DIPAC2011 - List of Authors (Wesch, S.)

Paper

Title

Page

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.

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
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.

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]