FEL2012 - List of Authors (Zhou, F.)

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.

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]

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.

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.

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]

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.