FEL2011 - List of Keywords (photon)

Paper	Title	Other Keywords	Page
MOPB28	Gas-filled Cell as a Narrow Bandwidth Bandpass Filter in the VUV Wavelength Range	radiation, FEL, resonance, simulation	73
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	We propose a method for spectrally filtering radiation in the VUV wavelength range by means of a monochromator constituted by a cell filled with a resonantly absorbing rare gas. Around particular wavelengths, the gas exhibits narrow-bandwidth absorbing resonances following the Fano profile. Within the photon energy range 60-65 eV, the correlation index of the Fano profiles for the photo-ionization spectra in He is equal to unity, meaning that the minimum of the cross-section is exactly zero. For sufficiently large column density in the gas cell, the spectrum of the incoming radiation will be attenuated by the background cross-section of many orders of magnitude, except for those wavelengths close to the point where the cross-section is zero. Remarkable advantages of a gas monochromator based on this principle are simplicity, efficiency and narrow-bandwidth. A gas monochromator installed in the experimental hall of a VUV SASE FEL facility would enable the delivery of a single-mode VUV laser beam. The design is identical to that of existing gas attenuator systems for VUV or X-ray FELs. We present feasibility study and exemplifications for the FLASH facility in the VUV regime.

MOPB32	System Trade Analysis for an FEL Facility	FEL, undulator, linac, emittance	89
	M.W. Reinsch, B. Austin, J.N. Corlett, L.R. Doolittle, G. Penn, D. Prosnitz, J. Qiang, A. Sessler, M. Venturini, J.S. Wurtele LBNL, Berkeley, California, USA
	Designing an FEL from scratch requires the design team to balance multiple science needs, FEL and accelerator physics constraints and engineering limitations. STAFF (System Trade Analysis for an FEL Facility) enables the user to rapidly explore a large range of Linac and FEL design options. The model utilzes analytical models such as the Ming Xie formulas when appropriate and look-up tables when necessary to maintain speed, flexibility and extensiblity. STAFF allows for physics models for FEL harmonics, wake fields, cavity higher-order modes and aspects of linac particle dynamics. The code will permit the user to study error tolerances and multiple beamlines so as to explore the full capabilities of an entire user facility. This makes it possible to optimize the integrated system in terms of performance metrics such as photons/pulse, photons/sec and tunability range while ensuring that unrealistic requirements are not put on either the electron beam quality, undulator field/gap requirements or other system elements. This paper will describe preliminary results from STAFF as applied to a CW FEL soft X-ray facility.

MOPC13	Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation	electron, radiation, linac, vacuum	125
	N. Sei AIST, Tsukuba, Ibaraki, Japan T. Takahashi Kyoto University, Research Reactor Institute, Osaka, Japan
	Funding: This study was financially supported by the Sumitomo foundation. We have studied a terahertz-wave spectrophotometry by using Compton backscattering of coherent radiations at the Kyoto University Research Reactor Institute. In the terahertz-wave spectrophotometry, the characteristics of the continuous-spectrum THz waves are converted into those of the other wavelengths which are easily measured by colliding the THz waves with a relativistic electron beam. Such the continuous-spectrum light beam by Compton backscattering is known in a field of astrophysics. We achieved to observe a continuous-spectrum visible beam resulting from Compton backscattering using coherent transition radiations from an L-band electron linear accelerator. The measured spectrum of the Compton backscattered photons was similar to that calculated from the spectrum of coherent transition radiation. In the presentation, the experimental results of terahertz-wave spectrophotometry will be explained in detail. N. Sei and T. Takahashi, Appl. Phys. Express 3 (2010) 052401.

TUPA02	Development of Material Analysis Facility in KU-FEL	FEL, laser, lattice, electron	190
	K. Yoshida, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	A mid infrared-free electron laser (MIR-FEL) (5-20 μm) facility (KU-FEL: Kyoto University Free Electron Laser) has been constructed for contributing to researches on energy science at Institute of Advanced Energy, Kyoto University. Up to now 12-14 μm FEL beam has been generated. When MIR-FEL with the wavelength matched to the molecular vibration mode is irradiated to the material, a particular chemical bond in the material will be selectively excited, or dissociated [1]. The selective photochemical reaction can be applied for surface modification and the evaluation of material in biochemistry, chemistry, and solid physics. Therefore, material analysis facility in combination with MIR-FEL is constructed. In the material analysis facility, advanced analysis systems such as photoluminescence measurement system, photoelectron spectroscopy, super centrifuge and high performance liquids chromatography, ICP emission spectroscopy, and high speed atomic force spectroscopy are installed. In this meeting, the development of material analysis facility will be introduced. [1] Jhon C.Tully, Science, 312(2006) 1004

TUPA19	Operation Modes and Longitudinal Layout for the SwissFEL Hard X-Ray Facility	linac, FEL, wakefield, undulator	235
	B. Beutner, S. Reiche Paul Scherrer Institut, Villigen, Switzerland
	The SwissFEL facility will produce coherent, ultrabright, and ultra-short photon pulses covering a wavelength range from 0.1 nm to 7 nm, requiring an emittance between 0.18 to 0.43 mm mrad at bunch charges between 10pC and 200pC. In nominal operation continous changes between these two bunch charges will be offered to the users in order to allow them an individual tradeoff between photon power and pulse length depending on thier requirements. The facility consists of an S-band rf-gun and booster and a C-band main linac, which accelerates the beam up to 5.8 GeV. Two compression chicanes will provide a nominal peak current of about 1-3 kA depending on the charge. In addition special operation setups for ultra short single mode photon pulses and large bandwidth will be availiable to users. In this paper different operation modes including nominal operation as well as special modes are presented and discussed in terms of photon performance and machine stability requiremnts.

TUPB04	Status of the FEL User Facility FLASH	FEL, radiation, electron, laser	267
	S. Schreiber, B. Faatz, J. Feldhaus, K. Honkavaara, R. Treusch, M. Vogt DESY, Hamburg, Germany
	The free-electron laser FLASH at DESY, Germany has been upgraded in 2010 and extended its wavelength range down to 4.1 nm. Beside the increased electron beam energy to 1.25 GeV, an other important upgrade is the installation of 3.9 GHz superconducting RF cavities in the injector. They are used to shape the longitudinal electron beam phase space. Now, significantly more FEL radiation energy per pulse of up to several hundreds of microjoules are achieved. Moreover, the system allows to adjust the FEL pulse length, from long pulses of more than 200 fs to short pulses well below 50 fs. The upgraded FLASH facility shows an excellent performance in terms of FEL radiation quality and stability as well as in reliability of operation. The 3rd user period started as scheduled in September 2010.

TUPB29	Status of the FERMI@Elettra Project	FEL, undulator, linac, laser	312
	M. Svandrlik, E. Allaria, E. Busetto, C. Callegari, D. Cocco, P. Craievich, I. Cudin, G. D'Auria, M.B. Danailov, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, M. Ferianis, R. Gobessi, E. Karantzoulis, M. Kiskinova, M. Lonza, C. Masciovecchio, S. Noè, F. Parmigiani, G. Penco, M. Trovò, A. Vascotto, R. Visintini, M. Zaccaria, D. Zangrando, M. Zangrando ELETTRA, Basovizza, Italy
	FERMI@Elettra is a seeded FEL user-facility covering the wavelength range from 100 nm (12 eV) to 4 nm (310 eV) located next to the third-generation synchrotron light source Elettra in Trieste, Italy. The facility is based on a normal conducting linac and covers the wavelength range with two FEL lines, FEL-1 and FEL-2. A photon distribution and diagnostic system transports the photons from the end of the two FEL lines to three experimental stations. Beneficial occupancy of the new undulator hall and experimental hall was given end of Summer 2010 when also all auxiliary systems were made available. The installation of the machine is now almost completed; commissioning of the linac has started in parallel to the installation activities and now commissioning of FEL-1 is in a well advanced status. The first seeded lasing from FEL-1 was actually observed in December 2010 and first experiments are starting in 2011. In this paper an overview of the facility will be given as well as the general status of installation and commissioning and a perspective into future developments and user programs.

WEPA02	Thermal Acoustic Sensor for High Pulse Energy X-ray FEL Beams	target, FEL, radiation, monitoring	334
	T.J. Smith, J.C. Frisch, E.M. Kraft, J. Loos SLAC, Menlo Park, California, USA G.S. Bentsen Rochester University, Rochester, New York, USA
	Funding: Work supported by Department of Energy Contract DE AC03 76SF00515 The pulse energy density of X-ray FELs will saturate or destroy conventional X-ray diagnostics, and the use of large beam attenuation will result in a beam that is dominated by harmonics. We present results at the LCLS from using a pulse energy detector based on the thermal acoustic effect. In this type of detector an X-ray resistant material (Boron Carbide for this system) intercepts the beam. The pulse heating of this material produces an acoustic pulse that can be detected with high frequency microphones to produce a signal that is linear in the absorbed energy.

WEPA20	Designing a Pulse-resolved Photon Diagnostic System for Shanghai SXFEL	diagnostics, FEL, laser, synchrotron	374
	Y.Q. Wu, J.H. Chen, J.N. Liu, R.Z. Tai, D. Wang, R. Wang, C.F. Xue, G.F. Zhao SINAP, Shanghai, People's Republic of China
	It is presented the design of photon diagnostic system for SSRF-XFEL, the X-ray Free Electron Laser facility in Shanghai Synchrotron Radiation Facility. The system mainly includes a diagnostic beamline with two branches and some diagnostic devices. In the direct passing branch, the intensity distribution of the spot is measured. A set of multi-slit plates are applied for measuring the spatial coherence of a single FEL pulse; In the deflecting branch, a high-resolution VLS-PGM type monochromator, with a simple manual adjusting system, is set up for detecting spectrum of single FEL pulse. The measuring range of wavelength is 45nm-3nm. A fast responding EUV CCD ensures a high pulse resolution to 100Hz.

THOB5	FEL Spectral Measurements at LCLS	FEL, electron, undulator, laser	461
	J.J. Welch, F.-J. Decker, Y.T. Ding, P. Emma, A.S. Fisher, J.C. Frisch, Z. Huang, R.H. Iverson, H. Loos, M. Messerschmidt, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515. Control and knowledge of the spectrum of FEL X-ray radiation at the LCLS is important to the quality and interpretation of experimental results. Narrow bandwidth is useful in experiments requiring high-brightness beams. Wide bandwidth is particularly useful for photon energy calibration using absorption spectra. Since LCLS was commissioned in 2009 measurements have been made of average and single shot spectra of X-ray FEL radiation at the LCLS over a range of 800 to 8000 eV, for fundamental and harmonic radiation. These include correlations with chirp, bunch current, undulator K-taper, electron beam energy, and charge as well as some specialized machine configurations. In this paper we present results and discuss the relationship of the electron beam energy distribution to the observed X-ray spectrum.
	Slides THOB5 [0.442 MB]

THPA13	A 54.167MHz Laser Wire System for Free Electron Laser in CAEP	electron, laser, FEL, gun	493
	D. Wu TUB, Beijing, People's Republic of China W. Bai, M. Li, H.B. Wang, J. Wang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	The laser wire (LW) method has been demonstrated as an effective non-interceptive technique for measuring transverse electron beam size of CW FELs and ERLs. To measure the beam size of a CW DC gun, which is built as an electron source of THz FEL in China Academy of Engineering Physics (CAEP), a high repetition LW system is proposed. The first proposed system is going to be installed at the exit of the DC gun, where the energy of electron beam is extremely low. In this paper, the LW system adapted to the FEL beam parameters is discussed, and the main parameters are given.

THPB08	Study of Reflective Optics for LFC-Camera	electron, optics, 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

THPB15	Metal Cathodes with Reduced Emittance and Enhanced Quantum Efficiency	emittance, cathode, FEL, electron	586
	C.M.R. Greaves, J. Feng, H.A. Padmore, W. Wan LBNL, Berkeley, California, USA D. Dowell AES, Princeton, New Jersey, USA
	In this paper, we report experimental results on photoemission from copper and silver surfaces. Using the technique of angle resolved photoemission spectroscopy (ARPES), we demonstrate that, for excess energy around 0.5 eV, the photoelectrons from the Cu(111) and Ag(111) surfaces generated by p-polarized light originate primarily from the well-known surface state with normalized emittance only a fraction of that of the polycrystalline copper cathode presently used in the RF guns. Meanwhile, we demonstrate that the enhancement of the quantum efficiency (QE) at grazing angle is closely related to the surface state as well. Furthermore, we show that the surface state can be easily restored by a simple anneal process, thus pointing to a practical way to reducing the emittance and QE of a metal cathode simultaniously.

THPB16	Beam Profile Measurements Using a Fast Gated CCD Camera and a Scintillation Screen to Suppress COTR	electron, radiation, FEL, diagnostics	590
	M. Yan Uni HH, Hamburg, Germany C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch DESY, Hamburg, Germany
	For standard beam profile measurements of high-brightness electron beams using optical transition radiation (OTR) screens, coherence effects induced by microbunching instabilities render direct imaging of the beam impossible. A technique of using a scintillation screen with a fast gated CCD camera has been demonstrated to successfully suppress coherent OTR (COTR) in transverse beam diagnostics at FLASH. The fast gated CCD camera has been installed next to a standard CCD camera setup and images the same viewing screens. The results of transverse beam profile measurements under operating conditions without COTR are compared for both setups. The fast gated camera has also been employed for longitudinal bunch profile measurements with a transverse deflecting structure (TDS). Results obtained under operating conditions with COTR are compared to those from longitudinal phase space measurements in a dispersive arm, where no coherence effects have been observed so far. In this paper, we examine the performance of the fast gated CCD camera for beam profile measurements and present further studies on the use of scintillation screens for high-energy electron beam diagnostics.

Paper

Title

Other Keywords

Page

MOPB28

Gas-filled Cell as a Narrow Bandwidth Bandpass Filter in the VUV Wavelength Range

radiation, FEL, resonance, simulation

73

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

We propose a method for spectrally filtering radiation in the VUV wavelength range by means of a monochromator constituted by a cell filled with a resonantly absorbing rare gas. Around particular wavelengths, the gas exhibits narrow-bandwidth absorbing resonances following the Fano profile. Within the photon energy range 60-65 eV, the correlation index of the Fano profiles for the photo-ionization spectra in He is equal to unity, meaning that the minimum of the cross-section is exactly zero. For sufficiently large column density in the gas cell, the spectrum of the incoming radiation will be attenuated by the background cross-section of many orders of magnitude, except for those wavelengths close to the point where the cross-section is zero. Remarkable advantages of a gas monochromator based on this principle are simplicity, efficiency and narrow-bandwidth. A gas monochromator installed in the experimental hall of a VUV SASE FEL facility would enable the delivery of a single-mode VUV laser beam. The design is identical to that of existing gas attenuator systems for VUV or X-ray FELs. We present feasibility study and exemplifications for the FLASH facility in the VUV regime.

MOPB32

System Trade Analysis for an FEL Facility

FEL, undulator, linac, emittance

89

M.W. Reinsch, B. Austin, J.N. Corlett, L.R. Doolittle, G. Penn, D. Prosnitz, J. Qiang, A. Sessler, M. Venturini, J.S. Wurtele
LBNL, Berkeley, California, USA

Designing an FEL from scratch requires the design team to balance multiple science needs, FEL and accelerator physics constraints and engineering limitations. STAFF (System Trade Analysis for an FEL Facility) enables the user to rapidly explore a large range of Linac and FEL design options. The model utilzes analytical models such as the Ming Xie formulas when appropriate and look-up tables when necessary to maintain speed, flexibility and extensiblity. STAFF allows for physics models for FEL harmonics, wake fields, cavity higher-order modes and aspects of linac particle dynamics. The code will permit the user to study error tolerances and multiple beamlines so as to explore the full capabilities of an entire user facility. This makes it possible to optimize the integrated system in terms of performance metrics such as photons/pulse, photons/sec and tunability range while ensuring that unrealistic requirements are not put on either the electron beam quality, undulator field/gap requirements or other system elements. This paper will describe preliminary results from STAFF as applied to a CW FEL soft X-ray facility.

MOPC13

Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation

electron, radiation, linac, vacuum

125

N. Sei
AIST, Tsukuba, Ibaraki, Japan
T. Takahashi
Kyoto University, Research Reactor Institute, Osaka, Japan

Funding: This study was financially supported by the Sumitomo foundation.
We have studied a terahertz-wave spectrophotometry by using Compton backscattering of coherent radiations at the Kyoto University Research Reactor Institute. In the terahertz-wave spectrophotometry, the characteristics of the continuous-spectrum THz waves are converted into those of the other wavelengths which are easily measured by colliding the THz waves with a relativistic electron beam. Such the continuous-spectrum light beam by Compton backscattering is known in a field of astrophysics. We achieved to observe a continuous-spectrum visible beam resulting from Compton backscattering using coherent transition radiations from an L-band electron linear accelerator*. The measured spectrum of the Compton backscattered photons was similar to that calculated from the spectrum of coherent transition radiation. In the presentation, the experimental results of terahertz-wave spectrophotometry will be explained in detail.
* N. Sei and T. Takahashi, Appl. Phys. Express 3 (2010) 052401.

TUPA02

Development of Material Analysis Facility in KU-FEL

FEL, laser, lattice, electron

190

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

A mid infrared-free electron laser (MIR-FEL) (5-20 μm) facility (KU-FEL: Kyoto University Free Electron Laser) has been constructed for contributing to researches on energy science at Institute of Advanced Energy, Kyoto University. Up to now 12-14 μm FEL beam has been generated. When MIR-FEL with the wavelength matched to the molecular vibration mode is irradiated to the material, a particular chemical bond in the material will be selectively excited, or dissociated [1]. The selective photochemical reaction can be applied for surface modification and the evaluation of material in biochemistry, chemistry, and solid physics. Therefore, material analysis facility in combination with MIR-FEL is constructed. In the material analysis facility, advanced analysis systems such as photoluminescence measurement system, photoelectron spectroscopy, super centrifuge and high performance liquids chromatography, ICP emission spectroscopy, and high speed atomic force spectroscopy are installed. In this meeting, the development of material analysis facility will be introduced.
[1] Jhon C.Tully, Science, 312(2006) 1004

TUPA19

Operation Modes and Longitudinal Layout for the SwissFEL Hard X-Ray Facility

linac, FEL, wakefield, undulator

235

B. Beutner, S. Reiche
Paul Scherrer Institut, Villigen, Switzerland

The SwissFEL facility will produce coherent, ultrabright, and ultra-short photon pulses covering a wavelength range from 0.1 nm to 7 nm, requiring an emittance between 0.18 to 0.43 mm mrad at bunch charges between 10pC and 200pC. In nominal operation continous changes between these two bunch charges will be offered to the users in order to allow them an individual tradeoff between photon power and pulse length depending on thier requirements. The facility consists of an S-band rf-gun and booster and a C-band main linac, which accelerates the beam up to 5.8 GeV. Two compression chicanes will provide a nominal peak current of about 1-3 kA depending on the charge. In addition special operation setups for ultra short single mode photon pulses and large bandwidth will be availiable to users. In this paper different operation modes including nominal operation as well as special modes are presented and discussed in terms of photon performance and machine stability requiremnts.

TUPB04

Status of the FEL User Facility FLASH

FEL, radiation, electron, laser

267

S. Schreiber, B. Faatz, J. Feldhaus, K. Honkavaara, R. Treusch, M. Vogt
DESY, Hamburg, Germany

The free-electron laser FLASH at DESY, Germany has been upgraded in 2010 and extended its wavelength range down to 4.1 nm. Beside the increased electron beam energy to 1.25 GeV, an other important upgrade is the installation of 3.9 GHz superconducting RF cavities in the injector. They are used to shape the longitudinal electron beam phase space. Now, significantly more FEL radiation energy per pulse of up to several hundreds of microjoules are achieved. Moreover, the system allows to adjust the FEL pulse length, from long pulses of more than 200 fs to short pulses well below 50 fs. The upgraded FLASH facility shows an excellent performance in terms of FEL radiation quality and stability as well as in reliability of operation. The 3rd user period started as scheduled in September 2010.

TUPB29

Status of the FERMI@Elettra Project

FEL, undulator, linac, laser

312

M. Svandrlik, E. Allaria, E. Busetto, C. Callegari, D. Cocco, P. Craievich, I. Cudin, G. D'Auria, M.B. Danailov, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, M. Ferianis, R. Gobessi, E. Karantzoulis, M. Kiskinova, M. Lonza, C. Masciovecchio, S. Noè, F. Parmigiani, G. Penco, M. Trovò, A. Vascotto, R. Visintini, M. Zaccaria, D. Zangrando, M. Zangrando
ELETTRA, Basovizza, Italy

FERMI@Elettra is a seeded FEL user-facility covering the wavelength range from 100 nm (12 eV) to 4 nm (310 eV) located next to the third-generation synchrotron light source Elettra in Trieste, Italy. The facility is based on a normal conducting linac and covers the wavelength range with two FEL lines, FEL-1 and FEL-2. A photon distribution and diagnostic system transports the photons from the end of the two FEL lines to three experimental stations. Beneficial occupancy of the new undulator hall and experimental hall was given end of Summer 2010 when also all auxiliary systems were made available. The installation of the machine is now almost completed; commissioning of the linac has started in parallel to the installation activities and now commissioning of FEL-1 is in a well advanced status. The first seeded lasing from FEL-1 was actually observed in December 2010 and first experiments are starting in 2011. In this paper an overview of the facility will be given as well as the general status of installation and commissioning and a perspective into future developments and user programs.

WEPA02

Thermal Acoustic Sensor for High Pulse Energy X-ray FEL Beams

target, FEL, radiation, monitoring

334

T.J. Smith, J.C. Frisch, E.M. Kraft, J. Loos
SLAC, Menlo Park, California, USA
G.S. Bentsen
Rochester University, Rochester, New York, USA

Funding: Work supported by Department of Energy Contract DE AC03 76SF00515
The pulse energy density of X-ray FELs will saturate or destroy conventional X-ray diagnostics, and the use of large beam attenuation will result in a beam that is dominated by harmonics. We present results at the LCLS from using a pulse energy detector based on the thermal acoustic effect. In this type of detector an X-ray resistant material (Boron Carbide for this system) intercepts the beam. The pulse heating of this material produces an acoustic pulse that can be detected with high frequency microphones to produce a signal that is linear in the absorbed energy.

WEPA20

Designing a Pulse-resolved Photon Diagnostic System for Shanghai SXFEL

diagnostics, FEL, laser, synchrotron

374

Y.Q. Wu, J.H. Chen, J.N. Liu, R.Z. Tai, D. Wang, R. Wang, C.F. Xue, G.F. Zhao
SINAP, Shanghai, People's Republic of China

It is presented the design of photon diagnostic system for SSRF-XFEL, the X-ray Free Electron Laser facility in Shanghai Synchrotron Radiation Facility. The system mainly includes a diagnostic beamline with two branches and some diagnostic devices. In the direct passing branch, the intensity distribution of the spot is measured. A set of multi-slit plates are applied for measuring the spatial coherence of a single FEL pulse; In the deflecting branch, a high-resolution VLS-PGM type monochromator, with a simple manual adjusting system, is set up for detecting spectrum of single FEL pulse. The measuring range of wavelength is 45nm-3nm. A fast responding EUV CCD ensures a high pulse resolution to 100Hz.

THOB5

FEL Spectral Measurements at LCLS

FEL, electron, undulator, laser

461

J.J. Welch, F.-J. Decker, Y.T. Ding, P. Emma, A.S. Fisher, J.C. Frisch, Z. Huang, R.H. Iverson, H. Loos, M. Messerschmidt, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515.
Control and knowledge of the spectrum of FEL X-ray radiation at the LCLS is important to the quality and interpretation of experimental results. Narrow bandwidth is useful in experiments requiring high-brightness beams. Wide bandwidth is particularly useful for photon energy calibration using absorption spectra. Since LCLS was commissioned in 2009 measurements have been made of average and single shot spectra of X-ray FEL radiation at the LCLS over a range of 800 to 8000 eV, for fundamental and harmonic radiation. These include correlations with chirp, bunch current, undulator K-taper, electron beam energy, and charge as well as some specialized machine configurations. In this paper we present results and discuss the relationship of the electron beam energy distribution to the observed X-ray spectrum.

Slides THOB5 [0.442 MB]

THPA13

A 54.167MHz Laser Wire System for Free Electron Laser in CAEP

electron, laser, FEL, gun

493

D. Wu
TUB, Beijing, People's Republic of China
W. Bai, M. Li, H.B. Wang, J. Wang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

The laser wire (LW) method has been demonstrated as an effective non-interceptive technique for measuring transverse electron beam size of CW FELs and ERLs. To measure the beam size of a CW DC gun, which is built as an electron source of THz FEL in China Academy of Engineering Physics (CAEP), a high repetition LW system is proposed. The first proposed system is going to be installed at the exit of the DC gun, where the energy of electron beam is extremely low. In this paper, the LW system adapted to the FEL beam parameters is discussed, and the main parameters are given.

THPB08

Study of Reflective Optics for LFC-Camera

electron, optics, 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

THPB15

Metal Cathodes with Reduced Emittance and Enhanced Quantum Efficiency

emittance, cathode, FEL, electron

586

C.M.R. Greaves, J. Feng, H.A. Padmore, W. Wan
LBNL, Berkeley, California, USA
D. Dowell
AES, Princeton, New Jersey, USA

In this paper, we report experimental results on photoemission from copper and silver surfaces. Using the technique of angle resolved photoemission spectroscopy (ARPES), we demonstrate that, for excess energy around 0.5 eV, the photoelectrons from the Cu(111) and Ag(111) surfaces generated by p-polarized light originate primarily from the well-known surface state with normalized emittance only a fraction of that of the polycrystalline copper cathode presently used in the RF guns. Meanwhile, we demonstrate that the enhancement of the quantum efficiency (QE) at grazing angle is closely related to the surface state as well. Furthermore, we show that the surface state can be easily restored by a simple anneal process, thus pointing to a practical way to reducing the emittance and QE of a metal cathode simultaniously.

THPB16

Beam Profile Measurements Using a Fast Gated CCD Camera and a Scintillation Screen to Suppress COTR

electron, radiation, FEL, diagnostics

590

M. Yan
Uni HH, Hamburg, Germany
C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch
DESY, Hamburg, Germany

For standard beam profile measurements of high-brightness electron beams using optical transition radiation (OTR) screens, coherence effects induced by microbunching instabilities render direct imaging of the beam impossible. A technique of using a scintillation screen with a fast gated CCD camera has been demonstrated to successfully suppress coherent OTR (COTR) in transverse beam diagnostics at FLASH. The fast gated CCD camera has been installed next to a standard CCD camera setup and images the same viewing screens. The results of transverse beam profile measurements under operating conditions without COTR are compared for both setups. The fast gated camera has also been employed for longitudinal bunch profile measurements with a transverse deflecting structure (TDS). Results obtained under operating conditions with COTR are compared to those from longitudinal phase space measurements in a dispersive arm, where no coherence effects have been observed so far. In this paper, we examine the performance of the fast gated CCD camera for beam profile measurements and present further studies on the use of scintillation screens for high-energy electron beam diagnostics.