DIPAC2011 - List of Authors (Gerth, C.)

Paper

Title

Page

1-MHz Line Detector for Intra-bunch-train Multichannel Feedback

137

L. Kotynia, D.R. Makowski, A. Mielczarek, A. Napieralski
TUL-DMCS, Łódź, Poland
C. Gerth, T. Jezynski, H. Schlarb, B. Schmidt, B. Steffen
DESY, Hamburg, Germany

Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285).
The measurement and control of the electron bunch length is one of the key diagnostics in linac-based free-electron lasers to reach the required peak current in the electron bunches. In order to use the multi-channel signals from longitudinal bunch shape measurements for intra train feedback for the European XFEL, line readout rates in the MHz range and low latencies are required, which is far more than commercial multichannel radiation detectors (line cameras) can provide. The paper presents a 256 channel detector that allows analyzing optical or infrared radiation with 1 MHz rate and a few microseconds latency using photodiode arrays, as needed for synchrotron light monitors, electro-optical bunch length measurements, or other laser based diagnostics. The proposed architecture aims at high frequency readout with low latency by using a multichannel electronic front-end designed for HEP, combined with Si or InGaAs detector arrays with very fast response time, and a low-latency data acquisition system. Currently the device is at the conceptual design stage.

Poster MOPD38 [3.262 MB]

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.

TUPD32

THz Radiation Diagnostics for Monitoring the Bunch Compression at the SwissFEL Injector Test Facility

374

C. Gerth, B. Schmidt, S. Wesch
DESY, Hamburg, Germany
R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott
PSI, Villigen, Switzerland

At the SwissFEL Injector Test Facility, installation of a magnetic chicane for longitudinal bunch compression is foreseen for the first half of 2011. Bunch compression will be accomplished by operating two S-band accelerating structures on-crest and two S-band structures at off-crest RF phases. An X-band structure for the linearization of the longitudinal phase space will be installed at a later stage. The detection of coherent synchrotron radiation or coherent diffraction radiation in the THz range can be used to monitor the bunch compression process and stabilize the RF phases by a beam-based feedback. In this paper, we study the source characteristics of the edge radiation emitted at the 4th dipole of the bunch compressor as well as the diffraction radiation generated by a metallic foil with a hole. Particle tracking simulations were used to model the bunch compression process for different operation modes. The performance of a bunch compression monitor consisting of focusing mirrors and band pass filters has been evaluated by simulating the THz radiation transport of the optical components.

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
MOPD38	1-MHz Line Detector for Intra-bunch-train Multichannel Feedback	137
	L. Kotynia, D.R. Makowski, A. Mielczarek, A. Napieralski TUL-DMCS, Łódź, Poland C. Gerth, T. Jezynski, H. Schlarb, B. Schmidt, B. Steffen DESY, Hamburg, Germany
	Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285). The measurement and control of the electron bunch length is one of the key diagnostics in linac-based free-electron lasers to reach the required peak current in the electron bunches. In order to use the multi-channel signals from longitudinal bunch shape measurements for intra train feedback for the European XFEL, line readout rates in the MHz range and low latencies are required, which is far more than commercial multichannel radiation detectors (line cameras) can provide. The paper presents a 256 channel detector that allows analyzing optical or infrared radiation with 1 MHz rate and a few microseconds latency using photodiode arrays, as needed for synchrotron light monitors, electro-optical bunch length measurements, or other laser based diagnostics. The proposed architecture aims at high frequency readout with low latency by using a multichannel electronic front-end designed for HEP, combined with Si or InGaAs detector arrays with very fast response time, and a low-latency data acquisition system. Currently the device is at the conceptual design stage.
	Poster MOPD38 [3.262 MB]

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.

TUPD32	THz Radiation Diagnostics for Monitoring the Bunch Compression at the SwissFEL Injector Test Facility	374
	C. Gerth, B. Schmidt, S. Wesch DESY, Hamburg, Germany R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott PSI, Villigen, Switzerland
	At the SwissFEL Injector Test Facility, installation of a magnetic chicane for longitudinal bunch compression is foreseen for the first half of 2011. Bunch compression will be accomplished by operating two S-band accelerating structures on-crest and two S-band structures at off-crest RF phases. An X-band structure for the linearization of the longitudinal phase space will be installed at a later stage. The detection of coherent synchrotron radiation or coherent diffraction radiation in the THz range can be used to monitor the bunch compression process and stabilize the RF phases by a beam-based feedback. In this paper, we study the source characteristics of the edge radiation emitted at the 4th dipole of the bunch compressor as well as the diffraction radiation generated by a metallic foil with a hole. Particle tracking simulations were used to model the bunch compression process for different operation modes. The performance of a bunch compression monitor consisting of focusing mirrors and band pass filters has been evaluated by simulating the THz radiation transport of the optical components.

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.