DIPAC2011 - List of Authors (Behrens, C.)

Paper	Title	Page
TUPD31	Measurement of the Slice Energy Spread Induced by a Transverse Deflecting RF Structure at FLASH	371
	C. Gerth, C. Behrens DESY, Hamburg, Germany
	Operation of a high-gain free-electron laser requires a high-brightness electron beam with high peak current and small slice energy spread. The slice energy spread can be measured with high longitudinal resolution by using a transverse deflecting structure in combination with viewing screen in a dispersive section. However, off-axis accelerating fields induce a correlated energy spread that depends inversely proportional on the longitudinal resolution. As a consequence, short bunches, which intrinsically require a high longitudinal resolution in order to be diagnosed, suffer from a large induced energy spread which limits the energy resolution. To be able to measure the impact of the transverse deflecting structure on the slice energy spread without distortions by space charge or coherent synchrotron radiation effects, we tailored short electron bunches with low peak currents by clipping low energy electrons in the collimator of the first bunch compressor at FLASH. In this paper, we present first systematic measurements of the correlated energy spread induced by a transverse deflecting structure. The results are compared with analytical calculations.

TUPD38	Design of a Single-Shot Prism Spectrometer in the Near- and Mid-Infrared Wavelength Range for Ultra-Short Bunch Length Diagnostics	386
	C. Behrens DESY, Hamburg, Germany A.S. Fisher, J.C. Frisch, A. Gilevich, H. Loos, J. Loos SLAC, Menlo Park, California, USA
	The successful operation of high-gain free-electron lasers (FEL) relies on the understanding, manipulation, and control of the parameters of the driving electron bunch. Present and future FEL facilities have the tendency to push the parameters for even shorter bunches with lengths below 10 fs and charges well below 100 pC. This is also the order of magnitude at laser-driven plasma-based electron accelerators. Devices to diagnose such ultra-short bunches even need longitudinal resolutions smaller than the bunch lengths, i.e. in the range of a few femtoseconds. This resolution is currently out of reach with time-domain diagnostics like RF-based deflectors, and approaches in the frequency-domain have to be considered to overcome this limitation. Our approach is to extract the information on the longitudinal bunch profile by means of infrared spectroscopy using a prism as dispersive element. In this paper, we present the design considerations on a broadband single-shot spectrometer in the near- and mid-infrared wavelength range (0.8 - 39.0 μm).

TUPD59	Suppression of Coherent Optical Transition Radiation in Transverse Beam Diagnostics by Utilising a Scintillation Screen with a Fast Gated CCD Camera	440
	M. Yan Uni HH, Hamburg, Germany C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch DESY, Hamburg, Germany
	Micro-bunching instabilities in high-brightness beams of linac-driven FELs can lead to coherence effects in the emission of optical transition radiation (OTR) used for standard transverse profile diagnostics, thus rendering it impossible to observe a direct image of the particle beam. By using a scintillation screen in combination with a fast gated CCD camera, coherence effects can be suppressed as OTR is created in an instantaneous process while scintillation light has a certain decay time. In addition, the emission of the scintillation light is a statistical process from many atoms which is completely insensitive to the longitudinal bunch structure and does not produce coherence effects. Gating the camera during the passage of the electron bunch should eliminate any influence of the coherent OTR (COTR). First experiments using this method have been performed successfully at FLASH as a proof-of-principle. In this paper, we study the applicability of scintillation screens for high-energy electron beams under operation conditions for which COTR is emitted. Experimental results together with simulations are presented and discussed in view of COTR suppression and spatial resolution.

Paper

Title

Page

Measurement of the Slice Energy Spread Induced by a Transverse Deflecting RF Structure at FLASH

371

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

Operation of a high-gain free-electron laser requires a high-brightness electron beam with high peak current and small slice energy spread. The slice energy spread can be measured with high longitudinal resolution by using a transverse deflecting structure in combination with viewing screen in a dispersive section. However, off-axis accelerating fields induce a correlated energy spread that depends inversely proportional on the longitudinal resolution. As a consequence, short bunches, which intrinsically require a high longitudinal resolution in order to be diagnosed, suffer from a large induced energy spread which limits the energy resolution. To be able to measure the impact of the transverse deflecting structure on the slice energy spread without distortions by space charge or coherent synchrotron radiation effects, we tailored short electron bunches with low peak currents by clipping low energy electrons in the collimator of the first bunch compressor at FLASH. In this paper, we present first systematic measurements of the correlated energy spread induced by a transverse deflecting structure. The results are compared with analytical calculations.

TUPD38

Design of a Single-Shot Prism Spectrometer in the Near- and Mid-Infrared Wavelength Range for Ultra-Short Bunch Length Diagnostics

386

C. Behrens
DESY, Hamburg, Germany
A.S. Fisher, J.C. Frisch, A. Gilevich, H. Loos, J. Loos
SLAC, Menlo Park, California, USA

The successful operation of high-gain free-electron lasers (FEL) relies on the understanding, manipulation, and control of the parameters of the driving electron bunch. Present and future FEL facilities have the tendency to push the parameters for even shorter bunches with lengths below 10 fs and charges well below 100 pC. This is also the order of magnitude at laser-driven plasma-based electron accelerators. Devices to diagnose such ultra-short bunches even need longitudinal resolutions smaller than the bunch lengths, i.e. in the range of a few femtoseconds. This resolution is currently out of reach with time-domain diagnostics like RF-based deflectors, and approaches in the frequency-domain have to be considered to overcome this limitation. Our approach is to extract the information on the longitudinal bunch profile by means of infrared spectroscopy using a prism as dispersive element. In this paper, we present the design considerations on a broadband single-shot spectrometer in the near- and mid-infrared wavelength range (0.8 - 39.0 μm).

TUPD59

Suppression of Coherent Optical Transition Radiation in Transverse Beam Diagnostics by Utilising a Scintillation Screen with a Fast Gated CCD Camera

440

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

Micro-bunching instabilities in high-brightness beams of linac-driven FELs can lead to coherence effects in the emission of optical transition radiation (OTR) used for standard transverse profile diagnostics, thus rendering it impossible to observe a direct image of the particle beam. By using a scintillation screen in combination with a fast gated CCD camera, coherence effects can be suppressed as OTR is created in an instantaneous process while scintillation light has a certain decay time. In addition, the emission of the scintillation light is a statistical process from many atoms which is completely insensitive to the longitudinal bunch structure and does not produce coherence effects. Gating the camera during the passage of the electron bunch should eliminate any influence of the coherent OTR (COTR). First experiments using this method have been performed successfully at FLASH as a proof-of-principle. In this paper, we study the applicability of scintillation screens for high-energy electron beams under operation conditions for which COTR is emitted. Experimental results together with simulations are presented and discussed in view of COTR suppression and spatial resolution.