FEL2014 - List of Authors (Feng, G.)

Paper

Title

Page

SASE Characteristics from Baseline European XFEL Undulators in the Tapering Regime

159

I.V. Agapov, G. Geloni
XFEL. EU, Hamburg, Germany
G. Feng, V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov
DESY, Hamburg, Germany

The output SASE characteristics of the baseline European XFEL, recently used in the TDRs of scientific instruments and X-ray optics, have been previously optimized assuming uniform undulators without considering the potential of undulator tapering in the SASE regime. Here we demonstrate that the performance of European XFEL sources can be significantly improved without additional hardware. The procedure consists in the optimization of the undulator gap configuration for each X-ray beamline. Here we provide a comprehensive description of the X-ray photon beam properties as a function of wavelength and bunch charge. Based on nominal parameters for the electron beam, we demonstrate that undulator tapering allows one to achieve up to a tenfold increase in peak power and photon spectral density in the conventional SASE regime.

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.

Paper	Title	Page
MOP056	SASE Characteristics from Baseline European XFEL Undulators in the Tapering Regime	159
	I.V. Agapov, G. Geloni XFEL. EU, Hamburg, Germany G. Feng, V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov DESY, Hamburg, Germany
	The output SASE characteristics of the baseline European XFEL, recently used in the TDRs of scientific instruments and X-ray optics, have been previously optimized assuming uniform undulators without considering the potential of undulator tapering in the SASE regime. Here we demonstrate that the performance of European XFEL sources can be significantly improved without additional hardware. The procedure consists in the optimization of the undulator gap configuration for each X-ray beamline. Here we provide a comprehensive description of the X-ray photon beam properties as a function of wavelength and bunch charge. Based on nominal parameters for the electron beam, we demonstrate that undulator tapering allows one to achieve up to a tenfold increase in peak power and photon spectral density in the conventional SASE regime.

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.