FEL2011 - List of Keywords (vacuum)

Paper	Title	Other Keywords	Page
MOPC13	Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation	photon, electron, radiation, linac	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.

TUPA08	The Control System for CAEP FEL	controls, FEL, EPICS, power-supply	206
	D. Zhang, M. Li, H.B. Wang, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	It describes a control system of CAEP Free Electron Laser (FEL), which is a distributed control system based on EPICS and Visual C++6.0. EPICS is popular in large accelerator laboratories in the world. It is a software toolkit for building process control system for a wide variety of experiment and industrial applications. The software tools in the kit provide independent and expandable modules for system configuration, distributed process control, run-time database, alarm manager, etc. It gives detailed description of the magnet power supply system , beam diagnostic system, including the hardware structure and software design. Other subsystems are also described in the paper. The control system has standard module, interoperability, and repeatability are available. The control system is simple direct, and stable.

WEOCI1	Beam Line Commissioning of a UV/VUV FEL at Jefferson Lab	FEL, laser, electron, cavity	326
	S.V. Benson, G.H. Biallas, K. Blackburn, D.B. Bullard, J.L. Coleman, C. Dickover, D. Douglas, F.K. Ellingsworth, P. Evtushenko, C.W. Gould, J.G. Gubeli, D. Hardy, C. Hernandez-Garcia, K. Jordan, J.M. Klopf, J. Kortze, R.A. Legg, M. Marchlik, S.W. Moore, G. Neil, T. Powers, D.W. Sexton, M.D. Shinn, C. Tennant, R.L. Walker, G.P. Williams, F.G. Wilson, S. Zhang JLAB, Newport News, Virginia, USA C. Clavero The College of William and Mary, Williamsburg, USA
	Funding: Work supported by U.S. DOE Contract DE-AC05-84-ER40150, Air Force Office of Scientific Research, DOE Basic Energy Sciences, Office of Naval Research, and the Joint Technology Office. Many novel applications in photon sciences require very high source brightness and/or short pulses in the vacuum ultra-violet (VUV). Jefferson Lab has commissioned a UV oscillator with high gain and has transported the third harmonic of the UV to a user lab. The experimental performance of the UV FEL is much better than simulated performance in both gain and efficiency. This success is important for efforts to push towards higher gain FELs at short wavelengths where mirrors absorb strongly. We will report on efforts to characterize the UV laser and the VUV coherent harmonics as well as designs to lase directly in the VUV wavelength range.
	Slides WEOCI1 [3.331 MB]

THOAI1	Pushing the Limits of Short Period Permanent Magnet Undulators	undulator, permanent-magnet, cryogenics, FEL	435
	J. Bahrdt HZB, Berlin, Germany
	Short period undulators to be used as FEL radiators permit lower electron energies and, thus, reduce linac and undulator lengths. The first X-ray FEL facility based on in-vacuum undulators goes into operation soon (SPRING-8 XFEL). Other in-vacuum undulator based FELs are under construction (SWISS-FEL) or are planned. The in-vacuum undulators have period lengths between 18mm (SPRING-8-X-FEL) and 15mm (SWISS-FEL). In the future the period length will be pushed further into the sub-cm regime. The technical implications of these devices will be discussed: New materials such as PrFeB-magnets are employed. They show their superior characteristics at cryogenic temperatures. Geometric and magnetic tolerances will be tighter and the construction and shimming concepts have to be revised. New magnetic measurement systems are required as well. Recently, a 9mm period length 20 period prototype undulator has been built in collaboration between Ludwig-Maximilian-University Munich and Helmholtz-Zentrum Berlin. The potential and the challenges of sub-cm undulators will be illustrated based on first results from this prototype.
	Slides THOAI1 [3.344 MB]

THPA07	A Multichannel Wavelength Resolved Coherent Radiation Detector for Bunch Profile Monitoring at FLASH	radiation, electron, factory, FEL	477
	S. Wesch, B. Schmidt DESY, Hamburg, Germany
	Measuring the wavelength integrated intensity of coherent radiation in the micrometer to millimeter regime (THz radiation) is a widespread method to monitor the compression process in FEL linacs. While these devices give valuable information about the overall bunch length, they don't provide any information on the longitudinal structure and shape of the bunches. In this paper, we present a real time bunch profile monitor based on wavelength resolved THz detection. An in-vacuum spectrometer with four dispersive gratings and parallel read out of 120 individual wavelength bins provides detailed information shot-to-shot information on the bunch shape. The device can be operated in short (4-40 μm) and long range (40-400 μm) mode to cover the entire longitudinal phase space for compressed bunches of the FLASH linac. It is used as online monitoring device just as for bunch profile measurements during machine development. It's sensitivity down to the few micrometer scale allows to study very short features of the bunch profile as well as microbunching phenomena in this regime.

THPA24	Development of Pr₂Fe₁₄B Cryogenic Undulator CPMU at SOLEIL	undulator, cryogenics, permanent-magnet, electron	523
	C. Benabderrahmane, P. Berteaud, N. Béchu, L. Chapuis, M.-E. Couprie, J.P. Daguerre, J.-M. Filhol, C. Herbeaux, A. Lestrade, M. Louvet, J.L. Marlats, K. Tavakoli, M. Valléau, D. Zerbib SOLEIL, Gif-sur-Yvette, France
	Short period, high field undulators can enable short wavelength FEL at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. A R&D programme for the construction of a 2 m long 18 mm period CPMU is under progress at SOLEIL. The use of PrFeB which features a 1.35 T remanence (Br) at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. For FELs, we can reach higher magnetic field of 1.91 T at lower gap of 3 mm. Pr was chosen instead of Nd magnetic material, because of the no appearance of the SRT phenomenon. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. The mounting inside the vacuum chamber enables the fitting of a dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature. The results of the magnetic measurements at low temperature and the comparison with the measurement at room temperature are reported. A U18 CPMU will be used in LUNEX5 project at SOLEIL.

THPB06	Coherent Terahertz Radiation Monitors for Multiple Spectral Bands	radiation, synchrotron, electron, synchrotron-radiation	572
	R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott, B. Smit, C. Vicario, C. Zimmerli Paul Scherrer Institut, Villigen, Switzerland C. Gerth DESY, Hamburg, Germany
	The SwissFEL Injector Test Facility is destined for demonstrating electron beam parameters that are suitable for FEL operation. Of particular interest is the on-line measurement of longitudinal phase space properties, as this provides insight into the bunch compression process. The spectral distribution of diffraction radiation offers a robust way to assess bunch length and longitudinal profile. The bunch length at the SwissFEL Injector Test Facility can be varied by changing the photocathode laser. Diffraction radiation is emitted as the electron bunches pass through a hole in a titanium foil. The emitted Terahertz radiation has been simulated by the code THz Transport, and the propagation to the detectors has been modeled.

THPB20	DC High Voltage Photoemission Electron Gun for CAEP FEL	gun, cathode, electron, high-voltage	598
	H.B. Wang, M. Li, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	The research on high average power Terahertz free electron laser requires more demanding specifications of electron source. DC high voltage electron guns with photoemission cathodes are a natural choice for generating the critical beams considering the condition of technology. Field emission from the electrode structures limits the operating voltage and cathode field gradient in these guns. A ceramic insulator determines the level of operating voltage. The photocathode operational lifetime is limited by the gun vacuum and by ion back bombardment. The designing thought and the technical solution to aforementioned issues are presented. The results of the beam dynamic simulation based on the design are displayed, normalized emittance at the location 120 cm far from the cathode surface: x=1.335 πmmmrad, y=1.364 πmmmrad, z=4.81 π*keV-deg, using the following initial beam parameters: the laser spot 4 mm in diameter, the laser pulse length FWHM 12 ps, the charge per bunch 35 pC and the accelerating voltage 350 kV. Now the DC photoemission gun is conditioning.

Paper

Title

Other Keywords

Page

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

photon, electron, radiation, linac

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.

TUPA08

The Control System for CAEP FEL

controls, FEL, EPICS, power-supply

206

D. Zhang, M. Li, H.B. Wang, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

It describes a control system of CAEP Free Electron Laser (FEL), which is a distributed control system based on EPICS and Visual C++6.0. EPICS is popular in large accelerator laboratories in the world. It is a software toolkit for building process control system for a wide variety of experiment and industrial applications. The software tools in the kit provide independent and expandable modules for system configuration, distributed process control, run-time database, alarm manager, etc. It gives detailed description of the magnet power supply system , beam diagnostic system, including the hardware structure and software design. Other subsystems are also described in the paper. The control system has standard module, interoperability, and repeatability are available. The control system is simple direct, and stable.

WEOCI1

Beam Line Commissioning of a UV/VUV FEL at Jefferson Lab

FEL, laser, electron, cavity

326

S.V. Benson, G.H. Biallas, K. Blackburn, D.B. Bullard, J.L. Coleman, C. Dickover, D. Douglas, F.K. Ellingsworth, P. Evtushenko, C.W. Gould, J.G. Gubeli, D. Hardy, C. Hernandez-Garcia, K. Jordan, J.M. Klopf, J. Kortze, R.A. Legg, M. Marchlik, S.W. Moore, G. Neil, T. Powers, D.W. Sexton, M.D. Shinn, C. Tennant, R.L. Walker, G.P. Williams, F.G. Wilson, S. Zhang
JLAB, Newport News, Virginia, USA
C. Clavero
The College of William and Mary, Williamsburg, USA

Funding: Work supported by U.S. DOE Contract DE-AC05-84-ER40150, Air Force Office of Scientific Research, DOE Basic Energy Sciences, Office of Naval Research, and the Joint Technology Office.
Many novel applications in photon sciences require very high source brightness and/or short pulses in the vacuum ultra-violet (VUV). Jefferson Lab has commissioned a UV oscillator with high gain and has transported the third harmonic of the UV to a user lab. The experimental performance of the UV FEL is much better than simulated performance in both gain and efficiency. This success is important for efforts to push towards higher gain FELs at short wavelengths where mirrors absorb strongly. We will report on efforts to characterize the UV laser and the VUV coherent harmonics as well as designs to lase directly in the VUV wavelength range.

Slides WEOCI1 [3.331 MB]

THOAI1

Pushing the Limits of Short Period Permanent Magnet Undulators

undulator, permanent-magnet, cryogenics, FEL

435

J. Bahrdt
HZB, Berlin, Germany

Short period undulators to be used as FEL radiators permit lower electron energies and, thus, reduce linac and undulator lengths. The first X-ray FEL facility based on in-vacuum undulators goes into operation soon (SPRING-8 XFEL). Other in-vacuum undulator based FELs are under construction (SWISS-FEL) or are planned. The in-vacuum undulators have period lengths between 18mm (SPRING-8-X-FEL) and 15mm (SWISS-FEL). In the future the period length will be pushed further into the sub-cm regime. The technical implications of these devices will be discussed: New materials such as PrFeB-magnets are employed. They show their superior characteristics at cryogenic temperatures. Geometric and magnetic tolerances will be tighter and the construction and shimming concepts have to be revised. New magnetic measurement systems are required as well. Recently, a 9mm period length 20 period prototype undulator has been built in collaboration between Ludwig-Maximilian-University Munich and Helmholtz-Zentrum Berlin. The potential and the challenges of sub-cm undulators will be illustrated based on first results from this prototype.

Slides THOAI1 [3.344 MB]

THPA07

A Multichannel Wavelength Resolved Coherent Radiation Detector for Bunch Profile Monitoring at FLASH

radiation, electron, factory, FEL

477

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

Measuring the wavelength integrated intensity of coherent radiation in the micrometer to millimeter regime (THz radiation) is a widespread method to monitor the compression process in FEL linacs. While these devices give valuable information about the overall bunch length, they don't provide any information on the longitudinal structure and shape of the bunches. In this paper, we present a real time bunch profile monitor based on wavelength resolved THz detection. An in-vacuum spectrometer with four dispersive gratings and parallel read out of 120 individual wavelength bins provides detailed information shot-to-shot information on the bunch shape. The device can be operated in short (4-40 μm) and long range (40-400 μm) mode to cover the entire longitudinal phase space for compressed bunches of the FLASH linac. It is used as online monitoring device just as for bunch profile measurements during machine development. It's sensitivity down to the few micrometer scale allows to study very short features of the bunch profile as well as microbunching phenomena in this regime.

THPA24

Development of Pr₂Fe₁₄B Cryogenic Undulator CPMU at SOLEIL

undulator, cryogenics, permanent-magnet, electron

523

C. Benabderrahmane, P. Berteaud, N. Béchu, L. Chapuis, M.-E. Couprie, J.P. Daguerre, J.-M. Filhol, C. Herbeaux, A. Lestrade, M. Louvet, J.L. Marlats, K. Tavakoli, M. Valléau, D. Zerbib
SOLEIL, Gif-sur-Yvette, France

Short period, high field undulators can enable short wavelength FEL at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. A R&D programme for the construction of a 2 m long 18 mm period CPMU is under progress at SOLEIL. The use of PrFeB which features a 1.35 T remanence (Br) at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. For FELs, we can reach higher magnetic field of 1.91 T at lower gap of 3 mm. Pr was chosen instead of Nd magnetic material, because of the no appearance of the SRT phenomenon. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. The mounting inside the vacuum chamber enables the fitting of a dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature. The results of the magnetic measurements at low temperature and the comparison with the measurement at room temperature are reported. A U18 CPMU will be used in LUNEX5 project at SOLEIL.

THPB06

Coherent Terahertz Radiation Monitors for Multiple Spectral Bands

radiation, synchrotron, electron, synchrotron-radiation

572

R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott, B. Smit, C. Vicario, C. Zimmerli
Paul Scherrer Institut, Villigen, Switzerland
C. Gerth
DESY, Hamburg, Germany

The SwissFEL Injector Test Facility is destined for demonstrating electron beam parameters that are suitable for FEL operation. Of particular interest is the on-line measurement of longitudinal phase space properties, as this provides insight into the bunch compression process. The spectral distribution of diffraction radiation offers a robust way to assess bunch length and longitudinal profile. The bunch length at the SwissFEL Injector Test Facility can be varied by changing the photocathode laser. Diffraction radiation is emitted as the electron bunches pass through a hole in a titanium foil. The emitted Terahertz radiation has been simulated by the code THz Transport, and the propagation to the detectors has been modeled.

THPB20

DC High Voltage Photoemission Electron Gun for CAEP FEL

gun, cathode, electron, high-voltage

598

H.B. Wang, M. Li, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

The research on high average power Terahertz free electron laser requires more demanding specifications of electron source. DC high voltage electron guns with photoemission cathodes are a natural choice for generating the critical beams considering the condition of technology. Field emission from the electrode structures limits the operating voltage and cathode field gradient in these guns. A ceramic insulator determines the level of operating voltage. The photocathode operational lifetime is limited by the gun vacuum and by ion back bombardment. The designing thought and the technical solution to aforementioned issues are presented. The results of the beam dynamic simulation based on the design are displayed, normalized emittance at the location 120 cm far from the cathode surface: x=1.335 π*mm*mrad, y=1.364 π*mm*mrad, z=4.81 π*keV-deg, using the following initial beam parameters: the laser spot 4 mm in diameter, the laser pulse length FWHM 12 ps, the charge per bunch 35 pC and the accelerating voltage 350 kV. Now the DC photoemission gun is conditioning.