FEL2014 - List of Authors (Hacker, K.E.)

Paper

Title

Page

Conceptual Study of a Self-seeding Scheme at FLASH2

53

T. Plath, L.L. Lazzarino
Uni HH, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355.
We present a conceptual study of a self-seeding installation at the new FEL beamline, FLASH2, at the free-electron laser at DESY, Hamburg. For self-seeding, light from a first set of undulators is filtered by a monochromator and thus acts as a seed for the gain process in the main undulator. This scheme has been tested at LCLS at SLAC with a diamond monochromator for hard X-rays and with a grating monochromator for soft X-rays covering energies between 700 and 1000 eV. For such a design to offer benefits at FLASH2, it must be modified to work with X-rays with wavelength of about 5 nm (248 eV) where the damage threshold of the monochromator in the setup and the divergence at longer wavelengths become an issue. An analysis of the potential performance and limitations of this setup is performed using GENESIS 1.3 and a method developed for the soft X-ray self-seeding experiment at the European XFEL. With a total of 9 undulators in the first stage and 8 undulators after the monochromator, a pulse energy contrast ratio of 4.5 was simulated with an initial peak current of 2.5 kA.

MOP060

Demonstration of SASE Suppression Through a Seeded Microbunching Instability

177

C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach
Uni HH, Hamburg, Germany
S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, E. Hass, K. Honkavaara, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov
DESY, Hamburg, Germany
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school 1355.
Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brilliance electron bunches needed for the operation of free-electron lasers. In this contribution, we demonstrate the application of a laser-induced microbunching instability to selectively suppress the SASE process. A significant decrease of photon pulse energies was observed at the free-electron laser FLASH in coincidence with overlap of 800 nm laser pulses and electron bunches within a modulator located approximately 40 meters upstream of the undulators. We discuss the underlying mechanisms based on longitudinal space charge amplification [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.

MOP083

Start-to-End Simulation for FLASH2 HGHG Option

244

G. Feng, S. Ackermann, J. Bödewadt, W. Decking, M. Dohlus, Y.A. Kot, T. Limberg, M. Scholz, I. Zagorodnov
DESY, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany
T. Plath
Uni HH, Hamburg, Germany

The Free-electron laser in Hamburg (FLASH) is the first FEL user facility to have produced extreme ultraviolet (XUV) and soft X-ray photons. In order to increase the beam time delivered to users, a major upgrade of FLASH named FLASH II is in progress. The electron beamline of FLASH2 consists of diagnostic and matching sections, a seeding undulator section and a SASE undulator section. In this paper, results from a start-to-end simulation for a FLASH2 High-Gain Harmonic Generation (HGHG) option are presented. For the beam dynamics simulation, space charge, coherent synchrotron radiation (CSR) and longitudinal cavity wake field effects are taken into account. In order to get electron beam bunches with small correlated and uncorrelated energy spread, RF parameters of the accelerating modules have been optimized as well as the parameters of the bunch compressors. Radiation simulations for the modulator and the radiator have been done with code Genesis 1.3 by using the particle distribution generated from the beam dynamics simulation. The results show that for a single stage HGHG, 33.6 nm wavelength FEL radiation can be seeded at FLASH2 with a 235 nm seeding laser.

MOP089

Overview of FEL Seeding Activities at FLASH

J. Bödewadt, S. Ackermann, R.W. Aßmann, N. Ekanayake, B. Faatz, G. Feng, I. Hartl, R. Ivanov, T. Laarmann, J.M. Mueller, T. Tanikawa
DESY, Hamburg, Germany
S. Ackermann, A. Azima, M. Drescher, L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Roßbach
Uni HH, Hamburg, Germany
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany

The free-electron laser facility FLASH at DESY operates since several years in SASE mode, delivering high-intensity FEL pulses in the extreme ultra violet and soft x-ray wavelength range for users. In order to get more control of the characteristics of the FEL pulses external FEL seeding has proven to be a reliable method to do so. At FLASH, an experimental setup to test several different external seeding methods has been installed since 2010. After successful demonstration of direct seeding at 38 nm, the setup is now being commissioned to operate in HGHG and EEHG mode. Furthermore, other studies on laser induced effects on the electron beam dynamics will be performed. Beside the experimental activities, a design for the seeding option for the FLASH2 beamline is currently under investigation. The goal for that is to develop a concept which is compatible with the operation of FLASH1 and which satisfies the high demands of the future user community. In this contribution, we give an overview of the activities on FEL seeding at FLASH.

MOP094

Indirect Measurements of NIR and UV Ultrashort Seed Laser Pulses using a Transverse Deflecting RF-Structure

272

N. Ekanayake, S. Ackermann
DESY, Hamburg, Germany
S. Ackermann, C. Lechner, Th. Maltezopoulos, T. Plath
Uni HH, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany

Seeding of free-electron lasers (FELs) using external coherent optical pulses recently became an area of interest as users demand spectrally and temporally coherent FEL radiation which is not achievable in traditional self-amplified spontaneous emission operation mode. Since temporal and spectral properties of the seed laser pulses are directly imprinted on the electron bunch, a proper characterization of these seed pulses is needed. However, the lack of any measurement technique capable of characterizing ultrashort seed laser pulses at the laser-electron interaction region is a primary drawback. In this paper we report indirect measurements of seed laser pulses in an undulator section using a transverse deflecting RF-structure (TDS-LOLA) at the free-electron laser FLASH at DESY. Temporally chirped and unchirped seed pulse length measurements will be compared with second-harmonic generation frequency-resolved optical gating measurements and theoretical simulations. Using this technique we will demonstrate that pulse artifacts such as pre- and post-pulses in the seed pulse in the femtosecond and picosecond timescales can be identified without any temporal ambiguity.
Authors acknowledge the support received from FLASH team and many groups at DESY in preparation and commissioning of experiments. We thank our colleagues in the FLASH seeding team for their support.

MOP095

HGHG AND EEHG MICROBUNCHES WITH CSR AND LSC

275

K.E. Hacker
DELTA, Dortmund, Germany

Funding: Work supported by BMBF (contract 05K13PE3) and DESY
Longitudinal space charge (LSC) forces in a drift and coherent synchrotron radiation (CSR) in a chicane are relevant for high gain harmonic generation (HGHG) and echo enabled harmonic generation (EEHG) seeding designs. These factors determine whether or not the modulator can be located significantly upstream of the radiator. The benefits and dangers of having a drift in between the radiator and the modulator are investigated and a measurement of the LSC enabled reduction of the energy spread of a seeded beam is presented.

MOP096

Enhancing the Harmonic Content of an HGHG Microbunch

281

K.E. Hacker
DELTA, Dortmund, Germany

Funding: BMBF grant 05K10PE1 and DESY
High Gain Harmonic Generation (HGHG) seeding has been demonstrated in the visible and ultraviolet, but it is limited in performance at high harmonics of the seed by the initial uncorrelated energy spread of the electron beam. A recent proposal from SINAP using a chirped electron beam and a canted pole undulator has suggested a new mechanism for cooling the uncorrelated energy spread of the electron beam in order to improve the performance of HGHG seeding at high harmonics. This note reviews the mechanism, the limitation of the concept and extrapolates to some new concepts using analogous mechanisms derived from transverse gradients of the laser properties. The impact of CSR wakes on the vanishingly short microbunches produced by the methods are also investigated.
[1] H. Deng and C. Feng, Phys. Rev. Lett. 111, 084801 (2013)

MOP097

A Concept for Seeding 4-40 nm FEL Radiation at FLASH2

286

K.E. Hacker
DELTA, Dortmund, Germany

Funding: Work supported by BMBF (contract 05K13PE3)
This note describes a scheme to seed the FLASH2 FEL over a range of 4-40 nm without impacting SASE capabilities. This scheme combines multiple seeding techniques, builds on current infrastructure and offers a maximized range of performance with higher pulse energies than what are available at lower-peak current facilities. The concept relies on Echo Enabled Harmonic Generation (EEHG), cascaded seeding, and Second Harmonic Afterburners (SHAB) while maintaining the possibility to operate with High Gain Harmonic Generation (HGHG) seeding at >30 nm wavelengths.

THP076

Measurements of the Timing Stability at the FLASH1 Seeding Experiment

913

C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach, M. Wieland
Uni HH, Hamburg, Germany
S. Ackermann, J. Bödewadt, H. Dachraoui, N. Ekanayake, B. Faatz, M. Felber, K. Honkavaara, T. Laarmann, J.M. Mueller, H. Schlarb, S. Schreiber, S. Schulz
DESY, Hamburg, Germany
G. Angelova Hamberg
Uppsala University, Uppsala, Sweden
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany
P.M. Salen, P. van der Meulen
FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4 and 05K13PE3 and the German Research Foundation programme graduate school 1355.
For seeding of a free-electron laser, the spatial and temporal overlap of the seed laser pulse and the electron bunch in the modulator is critical. To establish the temporal overlap, the time difference between pulses from the seed laser and spontaneous undulator radiation is reduced to a few pico-seconds with a combination of a photomultiplier tube and a streak camera. Finally, for the precise overlap the impact of the seed laser pulses on the electron bunches is observed. In this contribution, we describe the current experimental setup, discuss the techniques applied to establish the temporal overlap and analyze its stability.

Paper	Title	Page
MOP018	Conceptual Study of a Self-seeding Scheme at FLASH2	53
	T. Plath, L.L. Lazzarino Uni HH, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355. We present a conceptual study of a self-seeding installation at the new FEL beamline, FLASH2, at the free-electron laser at DESY, Hamburg. For self-seeding, light from a first set of undulators is filtered by a monochromator and thus acts as a seed for the gain process in the main undulator. This scheme has been tested at LCLS at SLAC with a diamond monochromator for hard X-rays and with a grating monochromator for soft X-rays covering energies between 700 and 1000 eV. For such a design to offer benefits at FLASH2, it must be modified to work with X-rays with wavelength of about 5 nm (248 eV) where the damage threshold of the monochromator in the setup and the divergence at longer wavelengths become an issue. An analysis of the potential performance and limitations of this setup is performed using GENESIS 1.3 and a method developed for the soft X-ray self-seeding experiment at the European XFEL. With a total of 9 undulators in the first stage and 8 undulators after the monochromator, a pulse energy contrast ratio of 4.5 was simulated with an initial peak current of 2.5 kA.

MOP060	Demonstration of SASE Suppression Through a Seeded Microbunching Instability	177
	C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, E. Hass, K. Honkavaara, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov DESY, Hamburg, Germany K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school 1355. Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brilliance electron bunches needed for the operation of free-electron lasers. In this contribution, we demonstrate the application of a laser-induced microbunching instability to selectively suppress the SASE process. A significant decrease of photon pulse energies was observed at the free-electron laser FLASH in coincidence with overlap of 800 nm laser pulses and electron bunches within a modulator located approximately 40 meters upstream of the undulators. We discuss the underlying mechanisms based on longitudinal space charge amplification [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.

MOP083	Start-to-End Simulation for FLASH2 HGHG Option	244
	G. Feng, S. Ackermann, J. Bödewadt, W. Decking, M. Dohlus, Y.A. Kot, T. Limberg, M. Scholz, I. Zagorodnov DESY, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany T. Plath Uni HH, Hamburg, Germany
	The Free-electron laser in Hamburg (FLASH) is the first FEL user facility to have produced extreme ultraviolet (XUV) and soft X-ray photons. In order to increase the beam time delivered to users, a major upgrade of FLASH named FLASH II is in progress. The electron beamline of FLASH2 consists of diagnostic and matching sections, a seeding undulator section and a SASE undulator section. In this paper, results from a start-to-end simulation for a FLASH2 High-Gain Harmonic Generation (HGHG) option are presented. For the beam dynamics simulation, space charge, coherent synchrotron radiation (CSR) and longitudinal cavity wake field effects are taken into account. In order to get electron beam bunches with small correlated and uncorrelated energy spread, RF parameters of the accelerating modules have been optimized as well as the parameters of the bunch compressors. Radiation simulations for the modulator and the radiator have been done with code Genesis 1.3 by using the particle distribution generated from the beam dynamics simulation. The results show that for a single stage HGHG, 33.6 nm wavelength FEL radiation can be seeded at FLASH2 with a 235 nm seeding laser.

MOP089	Overview of FEL Seeding Activities at FLASH
	J. Bödewadt, S. Ackermann, R.W. Aßmann, N. Ekanayake, B. Faatz, G. Feng, I. Hartl, R. Ivanov, T. Laarmann, J.M. Mueller, T. Tanikawa DESY, Hamburg, Germany S. Ackermann, A. Azima, M. Drescher, L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Roßbach Uni HH, Hamburg, Germany K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany
	The free-electron laser facility FLASH at DESY operates since several years in SASE mode, delivering high-intensity FEL pulses in the extreme ultra violet and soft x-ray wavelength range for users. In order to get more control of the characteristics of the FEL pulses external FEL seeding has proven to be a reliable method to do so. At FLASH, an experimental setup to test several different external seeding methods has been installed since 2010. After successful demonstration of direct seeding at 38 nm, the setup is now being commissioned to operate in HGHG and EEHG mode. Furthermore, other studies on laser induced effects on the electron beam dynamics will be performed. Beside the experimental activities, a design for the seeding option for the FLASH2 beamline is currently under investigation. The goal for that is to develop a concept which is compatible with the operation of FLASH1 and which satisfies the high demands of the future user community. In this contribution, we give an overview of the activities on FEL seeding at FLASH.

MOP094	Indirect Measurements of NIR and UV Ultrashort Seed Laser Pulses using a Transverse Deflecting RF-Structure	272
	N. Ekanayake, S. Ackermann DESY, Hamburg, Germany S. Ackermann, C. Lechner, Th. Maltezopoulos, T. Plath Uni HH, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany
	Seeding of free-electron lasers (FELs) using external coherent optical pulses recently became an area of interest as users demand spectrally and temporally coherent FEL radiation which is not achievable in traditional self-amplified spontaneous emission operation mode. Since temporal and spectral properties of the seed laser pulses are directly imprinted on the electron bunch, a proper characterization of these seed pulses is needed. However, the lack of any measurement technique capable of characterizing ultrashort seed laser pulses at the laser-electron interaction region is a primary drawback. In this paper we report indirect measurements of seed laser pulses in an undulator section using a transverse deflecting RF-structure (TDS-LOLA) at the free-electron laser FLASH at DESY. Temporally chirped and unchirped seed pulse length measurements will be compared with second-harmonic generation frequency-resolved optical gating measurements and theoretical simulations. Using this technique we will demonstrate that pulse artifacts such as pre- and post-pulses in the seed pulse in the femtosecond and picosecond timescales can be identified without any temporal ambiguity. Authors acknowledge the support received from FLASH team and many groups at DESY in preparation and commissioning of experiments. We thank our colleagues in the FLASH seeding team for their support.

MOP095	HGHG AND EEHG MICROBUNCHES WITH CSR AND LSC	275
	K.E. Hacker DELTA, Dortmund, Germany
	Funding: Work supported by BMBF (contract 05K13PE3) and DESY Longitudinal space charge (LSC) forces in a drift and coherent synchrotron radiation (CSR) in a chicane are relevant for high gain harmonic generation (HGHG) and echo enabled harmonic generation (EEHG) seeding designs. These factors determine whether or not the modulator can be located significantly upstream of the radiator. The benefits and dangers of having a drift in between the radiator and the modulator are investigated and a measurement of the LSC enabled reduction of the energy spread of a seeded beam is presented.

MOP096	Enhancing the Harmonic Content of an HGHG Microbunch	281
	K.E. Hacker DELTA, Dortmund, Germany
	Funding: BMBF grant 05K10PE1 and DESY High Gain Harmonic Generation (HGHG) seeding has been demonstrated in the visible and ultraviolet, but it is limited in performance at high harmonics of the seed by the initial uncorrelated energy spread of the electron beam. A recent proposal from SINAP using a chirped electron beam and a canted pole undulator has suggested a new mechanism for cooling the uncorrelated energy spread of the electron beam in order to improve the performance of HGHG seeding at high harmonics. This note reviews the mechanism, the limitation of the concept and extrapolates to some new concepts using analogous mechanisms derived from transverse gradients of the laser properties. The impact of CSR wakes on the vanishingly short microbunches produced by the methods are also investigated. [1] H. Deng and C. Feng, Phys. Rev. Lett. 111, 084801 (2013)

MOP097	A Concept for Seeding 4-40 nm FEL Radiation at FLASH2	286
	K.E. Hacker DELTA, Dortmund, Germany
	Funding: Work supported by BMBF (contract 05K13PE3) This note describes a scheme to seed the FLASH2 FEL over a range of 4-40 nm without impacting SASE capabilities. This scheme combines multiple seeding techniques, builds on current infrastructure and offers a maximized range of performance with higher pulse energies than what are available at lower-peak current facilities. The concept relies on Echo Enabled Harmonic Generation (EEHG), cascaded seeding, and Second Harmonic Afterburners (SHAB) while maintaining the possibility to operate with High Gain Harmonic Generation (HGHG) seeding at >30 nm wavelengths.

THP076	Measurements of the Timing Stability at the FLASH1 Seeding Experiment	913
	C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach, M. Wieland Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt, H. Dachraoui, N. Ekanayake, B. Faatz, M. Felber, K. Honkavaara, T. Laarmann, J.M. Mueller, H. Schlarb, S. Schreiber, S. Schulz DESY, Hamburg, Germany G. Angelova Hamberg Uppsala University, Uppsala, Sweden K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany P.M. Salen, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4 and 05K13PE3 and the German Research Foundation programme graduate school 1355. For seeding of a free-electron laser, the spatial and temporal overlap of the seed laser pulse and the electron bunch in the modulator is critical. To establish the temporal overlap, the time difference between pulses from the seed laser and spontaneous undulator radiation is reduced to a few pico-seconds with a combination of a photomultiplier tube and a streak camera. Finally, for the precise overlap the impact of the seed laser pulses on the electron bunches is observed. In this contribution, we describe the current experimental setup, discuss the techniques applied to establish the temporal overlap and analyze its stability.