FEL2012 - List of Authors (Huang, Z.)

Paper

Title

Page

A General Method for Analyzing 3-D Effects in FEL Amplifiers

81

P. Baxevanis, Z. Huang, R.D. Ruth
SLAC, Menlo Park, California, USA

FEL configurations in which the parameters of the electron beam vary along the undulator become relevant when considering new aspects of existing FELs or when exploring novel concepts. This paper describes a fully three-dimensional, analytical method suitable for studying such systems. As an example, we consider a seeded FEL driven by a beam with varying transverse sizes. In the context of the Vlasov-Maxwell formalism, a self-consistent equation governing the evolution of the radiation field amplitude is derived. An approximate solution to this equation is then obtained by employing an orthogonal expansion technique. This approach yields accurate estimates for both the amplified power and the radiation beam size. Specific numerical results are presented for two different sets of X-ray FEL parameters.

TUOAI02

Hard X-ray Self-Seeding at the LCLS

R.R. Lindberg, W. Berg, D. Shu, Yu. Shvyd'ko, S. Stoupin, E. Trakhtenberg, A. Zholents
ANL, Argonne, USA
J.W. Amann, F.-J. Decker, Y.T. Ding, Y. Feng, J.C. Frisch, D. Fritz, J.B. Hastings, Z. Huang, J. Krzywinski, H. Loos, A.A. Lutman, H.-D. Nuhn, D.F. Ratner, J.A. Rzepiela, D.R. Walz, J.J. Welch, J. Wu, D. Zhu
SLAC, Menlo Park, California, USA
V.D. Blank, S. Terentiev
TISNCM, Troitsk, Russia
P. Emma
LBNL, Berkeley, California, USA
S. Spampinati
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Funding: U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357
The Linac Coherent Light Source (LCLS) has produced extremely bright hard x-ray pulses using self-amplified spontaneous emission (SASE) since 2009. In SASE, the electron beam shot noise initiates the FEL gain, resulting in output radiation characterized by poor temporal coherence and a fluctuating spectrum whose normalized width is given by the FEL bandwidth. Recently, colleagues at DESY suggested a self-seeding scheme for the LCLS to reduce the bandwidth*. Here, the SASE produced in the first half of the undulator line is put through a simple diamond-based monochromator; the resulting monochromatic light trailing the main SASE pulse is used to seed the FEL interaction in the downstream undulators. We report on the experimental results implementing such a scheme at the LCLS, in which we have measured a reduction in bandwidth by a factor of 40-50 from that of SASE at 8-9 keV. The self-seeded FEL operates close to saturation, with the maximum output energy approximately equal to that with no seeding for low charge. The observed level of power fluctuations in the seeded output is presently rather large, and future plans focus on discovering their origins and reducing their magnitude.
* Geloni, V. Kocharyan ,and E.L. Saldin, DESY 10-133, arXiv:10⁰⁸.3036 (2010)

Slides TUOAI02 [22.104 MB]

TUOB04

Comparison of Hard X-Ray Self-seeding with SASE after a Monochromator at LCLS

217

J.J. Welch, F.-J. Decker, J.B. Hastings, Z. Huang, A.A. Lutman, M. Messerschmidt, J.L. Turner
SLAC, Menlo Park, California, USA

Funding: ** Work supported in part by the DOE Contract DE-AC02-76SF00515.
Self-seeding of a hard x-ray FEL was demonstrated at LCLS in January 2012 and produced a factor of 40-50 bandwidth reduction using a electron bunch charge of 20-40 pC*. For many hard x-ray users, the photon intensity after a monochromator is an important performance parameter. In this paper, we report results from a subsequent study of self-seeding performance using the Si (111) K-monochromator with a full bandwidth of 1.2 eV at 8.2 keV. These include a direct comparison of the average intensity of the monochromatized seeded beam with that of a monochromatized fully tuned-up SASE beam, in both cases using 150 pC bunch charge. The intensity distribution, fluctuations, and spatial profiles of the monochromatized radiation are studied and compared.
* J. Amann, et. al, Nature Photonics, to be published

Slides TUOB04 [1.417 MB]

TUOBI01

System Design for Self-Seeding the LCLS at Soft X-ray Energies

205

Y. Feng, J.W. Amann, D. Cocco, R.C. Field, J.B. Hastings, P.A. Heimann, Z. Huang, H. Loos, J.J. Welch, J. Wu
SLAC, Menlo Park, California, USA
K. Chow, P. Emma, L. Rodes, R.W. Schoenlein
LBNL, Berkeley, California, USA

Funding: Portions of this research were carried out at the LCLS at the SLAC. LCLS is an Office of Science User Facility operated for the U.S. DOE Office of Science by Stanford University
The complete design for self-seeding the LCLS at soft X-ray energies from 400 to 1000 eV based on a grating monochromator is described. The X-ray optics system consists of a toroidal variable-line-space (VLS) grating with a resolving power greater than 5000 for creating a nearly transform-limited seed pulse from the upstream SASE undulator for pulse durations of the order of 25 fs, and focusing mirrors for imaging the seed pulse onto the downstream seeding undulator. Diagnostics for ensuring overlap with the reentrant electron beam are included in the design. The optical system is sufficiently compact to fit within a single 3.4 m LCLS undulator segment. The electron chicane system which serves to delay the electron beam to match the less than 1 ps delay from the optical system is similar to the chicane used in the hard X-ray self-seeding at LCLS. The seeded FEL pulse is expected to be nearly transform-limited with a bandwidth in the 10-4 range, potentially increasing the low-charge FEL X-ray peak brightness by 1-2 orders of magnitude.

Slides TUOBI01 [6.749 MB]

WEOA04

Time-Resolved Images of Coherent Synchrotron Radiation Effects in the LCLS First Bunch Compressor

349

P. Emma
LBNL, Berkeley, California, USA
C. Behrens
DESY, Hamburg, Germany
Z. Huang, F. Zhou
SLAC, Menlo Park, California, USA

Funding: We thank the US Department of Energy under contract number DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) is an x-ray Free-Electron Laser (FEL) facility now in operation at SLAC. One of the limiting effects on electron beam brightness is the coherent synchrotron radiation (CSR) generated in the bunch compressor chicanes, which can significantly dilute the bend-plane (horizontal) emittance. Since simple emittance measurements* do not tell the full story, we would like to see the time-dependent CSR-kicks along the length of the bunch. We present measured images and simulations of the effects of CSR seen on an intercepting beam screen just downstream of the LCLS BC1 chicane while powering a skew quadrupole magnet near the center of the chicane [ ]. The skew quadrupole maps the time coordinate of the pre-BC1 bunch onto the vertical axis of the screen, allowing the time-dependent CSR-induced horizontal effects to become clearly visible.
* K. Bane et al., Phys. Rev. ST Accel. Beams 12, 030704 (2009).
** K. Bertsche, P. Emma, O. Shevchenko, "A Simple, Low Cost Longitudinal Phase Space Diagnostic", PAC'09, Vancouver, BC, Canada, 2009.

Slides WEOA04 [3.159 MB]

THOB02

Transverse Gradient Undulator to Enhance the FEL Performance for a Laser-plasma Accelerator

Z. Huang, Y.T. Ding
SLAC, Menlo Park, California, USA
C.B. Schroeder
LBNL, Berkeley, California, USA

Compact laser-plasma accelerators can produce high energy electron beams with low emittance, high peak current but a rather large energy spread. The large energy spread hinders the potential applications for coherent FEL radiation generation. In this paper, we discuss a method to compensate the effects of beam energy spread by introducing a transverse field variation into the FEL undulator. Such a transverse gradient undulator together with a properly dispersed beam can greatly reduce the effects of electron energy spread and jitters on FEL performance. We present theoretical analysis and numerical simulations for SASE and seeded XUV and soft x-ray FELs based on laser plasma accelerators.

Slides THOB02 [2.720 MB]

THOC04

Femtosecond X-ray Pulse Duration and Separation Measurement using a Cross-Correlation Technique

Y.T. Ding, F.-J. Decker, Z. Huang, H. Loos, J.J. Welch, J. Wu, F. Zhou
SLAC, Menlo Park, California, USA
P. Emma
LBNL, Berkeley, California, USA
C. Feng
SINAP, Shanghai, People's Republic of China

At the Linac Coherent Light Source (LCLS), the emittance-spoiling foil is a very simple and effective method to control the output x-ray pulse duration [*]. In addition, double slotted foil can be used to generate two femotsecond x-ray pulses with variable time delays. In this paper, we report the first measurement of x-ray pulse duration and double x-ray pulse separation by using a cross-correlation technique between x-rays and electrons [**]. The measured pulse separation can be used to calibrate the foil setup, and pulse duration of less than 3 fs rms has been achieved. This technique can be used to provide critical temporal diagnostics for x-ray experiments that employ the emittance-spoiling foil.
[*] P. Emma et al., PRL 92, 074801 (2004).
[**] G. Geloni et al., DESY 10-008.

Slides THOC04 [0.684 MB]

THPD31

Sub-femtosecond Hard X-Ray Pulse from Very Low Charge Beam at LCLS

606

V. Wacker
DESY, Hamburg, Germany
Y.T. Ding, J.C. Frisch, Z. Huang, C. Pellegrini, F. Zhou
SLAC, Menlo Park, California, USA

The Linac Coherent Light Source (LCLS) is an x-ray free-electron laser (FEL) at SLAC National Accelerator Laboratory, supporting a wide range of scientific research with an x-ray pulse length varying from a few to several hundred femtoseconds. There is also a large interest in even shorter, single-spike x-ray pulses, which will allow the investigation of matter at the atomic length (Å) and time scale (fs). In this paper, we investigate the FEL performance using 1pC and 3pC electron bunches at LCLS, based on the start-to-end simulations. With an optimization of the machine setup, simulations show that single spike, sub-femtosecond, hard x-ray pulses are achievable at this low charge.

THPD56

Two-color FEL Generation based on Emittance-spoiler Technique

654

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

Generation of two-pulse two-color x-ray radiation is attracting much attention within the free-electron laser (FEL) user community. Femtosecond x-ray pulses with variable durations and separation can be simply generated by the emittance-spoiler foil method* at the Linac Coherent Light Source (LCLS). In this paper, we describe three FEL schemes rely on the emittance-spoiler technique for the generation of two intense x-ray pulses with different colors. With a representative realistic set of parameters of LCLS, numerical simulations confirm that two femtosecond x-ray pulses at ten gigawatt level with different wavelengths around 1.8 nm can be generated by these schemes. The central wavelengths of the output pulses can be easily altered by changing strengths of the undulators.
*P. Emma et al., PRL 92, 074801 (2004).

THPD57

Application of laser-plasma accelerator beams to Free-Electron Lasers

658

C.B. Schroeder, C. Benedetti, E. Esarey, W. Leemans, J. van Tilborg
LBNL, Berkeley, California, USA
Y.T. Ding, Z. Huang
SLAC, Menlo Park, California, USA
F. Grüner, A.R. Maier
Uni HH, Hamburg, Germany

Funding: This work was supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No.DE-AC02-05CH11231.
Plasma waves excited by high-intensity, short-pulse lasers are able to generate hundreds of GV/m accelerating fields, enabling extremely compact accelerators for applications such as radiation generation. Laser-plasma accelerators (LPAs) produce ultrashort (femtosecond), 0.1-1 GeV electron bunches with high-peak (kA) currents and low (sub-micron) normalized transverse emittance, with 6D beam brightness comparable to state-of-the-art RF linac-based sources. FEL applications are presently limited by the longitudinal phase space distribution of the LPA beam. Beam phase space manipulation is considered to enable the application of LPA beams to FELs. LPA beam decompression (such that the energy spread over a coherence length is less than the FEL parameter) is examined as a path toward realizing an LPA-driven VUV FEL. The possibility of using a flat beam, with an energy correlation with transverse position, in a transverse gradient undulator is also explored. Laser-based FEL seeding options for improved coherence are considered.

Paper	Title	Page
MOPD22	A General Method for Analyzing 3-D Effects in FEL Amplifiers	81
	P. Baxevanis, Z. Huang, R.D. Ruth SLAC, Menlo Park, California, USA
	FEL configurations in which the parameters of the electron beam vary along the undulator become relevant when considering new aspects of existing FELs or when exploring novel concepts. This paper describes a fully three-dimensional, analytical method suitable for studying such systems. As an example, we consider a seeded FEL driven by a beam with varying transverse sizes. In the context of the Vlasov-Maxwell formalism, a self-consistent equation governing the evolution of the radiation field amplitude is derived. An approximate solution to this equation is then obtained by employing an orthogonal expansion technique. This approach yields accurate estimates for both the amplified power and the radiation beam size. Specific numerical results are presented for two different sets of X-ray FEL parameters.

TUOAI02	Hard X-ray Self-Seeding at the LCLS
	R.R. Lindberg, W. Berg, D. Shu, Yu. Shvyd'ko, S. Stoupin, E. Trakhtenberg, A. Zholents ANL, Argonne, USA J.W. Amann, F.-J. Decker, Y.T. Ding, Y. Feng, J.C. Frisch, D. Fritz, J.B. Hastings, Z. Huang, J. Krzywinski, H. Loos, A.A. Lutman, H.-D. Nuhn, D.F. Ratner, J.A. Rzepiela, D.R. Walz, J.J. Welch, J. Wu, D. Zhu SLAC, Menlo Park, California, USA V.D. Blank, S. Terentiev TISNCM, Troitsk, Russia P. Emma LBNL, Berkeley, California, USA S. Spampinati Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Funding: U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357 The Linac Coherent Light Source (LCLS) has produced extremely bright hard x-ray pulses using self-amplified spontaneous emission (SASE) since 2009. In SASE, the electron beam shot noise initiates the FEL gain, resulting in output radiation characterized by poor temporal coherence and a fluctuating spectrum whose normalized width is given by the FEL bandwidth. Recently, colleagues at DESY suggested a self-seeding scheme for the LCLS to reduce the bandwidth. Here, the SASE produced in the first half of the undulator line is put through a simple diamond-based monochromator; the resulting monochromatic light trailing the main SASE pulse is used to seed the FEL interaction in the downstream undulators. We report on the experimental results implementing such a scheme at the LCLS, in which we have measured a reduction in bandwidth by a factor of 40-50 from that of SASE at 8-9 keV. The self-seeded FEL operates close to saturation, with the maximum output energy approximately equal to that with no seeding for low charge. The observed level of power fluctuations in the seeded output is presently rather large, and future plans focus on discovering their origins and reducing their magnitude. Geloni, V. Kocharyan ,and E.L. Saldin, DESY 10-133, arXiv:10⁰⁸.3036 (2010)
	Slides TUOAI02 [22.104 MB]

TUOB04	Comparison of Hard X-Ray Self-seeding with SASE after a Monochromator at LCLS	217
	J.J. Welch, F.-J. Decker, J.B. Hastings, Z. Huang, A.A. Lutman, M. Messerschmidt, J.L. Turner SLAC, Menlo Park, California, USA
	Funding: ** Work supported in part by the DOE Contract DE-AC02-76SF00515. Self-seeding of a hard x-ray FEL was demonstrated at LCLS in January 2012 and produced a factor of 40-50 bandwidth reduction using a electron bunch charge of 20-40 pC. For many hard x-ray users, the photon intensity after a monochromator is an important performance parameter. In this paper, we report results from a subsequent study of self-seeding performance using the Si (111) K-monochromator with a full bandwidth of 1.2 eV at 8.2 keV. These include a direct comparison of the average intensity of the monochromatized seeded beam with that of a monochromatized fully tuned-up SASE beam, in both cases using 150 pC bunch charge. The intensity distribution, fluctuations, and spatial profiles of the monochromatized radiation are studied and compared. J. Amann, et. al, Nature Photonics, to be published
	Slides TUOB04 [1.417 MB]

TUOBI01	System Design for Self-Seeding the LCLS at Soft X-ray Energies	205
	Y. Feng, J.W. Amann, D. Cocco, R.C. Field, J.B. Hastings, P.A. Heimann, Z. Huang, H. Loos, J.J. Welch, J. Wu SLAC, Menlo Park, California, USA K. Chow, P. Emma, L. Rodes, R.W. Schoenlein LBNL, Berkeley, California, USA
	Funding: Portions of this research were carried out at the LCLS at the SLAC. LCLS is an Office of Science User Facility operated for the U.S. DOE Office of Science by Stanford University The complete design for self-seeding the LCLS at soft X-ray energies from 400 to 1000 eV based on a grating monochromator is described. The X-ray optics system consists of a toroidal variable-line-space (VLS) grating with a resolving power greater than 5000 for creating a nearly transform-limited seed pulse from the upstream SASE undulator for pulse durations of the order of 25 fs, and focusing mirrors for imaging the seed pulse onto the downstream seeding undulator. Diagnostics for ensuring overlap with the reentrant electron beam are included in the design. The optical system is sufficiently compact to fit within a single 3.4 m LCLS undulator segment. The electron chicane system which serves to delay the electron beam to match the less than 1 ps delay from the optical system is similar to the chicane used in the hard X-ray self-seeding at LCLS. The seeded FEL pulse is expected to be nearly transform-limited with a bandwidth in the 10-4 range, potentially increasing the low-charge FEL X-ray peak brightness by 1-2 orders of magnitude.
	Slides TUOBI01 [6.749 MB]

WEOA04	Time-Resolved Images of Coherent Synchrotron Radiation Effects in the LCLS First Bunch Compressor	349
	P. Emma LBNL, Berkeley, California, USA C. Behrens DESY, Hamburg, Germany Z. Huang, F. Zhou SLAC, Menlo Park, California, USA
	Funding: We thank the US Department of Energy under contract number DE-AC02-76SF00515. The Linac Coherent Light Source (LCLS) is an x-ray Free-Electron Laser (FEL) facility now in operation at SLAC. One of the limiting effects on electron beam brightness is the coherent synchrotron radiation (CSR) generated in the bunch compressor chicanes, which can significantly dilute the bend-plane (horizontal) emittance. Since simple emittance measurements* do not tell the full story, we would like to see the time-dependent CSR-kicks along the length of the bunch. We present measured images and simulations of the effects of CSR seen on an intercepting beam screen just downstream of the LCLS BC1 chicane while powering a skew quadrupole magnet near the center of the chicane [ ]. The skew quadrupole maps the time coordinate of the pre-BC1 bunch onto the vertical axis of the screen, allowing the time-dependent CSR-induced horizontal effects to become clearly visible. * K. Bane et al., Phys. Rev. ST Accel. Beams 12, 030704 (2009). ** K. Bertsche, P. Emma, O. Shevchenko, "A Simple, Low Cost Longitudinal Phase Space Diagnostic", PAC'09, Vancouver, BC, Canada, 2009.
	Slides WEOA04 [3.159 MB]

THOB02	Transverse Gradient Undulator to Enhance the FEL Performance for a Laser-plasma Accelerator
	Z. Huang, Y.T. Ding SLAC, Menlo Park, California, USA C.B. Schroeder LBNL, Berkeley, California, USA
	Compact laser-plasma accelerators can produce high energy electron beams with low emittance, high peak current but a rather large energy spread. The large energy spread hinders the potential applications for coherent FEL radiation generation. In this paper, we discuss a method to compensate the effects of beam energy spread by introducing a transverse field variation into the FEL undulator. Such a transverse gradient undulator together with a properly dispersed beam can greatly reduce the effects of electron energy spread and jitters on FEL performance. We present theoretical analysis and numerical simulations for SASE and seeded XUV and soft x-ray FELs based on laser plasma accelerators.
	Slides THOB02 [2.720 MB]

THOC04	Femtosecond X-ray Pulse Duration and Separation Measurement using a Cross-Correlation Technique
	Y.T. Ding, F.-J. Decker, Z. Huang, H. Loos, J.J. Welch, J. Wu, F. Zhou SLAC, Menlo Park, California, USA P. Emma LBNL, Berkeley, California, USA C. Feng SINAP, Shanghai, People's Republic of China
	At the Linac Coherent Light Source (LCLS), the emittance-spoiling foil is a very simple and effective method to control the output x-ray pulse duration []. In addition, double slotted foil can be used to generate two femotsecond x-ray pulses with variable time delays. In this paper, we report the first measurement of x-ray pulse duration and double x-ray pulse separation by using a cross-correlation technique between x-rays and electrons []. The measured pulse separation can be used to calibrate the foil setup, and pulse duration of less than 3 fs rms has been achieved. This technique can be used to provide critical temporal diagnostics for x-ray experiments that employ the emittance-spoiling foil. [] P. Emma et al., PRL 92, 074801 (2004). [**] G. Geloni et al., DESY 10-008.
	Slides THOC04 [0.684 MB]

THPD31	Sub-femtosecond Hard X-Ray Pulse from Very Low Charge Beam at LCLS	606
	V. Wacker DESY, Hamburg, Germany Y.T. Ding, J.C. Frisch, Z. Huang, C. Pellegrini, F. Zhou SLAC, Menlo Park, California, USA
	The Linac Coherent Light Source (LCLS) is an x-ray free-electron laser (FEL) at SLAC National Accelerator Laboratory, supporting a wide range of scientific research with an x-ray pulse length varying from a few to several hundred femtoseconds. There is also a large interest in even shorter, single-spike x-ray pulses, which will allow the investigation of matter at the atomic length (Å) and time scale (fs). In this paper, we investigate the FEL performance using 1pC and 3pC electron bunches at LCLS, based on the start-to-end simulations. With an optimization of the machine setup, simulations show that single spike, sub-femtosecond, hard x-ray pulses are achievable at this low charge.

THPD56	Two-color FEL Generation based on Emittance-spoiler Technique	654
	C. Feng, Y.T. Ding, Z. Huang, J. Krzywinski, A.A. Lutman SLAC, Menlo Park, California, USA
	Generation of two-pulse two-color x-ray radiation is attracting much attention within the free-electron laser (FEL) user community. Femtosecond x-ray pulses with variable durations and separation can be simply generated by the emittance-spoiler foil method* at the Linac Coherent Light Source (LCLS). In this paper, we describe three FEL schemes rely on the emittance-spoiler technique for the generation of two intense x-ray pulses with different colors. With a representative realistic set of parameters of LCLS, numerical simulations confirm that two femtosecond x-ray pulses at ten gigawatt level with different wavelengths around 1.8 nm can be generated by these schemes. The central wavelengths of the output pulses can be easily altered by changing strengths of the undulators. *P. Emma et al., PRL 92, 074801 (2004).

THPD57	Application of laser-plasma accelerator beams to Free-Electron Lasers	658
	C.B. Schroeder, C. Benedetti, E. Esarey, W. Leemans, J. van Tilborg LBNL, Berkeley, California, USA Y.T. Ding, Z. Huang SLAC, Menlo Park, California, USA F. Grüner, A.R. Maier Uni HH, Hamburg, Germany
	Funding: This work was supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No.DE-AC02-05CH11231. Plasma waves excited by high-intensity, short-pulse lasers are able to generate hundreds of GV/m accelerating fields, enabling extremely compact accelerators for applications such as radiation generation. Laser-plasma accelerators (LPAs) produce ultrashort (femtosecond), 0.1-1 GeV electron bunches with high-peak (kA) currents and low (sub-micron) normalized transverse emittance, with 6D beam brightness comparable to state-of-the-art RF linac-based sources. FEL applications are presently limited by the longitudinal phase space distribution of the LPA beam. Beam phase space manipulation is considered to enable the application of LPA beams to FELs. LPA beam decompression (such that the energy spread over a coherence length is less than the FEL parameter) is examined as a path toward realizing an LPA-driven VUV FEL. The possibility of using a flat beam, with an energy correlation with transverse position, in a transverse gradient undulator is also explored. Laser-based FEL seeding options for improved coherence are considered.