FEL2019 - List of Keywords (timing)

Paper	Title	Other Keywords	Page
TUP078	Impact of Electron Beam Energy Chirp on Seeded FELs	electron, FEL, laser, simulation	238
	G. Paraskaki, S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, J. Zemella DESY, Hamburg, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Seeded FELs enable the generation of fully coherent, transform-limited and high brightness FEL pulses, as the start-up process is driven by an external coherent light pulse. During the design process of such FELs, it is important to choose carefully the electron beam parameters to guarantee high performance. One of those parameters is the electron beam energy chirp. In this contribution, we show simulation results and we discuss how the electron beam energy chirp affects the final spectrum.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP078
About •	paper received ※ 16 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEB04	Few-Femtosecond Facility-Wide Synchronization of the European XFEL	laser, FEL, electron, FEM	318
	S. Schulz, M.K. Czwalinna, M. Felber, M. Fenner, C. Gerth, T. Kozak, T. Lamb, B. Lautenschlager, F. Ludwig, U. Mavrič, J. Müller, S. Pfeiffer, H. Schlarb, Ch. Schmidt, C. Sydlo, M. Titberidze, F. Zummack DESY, Hamburg, Germany
	The first facility-wide evaluation of the optical synchronization system at the European XFEL resulted in excellent arrival time stability of the electron bunches at the end of the 2 km long linac, being measured with two individual adjacent femtosecond-resolution bunch arrival time monitors. While each of the monitors is independently linked by a stabilized optical fiber to a master laser oscillator, with one being installed in the injector area and one in the experimental hall, these two reference lasers are tightly synchronized through another few-km long fiber link. Thus, not only the accelerator performance is being benchmarked, but equally the optical synchronization infrastructure itself. Stability on this level can only be achieved by locking the RF for cavity field control to the optical reference and requires an unprecedented synchronization of the master laser oscillator to the main RF oscillator, enabled by a novel RF/optical phase detector. Finally, with the seeders of the experiment’s optical lasers synchronized to the master laser oscillator, first experiments at two independent scientific instruments proved an X-ray/optical timing jitter of few tens of femtoseconds.
	Slides WEB04 [22.142 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEB04
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP003	Balanced Optical-Microwave Phase Detector for 800-nm Pulsed Lasers with Sub-Femtosecond Resolution	laser, detector, electron, operation	322
	K. Şafak, A. Berlin, E. Cano Vargas, H.P.H. Cheng, A. Dai, J. Derksen, M. Neuhaus, P. Schiepel Cycle GmbH, Hamburg, Germany F.X. Kärtner Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
	Novel light-matter interaction experiments conducted in free-electron lasers, ultrafast electron diffraction instruments and extreme light infrastructures require synchronous operation of microwave sources with femtosecond pulsed lasers [1]. In particular, Ti:sapphire lasers have become the most common near-infrared light source used in these facilities due to their wide-range tunability and their ability to generate ultrashort pulses at around 800-nm optical wavelength [2]. Therefore, a highly sensitive optical-to-microwave phase detector operating at 800 nm is an indispensable tool to synchronize these ubiquitous lasers to the microwave clocks of these facilities. Electro-optic sampling is one approach that has proven to be the most precise in extracting the relative phase noise between microwaves and optical pulse trains. However, their implementation at 800-nm wavelength has been so far limited [3]. Here, we show a balanced optical-microwave phase detector designed for 800-nm operation based on electro-optic sampling. The detector has a timing resolution of 0.01 fs RMS for offset frequencies above 100 Hz and a total noise floor of less than 10 fs RMS integrated from 1 Hz to 1 MHz. [1] M. Xin, K. Shafak and F. X. Kärtner, Optica, vol. 5, no. 12, pp. 1564-1578, 2018. [2] H. Yang et al., Scientific Reports, vol. 7, no. 39966, 2017. [3] M. Titberidze, DESY-THESIS-2017-040, 2017.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP003
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP004	Timing Stability Comparison Study of RF Synthesis Techniques	laser, FEM, FEL, electron	325
	E. Cano Vargas, F.X. Kärtner Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany A. Berlin, H.P.H. Cheng, A. Dai, J. Derksen, P. Schiepel, K. Şafak Cycle GmbH, Hamburg, Germany
	Funding: Deutsches Elektronen-Synchrotron (DESY); Cycle GmbH. High-precision and low-noise timing transfer from a master clock to different end stations of a free-electron laser (FEL) is an essential task.[1] Timing precisions ranging from few tens of femtoseconds to sub-femtoseconds are required for seeded FELs and attosecond science centers. Mode-locked lasers referenced to RF standards are commonly used as master oscillators, due to their superior stability and timing precision, depicting timing jitter in the attosecond range.[2] In this matter, one of the biggest challenges is to transfer the timing stability of mode-locked lasers to RF sources. Here, we compare and contrast two of the most common techniques used for laser-to-RF synthesis in FEL facilities: (i) RF signal extraction from the optical pulse train using photodiodes, and (ii) VCO-to-laser synchronization. Test setups are built to measure both the absolute phase noise of the generated RF signal and the relative timing jitter with respect to the mode-locked laser. Short-term timing jitter values varying between 10 and 100 fs are achieved for different test setups, while long term timing drift ranging to some hundreds of fs due to environmental influence are observed. [1] M. Xin, K. Shafak and F.X. Kärtner, Optica, vol. 5, no. 12, pp. 1564-1578, 2018. [2] J. Kim, F.X. Kärtner, Opt. Lett., vol. 32, pp. 3519-3521, 2007.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP004
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP007	Usage of the MicroTCA.4 Electronics Platform for Femtosecond Synchronization Systems	laser, FEL, controls, electron	332
	M. Felber, E.P. Felber, M. Fenner, T. Kozak, T. Lamb, J. Müller, K.P. Przygoda, H. Schlarb, S. Schulz, C. Sydlo, M. Titberidze, F. Zummack DESY, Hamburg, Germany
	At the European XFEL and FLASH at DESY optical synchronization systems are installed providing sub-10 femtosecond electron bunch arrival time stability and laser oscillator synchronization to carry out time-resolved pump-probe experiments with high precision. The synchronization system supplies critical RF stations with short- and long-term phase-stable reference signals for precise RF field detection and control while bunch arrival times are processed in beam-based feedbacks to further time-stabilize the FEL pulses. Experimental lasers are tightly locked to the optical reference using balanced optical cross-correlation. In this paper, we describe the electronic hardware for supervision and real-time control of the optical synchronization system. It comprises various MicroTCA.4 modules including fast digitizers, FPGA processor boards, and drivers for piezos and stepper-motors. Advantages of the system are the high-level of integration, state-of-the-art performance, flexibility, and remote maintainability.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP007
About •	paper received ※ 20 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP008	Multi-Beamline Operation at the European XFEL	FEL, kicker, electron, undulator	335
	L. Fröhlich, A. Aghababyan, V. Balandin, B. Beutner, F. Brinker, W. Decking, N. Golubeva, O. Hensler, Y. Janik, R. Kammering, H. Kay, T. Limberg, S. Liu, D. Nölle, F. Obier, M. Omet, M. Scholz, T. Wamsat, T. Wilksen, J. Wortmann DESY, Hamburg, Germany
	The European XFEL uses a unique beam distribution scheme to direct electron bunches to its three undulator lines. The accelerator delivers up to 600 microsecond long bunch trains, out of which parts or individual bunches can be selected for photon production in any of the FELs. This contribution gives a brief overview of the kicker-septum scheme facilitating this and highlights how even complex bunch patterns can easily be configured via the timing system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP008
About •	paper received ※ 19 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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WEP014	Long Pulse Kicker for European XFEL Beam Distribution	kicker, FEL, flattop, septum	357
	F. Obier, W. Decking, M. Hüning, J. Wortmann DESY, Hamburg, Germany
	A special feature of the European XFEL X-ray laser is the possibility to distribute the electron bunches of one beam pulse to different free-electron laser (FEL) beam-lines. This is achieved through a combination of kickers and a Lambertson DC septum. The integration of a beam abort dump allows a flexible selection of the bunch pattern at the FEL experiment, while the superconducting linear accelerator operates with constant beam loading. The driver linac of the FEL can deliver up to 600 µs long bunch trains with a repetition rate of 10 Hz and a maximum energy of 17.5 GeV. The FEL process poses very strict requirements on the stability of the beam position and hence on all upstream magnets. It was therefore decided to split the beam distribution system into two kicker systems, long pulse kickers with very stable amplitude (flat-top) and relatively slow pulses and fast stripline kickers with moderate stability but very fast pulses. This contribution gives a brief overview of the long pulse kicker system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP014
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP016	Precise Laser-to-RF Synchronization of Photocathode Lasers	laser, electron, controls, experiment	364
	M. Titberidze, M. Felber, T. Kozak, T. Lamb, J. Müller, H. Schlarb, S. Schulz, C. Sydlo, F. Zummack DESY, Hamburg, Germany
	RF photo-injectors are used in various large, mid and small-scale accelerator facilities such as X-ray Free Electron Lasers (XFELs), external injection-based laser-driven plasma accelerators (LPAs) and ultrafast electron diffraction (UED) sources. Many of these facilities require a high precision synchronization of the photo-injector laser system, either because of beam dynamics reasons or the photo-injector directly impacting pump-probe experiments carried out to study physical processes on femtosecond timescales. It is thus crucial to achieve synchronization in the order of 10 fs rms or below between the photocathode laser and the RF source driving the RF gun. In this paper, we present the laser-to-RF synchronization setup employed to lock a commercial near-infrared (NIR) photocathode laser oscillator to a 2.998 GHz RF source. Together with the first results achieving ~ 10 fs rms timing jitter in the measurement bandwidth from 10 Hz up to 1 MHz, we describe an advanced synchronization setup as a future upgrade, promising even lower timing jitter and most importantly long-term timing drift stability.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP016
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP030	All-Fiber Photonic, Ultralow-Noise, Robust Optical and Microwave Signal Generators for FELs and UED	laser, photon, radiation, operation	382
	J. Kim, I.J. Jeon, D. Kim, D. Kwon KAIST, Daejeon, Republic of Korea
	Funding: National Research Foundation of Korea (2018R1A2B3001793) and Korea Atomic Energy Research Institute Optical timing and synchronization is becoming a more important and essential element for ultrafast X-ray and electron science. As a result, compact, ultralow-noise, mechanically robust and long-term stable optical and microwave signal generators are highly desirable for future XFELs and UEDs. Here we show that the combination of mode-locked fiber laser and fiber delay-based stabilization method enables the generation of ultralow-noise optical and microwave signals. We show that all-PM fiber lasers can provide excellent mechanical robustness: stable laser operation over >1 hour is maintained even in continuous 1.5 g vibrations [1]. Using a compactly packaged fiber delay as the timing reference, we could stabilize the repetition-rate phase noise of mode-locked lasers down to -100 dBc/Hz and -160 dBc/Hz at 1 Hz and 10 kHz offset frequency, respectively, at 1 GHz carrier, which corresponds to only 1.4 fs rms absolute timing jitter [1 Hz - 100 kHz] [2]. With DDS-based electronics, low-noise and agile microwave frequency synthesizer was also realized [3]. This new class of photonic signal generator will be suitable for master oscillators in various accelerator-based light sources. [1] D. Kim et al., Opt. Lett. 44, 1068 (2019) [2] D. Kwon et al., Opt. Lett. 42, 5186 (2017) [3] J. Wei et al., Photon. Res. 6, 12 (2018)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP030
About •	paper received ※ 05 September 2019 paper accepted ※ 22 October 2019 issue date ※ 05 November 2019
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WEP031	Timing Synchronization Activities for Drift-Free Operation of Ultrafast Electron Diffraction System at KAERI	electron, laser, gun, detector	385
	J. Shin, J. Kim KAIST, Daejeon, Republic of Korea I.H. Baek, Y.U. Jeong, H.W. Kim, K. Oang, S. Park KAERI, Daejon, Republic of Korea
	Funding: This work is funded by KAERI (Grant number: 525350-19) Precise timing synchronization of an ultrafast electron diffraction facility is essential requirement for femtosecond resolution structure analysis. Recent studies of THz-based electron deflectors have enabled the timing drift measurement between ultrafast electrons and an optical pump beam with few femtosecond resolution [1]. In this work, we will introduce timing synchronization activities to suppress the drift of an electron beam. As timing drift of the electron beam originates from every sub-element, each timing drift contribution from RF transfer, RF-to-optical synchronization, and optical amplification is measured. Timing drift of RF transfer through coaxial cable, which exposed to temperature fluctuation, is actively stabilized from 2 ps to 50 fs by active feedback loop. Further additive drift from RF-to-optical synchronization is maintained below 100 fs. Also optical drift due to the regenerative amplifier, measured by optical correlator, is maintained below 20 fs over an hour. This work allows ultrafast electron diffraction system to operate with less drift correction procedure and increased user availability. [1] H. Yang et al., "10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources", Sci. Rep. 7, 39966 (2017).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP031
About •	paper received ※ 24 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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Paper

Title

Other Keywords

Page

TUP078

Impact of Electron Beam Energy Chirp on Seeded FELs

electron, FEL, laser, simulation

238

G. Paraskaki, S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, J. Zemella
DESY, Hamburg, Germany
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Seeded FELs enable the generation of fully coherent, transform-limited and high brightness FEL pulses, as the start-up process is driven by an external coherent light pulse. During the design process of such FELs, it is important to choose carefully the electron beam parameters to guarantee high performance. One of those parameters is the electron beam energy chirp. In this contribution, we show simulation results and we discuss how the electron beam energy chirp affects the final spectrum.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP078

About •

paper received ※ 16 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEB04

Few-Femtosecond Facility-Wide Synchronization of the European XFEL

laser, FEL, electron, FEM

318

S. Schulz, M.K. Czwalinna, M. Felber, M. Fenner, C. Gerth, T. Kozak, T. Lamb, B. Lautenschlager, F. Ludwig, U. Mavrič, J. Müller, S. Pfeiffer, H. Schlarb, Ch. Schmidt, C. Sydlo, M. Titberidze, F. Zummack
DESY, Hamburg, Germany

The first facility-wide evaluation of the optical synchronization system at the European XFEL resulted in excellent arrival time stability of the electron bunches at the end of the 2 km long linac, being measured with two individual adjacent femtosecond-resolution bunch arrival time monitors. While each of the monitors is independently linked by a stabilized optical fiber to a master laser oscillator, with one being installed in the injector area and one in the experimental hall, these two reference lasers are tightly synchronized through another few-km long fiber link. Thus, not only the accelerator performance is being benchmarked, but equally the optical synchronization infrastructure itself. Stability on this level can only be achieved by locking the RF for cavity field control to the optical reference and requires an unprecedented synchronization of the master laser oscillator to the main RF oscillator, enabled by a novel RF/optical phase detector. Finally, with the seeders of the experiment’s optical lasers synchronized to the master laser oscillator, first experiments at two independent scientific instruments proved an X-ray/optical timing jitter of few tens of femtoseconds.

Slides WEB04 [22.142 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEB04

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP003

Balanced Optical-Microwave Phase Detector for 800-nm Pulsed Lasers with Sub-Femtosecond Resolution

laser, detector, electron, operation

322

K. Şafak, A. Berlin, E. Cano Vargas, H.P.H. Cheng, A. Dai, J. Derksen, M. Neuhaus, P. Schiepel
Cycle GmbH, Hamburg, Germany
F.X. Kärtner
Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany

Novel light-matter interaction experiments conducted in free-electron lasers, ultrafast electron diffraction instruments and extreme light infrastructures require synchronous operation of microwave sources with femtosecond pulsed lasers [1]. In particular, Ti:sapphire lasers have become the most common near-infrared light source used in these facilities due to their wide-range tunability and their ability to generate ultrashort pulses at around 800-nm optical wavelength [2]. Therefore, a highly sensitive optical-to-microwave phase detector operating at 800 nm is an indispensable tool to synchronize these ubiquitous lasers to the microwave clocks of these facilities. Electro-optic sampling is one approach that has proven to be the most precise in extracting the relative phase noise between microwaves and optical pulse trains. However, their implementation at 800-nm wavelength has been so far limited [3]. Here, we show a balanced optical-microwave phase detector designed for 800-nm operation based on electro-optic sampling. The detector has a timing resolution of 0.01 fs RMS for offset frequencies above 100 Hz and a total noise floor of less than 10 fs RMS integrated from 1 Hz to 1 MHz.
[1] M. Xin, K. Shafak and F. X. Kärtner, Optica, vol. 5, no. 12, pp. 1564-1578, 2018.
[2] H. Yang et al., Scientific Reports, vol. 7, no. 39966, 2017.
[3] M. Titberidze, DESY-THESIS-2017-040, 2017.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP003

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP004

Timing Stability Comparison Study of RF Synthesis Techniques

laser, FEM, FEL, electron

325

E. Cano Vargas, F.X. Kärtner
Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
A. Berlin, H.P.H. Cheng, A. Dai, J. Derksen, P. Schiepel, K. Şafak
Cycle GmbH, Hamburg, Germany

Funding: Deutsches Elektronen-Synchrotron (DESY); Cycle GmbH.
High-precision and low-noise timing transfer from a master clock to different end stations of a free-electron laser (FEL) is an essential task.[1] Timing precisions ranging from few tens of femtoseconds to sub-femtoseconds are required for seeded FELs and attosecond science centers. Mode-locked lasers referenced to RF standards are commonly used as master oscillators, due to their superior stability and timing precision, depicting timing jitter in the attosecond range.[2] In this matter, one of the biggest challenges is to transfer the timing stability of mode-locked lasers to RF sources. Here, we compare and contrast two of the most common techniques used for laser-to-RF synthesis in FEL facilities: (i) RF signal extraction from the optical pulse train using photodiodes, and (ii) VCO-to-laser synchronization. Test setups are built to measure both the absolute phase noise of the generated RF signal and the relative timing jitter with respect to the mode-locked laser. Short-term timing jitter values varying between 10 and 100 fs are achieved for different test setups, while long term timing drift ranging to some hundreds of fs due to environmental influence are observed.
[1] M. Xin, K. Shafak and F.X. Kärtner, Optica, vol. 5, no. 12, pp. 1564-1578, 2018.
[2] J. Kim, F.X. Kärtner, Opt. Lett., vol. 32, pp. 3519-3521, 2007.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP004

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP007

Usage of the MicroTCA.4 Electronics Platform for Femtosecond Synchronization Systems

laser, FEL, controls, electron

332

M. Felber, E.P. Felber, M. Fenner, T. Kozak, T. Lamb, J. Müller, K.P. Przygoda, H. Schlarb, S. Schulz, C. Sydlo, M. Titberidze, F. Zummack
DESY, Hamburg, Germany

At the European XFEL and FLASH at DESY optical synchronization systems are installed providing sub-10 femtosecond electron bunch arrival time stability and laser oscillator synchronization to carry out time-resolved pump-probe experiments with high precision. The synchronization system supplies critical RF stations with short- and long-term phase-stable reference signals for precise RF field detection and control while bunch arrival times are processed in beam-based feedbacks to further time-stabilize the FEL pulses. Experimental lasers are tightly locked to the optical reference using balanced optical cross-correlation. In this paper, we describe the electronic hardware for supervision and real-time control of the optical synchronization system. It comprises various MicroTCA.4 modules including fast digitizers, FPGA processor boards, and drivers for piezos and stepper-motors. Advantages of the system are the high-level of integration, state-of-the-art performance, flexibility, and remote maintainability.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP007

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paper received ※ 20 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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WEP008

Multi-Beamline Operation at the European XFEL

FEL, kicker, electron, undulator

335

L. Fröhlich, A. Aghababyan, V. Balandin, B. Beutner, F. Brinker, W. Decking, N. Golubeva, O. Hensler, Y. Janik, R. Kammering, H. Kay, T. Limberg, S. Liu, D. Nölle, F. Obier, M. Omet, M. Scholz, T. Wamsat, T. Wilksen, J. Wortmann
DESY, Hamburg, Germany

The European XFEL uses a unique beam distribution scheme to direct electron bunches to its three undulator lines. The accelerator delivers up to 600 microsecond long bunch trains, out of which parts or individual bunches can be selected for photon production in any of the FELs. This contribution gives a brief overview of the kicker-septum scheme facilitating this and highlights how even complex bunch patterns can easily be configured via the timing system.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP008

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paper received ※ 19 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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WEP014

Long Pulse Kicker for European XFEL Beam Distribution

kicker, FEL, flattop, septum

357

F. Obier, W. Decking, M. Hüning, J. Wortmann
DESY, Hamburg, Germany

A special feature of the European XFEL X-ray laser is the possibility to distribute the electron bunches of one beam pulse to different free-electron laser (FEL) beam-lines. This is achieved through a combination of kickers and a Lambertson DC septum. The integration of a beam abort dump allows a flexible selection of the bunch pattern at the FEL experiment, while the superconducting linear accelerator operates with constant beam loading. The driver linac of the FEL can deliver up to 600 µs long bunch trains with a repetition rate of 10 Hz and a maximum energy of 17.5 GeV. The FEL process poses very strict requirements on the stability of the beam position and hence on all upstream magnets. It was therefore decided to split the beam distribution system into two kicker systems, long pulse kickers with very stable amplitude (flat-top) and relatively slow pulses and fast stripline kickers with moderate stability but very fast pulses. This contribution gives a brief overview of the long pulse kicker system.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP014

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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WEP016

Precise Laser-to-RF Synchronization of Photocathode Lasers

laser, electron, controls, experiment

364

M. Titberidze, M. Felber, T. Kozak, T. Lamb, J. Müller, H. Schlarb, S. Schulz, C. Sydlo, F. Zummack
DESY, Hamburg, Germany

RF photo-injectors are used in various large, mid and small-scale accelerator facilities such as X-ray Free Electron Lasers (XFELs), external injection-based laser-driven plasma accelerators (LPAs) and ultrafast electron diffraction (UED) sources. Many of these facilities require a high precision synchronization of the photo-injector laser system, either because of beam dynamics reasons or the photo-injector directly impacting pump-probe experiments carried out to study physical processes on femtosecond timescales. It is thus crucial to achieve synchronization in the order of 10 fs rms or below between the photocathode laser and the RF source driving the RF gun. In this paper, we present the laser-to-RF synchronization setup employed to lock a commercial near-infrared (NIR) photocathode laser oscillator to a 2.998 GHz RF source. Together with the first results achieving ~ 10 fs rms timing jitter in the measurement bandwidth from 10 Hz up to 1 MHz, we describe an advanced synchronization setup as a future upgrade, promising even lower timing jitter and most importantly long-term timing drift stability.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP016

About •

paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEP030

All-Fiber Photonic, Ultralow-Noise, Robust Optical and Microwave Signal Generators for FELs and UED

laser, photon, radiation, operation

382

J. Kim, I.J. Jeon, D. Kim, D. Kwon
KAIST, Daejeon, Republic of Korea

Funding: National Research Foundation of Korea (2018R1A2B3001793) and Korea Atomic Energy Research Institute
Optical timing and synchronization is becoming a more important and essential element for ultrafast X-ray and electron science. As a result, compact, ultralow-noise, mechanically robust and long-term stable optical and microwave signal generators are highly desirable for future XFELs and UEDs. Here we show that the combination of mode-locked fiber laser and fiber delay-based stabilization method enables the generation of ultralow-noise optical and microwave signals. We show that all-PM fiber lasers can provide excellent mechanical robustness: stable laser operation over >1 hour is maintained even in continuous 1.5 g vibrations [1]. Using a compactly packaged fiber delay as the timing reference, we could stabilize the repetition-rate phase noise of mode-locked lasers down to -100 dBc/Hz and -160 dBc/Hz at 1 Hz and 10 kHz offset frequency, respectively, at 1 GHz carrier, which corresponds to only 1.4 fs rms absolute timing jitter [1 Hz - 100 kHz] [2]. With DDS-based electronics, low-noise and agile microwave frequency synthesizer was also realized [3]. This new class of photonic signal generator will be suitable for master oscillators in various accelerator-based light sources.
[1] D. Kim et al., Opt. Lett. 44, 1068 (2019)
[2] D. Kwon et al., Opt. Lett. 42, 5186 (2017)
[3] J. Wei et al., Photon. Res. 6, 12 (2018)

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP030

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paper received ※ 05 September 2019 paper accepted ※ 22 October 2019 issue date ※ 05 November 2019

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WEP031

Timing Synchronization Activities for Drift-Free Operation of Ultrafast Electron Diffraction System at KAERI

electron, laser, gun, detector

385

J. Shin, J. Kim
KAIST, Daejeon, Republic of Korea
I.H. Baek, Y.U. Jeong, H.W. Kim, K. Oang, S. Park
KAERI, Daejon, Republic of Korea

Funding: This work is funded by KAERI (Grant number: 525350-19)
Precise timing synchronization of an ultrafast electron diffraction facility is essential requirement for femtosecond resolution structure analysis. Recent studies of THz-based electron deflectors have enabled the timing drift measurement between ultrafast electrons and an optical pump beam with few femtosecond resolution [1]. In this work, we will introduce timing synchronization activities to suppress the drift of an electron beam. As timing drift of the electron beam originates from every sub-element, each timing drift contribution from RF transfer, RF-to-optical synchronization, and optical amplification is measured. Timing drift of RF transfer through coaxial cable, which exposed to temperature fluctuation, is actively stabilized from 2 ps to 50 fs by active feedback loop. Further additive drift from RF-to-optical synchronization is maintained below 100 fs. Also optical drift due to the regenerative amplifier, measured by optical correlator, is maintained below 20 fs over an hour. This work allows ultrafast electron diffraction system to operate with less drift correction procedure and increased user availability.
[1] H. Yang et al., "10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources", Sci. Rep. 7, 39966 (2017).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP031

About •

paper received ※ 24 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)