FEL2012 - List of Authors (Decker, F.-J.)

Paper

Title

Page

High-brightness Electron Beam Evolution In Time Following Laser-Based Cleaning of the LCLS Cathode

193

F. Zhou, A. Brachmann, F.-J. Decker, P. Emma, R.H. Iverson, P. Stefan, J.L. Turner
SLAC, Menlo Park, California, USA

Funding: The work supported under DOE contract No. DE-AC02-76SF00515.
Laser-based techniques have been widely used for cleaning metal photocathodes to increase quantum efficiency (QE). However, the impact of laser cleaning on the cathode uniformity and final quality of the electron beam is not understood. We are evaluating whether the technique can be applied to revive photocathodes used for electron beam sources of advanced x-ray free electron laser (FEL) facilities, such as the Linac Coherent Light Source (LCLS) at the SLAC. The laser-based cleaning was applied to two separate areas of the LCLS photocathode on July 4 and July 26, 2011, respectively. Since the cleaning performed, routine operation has shown a slow evolution of both the QE and the transverse emittance, with a significant improvement of both over 2-3 weeks. Currently, the LCLS photocathode QE is constant at about 1.2·10^-4 with a normalized injector emittance of about 0.3 μm for a 150-pC bunch charge. The laser cleaning technique becomes a viable tool to revive the LCLS photocathode. We present these observations of the QE and emittance evolution after laser-based cleaning of the LCLS photocathode,and the thermal emittance for different QE.

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]

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]

Paper	Title	Page
MOPD62	High-brightness Electron Beam Evolution In Time Following Laser-Based Cleaning of the LCLS Cathode	193
	F. Zhou, A. Brachmann, F.-J. Decker, P. Emma, R.H. Iverson, P. Stefan, J.L. Turner SLAC, Menlo Park, California, USA
	Funding: The work supported under DOE contract No. DE-AC02-76SF00515. Laser-based techniques have been widely used for cleaning metal photocathodes to increase quantum efficiency (QE). However, the impact of laser cleaning on the cathode uniformity and final quality of the electron beam is not understood. We are evaluating whether the technique can be applied to revive photocathodes used for electron beam sources of advanced x-ray free electron laser (FEL) facilities, such as the Linac Coherent Light Source (LCLS) at the SLAC. The laser-based cleaning was applied to two separate areas of the LCLS photocathode on July 4 and July 26, 2011, respectively. Since the cleaning performed, routine operation has shown a slow evolution of both the QE and the transverse emittance, with a significant improvement of both over 2-3 weeks. Currently, the LCLS photocathode QE is constant at about 1.2·10^-4 with a normalized injector emittance of about 0.3 μm for a 150-pC bunch charge. The laser cleaning technique becomes a viable tool to revive the LCLS photocathode. We present these observations of the QE and emittance evolution after laser-based cleaning of the LCLS photocathode,and the thermal emittance for different QE.

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]

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]