FEL Technology

TUBIS01 Attosecond X-ray Pulses in the LCLS using the Slotted Foil Method
Paul J Emma, Zhirong Huang (SLAC, Menlo Park, California), Michael Borland (ANL/APS, Argonne, Illinois)

A proposal has been made to generate femtosecond and sub-femtosecond x-ray pulses in the Linac Coherent Light Source (LCLS) SASE FEL by using a slotted spoiler foil located at the center of the second bunch compressor chicane. This previous study highlighted a simple case, using the nominal LCLS parameters, to produce a 2-fsec fwhm, 8-keV x-ray pulse. The study also pointed out the possibility of attaining sub-femtosecond pulses by somewhat modifying the LCLS compression parameters, but did not undertake a full tracking simulation for this more aggressive case. We take the opportunity here to study this `attosecond' case in detail, including a full tracking simulation, pushing the limit of the technique.

TUAOS03 Large-Scale Timing Distribution and RF-Synchronization for FEL Facilities
Jung-Won Kim, Fatih Oemer Ilday, Franz Kaertner, Oliver Muecke, Michael Perrott (MIT, Cambridge, Massachusetts), William S Graves, David Moncton, Townsend Zwart (MIT/BLAC, Middleton, Massachusetts)

For future advances in accelerator physics in general and seeding of FELs in particular, precise synchronization between seed radiation, low-level RF-systems and photo-injector laser is required. Typical synchronization methods based on direct photodetection are limited by the detector nonlinearities, which lead to amplitude-to-phase conversion and introduce timing jitter. A new synchronization scheme for extraction of low jitter RF-signals from optical pulse trains distributed by mode-locked lasers is proposed. It is robust against photodetector nonlinearities. The scheme is based on a transfer of timing information into an intensity imbalance between the two output beams from a Sagnac-loop interferometer. As a first experimental demonstration, sub-100 fs timing jitter between the extracted 2 GHz RF-signal and the 100 MHz optical pulse train from a mode-locked Ti:sapphire laser is demonstrated. Numerical simulations show that scaling to sub-femtosecond precision is possible. Together with mode-locked fiber lasers and timing stabilized fiber-link, this scheme can be applied for the large-scale precise timing distribution and synchronization of free-electron laser facilities.

TUAOS04 High Temporal Resolution, Single-Shot Electron Bunch-Length Measurements
Giel Berden, Britta Redlich, Lex van der Meer (FOM Rijnhuizen, Nieuwegein), Steven Jamison (Strathclyde University, Glasgow), Allan Gillespie, Allan MacLeod (UAD, Dundee)

A new technique, combining electro-optic detection of the Coulomb field of an electron bunch with single-shot cross-correlation of optical pulses is used to enable single-shot measurements of the electric field profile of sub-picosecond electron bunches. As in our previous "spectral decoding" technique (I. Wilke et al., Phys. Rev. Lett. 88(12) 2002), the electric field of the electron bunch is encoded electro-optically on an optical pulse. However, the new "temporal decoding" method offers a much better time resolution since it overcomes a fundamental time-resolution limit of the spectral decoding method, which arises from the inseparability of time and frequency properties of the probing optical pulse. The temporal decoding technique has been applied to the measurement of 50 MeV electron bunches in the FELIX free electron laser, showing the longitudinal profile of single bunches of around 650 fs FWHM. The method is non-destructive and real-time, and therefore ideal for online monitoring of the longitudinal shape of single electron bunches. At FELIX we have used it for real-time optimization of sub-picosecond electron bunches.

THBOC02 Recent Results and Perspectives of the Low Emittance Photo Injector at PITZ
Frank Stephan, Juergen Baehr, Ulrich Gensch, Hans-Juergen Grabosch, Jang Hui Han, Mikhail Krasilnikov, Dirk Lipka, Velizar Miltchev, Anne Oppelt, Bagrat Petrosyan, Dietrich Pose, Sabine Riemann, Lazar Staykov (DESY Zeuthen, Zeuthen), Michael von Hartrott, Eberhardt Jaeschke, Dieter Krämer, Dieter Richter (BESSY GmbH, Berlin), Galina Asova, Gancho Dimitrov (DESY Zeuthen, Zeuthen; INRNE, Sofia), Karen Abrahamyan (DESY Zeuthen, Zeuthen; YerPhI, Yerevan), Ilja Bohnet, Jean-Paul Carneiro, Klaus Floettmann, Siegfried Schreiber (DESY, Hamburg), Paolo Michelato, Laura Monaco, Carlo Pagani, Daniele Sertore (INFN/LASA, Segrate (MI)), Ivan Tsakov (INRNE, Sofia), Wolfgang Sandner, Ingo Will (MBI, Berlin), Wolfgang Ackermann, Wolfgang F.O. Mueller, S. Schnepp, Stefan Setzer, Thomas Weiland (TU Darmstadt, Darmstadt), Joerg Rossbach (Uni HH, Hamburg)

The Photo Injector Test Facility at DESY Zeuthen (PITZ) was built to study the production of minimum transverse emittance electron beams for Free Electron Lasers. In November 2003 the electron beam from the RF gun was fully characterized at PITZ. For a bunch charge of 1 nC a minimum normalized projected beam emittance of 1.5 π mm mrad in the vertical plane and a minimum geometrical average of both transverse planes of 1.7 π mm mrad have been achieved. This fulfils the requirements of the VUV-FEL at DESY Hamburg. In this contribution an overview on the measured electron beam and high duty cycle RF parameters including transverse emittance, thermal emittance, bunch length, momentum and momentum spread will be given. In addition, planned major upgrades and first results towards fulfilling the even more challenging requirements for the European XFEL will be discussed. This includes the increase of the accelerating gradient on the photo-cathode and the improvement of the transverse and longitudinal laser beam parameters.

THBOC03 Emittance Measurement on the CeB6 Electron Gun for the SPring-8 Compact SASE Source
Kazuaki Togawa, Hitoshi Baba, Takahiro Inagaki, Kazuyuki Onoe, Tsumoru Shintake, Takashi Tanaka (RIKEN Spring-8 Harima, Hyogo), Hiroshi Matsumoto (KEK, Ibaraki)

A high-volatage pulsed electron gun has been constructed for the injector system of the soft X-ray FEL project at SPring-8 (SCSS project). A CeB6 single crystal was chosen as a thermionic cathode, because of its excellent emission properties. The gun voltage of -500 kV was chosen to reduce emittance growth due to space charge. We have succeeded in generating a 500 keV beam with 1 A peak current and 3 micro-sec FWHM. The beam was very stable with low jitter. The beam emittance has been measured by means of double-slits method, and the normalized rms emittance of 1.1 pi-mm-mrad has been obtained. We report on the experimental result on the emittance measurement of the CeB6 electron gun.

THBOC04 Ampere Average Current Photoinjector and Energy Recovery Linac
Ilan Ben-Zvi, A. Burrill, R. Calaga, P. Cameron, X. Chang, D. Gassner, H. Hahn, A. Hershcovitch, H.C. Hseuh, P. Johnson, D. Kayran, J. Kewisch, R. Lambiase, Vladimir N. Litvinenko, G. McIntyre, A. Nicoletti, J. Rank, T. Roser, J. Scaduto, K. Smith, T. Srinivasan-Rao, K.-C. Wu, A. Zaltsman, Y. Zhao (BNL, Upton, Long Island, New York), H. Bluem, A. Burger, Mike Cole, A. Favale, D. Holmes, John Rathke, Tom Schultheiss, A. Todd (AES, Medford, NY), J. Delayen, W. Funk, L. Phillips, Joe Preble (Jefferson Lab, Newport News, Virginia)

High-power Free-Electron Lasers were made possible by advances in superconducting linac operated in an energy-recovery mode, as demonstrated by the spectacular success of the Jefferson Laboratory IR-Demo. In order to get to much higher power levels, say a fraction of a megawatt average power, many technological barriers are yet to be broken. BNL’s Collider-Accelerator Department is pursuing some of these technologies for a different application, that of electron cooling of high-energy hadron beams. I will describe work on CW, high-current and high-brightness electron beams. This will include a description of a superconducting, laser-photocathode RF gun employing a new secondary-emission multiplying cathode and an accelerator cavity, both capable of producing of the order of one ampere average current.

THBOC05 Status of the 3 1/2 Cell Rossendorf Superconducting RF Gun
Dietmar Janssen, Hartmut Buettig, Pavel Evtushenko, Ulf Lehnert, Peter Michel, Christof Schneider, Juergen Stephan, Jochen Teichert (FZR, Dresden), Slava Kruchkov, Oleg Myskin, Vladimir Volkov (BINP, Novosibirsk)

In Rossendorf it was shown for the first time that a RF electron gun where a photo cathode is inside a superconducting cavity, works stable over a period of seven weeks. At 4.2K no change of the quality factor Q = 2.5 108 has been observed [1]. The experimental results were the basis for the design of a new 3.4 cell superconducting RF photo electron gun [2]. The paper presents details of different components of this gun, explains the status of manufacturing and gives results of first test measurements. Furthermore, the idea is discussed to use for emittance compensation instead of a static magnetic field which is inside the cavity of a normal conducting RF gun in the superconducting gun cavity an additional magnetic RF field (TE011 mode) . By computer simulation the attraction of this idea is demonstrated.

TUBOS02 Longitudinal Space Charge Effects in the JLAB IR FEL SRF Linac
Carlos Hernandez-Garcia, Kevin Beard, Chris Behre, Stephen Vincent Benson, George Herman Biallas, James Boyce, David Douglas, Fred Dylla, Richard Evans, Al Grippo, Joe Gubeli, David Hardy, Kevin Jordan, Lia Merminga, George Neil, Joe Preble, Michelle D. Shinn, Tim Siggins, Richard Walker, Gwyn Williams, Byung Yunn, Shukui Zhang (Jefferson Lab, Newport News, Virginia)

Observations of energy spread asymmetry when operating the Linac on either side of crest and longitudinal emittance growth have been confirmed by extending PARMELA simulations from the injector to the end of the first SRF Linac module. The asymmetry can be explained by the interaction of the accelerating electric field with that from longitudinal space charge effects within the electron bunch. This can be a major limitation to performance in FEL accelerators.

TUBOS04 LCLS Undulator Design Development
Isaac Vasserman, Roger J. Dejus, Patric Den Hartog, Elizabeth Moog, Shigemi Sasaki, Emil Trakhtenberg, Marion White (ANL/APS, Argonne, Illinois)

The fractional variation in deflection parameter K between segments of the 130.4-m-long undulator line for the Linac Coherent Light Source (LCLS) must be < 1.5 x 10-4. Mechanical shims were used to set the undulator gap to control K in the prototype, but this is too tedious a procedure to be used for all 33 undulator segments. Although the prototype undulator met all of the LCLS specifications, development continued in order to simplify the system. Various other alternatives for adjusting the field were considered. A canted-pole geometry was adopted that allows the K value to be changed by lateral translation of the entire undulator segment. This scheme also facilitates tapering the undulator line to accommodate energy loss in the electron beam. The prototype undulator was subsequently modified to test the canted-pole concept. Magnetic measurements demonstrated that the undulator with canted poles meets all LCLS specifications, and is more cost-effective to implement.

TUBOS05 Commissioning of the TTF Linac Injector at the DESY VUV-FEL
Katja Honkavaara (DESY, Hamburg)

The upgrade of the TESLA Test Facility (TTF) Linac at DESY is almost completed. With electron beam energies up to 1 GeV, it will be able to drive a new SASE FEL user facility (VUV-FEL) in the wavelength range from VUV to soft X-rays. The first phase of the redesigned photoinjector is finished. We report on its commissioning during spring 2004, including the first measurements of electron beam parameters. Since this injector is also a prototype for the XFEL injector, the results obtained are important for future SASE XFEL drive linacs.

THPOS65 A Novel Diagnostics of Ultrashort Electron Bunches Based on Detection of Coherent Radiation from Bunched Electron Beam in an Undulator
Evgeny L. Saldin, Evgeny A. Schneidmiller, Mikhail V. Yurkov (DESY, Hamburg)

We propose a new method for measurements of the longitudinal profile of 100 femtosecond electron bunches for X-ray Free Electron Lasers (XFELs). The method is based on detection of coherent undulator radiation produced by modulated electron beam. Seed optical quantum laser is used to produce exact optical replica of ultrashort electron bunches. The replica is generated in apparatus which consists of an input undulator (energy modulator), and output undulator (radiator) separated by a dispersion section. The radiation in the output undulator is excited by the electron bunch modulated at the optical wavelength and rapidly reaches a hundred-MW-level power. We then use the now-standard method of ultrashort laser pulse-shape measurement, a tandem combination of autocorrelator and spectrum (FROG -- frequency resolved optical gating) providing real-time single-shot measurements of the electron bunch structure. The big advantage of proposed technique is that it can be used to determine the slice energy spread and emittance in multishot measurements. We illustrate with numerical examples the potential of the proposed method for electron beam diagnostics at the European X-ray FEL.

TUPOS01 Industrial Production of Superconducting 1.3 GHz Accelerator Modules and components for FEL application
Michael Pekeler, Hanspeter Vogel, Peter vom Stein (ACCEL, Bergisch Gladbach)

Daresbury Laboratory contracted ACCEL in April for the delivery of two superconducting 1.3 GHz modules for the R&D phase of their 4GLS project. The modules are delivered with guaranteed performance on cavity voltage and cryogenic losses. The modules contain 2 TESLA type cavities each and are of the design developed at Forschungszentrum Rossendorf. To investigate the capabilities of our cavity treatment and preparation techniques, our infrastructure was further upgraded to allow chemical treatment and high pressure rinsing of TESLA cavities. First test results on TESLA cavities produced for BESSY are very encouraging. 23 MV/m accelerating gradient were achieved in the cold vertical test. In addition 12 power couplers of the TTF III type were produced for DESY and BESSY. The conditioning of those couplers was performed at DESY in a very short time of approximately 50 hours demonstrating our high quality surface treatment capabilities.

TUPOS02 Collimation System for the BESSY FEL
Thorsten Kamps (BESSY GmbH, Berlin)

Beam collimation is an essential element for the successful running of a linear accelerator based free electron laser. The task of the collimation system is to protect the undulator modules against mis-steered beam and dark-current. This is achieved by a set of apertures limiting the succeeding transverse phase space volume and a magnetic dogleg structure for longitudinal phase space filtering. In the following the design of the BESSY FEL collimation section is described together with detailed simulation studies.

TUPOS03 High Power RF Conditioning and Measurement of Longitudinal Emittance at PITZ
Juergen Baehr, Hans-Juergen Grabosch, Jang Hui Han, Mikhail Krasilnikov, Dirk Lipka, Velizar Miltchev, Anne Oppelt, Bagrat Petrosyan, Dietrich Pose, Sabine Riemann, Lazar Staykov, Frank Stephan (DESY Zeuthen, Zeuthen), Dieter Richter, Michael v. Hartrott (BESSY GmbH, Berlin), Galina Asova, Gancho Dimitrov (DESY Zeuthen, Zeuthen; INRNE, Sofia), Karen Abrahamyan (DESY Zeuthen, Zeuthen; YerPhI, Yerevan), Ilja Bohnet, Jean-Paul Carneiro, Klaus Floettmann, Siegfried Schreiber (DESY, Hamburg), Paolo Michelato, Laura Monaco, Daniele Sertore (INFN/LASA, Segrate (MI))

In 2003 the PITZ RF-gun at DESY Zeuthen has been fully characterized. After RF conditioning 3.2MW input power at 10Hz and a RF-pulse length of 0.9ms has been reached. This correponds to a gradient of 42MV/m at the cathode. The goal is to increase the accelerating gradient of the gun and the duty cycle significantly. The motivation is based on the expectation of a remarkable increase in beam quality at higher gradients. A high duty cycle is of advantage for FEL users. The conditioning procedure was started in spring 2004. The paper will report about procedure and results of this program. The preparation of an experimental setup for the measurement of the complete longitudinal phase space at about 5 MeV using a streak camera will be finished in summer 2004. Cherenkov light created by Silica aerogel radiators in the dispersive arm of PITZ is transmitted to a streak camera by an optical transmission line. The light distribution of the momentum spectrum is projected onto the entrance slit of the streak camera. The setup and first results will be presented.

TUPOS04 An Electromagnetic Undulator for the Far Infrared at ELBE
Thomas Dekorsy, Karim Fahmy, Eckart Grosse, Peter Michel, Wolfgang Seidel, Andreas Wolf, Rudi Wuensch (FZR, Dresden)

The first lasing in the mid IR at the ELBE FEL allows us to specify the parameters of a new undulator for longer wavelengths to complement the U27 undulator which is useful up to about 25 microns. In the longer wavelength region FELs constitute a unique radiation source with appealing properties. Radiation quanta in this range (2 - 10 THz) are appropriate for the low-energy spectroscopy of various interesting modes in solid state quantum structures as well as in complex biological systems. Their study establishes the basis for understanding phenomena in semiconductors and elucidating biological processes of interest for medical innovations. We envisage an electromagnetic undulator with a period of 90 - 100 mm. Using the ELBE beam IR light from 20 to 150 microns and beyond can be produced. To keep the transverse beam extension small the IR beam is to be guided by a partial waveguide inside the undulator. Appropriate bifocal resonator mirrors minimize the mode coupling losses at the exits of the waveguide. Detailed calculations and computer simulations predict an outcoupled laser power of roughly 50 W at 150 microns which will be transported to experimental stations.

TUPOS06 Bunch Length Measurements at the SLS Linac Using Electro Optical Sampling
Bernd Steffen, Sara Casalbuoni, Peter Schmüser, Stefan Simrock (DESY, Hamburg), Timo Korhonen, Thomas Schilcher, Volker Schlott, Hans Sigg, Daniel Suetterlin (PSI, Villigen), Manfred Tonutti, Axel Winter (RWTH, Aachen)

The temporal profile of the electron bunches in the SLS Linac was determined by means of electro-optical techniques. In a first experiment a mode locked Ti:Sa Laser with 15 fs pulse width (FWHM) was used for coincidence and sampling measurements between the laser pulse and the coherent transition radiation (CTR) generated by short electron bunches. A synchronization accuracy of 70 fs rms between the 3 GHz Linac RF and the 81 MHz repetition frequency of the laser was achieved, which is important for the optimum time resolution of the applied electro-optical sampling technique. In a second experiment a mode locked Nd:YAG laser with 400 ps long pulses will be used for electro-optical autocorrelation measurements between the CTR and the laser pulses. This alternative technique promises single shot capability and requires much relaxed synchronization stability between laser and electron beam.

TUPOS07 Longitudinal Bunch Shape Diagnostics with Coherent Radiation and a Transverse Deflecting Cavity at TTF2
Oliver Grimm, Lars Froehlich, K. Klose, M. Nagl, O. Peters, Holger Schlarb (DESY, Hamburg), Paul J Emma, D. McCormick, M. Ross, T.J. Smith (SLAC, Menlo Park, California), Joerg Rossbach (Uni HH, Hamburg)

The VUV-FEL at DESY, Hamburg, will require novel techniques to characterize the longitudinal charge distribution of the electron bunches that drive the free-electron laser. Two reasons are the short bunch lengths that will be obtained by the bunch compression schemes and the high sensitivity of the lasing process to spikes in the charge distribution. This contribution will give an overview of the different measurement techniques to access bunch lengths on the order of 50 μ m. Approaches to reconstruct the bunch shape by Fourier analysis of the coherent part of the infrared spectrum of synchrotron, transition, diffraction and undulator radiation will be presented. Furthermore, methods working in the time domain, like the use of transverse mode cavities or the principle of electro-optical sampling, will be discussed. Examples from TTF2 will be used to show possible technical implementations of the corresponding techniques.

TUPOS09 Transverse Emittance Measurements at the Photo Injector Test Facility at DESY Zeuthen
Velizar Miltchev, Juergen Baehr, Hans-Juergen Grabosch, Jang Hui Han, Mikhail Krasilnikov, Dirk Lipka, Anne Oppelt, Bagrat Petrosyan, Dietrich Pose, Sabine Riemann, Lazar Staykov, Frank Stephan (DESY Zeuthen, Zeuthen), Michael von Hartrott, Dieter Richter (BESSY GmbH, Berlin), Galina Asova, Gancho Dimitrov (DESY Zeuthen, Zeuthen; INRNE, Sofia), Karen Abrahamyan (DESY Zeuthen, Zeuthen; YerPhI, Yerevan), Jean-Paul Carneiro, Klaus Floettmann, Siegfried Schreiber (DESY, Hamburg), Paolo Michelato, Laura Monaco, Daniele Sertore (INFN/LASA, Segrate (MI)), Ivan Tsakov (INRNE, Sofia), Ingo Will (MBI, Berlin), Wolfgang Ackermann, S. Schnepp, Stefan Setzer (TU Darmstadt, Darmstadt)

The main goal of the Photo Injector Test Facility at DESY Zeuthen (PITZ) is the development of electron sources for Free Electron Lasers. The presented contribution summarizes the transverse emittance studies done for producing an electron beam that meets the requirements of the TTF2 VUV-FEL. Systematic measurements of the beam emittance in a wide range of parameters (e.g. bunch charge, RF phase, solenoid fields) will be presented and compared with simulations. The impact of the laser pulse longitudinal and transverse profile on the beam emittance will be demonstrated. Results of thermal emittance measurements will be discussed.

TUPOS10 The Short-Range Wakefields in the BTW Accelerating Structure of the Elettra Linac
Paolo Craievich, Gerardo D'Auria (Elettra, Basovizza, Trieste), Thomas Weiland, Igor Zagorodnov (TU Darmstadt, Darmstadt)

Future FEL operations in the ELETTRA LINAC require a high quality beam with an ultra short bunch. The knowledge of the short-range wakefields in the backward traveling wave (BTW) accelerating structure is needed to predict the beam quality in term of the single bunch energy spread and emittance. To calculate the effect of the longitudinal and transverse wakefileds we have used the time domain numerical approch with a new implicit scheme for calculation of wake potential of short bunches in long structure [1,2]. The wake potentials of the BTW structure are calculated numerically for very short bunches and analytical approximations for wake functions in short and long ranges are obtained by fitting procedures based on analytical estimations.

TUPOS11 The SPARX Project : R&D Activity towards X-rays FEL Sources
David Alesini, M. Bellaveglia, Sergio Bertolucci, M.E. Biagini, R. Boni, Manuela Boscolo, Michele Castellano, A. Clozza, G. Di Pirro, A. Drago, A. Esposito, Massimo Ferrario, D. Filippetto, V. Fusco, A. Gallo, A. Ghigo, Susanna Guiducci, M. Incurvati, C. Ligi, F. Marcellini, Mauro Migliorati, Andrea Mostacci, Luigi Palumbo, L. Pellegrino, Miro Preger, P. Raimondi, R. Ricci, C. Sanelli, Mario Serio, F. Sgamma, Bruno Spataro, A. Stecchi, A. Stella, Franco Tazzioli, Cristina Vaccarezza, Mario Vescovi, C. Vicario (INFN/LNF, Frascati (Roma)), Franco Ciocci, Giuseppe Dattoli, Antonio Di Pace, Andrea Doria, Francesco Flora, Gian Piero Gallerano, Luca Giannessi, Emilio Giovenale, Giovanni Messina, Luca Mezi, Pier Luigi Ottaviani, Simonetta Pagnutti, Giovanni Parisi, Luigi Picardi, Marcello Quattromini, Alberto Renieri, Concetta Ronsivalle, A. Torre, Alberto Zucchini (ENEA C.R. Frascati, Frascati - Roma), F. Alessandria, A. Bacci, Ilario Boscolo, F. Broggi, S. Cialdi, C. De Martinis, D. Giove, C. Maroli, M. Mauri, V. Petrillo, M. Romè, Luca Serafini (INFN Milano, Milano), Mario Mattioli, Pietro Musumeci (INFN Roma, Roma), L. Catani, E. Chiadroni, A. Cianchi, Carlo Schaerf (INFN-Roma2, Roma), S. De Silvestri, M. Nisoli, S. Stagira (Politecnico di Milano, Milano), Paul J Emma (SLAC, Menlo Park, California), James B Rosenzweig (UCLA, Los Angeles, California), Sven Reiche (UCLA/DPA, Los Angeles - California)

SPARX is an evolutionary project proposed by a collaboration among ENEA-INFN-CNR-Università di Roma Tor Vergata aiming at the construction of a FEL-SASE X-ray source in the Tor Vergata Campus. The first phase of the SPARX project, funded by Government Agencies, will be focused on the R&D activity on critical components and techniques for future X-ray facilities. The R&D plans for the FEL source will be developped along two lines: (a) use of the SPARC high brightness photo-injector to develop experimental test on RF compression techniques and other beam physics issues, like emittance degradation in magnetic compressors due to CSR; (b) development of new undulator design concepts and up-grading of the FEL SPARC source to enhance the non linear harmonic generation mechanism, design and test of e-beam conditioning, prebunching and seeding. A parallel program will be aimed at the development of high repetition rate S-band gun, high Quantum Efficiency cathodes, high gradient X-band RF accelerating structures and harmonic generation in gas. In a second phase we plan to explore production of X-rays in a SASE-FEL with harmonic generation, upgrading existing facilities.

TUPOS12 Spectral Analysys of Charge Emission Spatial Inhomogeneities and Emittance Dilution in RF Guns
Marcello Quattromini, Luca Giannessi, Concetta Ronsivalle (ENEA C.R. Frascati, Frascati - Roma)

The effects of fluctuations in cathode's quantum efficiency and other sources of dishomogeneities in the performances of a typical RF photoinjector have been investigated with TREDI numerical simulations. The RF gun layout includes a focusing solenoid in a configuration aimed at minimizing the emittance growth due to space charge effects.

TUPOS13 On-Line Spectral Monitoring of the VUV FEL Beam at DESY
Piergiorgio Nicolosi, Maria-Guglielmina Pelizzo, Luca Poletto (INFM-LUXOR, Padova), Joseph Feldhaus, Ulrich Hahn, U. Jastrow, Elke Ploenjes, Kai Tiedtke (DESY, Hamburg)

A grazing-incidence flat-field spectrometer has been designed. The optical design is based on a Kirkpatrick-Baez configuration in which one of the optical elements is a spherical mirror and the other is a spherical grating [1]. This configuration gives high spectral and spatial resolution even for a large field-of-view. The grating is a variable-line-spaced one, in which the groove spacing changes along the surface following a polynomial law in order to obtain a flat-field focal surface nearly parallel to the grating normal. The detector can be both an EUV-enhanced CCD and a MCP-based detector. The spectrometer was tested in the 5-45 nm spectral region with spectra emitted both by a laser-produced-plasma and by a hollow-cathode lamp. Spectral resolution of about 2000 was measured at 20 nm, in good agreement with the theoretical predictions. Spatial resolution better than 0.1 mm over 2 mm field-of-view has been measured. At present, the instrument is installed at DESY (Hamburg, Germany) on the TESLA-Test-Facility and will be used for the monitoring of the spectral emission of the FEL radiation in the 25-45 nm spectral region.

TUPOS14 ABCD Matrix Method: a Case Study
Zakir F. Seidov, Yosef Pinhasi, Asher Yahalom (The College of Judea and Samaria, Ariel)

In the Israeli Electrostatic Accelerator FEL, the distance between the accelerator's end and the wiggler's entrance is about 2.1 m, and 1.4 MeV electron beam is transported through this space using four similar quadrupoles (FODO-channel). The transfer matrix method (ABCD matrix method) was used for simulating the beam transport, a set of programs is written in the several programming languages (MATHEMATICA, MATLAB, MATCAD, MAPLE) and reasonable agreement is demonstrated between experimental results and simulations. Comparison of ABCD matrix method with the direct "numerical experiments" using EGUN, ELOP, and GPT programs with and without taking into account the space-charge effects showed the agreement to be good enough as well. Also the inverse problem of finding emittance of the electron beam at the S1 screen position (before FODO-channel), by using the spot image at S2 screen position (after FODO-channel) as function of quad currents, is considered. Spot and beam at both screens are described as tilted eellipses with diameters and orientation angle of which being found by STB (Spot-to-Beam) procedure, and trace-ellipse transformation is used to found emittance at S1 position.

TUPOS15 Spot-to-Beam Procedure
Zakir F. Seidov, Yosef Pinhasi, Asher Yahalom (The College of Judea and Samaria, Ariel)

We describe the interactive "STB" (spot_to_beam) MATHEMATICA procedure for a) approximating the spot image at the screen as ellipse, b) getting five parameters of the elliptic beam (two diameters, center coordinates, and orientation angle). The basic idea is to "map" the reference holes at screen onto the X-Y plane normal to the beam direction (Z-axis). All distortions of the image, e.g., due to camera-screen disposition can be, in principle, taken into account,assuming that the hole positions at screen and the orientation of the screen are known. With the non-linear LMS fitting, the "curved-coordinate-system" of the holes at image is transferred to the Cartesian coordinate system at XY-plane. Then the fitting ellipse is found in this latter system, by solving the system of N linear equations for 5 unknown parameters of beam ellipse, where N>5 is a number of reference points on edge of spot image. The examples of the real measurements at various screens will be demonstrated. The accuracy of beam diameters is about .1 mm depending on quality of picture and the perator's experience. The procedure is to be used in the routine measurements in the Israeli FEL.

TUPOS17 Guiding Optics System for LEBRA FEL User Facility
Toshinari Tanaka, Ken Hayakawa, Yasushi Hayakawa, Isamu Sato (LEBRA, Funabashi)

A guiding optics system for LEBRA FEL facility was completed in 2003. The optical beam extracted from the Infrared FEL resonator is guided through a long vacuum system to user’s experimental rooms, where maximum 17 aluminum-coated mirrors are used in the guiding optics. The maximum length of the optical line is approximately 50 m. Therefore, the FEL extracted through a coupling hole in a resonator mirror has to be converted to a parallel beam. The conversion optics consists of an elliptic mirror and a parabolic mirror aligned to form a confocal configuration. The diffraction profiles of a guide laser extracted through the coupling hole have shown approximately identical patterns at output ports of the experimental facility. The guiding optics has two monitoring ports consisting of fluorite beam splitters, which is useful for simultaneous measurement of the power and the spectrum of the FEL during user experiments.

TUPOS18 Upgrade of a Photocathode RF Gun at SPring-8
Tsutomu Taniuchi, Takao Asaka, Hideki Dewa, Hirofumi Hanaki, Toshiaki Kobayashi, Akihiko Mizuno, Shinsuke Suzuki, Hiromitsu Tomizawa, Kenichi Yanagida (JASRI-SPring-8, Hyogo), M. Uesaka (UTNL, Ibaraki)

The test bench of a photocathode RF gun at SPring-8 has been upgraded. The radiation shielded area was expanded about 3 times larger and the maximum beam energy was increased from up to 30 MeV including a 3-m long accelerating tube. The clean room for the drive laser system was newly built and the performance and reliability of the laser was improved. After the construction of the shielded room and set up of the components, the RF conditioning of the waveguides, the gun cavity and the accelerating tube was successfully performed and the beam characteristics such as the emittance and bunch length were measured. In this presentation, further plans for the improvement of the beam quality will also be presented.

TUPOS19 FEL Simulation Code for Undulator Performance Estimation
Takashi Tanaka (RIKEN Spring-8 Harima, Hyogo)

In an FEL project based on the principle of SASE, a long undulator with a good field quality should be installed to ensure saturation. The performance of the undulator as a (spontaneous) synchrotron light source is represented by phase errors as well as the trajectory straightness. In addition, the synchrotron radiation from an undulator is easily calculated by Fourier transforming the electric field generated by an electron passing through the undulator field. On the other hand, an FEL simulation should be carried out with the actual magnetic field taken into account in order to estimate the undulator performance as an FEL driver. We have recently developed an FEL simulation code for such a purpose, the details of which will be presented in this paper.

TUPOS20 Electron Beam Simulations on the SCSS Accelerator
Toru Hara, Hideo Kitamura, Tsumoru Shintake (RIKEN Spring-8 Harima, Hyogo)

The SPring-8 Compact SASE Source (SCSS) is a SASE-FEL project aiming at soft X-ray radiation at its first stage using 1 GeV electron beams. One of the unique features of the SCSS is the use of a pulsed high-voltage electron gun with a thermionic cathode. Main reason for this choice is its high stability and the well developed technology relating to the gun. Meanwhile, the electron bunch should be compressed properly at the injector in order to obtain sufficient peak currents. In this presentation, the results of the electron beam simulations along the accelerator and the expected parameters of the electron beam will be given.

TUPOS21 Reducing Back-Bombardment Effect Using Thermionic Cathode in IAE RF Gun
Toshiteru Kii, Kazushi Hayakawa, Kai Masuda, Shio Murakami, Hideaki Ohgaki, Tetsuo Yamazaki, Kiyoshi Yoshikawa, Heishun Zen (Kyoto University, Kyoto)

We have numerically studied on improvement of electron beam macro-pulse properties from thermionic RF gun [1,2]. Beam properties, such as energy spectrum, macro-pulse duration and emittance were measured with a 2 mm diameter slim thermionic dispenser cathode. Effect of the transverse magnetic field to reduce back-streaming electrons to these properties was studied experimentally. Comparison with measured and numerical results will be discussed. Effect of a non-flat RF input to compensate a decreasing beam energy during macropulse due to a back-bombardment effect will be also presented.

TUPOS22 Renewal of KU-FEL Facility
Toshiteru Kii, Kazushi Hayakawa, Kai Masuda, Shio Murakami, Hideaki Ohgaki, Tetsuo Yamazaki, Kiyoshi Yoshikawa, Heishun Zen (Kyoto University, Kyoto)

Users demands to a high power tunable IR laser are increasing in Japan in energy-related science, such as basic study of high-efficiency solar cells, generation of new energy source of alcohol and/or H2 from polluted gas, and separation of DNA and/or RNA. To satisfy these demands, we decided to renew our FEL facility more user friendly and to operate more flexibly. Construction and fundamental studies on the KU-FEL have been carried out at a building of Institute of Chemical Research where few other accelerators are operating. Therefore, available machine time for our experiments is quite limited. We are now modifying the room by adding concrete walls of 2-m thickness and some space for users will be available. The present FEL system will be moved to the room A photocathode RF-gun system will be nearly added to the system and the present thermionic RF-gun will be used ternatively according to the demands of users. The photocathode material will be Cs2Te. The room with the shielding will be completed in June, 2004, and we will moved the machine shortly. We hope to resume the operation of the linac in fall of 2004. The FEL is expected lasing in the next year.

TUPOS23 Beam Property Measurements on the KU-FEL Linac
Kai Masuda, Kazushi Hayakawa, Toshiteru Kii, Shio Murakami, Hideaki Ohgaki, Tetsuo Yamazaki, Kiyoshi Yoshikawa, Heishun Zen (Kyoto University, Kyoto)

An infrared FEL facility is under construction for advanced energy researches [1]. Electron beams of around 30 MeV have been obtained by an S-band 4.5-cell rf gun with a thermionic cathode, and a recently installed 3-m accelerating tube. A 180 degree arc consisting of three bending magnets have been also set up for bunch compression, and beam property measurements are under way. Transverse phase space distributions and resultant emittances have been obtained through the tomographic technique [2] by use of a quadrupole magnet, an alumina phosphor screen and a CCD camera. An OTR screen is being prepared for a higher spatial resolution as well as for longitudinal bunch shape measurements by use of a streak camera of 0.2 psec resolution. Comparison with the start-to-end simulation results [3] will be also presented.

TUPOS24 Upgrade Design of KU-FEL Driver Linac Using Photo-Cathode RF-GUN
Hideaki Ohgaki, Kazushi Hayakawa, Toshiteru Kii, Kai Masuda, Shio Murakami, Tetsuo Yamazaki, Kiyoshi Yoshikawa, Heishun Zen (Kyoto University, Kyoto)

An infrared FEL facility is under construction at Institute of Advanced Energy, Kyoto University[1]. The electron beam of 30 MeV has been successfully accelerated by the S-band linac consisted of thermionic RF-gun[2]. To reduce the back-bombardment effect in the 4.5-cell RF gun, several attempts have been done and the macro-pulse duration of 3 μs has been achieved[3]. However, there still needs several efforts to obtain enough macro-pulse duration[4]. Upgrade from the thermionic RF-gun to a photo-cathode RF-gun is a short-cut solution. So a design work for the system upgrade has been performed. The system will use not only a 1.5-cell photo-cathode RF-gun, but also use the existing thermionic RF-gun. A Gun-to-Linac beam transport system was designed for two different injectors. Numerical calculation of the beam property has been performed by PARMELA to compare the existing one. We will discuss on the expected FEL gain with the upgraded driver system.

TUPOS25 First Model of the Edge-Focusing Wiggler for SASE
Shigeru Kashiwagi, Goro Isoyama, Ryukou Kato, Kenji Kobayashi, Takanori Noda (ISIR, Osaka), Kimichika Tsuchiya, Shigeru Yamamoto (KEK, Ibaraki)

We are developing a new type of wiggler named the edge-focusing (EF) wiggler, which produces the strong transverse focusing field incorporated with the normal wiggler field. The idea of the EF wiggler* and development of permanent magnet blocks with small magnetization errors for the wiggler** were reported at the two preceding FEL conferences. We have fabricated the first model of the EF wiggler to evaluate its performance. It is a five-period planar wiggler with an edge angle of 2 degrees and a period length of 60 mm. The magnetic field in the wiggler is measured with a Hole probe at a magnet gap of 30 mm. It is experimentally confirmed that a high field gradient of 1.0 T /m is realized along the beam axis in the EF wiggler. In this paper, we will report results of the magnetic field measurement and its analysis for the first mode of the EF wiggler.

TUPOS26 Upgrade of the L-Band Linac at ISIR, Osaka University for a Far-Infrared FEL
Ryukou Kato, Goro Isoyama, Shigeru Kashiwagi, Shoji Suemine, Tamotsu Yamamoto (ISIR, Osaka)

We are developing the far-infrared free-electron laser (FEL) using the L-band electron linac at the Institute of Scientific and Industrial Research (ISIR), Osaka University. The first lasing of the FEL was obtained at wavelengths from 32 to 40 μm in 1994, and the wavelength region has been extended up to 150 μm. The linac was designed and constructed for producing the high-intensity single-bunch beam for pulse radiolysis, so that the filling time of the accelerating structure is 1.8 μs long and the maximum macropulse length of the electron beam is limited to 2 μs, though the duration of the RF pulse can be extended to 4 μs. As a result, the FEL could not reach power saturation because the number of amplification times was limited. Recently, the linac has been extensively remodeled to realize high operational stability and reproducibility for advanced studies in beam science and technology. Almost all the peripheral components are replaced with new ones. At this opportunity, the linac is also made suitable for FEL so that the macropule can be extended up to 6 μs in duration for power saturation of the FEL. The modification of the linac has been completed and commissioning is now in progress. In this paper, we will report performance and characteristics of the linac after modification.

TUPOS27 Development of Compact Soft X-ray Source Based on Laser Undulator
Ryunosuke Kuroda, K. Hidume, S. Minamiguchi, T. Saito, D. Ueyama, Masakazu Washio (RISE, Tokyo), Shigeru Kashiwagi (ISIR, Osaka), Hitoshi Hayano, Junji Urakawa (KEK, Ibaraki)

A compact soft X-ray source is required in various research fields such as material and biological science. The laser undulator based on backward Compton scattering has been developed as a compact soft X-ray source for the biological observation at Waseda University. It is performed in a water window region (250eV - 500 eV) using the interaction between 1047 nm Nd:YLF laser and 4 MeV high quality electron beam generated from rf gun system. The range of energy in the water window region has K-shell absorption edges of Oxygen, Carbon and Nitrogen, which mainly constitute of living body. Since the absorption coefficient of water is much smaller than the protein’s coefficient in this range, a dehydration of the specimens is not necessary. As a preliminary experiment, about 300 eV X-ray generation was carried out. As next step, soft X-ray optics with zone plate was proposed for Soft X-ray microscopy. In this conference, we will report details and results of the experiment.

TUPOS29 Repetitive Bunches from RF-Photo Gun Radiate Coherently
C.A.J. van der Geer, M.J. de Loos, S.B. van der Geer (PP, Soest), Dino Jaroszynski (Strathclyde University, Glasgow)

We consider to feed the laser wake field accelerator of the alpha-X project by a train of low charge pancake electron bunches to reduce undesired expansion due to space-charge forces. To this purpose the photo excitation laser of the rf-injector is split into a train of sub-pulses, such that each of the produced electron bunches falls into a successive ponderomotive well of the plasma accelerator. This way the total accelerated charge is not reduced. The repetitive photo gun can be tested, at low energy, by connecting it directly to the undulator and monitoring the radiation. The assertions are based on the results of new GPT simulations.

TUPOS32 Research on the Undulator Used for PKU-FEL
Huihua Lu, Wan Chen, Jianping Dai, Yanan Li, Caitu Shi, Yufeng Yang, Jiejia Zhuang (IHEP BFEL, Beijing)

A 5m-long combined function undulator used for the Peking University Infrared SASE FEL facility (PKU-FEL) is currently under construction at IHEP, and a 10 period prototype has already been developed. This paper describes the design study of the undulator, which is a hybrid planar magnet structure with extra focusing. The results of magnetic measurements performed on the prototype are also reported and discussed, and it demonstrates that the proposed combined function magnet structure is very promising for the use in the SASE FEL at Peking University.

TUPOS33 Study on the Planar Undulator Scheme with Focusing Properties for PKU-FEL
Yuantao Ding, Jia'er Chen, Senlin Huang, Yugang Wang, Kui Zhao, Jiejia Zhuang (PKU/IHIP, Beijing)

An IR range SASE FEL test facility will be built at Peking University. The project is designed to get the SASE FEL at 7 micron driven by a superconducting accelerator. A hybrid planar Nd-Fe-B undulator is employed and the optimization of the external focus system for the undulator is studied. In the PKU-FEL facility, the electron energy is about 30-40 MeV. The combined function undulator with FODO lattice imposes quite stringent tolerances on the strength of the quads. To solve this problem, the weak natural focusing of the undulator in the vertical plane together with horizontally focusing quads, is proposed to supply the focusing in the facility. The combined function undulator of FOFO lattice and FF lattice in the horizontal plane are studied. Compared with the FODO lattice, the FOFO and FF lattice make the saturation a bit longer and the requirements of the field accuracy for the focusing system are much reduced.

TUPOS34 Beam Loading Tests on DC-SC Photoinjector at Peking University
Senlin Huang, Jia'er Chen, Xiangqiang Chu, Yuantao Ding, Jiankui Hao, Fei Jiao, Lin Lin, Xiangyang Lu, Shengwen Quan, Guimei Wang, Lifang Wang, Rong Xiang, Binping Xiao, Datao Xie, Limin Yang, Baocheng Zhang, Kui Zhao, Feng Zhu (PKU/IHIP, Beijing)

Since the beginning of commissioning in February 2003, lots of tests on the DC-SC photoinjector test facility have been performed. At present, Q0 of the 1+1/2-cell cavity has reached ~1E8 (at 4.2K) and the average gradient was about 4MeV/m. The DC photogun can provide stable electron beams. When the power of output laser went up to 100mW (266nm), the average beam current reached 400μA. Beam loading tests have been carried out, and SC acceleration was achieved. Average current of electron beams is about 100μA after acceleration.Further investigations are in progress to improve diagnostics system and to measure the emittance, energy spread and pulse length of electron beams.

TUPOS35 The Drive Laser System for DC-SC Injector
Xiangyang Lu, Lin Lin, Shengwen Quan, Fang Wang, Kui Zhao (PKU/IHIP, Beijing)

PKU-SCAF has developed a photoinjector which adopt a 1+1/2 cell super conducting cavity and DC electron gun. We also developed a low cost drive laser system for the photocathode DC gun to provide high average beam current. This laser system include a commercial high repetition rate, ps, all solid-state laser, the home made SHG and FHG, Fourier relay optics and the uniform illumination optics. The test results shows the output power at 266 nm of the laser system is more than 1.2W and got more than 500 A beam current from CsTe cathode from the DC gun.

TUPOS36 Simplified Method for Experimental Spectral Ratio Calculation of CHG-FEL
Nian Chen, Duohui He, Ge Li, Yuhui Li, Pengfei Zhang, Shancai Zhang (USTC/NSRL, Hefei, Anhui)

The goal of the coherent harmonic generation free-electron laser (CHG-FEL) experiment in NSRL is to gain a 266nm coherent radiation and a large spectral ratio which is defined as the ratio of coherent intensity to incoherent intensity in infinitesimal bandwidth and solid angle aperture. The intensity measurements are made through a spectrometer whose spectral and angular aperture is much larger than the actual apertures of coherent radiation and smaller than those of incoherent radiation. So the measured ratio is integral ratio integrated over the actual apertures of the measurement system. This paper is mainly on giving a formula and designing a computer program to calculate the spectral ratio according to the bandwidth and solid angle aperture of the measurement system, taking into account the measured magnetic field of optical klystron and the energy spread of the electron beam. The code will soon be employed in our next turn experiment.

TUPOS37 Multi-Objective Optimization for Pure Permanent-Magnet Undulator Magnets Ordering Using Modified Simulated Annealing
Nian Chen, Duohui He, Ge Li (USTC/NSRL, Hefei, Anhui)

Undulator field errors influence the electron beam trajectories and lower the radiation quality. Angular deflection of electron beam is determined by first field integral, orbital displacement of electron beam is determined by second field integral and radiation quality can be evaluated by rms field error or phase error. Appropriate ordering of magnets can greatly reduce the errors. We apply a modified simulated annealing algorithm to this multi-objective optimization problem, taking first field integral, second field integral and rms field error as objective functions. Undulator with small field errors can be designed by this method within a reasonable calculation time even for the case of hundreds of magnets (first field integral reduced to 10-6T·m, second integral to 10-6T·m2 and rms field error to 0.01%). Thus, the field correction after assembling of undulator will be greatly simplified. This paper gives the optimizing process in detail and puts forward a new method to quickly calculate the rms field error and field integrals.

TUPOS38 Design of Undulator for the Shanghai DUV-FEL
Qika Jia, Duohui He, Shengkuan Lu, Shancai Zhang (USTC/NSRL, Hefei, Anhui), Yun Cao, Zhimin Dai, Zhentang Zhao, Qiaogen Zhou (SINAP, Jiading, Shanghai)

The design study of the undu1ator for Shanghai deep ultra violate free electron laser source (SDUV-FEL) is presented. The optimum undulator parameters for the FEL performance have been studied. The scheme of focusing and segmentation is discussed. The requirements of undulator magnet field and main technical demand are given.

TUPOS39 Study of Control Grid Thermionic Cathode RF Gun
Jin Xiao, Liu Jie, Li Ming, Yang Xinfan, Shen Xumin, Chen Yanan, Xu Zhou (CAEP/IAP, Mianyang, Sichuan)

In this paper, the beam loading effect of RF Gun was analyzed. To minimize the energy spread, the grid control RF Gun was introduced. The result shows that the grid congrol RF Gun can increase electron beam within 1% energy spread.

TUPOS40 Superconducting Undulator with Variably Polarized Light
Ching-Shiang Hwang, C.H. Chang, Tai Ching Fan, W.P. Li, P.H. Lin (NSRRC, Hsinchu)

This study investigates planar in-vacuo superconducting undulators with periodic length of 5 cm (IVSU5) producing linearly and circularly polarized infrared rays or xrays source. The vertically wound racetrack coil is selected for the coil and pole fabrication of the IVSU5. When the up and down magnetic pole arrays with alternative directions rotated wires in the horizontal plane, a helical field radiates circularly polarized light in the electron storage ring, the free electron laser (FEL), and the energy recovery linac (ERL) facilities. Meanwhile, an un-rotated wire is constructed together with the rotated wire on the same undulator is used to switch the linear horizontal and vertical, the right- and left-circular polarization radiation. Given a periodic length of 5 cm and a gap of 23 mm, the maximum magnetic flux density in the helical undulator are Bz = 1.5 T and Bx = 0.5 T when the wires rotated by 20°. This article describes the main factors of the planar and helical undulator design for FEL and the concepts concerning the magnet array structures of the superconducting undulators. The photon flux and the mechanism of the switching polarization radiation are discussed.

TUPOS43 Commissioning of Strong Tapered Undulator Developed for IFEL Accelerator
Sergey Tolmachev, Alexander Varfolomeev, Alexander Varfolomeev Jr., Timofey Yarovoi (RRC Kurchatov Institute, Moscow), Pietro Musumeci, Claudio Pellegrini, James B Rosenzweig (UCLA, Los Angeles, California)

Description is presented of the KIAE-2p planar undulator device manufactured for the UCLA – Kurchatov Institute IFEL project (see PAC2001 Proceedings, p.p. 4008-4010 and PAC2003 Proceedings). Physical requirements for the undulator and simulations results on the design were given earlier (Nucl. Instr. and Meth. A483 (2002) 372-382). Here we describe main technological aspects enabled to fabricate the installation responding to the stringent requirements on mechanical construction accuracy and magnetic field strong tapering. Main parameters of the tuned undulator including last results of the magnetic field measurements by different methods are given. The obtained magnetic fields were used for final simulations of the acceleration process. It is shown that capture of 30% of electrons is provided in the acceleration process with energy gain from initial 14 MeV up to 50 MeV for nominal electron beam and laser beam parameters. Special analysis of the undulator acceptances for these parameters was made. It is shown that the acceleration takes place up to energies > 30 MeV for rather wide deviations from nominal ones in laser pulse energy, Rayleigh length and e.b. emittance.

TUPOS45 FEL and Libera both Push Performance into New Frontiers
Rok Ursic, B. Solar (Instrumentation Technologies, Solkan)

Free Electron Lasers and Libera electron beam position processor share a common vocation – they both push performance into new frontiers. Advances in electron accelerator technology that enabled FELs to fulfill their earliest days promises have also been due to the recent developments in the beam instrumentation. Libera that has till know been successfully employed in the light sources projects promises to become an indispensable tool also in the FEL field. The three main advantages of Libera are: all-in-one, customization and connectivity. All-in-one is the concept of unification of various building blocks and thus various functionalities in one product. The customization is enabled by the product’s reconfigurability that allows it to grow and support new requirements and application without changing hardware. The consequence of the two is the capacity of the single instrument to perform a variety of tasks that before were split among different devices. Connectivity improves the communication between controls and beam diagnostics, brings out-of-the crate-freedom and opens unforeseen possibilities for inter-accelerator cooperation and remote technical support.

TUPOS47 Optical Systems for the Fourth Generation Light Source, 4GLS
Frances Quinn, Marion Bowler, Mike MacDonald, Mark Roper (CCLRC/DL/SRD, Warrington)

4GLS is a multi-user, multi-source facility proposed for construction at Daresbury Laboratory in the UK. By exploiting super-conducting linac technology with energy recovery, it will combine three free electron lasers and a range of conventional synchrotron radiation sources covering the THz to SXR region. The facility will provide femtosecond pulses at high repetition rate, with the FELs delivering GW power in the VUV and XUV region. This paper discusses the options and challenges for the optical systems associated with the suite of photon sources. The beamlines will need to operate both independently and in flexible, synchronised combinations. Together with the requirements for preserving the ultra-bright, fast pulse properties, this places unique demands on the design, layout and operational modes. The paper summarises current technical achievements and identifies the research and development necessary before detailed design of the 4GLS optical systems.

TUPOS48 A Concept for z-Dependent Microbunching Measurements with Coherent X-ray Transition Radiation in a SASE FEL
Alex H. Lumpkin (ANL/APS, Argonne, Illinois), William M. Fawley (LBNL/CBP, Berkeley, California), Don W. Rule (NSWC-CD, West Bethesda)

Previously, measurements in the visible to VUV regimes of z-dependent microbunching in a self-amplified spontaneous emission (SASE) free-electron laser (FEL) have provided important information about the fundamental mechanisms. In those experiments a thin metal foil was used to block the more intense SASE radiation and to generate coherent optical transition radiation (COTR) as one source in a two-foil interferometer. However, for the proposed Linac Coherent Light Source (LCLS), the intense SASE emission is either too strongly transmitted at 1.5 angstroms or the needed foil thickness for blocking scatters the electron beam too much. Since coherent x-ray transition radiation (CXTR) is emitted in an annulus with opening angle 1/γ = 36 µrad for 14.09-GeV electrons, one could use a thin foil or foil stack to generate the XTR and CXTR and an annular crystal to wavelength sort the radiation. The combined selectivity will favor the CXTR over SASE by about eight orders of magnitude. Time-dependent GINGER simulations support the z-dependent gain evaluation plan.

TUPOS49 First Direct Comparisons of a COTRI Analytical Model to Data from a SASE FEL at 540, 265, and 157 nm
Alex H. Lumpkin, Roger J. Dejus (ANL/APS, Argonne, Illinois), Don W. Rule (NSWC-CD, West Bethesda)

We have been addressing fundamental aspects of the microbunching that is induced by the self-amplified spontaneous emission (SASE) free-electron laser (FEL) process using coherent optical transition radiation interferometry (COTRI) techniques. Over the last several years we have extended operations from the visible to the VUV regime at the Advanced Photon Source (APS) low-energy undulator test line (LEUTL) project. We have now performed our first direct comparisons of the results of an analytical model to COTRI experimental data at 540, 265, and 157 nm. The direct comparisons illustrate a number of details in the images that are not matched by the simplifying assumption of a single Gaussian transverse beam profile of the size consistent with the incoherent OTR measurements. This result indicates there are localized transverse portions of the beam distribution with a higher bunching fraction than the mean. The different beam energies used result in different overlaps of relevant functions,and this aspect probed the model’s applicability and sensitivities.

TUPOS50 Use of VUV Imaging to Evaluate COTR and Beam-Steering Effects in a SASE FEL at 130 nm
Alex H. Lumpkin, Yong-Chul Chae, Roger J. Dejus, Mark Erdmann, John W. Lewellen, Yuelin Li (ANL/APS, Argonne, Illinois)

We have continued to explore VUV operations on the Advanced Photon Source (APS) self-amplified spontaneous emission (SASE) free-electron laser (FEL). With the installation of a fifth VUV imaging station located after undulator 7 of an eight-undulator series, we have performed our most complete SASE gain curve measurements at 130 nm as well as obtaining beam profile, position, and divergence information. This is the shortest wavelength to date for our complementary coherent optical transition radiation (COTR) measurements. We have also done the first experimental test of Tanaka et al.’s analytical model for the effects of a single-kick error of the e-beam on gain and microbunching in a SASE FEL. In addition, we compared the e-beam image centroid positions with those of the alignment laser at the available cameras and the local rf BPM readings to sort out the effective trajectory and its effect on overall gain. The FEL performance was consistent with GENESIS simulations of the experiment described in detail in a companion paper.

TUPOS51 Test of Horizontal Magnetic Field Measurements in the Presence of a Strong Vertical Field
Isaac Vasserman (ANL/APS, Argonne, Illinois)

Trajectory straightness is an important parameter defining the performance of free-electron laser (FEL) devices. The first test of horizontal field measurements using Hall probes was done in 1998 as a preparation to the tuning of undulators for the FEL project at the Advanced Photon Source. This work continues the 1998 work, now associated with Linac Coherent Light Source (LCLS) project. Tolerances for the LCLS FEL undulator specify 2 um trajectory excursion in both (horizontal and vertical) planes for a particle energy of 14.1 GeV, which means that measurements of a small horizontal field in presence of strong (up to 1.5 T) vertical field are required. Hall probe measurements under such conditions are complicated due to a planar Hall probe effect. Previous tests done in 1998 showed that a 2- axis Sentron probe is a possible choice. The high sensitivity of horizontal field integrals to the vertical position of the sensor was observed. It was shown that this probe could be used for fast measurements and tuning of the device. The Sentron probe was recently used for LCLS prototype measurements and tuning. Rather good agreement with reference moving coil measurements was obtained.

TUPOS52 Development and Measurement of Strain Free RF Photoinjector Vacuum Windows
Sandra G. Biedron (ANL, Argonne, Illinois), John W. Lewellen (ANL, Argonne, Illinois; ANL/APS, Argonne, Illinois), Lahsen Assoufid, Yuelin Li, Jun Qian (ANL/APS, Argonne, Illinois), Marcus Babzien (BNL, Upton, Long Island, New York), Gregory Gill (ISI, Sarasota Florida)

RF photoinjectors produce the highest brightness electron bunches only under nearly ideal illumination by a drive laser. The vacuum window used to introduce the laser beam is an essential element that may potentially degrade any distribution, making it difficult or impossible to know the actual uniformity achieved at the cathode. Because of the necessity to obtain ultrahigh vacuum near the photoinjector, some restrictions are imposed on the fabrication technology available to manufacture distortion-free windows. At the UV wavelengths commonly used for photoinjectors, it is challenging to measure and eliminate degradation caused by vacuum windows. Here, we discuss the initial laser-based measurements of a strain-free, coated, UHV window manufactured by Insulator Seal in collaboration with members of Brookhaven and Argonne National Laboratories.

TUPOS54 Comparison of Parmela and MAFIA Simulations of Beam Dynamics in High Current Photoinjector
Sergey S Kurennoy (LANL/LANSCE, Los Alamos, New Mexico)

A high-current RF photoinjector producing low-emittance electron beam is an important technology for high-power CW FEL. LANL-AES team designed a 2.5-cell, pi-mode, 700-MHz normal-conducting RF photoinjector with magnetic emittance compensation. With the electric field gradients of 7, 7, and 5 MV/m in the three subsequent cells, the photoinjector will produce a 2.5-MeV electron beam with 3-nC charge per bunch and the transverse rms emittance 7 mm-mrad. Beam dynamics in the photoinjector has been modeled in details. In addition to the usual approach, with fields calculated by Superfish-Poisson and beam simulations performed by Parmela, we also used MAFIA group of codes, both to calculate cavity fields and to model beam dynamics with its particle-in-cell module TS. The second way naturally includes wake-field effects into consideration. The simulation results and comparison between two approaches will be presented.

TUPOS56 RF Design for the Linac Coherent Light Source (LCLS) Injector
D. H. Dowell, Lynn D. Bentson, Richard F. Boyce, J. A. Hodgson, Zenghai Li, C. Limborg-Deprey, Liling Xiao, Nancy Yu (SLAC, Menlo Park, California), Steve M. Gierman, John F. Schmerge (SLAC/LCLS, Menlo Park, California)

The Linac Coherent Light Source (LCLS) will be the world’s first free electron laser, and the successful operation of this very short-wavelength FEL will require excellent beam quality from its electron source. Therefore a critical component is the RF photocathode injector. This paper describes the design issues of the LCLS RF gun and accelerator structures. The injector consists of a 1.6 cell s-band gun followed by two 3-meter SLAC sections. The gun and the first RF section will have dual RF feeds both to eliminate transverse RF kicks and to reduce the pulsed heating of the coupling ports. In addition, the input coupler cavity of the first accelerator section will be specially shaped to greatly reduce the RF quadrupole fields. The design for the accelerator section is now complete, and the RF design of the gun’s dual coupler and the full cell shape is in progress. These and other aspects of the gun and structure designs will be discussed.

TUPOS57 Optimal RF Systems for Lightly Loaded Superconducting Structures
Townsend Zwart, Dan Cheever, William S Graves, D. Wang, Abbi Zolfaghari (MIT/BLAC, Middleton, Massachusetts)

Recent developments in the field of RF accelerators have created a demand for power amplifiers that can support very high accelerating gradients, 15-25 MV/m, in superconducting structures with extremely low losses. Free electron lasers (FEL’s) with modest beam current, I< 10 uA, or based on energy recovery linacs (ERL’s) may have intrinsic power demands of less than 1 kW/m. We present the design of an amplifier and external tuner system that will efficiently meet this requirement. The RF amplifier, an Inductive Output Tube (IOT), offers high AC/RF efficiency, flexible power output and switching capability without the need for external modulation. The tuner circuit makes use of low loss ferrite phase shifters to create a moderate quality standing wave (Q~100-1000) between the amplifier and the superconducting cavity. An alternative design based on a shorter cavity structure and employing solid state amplifiers is also presented. The expected performance characteristics of both systems are described.

TUPOS58 Electron Beam Diagnostics Using Diffraction Radiation
Bibo Feng, William E. Gabella (FEL Center, Vanderbilt University, Nashville, TN), Steven E. Csorna, Tamas R. Sashalmi (Vanderbilt/DPA, Nashville - Tennessee)

Diffraction radiation, emitted from ralativistic electron bunches, has the potential applications of non-intercepting electron beam diagnostics. The electron longitudinal distribution in a bunch can be obtained from the coherent diffraction radiation spectrum; the beam transverse properties, such as beam size, divergence and emittance, can be measured through the analysis of the angular distribution of the diffraction radiation. The design study and initial experimental results at the Vanderbilt FEL facility will be presented.

TUPOS59 Simulations of the Newark FIR FEL Operation
Jianjun Zheng, Ken K. Chin (NJIT, Newark), John M.J. Madey, Eric Szarmes (UHM-Physics, Honolulu, Hawaii)

The operation of the NJIT/Rutgers FIR FEL is simulated for the first time sing the slightly modified UH code. The lasering behavior is explored for a wide range of parameters. Particularly, we studied the effects on the operation of the microtron based FEL due to the electron beam pulse phase instability which is possibly caused by the microtron cathode back heating. The study shows that for a small phase slew, systematic or random, there is little effect on the normal operation of the FEL. However, a dramatic phase slew of the e-pulse lasting for 1μs kills the operation of the FEL. We estimated the tolerance of the phase instability and discussed the proper operation condition of the device.

TUPOS60 Making an Inexpensive Electromagnetic Wiggler Using Sheet Materials for the Coils
George Herman Biallas, Stephen Vincent Benson, Thomas Hiatt, George Neil, Michael Snyder (Jefferson Lab, Newport News, Virginia)

An inexpensive electromagnetic wiggler, made with twenty-eight, 4 cm periods with a K of 1 and gap of 2.6 cm was made within 10 weeks after receipt of order by an industrial machine shop. The coil design used sheet and plate materials cut to shapes using water jet cutting and was assembled in a simple stack design. The coil design extends the serpentine conductor design of the Duke OK4 to more and smaller conductors. The coils are conduction cooled to imbedded cooling plates. The wiggler features graded end pole fields, trim coil compensation for end field errors and mirror plates on the ends to avoid three dimensional end field effects. Details of the methods used in construction and the wiggler performance are presented.

TUPOS61 Performance and Modeling of the JLab IR FEL Upgrade Injector
Carlos Hernandez-Garcia, Kevin Beard, Stephen Vincent Benson, George Herman Biallas, Don Bullard, David Douglas, Fred Dylla, Richard Evans, Al Grippo, Joe Gubeli, Kevin Jordan, George Neil, Michelle D. Shinn, Tim Siggins, Richard Walker, Byung Yunn, Shukui Zhang (Jefferson Lab, Newport News, Virginia)

The JLab IR Upgrade Injector has delivered up to 9.1 mA CW of electron beam current at 9 MeV. The injector is driven by a 350 kV DC Photocathode Gun. Injector behavior and beam-based measurements are in very good agreement with PARMELA simulations. The injected beam envelopes were established by measuring beam spot sizes and comparing them with those predicted by a transport matrix based model. The emittances were measured by fitting an initial trial beam matrix to the measured data. The injected bunch length was established by measuring the energy spread downstream of the Linac while operating at either side of crest.

TUPOS62 Short Electron Beam Bunch Characterization Through Measurement of Terahertz Radiation
Shukui Zhang, Stephen Vincent Benson, David Douglas, Michelle D. Shinn, Gwyn Williams (Jefferson Lab, Newport News, Virginia)

Characterization of the electron beam bunch length of the upgrade FEL at Jefferson Lab was performed by analyzing the FTIR spectra of the coherent terahertz pulses. The results are compared with autocorrelation from a scanning polarization autocorrelator that measures the optical transition radiation. The limitations of the different methods to such a characterization are presented in this paper.

TUPOS63 RF Sources for 3rd & 4th Generation Light Sources
Stephan Lenci, Adam Balkcum, Heinz Bohlen, Albert Mizuhara, Edward Wright (CPI/MPP, Palo Alto, CA), Yanxia Li, R. Tornoe (CPI/EIMAC, San Carlos, California)

The growing number of third and fourth generation light sources has resulted in an increase of the available rf sources to power them. Single beam klystrons are the traditional power source, but the development of IOT’s and multiple-beam klystrons (MBK’s) in L-Band have increased the options for these machines. The Eimac division of CPI has recently built and tested a prototype L-Band IOT, which delivered 30 kW CW at 1.3 GHz. Future work includes the building of an IOT at 1.5 GHz. Meanwhile the MPP division of CPI is currently testing the prototype 10 MW peak, 1.3 GHz MBK for the TESLA x-ray free-electron laser (XFEL). Test results for these new products as well as information on all CPI products at 500 MHz, 1.3 GHz, and 1.5 GHz will be presented.

TUPOS64 High Current Energy Recovery Linac at BNL
Vladimir N. Litvinenko, Donald Barton, D. Beavis, Ilan Ben-Zvi, Michael Blaskiewicz, J.M. Brennan, A. Burrill, R. Calaga, P. Cameron, X. Chang, Roger Connolly, D. Gassner, H. Hahn, A. Hershcovitch, H.C. Hseuh, P. Johnson, D. Kayran, J. Kewisch, R. Lambiase, G. McIntyre, W. Meng, T. C. Nehring, A. Nicoletti, D. Pate, J. Rank, T. Roser, T. Russo, J. Scaduto, K. Smith, T. Srinivasan-Rao, N. Williams, K.-C. Wu, Vitaly Yakimenko, K. Yip, A. Zaltsman, Y. Zhao (BNL, Upton, Long Island, New York), H. Bluem, A. Burger, Mike Cole, A. Favale, D. Holmes, John Rathke, Tom Schultheiss, A. Todd (AES, Medford, NY), J. Delayen, W. Funk, L. Phillips, Joe Preble (Jefferson Lab, Newport News, Virginia)

We present the design, the parameters of a small test Energy Recovery Linac (ERL) facility, which is under construction at Collider-Accelerator Department, BNL. This R&D facility has goals to demonstrate CW operation of ERL with average beam current in the range of 0.1 - 1 ampere, combined with very high efficiency of energy recovery. A possibility for future up-grade to a two-pass ERL is considered. The heart of the facility is a 5-cell 700 MHz super-conducting RF linac with HOM damping. Flexible lattice of ERL provides a test-bed for testing issues of transverse and longitudinal instabilities and diagnostics of intense CW e-beam. ERL is also perfectly suited for a far-IR FEL. We present the status and our plans for construction and commissioning of this facility.

TUPOS65 Thermal and Field Enhanced Photoemission: Comparison of Theory to Experiment
Kevin Lynn Jensen (NRL/ESTD, Washington), David L. Demske, Donald W. Feldman, Nate Moody, Patrick Gerard O'Shea (IREAP, College Park, Maryland)

Photocathodes are a critical component of high-gain FEL’s and the analysis of their emission is complex. Relating their performance under laboratory conditions to conditions of an rf photoinjector is difficult. Useful models must account for cathode surface conditions and material properties, as well as drive laser parameters. We have developed a time-dependent model accounting for the effects of laser heating and thermal propagation on photoemission. It accounts for surface conditions (coating, field enhancement, reflectivity), laser parameters (duration, intensity, wavelength), and material characteristics (reflectivity, laser penetration depth, scattering rates) to predict current distribution and quantum efficiency. The applicatIon will focus on photoemission from metals and, in particular, dispenser photocathodes: the later introduces complications such as coverage non-uniformity and field enhancement. The performance of experimentally characterized photocathodes will be extrapolated to 0.1 - 1 nC bunches in 10 ps pulses under fields of 10 - 50 MV/cm and other conditions typical of high gain FELs.

TUPOS67 A Mode Locked UV-FEL
Parviz Parvin (AUT, Tehran; AEOI-RCLA, Tehran), Zahra Zamanipour (AEOI-RCLA, Tehran), B. Sajad (AU, Vanak, Tehran), G. R. Davoud-Abadi, F. Ebadpoor (AUT, Tehran), B. Jaleh (BASU Physics, Hamadan), A. Basam (IHU, Tehran)

An appropriate resonator has been designed to generate femtosecond mode locked pulses in a UV FEL with the modulator performance based on the gain switching. The gain broadening due to electron energy spread affects on the gain parameters, small signal gain (γ0) and saturation intensity (Is), to determine the optimum output coupling as small.