FEL2011 - Table of Session: WEPB (FEL Technology)

Paper	Title	Page
WEPB02	Study of Highly Isochronous Beamlines for FEL Seeding	391
	C. Sun, H. Nishimura, G. Penn, M.W. Reinsch, D. Robin, F. Sannibale, C. Steier, W. Wan LBNL, Berkeley, California, USA
	Recently seeding schemes, such as ECHO for short (nm) wavelength FELs, have been proposed. These schemes require that the nm level longitudinal bunch structure be preserved over distance of several meters. This poses a challenge for the beamline design. In this paper we present our studies of several solutions for beamlines that are nearly isochronous.

WEPB03	LCLS-II Undulator Tolerance Analysis	394
	H.-D. Nuhn, J. Wu SLAC, Menlo Park, California, USA S. Marks LBNL, Berkeley, California, USA
	Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515 The SLAC National Accelerator Laboratory is constructing the new FEL user facility LCLS-II, as a major upgrade to the Linear Coherent Light Source (LCLS). The upgrade will include two new Free Electron Lasers, to generate soft (SXR) and hard X-ray (HXR) SASE FEL radiation, based on planar, variable gap hybrid undulators with two different undulator periods (SXR 55 mm, HXR 32 mm). An systematic FEL tolerance analysis for the undulator lines, including tuning, alignment, yaw deformation, and phase correction tolerances has been performed. The methods and results are presented in this work.

WEPB04	Position Stability Monitoring of the LCLS Undulator Quadrupoles	398
	H.-D. Nuhn, G.L. Gassner, F. Peters SLAC, Menlo Park, California, USA
	Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515 In the era of SASE FELs, the demand for position stability of undulator components scales down to the range of sub-micrometers per day. Simultaneously, the undulator length increases significantly, in order to reach X-ray wavelengths. To minimize the impact of the outside environment, the LCLS undulator is placed underground, but reliable data about ground motion inside such a tunnel were not available in the required stability range. Therefore, a new position monitor system has been developed and installed for the LCLS undulator. That system is capable to measure X-, Y- and Roll positions of each of the 33 undulator quadrupoles, with respect to stretched wires. Instrument resolution is about 20 nm and instrument drift is negligible small. Position data of individual quadrupoles can be correlated along the entire undulator, which has a length of 132 m. The system is under continuous operation since 2009. The report describes long term experience with the running system and the observed position stability of the undulator quadrupoles.

WEPB05	Experiments on Femtosecond Stabilization of Fiber Link for Shanghai Soft-XFEL	402
	X.P. Ma IHEP, Beijing, People's Republic of China B. Liu SINAP, Shanghai, People's Republic of China
	The Shanghai Soft X-ray Free Electron Laser (SXFEL) facility will be constructed in the Shanghai Synchrotron Radiation Facility (SSRF) campus. SXFEL will operate in the HGHG and/or EEHG mode and require a femtosecond timing distribution system as well as the synchronization between femtosecond pulsed lasers, femtosecond pulsed X-rays, CW microwave signals and electron bunches with 10 fs precision. The pulsed fiber laser based femtosecond T&S system which has been proposed by the MIT/DESY team is adopted. In this paper the status of the femtosecond T&S system for SXFEL is introduced. Some initial progress of the phase stabilization by electronics control when laser pulses transport though long optical fibers is presented.

WEPB14	Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflector	405
	C. Behrens DESY, Hamburg, Germany Y.T. Ding, P. Emma, J.C. Frisch, Z. Huang, P. Krejcik, H. Loos, M.-H. Wang SLAC, Menlo Park, California, USA
	The measurement of ultra-short electron bunches on the femtosecond time scale constitutes a very challenging problem. In X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of sub-ten femtosecond X-ray pulses is possible, and some efforts have been put into both ultra-short electron and X-ray beam diagnostics. Here we propose a single-shot method using a transverse deflector (X-band) after the undulator to reconstruct both the electron bunch and X-ray temporal profiles. Simulation studies show that about 1 fs (rms) time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and pulse lengths. The jitter, resolution and other related issues will be discussed.

WEPB15	Reversible Electron Beam Heater for Suppression of Microbunching Instabilities Based on Transverse Deflecting Cavities	409
	C. Behrens DESY, Hamburg, Germany Z. Huang, D. Xiang SLAC, Menlo Park, California, USA
	The presence of the microbunching instability due to the compression of high-brightness electron beams at existing and future X-ray free-electron lasers (FEL) results in restrictions on the attainable lasing performance and renders diagnostics like beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e. heating the beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of seeded FELs. In this paper, we present a reversible electron beam heating system based on two transverse deflecting cavities (TCAV) in front and behind a bunch compressor chicane. The additional energy spread will be introduced in the first TCAV, which suppresses the microbunching instability, and then will be eliminated in the second TCAV. We show the feasibility of the suppression of microbunching instabilities based on calculations and simulations, and set limits to the acceptable jitter tolerances.

WEPB16	Study for Evaluation of Undulator Magnetic Field Using Vibrating Wire Method	413
	Y. Tanaka Tohoku University, School of Science, Sendai, Japan H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	A test accelerator for a terahertz source project (t-ACTS) has been progressed at the Electron Light Science Centre, Tohoku University, in which a generation of intense coherent terahertz radiation from the very short electron bunch will be demonstrated. A narrow-band coherent terahertz radiation using an undulator has been considered to be implemented. We have constructed a planer undulator that is basically a Halbach type composed of permanent magnet blocks. The period length of the undulator and the number of periods are 100 mm and 25, respectively. The vibrating wire method is studied to measure the periodic magnetic field of the undulator. A thin copper-beryllium wire is placed on beam axis in the undulator, and an AC current flow is applied in the wire. By measuring amplitudes and phases of standing waves excited on the wire by the Lorentz force between AC current and magnetic field, we can reconstruct the magnetic field distribution along the wire. We discuss relations between reproducibility of the undulator field and the mode harmonics number used for the reconstruction. The results of preliminary measurement using the vibrating wire will be shown in this conference.

WEPB17	Evaluation of Lasing Range with a 1.8 m Undulator in KU-FEL	417
	K. Ishida, M. A. Bakr, Y.W. Choi, H. Imon, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	In KU-FEL (Kyoto University FEL) 12-14 μm FEL has been available by using a 40 MeV S-bend linac and 1.6 m undulator. We are going to install 1.8 m undulator which was used in JAEA to extend the lasing range of KU-FEL. Numerical evaluation of the lasing range has been carried out by using GENESIS1.3. However, this work used an ideal undulator field data which was measured by JAEA in several years before. Therefore we re-measured the undulator field for different gaps. Then we evaluated the FEL gain and possible lasing range with 1.8 m undulator using measured undulator field. The undulator field measurement, FEL gain calculations and evaluation of lasing range in KU-FEL will be presented in the conference.

WEPB18	Development of the First U48 Undulator Prototype for the European X-ray Free Electron Laser	420
	H.H. Lu, W. Chen, X. Feng, X.M. Jiang, C. Shi, S.C. Sun, M.T. Wang, Z.X. Wang, Y.F. Yang IHEP, Beijing, People's Republic of China Y. Li, J. Pflüger European XFEL GmbH, Hamburg, Germany
	Funding: MOST973 Program The European XFEL will be a user facility consisting of three beamlines named SASE1/2/3 at the first stage. The first undulator prototype U48 for the European XFEL SASE2 beamline has been developed and tested by IHEP, China. Its magnetic design and specifications are briefly given. Development of U48, including magnetic material, mechanical structure, control system and assembly, are introduced. Magnetic tuning and test results are presented and discussed.

WEPB19	Enhancement of Undulator Field in Bulk HTSC Staggered Array Undulator with Hybrid Configuration	424
	R. Kinjo, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, K. Komai, K. Masuda, K. Nagasaki, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	Funding: This work was supported by the Grant-in-Aid for Scientific Research B and JSPS Fellows by the Ministry of Education, Culture, Sports, Science and Technology of Japan The purpose of this study is enhancement of the undulator field and it's stability in bulk high temperature superconductor staggered array undulator by introducing hybrid configuration. The authors made the magnetic field calculations with some hybrid configurations consists of bulk HTSCs, ferromagnetic pieces and permanent magnets. We also made prototype measurements. The results shows the hybrid configuration can generates stronger and more uniform magnetic field than bulk-HTSCs-only configuration. In this conference, numerical and experimental results of the hybrid configuration will be presented.

WEPB20	The Design Of A Multi-Beam Electron Gun For A Photonic Free-Electron Laser	427
	J.H.H. Lee, K.-J. Boller, T. Denis, P.J.M. van der Slot Mesa+, Enschede, The Netherlands
	Funding: This research is supported by the Dutch Technology Foundation STW, applied science division of NWO and the Technology Program of the Ministry of Economic Affairs. The photonic Free-Electron Laser (pFEL) is a novel slow-wave device which relies on a photonic crystal (PhC) to synchronize the Cherenkov electromagnetic radiation generated from the co-propagating electron beams. The advantage of pFEL is in its frequency- and power-scaling properties. The scale invariance of Maxwell’s equations allows the use of the same beam energy to operate at higher frequencies when the PhC is correspondingly scaled. On the other hand, power-scaling is achieved by varying the number of electron beams propagating in parallel through the PhC. To produce a set of parallel beams, we have designed a multi-beam electron gun using flat cathodes, which produces a total current of 1 A at a beam voltage of 14 kV. We will present the design of this gun together with the expected performance. In addition, we have investigated the beam transport system and will discuss the options for guiding the beams through the PhC.

WEPB22	An Optical Streaking Method for Measuring Femtosecond Electron Bunches	431
	Y.T. Ding, K.L.F. Bane, Z. Huang SLAC, Menlo Park, California, USA
	The measurement of the ultra-short electron bunch on the femotosecond time scale constitutes a very challenging problem. In the X-ray free electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of a sub-ten femtoseconds electron beam at low charge operation mode is possible, based on indirect measurements and computer simulations. Direct measurements are not available due to the resolution limit of the present diagnostics. We propose a new method based on the energy modulation of the ultra-short electron bunch by interacting with an optical laser in a short wiggler. Compared with a laser-based transverse deflector, which requires the laser wavelength much longer than the electron bunch length, here we propose a scheme to use a laser with its wavelength shorter than the electron bunch length, where the slope on the laser intensity envelope has been used to help distinguish the different periods. The calibration is simple and it is possible to reconstruct the bunch longitudinal profile from a single shot measurement.

Paper

Title

Page

Study of Highly Isochronous Beamlines for FEL Seeding

391

C. Sun, H. Nishimura, G. Penn, M.W. Reinsch, D. Robin, F. Sannibale, C. Steier, W. Wan
LBNL, Berkeley, California, USA

Recently seeding schemes, such as ECHO for short (nm) wavelength FELs, have been proposed. These schemes require that the nm level longitudinal bunch structure be preserved over distance of several meters. This poses a challenge for the beamline design. In this paper we present our studies of several solutions for beamlines that are nearly isochronous.

WEPB03

LCLS-II Undulator Tolerance Analysis

394

H.-D. Nuhn, J. Wu
SLAC, Menlo Park, California, USA
S. Marks
LBNL, Berkeley, California, USA

Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
The SLAC National Accelerator Laboratory is constructing the new FEL user facility LCLS-II, as a major upgrade to the Linear Coherent Light Source (LCLS). The upgrade will include two new Free Electron Lasers, to generate soft (SXR) and hard X-ray (HXR) SASE FEL radiation, based on planar, variable gap hybrid undulators with two different undulator periods (SXR 55 mm, HXR 32 mm). An systematic FEL tolerance analysis for the undulator lines, including tuning, alignment, yaw deformation, and phase correction tolerances has been performed. The methods and results are presented in this work.

WEPB04

Position Stability Monitoring of the LCLS Undulator Quadrupoles

398

H.-D. Nuhn, G.L. Gassner, F. Peters
SLAC, Menlo Park, California, USA

Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
In the era of SASE FELs, the demand for position stability of undulator components scales down to the range of sub-micrometers per day. Simultaneously, the undulator length increases significantly, in order to reach X-ray wavelengths. To minimize the impact of the outside environment, the LCLS undulator is placed underground, but reliable data about ground motion inside such a tunnel were not available in the required stability range. Therefore, a new position monitor system has been developed and installed for the LCLS undulator. That system is capable to measure X-, Y- and Roll positions of each of the 33 undulator quadrupoles, with respect to stretched wires. Instrument resolution is about 20 nm and instrument drift is negligible small. Position data of individual quadrupoles can be correlated along the entire undulator, which has a length of 132 m. The system is under continuous operation since 2009. The report describes long term experience with the running system and the observed position stability of the undulator quadrupoles.

WEPB05

Experiments on Femtosecond Stabilization of Fiber Link for Shanghai Soft-XFEL

402

X.P. Ma
IHEP, Beijing, People's Republic of China
B. Liu
SINAP, Shanghai, People's Republic of China

The Shanghai Soft X-ray Free Electron Laser (SXFEL) facility will be constructed in the Shanghai Synchrotron Radiation Facility (SSRF) campus. SXFEL will operate in the HGHG and/or EEHG mode and require a femtosecond timing distribution system as well as the synchronization between femtosecond pulsed lasers, femtosecond pulsed X-rays, CW microwave signals and electron bunches with 10 fs precision. The pulsed fiber laser based femtosecond T&S system which has been proposed by the MIT/DESY team is adopted. In this paper the status of the femtosecond T&S system for SXFEL is introduced. Some initial progress of the phase stabilization by electronics control when laser pulses transport though long optical fibers is presented.

WEPB14

Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflector

405

C. Behrens
DESY, Hamburg, Germany
Y.T. Ding, P. Emma, J.C. Frisch, Z. Huang, P. Krejcik, H. Loos, M.-H. Wang
SLAC, Menlo Park, California, USA

The measurement of ultra-short electron bunches on the femtosecond time scale constitutes a very challenging problem. In X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of sub-ten femtosecond X-ray pulses is possible, and some efforts have been put into both ultra-short electron and X-ray beam diagnostics. Here we propose a single-shot method using a transverse deflector (X-band) after the undulator to reconstruct both the electron bunch and X-ray temporal profiles. Simulation studies show that about 1 fs (rms) time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and pulse lengths. The jitter, resolution and other related issues will be discussed.

WEPB15

Reversible Electron Beam Heater for Suppression of Microbunching Instabilities Based on Transverse Deflecting Cavities

409

C. Behrens
DESY, Hamburg, Germany
Z. Huang, D. Xiang
SLAC, Menlo Park, California, USA

The presence of the microbunching instability due to the compression of high-brightness electron beams at existing and future X-ray free-electron lasers (FEL) results in restrictions on the attainable lasing performance and renders diagnostics like beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e. heating the beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of seeded FELs. In this paper, we present a reversible electron beam heating system based on two transverse deflecting cavities (TCAV) in front and behind a bunch compressor chicane. The additional energy spread will be introduced in the first TCAV, which suppresses the microbunching instability, and then will be eliminated in the second TCAV. We show the feasibility of the suppression of microbunching instabilities based on calculations and simulations, and set limits to the acceptable jitter tolerances.

WEPB16

Study for Evaluation of Undulator Magnetic Field Using Vibrating Wire Method

413

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

A test accelerator for a terahertz source project (t-ACTS) has been progressed at the Electron Light Science Centre, Tohoku University, in which a generation of intense coherent terahertz radiation from the very short electron bunch will be demonstrated. A narrow-band coherent terahertz radiation using an undulator has been considered to be implemented. We have constructed a planer undulator that is basically a Halbach type composed of permanent magnet blocks. The period length of the undulator and the number of periods are 100 mm and 25, respectively. The vibrating wire method is studied to measure the periodic magnetic field of the undulator. A thin copper-beryllium wire is placed on beam axis in the undulator, and an AC current flow is applied in the wire. By measuring amplitudes and phases of standing waves excited on the wire by the Lorentz force between AC current and magnetic field, we can reconstruct the magnetic field distribution along the wire. We discuss relations between reproducibility of the undulator field and the mode harmonics number used for the reconstruction. The results of preliminary measurement using the vibrating wire will be shown in this conference.

WEPB17

Evaluation of Lasing Range with a 1.8 m Undulator in KU-FEL

417

K. Ishida, M. A. Bakr, Y.W. Choi, H. Imon, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

In KU-FEL (Kyoto University FEL) 12-14 μm FEL has been available by using a 40 MeV S-bend linac and 1.6 m undulator. We are going to install 1.8 m undulator which was used in JAEA to extend the lasing range of KU-FEL. Numerical evaluation of the lasing range has been carried out by using GENESIS1.3. However, this work used an ideal undulator field data which was measured by JAEA in several years before. Therefore we re-measured the undulator field for different gaps. Then we evaluated the FEL gain and possible lasing range with 1.8 m undulator using measured undulator field. The undulator field measurement, FEL gain calculations and evaluation of lasing range in KU-FEL will be presented in the conference.

WEPB18

Development of the First U48 Undulator Prototype for the European X-ray Free Electron Laser

420

H.H. Lu, W. Chen, X. Feng, X.M. Jiang, C. Shi, S.C. Sun, M.T. Wang, Z.X. Wang, Y.F. Yang
IHEP, Beijing, People's Republic of China
Y. Li, J. Pflüger
European XFEL GmbH, Hamburg, Germany

Funding: MOST973 Program
The European XFEL will be a user facility consisting of three beamlines named SASE1/2/3 at the first stage. The first undulator prototype U48 for the European XFEL SASE2 beamline has been developed and tested by IHEP, China. Its magnetic design and specifications are briefly given. Development of U48, including magnetic material, mechanical structure, control system and assembly, are introduced. Magnetic tuning and test results are presented and discussed.

WEPB19

Enhancement of Undulator Field in Bulk HTSC Staggered Array Undulator with Hybrid Configuration

424

R. Kinjo, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, K. Komai, K. Masuda, K. Nagasaki, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

Funding: This work was supported by the Grant-in-Aid for Scientific Research B and JSPS Fellows by the Ministry of Education, Culture, Sports, Science and Technology of Japan
The purpose of this study is enhancement of the undulator field and it's stability in bulk high temperature superconductor staggered array undulator by introducing hybrid configuration. The authors made the magnetic field calculations with some hybrid configurations consists of bulk HTSCs, ferromagnetic pieces and permanent magnets. We also made prototype measurements. The results shows the hybrid configuration can generates stronger and more uniform magnetic field than bulk-HTSCs-only configuration. In this conference, numerical and experimental results of the hybrid configuration will be presented.

WEPB20

The Design Of A Multi-Beam Electron Gun For A Photonic Free-Electron Laser

427

J.H.H. Lee, K.-J. Boller, T. Denis, P.J.M. van der Slot
Mesa+, Enschede, The Netherlands

Funding: This research is supported by the Dutch Technology Foundation STW, applied science division of NWO and the Technology Program of the Ministry of Economic Affairs.
The photonic Free-Electron Laser (pFEL) is a novel slow-wave device which relies on a photonic crystal (PhC) to synchronize the Cherenkov electromagnetic radiation generated from the co-propagating electron beams. The advantage of pFEL is in its frequency- and power-scaling properties. The scale invariance of Maxwell’s equations allows the use of the same beam energy to operate at higher frequencies when the PhC is correspondingly scaled. On the other hand, power-scaling is achieved by varying the number of electron beams propagating in parallel through the PhC. To produce a set of parallel beams, we have designed a multi-beam electron gun using flat cathodes, which produces a total current of 1 A at a beam voltage of 14 kV. We will present the design of this gun together with the expected performance. In addition, we have investigated the beam transport system and will discuss the options for guiding the beams through the PhC.

WEPB22

An Optical Streaking Method for Measuring Femtosecond Electron Bunches

431

Y.T. Ding, K.L.F. Bane, Z. Huang
SLAC, Menlo Park, California, USA

The measurement of the ultra-short electron bunch on the femotosecond time scale constitutes a very challenging problem. In the X-ray free electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of a sub-ten femtoseconds electron beam at low charge operation mode is possible, based on indirect measurements and computer simulations. Direct measurements are not available due to the resolution limit of the present diagnostics. We propose a new method based on the energy modulation of the ultra-short electron bunch by interacting with an optical laser in a short wiggler. Compared with a laser-based transverse deflector, which requires the laser wavelength much longer than the electron bunch length, here we propose a scheme to use a laser with its wavelength shorter than the electron bunch length, where the slope on the laser intensity envelope has been used to help distinguish the different periods. The calibration is simple and it is possible to reconstruct the bunch longitudinal profile from a single shot measurement.