FEL2011 - List of Authors (Behrens, C.)

Paper

Title

Page

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.

THOCI1

Measurement and Control of the Longitudinal Phase Space at High-Gain Free-electron Lasers

C. Behrens, C. Gerth
DESY, Hamburg, Germany

Free-electron lasers provide a high degree of flexibility in terms of pulse intensity and wavelength range. In the case of high-gain FELs with a two-frequency accelerator in front of the bunch compressors, the flexibility is extended with electron bunch shape and length tunability. The final goal is to get control of the FEL photon pulses which might be achieved by controlling the longitudinal phase space (LPS) of the driving electron bunch. This can be achieved by using transverse deflecting structures/cavities (TDS/C) in combination with energy spectrometers which provide a direct measurement method with high resolutions in both energy and time. In this talk, the basic concepts of longitudinal phase space diagnostics, using transverse deflecting structures/cavities in combination with energy spectrometers, will be discussed with examples from FLASH at DESY and LCLS at SLAC. The obtainable resolutions and limitations due to the accelerator optics, induced energy spread by the TDS/C itself, and coherent synchrotron radiation will be shown by simulations and measurements. Finally, an overview of planned LPS diagnostics at other facilities, like the European XFEL, will be presented.

Slides THOCI1 [3.849 MB]

THPB16

Beam Profile Measurements Using a Fast Gated CCD Camera and a Scintillation Screen to Suppress COTR

590

M. Yan
Uni HH, Hamburg, Germany
C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch
DESY, Hamburg, Germany

For standard beam profile measurements of high-brightness electron beams using optical transition radiation (OTR) screens, coherence effects induced by microbunching instabilities render direct imaging of the beam impossible. A technique of using a scintillation screen with a fast gated CCD camera has been demonstrated to successfully suppress coherent OTR (COTR) in transverse beam diagnostics at FLASH. The fast gated CCD camera has been installed next to a standard CCD camera setup and images the same viewing screens. The results of transverse beam profile measurements under operating conditions without COTR are compared for both setups. The fast gated camera has also been employed for longitudinal bunch profile measurements with a transverse deflecting structure (TDS). Results obtained under operating conditions with COTR are compared to those from longitudinal phase space measurements in a dispersive arm, where no coherence effects have been observed so far. In this paper, we examine the performance of the fast gated CCD camera for beam profile measurements and present further studies on the use of scintillation screens for high-energy electron beam diagnostics.

Paper	Title	Page
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.

THOCI1	Measurement and Control of the Longitudinal Phase Space at High-Gain Free-electron Lasers
	C. Behrens, C. Gerth DESY, Hamburg, Germany
	Free-electron lasers provide a high degree of flexibility in terms of pulse intensity and wavelength range. In the case of high-gain FELs with a two-frequency accelerator in front of the bunch compressors, the flexibility is extended with electron bunch shape and length tunability. The final goal is to get control of the FEL photon pulses which might be achieved by controlling the longitudinal phase space (LPS) of the driving electron bunch. This can be achieved by using transverse deflecting structures/cavities (TDS/C) in combination with energy spectrometers which provide a direct measurement method with high resolutions in both energy and time. In this talk, the basic concepts of longitudinal phase space diagnostics, using transverse deflecting structures/cavities in combination with energy spectrometers, will be discussed with examples from FLASH at DESY and LCLS at SLAC. The obtainable resolutions and limitations due to the accelerator optics, induced energy spread by the TDS/C itself, and coherent synchrotron radiation will be shown by simulations and measurements. Finally, an overview of planned LPS diagnostics at other facilities, like the European XFEL, will be presented.
	Slides THOCI1 [3.849 MB]

THPB16	Beam Profile Measurements Using a Fast Gated CCD Camera and a Scintillation Screen to Suppress COTR	590
	M. Yan Uni HH, Hamburg, Germany C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch DESY, Hamburg, Germany
	For standard beam profile measurements of high-brightness electron beams using optical transition radiation (OTR) screens, coherence effects induced by microbunching instabilities render direct imaging of the beam impossible. A technique of using a scintillation screen with a fast gated CCD camera has been demonstrated to successfully suppress coherent OTR (COTR) in transverse beam diagnostics at FLASH. The fast gated CCD camera has been installed next to a standard CCD camera setup and images the same viewing screens. The results of transverse beam profile measurements under operating conditions without COTR are compared for both setups. The fast gated camera has also been employed for longitudinal bunch profile measurements with a transverse deflecting structure (TDS). Results obtained under operating conditions with COTR are compared to those from longitudinal phase space measurements in a dispersive arm, where no coherence effects have been observed so far. In this paper, we examine the performance of the fast gated CCD camera for beam profile measurements and present further studies on the use of scintillation screens for high-energy electron beam diagnostics.