FEL2011 - Table of Session: TUOA (FEL Theory)

Paper

Title

Page

Hard X-ray Self-seeding for XFELs: Towards Coherent FEL Pulses

148

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

Start-up from shot noise limits the longitudinal coherence of typical SASE XFEL pulses. Self-seeding schemes provide an elegant solution to this problem. However, their applicability to the baseline of already working or designed XFELs is subject to constraints, including minimal changes to the baseline design and possibility to recover the baseline mode of operation. Here we discuss a recently proposed single-bunch self-seeding scheme for hard X-rays. The physical principles of this scheme can be extended to soft X-rays as well. The method is based on a particular kind of monochromator, which relies on the use of a single crystal in Bragg-transmission geometry. In its simplest configuration, the setup consists of an input undulator and an output undulator separated by such monochromator. Several, more advanced configurations can be considered. For example, for high repetition rates of the X-ray pulses, or when a high spectral purity of the output radiation is requested, the simplest two-undulator configuration is not optimal: three or more undulators separated by monochromators can then be used. Exemplifications, based on facilities working or under construction will be discussed.

Slides TUOAI1 [2.818 MB]

TUOA2

Collective and Individual Aspects of Fluctuations in Relativistic Electron Beams for Free Electron Lasers

156

K.-J. Kim, R.R. Lindberg
ANL, Argonne, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Fluctuations in highly bright, relativistic electron beam for free electron lasers (FELs) exhibit both collective as well as individual particle aspects[1]. If the collective part characterized by plasma oscillation dominate, then it might be feasible to suppress the shot noise[2]. To study these issues, we solve the 1-D coupled Poisson-Klimontovich equations by the Laplace transform technique. We find the density fluctuations to be a linear combination of the collective plasma oscillation and the random motion of Debye-screened dressed particles[3]. The relative magnitude ξ of the random to the collective part can be computed explicitly. For the LCLS case, we find that ξ is about unity for electron beams just prior to the λ = 1.5 Å FEL, and about 1% for the beam at 135 MeV at λ = 1 μm. The “position noise” (bunching factor) could be reduced to about ξ by a quarter of plasma oscillation. However, this leads to an increase in the “momentum noise”, which contributes significantly to the growth of the self-amplified spontaneous emission.
[1] D. Pines, D. Bohm, Phys. Rev.,85,338 (1952)
[2] A. Gover, E. Dyunin, Phys. Rev.Letters, 102,154801 (2009)
[3] S. Ichimaru, Basic Principles of Plasma Physics, The Benjamin/Cummins Pub. Co. (1973)

Slides TUOA2 [0.361 MB]

TUOA3

Three-dimensional Kinetic Theory of Longitudinal Space-charge Interactions in a Thermal Relativistic Electron Beam

A. Marinelli, E. Hemsing, J.B. Rosenzweig
UCLA, Los Angeles, California, USA

We develop an analytical model of space-charge interactions leading to longitudinal plasma oscillations and space-charge induced microbunching amplification. Our theory is based on a modal description of space-charge waves which includes energy spread, emittance, betatron motion and geometrical effects due to the finite size of the beam. In analogy with the three-dimensional theory of free-electron lasers, we derive a dispersion relation for the space-charge oscillation modes that can be expressed in terms of four dimensionless parameters. We find approximate variational solutions as well as numerical solutions with a discretization method. Finally we we apply this model to the optimization of a longitudinal space-charge amplification experiment.

Slides TUOA3 [3.254 MB]

TUOA4

Toward TW-level, Hard X-ray Pulses at LCLS

160

W.M. Fawley, J.C. Frisch, Z. Huang, Y. Jiao, H.-D. Nuhn, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA
S. Reiche
Paul Scherrer Institut, Villigen, Switzerland

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
Coherent diffraction imaging of complex molecules, like proteins, requires a large number of hard X-ray photons, ~10⁺¹³/pulse, within a time ~10 fs or less. This is equivalent to a peak power of about one TW, much larger than that currently generated by LCLS or other proposed X-ray FELs. We study the feasibility of producing such pulses from LCLS and the proposed LCLS-II, employing a configuration beginning with a SASE amplifier, followed by a "self-seeding" crystal monochromator [1], and finishing with a long tapered undulator. Results suggest that TW-level output power at 8 keV is possible, with a total undulator length below 200 m. We use a 40 pC electron bunch charge, normalized transverse emittance of 0.2-mm-mrad, peak current of 4 kA, and electron energy about 14 GeV. We present a tapering strategy that extends the original "resonant particle" formalism by optimizing the transport lattice to maximize optical guiding and enhance net energy extraction. We also discuss the transverse and longitudinal coherence properties of the output radiation pulse. Fluctuation of such a tapered FEL is studied with realistic jitter measured at LCLS and with start-to-end simulation.

Slides TUOA4 [9.357 MB]

Paper	Title	Page
TUOAI1	Hard X-ray Self-seeding for XFELs: Towards Coherent FEL Pulses	148
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	Start-up from shot noise limits the longitudinal coherence of typical SASE XFEL pulses. Self-seeding schemes provide an elegant solution to this problem. However, their applicability to the baseline of already working or designed XFELs is subject to constraints, including minimal changes to the baseline design and possibility to recover the baseline mode of operation. Here we discuss a recently proposed single-bunch self-seeding scheme for hard X-rays. The physical principles of this scheme can be extended to soft X-rays as well. The method is based on a particular kind of monochromator, which relies on the use of a single crystal in Bragg-transmission geometry. In its simplest configuration, the setup consists of an input undulator and an output undulator separated by such monochromator. Several, more advanced configurations can be considered. For example, for high repetition rates of the X-ray pulses, or when a high spectral purity of the output radiation is requested, the simplest two-undulator configuration is not optimal: three or more undulators separated by monochromators can then be used. Exemplifications, based on facilities working or under construction will be discussed.
	Slides TUOAI1 [2.818 MB]

TUOA2	Collective and Individual Aspects of Fluctuations in Relativistic Electron Beams for Free Electron Lasers	156
	K.-J. Kim, R.R. Lindberg ANL, Argonne, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Fluctuations in highly bright, relativistic electron beam for free electron lasers (FELs) exhibit both collective as well as individual particle aspects[1]. If the collective part characterized by plasma oscillation dominate, then it might be feasible to suppress the shot noise[2]. To study these issues, we solve the 1-D coupled Poisson-Klimontovich equations by the Laplace transform technique. We find the density fluctuations to be a linear combination of the collective plasma oscillation and the random motion of Debye-screened dressed particles[3]. The relative magnitude ξ of the random to the collective part can be computed explicitly. For the LCLS case, we find that ξ is about unity for electron beams just prior to the λ = 1.5 Å FEL, and about 1% for the beam at 135 MeV at λ = 1 μm. The “position noise” (bunching factor) could be reduced to about ξ by a quarter of plasma oscillation. However, this leads to an increase in the “momentum noise”, which contributes significantly to the growth of the self-amplified spontaneous emission. [1] D. Pines, D. Bohm, Phys. Rev.,85,338 (1952) [2] A. Gover, E. Dyunin, Phys. Rev.Letters, 102,154801 (2009) [3] S. Ichimaru, Basic Principles of Plasma Physics, The Benjamin/Cummins Pub. Co. (1973)
	Slides TUOA2 [0.361 MB]

TUOA3	Three-dimensional Kinetic Theory of Longitudinal Space-charge Interactions in a Thermal Relativistic Electron Beam
	A. Marinelli, E. Hemsing, J.B. Rosenzweig UCLA, Los Angeles, California, USA
	We develop an analytical model of space-charge interactions leading to longitudinal plasma oscillations and space-charge induced microbunching amplification. Our theory is based on a modal description of space-charge waves which includes energy spread, emittance, betatron motion and geometrical effects due to the finite size of the beam. In analogy with the three-dimensional theory of free-electron lasers, we derive a dispersion relation for the space-charge oscillation modes that can be expressed in terms of four dimensionless parameters. We find approximate variational solutions as well as numerical solutions with a discretization method. Finally we we apply this model to the optimization of a longitudinal space-charge amplification experiment.
	Slides TUOA3 [3.254 MB]

TUOA4	Toward TW-level, Hard X-ray Pulses at LCLS	160
	W.M. Fawley, J.C. Frisch, Z. Huang, Y. Jiao, H.-D. Nuhn, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA S. Reiche Paul Scherrer Institut, Villigen, Switzerland
	Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. Coherent diffraction imaging of complex molecules, like proteins, requires a large number of hard X-ray photons, ~10⁺¹³/pulse, within a time ~10 fs or less. This is equivalent to a peak power of about one TW, much larger than that currently generated by LCLS or other proposed X-ray FELs. We study the feasibility of producing such pulses from LCLS and the proposed LCLS-II, employing a configuration beginning with a SASE amplifier, followed by a "self-seeding" crystal monochromator [1], and finishing with a long tapered undulator. Results suggest that TW-level output power at 8 keV is possible, with a total undulator length below 200 m. We use a 40 pC electron bunch charge, normalized transverse emittance of 0.2-mm-mrad, peak current of 4 kA, and electron energy about 14 GeV. We present a tapering strategy that extends the original "resonant particle" formalism by optimizing the transport lattice to maximize optical guiding and enhance net energy extraction. We also discuss the transverse and longitudinal coherence properties of the output radiation pulse. Fluctuation of such a tapered FEL is studied with realistic jitter measured at LCLS and with start-to-end simulation.
	Slides TUOA4 [9.357 MB]