FEL2011 - List of Keywords (optics)

Paper	Title	Other Keywords	Page
TUPA18	Considerations about Optics-Based Phase-Space Measurements at Linac-Based FEL Facilities	quadrupole, lattice, emittance, diagnostics	231
	B. Beutner, E. Prat Paul Scherrer Institut, Villigen, Switzerland
	Transverse phase-space measurements are an essential issue for FEL facilities. After acceleration in the injector the energy is sufficiently high to bring the beam out of the space-charge dominated regime, thus optics based techniques are favored. The beam moments at a given point in the machine are fitted to beam size values downstream with different phase advances between the reconstruction and the measurement point. Two principle methods are possible. Beam sizes can be measured at different positions in the beam line keeping the lattice unchanged. The other possibility is to actively change quadrupoles and use only one screen. These two techniques are compared in this paper including monte-carlo studies on systematic errors using the SwissFEL Injector Test Facility as an example. On the other hand beam size measurements, which are done with OTR screens at SwissFEL Injector Test Facility, are critical for such measurements. An analysis of these images can be an issue, especially if the signal-to-noise is compromised for example by low bunch charges. This study on the phase-space measurement techniques will be completed by a discussion of the image post-processing procedures.

WEPA19	Report on the Redesign of the Fibre Link Stabilisation Units at FLASH	laser, controls, alignment, free-electron-laser	370
	M.K. Bock, M. Bousonville, M. Felber, P. Gessler, T. Lamb, H. Schlarb, B. Schmidt, S. Schulz DESY, Hamburg, Germany M. Kuntzsch HZDR, Dresden, Germany
	Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285) Recently, the fibre link stabilisation unit of the optical synchronisation system at FLASH has been subject to several design changes involving some major issues. Enhancements of the optical design have led to improvements in the efficiency of the free space optics and a new optical delay line allows for a more than two times longer adjustment range. The amplitude noise, encountered previously at the remote station of the links, was drastically decreased by a new beam splitting configuration. In future, this new link design will not only be used for the planned additional fibre links at FLASH, but it will also replace the already installed ones. In this paper we report on the changes of opto-mechanical design and we present first results from the recently commissioned links.

THPA02	Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane	emittance, electron, FEL, dipole	469
	R. Li, R.A. Legg, B. Terzić JLAB, Newport News, Virginia, USA J. Bisognano, R.A. Bosch UW-Madison/SRC, Madison, Wisconsin, USA
	Funding: This work was supported by U.S. DOE under Contract No. DE-AC05-06OR23177. The endeavor to reach higher brightness of electron bunches in the design of future FEL is seriously challenged by the CSR effect in magnetic bends. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the compression process, the behavior of the CSR interaction force will be influenced by the evolution of the 2D bunch distribution. Here we explore this 2D effect using semi-analytical and numerical study of the retarded potentials for an evolving 4D Gaussian phase space distribution with initial energy chirp. We will present results of our systematic exploration of this two-dimensional effect. We will display the interesting dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread around minimum bunch length, and show the comparison of these results with their 1D counterpart. Physical interpretation will also be discussed.

THPB01	Optical Comb and Interferometer Development for Laser Synchronization in Femtosecond FELs	laser, FEL, controls, feedback	561
	R.B. Wilcox, J.M. Byrd LBNL, Berkeley, California, USA R. Holzwarth Menlo Systems GmbH, Martinsried, Germany
	Funding: This work supported by the U.S. Department of Energy under contract DE-AC02-05CH11231 We describe a method of synchronizing lasers in FELs to potential sub-femtosecond precision using interferometry and optical clock techniques, and show supporting experimental results. This precision is needed for pump/probe experiments in ultrafast FELs. The proposed system consists of carrier/offset phase stabilized, pulsed lasers synchronized via a single optical frequency delivered over fiber, analogous to RF oscillators synchronized with a reference frequency, but at 200 to 400THz. Our tests of modelocked lasers, interferometers and stabilized CW lasers show that subsystems can perform to the required precision. We have synchronized fiber lasers to less than 10fs jitter using two different frequency comb line locking schemes, and demonstrated interferometers in a working FEL with less than 100as jitter over 150m fiber. Based on these tests and published work by others, we calculate the performance of an optimized, integrated timing system to be less than 1fs in the short term. Long term stability is maintained by feedback from X-ray/optical cross-correlation at the experiment.

THPB05	Modeling of the Beam Break Up Instability in Berlin Energy Recovery Linac Project	linac, cavity, HOM, solenoid	568
	Y. Petenev, A.V. Bondarenko, A.N. Matveenko HZB, Berlin, Germany
	Helmholtz-Zentrum Berlin officially started Jan. 2011 the design and construction of the Berlin Energy Recovery Linac Project BERLinPro. The initial goal of this compact ERL is to develop the ERL accelerator physics and technology required to accelerate a high-current low emittance beam. The conversion efficiency of an FEL is about 1% therefore superconducting ERL-based FEL machines look promising. One of the problems of superconducting ERL machines is the Beam Break Up (BBU) instability which limits the current. In this work the threshold current of the BBU instability was calculated for the BERLinPro. The comparison of two 100 MeV linacs based on different type of superconducting cavities is made. Different methods of BBU suppression are investigated (e.g. the influence of solenoid, pseudo-reflector and quadruple triplets in the linac structure on the BBU threshold).

THPB08	Study of Reflective Optics for LFC-Camera	electron, photon, gun, simulation	576
	K. Nanbu Tohoku University, School of Science, Sendai, Japan H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, Y. Tanaka Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003. A test accelerator for the terahertz source project (t-ACTS) employing isochronous ring and bunched free electron laser has been under development at Tohoku University [1,2]. Stable production of very short electron bunches is a key issue for the t-ACTS project. We have chosen thermionic RF gun for the injector of t-ACTS because of stability, multi-bunch operation and cheaper cost. The longitudinal phase space distribution of the beam extracted from the rf-gun is crucial for the final bunch length of electron beam passing through bunch compression process. Therefore, measurement of the longitudinal phase space of the beam is indispensable for efficient bunch compression. In order to measure the electron distribution in the longitudinal phase space of relatively lower energy beam, we have been developing a novel method to observe the energy spectrum employing a velocity dependence of opening angle of Cherenkov radiation, namely Linear Focal Cherenkov (LFC) ring camera. We describe principle of LFC camera and discuss relations between surface roughness of Cherenkov radiator and energy resolution in this conference. [1] H. Hama et al., New J. Phys. 8 (2006) 292, [2] H. Hama and M. Yasuda, Proc. of FEL2009, (2009) 394

THPB19	Investigations of OTR Polarization Effects in Beam-profile Monitors	polarization, radiation, electron, emittance	594
	A.H. Lumpkin, A.S. Johnson, J. Ruan, R.M. Thurman-Keup Fermilab, Batavia, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The characterization of transverse beam size using optical transition radiation (OTR) imaging is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is growing empirical evidence that the utilization of the polarization component orthogonal to the dimension of interest results in a smaller observed projected image profile. We have continued investigations of this phenomenon with a more controlled experiment where the linear polarizers are selectable in a filter wheel which also included a blank glass position to compensate for the optical path. The aperture for light collection is thus kept fixed compared to our previous tests. We also have balanced the digital camera gain to present similar signal levels to the data analysis program for both the total OTR and the polarized components. At the relatively low Lorentz factor (gamma) of 30, we observed 10-15% projected profile size reductions on a 65-micron beam size case with the perpendicularly polarized components. This anomalous effect in magnitude is compared to results from a standard OTR point-spread-function model.

Paper

Title

Other Keywords

Page

TUPA18

Considerations about Optics-Based Phase-Space Measurements at Linac-Based FEL Facilities

quadrupole, lattice, emittance, diagnostics

231

B. Beutner, E. Prat
Paul Scherrer Institut, Villigen, Switzerland

Transverse phase-space measurements are an essential issue for FEL facilities. After acceleration in the injector the energy is sufficiently high to bring the beam out of the space-charge dominated regime, thus optics based techniques are favored. The beam moments at a given point in the machine are fitted to beam size values downstream with different phase advances between the reconstruction and the measurement point. Two principle methods are possible. Beam sizes can be measured at different positions in the beam line keeping the lattice unchanged. The other possibility is to actively change quadrupoles and use only one screen. These two techniques are compared in this paper including monte-carlo studies on systematic errors using the SwissFEL Injector Test Facility as an example. On the other hand beam size measurements, which are done with OTR screens at SwissFEL Injector Test Facility, are critical for such measurements. An analysis of these images can be an issue, especially if the signal-to-noise is compromised for example by low bunch charges. This study on the phase-space measurement techniques will be completed by a discussion of the image post-processing procedures.

WEPA19

Report on the Redesign of the Fibre Link Stabilisation Units at FLASH

laser, controls, alignment, free-electron-laser

370

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

Funding: This work is partly supported by IRUVX-PP an EU co-funded project under FP7 (Grant Agreement 211285)
Recently, the fibre link stabilisation unit of the optical synchronisation system at FLASH has been subject to several design changes involving some major issues. Enhancements of the optical design have led to improvements in the efficiency of the free space optics and a new optical delay line allows for a more than two times longer adjustment range. The amplitude noise, encountered previously at the remote station of the links, was drastically decreased by a new beam splitting configuration. In future, this new link design will not only be used for the planned additional fibre links at FLASH, but it will also replace the already installed ones. In this paper we report on the changes of opto-mechanical design and we present first results from the recently commissioned links.

THPA02

Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane

emittance, electron, FEL, dipole

469

R. Li, R.A. Legg, B. Terzić
JLAB, Newport News, Virginia, USA
J. Bisognano, R.A. Bosch
UW-Madison/SRC, Madison, Wisconsin, USA

Funding: This work was supported by U.S. DOE under Contract No. DE-AC05-06OR23177.
The endeavor to reach higher brightness of electron bunches in the design of future FEL is seriously challenged by the CSR effect in magnetic bends. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the compression process, the behavior of the CSR interaction force will be influenced by the evolution of the 2D bunch distribution. Here we explore this 2D effect using semi-analytical and numerical study of the retarded potentials for an evolving 4D Gaussian phase space distribution with initial energy chirp. We will present results of our systematic exploration of this two-dimensional effect. We will display the interesting dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread around minimum bunch length, and show the comparison of these results with their 1D counterpart. Physical interpretation will also be discussed.

THPB01

Optical Comb and Interferometer Development for Laser Synchronization in Femtosecond FELs

laser, FEL, controls, feedback

561

R.B. Wilcox, J.M. Byrd
LBNL, Berkeley, California, USA
R. Holzwarth
Menlo Systems GmbH, Martinsried, Germany

Funding: This work supported by the U.S. Department of Energy under contract DE-AC02-05CH11231
We describe a method of synchronizing lasers in FELs to potential sub-femtosecond precision using interferometry and optical clock techniques, and show supporting experimental results. This precision is needed for pump/probe experiments in ultrafast FELs. The proposed system consists of carrier/offset phase stabilized, pulsed lasers synchronized via a single optical frequency delivered over fiber, analogous to RF oscillators synchronized with a reference frequency, but at 200 to 400THz. Our tests of modelocked lasers, interferometers and stabilized CW lasers show that subsystems can perform to the required precision. We have synchronized fiber lasers to less than 10fs jitter using two different frequency comb line locking schemes, and demonstrated interferometers in a working FEL with less than 100as jitter over 150m fiber. Based on these tests and published work by others, we calculate the performance of an optimized, integrated timing system to be less than 1fs in the short term. Long term stability is maintained by feedback from X-ray/optical cross-correlation at the experiment.

THPB05

Modeling of the Beam Break Up Instability in Berlin Energy Recovery Linac Project

linac, cavity, HOM, solenoid

568

Y. Petenev, A.V. Bondarenko, A.N. Matveenko
HZB, Berlin, Germany

Helmholtz-Zentrum Berlin officially started Jan. 2011 the design and construction of the Berlin Energy Recovery Linac Project BERLinPro. The initial goal of this compact ERL is to develop the ERL accelerator physics and technology required to accelerate a high-current low emittance beam. The conversion efficiency of an FEL is about 1% therefore superconducting ERL-based FEL machines look promising. One of the problems of superconducting ERL machines is the Beam Break Up (BBU) instability which limits the current. In this work the threshold current of the BBU instability was calculated for the BERLinPro. The comparison of two 100 MeV linacs based on different type of superconducting cavities is made. Different methods of BBU suppression are investigated (e.g. the influence of solenoid, pseudo-reflector and quadruple triplets in the linac structure on the BBU threshold).

THPB08

Study of Reflective Optics for LFC-Camera

electron, photon, gun, simulation

576

K. Nanbu
Tohoku University, School of Science, Sendai, Japan
H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, Y. Tanaka
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan

Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003.
A test accelerator for the terahertz source project (t-ACTS) employing isochronous ring and bunched free electron laser has been under development at Tohoku University [1,2]. Stable production of very short electron bunches is a key issue for the t-ACTS project. We have chosen thermionic RF gun for the injector of t-ACTS because of stability, multi-bunch operation and cheaper cost. The longitudinal phase space distribution of the beam extracted from the rf-gun is crucial for the final bunch length of electron beam passing through bunch compression process. Therefore, measurement of the longitudinal phase space of the beam is indispensable for efficient bunch compression. In order to measure the electron distribution in the longitudinal phase space of relatively lower energy beam, we have been developing a novel method to observe the energy spectrum employing a velocity dependence of opening angle of Cherenkov radiation, namely Linear Focal Cherenkov (LFC) ring camera. We describe principle of LFC camera and discuss relations between surface roughness of Cherenkov radiator and energy resolution in this conference.
[1] H. Hama et al., New J. Phys. 8 (2006) 292,
[2] H. Hama and M. Yasuda, Proc. of FEL2009, (2009) 394

THPB19

Investigations of OTR Polarization Effects in Beam-profile Monitors

polarization, radiation, electron, emittance

594

A.H. Lumpkin, A.S. Johnson, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The characterization of transverse beam size using optical transition radiation (OTR) imaging is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is growing empirical evidence that the utilization of the polarization component orthogonal to the dimension of interest results in a smaller observed projected image profile. We have continued investigations of this phenomenon with a more controlled experiment where the linear polarizers are selectable in a filter wheel which also included a blank glass position to compensate for the optical path. The aperture for light collection is thus kept fixed compared to our previous tests. We also have balanced the digital camera gain to present similar signal levels to the data analysis program for both the total OTR and the polarized components. At the relatively low Lorentz factor (gamma) of 30, we observed 10-15% projected profile size reductions on a 65-micron beam size case with the perpendicularly polarized components. This anomalous effect in magnitude is compared to results from a standard OTR point-spread-function model.