FEL2013 - List of Keywords (vacuum)

Paper	Title	Other Keywords	Page
MOPSO06	Paraxial Approximation in CSR Modeling Using the Discontinuous Galerkin Method	impedance, simulation, radiation, synchrotron	32
	D. A. Bizzozero, J.A. Ellison, K.A. Heinemann, S.R. Lau UNM, Albuquerque, New Mexico, USA
	Funding: This work was primarily supported by DOE under DE-FG-99ER41104. The work of DB and SL was partially supported by NSF grant PHY 0855678 to the University of New Mexico. We continue our study* of CSR from a bunch moving on an arbitrary curved trajectory. In that study we developed an accurate 2D CSR Vlasov-Maxwell code (VM3@A) and applied it to a four dipole chicane bunch compressor. Our starting point now is the well-established paraxial approximation** with boundary conditions for a perfectly conducting vacuum chamber with uniform cross-section. This is considerably different from our previous approach* where we calculated the fields from an integral over history, using parallel plate boundary conditions. In this study, we present a Discontinuous Galerkin (DG) method for the paraxial approximation equations. Our basic tool is a MATLAB DG code on a GPU using MATLAB's gpuArray; the code was developed by one of us (DB). We discuss our results in the context of previous work and outline future applications for DG, including a Vlasov-Maxwell study. * See PRST-AB 12 080704 (2009) and Proceedings from ICAP2012 TUSDC2. ** See PRST-AB 7 054403 (2004), PRST-AB 12 104401 (2009) and Jpn. J. Appl. Phys. 51 016401 (2012).

MOPSO43	High Power Laser Transport System for Laser Cooling to Counteract Back-Bombardment Heating in Microwave Thermionic Electron Guns	laser, gun, electron, coupling	75
	J.M.D. Kowalczyk, M.R. Hadmack, J. Madey, E.B. Szarmes, M.H.E.H. Vinci University of Hawaii, Honolulu, HI, USA
	Funding: This work was funded by the Department of Homeland Security through grant #2011-DN-077-ARI055-03. Heat from a high power, short pulse laser deposited on the surface of a thermionic electron gun cathode will diffuse into the bulk producing a surface cooling effect that counteracts the electron back-bombardment (BB) heating intrinsic to the gun. The resulting constant temperature stabilizes the current allowing extension of the gun’s peak current and duty cycle. To enable this laser cooling, high power laser pulses must be transported to the high radiation zone of the electron gun, and their transverse profile must be converted from Gaussian to top-hat to uniformly cool the cathode. A fiber optic transport system is simple, inexpensive, and will convert a Gaussian to a top-hat profile. Coupling into the fiber efficiently and without damage is difficult as tight focusing is required at the input and, if coupled in air, the high fluence will breakdown the air resulting in lost energy. We have devised a vacuum fiber coupler (VFC) that allows the focus to occur in vacuum, avoiding the breakdown of air, and have successfully transported 10 ns long, 85 mJ pulses from a 1064 nm Nd:YAG laser through 20 m of 1 mm diameter fiber enabling testing of the laser cooling concept.

TUOCNO03	Progress in a Photocathode DC Gun at the Compact ERL	gun, cathode, acceleration, high-voltage	184
	N. Nishimori, R. Hajima, S.M. Matsuba, R. Nagai JAEA, Ibaraki-ken, Japan Y. Honda, T. Miyajima, M. Yamamoto KEK, Ibaraki, Japan H. Iijima, M. Kuriki HU/AdSM, Higashi-Hiroshima, Japan M. Kuwahara Nagoya University, Nagoya, Japan
	Photocathode DC gun to produce a train of electron bunch at high-average current and small emittance is a key component of advanced accelerators for high-power beams. However, DC guns operated at a voltage above 350 kV have suffered from field emitted electrons from a support rod since the development of Lasertron in 1980's. This critical issue has been resolved by a novel configuration, segmented insulator and guard rings, adopted in a DC gun at JAEA and stable application of high voltage at 550 kV has been demonstrated. The gun has been installed at the Compact ERL at KEK and ready for the beam generation. Similar type of DC guns are under development at KEK, Cornell, JLAB and IHEP. In this talk, we present progress in photocathode DC gun for high voltage and small emittance.
	Slides TUOCNO03 [4.946 MB]

TUPSO17	Status of the Manufacturing Process for the SwissFEL C-Band Accelerating Structures	laser, linac, radio-frequency, coupling	245
	U. Ellenberger, H. Blumer, L. Paly, C. Zumbach Paul Scherrer Institute, Villigen PSI, Switzerland M. Bopp, H. Fitze, F. Löhl PSI, Villigen PSI, Switzerland
	For the SwissFEL project a total of 104 C-band (or approximately 6 GHz for 5’712 MHz required) accelerating structures are needed. After developing and RF-testing of several short structures (0.5m), three 2meter prototypes have been produced successfully in-house. Avoiding any RF-tuning after fabrication, a high precision machining of the components is necessary. Special procedures were developed and handling equipment was built in order to maintain the accuracy during stacking and vacuum brazing of the parts for the C-band structures. This paper summarizes the manufacturing techniques and the mechanical test results for constant subvolumes to match the required klystron frequency of 5’712 MHz

TUPSO21	SwissFEL Cathode Load-lock System	cathode, gun, laser, extraction	259
	R. Ganter, M. Bopp, N. Gaiffi, T. Le Quang, M. Pedrozzi, M. Schaer, T. Schietinger, L. Schulz, L. Stingelin, A. Trisorio PSI, Villigen PSI, Switzerland
	The SwissFEL electron source is an RF photo-injector in which the photo-cathode plug can be exchanged. Without load-lock, the cathode exchange takes about one week and cathode surface gets contaminated in the atmosphere during installation, leading to unpredictable quantum efficiency (QE) fluctuations. This motivated the construction of a load lock system to prepare and insert cathodes in the photo-injector. This load lock system consists of three parts: the preparation chamber, the transportable vacuum suitcase and the gun load lock chamber. This three parts system gives the possibility to prepare the cathode surface with methods like vacuum firing and plasma cleaning. The QE can be checked and the plug can be inserted in the gun without breaking vacuum. This will allow establishing an optimized a reproducible cathode preparation procedure. Since several cathodes can be loaded in advance, the exchange procedure reduces the machine shutdown to a few hours (shorter RF conditioning). The system is described and first experience with its use is reported.

TUPSO25	Status of the EU-XFELl Laser Heater	laser, undulator, electron, alignment	271
	M. Hamberg, V.G. Ziemann Uppsala University, Uppsala, Sweden
	Funding: This work was supported by the Swedish Research Council under contract number DNR-828-2008-1093. We describe the technical layout and the status of the laser heater system for the EuXFEL. The laser heater is needed to increase the momentum spread of the electron beam to prevent micro-bunching instabilities in the linac.

TUPSO27	Design for a Fast, XFEL-Quality Wire Scanner	photon, radiation, electron, instrumentation	276
	M.A. Harrison, R.B. Agustsson, T.J. Campese, P.S. Chang, A.Y. Murokh, M. Ruelas RadiaBeam, Santa Monica, USA
	RadiaBeam Technologies has designed and manufactured a new wire scanner for high-speed emittance measurements of XFEL-type beams of energy 139 MeV. Using three 25-micron thick tungsten wires, this wire scanner measures vertical and horizontal beam size as well as transverse spatial correlation in one pass. The intensity of the beam at a wire position is determined from emitted bremsstrahlung photons as measured by a BGO scintillator system. The wires are transported on a two-ended support structure moved by a ball-screw linear stage. The double-ended structure reduces vibrations in the wire holder, and the two-bellows design negates the effects of air pressure on the motion. The expected minimum beam size measurable by this system is on the order of 10 microns with 0.1-micron accuracy. To achieve this, new algorithms are presented that reduce the effect of the non-zero thickness of the wire on the wire scan output. In addition, novel calculations are presented for determining the elliptical geometric parameters (vertical and horizontal beam size and correlation, or alternatively, the axis lengths and rotation) of the beam from the wire scanner measurements.

TUPSO30	Conditioning Status of the First XFEL Gun at PITZ	gun, solenoid, cathode, cavity	282
	I.I. Isaev, J.D. Good, M. Groß, L. Hakobyan, L. Jachmann, M. Khojoyan, W. Köhler, G. Kourkafas, M. Krasilnikov, D. Malyutin, B. Marchetti, R. Martin, A. Oppelt, M. Otevřel, B. Petrosyan, D. Richter, A. Shapovalov, F. Stephan, G. Vashchenko, R.W. Wenndorff DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria P. Boonpornprasert, S. Rimjaem Chiang Mai University, Chiang Mai, Thailand M.A. Nozdrin JINR, Dubna, Moscow Region, Russia G. Pathak Uni HH, Hamburg, Germany
	The paper describes the recent results of conditioning and dark current measurements for the photocathode RF gun at the photoinjector test facility at DESY, Zeuthen site (PITZ). The aim of PITZ is to develop and operate an optimized photo injector for free electron lasers and linear accelerators which require high quality beams. In order to get high gradients in the RF gun extensive conditioning is required. A data analysis of the conditioning process is based on data saved by a Data Acquisition system (DAQ). Conditioning results of the first gun cavity for the XFEL is presented. The events which occurred during the conditioning are briefly described.

TUPSO33	The Commissioning of Tess: An Experimental Facility for Measuring the Electron Energy Distribution From Photocathodes	electron, cathode, laser, brightness	290
	L.B. Jones, R.J. Cash, B.D. Fell, K.J. Middleman, B.L. Militsyn, T.C.Q. Noakes STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom D.V. Gorshkov, H.E. Scheibler, A.S. Terekhov ISP, Novosibirsk, Russia
	ASTeC have developed a Transverse Energy Spread Spectrometer (TESS) – an experimental facility to characterise the energy distribution of electrons emitted by a photocathode. Electron injector brightness is fundamentally limited by the width of this distribution or energy spread, and brightness will be increased significantly by reducing the longitudinal and transverse energy spread at source. TESS supports photocathode performance measurements at room and LN2-temperature under illumination from a range of fixed- and variable-wavelength light sources, allowing characterisation of both metal and semiconductor photocathodes. Preliminary work with GaAs* has shown that electron energy spread is dependent on the quantum efficiency (Q.E.) of the photocathode source, and TESS includes a piezo-electric leak valve to allow controlled degradation of the photocathode Q.E. whilst monitoring the energy spread of emitted electrons. This system offers huge potential to support future photocathode R&D work into a range of photocathode materials. Using GaAs photocathodes activated to high levels of Q.E. in our photocathode preparation facility*, we present commissioning results for TESS. Proc. IPAC ’12, TUPPD067, 1557-1559 ** Proc. IPAC ’11, THPC129, 3185-3187

TUPSO43	Status of the SwissFEL C-band Linear Accelerator	linac, controls, klystron, low-level-rf	317
	F. Löhl, J. Alex, H. Blumer, M. Bopp, H.-H. Braun, A. Citterio, H. Fitze, H. Jöhri, T. Kleeb, L. Paly, J.-Y. Raguin, L. Schulz, R. Zennaro PSI, Villigen PSI, Switzerland U. Ellenberger Paul Scherrer Institute, Villigen PSI, Switzerland
	This paper will summarize the status of the linear accelerator of the Swiss free-electron laser SwissFEL. It will be based on C-band technology and will use solid-state modulators and a novel type of C-band accelerating structures which has been designed at PSI. Initial test results of first 2 m long structures will be presented together with measurements performed with the first BOC-type pulse compressors. Furthermore, we will present first results of a water cooling system for the accelerating structures and the pulse compressors.

TUPSO52	R&D Towards a Delta-type Undulator for the LCLS	undulator, polarization, FEL, radiation	348
	H.-D. Nuhn, S.D. Anderson, G.B. Bowden, Y. Ding, G.L. Gassner, Z. Huang, E.M. Kraft, Yu.I. Levashov, F. Peters, F.E. Reese, J.J. Welch, Z.R. Wolf, J. Wu SLAC, Menlo Park, California, USA A.B. Temnykh Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The LCLS generates linearly polarized, intense, high brightness x-ray pulses from planar fixed-gap undulators. While the fixed-gap design supports a very successful and tightly controlled alignment concept, it provides only limited taper capability (up to 1% through canted pole and horizontal position adjustability) and lacks polarization control. The latter is of great importance for soft x-ray experiments. A new compact undulator design (Delta) has been developed and tested with a 30-cm-long in-vacuum prototype at Cornell University, which adds those missing properties to the LCLS undulator design and is readily adapted to the LCLS alignment concept. Tuning Delta undulators within tight, FEL type tolerances is a challenge due to the fact that the magnetic axis and the magnet blocks are not easily accessible for measurements and tuning in the fully assembled state. An R&D project is underway to install a 3.2-m long out-of-vacuum device in place of the last LCLS undulator, to provide controllable levels of polarized radiation and to develop measurement and tuning techniques to achieve x-ray FEL type tolerances. Presently, the installation of the device is scheduled for August 2013.

TUPSO55	300 mm Electromagnetic Wiggler for ELBE	wiggler, electron, insertion, insertion-device	353
	C.W. Ostenfeld, M. Pedersen Danfysik A/S, Taastrup, Denmark
	Danfysik has designed and built a 300 mm fixed-gap electromagnetic wiggler for the ELBE radiation source at Helmholz Zentrum Dresden Rossendorff. This wiggler will serve as a source of narrow-band THz radiation in the 100 μm to 10 mm range. Due to careful magnetic modelling, and an effective shimming process, we were able to deliver magnetic performance at a high level. We present the details of the modelling, as well as magnetic results.

TUPSO75	Design Analysis and High Power RF Test of a 3.9 GHz 5-cell Deflecting-mode Cavity in a Cryogenic Operation	cavity, simulation, cryomodule, coupling	399
	Y.-M. Shin Northern Illinois University, DeKalb, Illinois, USA M.D. Church Fermilab, Batavia, USA
	A 3.9 GHz deflecting mode (π, TM110) cavity has been long used for six-dimensional phase-space beam manipulation tests [1 - 5] at the A0 Photo-Injector Lab (16 MeV) in Fermilab and their extended applications with vacuum cryomodules are currently planned at the Advanced Superconducting Test Accelerator (ASTA) user facility (> 50 MeV). Despite the successful test results, the cavity, however, demonstrated limited RF performance during liquid nitrogen (LN2) ambient operation that was inferior to theoretical prediction. We have been performing full analysis of the designed cavity by analytic calculation and comprehensive system simulation analysis to solve complex thermodynamics and mechanical stresses. The re-assembled cryomodule is currently under the test with a 50 kW klystron at the Fermilab A0 beamline, which will benchmark the modeling analysis. The test result will be used to design vacuum cryomodules for the 3.9 GHz deflecting mode cavity that will be employed at the ASTA facility for beam diagnostics and phase-space control. [1] D. A. Edwards, LINAC 2002 [2] Y.-E Sun, PRTAB 2004 [3] P. Piot, PRSTAB2006 [4] J. Ruand et al., PRL 2011 [5] Y.-E. Sun, et al., PRL 2010

TUPSO82	Spectroscopy System for LCLS Photocathodes	electron, gun, cathode, emittance	421
	P. Stefan, A. Brachmann, T. Vecchione SLAC, Menlo Park, California, USA
	Funding: Work supported by US DOE contract DE-AC02-76SF00515. Photocathode reliability is important from an operational standpoint. Unfortunately LCLS copper photocathodes have not always been reliable. Some have operated well for long periods of time while others have required continual maintenance. It is believed that the observed variations in quantum efficiency, emittance and lifetimes are inherently surface related, corresponding to changes in composition or morphology. The RF Electron-gun Cathode, Electron Surface Spectrometer, or RECESS, system has been commissioned to study this by making essential measurements that could not be obtained otherwise. These involve photocathode surface chemical characterization. The system is designed to use a combination of angle-resolved ultraviolet and x-ray photoelectron spectroscopy and is capable of either stand-alone operation or interoperability with a beam line at SSRL. Here we report on the first commissioning spectra and the direction of the project going forward.

TUPSO83	Quantum Efficiency and Transverse Momentum From Metals	electron, brightness, FEL, laser	424
	T. Vecchione, D. Dowell SLAC, Menlo Park, California, USA J. Feng, H.A. Padmore, W. Wan LBNL, Berkeley, California, USA
	Funding: Work supported by US DOE contracts DE-AC02-05CH11231, KC0407-ALSJNT-I0013, and DE-SC000571. QE and transverse momentum are key parameters limiting the achievable brightness of FELs. Despite the importance, little data is available to substantiate current models. Expressions for each and experimental confirmation of each expression with respect to excess energy are presented. Novel instrumentation and analysis techniques developed are described.

TUPSO84	SLAC RF Gun Photocathode Test Facility	gun, laser, emittance, diagnostics	427
	T. Vecchione, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, H. Loos, J. Sheppard, S.P. Weathersby, F. Zhou SLAC, Menlo Park, California, USA
	Funding: Work supported by US DOE contract DE-AC02-76SF00515. A RF gun photocathode test facility has been commissioned at SLAC. The facility consists of a S-band gun, high power RF, a UV drive laser and beam diagnostics. Here we report on the capabilities of the facility demonstrated during commissioning. Currently the facility is being used to study in-situ laser processing of copper photocathodes. In the future the facility will be used to study fundamental gun and photocathode performance limitations and enhancement strategies. Eventually it is envisioned to integrate a load lock and plug into the gun enabling the evaluation of high performance surface sensitive semiconductor photocathodes and the incorporation of ex-situ surface science analytical techniques.

WEPSO73	High Average Power Seed Laser Design for High Reprate FELs	laser, FEL, electron, controls	697
	R.B. Wilcox, G. Marcus, G. Penn LBNL, Berkeley, California, USA T. Metzger, M. Schultze TRUMPF Scientific Lasers GmbH + Co. KG, Munchen-Unterfoehring, Germany
	Funding: US Department of Energy, under Contract Numbers DE-AC02-0SCH11231. In the proposed Next Generation Light Source (NGLS), FEL designs use lasers to seed the FEL in an HGHG scheme or bunch the electron beam in an E-SASE scheme. The FELs would run at 100kHz to 1MHz, requiring high average power lasers. For the seeded FEL, laser modulation is applied at 200-240nm, with 250-700MW peak power depending on pulse length, which can vary from 100-10fs. The laser consists of a broadband oscillator and amplitude/phase shaper seeding an optical parametric amplifier (OPA). After recompression, the ~800nm pulse is converted to the fourth harmonic. Losses could be high enough to require 250W at 100kHz, making the OPA ~100x more powerful than existing femtosecond OPAs. In the E-SASE scheme, a single cycle of 5 micron light bunches the beam, which then radiates a short X-ray burst. This requires 100% fractional bandwidth, and precise phase control of the e-field within the pulse, as well as broad band compensation of dispersion throughout the laser path. Bandwidth can be increased by splitting the amplified spectrum into segments and coherently recombining. We present design concepts that are expected to meet requirements, and identify R&D needs.

WEPSO84	Present Status of Kyoto University Free Electron Laser	undulator, FEL, electron, cavity	711
	H. Zen, M. Inukai, T. Kii, R. Kinjo, K. Masuda, K. Mishima, H. Negm, H. Ohgaki, K. Okumura, M. Omer, K. Torgasin, K. Yoshida Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	A mid-infrared FEL named as KU-FEL (Kyoto University FEL) has been developed for energy related sciences [1]. After the achievement of the first lasing and the power saturation in 2008 [2, 3], we have been working to extend the tunable range of the FEL [4]. By replacing the original 1.6-m undulator into a 1.8 m one, the tunable range was expanded from 10-13 to 5-15 μm in January 2012. Then we fabricated a new undulator duct to reduce the minimum undulator gap from 20 to 15 mm. At 15-mm gap, the FEL gain can be expected to be twice as high as that at 20 mm gap. Commissioning of the new duct will be done in the end of this April. In this presentation, we will report on the result of the commissioning such as tunable range of KU-FEL and the estimated FEL gain, which would be compared with a simulation. [1] H. Zen, et al., Infrared Phys. Techn., 51, 382 (2008) [2] H. Ohgaki, et al., Proc. of FEL08, 4 (2008) [3] H. Ohgaki, et al., Proc. of FEL2009, 572 (2009) [4] H. Zen, et al., Proc. of FEL2012

Paper

Title

Other Keywords

Page

MOPSO06

Paraxial Approximation in CSR Modeling Using the Discontinuous Galerkin Method

impedance, simulation, radiation, synchrotron

32

D. A. Bizzozero, J.A. Ellison, K.A. Heinemann, S.R. Lau
UNM, Albuquerque, New Mexico, USA

Funding: This work was primarily supported by DOE under DE-FG-99ER41104. The work of DB and SL was partially supported by NSF grant PHY 0855678 to the University of New Mexico.
We continue our study* of CSR from a bunch moving on an arbitrary curved trajectory. In that study we developed an accurate 2D CSR Vlasov-Maxwell code (VM3@A) and applied it to a four dipole chicane bunch compressor. Our starting point now is the well-established paraxial approximation** with boundary conditions for a perfectly conducting vacuum chamber with uniform cross-section. This is considerably different from our previous approach* where we calculated the fields from an integral over history, using parallel plate boundary conditions. In this study, we present a Discontinuous Galerkin (DG) method for the paraxial approximation equations. Our basic tool is a MATLAB DG code on a GPU using MATLAB's gpuArray; the code was developed by one of us (DB). We discuss our results in the context of previous work and outline future applications for DG, including a Vlasov-Maxwell study.
* See PRST-AB 12 080704 (2009) and Proceedings from ICAP2012 TUSDC2.
** See PRST-AB 7 054403 (2004), PRST-AB 12 104401 (2009) and Jpn. J. Appl. Phys. 51 016401 (2012).

MOPSO43

High Power Laser Transport System for Laser Cooling to Counteract Back-Bombardment Heating in Microwave Thermionic Electron Guns

laser, gun, electron, coupling

75

J.M.D. Kowalczyk, M.R. Hadmack, J. Madey, E.B. Szarmes, M.H.E.H. Vinci
University of Hawaii, Honolulu, HI, USA

Funding: This work was funded by the Department of Homeland Security through grant #2011-DN-077-ARI055-03.
Heat from a high power, short pulse laser deposited on the surface of a thermionic electron gun cathode will diffuse into the bulk producing a surface cooling effect that counteracts the electron back-bombardment (BB) heating intrinsic to the gun. The resulting constant temperature stabilizes the current allowing extension of the gun’s peak current and duty cycle. To enable this laser cooling, high power laser pulses must be transported to the high radiation zone of the electron gun, and their transverse profile must be converted from Gaussian to top-hat to uniformly cool the cathode. A fiber optic transport system is simple, inexpensive, and will convert a Gaussian to a top-hat profile. Coupling into the fiber efficiently and without damage is difficult as tight focusing is required at the input and, if coupled in air, the high fluence will breakdown the air resulting in lost energy. We have devised a vacuum fiber coupler (VFC) that allows the focus to occur in vacuum, avoiding the breakdown of air, and have successfully transported 10 ns long, 85 mJ pulses from a 1064 nm Nd:YAG laser through 20 m of 1 mm diameter fiber enabling testing of the laser cooling concept.

TUOCNO03

Progress in a Photocathode DC Gun at the Compact ERL

gun, cathode, acceleration, high-voltage

184

N. Nishimori, R. Hajima, S.M. Matsuba, R. Nagai
JAEA, Ibaraki-ken, Japan
Y. Honda, T. Miyajima, M. Yamamoto
KEK, Ibaraki, Japan
H. Iijima, M. Kuriki
HU/AdSM, Higashi-Hiroshima, Japan
M. Kuwahara
Nagoya University, Nagoya, Japan

Photocathode DC gun to produce a train of electron bunch at high-average current and small emittance is a key component of advanced accelerators for high-power beams. However, DC guns operated at a voltage above 350 kV have suffered from field emitted electrons from a support rod since the development of Lasertron in 1980's. This critical issue has been resolved by a novel configuration, segmented insulator and guard rings, adopted in a DC gun at JAEA and stable application of high voltage at 550 kV has been demonstrated. The gun has been installed at the Compact ERL at KEK and ready for the beam generation. Similar type of DC guns are under development at KEK, Cornell, JLAB and IHEP. In this talk, we present progress in photocathode DC gun for high voltage and small emittance.

Slides TUOCNO03 [4.946 MB]

TUPSO17

Status of the Manufacturing Process for the SwissFEL C-Band Accelerating Structures

laser, linac, radio-frequency, coupling

245

U. Ellenberger, H. Blumer, L. Paly, C. Zumbach
Paul Scherrer Institute, Villigen PSI, Switzerland
M. Bopp, H. Fitze, F. Löhl
PSI, Villigen PSI, Switzerland

For the SwissFEL project a total of 104 C-band (or approximately 6 GHz for 5’712 MHz required) accelerating structures are needed. After developing and RF-testing of several short structures (0.5m), three 2meter prototypes have been produced successfully in-house. Avoiding any RF-tuning after fabrication, a high precision machining of the components is necessary. Special procedures were developed and handling equipment was built in order to maintain the accuracy during stacking and vacuum brazing of the parts for the C-band structures. This paper summarizes the manufacturing techniques and the mechanical test results for constant subvolumes to match the required klystron frequency of 5’712 MHz

TUPSO21

SwissFEL Cathode Load-lock System

cathode, gun, laser, extraction

259

R. Ganter, M. Bopp, N. Gaiffi, T. Le Quang, M. Pedrozzi, M. Schaer, T. Schietinger, L. Schulz, L. Stingelin, A. Trisorio
PSI, Villigen PSI, Switzerland

The SwissFEL electron source is an RF photo-injector in which the photo-cathode plug can be exchanged. Without load-lock, the cathode exchange takes about one week and cathode surface gets contaminated in the atmosphere during installation, leading to unpredictable quantum efficiency (QE) fluctuations. This motivated the construction of a load lock system to prepare and insert cathodes in the photo-injector. This load lock system consists of three parts: the preparation chamber, the transportable vacuum suitcase and the gun load lock chamber. This three parts system gives the possibility to prepare the cathode surface with methods like vacuum firing and plasma cleaning. The QE can be checked and the plug can be inserted in the gun without breaking vacuum. This will allow establishing an optimized a reproducible cathode preparation procedure. Since several cathodes can be loaded in advance, the exchange procedure reduces the machine shutdown to a few hours (shorter RF conditioning). The system is described and first experience with its use is reported.

TUPSO25

Status of the EU-XFELl Laser Heater

laser, undulator, electron, alignment

271

M. Hamberg, V.G. Ziemann
Uppsala University, Uppsala, Sweden

Funding: This work was supported by the Swedish Research Council under contract number DNR-828-2008-1093.
We describe the technical layout and the status of the laser heater system for the EuXFEL. The laser heater is needed to increase the momentum spread of the electron beam to prevent micro-bunching instabilities in the linac.

TUPSO27

Design for a Fast, XFEL-Quality Wire Scanner

photon, radiation, electron, instrumentation

276

M.A. Harrison, R.B. Agustsson, T.J. Campese, P.S. Chang, A.Y. Murokh, M. Ruelas
RadiaBeam, Santa Monica, USA

RadiaBeam Technologies has designed and manufactured a new wire scanner for high-speed emittance measurements of XFEL-type beams of energy 139 MeV. Using three 25-micron thick tungsten wires, this wire scanner measures vertical and horizontal beam size as well as transverse spatial correlation in one pass. The intensity of the beam at a wire position is determined from emitted bremsstrahlung photons as measured by a BGO scintillator system. The wires are transported on a two-ended support structure moved by a ball-screw linear stage. The double-ended structure reduces vibrations in the wire holder, and the two-bellows design negates the effects of air pressure on the motion. The expected minimum beam size measurable by this system is on the order of 10 microns with 0.1-micron accuracy. To achieve this, new algorithms are presented that reduce the effect of the non-zero thickness of the wire on the wire scan output. In addition, novel calculations are presented for determining the elliptical geometric parameters (vertical and horizontal beam size and correlation, or alternatively, the axis lengths and rotation) of the beam from the wire scanner measurements.

TUPSO30

Conditioning Status of the First XFEL Gun at PITZ

gun, solenoid, cathode, cavity

282

I.I. Isaev, J.D. Good, M. Groß, L. Hakobyan, L. Jachmann, M. Khojoyan, W. Köhler, G. Kourkafas, M. Krasilnikov, D. Malyutin, B. Marchetti, R. Martin, A. Oppelt, M. Otevřel, B. Petrosyan, D. Richter, A. Shapovalov, F. Stephan, G. Vashchenko, R.W. Wenndorff
DESY Zeuthen, Zeuthen, Germany
G. Asova
INRNE, Sofia, Bulgaria
P. Boonpornprasert, S. Rimjaem
Chiang Mai University, Chiang Mai, Thailand
M.A. Nozdrin
JINR, Dubna, Moscow Region, Russia
G. Pathak
Uni HH, Hamburg, Germany

The paper describes the recent results of conditioning and dark current measurements for the photocathode RF gun at the photoinjector test facility at DESY, Zeuthen site (PITZ). The aim of PITZ is to develop and operate an optimized photo injector for free electron lasers and linear accelerators which require high quality beams. In order to get high gradients in the RF gun extensive conditioning is required. A data analysis of the conditioning process is based on data saved by a Data Acquisition system (DAQ). Conditioning results of the first gun cavity for the XFEL is presented. The events which occurred during the conditioning are briefly described.

TUPSO33

The Commissioning of Tess: An Experimental Facility for Measuring the Electron Energy Distribution From Photocathodes

electron, cathode, laser, brightness

290

L.B. Jones, R.J. Cash, B.D. Fell, K.J. Middleman, B.L. Militsyn, T.C.Q. Noakes
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
D.V. Gorshkov, H.E. Scheibler, A.S. Terekhov
ISP, Novosibirsk, Russia

ASTeC have developed a Transverse Energy Spread Spectrometer (TESS) – an experimental facility to characterise the energy distribution of electrons emitted by a photocathode. Electron injector brightness is fundamentally limited by the width of this distribution or energy spread, and brightness will be increased significantly by reducing the longitudinal and transverse energy spread at source. TESS supports photocathode performance measurements at room and LN2-temperature under illumination from a range of fixed- and variable-wavelength light sources, allowing characterisation of both metal and semiconductor photocathodes. Preliminary work with GaAs* has shown that electron energy spread is dependent on the quantum efficiency (Q.E.) of the photocathode source, and TESS includes a piezo-electric leak valve to allow controlled degradation of the photocathode Q.E. whilst monitoring the energy spread of emitted electrons. This system offers huge potential to support future photocathode R&D work into a range of photocathode materials. Using GaAs photocathodes activated to high levels of Q.E. in our photocathode preparation facility**, we present commissioning results for TESS.
* Proc. IPAC ’12, TUPPD067, 1557-1559
** Proc. IPAC ’11, THPC129, 3185-3187

TUPSO43

Status of the SwissFEL C-band Linear Accelerator

linac, controls, klystron, low-level-rf

317

F. Löhl, J. Alex, H. Blumer, M. Bopp, H.-H. Braun, A. Citterio, H. Fitze, H. Jöhri, T. Kleeb, L. Paly, J.-Y. Raguin, L. Schulz, R. Zennaro
PSI, Villigen PSI, Switzerland
U. Ellenberger
Paul Scherrer Institute, Villigen PSI, Switzerland

This paper will summarize the status of the linear accelerator of the Swiss free-electron laser SwissFEL. It will be based on C-band technology and will use solid-state modulators and a novel type of C-band accelerating structures which has been designed at PSI. Initial test results of first 2 m long structures will be presented together with measurements performed with the first BOC-type pulse compressors. Furthermore, we will present first results of a water cooling system for the accelerating structures and the pulse compressors.

TUPSO52

R&D Towards a Delta-type Undulator for the LCLS

undulator, polarization, FEL, radiation

348

H.-D. Nuhn, S.D. Anderson, G.B. Bowden, Y. Ding, G.L. Gassner, Z. Huang, E.M. Kraft, Yu.I. Levashov, F. Peters, F.E. Reese, J.J. Welch, Z.R. Wolf, J. Wu
SLAC, Menlo Park, California, USA
A.B. Temnykh
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The LCLS generates linearly polarized, intense, high brightness x-ray pulses from planar fixed-gap undulators. While the fixed-gap design supports a very successful and tightly controlled alignment concept, it provides only limited taper capability (up to 1% through canted pole and horizontal position adjustability) and lacks polarization control. The latter is of great importance for soft x-ray experiments. A new compact undulator design (Delta) has been developed and tested with a 30-cm-long in-vacuum prototype at Cornell University, which adds those missing properties to the LCLS undulator design and is readily adapted to the LCLS alignment concept. Tuning Delta undulators within tight, FEL type tolerances is a challenge due to the fact that the magnetic axis and the magnet blocks are not easily accessible for measurements and tuning in the fully assembled state. An R&D project is underway to install a 3.2-m long out-of-vacuum device in place of the last LCLS undulator, to provide controllable levels of polarized radiation and to develop measurement and tuning techniques to achieve x-ray FEL type tolerances. Presently, the installation of the device is scheduled for August 2013.

TUPSO55

300 mm Electromagnetic Wiggler for ELBE

wiggler, electron, insertion, insertion-device

353

C.W. Ostenfeld, M. Pedersen
Danfysik A/S, Taastrup, Denmark

Danfysik has designed and built a 300 mm fixed-gap electromagnetic wiggler for the ELBE radiation source at Helmholz Zentrum Dresden Rossendorff. This wiggler will serve as a source of narrow-band THz radiation in the 100 μm to 10 mm range. Due to careful magnetic modelling, and an effective shimming process, we were able to deliver magnetic performance at a high level. We present the details of the modelling, as well as magnetic results.

TUPSO75

Design Analysis and High Power RF Test of a 3.9 GHz 5-cell Deflecting-mode Cavity in a Cryogenic Operation

cavity, simulation, cryomodule, coupling

399

Y.-M. Shin
Northern Illinois University, DeKalb, Illinois, USA
M.D. Church
Fermilab, Batavia, USA

A 3.9 GHz deflecting mode (π, TM110) cavity has been long used for six-dimensional phase-space beam manipulation tests [1 - 5] at the A0 Photo-Injector Lab (16 MeV) in Fermilab and their extended applications with vacuum cryomodules are currently planned at the Advanced Superconducting Test Accelerator (ASTA) user facility (> 50 MeV). Despite the successful test results, the cavity, however, demonstrated limited RF performance during liquid nitrogen (LN2) ambient operation that was inferior to theoretical prediction. We have been performing full analysis of the designed cavity by analytic calculation and comprehensive system simulation analysis to solve complex thermodynamics and mechanical stresses. The re-assembled cryomodule is currently under the test with a 50 kW klystron at the Fermilab A0 beamline, which will benchmark the modeling analysis. The test result will be used to design vacuum cryomodules for the 3.9 GHz deflecting mode cavity that will be employed at the ASTA facility for beam diagnostics and phase-space control.
[1] D. A. Edwards, LINAC 2002
[2] Y.-E Sun, PRTAB 2004
[3] P. Piot, PRSTAB2006
[4] J. Ruand et al., PRL 2011
[5] Y.-E. Sun, et al., PRL 2010

TUPSO82

Spectroscopy System for LCLS Photocathodes

electron, gun, cathode, emittance

421

P. Stefan, A. Brachmann, T. Vecchione
SLAC, Menlo Park, California, USA

Funding: Work supported by US DOE contract DE-AC02-76SF00515.
Photocathode reliability is important from an operational standpoint. Unfortunately LCLS copper photocathodes have not always been reliable. Some have operated well for long periods of time while others have required continual maintenance. It is believed that the observed variations in quantum efficiency, emittance and lifetimes are inherently surface related, corresponding to changes in composition or morphology. The RF Electron-gun Cathode, Electron Surface Spectrometer, or RECESS, system has been commissioned to study this by making essential measurements that could not be obtained otherwise. These involve photocathode surface chemical characterization. The system is designed to use a combination of angle-resolved ultraviolet and x-ray photoelectron spectroscopy and is capable of either stand-alone operation or interoperability with a beam line at SSRL. Here we report on the first commissioning spectra and the direction of the project going forward.

TUPSO83

Quantum Efficiency and Transverse Momentum From Metals

electron, brightness, FEL, laser

424

T. Vecchione, D. Dowell
SLAC, Menlo Park, California, USA
J. Feng, H.A. Padmore, W. Wan
LBNL, Berkeley, California, USA

Funding: Work supported by US DOE contracts DE-AC02-05CH11231, KC0407-ALSJNT-I0013, and DE-SC000571.
QE and transverse momentum are key parameters limiting the achievable brightness of FELs. Despite the importance, little data is available to substantiate current models. Expressions for each and experimental confirmation of each expression with respect to excess energy are presented. Novel instrumentation and analysis techniques developed are described.

TUPSO84

SLAC RF Gun Photocathode Test Facility

gun, laser, emittance, diagnostics

427

T. Vecchione, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, H. Loos, J. Sheppard, S.P. Weathersby, F. Zhou
SLAC, Menlo Park, California, USA

Funding: Work supported by US DOE contract DE-AC02-76SF00515.
A RF gun photocathode test facility has been commissioned at SLAC. The facility consists of a S-band gun, high power RF, a UV drive laser and beam diagnostics. Here we report on the capabilities of the facility demonstrated during commissioning. Currently the facility is being used to study in-situ laser processing of copper photocathodes. In the future the facility will be used to study fundamental gun and photocathode performance limitations and enhancement strategies. Eventually it is envisioned to integrate a load lock and plug into the gun enabling the evaluation of high performance surface sensitive semiconductor photocathodes and the incorporation of ex-situ surface science analytical techniques.

WEPSO73

High Average Power Seed Laser Design for High Reprate FELs

laser, FEL, electron, controls

697

R.B. Wilcox, G. Marcus, G. Penn
LBNL, Berkeley, California, USA
T. Metzger, M. Schultze
TRUMPF Scientific Lasers GmbH + Co. KG, Munchen-Unterfoehring, Germany

Funding: US Department of Energy, under Contract Numbers DE-AC02-0SCH11231.
In the proposed Next Generation Light Source (NGLS), FEL designs use lasers to seed the FEL in an HGHG scheme or bunch the electron beam in an E-SASE scheme. The FELs would run at 100kHz to 1MHz, requiring high average power lasers. For the seeded FEL, laser modulation is applied at 200-240nm, with 250-700MW peak power depending on pulse length, which can vary from 100-10fs. The laser consists of a broadband oscillator and amplitude/phase shaper seeding an optical parametric amplifier (OPA). After recompression, the ~800nm pulse is converted to the fourth harmonic. Losses could be high enough to require 250W at 100kHz, making the OPA ~100x more powerful than existing femtosecond OPAs. In the E-SASE scheme, a single cycle of 5 micron light bunches the beam, which then radiates a short X-ray burst. This requires 100% fractional bandwidth, and precise phase control of the e-field within the pulse, as well as broad band compensation of dispersion throughout the laser path. Bandwidth can be increased by splitting the amplified spectrum into segments and coherently recombining. We present design concepts that are expected to meet requirements, and identify R&D needs.

WEPSO84

Present Status of Kyoto University Free Electron Laser

undulator, FEL, electron, cavity

711

H. Zen, M. Inukai, T. Kii, R. Kinjo, K. Masuda, K. Mishima, H. Negm, H. Ohgaki, K. Okumura, M. Omer, K. Torgasin, K. Yoshida
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

A mid-infrared FEL named as KU-FEL (Kyoto University FEL) has been developed for energy related sciences [1]. After the achievement of the first lasing and the power saturation in 2008 [2, 3], we have been working to extend the tunable range of the FEL [4]. By replacing the original 1.6-m undulator into a 1.8 m one, the tunable range was expanded from 10-13 to 5-15 μm in January 2012. Then we fabricated a new undulator duct to reduce the minimum undulator gap from 20 to 15 mm. At 15-mm gap, the FEL gain can be expected to be twice as high as that at 20 mm gap. Commissioning of the new duct will be done in the end of this April. In this presentation, we will report on the result of the commissioning such as tunable range of KU-FEL and the estimated FEL gain, which would be compared with a simulation.
[1] H. Zen, et al., Infrared Phys. Techn., 51, 382 (2008)
[2] H. Ohgaki, et al., Proc. of FEL08, 4 (2008)
[3] H. Ohgaki, et al., Proc. of FEL2009, 572 (2009)
[4] H. Zen, et al., Proc. of FEL2012