR generated by the cylindrical target is wider than the one from the flat target. But in this case the radiation generated by particles with different impact-parameters relative to a cylinder axes depends on the point of interaction. Proper choice of cylinder parameters allows to obtain beam profile image without any additional optics. In this report we present the simulation results and show how the radiation from the cylindrical target may be used for the bunch transverse profile diagnostics with good space resolution.

TUPD54

Comparison of Different Radiators used to Measure the Transverse Characteristics of Low Energy Electron Beams at PITZ

electron, cathode, laser, radiation

428

S. Rimjaem, G. Asova, J.W. Bähr, H.-J. Grabosch, M. Gross, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger
DESY Zeuthen, Zeuthen, Germany
D. Richter
HZB, Berlin, Germany

The photoinjector test facility at DESY, Zeuthen site (PITZ), has been established for developing and optimizing electron sources for linac based Free Electron Lasers (FELs). Characterizations of electron beams with maximum energies of about 25 MeV are carried out at PITZ. In order to study properties of electron beams, several diagnostic systems are applied. One of the important investigations is the study of transverse beam profiles at different beam conditions. Three screen types -YAG powder coated, optical transition radiation (OTR), and CVD-diamond screen- are used as beam profile monitors and are installed in screen stations at different locations along the beam transport line. In addition, wire scanner systems are available in the beamline for the same purpose. In this contribution a comparison of measurement results from all three screen types and the wire scanner used to characterize long pulse trains will be presented and discussed.

Poster TUPD54 [0.193 MB]

TUPD59

Suppression of Coherent Optical Transition Radiation in Transverse Beam Diagnostics by Utilising a Scintillation Screen with a Fast Gated CCD Camera

electron, simulation, laser, linac

440

M. Yan
Uni HH, Hamburg, Germany
C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch
DESY, Hamburg, Germany

Micro-bunching instabilities in high-brightness beams of linac-driven FELs can lead to coherence effects in the emission of optical transition radiation (OTR) used for standard transverse profile diagnostics, thus rendering it impossible to observe a direct image of the particle beam. By using a scintillation screen in combination with a fast gated CCD camera, coherence effects can be suppressed as OTR is created in an instantaneous process while scintillation light has a certain decay time. In addition, the emission of the scintillation light is a statistical process from many atoms which is completely insensitive to the longitudinal bunch structure and does not produce coherence effects. Gating the camera during the passage of the electron bunch should eliminate any influence of the coherent OTR (COTR). First experiments using this method have been performed successfully at FLASH as a proof-of-principle. In this paper, we study the applicability of scintillation screens for high-energy electron beams under operation conditions for which COTR is emitted. Experimental results together with simulations are presented and discussed in view of COTR suppression and spatial resolution.

TUPD91

Comparative Studies of Reconstruction Methods to Achieve Multi-Dimensional Phase Space Information

emittance, diagnostics, proton, ion

521

C. Gabor
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
A.P. Letchford
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
D. Reggiani, M. Seidel
PSI, Villigen, Switzerland

High Intensity Proton Accelerators like SNS, PSI or future machines like ESS or Isis upgrade cannot tolerate high losses due to activation. Standard beam diagnostics may not provide enough information about potential loss sources like beam filamentation or halo. Moreover, the application of interceptive methods like slits or pepperpot can be seriously discouraged by either high power deposition or explicit requirements for non-destructive methods like on-line diagnostics near superconducting cavities. Reconstruction of the beam distribution with a tomography method based on Maximum Entropy could help to overcome those problems and is easily to integrate in already existing facilities because the algorithm does not depend on the experimental profile measurement technique. Furthermore beam tomography can be employed on both spatial and phase-space reconstruction. The paper compares results from two different software packages from PSI (Maximum Entropy Tomography MENT) with the code used at RAL (MemSys 5).

TUPD97

Diagnostic System of TAC IR FEL Facility

electron, emittance, linac, diagnostics

536

Z. Nergiz
N.U, Nigde, Turkey
A. Aksoy
Ankara University, Faculty of Engineering, Tandogan, Ankara, Turkey
S. Ceylan, S. Özkorucuklu
SDU, Isparta, Turkey
C. Kaya
HZDR, Dresden, Germany

The TAC (Turkish Accelerator Center) IR FEL facility which is named as Turkish Accelerator and Radiation Laboratory at Ankara, TARLA will be based on a 15-40 MeV electron linac accompanying two different undulators with 2.5 cm and 9 cm periods in order to obtain IR FEL ranging between 2-250 microns. The electron linac will consist of two sequenced modules, each housing two 9-cell superconducting TESLA cavities for cw operation. It is planned that the TARLA facility will be completed in 2013 at Golbasi campus of Ankara University. This facility will give an opportunity to the scientists and industry to use FEL in research and development in Turkey and our region. In this study, the main structure of the facility and planned electron beam diagnostics system is given in detail.

Poster TUPD97 [0.514 MB]

WEOA01

Summary of COTR Effects

radiation, emittance, diagnostics, electron

539

S. Wesch, B. Schmidt
DESY, Hamburg, Germany

Coherent transition radiation in the visible regime (COTR) has become a serious issue in FEL - Linacs disturbing the measurement of beam profiles by OTR screens up to a level, where this diagnostics becomes totally impossible. The talk will summarize the measured COTR effects from LCLS, FLASH and other machines and the investigations done so far into the dependence of the effect on beam and machine parameters. The status of the theoretical background and understanding of its origin will be discussed as well as proposals and experiences with possible remedies.

Slides WEOA01 [2.520 MB]

WEOA02

Experimental Investigations of Backward Transition Radiation from Flat Target in Extreme Ultraviolet Region

radiation, target, diagnostics, electron

544

L.G. Sukhikh, G. Kube
DESY, Hamburg, Germany
D. Krambrich, W. Lauth
IKP, Mainz, Germany
Yu.A. Popov, A. Potylitsyn
Tomsk Polytechnic University, Tomsk, Russia

Forward transition radiation in X-ray range and backward transition radiation (BTR) in optical spectral region are investigated in details due to their use for purposes of particle and beam diagnostics. In order to improve diagnostics tools we proposed to use BTR in extreme ultraviolet (EUV) region [*,**], where theoretical models are existing only. We performed experimental investigations of BTR characteristics in EUV spectral region generated by a molybdenum target at 855 MeV electron beam of the MAMI-B (Mainz, Germany). Angular patterns and intensities of BTR both in optical and EUV regions for different observation angles were investigated. The measured intensity of optical BTR agrees with a theory with reasonable accuracy but one in EUV region is more intense than theoretically predicted. Our experimental estimation of the experimental BTR yield in EUV region is (2.4/3.6)•10⁻⁴ photons/electron and this is more than 4 / 6 times higher than the theoretical value.
* L.G. Sukhikh, S.Yu.Gogolev and A.P.Potylitsyn, Nucl. Instrum. Methods Phys. Res., Sect. A 623, 567 (2010)
** L.G. Sukhikh, S.Yu.Gogolev and A.P.Potylitsyn, J. Phys.: Conf. Ser. 236, 012011 (2010).

Slides WEOA02 [6.967 MB]

WEOC03

Dark Current Monitor for the European XFEL

simulation, solenoid, controls, impedance

572

D. Lipka, W. Kleen, J. Lund-Nielsen, D. Nölle, S. Vilcins, V. Vogel
DESY, Hamburg, Germany

Dark current is produced due from field emission in the accelerator. This generates a radiation background in the tunnel which damages the electronics and activates components. To decrease the dark current different methods like kickers and collimators are used. To control the dark current level and measure and optimize the efficiency of dark current reduction dark current monitors are required. To measure the dark current a cavity was designed and built with the operation frequency of the accelerator. Here the small charge of the dark current present in every RF bucket induces and superimposes a field up to a measurable level. The cavity is proven at the PITZ facility. In addition to dark current levels down to 50 nA, the monitor allows for charge measurements resolution below pC, better than the Faraday cup. In addition the ratio of amplitudes from higher order monopole modes is a function of the bunch length. Measurements show the same trend of bunch length compared with a destructive streak camera method with comparable resolution. Therefore this monitor is able to measure bunch charge, dark current and bunch length in a non-destructive manner.

Slides WEOC03 [0.935 MB]