FEL2017 - List of Authors (Rossbach, J.)

Paper	Title	Page
MOP003	Concept for a Seeded FEL at FLASH2	34
	C. Lechner, R.W. Aßmann, J. Bödewadt, M. Dohlus, N. Ekanayake, G. Feng, I. Hartl, T. Laarmann, T. Lang, L. Winkelmann, I. Zagorodnov DESY, Hamburg, Germany A. Azima, M. Drescher, Th. Maltezopoulos, T. Plath, J. Roßbach, W. Wurth University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany S. Khan, T. Plath DELTA, Dortmund, Germany
	The free-electron laser (FEL) FLASH is a user facility delivering photon pulses down to 4 nm wavelength. Recently, the second FEL undulator beamline 'FLASH2' was added to the facility. Operating in self-amplified spontaneous emission (SASE) mode, the exponential amplification process is initiated by shot noise of the electron bunch resulting in photon pulses of limited temporal coherence. In seeded FELs, the FEL process is initiated by coherent seed radiation, improving the longitudinal coherence of the generated photon pulses. The conceptual design of a possible seeding option for the FLASH2 beamline envisages the installation of the hardware needed for high-gain harmonic generation (HGHG) seeding upstream of the already existing undulator system. In this contribution, we present the beamline design and numerical simulations of the seeded FEL.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP003
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MOP028	Extraction of the Longitudinal Profile of the Transverse Emittance From Single-Shot RF Deflector Measurements at sFLASH	98
	T. Plath, Ph. Amstutz, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, J. Roßbach University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany J. Bödewadt, N. Ekanayake, T. Laarmann, C. Lechner DESY, Hamburg, Germany S. Khan DELTA, Dortmund, Germany
	The gain length of the free-electron laser (FEL) process strongly depends on the slice energy spread, slice emittance, and current of the electron bunch. At an FEL with only moderately compressed electron bunches, the slice energy spread is mainly determined by the compression process. In this regime, single-shot measurements using a transverse deflecting rf cavity enable the extraction of the longitudinal profile of the transverse emittance. At the free-electron laser FLASH at DESY, this technique was used to determine the slice properties of the electron bunch set up for seeded operation in the sFLASH experiment. Thereby, the performance of the seeded FEL process as a function of laser-electron timing can be predicted from these slice properties with the semi-analytical Ming-Xie model where only confined fractions of the electron bunch are stimulated to lase. The prediction is well in line with the FEL peak power observed during an experimental laser-electron timing scan. The power profiles of the FEL pulses were reconstructed from the longitudinal phase-space measurements of the seeded electron bunch that was measured with the rf deflector.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP028
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MOP042	Status of Seeding Development at sFLASH	136
	V. Grattoni, R.W. Aßmann, J. Bödewadt, I. Hartl, T. Laarmann, C. Lechner, M.M. Mohammad Kazemi, A. Przystawik DESY, Hamburg, Germany A. Azima, M. Drescher, W. Hillert, L.L. Lazzarino, V. Miltchev, J. Roßbach University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany S. Khan, N.M. Lockmann, T. Plath DELTA, Dortmund, Germany
	The experimental seeding setup at FLASH has operated now for two years in high-gain harmonic generation mode. Using a transverse deflecting structure downstream of the seeding section allows a temporal characterization of seeded electron bunches. In addition, temporal characterization of the seeded FEL beam can be performed in a dedicated diagnostic hutch. In this contribution, we give an overview of the latest achievements and present an outlook of the planned studies.
	Poster MOP042 [1.718 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP042
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MOP064	An Experimental Setup for Probing the Thermal Properties of Diamond Regarding Its Use in an XFELO	200
	C.P. Maag, I. Bahns, J. Roßbach, P. Thiessen University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany H. Sinn XFEL. EU, Hamburg, Germany J. Zemella DESY, Hamburg, Germany
	Funding: Work supported by BMBF (FKZ 05K13GU4 + FKZ 05K16GU4) This work presents an pump-probe setup for measuring the thermal evolution of diamond crystals at cryogenic temperatures under the heat load conditions of an X-ray free electron laser oscillator (XFELO). As the diamond Bragg reflectors of an XFELO are subjected to intense heat loads during operation, the correct understanding of the thermal evolution in diamond plays a major role in the correct modeling of an XFELO. Stoupin et al.* did a room temperature x-ray diffraction measurement on the nanosecond transient thermal response of diamond to an optical pulse. The measurements presented in this paper for the first time incorporate effects due to the very short penetration depth of only a few μm of an XFELO pulse in combination with the high mean free path in diamond at cryogenic temperatures. While at room temperature the heat equation based on Fourier's law accurately fits the measured results, this vastly changes due to the onset of ballistic processes at cryogenic temperatures. These changes, which are hard to predict theoretically, show the necessity of measurements of the thermal evolution in diamond with special regard to a correct mimicking of the heat load in an XFELO. *S. Stoupin et al., Phys. Rev. B, vol. 86, p. 054301, 2012.
	Poster MOP064 [2.239 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP064
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TUC02	Thermal and Mechanical Stability of Bragg Reflectors under Pulsed XFEL Radiation	240
	I. Bahns, C.P. Maag, J. Roßbach, P. Thiessen University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany H. Sinn, V. Sleziona XFEL. EU, Hamburg, Germany J. Zemella DESY, Hamburg, Germany
	Funding: BMBF FKZ 05K16GU4 Free-electron laser(FEL) x-ray radiation can deliver pulses with a huge amount of energy in short time duration. X-ray optics like Bragg reflectors therefore must be chosen in a way that they can withstand radiation-material interaction without getting damaged so that they can maintain their technical functionality. Therefore thermal and mechanical reactions of Bragg reflectors to the radiation induced thermal strain and force (radiation pressure) have been considered in this study. The theory of thermoelasticity has been used to simulate the strain conditions at saturation of the amplifying process in an X-ray free-electron laser oscillator(XFELO). One aim of this study was to investigate, if the radiation pressure could be an effect that gives a considerable contribution to the strain propagation. The results of the simulations have shown that, if Bragg backscattering of the X-ray pulse by a diamond crystal with 99% reflectivity and 1% absorptivity is assumed, the value of the thermally induced strain is about two magnitudes higher than the radiation pressure induced strain.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUC02
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TUP042	Determination of the Slice Energy Spread of Ultra-Relativistic Electron Beams by Scanning Seeded Coherent Undulator Radiation	326
	J. Bödewadt, R.W. Aßmann, C. Lechner, M.M. Mohammad Kazemi DESY, Hamburg, Germany L.L. Lazzarino, T. Plath, J. Roßbach University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Modern high-gain free-electron lasers make use of high-brightness ultra-relativistic electron beams. The uncorrelated energy spread of these beams is upon creation of the beam in the sub-permille range and below the resolution of state-of-the-art diagnostics. One method to determine the slice energy spread is to use an external seed laser to imprint a coherent microbunching structure that gives rise to coherent radiation processes, different radiation sources such as transition radiation, synchrotron radiation, or undulator radiation and others. Here, we present a method and show measurements to determine the slice energy spread using an external seed laser with 266 nm wavelength to produce coherent undulator radiation at higher harmonics. The distribution of these harmonics allows retrieval of the electron beam slice energy spread with high precision.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP042
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Concept for a Seeded FEL at FLASH2

34

C. Lechner, R.W. Aßmann, J. Bödewadt, M. Dohlus, N. Ekanayake, G. Feng, I. Hartl, T. Laarmann, T. Lang, L. Winkelmann, I. Zagorodnov
DESY, Hamburg, Germany
A. Azima, M. Drescher, Th. Maltezopoulos, T. Plath, J. Roßbach, W. Wurth
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
S. Khan, T. Plath
DELTA, Dortmund, Germany

The free-electron laser (FEL) FLASH is a user facility delivering photon pulses down to 4 nm wavelength. Recently, the second FEL undulator beamline 'FLASH2' was added to the facility. Operating in self-amplified spontaneous emission (SASE) mode, the exponential amplification process is initiated by shot noise of the electron bunch resulting in photon pulses of limited temporal coherence. In seeded FELs, the FEL process is initiated by coherent seed radiation, improving the longitudinal coherence of the generated photon pulses. The conceptual design of a possible seeding option for the FLASH2 beamline envisages the installation of the hardware needed for high-gain harmonic generation (HGHG) seeding upstream of the already existing undulator system. In this contribution, we present the beamline design and numerical simulations of the seeded FEL.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP003

Export •

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

MOP028

Extraction of the Longitudinal Profile of the Transverse Emittance From Single-Shot RF Deflector Measurements at sFLASH

98

T. Plath, Ph. Amstutz, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, J. Roßbach
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
J. Bödewadt, N. Ekanayake, T. Laarmann, C. Lechner
DESY, Hamburg, Germany
S. Khan
DELTA, Dortmund, Germany

The gain length of the free-electron laser (FEL) process strongly depends on the slice energy spread, slice emittance, and current of the electron bunch. At an FEL with only moderately compressed electron bunches, the slice energy spread is mainly determined by the compression process. In this regime, single-shot measurements using a transverse deflecting rf cavity enable the extraction of the longitudinal profile of the transverse emittance. At the free-electron laser FLASH at DESY, this technique was used to determine the slice properties of the electron bunch set up for seeded operation in the sFLASH experiment. Thereby, the performance of the seeded FEL process as a function of laser-electron timing can be predicted from these slice properties with the semi-analytical Ming-Xie model where only confined fractions of the electron bunch are stimulated to lase. The prediction is well in line with the FEL peak power observed during an experimental laser-electron timing scan. The power profiles of the FEL pulses were reconstructed from the longitudinal phase-space measurements of the seeded electron bunch that was measured with the rf deflector.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP028

Export •

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

MOP042

Status of Seeding Development at sFLASH

136

V. Grattoni, R.W. Aßmann, J. Bödewadt, I. Hartl, T. Laarmann, C. Lechner, M.M. Mohammad Kazemi, A. Przystawik
DESY, Hamburg, Germany
A. Azima, M. Drescher, W. Hillert, L.L. Lazzarino, V. Miltchev, J. Roßbach
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
S. Khan, N.M. Lockmann, T. Plath
DELTA, Dortmund, Germany

The experimental seeding setup at FLASH has operated now for two years in high-gain harmonic generation mode. Using a transverse deflecting structure downstream of the seeding section allows a temporal characterization of seeded electron bunches. In addition, temporal characterization of the seeded FEL beam can be performed in a dedicated diagnostic hutch. In this contribution, we give an overview of the latest achievements and present an outlook of the planned studies.

Poster MOP042 [1.718 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP042

Export •

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

MOP064

An Experimental Setup for Probing the Thermal Properties of Diamond Regarding Its Use in an XFELO

200

C.P. Maag, I. Bahns, J. Roßbach, P. Thiessen
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
H. Sinn
XFEL. EU, Hamburg, Germany
J. Zemella
DESY, Hamburg, Germany

Funding: Work supported by BMBF (FKZ 05K13GU4 + FKZ 05K16GU4)
This work presents an pump-probe setup for measuring the thermal evolution of diamond crystals at cryogenic temperatures under the heat load conditions of an X-ray free electron laser oscillator (XFELO). As the diamond Bragg reflectors of an XFELO are subjected to intense heat loads during operation, the correct understanding of the thermal evolution in diamond plays a major role in the correct modeling of an XFELO. Stoupin et al.* did a room temperature x-ray diffraction measurement on the nanosecond transient thermal response of diamond to an optical pulse. The measurements presented in this paper for the first time incorporate effects due to the very short penetration depth of only a few μm of an XFELO pulse in combination with the high mean free path in diamond at cryogenic temperatures. While at room temperature the heat equation based on Fourier's law accurately fits the measured results, this vastly changes due to the onset of ballistic processes at cryogenic temperatures. These changes, which are hard to predict theoretically, show the necessity of measurements of the thermal evolution in diamond with special regard to a correct mimicking of the heat load in an XFELO.
*S. Stoupin et al., Phys. Rev. B, vol. 86, p. 054301, 2012.

Poster MOP064 [2.239 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP064

Export •

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

TUC02

Thermal and Mechanical Stability of Bragg Reflectors under Pulsed XFEL Radiation

240

I. Bahns, C.P. Maag, J. Roßbach, P. Thiessen
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
H. Sinn, V. Sleziona
XFEL. EU, Hamburg, Germany
J. Zemella
DESY, Hamburg, Germany

Funding: BMBF FKZ 05K16GU4
Free-electron laser(FEL) x-ray radiation can deliver pulses with a huge amount of energy in short time duration. X-ray optics like Bragg reflectors therefore must be chosen in a way that they can withstand radiation-material interaction without getting damaged so that they can maintain their technical functionality. Therefore thermal and mechanical reactions of Bragg reflectors to the radiation induced thermal strain and force (radiation pressure) have been considered in this study. The theory of thermoelasticity has been used to simulate the strain conditions at saturation of the amplifying process in an X-ray free-electron laser oscillator(XFELO). One aim of this study was to investigate, if the radiation pressure could be an effect that gives a considerable contribution to the strain propagation. The results of the simulations have shown that, if Bragg backscattering of the X-ray pulse by a diamond crystal with 99% reflectivity and 1% absorptivity is assumed, the value of the thermally induced strain is about two magnitudes higher than the radiation pressure induced strain.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUC02

Export •

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

TUP042

Determination of the Slice Energy Spread of Ultra-Relativistic Electron Beams by Scanning Seeded Coherent Undulator Radiation

326

J. Bödewadt, R.W. Aßmann, C. Lechner, M.M. Mohammad Kazemi
DESY, Hamburg, Germany
L.L. Lazzarino, T. Plath, J. Roßbach
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Modern high-gain free-electron lasers make use of high-brightness ultra-relativistic electron beams. The uncorrelated energy spread of these beams is upon creation of the beam in the sub-permille range and below the resolution of state-of-the-art diagnostics. One method to determine the slice energy spread is to use an external seed laser to imprint a coherent microbunching structure that gives rise to coherent radiation processes, different radiation sources such as transition radiation, synchrotron radiation, or undulator radiation and others. Here, we present a method and show measurements to determine the slice energy spread using an external seed laser with 266 nm wavelength to produce coherent undulator radiation at higher harmonics. The distribution of these harmonics allows retrieval of the electron beam slice energy spread with high precision.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP042

Export •

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