DIPAC2011 - List of Authors (Schmidt, B.)

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]

TUPD28

Benchmarking the Performance of the Present Bunch Arrival Time Monitors at FLASH

365

M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz
DESY, Hamburg, Germany

Funding: This work is partly supported by IRUVX-PP, an EU co-funded project under FP7 (Grant Agreement 211285)
Presently, at FLASH four bunch arrival time monitors (BAM) are installed and in permanent operation. Moreover, they are incorporated in a longitudinal intra-bunch train feedback. In this paper, we present a review of the performance and the limitations of the current BAM design, based on the most recent machine studies. The detection principle of the monitor implements the electro-optical modulation of synchronised laser pulses. The RF and electro-optical front-ends are designed to be operated in a frequency band from DC up to 10 GHz. This allows for measuring the arrival time of each individual electron bunch at femtosecond resolution. The current design of the BAMs has been tested under the influence of disturbances on the arrival time measurement, such as variation of the bunch charge as well as deviation from the reference transverse bunch position. Those results will be incorporated in an upcoming design revision to upgrade the application and robustness of the BAMs.

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.

TUPD35

Development of an Alternative, Photodiode-Based, Femtosecond Stable Detection Principle for the Link Stabilization in the Optical Synchronization Systems at FLASH and XFEL

380

T. Lamb, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz
DESY, Hamburg, Germany

Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285).
The fs-stable timing information in the optical synchronization system at FLASH and the upcoming European XFEL is based on the distribution of laser pulses in optical fibers. The optical length of the fibers is continuously monitored and drifts in signal propagation time are actively compensated in order to provide a phase stable pulse train at the end of the fiber link. At present, optical cross-correlation is used to measure the optical length changes. To overcome some of the disadvantages of the current scheme, a different approach for the detection of the optical fiber link length variation was developed. This new scheme uses 10GHz photodiodes to measure the amplitude modulation of harmonics created by overlapping two pulse trains. The long-term stability of the prototype of this detector over 33h was demonstrated to be below 5fs (peak-to-peak) with a rms jitter of about 0.86fs. The detection principle itself is practically insensitive to environmental influences and needs only about 10% of the optical power, compared to the optical cross-correlator.

TUPD36

Progress and Status of the Laser-based Synchronization System at FLASH

383

S. Schulz, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt
DESY, Hamburg, Germany

Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285).
The free-electron lasers FLASH and European XFEL demand a high timing accuracy between the electron bunches and external laser systems for both exploitation of the short VUV and X-ray pulses in time-resolved pump-probe experiments and seeded operation modes. The required precision can only be achieved with laser-based synchronization schemes. The prototype system installed at FLASH is continuously evolving and subject to improvements. In this paper, we give an overview on the present status, report on the latest developments and extensions, and discuss future challenges. Particularly, the recent move to a new type of master laser oscillator led to a significant enhancement of the robustness and reliability. Consequently, research can focus on the implementation of the electron bunch arrival time feedback, new technologies for timing distribution and integration of Ti:sapphire lasers into the optical synchronization system.

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.

WEOA01

Summary of COTR Effects

539

S. Wesch, B. Schmidt
DESY, Hamburg, Germany

Coherent transition radiation in the visible regime (COTR) has become a serious issue in FEL - Linacs disturbing the measurement of beam profiles by OTR screens up to a level, where this diagnostics becomes totally impossible. The talk will summarize the measured COTR effects from LCLS, FLASH and other machines and the investigations done so far into the dependence of the effect on beam and machine parameters. The status of the theoretical background and understanding of its origin will be discussed as well as proposals and experiences with possible remedies.

Slides WEOA01 [2.520 MB]

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]

TUPD28	Benchmarking the Performance of the Present Bunch Arrival Time Monitors at FLASH	365
	M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz DESY, Hamburg, Germany
	Funding: This work is partly supported by IRUVX-PP, an EU co-funded project under FP7 (Grant Agreement 211285) Presently, at FLASH four bunch arrival time monitors (BAM) are installed and in permanent operation. Moreover, they are incorporated in a longitudinal intra-bunch train feedback. In this paper, we present a review of the performance and the limitations of the current BAM design, based on the most recent machine studies. The detection principle of the monitor implements the electro-optical modulation of synchronised laser pulses. The RF and electro-optical front-ends are designed to be operated in a frequency band from DC up to 10 GHz. This allows for measuring the arrival time of each individual electron bunch at femtosecond resolution. The current design of the BAMs has been tested under the influence of disturbances on the arrival time measurement, such as variation of the bunch charge as well as deviation from the reference transverse bunch position. Those results will be incorporated in an upcoming design revision to upgrade the application and robustness of the BAMs.

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.

TUPD35	Development of an Alternative, Photodiode-Based, Femtosecond Stable Detection Principle for the Link Stabilization in the Optical Synchronization Systems at FLASH and XFEL	380
	T. Lamb, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz DESY, Hamburg, Germany
	Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285). The fs-stable timing information in the optical synchronization system at FLASH and the upcoming European XFEL is based on the distribution of laser pulses in optical fibers. The optical length of the fibers is continuously monitored and drifts in signal propagation time are actively compensated in order to provide a phase stable pulse train at the end of the fiber link. At present, optical cross-correlation is used to measure the optical length changes. To overcome some of the disadvantages of the current scheme, a different approach for the detection of the optical fiber link length variation was developed. This new scheme uses 10GHz photodiodes to measure the amplitude modulation of harmonics created by overlapping two pulse trains. The long-term stability of the prototype of this detector over 33h was demonstrated to be below 5fs (peak-to-peak) with a rms jitter of about 0.86fs. The detection principle itself is practically insensitive to environmental influences and needs only about 10% of the optical power, compared to the optical cross-correlator.

TUPD36	Progress and Status of the Laser-based Synchronization System at FLASH	383
	S. Schulz, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt DESY, Hamburg, Germany
	Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285). The free-electron lasers FLASH and European XFEL demand a high timing accuracy between the electron bunches and external laser systems for both exploitation of the short VUV and X-ray pulses in time-resolved pump-probe experiments and seeded operation modes. The required precision can only be achieved with laser-based synchronization schemes. The prototype system installed at FLASH is continuously evolving and subject to improvements. In this paper, we give an overview on the present status, report on the latest developments and extensions, and discuss future challenges. Particularly, the recent move to a new type of master laser oscillator led to a significant enhancement of the robustness and reliability. Consequently, research can focus on the implementation of the electron bunch arrival time feedback, new technologies for timing distribution and integration of Ti:sapphire lasers into the optical synchronization system.

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.

WEOA01	Summary of COTR Effects	539
	S. Wesch, B. Schmidt DESY, Hamburg, Germany
	Coherent transition radiation in the visible regime (COTR) has become a serious issue in FEL - Linacs disturbing the measurement of beam profiles by OTR screens up to a level, where this diagnostics becomes totally impossible. The talk will summarize the measured COTR effects from LCLS, FLASH and other machines and the investigations done so far into the dependence of the effect on beam and machine parameters. The status of the theoretical background and understanding of its origin will be discussed as well as proposals and experiences with possible remedies.
	Slides WEOA01 [2.520 MB]