FEL2012 - List of Authors (Saldin, E.)

Paper

Title

Page

On Quantum Effects in Spontaneous Emission by a Relativistic Electron Beam in an Undulator

29

G. Geloni, V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

Robb and Bonifacio (2011) claimed that a previously neglected quantum effect results in noticeable changes in the evolution of the energy distribution associated with spontaneous emission in long undulators. They revisited theoretical models used to describe the emission of radiation by relativistic electrons, and claimed that in the asymptotic limit for a large number of undulator periods the evolution of the electron energy distribution occurs as discrete energy groups according to Poisson distribution. These novel results are based on a one-dimensional model of spontaneous emission and assume that electrons are sheets of charge. However, electrons are point-like particles and the bandwidth of the angular-integrated spectrum of undulator radiation is independent of the number of undulator periods. The evolution of the energy distribution studied with a three-dimensional theory is consistent with a continuous diffusive process. We also review how quantum diffusion of electron energy in an undulator with small undulator parameter can be analyzed using the Thomson cross-section expression, unlike the conventional treatment based on the expression for the Lienard-Wiechert fields.

Slides MOOC03 [0.980 MB]

MOPD02

Pulse-front Tilt Caused by the Use of a Grating Monochromator and Self-seeding of Soft X-ray FELs

41

G. Geloni, V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

Self-seeding is a promising approach to significantly narrow the SASE bandwidth of XFELs to produce nearly transform-limited pulses. The development of such schemes in the soft X-ray wavelength range necessarily involves gratings as dispersive elements. These introduce, in general, a pulse-front tilt, which is directly proportional to the angular dispersion. Pulse-front tilt may easily lead to a seed signal decrease by a factor two or more. Suggestions on how to minimize the pulse-front tilt effect in the self-seeding setup are given.

TUPD12

Extension of Self-seeding to Hard X-rays > 10 keV as a Way to Increase User Access at the European XFEL

253

G. Geloni
XFEL. EU, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

We propose to use a self-seeding scheme with single crystal monochromator at the European X-ray FEL to produce monochromatic, high-power radiation at 16 keV. The FEL power of the transform-limited pulses can reach about 100 GW by exploiting tapering in the tunable-gap baseline undulator. The combination of high photon energy, high peak power, and very narrow bandwidth opens a new range of applications, and allows to increase the user capacity and exploit the high repetition rate of the European XFEL. Dealing with monochromatic hard X-ray radiation one may use crystals as deflectors with minimum beam loss. To this end, a photon beam distribution system based on the use of crystals in the Bragg reflection geometry is proposed for future study and possible extension of the baseline facility. They can be repeated a number of times to form an almost complete (one meter scale) ring with an angle of 20 degrees between two neighboring lines. The reflectivity of crystal deflectors can be switched fast enough by flipping the crystals with piezo-electric devices. It is then possible to distribute monochromatic hard X-rays among 10 independent instruments.

WEPD09

Scheme for Generating and Transporting THz Radiation to the X-ray Experimental Hall at the European XFEL

389

W. Decking, G. Geloni, V. Kocharyan, E. Saldin, I. Zagorodnov
DESY, Hamburg, Germany

We consider generation of THz radiation from the spent electron beam downstream of the SASE2 undulator in the electron beam dump area. The THz output must propagate at least for 250 meters through the photon beam tunnel to the experimental hall to reach the SASE2 X-ray hutches. We propose to use an open beam waveguide such as an iris guide as transmission line. In order to efficiently couple radiation into the iris transmission line, generation of the THz radiation pulse can be performed directly within the iris guide. The line transporting the THz radiation to the SASE2 X-ray hutches introduces a path delay of about 20 m. Since THz pump/X-ray probe experiments should be enabled, we propose to exploit the European XFEL baseline multi-bunch mode of operation, with 222 ns electron bunch separation, in order to cope with the delay between THz and X-ray pulses. We present start-to-end simulations for 1 nC bunch operation-parameters, optimized for THz pump/X-ray probe experiments. Detailed characterization of the THz and SASE X-ray radiation pulses is performed. Highly focused THz beams will approach the high field limit of 1 V/atomic size.

WEPD10

Conceptual Design of an Undulator System for a Dedicated Bio-imaging Beamline at the European X-ray FEL

393

G. Geloni, V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

We describe a future possible upgrade of the European XFEL consisting in the construction of an undulator beamline dedicated coherent diffraction imaging of complex molecules. Crucial parameters are photon energy range, peak power, and pulse duration. The peak power is maximized in the photon energy range between 3 keV and 12 keV by the use of a very efficient combination of self-seeding, fresh bunch and tapered undulator techniques. The unique combination of ultra-high peak power of 1 TW in the entire energy range, and ultrashort pulse duration tunable from 2 fs to 10 fs, would allow for single shot coherent imaging of protein molecules with size larger than 10 nm. Also, the new beamline would enable ima ing of large biological structures in the water window, between 0.3 and 0.4 keV. In order to make use of standardized components, at present we favor the use of SASE3-type undulator segments. The number segments, 40, is determined by the tapered length for the design output power of 1 TW. The present plan assumes the use of a nominal electron bunch with charge of 0.1 nC. Experiments would be performed without interference with the other three undulator beamlines.

Paper	Title	Page
MOOC03	On Quantum Effects in Spontaneous Emission by a Relativistic Electron Beam in an Undulator	29
	G. Geloni, V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	Robb and Bonifacio (2011) claimed that a previously neglected quantum effect results in noticeable changes in the evolution of the energy distribution associated with spontaneous emission in long undulators. They revisited theoretical models used to describe the emission of radiation by relativistic electrons, and claimed that in the asymptotic limit for a large number of undulator periods the evolution of the electron energy distribution occurs as discrete energy groups according to Poisson distribution. These novel results are based on a one-dimensional model of spontaneous emission and assume that electrons are sheets of charge. However, electrons are point-like particles and the bandwidth of the angular-integrated spectrum of undulator radiation is independent of the number of undulator periods. The evolution of the energy distribution studied with a three-dimensional theory is consistent with a continuous diffusive process. We also review how quantum diffusion of electron energy in an undulator with small undulator parameter can be analyzed using the Thomson cross-section expression, unlike the conventional treatment based on the expression for the Lienard-Wiechert fields.
	Slides MOOC03 [0.980 MB]

MOPD02	Pulse-front Tilt Caused by the Use of a Grating Monochromator and Self-seeding of Soft X-ray FELs	41
	G. Geloni, V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	Self-seeding is a promising approach to significantly narrow the SASE bandwidth of XFELs to produce nearly transform-limited pulses. The development of such schemes in the soft X-ray wavelength range necessarily involves gratings as dispersive elements. These introduce, in general, a pulse-front tilt, which is directly proportional to the angular dispersion. Pulse-front tilt may easily lead to a seed signal decrease by a factor two or more. Suggestions on how to minimize the pulse-front tilt effect in the self-seeding setup are given.

TUPD12	Extension of Self-seeding to Hard X-rays > 10 keV as a Way to Increase User Access at the European XFEL	253
	G. Geloni XFEL. EU, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	We propose to use a self-seeding scheme with single crystal monochromator at the European X-ray FEL to produce monochromatic, high-power radiation at 16 keV. The FEL power of the transform-limited pulses can reach about 100 GW by exploiting tapering in the tunable-gap baseline undulator. The combination of high photon energy, high peak power, and very narrow bandwidth opens a new range of applications, and allows to increase the user capacity and exploit the high repetition rate of the European XFEL. Dealing with monochromatic hard X-ray radiation one may use crystals as deflectors with minimum beam loss. To this end, a photon beam distribution system based on the use of crystals in the Bragg reflection geometry is proposed for future study and possible extension of the baseline facility. They can be repeated a number of times to form an almost complete (one meter scale) ring with an angle of 20 degrees between two neighboring lines. The reflectivity of crystal deflectors can be switched fast enough by flipping the crystals with piezo-electric devices. It is then possible to distribute monochromatic hard X-rays among 10 independent instruments.

WEPD09	Scheme for Generating and Transporting THz Radiation to the X-ray Experimental Hall at the European XFEL	389
	W. Decking, G. Geloni, V. Kocharyan, E. Saldin, I. Zagorodnov DESY, Hamburg, Germany
	We consider generation of THz radiation from the spent electron beam downstream of the SASE2 undulator in the electron beam dump area. The THz output must propagate at least for 250 meters through the photon beam tunnel to the experimental hall to reach the SASE2 X-ray hutches. We propose to use an open beam waveguide such as an iris guide as transmission line. In order to efficiently couple radiation into the iris transmission line, generation of the THz radiation pulse can be performed directly within the iris guide. The line transporting the THz radiation to the SASE2 X-ray hutches introduces a path delay of about 20 m. Since THz pump/X-ray probe experiments should be enabled, we propose to exploit the European XFEL baseline multi-bunch mode of operation, with 222 ns electron bunch separation, in order to cope with the delay between THz and X-ray pulses. We present start-to-end simulations for 1 nC bunch operation-parameters, optimized for THz pump/X-ray probe experiments. Detailed characterization of the THz and SASE X-ray radiation pulses is performed. Highly focused THz beams will approach the high field limit of 1 V/atomic size.

WEPD10	Conceptual Design of an Undulator System for a Dedicated Bio-imaging Beamline at the European X-ray FEL	393
	G. Geloni, V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	We describe a future possible upgrade of the European XFEL consisting in the construction of an undulator beamline dedicated coherent diffraction imaging of complex molecules. Crucial parameters are photon energy range, peak power, and pulse duration. The peak power is maximized in the photon energy range between 3 keV and 12 keV by the use of a very efficient combination of self-seeding, fresh bunch and tapered undulator techniques. The unique combination of ultra-high peak power of 1 TW in the entire energy range, and ultrashort pulse duration tunable from 2 fs to 10 fs, would allow for single shot coherent imaging of protein molecules with size larger than 10 nm. Also, the new beamline would enable ima ing of large biological structures in the water window, between 0.3 and 0.4 keV. In order to make use of standardized components, at present we favor the use of SASE3-type undulator segments. The number segments, 40, is determined by the tapered length for the design output power of 1 TW. The present plan assumes the use of a nominal electron bunch with charge of 0.1 nC. Experiments would be performed without interference with the other three undulator beamlines.