FEL2011 - List of Authors (Huang, Z.)

Paper

Title

Page

Studies for Polarization Control at LCLS

31

E. Allaria, Y.T. Ding, P. Emma, Z. Huang, H.-D. Nuhn, M. Rowen, J.J. Welch, J. Wu
SLAC, Menlo Park, California, USA

In order to improve the capabilities of LCLS to meet more of the user requirements it has been proposed to implement a method to produce circularly polarized coherent radiation in the LCLS free electron laser. In this work we will present the results of a new set of studies and simulations that have been done for adding polarization control to LCLS using circularly polarizing undulators. Attention has been focused mainly on the use of variable gap APPLE-II undulators to be used at the end of a long SASE radiator that is based on the standard planar LCLS undulators. Issues like polarization contamination from the planar polarized light, polarization fluctuation and the choice of undulator configuration have been studied.

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]

WEOA2

SASE FEL Pulse Duration Analysis from Spectral Correlation Function

318

A.A. Lutman, Y.T. Ding, Y. Feng, Z. Huang, J. Krzywinski, M. Messerschmidt, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
A new method to measure the X-rays pulse duration through the analysis of the statistical properties of the SASE FEL spectra has been developed. The information on the pulse duration is contained in the correlation function of the intensity spectra measured after a spectrometer. The spectral correlation function is derived analytically for different profile shapes in the exponential growth regime and issues like spectral central frequency jitter and shot by shot statistical gain are addressed. Numerical simulations will show that the method is applicable also in saturation regime and that both pulse duration and spectrometer resolution can be recovered from the spectral correlation function. The method has been experimentally demonstrated at LCLS, measuring the soft X-rays pulse durations for different electron bunch lengths, and the evolution of the pulse durations for different undulator distances. Shorter pulse durations down to 13 fs FWHM have been measured using the slotted foil.

Slides WEOA2 [0.758 MB]

WEPA06

Experimental Studies with Spatial Gaussian-cut Laser for the LCLS Photocathode Gun

341

F. Zhou, A. Brachmann, P. Emma, A. Gilevich, Z. Huang
SLAC, Menlo Park, California, USA

Funding: U.S. Department of Energy under contract DE-AC02-76SF00515
To further enhance the LCLS injector performances or simplify its operating conditions, we are evaluating the various parameters including the photocathode drive laser. Simulations show that both the projected and time-sliced emittances with spatial Gaussian profiles having reasonable tail-cutoff are better than those with uniform one. The simulated results are also supported by theoretical analyses. In the LCLS, the spatial uniform or quasi-Gaussian laser profiles are conveniently obtained by adjusting the optics of telescope upstream of an iris, used to define laser size on the cathode. Preliminary beam studies at the LCLS show that both the projected and time-sliced emittances with spatial quasi-Gaussian laser are almost as good as, although not better than, those with uniform one, and also laser transmission through the iris with the quasi-Gaussian is twice that with uniform one, which is to ease copper cathode operations and thus improve the LCLS operation efficiency. More beam studies are planned in the coming summer to measure FEL performances with the quasi-Gaussian in comparison with the uniform one. All simulations and measurements are presented.

WEPB14

Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflector

405

C. Behrens
DESY, Hamburg, Germany
Y.T. Ding, P. Emma, J.C. Frisch, Z. Huang, P. Krejcik, H. Loos, M.-H. Wang
SLAC, Menlo Park, California, USA

The measurement of ultra-short electron bunches on the femtosecond time scale constitutes a very challenging problem. In X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of sub-ten femtosecond X-ray pulses is possible, and some efforts have been put into both ultra-short electron and X-ray beam diagnostics. Here we propose a single-shot method using a transverse deflector (X-band) after the undulator to reconstruct both the electron bunch and X-ray temporal profiles. Simulation studies show that about 1 fs (rms) time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and pulse lengths. The jitter, resolution and other related issues will be discussed.

WEPB15

Reversible Electron Beam Heater for Suppression of Microbunching Instabilities Based on Transverse Deflecting Cavities

409

C. Behrens
DESY, Hamburg, Germany
Z. Huang, D. Xiang
SLAC, Menlo Park, California, USA

The presence of the microbunching instability due to the compression of high-brightness electron beams at existing and future X-ray free-electron lasers (FEL) results in restrictions on the attainable lasing performance and renders diagnostics like beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e. heating the beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of seeded FELs. In this paper, we present a reversible electron beam heating system based on two transverse deflecting cavities (TCAV) in front and behind a bunch compressor chicane. The additional energy spread will be introduced in the first TCAV, which suppresses the microbunching instability, and then will be eliminated in the second TCAV. We show the feasibility of the suppression of microbunching instabilities based on calculations and simulations, and set limits to the acceptable jitter tolerances.

WEPB22

An Optical Streaking Method for Measuring Femtosecond Electron Bunches

431

Y.T. Ding, K.L.F. Bane, Z. Huang
SLAC, Menlo Park, California, USA

The measurement of the ultra-short electron bunch on the femotosecond time scale constitutes a very challenging problem. In the X-ray free electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of a sub-ten femtoseconds electron beam at low charge operation mode is possible, based on indirect measurements and computer simulations. Direct measurements are not available due to the resolution limit of the present diagnostics. We propose a new method based on the energy modulation of the ultra-short electron bunch by interacting with an optical laser in a short wiggler. Compared with a laser-based transverse deflector, which requires the laser wavelength much longer than the electron bunch length, here we propose a scheme to use a laser with its wavelength shorter than the electron bunch length, where the slope on the laser intensity envelope has been used to help distinguish the different periods. The calibration is simple and it is possible to reconstruct the bunch longitudinal profile from a single shot measurement.

THOB5

FEL Spectral Measurements at LCLS

461

J.J. Welch, F.-J. Decker, Y.T. Ding, P. Emma, A.S. Fisher, J.C. Frisch, Z. Huang, R.H. Iverson, H. Loos, M. Messerschmidt, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515.
Control and knowledge of the spectrum of FEL X-ray radiation at the LCLS is important to the quality and interpretation of experimental results. Narrow bandwidth is useful in experiments requiring high-brightness beams. Wide bandwidth is particularly useful for photon energy calibration using absorption spectra. Since LCLS was commissioned in 2009 measurements have been made of average and single shot spectra of X-ray FEL radiation at the LCLS over a range of 800 to 8000 eV, for fundamental and harmonic radiation. These include correlations with chirp, bunch current, undulator K-taper, electron beam energy, and charge as well as some specialized machine configurations. In this paper we present results and discuss the relationship of the electron beam energy distribution to the observed X-ray spectrum.

Slides THOB5 [0.442 MB]

THOC4

Transverse Size and Distribution of FEL X-ray Radiation of the LCLS

465

J.L. Turner, F.-J. Decker, Y.T. Ding, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, M. Messerschmidt, S.P. Moeller, H.-D. Nuhn, D.F. Ratner, J.J. Welch, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Understanding and controlling the transverse size and distribution of FEL X-ray radiation of the LCLS at the SLAC National Accelerator Laboratory is discussed. Understanding divergence, source size, and distributions under various conditions is a convolution of many effects such as the electron distribution, the undulator alignment, micro-bunching suppression, and beta-match. Measurements of transverse size along the X-ray pulse and other studies designed to sort out the dominant effects are presented and discussed.

Slides THOC4 [1.874 MB]

THPB31

Multiple FELs from the One LCLS Undulator

629

F.-J. Decker, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, S.P. Moeller, H.-D. Nuhn, J.L. Turner, J.J. Welch, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Science, under Contract DE-AC02-76SF00515.
The FEL of the Linac Coherent Light Source (LCLS) at SLAC is generated in a 132 m long undulator. By introducing a kink in the undulator setup and launching different electron pulses with a small kick, we achieved two FEL beams with a separation of about 10 σ. These beams were separated at down stream mirrors and brought to the entrances of the soft and hard X-ray hutches. This was done at low energy creating soft X-rays which require only a shorter length to get to saturation. At high energy the whole undulator has to be "re-pointed" pulse by pulse. This can be done using 33 undulator correctors creating two straight lines for the photons with small angle to point the FEL to different mirrors pulse by pulse even at high energy. Experiments will be presented and further ideas discussed to get different energy photons created and sent to the soft and hard X-ray mirrors and experiments.

Paper	Title	Page
MOPB08	Studies for Polarization Control at LCLS	31
	E. Allaria, Y.T. Ding, P. Emma, Z. Huang, H.-D. Nuhn, M. Rowen, J.J. Welch, J. Wu SLAC, Menlo Park, California, USA
	In order to improve the capabilities of LCLS to meet more of the user requirements it has been proposed to implement a method to produce circularly polarized coherent radiation in the LCLS free electron laser. In this work we will present the results of a new set of studies and simulations that have been done for adding polarization control to LCLS using circularly polarizing undulators. Attention has been focused mainly on the use of variable gap APPLE-II undulators to be used at the end of a long SASE radiator that is based on the standard planar LCLS undulators. Issues like polarization contamination from the planar polarized light, polarization fluctuation and the choice of undulator configuration have been studied.

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]

WEOA2	SASE FEL Pulse Duration Analysis from Spectral Correlation Function	318
	A.A. Lutman, Y.T. Ding, Y. Feng, Z. Huang, J. Krzywinski, M. Messerschmidt, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. A new method to measure the X-rays pulse duration through the analysis of the statistical properties of the SASE FEL spectra has been developed. The information on the pulse duration is contained in the correlation function of the intensity spectra measured after a spectrometer. The spectral correlation function is derived analytically for different profile shapes in the exponential growth regime and issues like spectral central frequency jitter and shot by shot statistical gain are addressed. Numerical simulations will show that the method is applicable also in saturation regime and that both pulse duration and spectrometer resolution can be recovered from the spectral correlation function. The method has been experimentally demonstrated at LCLS, measuring the soft X-rays pulse durations for different electron bunch lengths, and the evolution of the pulse durations for different undulator distances. Shorter pulse durations down to 13 fs FWHM have been measured using the slotted foil.
	Slides WEOA2 [0.758 MB]

WEPA06	Experimental Studies with Spatial Gaussian-cut Laser for the LCLS Photocathode Gun	341
	F. Zhou, A. Brachmann, P. Emma, A. Gilevich, Z. Huang SLAC, Menlo Park, California, USA
	Funding: U.S. Department of Energy under contract DE-AC02-76SF00515 To further enhance the LCLS injector performances or simplify its operating conditions, we are evaluating the various parameters including the photocathode drive laser. Simulations show that both the projected and time-sliced emittances with spatial Gaussian profiles having reasonable tail-cutoff are better than those with uniform one. The simulated results are also supported by theoretical analyses. In the LCLS, the spatial uniform or quasi-Gaussian laser profiles are conveniently obtained by adjusting the optics of telescope upstream of an iris, used to define laser size on the cathode. Preliminary beam studies at the LCLS show that both the projected and time-sliced emittances with spatial quasi-Gaussian laser are almost as good as, although not better than, those with uniform one, and also laser transmission through the iris with the quasi-Gaussian is twice that with uniform one, which is to ease copper cathode operations and thus improve the LCLS operation efficiency. More beam studies are planned in the coming summer to measure FEL performances with the quasi-Gaussian in comparison with the uniform one. All simulations and measurements are presented.

WEPB14	Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflector	405
	C. Behrens DESY, Hamburg, Germany Y.T. Ding, P. Emma, J.C. Frisch, Z. Huang, P. Krejcik, H. Loos, M.-H. Wang SLAC, Menlo Park, California, USA
	The measurement of ultra-short electron bunches on the femtosecond time scale constitutes a very challenging problem. In X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of sub-ten femtosecond X-ray pulses is possible, and some efforts have been put into both ultra-short electron and X-ray beam diagnostics. Here we propose a single-shot method using a transverse deflector (X-band) after the undulator to reconstruct both the electron bunch and X-ray temporal profiles. Simulation studies show that about 1 fs (rms) time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and pulse lengths. The jitter, resolution and other related issues will be discussed.

WEPB15	Reversible Electron Beam Heater for Suppression of Microbunching Instabilities Based on Transverse Deflecting Cavities	409
	C. Behrens DESY, Hamburg, Germany Z. Huang, D. Xiang SLAC, Menlo Park, California, USA
	The presence of the microbunching instability due to the compression of high-brightness electron beams at existing and future X-ray free-electron lasers (FEL) results in restrictions on the attainable lasing performance and renders diagnostics like beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e. heating the beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of seeded FELs. In this paper, we present a reversible electron beam heating system based on two transverse deflecting cavities (TCAV) in front and behind a bunch compressor chicane. The additional energy spread will be introduced in the first TCAV, which suppresses the microbunching instability, and then will be eliminated in the second TCAV. We show the feasibility of the suppression of microbunching instabilities based on calculations and simulations, and set limits to the acceptable jitter tolerances.

WEPB22	An Optical Streaking Method for Measuring Femtosecond Electron Bunches	431
	Y.T. Ding, K.L.F. Bane, Z. Huang SLAC, Menlo Park, California, USA
	The measurement of the ultra-short electron bunch on the femotosecond time scale constitutes a very challenging problem. In the X-ray free electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of a sub-ten femtoseconds electron beam at low charge operation mode is possible, based on indirect measurements and computer simulations. Direct measurements are not available due to the resolution limit of the present diagnostics. We propose a new method based on the energy modulation of the ultra-short electron bunch by interacting with an optical laser in a short wiggler. Compared with a laser-based transverse deflector, which requires the laser wavelength much longer than the electron bunch length, here we propose a scheme to use a laser with its wavelength shorter than the electron bunch length, where the slope on the laser intensity envelope has been used to help distinguish the different periods. The calibration is simple and it is possible to reconstruct the bunch longitudinal profile from a single shot measurement.

THOB5	FEL Spectral Measurements at LCLS	461
	J.J. Welch, F.-J. Decker, Y.T. Ding, P. Emma, A.S. Fisher, J.C. Frisch, Z. Huang, R.H. Iverson, H. Loos, M. Messerschmidt, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515. Control and knowledge of the spectrum of FEL X-ray radiation at the LCLS is important to the quality and interpretation of experimental results. Narrow bandwidth is useful in experiments requiring high-brightness beams. Wide bandwidth is particularly useful for photon energy calibration using absorption spectra. Since LCLS was commissioned in 2009 measurements have been made of average and single shot spectra of X-ray FEL radiation at the LCLS over a range of 800 to 8000 eV, for fundamental and harmonic radiation. These include correlations with chirp, bunch current, undulator K-taper, electron beam energy, and charge as well as some specialized machine configurations. In this paper we present results and discuss the relationship of the electron beam energy distribution to the observed X-ray spectrum.
	Slides THOB5 [0.442 MB]

THOC4	Transverse Size and Distribution of FEL X-ray Radiation of the LCLS	465
	J.L. Turner, F.-J. Decker, Y.T. Ding, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, M. Messerschmidt, S.P. Moeller, H.-D. Nuhn, D.F. Ratner, J.J. Welch, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515 Understanding and controlling the transverse size and distribution of FEL X-ray radiation of the LCLS at the SLAC National Accelerator Laboratory is discussed. Understanding divergence, source size, and distributions under various conditions is a convolution of many effects such as the electron distribution, the undulator alignment, micro-bunching suppression, and beta-match. Measurements of transverse size along the X-ray pulse and other studies designed to sort out the dominant effects are presented and discussed.
	Slides THOC4 [1.874 MB]

THPB31	Multiple FELs from the One LCLS Undulator	629
	F.-J. Decker, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, S.P. Moeller, H.-D. Nuhn, J.L. Turner, J.J. Welch, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Science, under Contract DE-AC02-76SF00515. The FEL of the Linac Coherent Light Source (LCLS) at SLAC is generated in a 132 m long undulator. By introducing a kink in the undulator setup and launching different electron pulses with a small kick, we achieved two FEL beams with a separation of about 10 σ. These beams were separated at down stream mirrors and brought to the entrances of the soft and hard X-ray hutches. This was done at low energy creating soft X-rays which require only a shorter length to get to saturation. At high energy the whole undulator has to be "re-pointed" pulse by pulse. This can be done using 33 undulator correctors creating two straight lines for the photons with small angle to point the FEL to different mirrors pulse by pulse even at high energy. Experiments will be presented and further ideas discussed to get different energy photons created and sent to the soft and hard X-ray mirrors and experiments.