FEL2014 - List of Keywords (vacuum)

Paper	Title	Other Keywords	Page
MOP003	Helical Undulator Radiation in Internally Coated Metallic Pipe	radiation, undulator, synchrotron-radiation, impedance	26
	T.L. Vardanyan, A. Grigoryan, L.V. Hovakimyan, M. Ivanyan, A.V. Tsakanian, V.M. Tsakanov CANDLE SRI, Yerevan, Armenia
	The vacuum chambers of many advanced undulator sources are coated internally in order to reduce the impedance of the vacuum chamber or improve the vacuum performance. Although the impedances and radiation properties of the internally coated metallic pipes for straightforward moving charge are well studied, the peculiarities of the particles wiggling motion on the radiation characteristics in such structure are missed. In this paper we obtain exact expressions for the fields of a particle moving along a spiral path, as in the single-layer resistive as well as in the two-layer metallic waveguides, modelling NEG coating of the waveguide walls. Based on these results, it will be possible to obtain the necessary characteristics of the radiation of helical undulators, very close to reality. The solution is obtained as a superposition of a particular solution of inhomogeneous Maxwell's equations in a waveguide with perfectly conducting walls, and the solutions of the homogeneous Maxwell equations in the single-layer and double-layer resistive waveguides. Solution in the form of the multipole expansion for inhomogeneous Maxwell's equations for a waveguide with perfectly conducting walls, are also obtained in this study.

MOP010	The Photon Beam Loss Monitors as a Part of Equipment Protection System at European XFEL	photon, detector, radiation, beam-transport	37
	N. Gerasimova, H. Sinn XFEL. EU, Hamburg, Germany S. Dziarzhytski, R. Treusch DESY, Hamburg, Germany
	For the X-ray beam transport systems, the problem of potential damage to the equipment by mis-steered photon beam emerged with advent of powerful X-ray FELs. In particular high repetition rate machines as European XFEL, where not only focused beam can produce ablation, but even unfocused beam can melt the beamline components while machine operates in multibunch mode, demand for implementation of equipment protection. Here we report on development of photon beam loss monitors at European XFEL facility. The photon beam loss monitors will react on the mis-steered photon beam and interface the machine protection system. The prototype comprises the vacuum chamber with fluorescence crystals positioned outside the photon beampath. The fast sub-hundred ns fluorescence induced by mis-steered beam can be detected by photomultiplier tube allowing for intra-train reaction of machine protection system. First tests have been carried out at FLASH and shown the feasibility of detection based on PMT-detected fluorescence. In addition to efficient YAG:Ce crystal, the robust low-Z material as CVD microcrystalline diamonds has shown a potential to be used as fluorescence crystals.

MOP015	A Power Switching Ionization Profile Monitor (3D-IPM)	laser, electron, ion, detector	47
	H.F. Breede, H.-J. Grabosch, M. Sachwitz, L.V. Vu DESY Zeuthen, Zeuthen, Germany
	FLASH at DESY in Hamburg is a linear accelerator to produce soft x-ray laser light ranging from 4.1 to 45 nm. To ensure the operation stability of FLASH, monitoring of the beam is mandatory. Two Ionization Profile Monitors (IPM) detect the lateral x and y position and profile changes of the beam. The functional principle of the IPM is based on the detection of particles, generated by interaction of the beam with the residual gas in the beam line. The newly designed IPM enables the combined evaluation of the horizontal and vertical position as well as the profile. A compact monitor, consisting of two micro-channel plates (MCP) is assembled on a conducting cage along with toggled electric fields in a rectangular vacuum chamber. The particles created by the photon beam, drift in the homogenous electrical field towards the respective MCP, which produces an image of the beam profile on an attached phosphor screen. A camera for each MCP is used for assessment. This indirect detection scheme operates over a wide dynamic range and allows the live detection of the clear position and the shape of the beam. The final design is presented.
	Poster MOP015 [1.314 MB]

MOP023	Development of a Magnetic System to Cancel the Attractive Force toward Structural Reform of Undulators	undulator, multipole, experiment, synchrotron	75
	R. Kinjo, T. Tanaka RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan A. Kagamihata, T. Seike JASRI/SPring-8, Sayo-gun, Japan S. Yamamoto KEK, Tsukuba, Japan
	As part of a development on a compact and lightweight structure toward structural reform of undulators, cancellation of magnetic attractive force is being studied. Undulators usually require rigid mechanical components and frames to control the magnet gap precisely against the large attractive force in between. If the attractive force is canceled out near the point of load, the requirement for the undulator structure is relaxed and the cost and lead time of construction and installation are saved largely. For that purpose, we have proposed to add periodically-magnetized monolithic magnets beside the main magnets, which are expected to generate a repulsive force having the same gap-dependency as the attractive force in a cost-effective way. In the conference, the present status of the development of the force cancellation system will be presented, with a focus on the result of preliminary experiments using the periodically-magnetized magnets. Also introduced will be a development plan for the compact and lightweight undulator based on the cancellation system.

MOP041	Summary of the U15 Prototype Magnetic Performance	undulator, electron, quadrupole, photon	111
	M. Calvi, M. Aiba, M. Brügger, S. Danner, R. Ganter, C. Ozkan, T. Schmidt PSI, Villigen PSI, Switzerland
	The first undulator prototype (U15) was assembled and magnetically tested. The instrumentation and the algorithms developed for the undulator optimization are presented and a comparison among different approaches is reviewed. The magnetic measurement results before and after the installation of the vacuum components are discussed. The summary of the undulator test with 100 MeV electron beam is presented and the impact of the radiation on the magnetics is addressed.

MOP043	Magnetic Design of an Apple III Undulator for SwissFEL	undulator, polarization, operation, alignment	116
	T. Schmidt, A. Anghel, P. Boehler, M. Brügger, M. Calvi, S. Danner, P. Huber, A. Keller, M. Locher PSI, Villigen PSI, Switzerland
	In the frame of the SwissFEL project a soft x-ray line is planned in the coming years to cover the wavelength between 0.7 and 7.0nm. Based on the good experience at the SLS storage ring with Apple undulator as source of variable polarized light, Apple III type undulators are also foreseen at the SwissFEL. In this paper the design of these devices is introduced and the preliminary magnetic configuration together with the optimization strategy is presented in details.

TUA03	A GaAs Photoemission DC Gun for CAEP High-average-power THz FEL	gun, cathode, high-voltage, FEL	318
	H. Wang, K. Li, M. Li, D. Wu, D.X. Xiao, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	FEL-THz plays an important role in THz science and technology research, for high power output and tunable wavelength, which is indispensable to material, biology, medical research. Now, the construction is underway at China Academy of Engineering Physics (CAEP) on high-average-power FEL THz source, and the demonstration of stable, reliable, high brightness, high power electron source operation is one of key issues. The components of the system were constructed and the performance tests are still on. The lifetime of the Negative Electron Affinity (NEA) surface is about 40 hours, which is limitied mainly by vacuum. Up to now, the gun can supply 5mA beam current and has been employed for preliminary experiments. In this paper, the design considerations and present status are given.
	Slides TUA03 [1.182 MB]

TUP023	Modeling CSR in a Vacuum Chamber by Partial Fourier Analysis and the Discontinuous Galerkin Method	synchrotron-radiation, impedance, synchrotron, radiation	419
	D. A. Bizzozero, J.A. Ellison UNM, Albuquerque, New Mexico, USA R.L. Warnock SLAC, Menlo Park, California, USA
	Funding: Work supported by DOE contracts DE-FG-99ER41104 and DE-AC03-76SF00515. We continue our study of CSR* from a bunch on an arbitrary curved orbit in a plane, which used a Fourier transform in s-ct. The vacuum chamber has rectangular cross section with possibly varying horizontal width. We use the slowly varying amplitude approximation, and invoke a Fourier expansion in the vertical coordinate y, which meets the boundary conditions on the top and bottom plates and makes contact with the Bessel equation of the frequency domain treatment. The fields are defined by a PDE in s and x, first order in s, which is discretized in x by finite differences (FD) or the discontinuous Galerkin method (DG). We compare results of FD and DG, and also compare to our earlier calculations in 3D (paraxial) which did not use the Fourier series in y,. This approach provides more transparency in the physical description, and when only a few y-modes are needed, provides a large reduction in computation time. See FEL13 Proceedings MOPSO06: http://accelconf.web.cern.ch/AccelConf/FEL2013/papers/mopso06.pdf ** See PRST-AB 7 054403 (2004) and Jpn. J. Appl. Phys. 51 016401 (2012).

THA03	A Plan for the Development of Superconducting Undulator Prototypes for LCLS-II and Future FELs	undulator, FEL, linac, electron	649
	P. Emma, N.R. Holtkamp, H.-D. Nuhn SLAC, Menlo Park, California, USA D. Arbelaez, J.N. Corlett, S.A. Myers, S. Prestemon, D. Schlueter LBNL, Berkeley, California, USA C.L. Doose, J.D. Fuerst, E. Gluskin, Q.B. Hasse, Y. Ivanyushenkov, M. Kasa, G. Pile, E. Trakhtenberg ANL, Argonne, Ilinois, USA
	Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515, DE-AC02-05CH11231, and DE-AC02-06CH11357. Undulators serve as the primary source of radiation for modern storage rings, and more recently for the advent of Free-Electron Lasers (FELs). The performance of future FELs can be greatly enhanced using the much higher magnetic fields of superconducting undulators (SCU). For example, the LCLS-II hard x-ray undulator can be shortened by up to 70 m using an SCU in place of a PMU (permanent magnet undulator), or its spectral performance can be critically improved when using a similar length. In addition, SCUs are expected to be orders of magnitude less sensitive to radiation dose; a major issue at LCLS-II with its 1-MHz electron bunch rate. We present a funded R&D collaboration between SLAC, ANL, and LBNL, which aims to demonstrate the viability of superconducting undulators for FELs by building, testing, measuring, and tuning two 1.5-m long planar SCU prototypes using two different technologies: NbTi at ANL and Nb3Sn at LBNL. Our goal is to review and reassess the LCLS-II HXR baseline plans (PMU) in July of 2015, after the development and evaluation of both prototypes, possibly in favor of an SCU for LCLS-II.
	Slides THA03 [29.468 MB]

THP030	Recent Photocathode R&D for the LCLS injector	laser, cathode, gun, emittance	769
	F. Zhou, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, J.R. Lewandowski, J. Sheppard, T. Vecchione, S. Vetter, S.P. Weathersby SLAC, Menlo Park, California, USA
	Funding: US DOE under contract No. DE-AC02-76SF00515 Systematic studies of the copper photocathodes identical to those used in the LCLS injector gun has been carried out at SLAC’s RF gun test facility. Recent observations at the gun test facility indicate that the pre-cleaning of the cathode prior to the installation in the gun is the major cause of the lower initial QE (~10^-6) in the RF gun. All of four cathodes tested in the gun test facility have reliable higher initial QE, 4-8·10^-5, with removal of pre-cleaning step. All of details will be described in the paper. A robust laser-assisted processing recipe has been developed. With this recipe, QE can be repeatedly evolved to about 1x10^-4 within 3-4 weeks following the laser processing, and within 1-2 days the emittance is recovered to the values as observed prior to the laser processing. When compared to previous recipe used for the present LCLS cathode, the new recipe uses lower laser fluence and provides faster emittance recovery. Laser pointing stability is a key requirement for the success of the technique. This paper presents all details of the studies for four cathodes with over a few tens of laser-assisted spots and compares the results with the present LCLS cathode.

THP033	Mechanical Design for a Corrugated Plate Dechirper System for LCLS	wakefield, quadrupole, controls, electron	785
	M.A. Harrison, P. Frigola, D.W. Martin, A.Y. Murokh, M. Ruelas RadiaBeam Systems, Santa Monica, California, USA Z. Huang, R.H. Iverson, T.J. Maxwell, Z. Zhang SLAC, Menlo Park, California, USA
	Funding: This work is supported by Department of Energy grant number DE-SC0009550. RadiaBeam Systems is developing a novel passive chirp removal system using corrugated plates as studied by Bane and Stupakov.* Following on from low-energy experiments at BNL-ATF,** RBS will install a much larger and powerful system for removing the chirp from the 3-GeV beams in the LTU section at LCLS. The larger plates will present new challenges in the areas of manufacturing and mechanical control. In this paper we review the requirements for the dimensions of the corrugated plates for proper operation and the infrastructure necessary for precisely placing the plates so as not to adversely disrupt the beam. * K. Bane, et al "Corrugated Pipe as a Beam Dechirper," SLAC-PUB-14925, 2012 ** Harrison, M., et al "Removal of Residual Chirp in Compressed Beams Using a Passive Wakefield Technique." NaPAC13, 2013

THP046	Cu and Cs2Te Cathodes Preparation and QE History at the SwissFEL Injector Test Facility.	cathode, laser, operation, gun	832
	J. Bossert, R. Ganter, M. Schaer, T. Schietinger PSI, Villigen PSI, Switzerland
	The installation of a load-lock chamber attached to the SwissFEL gun gives the possibility to carefully prepare the metallic cathodes under vacuum and also to use semiconductor cathodes like Cs2Te cathodes which cannot be transported through air. The paper presents the preparation procedures used for copper (QE>1.e-4) and Cs2Te cathodes (based on a CERN recipe) together with surface analysis results (SEM, EDX, interferometry, microscopy). Finally, the QE evolutions obtained in the SwissFEL Injector test facility as well as in a test stand are discussed for both materials.

THP049	High Power RF Test and Analysis of Dark Current in the SwissFEL-gun	gun, cathode, solenoid, laser	843
	P. Craievich, S. Bettoni, M. Bopp, A. Citterio, C. Ozkan, M. Pedrozzi, J.-Y. Raguin, M. Schaer, A. Scherer, T. Schietinger, L. Stingelin PSI, Villigen PSI, Switzerland
	To fulfill the beam quality and operational requirements of the SwissFEL project, currently under construction at the Paul Scherrer Institut, a new RF photocathode gun for the electron source was designed and manufactured in house. A 2.6 cell S-band gun operating with near-perfect rotationally symmetric RF field was designed to operate with a 100MV/m cathode field at a repetition rate of 100Hz with average power dissipation of 0.9kW with pulse duration of 1us. The first SwissFEL-gun is now fabricated and installed in the SwissFEL Injector Test Facility (SITF). The frequency spectrum and field balance, through bead-pulling, have been directly verified in-situ and then the gun has been operated with high-power RF. The results of bead-pull measurements and high-power tests are presented and discussed. In addition the emitted dark current was also measured during the high-power tests and the charge within the RF pulse was measured as a function of the peak cathode field at different pulse durations. Faraday cup data were taken for cathode peak RF fields up to 100MV/m for the case of a diamond-turned polycrystalline copper cathode.

THP056	The SwissFEL C-band RF Pulse Compressor: Manufacturing and Proof of Precision by RF Measurements	cavity, coupling, resonance, klystron	859
	U. Ellenberger, H. Blumer, M. Heusser, M. Kleeb, L. Paly, M. Probst, T. Stapf Paul Scherrer Institute, Villigen PSI, Switzerland M. Bopp, A. Citterio, R. Zennaro PSI, Villigen PSI, Switzerland
	A pulse compressor is required to compress the RF power distributed to the four accelerating structures of a single C-band (5712 GHz) module of the SwissFEL. The pulse compressor is of the barrel open cavity (BOC) type. A total of 26 BOC devices are necessary to operate the linear accelerator (26 modules or 10⁴ C-band structures) of SwissFEL X-ray laser. The C-band BOC combines the advantages of compactness and large RF efficiency i.e. large compression factor. Key features of the BOC are described and how they have been implemented in the manufacturing and tuning processes. RF measurements of the BOC are presented to account for the mechanical precision reached by manufacturing. Up to August 2014 about 6 BOCs have been manufactured in-house and one has been high power tested in a RF test stand to simulate the operation in SwissFEL.

THP063	Production of C-band Disk-loaded type CG Accelerating Structures	operation, cavity, resonance, acceleration	885
	N. Shigeoka, S. Miura, D. Suzuki MHI, Hiroshima, Japan T. Asaka, T. Inagaki, Y. Otake, T. Sakurai RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan H. Ego JASRI/SPring-8, Hyogo-ken, Japan
	In April 2013, MITSUBISHI HEAVY INDUSTRIES, LTD. contracted with RIKEN to produce six C-band disk-loaded type and constant gradient (CG) accelerating structures for removal of SCSS. These structures were newly designed by RIKEN for operation with an acceleration gradient of over 45 MeV/m and a repletion rate of 120 pps. The first structure was delivered in August 2013 to RIKEN and the other five was also delivered in March 2014. The accelerating structures were stacked from one hundred accelerating cells and formed by the vacuum brazing method. These cells using oxygen free copper were ultra-precisely machined. Unlike the C-band choke-mode type structures, which MHI manufactured in past for SACLA, the accelerating cells of the CG structure can be tuned after the brazing by pushing dimpling at the tuning hole of each cell. Demands of a VSWR < 1.1 and a phase error < 3 degree are fulfilled after the tuning by using the nodal shift method, which corrects cell frequency shifts due to the machining errors of cells and a cell’s deformation by the heat cycle of the brazing. The detailed results of the production and low-power RF tests will be presented in this presentation.
	Poster THP063 [0.623 MB]

THP082	Measurements of Compressed Bunch Temporal Profile using Electro-Optic Monitor at SITF	laser, electron, diagnostics, optics	922
	Ye. Ivanisenko, V. Schlott PSI, Villigen PSI, Switzerland P. Peier DESY, Hamburg, Germany
	Funding: The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n.°290605 (PSI-FELLOW/COFUND) The SwissFEL Injector Test Facility (SITF) is an electron linear accelerator with a single bunch compression stage at Paul Scherrer Institute (PSI) in Switzerland. Electro-optic monitors (EOMs) are available for bunch temporal profile measurements before and after the bunch compressor. The profile reconstruction is based upon spectral decoding technique. This diagnostic method is non-invasive, compact and cost-effective. It does not have high resolution and wide dynamic range of an RF transverse deflecting structure (TDS), but it is free of transverse beam size influence, what makes it a perfect tool for fast compression tuning. We present results of EOM and TDS measurements with down to 150 fs long bunches after the compression stage at SITF.

THP091	Design and Test of Wire-Scanners for SwissFEL	electron, FEL, monitoring, booster	948
	G.L. Orlandi, M. Baldinger, H. Brands, P. Heimgartner, R. Ischebeck, A. Kammerer, F. Löhl, R. Lüscher, P. Mohanmurthy, C. Ozkan, B. Rippstein, V. Schlott, L. Schulz, C. Seiler, S. Trovati, P. Valitutti, D. Zimoch PSI, Villigen PSI, Switzerland
	The SwissFEL light-facility will provide coherent X-rays in the wavelength region 7-0.7 nm and 0.7-0.1 nm. In SwissFEL, view-screens and wire-scanners will be used to monitor the transverse profile of a 200/10pC electron beam with a normalized emittance of 0.4/0.2 mm.mrad and a final energy of 5.7 GeV. Compared to view screens, wire-scanners offer a quasi-non-destructive monitoring of the beam transverse profile without suffering from possible micro-bunching of the electron beam. The main aspects of the design, laboratory characterization and beam-test of the SwissFEL wire-scanner prototype will be presented.

Paper

Title

Other Keywords

Page

MOP003

Helical Undulator Radiation in Internally Coated Metallic Pipe

radiation, undulator, synchrotron-radiation, impedance

26

T.L. Vardanyan, A. Grigoryan, L.V. Hovakimyan, M. Ivanyan, A.V. Tsakanian, V.M. Tsakanov
CANDLE SRI, Yerevan, Armenia

The vacuum chambers of many advanced undulator sources are coated internally in order to reduce the impedance of the vacuum chamber or improve the vacuum performance. Although the impedances and radiation properties of the internally coated metallic pipes for straightforward moving charge are well studied, the peculiarities of the particles wiggling motion on the radiation characteristics in such structure are missed. In this paper we obtain exact expressions for the fields of a particle moving along a spiral path, as in the single-layer resistive as well as in the two-layer metallic waveguides, modelling NEG coating of the waveguide walls. Based on these results, it will be possible to obtain the necessary characteristics of the radiation of helical undulators, very close to reality. The solution is obtained as a superposition of a particular solution of inhomogeneous Maxwell's equations in a waveguide with perfectly conducting walls, and the solutions of the homogeneous Maxwell equations in the single-layer and double-layer resistive waveguides. Solution in the form of the multipole expansion for inhomogeneous Maxwell's equations for a waveguide with perfectly conducting walls, are also obtained in this study.

MOP010

The Photon Beam Loss Monitors as a Part of Equipment Protection System at European XFEL

photon, detector, radiation, beam-transport

37

N. Gerasimova, H. Sinn
XFEL. EU, Hamburg, Germany
S. Dziarzhytski, R. Treusch
DESY, Hamburg, Germany

For the X-ray beam transport systems, the problem of potential damage to the equipment by mis-steered photon beam emerged with advent of powerful X-ray FELs. In particular high repetition rate machines as European XFEL, where not only focused beam can produce ablation, but even unfocused beam can melt the beamline components while machine operates in multibunch mode, demand for implementation of equipment protection. Here we report on development of photon beam loss monitors at European XFEL facility. The photon beam loss monitors will react on the mis-steered photon beam and interface the machine protection system. The prototype comprises the vacuum chamber with fluorescence crystals positioned outside the photon beampath. The fast sub-hundred ns fluorescence induced by mis-steered beam can be detected by photomultiplier tube allowing for intra-train reaction of machine protection system. First tests have been carried out at FLASH and shown the feasibility of detection based on PMT-detected fluorescence. In addition to efficient YAG:Ce crystal, the robust low-Z material as CVD microcrystalline diamonds has shown a potential to be used as fluorescence crystals.

MOP015

A Power Switching Ionization Profile Monitor (3D-IPM)

laser, electron, ion, detector

47

H.F. Breede, H.-J. Grabosch, M. Sachwitz, L.V. Vu
DESY Zeuthen, Zeuthen, Germany

FLASH at DESY in Hamburg is a linear accelerator to produce soft x-ray laser light ranging from 4.1 to 45 nm. To ensure the operation stability of FLASH, monitoring of the beam is mandatory. Two Ionization Profile Monitors (IPM) detect the lateral x and y position and profile changes of the beam. The functional principle of the IPM is based on the detection of particles, generated by interaction of the beam with the residual gas in the beam line. The newly designed IPM enables the combined evaluation of the horizontal and vertical position as well as the profile. A compact monitor, consisting of two micro-channel plates (MCP) is assembled on a conducting cage along with toggled electric fields in a rectangular vacuum chamber. The particles created by the photon beam, drift in the homogenous electrical field towards the respective MCP, which produces an image of the beam profile on an attached phosphor screen. A camera for each MCP is used for assessment. This indirect detection scheme operates over a wide dynamic range and allows the live detection of the clear position and the shape of the beam. The final design is presented.

Poster MOP015 [1.314 MB]

MOP023

Development of a Magnetic System to Cancel the Attractive Force toward Structural Reform of Undulators

undulator, multipole, experiment, synchrotron

75

R. Kinjo, T. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
A. Kagamihata, T. Seike
JASRI/SPring-8, Sayo-gun, Japan
S. Yamamoto
KEK, Tsukuba, Japan

As part of a development on a compact and lightweight structure toward structural reform of undulators, cancellation of magnetic attractive force is being studied. Undulators usually require rigid mechanical components and frames to control the magnet gap precisely against the large attractive force in between. If the attractive force is canceled out near the point of load, the requirement for the undulator structure is relaxed and the cost and lead time of construction and installation are saved largely. For that purpose, we have proposed to add periodically-magnetized monolithic magnets beside the main magnets, which are expected to generate a repulsive force having the same gap-dependency as the attractive force in a cost-effective way. In the conference, the present status of the development of the force cancellation system will be presented, with a focus on the result of preliminary experiments using the periodically-magnetized magnets. Also introduced will be a development plan for the compact and lightweight undulator based on the cancellation system.

MOP041

Summary of the U15 Prototype Magnetic Performance

undulator, electron, quadrupole, photon

111

M. Calvi, M. Aiba, M. Brügger, S. Danner, R. Ganter, C. Ozkan, T. Schmidt
PSI, Villigen PSI, Switzerland

The first undulator prototype (U15) was assembled and magnetically tested. The instrumentation and the algorithms developed for the undulator optimization are presented and a comparison among different approaches is reviewed. The magnetic measurement results before and after the installation of the vacuum components are discussed. The summary of the undulator test with 100 MeV electron beam is presented and the impact of the radiation on the magnetics is addressed.

MOP043

Magnetic Design of an Apple III Undulator for SwissFEL

undulator, polarization, operation, alignment

116

T. Schmidt, A. Anghel, P. Boehler, M. Brügger, M. Calvi, S. Danner, P. Huber, A. Keller, M. Locher
PSI, Villigen PSI, Switzerland

In the frame of the SwissFEL project a soft x-ray line is planned in the coming years to cover the wavelength between 0.7 and 7.0nm. Based on the good experience at the SLS storage ring with Apple undulator as source of variable polarized light, Apple III type undulators are also foreseen at the SwissFEL. In this paper the design of these devices is introduced and the preliminary magnetic configuration together with the optimization strategy is presented in details.

TUA03

A GaAs Photoemission DC Gun for CAEP High-average-power THz FEL

gun, cathode, high-voltage, FEL

318

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

FEL-THz plays an important role in THz science and technology research, for high power output and tunable wavelength, which is indispensable to material, biology, medical research. Now, the construction is underway at China Academy of Engineering Physics (CAEP) on high-average-power FEL THz source, and the demonstration of stable, reliable, high brightness, high power electron source operation is one of key issues. The components of the system were constructed and the performance tests are still on. The lifetime of the Negative Electron Affinity (NEA) surface is about 40 hours, which is limitied mainly by vacuum. Up to now, the gun can supply 5mA beam current and has been employed for preliminary experiments. In this paper, the design considerations and present status are given.

Slides TUA03 [1.182 MB]

TUP023

Modeling CSR in a Vacuum Chamber by Partial Fourier Analysis and the Discontinuous Galerkin Method

synchrotron-radiation, impedance, synchrotron, radiation

419

D. A. Bizzozero, J.A. Ellison
UNM, Albuquerque, New Mexico, USA
R.L. Warnock
SLAC, Menlo Park, California, USA

Funding: Work supported by DOE contracts DE-FG-99ER41104 and DE-AC03-76SF00515.
We continue our study of CSR* from a bunch on an arbitrary curved orbit in a plane, which used a Fourier transform in s-ct. The vacuum chamber has rectangular cross section with possibly varying horizontal width. We use the slowly varying amplitude approximation, and invoke a Fourier expansion in the vertical coordinate y, which meets the boundary conditions on the top and bottom plates and makes contact with the Bessel equation of the frequency domain treatment. The fields are defined by a PDE in s and x, first order in s, which is discretized in x by finite differences (FD) or the discontinuous Galerkin method (DG). We compare results of FD and DG, and also compare to our earlier calculations in 3D (paraxial) which did not use the Fourier series in y*,**. This approach provides more transparency in the physical description, and when only a few y-modes are needed, provides a large reduction in computation time.
* See FEL13 Proceedings MOPSO06: http://accelconf.web.cern.ch/AccelConf/FEL2013/papers/mopso06.pdf
** See PRST-AB 7 054403 (2004) and Jpn. J. Appl. Phys. 51 016401 (2012).

THA03

A Plan for the Development of Superconducting Undulator Prototypes for LCLS-II and Future FELs

undulator, FEL, linac, electron

649

P. Emma, N.R. Holtkamp, H.-D. Nuhn
SLAC, Menlo Park, California, USA
D. Arbelaez, J.N. Corlett, S.A. Myers, S. Prestemon, D. Schlueter
LBNL, Berkeley, California, USA
C.L. Doose, J.D. Fuerst, E. Gluskin, Q.B. Hasse, Y. Ivanyushenkov, M. Kasa, G. Pile, E. Trakhtenberg
ANL, Argonne, Ilinois, USA

Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515, DE-AC02-05CH11231, and DE-AC02-06CH11357.
Undulators serve as the primary source of radiation for modern storage rings, and more recently for the advent of Free-Electron Lasers (FELs). The performance of future FELs can be greatly enhanced using the much higher magnetic fields of superconducting undulators (SCU). For example, the LCLS-II hard x-ray undulator can be shortened by up to 70 m using an SCU in place of a PMU (permanent magnet undulator), or its spectral performance can be critically improved when using a similar length. In addition, SCUs are expected to be orders of magnitude less sensitive to radiation dose; a major issue at LCLS-II with its 1-MHz electron bunch rate. We present a funded R&D collaboration between SLAC, ANL, and LBNL, which aims to demonstrate the viability of superconducting undulators for FELs by building, testing, measuring, and tuning two 1.5-m long planar SCU prototypes using two different technologies: NbTi at ANL and Nb3Sn at LBNL. Our goal is to review and reassess the LCLS-II HXR baseline plans (PMU) in July of 2015, after the development and evaluation of both prototypes, possibly in favor of an SCU for LCLS-II.

Slides THA03 [29.468 MB]

THP030

Recent Photocathode R&D for the LCLS injector

laser, cathode, gun, emittance

769

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

Funding: US DOE under contract No. DE-AC02-76SF00515
Systematic studies of the copper photocathodes identical to those used in the LCLS injector gun has been carried out at SLAC’s RF gun test facility. Recent observations at the gun test facility indicate that the pre-cleaning of the cathode prior to the installation in the gun is the major cause of the lower initial QE (~10^-6) in the RF gun. All of four cathodes tested in the gun test facility have reliable higher initial QE, 4-8·10^-5, with removal of pre-cleaning step. All of details will be described in the paper. A robust laser-assisted processing recipe has been developed. With this recipe, QE can be repeatedly evolved to about 1x10^-4 within 3-4 weeks following the laser processing, and within 1-2 days the emittance is recovered to the values as observed prior to the laser processing. When compared to previous recipe used for the present LCLS cathode, the new recipe uses lower laser fluence and provides faster emittance recovery. Laser pointing stability is a key requirement for the success of the technique. This paper presents all details of the studies for four cathodes with over a few tens of laser-assisted spots and compares the results with the present LCLS cathode.

THP033

Mechanical Design for a Corrugated Plate Dechirper System for LCLS

wakefield, quadrupole, controls, electron

785

M.A. Harrison, P. Frigola, D.W. Martin, A.Y. Murokh, M. Ruelas
RadiaBeam Systems, Santa Monica, California, USA
Z. Huang, R.H. Iverson, T.J. Maxwell, Z. Zhang
SLAC, Menlo Park, California, USA

Funding: This work is supported by Department of Energy grant number DE-SC0009550.
RadiaBeam Systems is developing a novel passive chirp removal system using corrugated plates as studied by Bane and Stupakov.* Following on from low-energy experiments at BNL-ATF,** RBS will install a much larger and powerful system for removing the chirp from the 3-GeV beams in the LTU section at LCLS. The larger plates will present new challenges in the areas of manufacturing and mechanical control. In this paper we review the requirements for the dimensions of the corrugated plates for proper operation and the infrastructure necessary for precisely placing the plates so as not to adversely disrupt the beam.
* K. Bane, et al "Corrugated Pipe as a Beam Dechirper," SLAC-PUB-14925, 2012
** Harrison, M., et al "Removal of Residual Chirp in Compressed Beams Using a Passive Wakefield Technique." NaPAC13, 2013

THP046

Cu and Cs2Te Cathodes Preparation and QE History at the SwissFEL Injector Test Facility.

cathode, laser, operation, gun

832

J. Bossert, R. Ganter, M. Schaer, T. Schietinger
PSI, Villigen PSI, Switzerland

The installation of a load-lock chamber attached to the SwissFEL gun gives the possibility to carefully prepare the metallic cathodes under vacuum and also to use semiconductor cathodes like Cs2Te cathodes which cannot be transported through air. The paper presents the preparation procedures used for copper (QE>1.e-4) and Cs2Te cathodes (based on a CERN recipe) together with surface analysis results (SEM, EDX, interferometry, microscopy). Finally, the QE evolutions obtained in the SwissFEL Injector test facility as well as in a test stand are discussed for both materials.

THP049

High Power RF Test and Analysis of Dark Current in the SwissFEL-gun

gun, cathode, solenoid, laser

843

P. Craievich, S. Bettoni, M. Bopp, A. Citterio, C. Ozkan, M. Pedrozzi, J.-Y. Raguin, M. Schaer, A. Scherer, T. Schietinger, L. Stingelin
PSI, Villigen PSI, Switzerland

To fulfill the beam quality and operational requirements of the SwissFEL project, currently under construction at the Paul Scherrer Institut, a new RF photocathode gun for the electron source was designed and manufactured in house. A 2.6 cell S-band gun operating with near-perfect rotationally symmetric RF field was designed to operate with a 100MV/m cathode field at a repetition rate of 100Hz with average power dissipation of 0.9kW with pulse duration of 1us. The first SwissFEL-gun is now fabricated and installed in the SwissFEL Injector Test Facility (SITF). The frequency spectrum and field balance, through bead-pulling, have been directly verified in-situ and then the gun has been operated with high-power RF. The results of bead-pull measurements and high-power tests are presented and discussed. In addition the emitted dark current was also measured during the high-power tests and the charge within the RF pulse was measured as a function of the peak cathode field at different pulse durations. Faraday cup data were taken for cathode peak RF fields up to 100MV/m for the case of a diamond-turned polycrystalline copper cathode.

THP056

The SwissFEL C-band RF Pulse Compressor: Manufacturing and Proof of Precision by RF Measurements

cavity, coupling, resonance, klystron

859

U. Ellenberger, H. Blumer, M. Heusser, M. Kleeb, L. Paly, M. Probst, T. Stapf
Paul Scherrer Institute, Villigen PSI, Switzerland
M. Bopp, A. Citterio, R. Zennaro
PSI, Villigen PSI, Switzerland

A pulse compressor is required to compress the RF power distributed to the four accelerating structures of a single C-band (5712 GHz) module of the SwissFEL. The pulse compressor is of the barrel open cavity (BOC) type. A total of 26 BOC devices are necessary to operate the linear accelerator (26 modules or 10⁴ C-band structures) of SwissFEL X-ray laser. The C-band BOC combines the advantages of compactness and large RF efficiency i.e. large compression factor. Key features of the BOC are described and how they have been implemented in the manufacturing and tuning processes. RF measurements of the BOC are presented to account for the mechanical precision reached by manufacturing. Up to August 2014 about 6 BOCs have been manufactured in-house and one has been high power tested in a RF test stand to simulate the operation in SwissFEL.

THP063

Production of C-band Disk-loaded type CG Accelerating Structures

operation, cavity, resonance, acceleration

885

N. Shigeoka, S. Miura, D. Suzuki
MHI, Hiroshima, Japan
T. Asaka, T. Inagaki, Y. Otake, T. Sakurai
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
H. Ego
JASRI/SPring-8, Hyogo-ken, Japan

In April 2013, MITSUBISHI HEAVY INDUSTRIES, LTD. contracted with RIKEN to produce six C-band disk-loaded type and constant gradient (CG) accelerating structures for removal of SCSS. These structures were newly designed by RIKEN for operation with an acceleration gradient of over 45 MeV/m and a repletion rate of 120 pps. The first structure was delivered in August 2013 to RIKEN and the other five was also delivered in March 2014. The accelerating structures were stacked from one hundred accelerating cells and formed by the vacuum brazing method. These cells using oxygen free copper were ultra-precisely machined. Unlike the C-band choke-mode type structures, which MHI manufactured in past for SACLA, the accelerating cells of the CG structure can be tuned after the brazing by pushing dimpling at the tuning hole of each cell. Demands of a VSWR < 1.1 and a phase error < 3 degree are fulfilled after the tuning by using the nodal shift method, which corrects cell frequency shifts due to the machining errors of cells and a cell’s deformation by the heat cycle of the brazing. The detailed results of the production and low-power RF tests will be presented in this presentation.

Poster THP063 [0.623 MB]

THP082

Measurements of Compressed Bunch Temporal Profile using Electro-Optic Monitor at SITF

laser, electron, diagnostics, optics

922

Ye. Ivanisenko, V. Schlott
PSI, Villigen PSI, Switzerland
P. Peier
DESY, Hamburg, Germany

Funding: The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n.°290605 (PSI-FELLOW/COFUND)
The SwissFEL Injector Test Facility (SITF) is an electron linear accelerator with a single bunch compression stage at Paul Scherrer Institute (PSI) in Switzerland. Electro-optic monitors (EOMs) are available for bunch temporal profile measurements before and after the bunch compressor. The profile reconstruction is based upon spectral decoding technique. This diagnostic method is non-invasive, compact and cost-effective. It does not have high resolution and wide dynamic range of an RF transverse deflecting structure (TDS), but it is free of transverse beam size influence, what makes it a perfect tool for fast compression tuning. We present results of EOM and TDS measurements with down to 150 fs long bunches after the compression stage at SITF.

THP091

Design and Test of Wire-Scanners for SwissFEL

electron, FEL, monitoring, booster

948

G.L. Orlandi, M. Baldinger, H. Brands, P. Heimgartner, R. Ischebeck, A. Kammerer, F. Löhl, R. Lüscher, P. Mohanmurthy, C. Ozkan, B. Rippstein, V. Schlott, L. Schulz, C. Seiler, S. Trovati, P. Valitutti, D. Zimoch
PSI, Villigen PSI, Switzerland

The SwissFEL light-facility will provide coherent X-rays in the wavelength region 7-0.7 nm and 0.7-0.1 nm. In SwissFEL, view-screens and wire-scanners will be used to monitor the transverse profile of a 200/10pC electron beam with a normalized emittance of 0.4/0.2 mm.mrad and a final energy of 5.7 GeV. Compared to view screens, wire-scanners offer a quasi-non-destructive monitoring of the beam transverse profile without suffering from possible micro-bunching of the electron beam. The main aspects of the design, laboratory characterization and beam-test of the SwissFEL wire-scanner prototype will be presented.