FEL2012 - List of Authors (Rossbach, J.)

Paper

Title

Page

First Direct Seeding at 38nm

197

C. Lechner, A. Azima, J. Bödewadt, M. Drescher, E. Hass, U. Hipp, Th. Maltezopoulos, V. Miltchev, M. Rehders, J. Rönsch-Schulenburg, J. Roßbach, R. Tarkeshian, M. Wieland
Uni HH, Hamburg, Germany
S. Ackermann, S. Bajt, H. Dachraoui, H. Delsim-Hashemi, S. Düsterer, B. Faatz, K. Honkavaara, T. Laarmann, M. Mittenzwey, H. Schlarb, S. Schreiber, L. Schroedter, M. Tischer
DESY, Hamburg, Germany
F. Curbis
MAX-lab, Lund, Sweden
R. Ischebeck
PSI, Villigen PSI, Switzerland
S. Khan
DELTA, Dortmund, Germany
V. Wacker
University of Hamburg, Hamburg, Germany

Funding: The project is supported by the Federal Ministry of Education and Research of Germany under contract No. 05 K10GU1 and by the German Research Foundation programme graduate school 1355.
The sFLASH project at DESY is an experiment to study direct seeding using a source based on the high-harmonic generation (HHG) process. In contrast to SASE, a seeded FEL exhibits greatly improved longitudinal coherence and higher shot-to-shot stability (both spectral and energetic). In addition, the output of the seeded FEL is intrinsically synchronized to the HHG drive laser, thus enabling pump-probe experiments with a resolution of the order of 10 fs. The installation and successful commissioning of the sFLASH components in 2010/2011 has been followed by a planned upgrade in autumn 2011. As a result of these improvements, in spring 2012 direct HHG seeding at 38 nm has been successfully demonstrated. In this contribution, we describe the experimental layout and announce the first seeding at 38 nm.

Slides TUOAI01 [11.553 MB]

TUPD11

Optimization of HHG Seeding at Flash II

249

S. Ackermann, B. Faatz
DESY, Hamburg, Germany
V. Miltchev, J. Roßbach
Uni HH, Hamburg, Germany

FLASH* delivers coherent FEL radiation suitable for a variety of scientific purposes. In order to provide more beam time to the photon experiments, the FLASH II project, consisting of a second undulator branch and a new experimental Hall driven by the same superconducting modules as FLASH today has been started in 2008. While in the present undulator the kinetic energy of the electrons has to be changed in order to change the wavelength, the new beamline will benefit from variable gap undulators which will allow to have largely independent radiation wavelength; in the range of 10 to 40 nm an HHG seeding option is foreseen which will improve radiation quality for users beyond SASE. For experiments it is important to have the source point of the FEL radiation at the same position, close to the end of the undulator. However, one would like to keep the HHG focus at a fixed longitudinal position, such that wavelength changes will not require adjustments of the HHG focus. In this contribution, we will present the optimization of these conflicting requirements by opening undulator gaps at wavelength dependent positions, keeping both the seeding point and the source point for users fixed.
* The Free-Electron Laser in Hamburg

WEPD07

Status of the FLASH II Project

381

K. Honkavaara, S. Ackermann, V. Ayvazyan, N. Baboi, V. Balandin, W. Decking, S. Düsterer, H.-J. Eckoldt, B. Faatz, M. Felber, J. Feldhaus, N. Golubeva, M. Körfer, M. Kuhlmann, T. Laarmann, A. Leuschner, L. Lilje, T. Limberg, N. Mildner, D. Nölle, F. Obier, A. Petrov, E. Plönjes, K. Rehlich, H. Remde, H. Schlarb, B. Schmidt, M. Schmitz, M. Scholz, S. Schreiber, H. Schulte-Schrepping, J. Spengler, M. Staack, N. Stojanovic, K.I. Tiedtke, M. Tischer, R. Treusch, M. Vogt, H.C. Weddig, T. Wohlenberg
DESY, Hamburg, Germany
M. Drescher, A. Hage, V. Miltchev, R. Riedel, J. Rönsch-Schulenburg, J. Roßbach, M. Schulz, A. Willner
Uni HH, Hamburg, Germany
F. Tavella
HIJ, Jena, Germany

The extension of the FLASH facility at DESY (Hamburg, Germany) - FLASH II Project - is under way. The extension includes a second undulator line with variable gap undulators to allow a more flexible operation, and a new experimental hall for photon experiments. The present FLASH linac will drive the both undulator beamlines. Civil construction of the new buildings has been started in autumn 2011 continuing in several steps until early 2013. The design of the new beamline including the extraction from the FLASH linac and the undulator is mostly finished, and the manufacturing of the components is under way. The mounting of the beamline will start in autumn 2012, and the commissioning with beam is scheduled for second half of 2013. We report here the design of the different phases of the project including the time schedule up to the first user operation.

WEPD28

Electron Optics and Magnetic Chicane for Matching an XFEL-Oscillator Cavity into a Beamline at the European XFEL Laboratory

425

C.P. Maag
DESY, Hamburg, Germany
J. Roßbach, J. Zemella
Uni HH, Hamburg, Germany

At DESY the European XFEL (X-Ray Free-Electron Laser) laboratory is currently under construction. Due to the time structure of its electron bunch trains it is in principle possible to run a FELO (Free-Electron Laser Oscillator) at the European XFEL. The major elements of a FELO are the cavity and the undulator. To couple the electron beam with the required beta functions into the cavity, a magnetic chicane and an appropriate focusing structure are considered. In this paper we discuss the lattice design of the magnetic chicane and the focusing section. We also present the results of the beam dynamics simulations performed.

WEPD29

Numerical Simulations of an XFELO for the European XFEL driven by a Spent Beam

429

J. Zemella, C.P. Maag, J. Roßbach
Uni HH, Hamburg, Germany
H. Sinn
XFEL. EU, Hamburg, Germany
M. Tolkiehn
DESY, Hamburg, Germany

The European XFEL will be an X-ray free electron laser laboratory at DESY in Hamburg Germany. In the baseline design the light pulses will be generated in long undulators via the SASE process. The wavelengths of the light pulses will be between 5 nm and 0.05 nm. Since SASE pulses have a poor longitudinal coherence a lot of research is ongoing to overcome the statistical fluctuations of the SASE pulses. Some years ago Kim et al. proposed an FEL oscillator for light sources based on energy-recovery linacs (ERL), using Diamond Bragg crystals to perform a high reflective cavity in the X-ray regime (XFELO). Since the European XFEL will be based on superconducting accelerator structures it will deliver a long train of electron bunches which might be suitable to support an XFELO arrangement as well. In particular, the spent beam at the exit of a SASE FEL might be still qualified to drive an XFELO. Theoretical simulations of an oscillator based on Diamond crystals for the European XFEL will be presented using electron bunches of a spent beam.

THPD33

Generation of Ultra-short Electron Bunches at FLASH

610

J. Rönsch-Schulenburg, E. Hass, A. Kuhl, T. Plath, M. Rehders, J. Roßbach
Uni HH, Hamburg, Germany
A. Angelovski, R. Jakoby, A. Penirschke
TU Darmstadt, Darmstadt, Germany
N. Baboi, M. Bousonville, M.K. Czwalinna, C. Gerth, K. Klose, T. Limberg, U. Mavrič, H. Schlarb, B. Schmidt, S. Schreiber, B. Steffen, C. Sydlo, S. Vilcins, S. Wesch
DESY, Hamburg, Germany
S. Schnepp, T. Weiland
TEMF, TU Darmstadt, Darmstadt, Germany

Funding: The work is supported by German Federal Ministry of Education and Research (BMBF) within Joint Project - FSP 301 under the contract number 05K10GU2.
In order to produce radiation pulses of a few femtoseconds at FELs like FLASH, different concepts have been proposed. Probably the most robust method is to create an electron bunch, which is in the most extreme case as short as one longitudinal optical mode. For FLASH this translates into a bunch length of a few micrometers only. In order to mitigate space charge effects, the bunch charge needs to be about 20 pC. The technical requirements to achieve this goal are discussed. This includes beam dynamics studies to optimize the injection and compression of small charge electron bunches. A reduced photo injector laser pulse duration helps to relax the RF tolerance which scales linear with the compression factor. A new photo injector laser with sub-picosecond pulse duration in combination with a stretcher is used to optimize the initial bunch length. The commissioning of the new laser system and first experiments are described. Limitations of the presently available electron beam diagnostics at FLASH for short, low charge bunches are analyzed. Improvements of the longitudinal phase space diagnostics and the commissioning of a more sensitive beam arrival time monitor are described.

THPD37

Beam Dynamic Studies for the Generation of Short SASE Pulses at FLASH

614

M. Rehders, J. Roßbach
Uni HH, Hamburg, Germany
J. Rönsch-Schulenburg
CFEL, Hamburg, Germany
H. Schlarb, S. Schreiber
DESY, Hamburg, Germany

Funding: The project is supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301.
Many users at FLASH work on pump-probe experiments, where time resolution is determined by the duration of the SASE pulses. Therefore users have expressed the strong wish for shorter XUV pulses. The shortest possible pulse is a single longitudinal optical mode of the SASE radiation. The most direct way to realize this at FLASH would be to reduce the electron bunch length to only a few μm at the entrance of the undulator section. In the ideal case a bunch charge of 20pC is sufficient for the generation of such short bunches. A shorter bunch duration directly at the photo-cathode helps to overcome technical limitations of the bunch compression due to RF induced non-linearities and collective effects. Beam dynamic studies are being performed to optimize the parameters of the photo injector laser, of the accelerating modules, and of the bunch compression. This includes particle tracking starting from the cathode though the accelerating modules with the ASTRA code and through the dipole chicanes using CSRtrack. A comparison of the beam dynamics simulations with measurements is presented in this contribution. The expected SASE pulses are being simulated with the Genesis code.

Paper	Title	Page
TUOAI01	First Direct Seeding at 38nm	197
	C. Lechner, A. Azima, J. Bödewadt, M. Drescher, E. Hass, U. Hipp, Th. Maltezopoulos, V. Miltchev, M. Rehders, J. Rönsch-Schulenburg, J. Roßbach, R. Tarkeshian, M. Wieland Uni HH, Hamburg, Germany S. Ackermann, S. Bajt, H. Dachraoui, H. Delsim-Hashemi, S. Düsterer, B. Faatz, K. Honkavaara, T. Laarmann, M. Mittenzwey, H. Schlarb, S. Schreiber, L. Schroedter, M. Tischer DESY, Hamburg, Germany F. Curbis MAX-lab, Lund, Sweden R. Ischebeck PSI, Villigen PSI, Switzerland S. Khan DELTA, Dortmund, Germany V. Wacker University of Hamburg, Hamburg, Germany
	Funding: The project is supported by the Federal Ministry of Education and Research of Germany under contract No. 05 K10GU1 and by the German Research Foundation programme graduate school 1355. The sFLASH project at DESY is an experiment to study direct seeding using a source based on the high-harmonic generation (HHG) process. In contrast to SASE, a seeded FEL exhibits greatly improved longitudinal coherence and higher shot-to-shot stability (both spectral and energetic). In addition, the output of the seeded FEL is intrinsically synchronized to the HHG drive laser, thus enabling pump-probe experiments with a resolution of the order of 10 fs. The installation and successful commissioning of the sFLASH components in 2010/2011 has been followed by a planned upgrade in autumn 2011. As a result of these improvements, in spring 2012 direct HHG seeding at 38 nm has been successfully demonstrated. In this contribution, we describe the experimental layout and announce the first seeding at 38 nm.
	Slides TUOAI01 [11.553 MB]

TUPD11	Optimization of HHG Seeding at Flash II	249
	S. Ackermann, B. Faatz DESY, Hamburg, Germany V. Miltchev, J. Roßbach Uni HH, Hamburg, Germany
	FLASH* delivers coherent FEL radiation suitable for a variety of scientific purposes. In order to provide more beam time to the photon experiments, the FLASH II project, consisting of a second undulator branch and a new experimental Hall driven by the same superconducting modules as FLASH today has been started in 2008. While in the present undulator the kinetic energy of the electrons has to be changed in order to change the wavelength, the new beamline will benefit from variable gap undulators which will allow to have largely independent radiation wavelength; in the range of 10 to 40 nm an HHG seeding option is foreseen which will improve radiation quality for users beyond SASE. For experiments it is important to have the source point of the FEL radiation at the same position, close to the end of the undulator. However, one would like to keep the HHG focus at a fixed longitudinal position, such that wavelength changes will not require adjustments of the HHG focus. In this contribution, we will present the optimization of these conflicting requirements by opening undulator gaps at wavelength dependent positions, keeping both the seeding point and the source point for users fixed. * The Free-Electron Laser in Hamburg

WEPD07	Status of the FLASH II Project	381
	K. Honkavaara, S. Ackermann, V. Ayvazyan, N. Baboi, V. Balandin, W. Decking, S. Düsterer, H.-J. Eckoldt, B. Faatz, M. Felber, J. Feldhaus, N. Golubeva, M. Körfer, M. Kuhlmann, T. Laarmann, A. Leuschner, L. Lilje, T. Limberg, N. Mildner, D. Nölle, F. Obier, A. Petrov, E. Plönjes, K. Rehlich, H. Remde, H. Schlarb, B. Schmidt, M. Schmitz, M. Scholz, S. Schreiber, H. Schulte-Schrepping, J. Spengler, M. Staack, N. Stojanovic, K.I. Tiedtke, M. Tischer, R. Treusch, M. Vogt, H.C. Weddig, T. Wohlenberg DESY, Hamburg, Germany M. Drescher, A. Hage, V. Miltchev, R. Riedel, J. Rönsch-Schulenburg, J. Roßbach, M. Schulz, A. Willner Uni HH, Hamburg, Germany F. Tavella HIJ, Jena, Germany
	The extension of the FLASH facility at DESY (Hamburg, Germany) - FLASH II Project - is under way. The extension includes a second undulator line with variable gap undulators to allow a more flexible operation, and a new experimental hall for photon experiments. The present FLASH linac will drive the both undulator beamlines. Civil construction of the new buildings has been started in autumn 2011 continuing in several steps until early 2013. The design of the new beamline including the extraction from the FLASH linac and the undulator is mostly finished, and the manufacturing of the components is under way. The mounting of the beamline will start in autumn 2012, and the commissioning with beam is scheduled for second half of 2013. We report here the design of the different phases of the project including the time schedule up to the first user operation.

WEPD28	Electron Optics and Magnetic Chicane for Matching an XFEL-Oscillator Cavity into a Beamline at the European XFEL Laboratory	425
	C.P. Maag DESY, Hamburg, Germany J. Roßbach, J. Zemella Uni HH, Hamburg, Germany
	At DESY the European XFEL (X-Ray Free-Electron Laser) laboratory is currently under construction. Due to the time structure of its electron bunch trains it is in principle possible to run a FELO (Free-Electron Laser Oscillator) at the European XFEL. The major elements of a FELO are the cavity and the undulator. To couple the electron beam with the required beta functions into the cavity, a magnetic chicane and an appropriate focusing structure are considered. In this paper we discuss the lattice design of the magnetic chicane and the focusing section. We also present the results of the beam dynamics simulations performed.

WEPD29	Numerical Simulations of an XFELO for the European XFEL driven by a Spent Beam	429
	J. Zemella, C.P. Maag, J. Roßbach Uni HH, Hamburg, Germany H. Sinn XFEL. EU, Hamburg, Germany M. Tolkiehn DESY, Hamburg, Germany
	The European XFEL will be an X-ray free electron laser laboratory at DESY in Hamburg Germany. In the baseline design the light pulses will be generated in long undulators via the SASE process. The wavelengths of the light pulses will be between 5 nm and 0.05 nm. Since SASE pulses have a poor longitudinal coherence a lot of research is ongoing to overcome the statistical fluctuations of the SASE pulses. Some years ago Kim et al. proposed an FEL oscillator for light sources based on energy-recovery linacs (ERL), using Diamond Bragg crystals to perform a high reflective cavity in the X-ray regime (XFELO). Since the European XFEL will be based on superconducting accelerator structures it will deliver a long train of electron bunches which might be suitable to support an XFELO arrangement as well. In particular, the spent beam at the exit of a SASE FEL might be still qualified to drive an XFELO. Theoretical simulations of an oscillator based on Diamond crystals for the European XFEL will be presented using electron bunches of a spent beam.

THPD33	Generation of Ultra-short Electron Bunches at FLASH	610
	J. Rönsch-Schulenburg, E. Hass, A. Kuhl, T. Plath, M. Rehders, J. Roßbach Uni HH, Hamburg, Germany A. Angelovski, R. Jakoby, A. Penirschke TU Darmstadt, Darmstadt, Germany N. Baboi, M. Bousonville, M.K. Czwalinna, C. Gerth, K. Klose, T. Limberg, U. Mavrič, H. Schlarb, B. Schmidt, S. Schreiber, B. Steffen, C. Sydlo, S. Vilcins, S. Wesch DESY, Hamburg, Germany S. Schnepp, T. Weiland TEMF, TU Darmstadt, Darmstadt, Germany
	Funding: The work is supported by German Federal Ministry of Education and Research (BMBF) within Joint Project - FSP 301 under the contract number 05K10GU2. In order to produce radiation pulses of a few femtoseconds at FELs like FLASH, different concepts have been proposed. Probably the most robust method is to create an electron bunch, which is in the most extreme case as short as one longitudinal optical mode. For FLASH this translates into a bunch length of a few micrometers only. In order to mitigate space charge effects, the bunch charge needs to be about 20 pC. The technical requirements to achieve this goal are discussed. This includes beam dynamics studies to optimize the injection and compression of small charge electron bunches. A reduced photo injector laser pulse duration helps to relax the RF tolerance which scales linear with the compression factor. A new photo injector laser with sub-picosecond pulse duration in combination with a stretcher is used to optimize the initial bunch length. The commissioning of the new laser system and first experiments are described. Limitations of the presently available electron beam diagnostics at FLASH for short, low charge bunches are analyzed. Improvements of the longitudinal phase space diagnostics and the commissioning of a more sensitive beam arrival time monitor are described.

THPD37	Beam Dynamic Studies for the Generation of Short SASE Pulses at FLASH	614
	M. Rehders, J. Roßbach Uni HH, Hamburg, Germany J. Rönsch-Schulenburg CFEL, Hamburg, Germany H. Schlarb, S. Schreiber DESY, Hamburg, Germany
	Funding: The project is supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301. Many users at FLASH work on pump-probe experiments, where time resolution is determined by the duration of the SASE pulses. Therefore users have expressed the strong wish for shorter XUV pulses. The shortest possible pulse is a single longitudinal optical mode of the SASE radiation. The most direct way to realize this at FLASH would be to reduce the electron bunch length to only a few μm at the entrance of the undulator section. In the ideal case a bunch charge of 20pC is sufficient for the generation of such short bunches. A shorter bunch duration directly at the photo-cathode helps to overcome technical limitations of the bunch compression due to RF induced non-linearities and collective effects. Beam dynamic studies are being performed to optimize the parameters of the photo injector laser, of the accelerating modules, and of the bunch compression. This includes particle tracking starting from the cathode though the accelerating modules with the ASTRA code and through the dipole chicanes using CSRtrack. A comparison of the beam dynamics simulations with measurements is presented in this contribution. The expected SASE pulses are being simulated with the Genesis code.