• E. Prat, W. Decking, T. Limberg
  DESY, Hamburg

This paper studies the impact of transverse dispersion on the SASE radiation power sensitivity with respect to the electron beam energy off-set. Both measurements and simulations are presented. By correcting the spurious dispersion inside the undulator region, the electron beam energy bandwidth is increased considerably, which decreases the SASE power jitter due to electron energy fluctuations.

• E. Prat, C. Gerth, K.E. Hacker
  DESY, Hamburg

At the Free Electron Laser in Hamburg (FLASH), when the electron beam is accelerated some degrees off-crest in the first accelerator module as during SASE operation, a correlation between the longitudinal position and the beam energy is induced. Between the second and the third dipole of the first bunch compressor (BC2), the horizontal beam position correlates linearly with the beam energy. With additional vertical dispersion, the beam is tilted in the x-y plane in this region, thereby increasing the projected vertical emittance. A systematic study of how vertical dispersion tilts the beam at the BC2 and causes an increase of the vertical emittance is presented here. The dispersion is generated by applying vertical trajectory bumps through the first accelerator module.

• M. Hohmann
  Transtechnik, Holzkirchen

The High-Voltage-all-solid-state-Modular-Power-Supplies HiVoMoPS-concept is a patented solution for a solid state Klystron Modulator or High-Voltage Power supply, as a special type of Marx-Generator. In applications for klystron modulators like the XFEL-project (esp. the 3th-harmonics, or main klystron supply), the biggest advantages are the pulse length for the klystrons can changed between 0.5ms (or shorter) to 3.0ms, repetition rate can be up to 30Hz or higher) by up to 50kV (or higher, >100kV), and the pulseform can be changed by additional submoduls and software features. Additional advantages for this HiVoMoPS are no kind of pulse transformer, bouncer circuits or crowbar circuits.

• M. Hänel, G. Klemz, M. Krasilnikov, J. Rönsch, F. Stephan
  DESY Zeuthen, Zeuthen
• I. Will
  MBI, Berlin

The Photo Injector Test facility at DESY, Zeuthen site, PITZ, develops and optimizes high brightness electron sources for Free Electron Lasers such as FLASH and the European XFEL. In last years shutdown period different components of the facility have been upgraded. One of the key upgrades was the installation of a new laser system with a larger spectral bandwidth. This allows for rise- and fall-times of less than 2ps of the temporally flat top laser pulses having a FWHM of up to 25ps. In this paper we report on the investigations of modulations in the electron bunch momentum spectra when modifying parameters of the laser system such as bandwidth or longitudinal pulse shape.

• S. Rimjaem, J.W. Bähr, C.H. Boulware, H.-J. Grabosch, M. Hänel, Ye. Ivanisenko, G. Klemz, M. Krasilnikov, M. Otevrel, B. Petrosyan, S. Riemann, J. Rönsch, R. Spesyvtsev, F. Stephan
  DESY Zeuthen, Zeuthen
• G. Asova, L. Staykov
  INRNE, Sofia
• K. Flöttmann, S. Lederer, S. Schreiber
  DESY, Hamburg
• L. Hakobyan, M.K. Khojoyan
  YerPhI, Yerevan
• M.A. Nozdrin
  JINR, Dubna, Moscow Region
• B. D. O'Shea
  UCLA, Los Angeles, California
• R. Richter
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
• A. Shapovalov
  MEPhI, Moscow
• G. Vashchenko
  NSC/KIPT, Kharkov
• I. Will
  MBI, Berlin

At the Photo Injector Test facility at DESY, Zeuthen site, (PITZ) development and optimization of high brightness electron sources for Free Electron Lasers (FELs) like FLASH and the European XFEL are performed. In 2008, the PITZ facility was substantially upgraded. A new 1.6-cell L-band RF-gun cavity treated with an improved surface cleaning technique, a new photocathode laser system allowing shorter rise and fall times of the flat hat temporal distribution and several new diagnostics components have been installed. Since the transverse emittance is a key property of high brightness electron sources a major part of the measurement program at PITZ is devoted to the transverse phase space optimization. Recent results of emittance measurements using the upgraded facility are reported and discussed in this contribution.

• O. Ferrando, E. Karantzoulis
  ELETTRA, Basovizza

A beam dump transfer line (Main Beam Dump TL) has been designed to transport the electrons from each FERMI radiator to the beam dump. The line matches the e-beam optics from the end of the undulator chains of FEL1 and FEL2 for all photon wavelengths and polarizations required by the FERMI project. The transfer line is also equipped with different types of instrumentation to characterize the beam in terms of emittance, energy spread and jitter of the electron bunches and so demands a flexible optics interchangeable between measurements and normal operations. The line may also accommodate a coherent infrared source with particular requirements on the optics. The beam optics, the line design, and the various operating modes will be presented and discussed.

• M. Veronese, M.B. Danailov, M. Ferianis
  ELETTRA, Basovizza
• D. Filippetto
  INFN/LNF, Frascati (Roma)
• S.P. Jamison
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire

EOS and coherent radiation based diagnostics of sub-psec electron bunches are longitudinal diagnostics adopted for FERMI and other 4th generation light sources. The performance of both kind of diagnostics depends on the material properties in the THz spectral range. There is a need to characterise the transmission of windows materials and to understand the absolute efficiency of electro-optic detectors. This requirement for absolute EO efficiency is particularly important given observed variations between individual crystals with nominal identical specifications. In this paper we report measurements with THz pulses produced with photoconductive emitters. Our main goal was the characterization of EO crystals such as ZnTe and GaP for EOS and THz windows materials and humidity absorption. Good agreement is found for EO between experimental results and theoretical calculations concerning temporal resolution.

• M. Esposito, M. Paris, F. Sgamma, S. Tomassini, M. Troiani
  INFN/LNF, Frascati (Roma)

The SPARC project is a collaboration between ENEA and INFN on an R&D activity oriented to the development of a high-brightness photoinjector to drive SASE FEL experiments. Tolerances for the alignment of the accelerator components were very tight and it has been quite a challenge to obtain them using standard techniques and instruments such as optical levels, theodolites and laser trackers. A description of the alignment and fiducialisation procedures of the accelerator components is presented.

• M. Zambelli, M. Kokole, T. Milharcic
  KYMA, Trieste
• B. Diviacco, D. Zangrando
  ELETTRA, Basovizza
• G. Soregaroli, M. Tedeschi
  Euromisure srl, Pieve S. Giacomo (CREMONA)

The today’s forefront of light source facilities is represented by the so-called 4th generation light sources, i.e. linear accelerators of electrons named “Free-Electron Lasers” or “FEL”. In FELs, electrons are not accumulated in a storage ring, but they are generated and accelerated with a “single-pass” process. In these conditions the only possibility of generating light is through the use of long chains of undulators. The characteristics and performances of the magnetic material used in undulators is pushed to the limit of the available technology. In spite of the high accuracy of manufacturing these magnet blocks must be further characterised one by one and appropriately coupled in order to achieve optimal uniformity of magnetic characteristics of the finished undulator. This presentation illustrates the work carried out at Elettra light source facility of Sincrotrone Trieste SCpA (ST) and at Kyma (spin-off company of ST) in order to characterize pure permanent magnet blocks used in manufacturing of undulators for the next 4th generation facility being built at the Basovizza site of ST, i.e. the new Free-Electron Laser called “FERMI@Elettra”.

• S.M. Matsubara
  RIKEN/SPring-8, Hyogo
• A. Maekawa
  The University of Tokyo, Nuclear Professional School, Ibaraki-ken
• H. Tomizawa
  JASRI/SPring-8, Hyogo-ken

High-brightness electron bunches are required with low slice emittance and bunch length of 30 fs (FWHM) in a targeting lasing part for XFEL/Spring-8. In order to obtain maximum brightness, it is very important to measure 3D bunch charge distribution (BCD) in real-time for future X-ray light sources (XFEL, ERL, etc). Therefore, we are developing a single-shot, non-destructive, and real-time 3D-BCD monitor based on Electro-Optical Sampling with a manner of spectral decoding. The monitor system requires for a probe laser source to realize a higher temporal resolution. The laser source has broad spectrum of over 400 nm width and a linear-chirp of over 3,000 fs² to be few-ps pulse duration. Then, the shape in the frequency regions is rectangular. The liner-chirp is supplied by using a broadband AO-modulator (DAZZLER) which is possible to remove higher order dispersions. The laser pulses will be amplified to be micro-joule pulse-energy with a manner of NOPA. The laser source with such as the properties is mentioned in this report. We expect the feasibility of 20 fs temporal resolution by using this laser source with an organic crystal such as a DAST crystal.

• A. Mizuno, H. Dewa, H. Hanaki, T. Taniuchi, H. Tomizawa
  JASRI/SPring-8, Hyogo-ken

Generally, vertical and horizontal emittance asymmetry has recognized as one of the problem of the high brightness, low emittance electron source like photo-cathode RF gun. As for the SPring-8 photo-cathode RF gun, the asymmetry also exists, the vertical emittance is always bigger than the horizontal one. We have been tackled this problem for several years and been eliminated some causes. Though, the asymmetry still remained. We calculated 3D electro-magnetic fields data of S-band traveling accelerator structure by MW STUDIO and calculated emittance by self-made 3D particle tracking code using these data. As a result, radial displacement of the magnetic field from mechanical center in a coupler cell of the accelerator structure is turned out to be one of the cause of these asymmetry. Though a slice emittance in the bunch keep constant, projected emittance of the whole bunch becomes worse in the coupler cell, since the fields' displacement effect on the each slice emittance is changed with rf time evolution. In the paper, we show simulation results and comparative discussion with experimental results.

• N. Nishimori, R. Hajima, H. Iijima, R. Nagai
  JAEA/ERL, Ibaraki
• Y. Honda, T. Miyajima, T. Muto, M. Yamamoto
  KEK, Ibaraki
• M. Kuriki
  HU/AdSM, Higashi-Hiroshima
• M. Kuwahara, T. Nakanishi, S. Okumi
  Nagoya University, Nagoya

Energy recovery linac (ERL) based next generation light sources such as X-ray oscillator require high brightness electron gun. We have developed a 500-kV, 10-mA photocathode DC gun by the collaboration efforts of JAEA, KEK, Hiroshima Univ. and Nagoya Univ. A segmented cylindrical ceramic insulator with guard rings is employed to improve stability and robustness at high voltage operation by keeping secondary electrons away from the ceramic surface. A Cockcroft-Walton power supply is installed in a SF6 tank and high voltage test up to 550kV was successfully done. All the vacuum chambers are made of chmically polished titanium alloy with very low out-gassing. A photocathode preparation system was assembled and vacuum test is performed. Up-to-date status of the gun development will be presented in detail.

• K. Masuda, T. Kii, H. Ohgaki, T. Shiiyama
  Kyoto IAE, Kyoto
• K. Kanno, E. Tanabe
  AET Japan, Inc., Kawasaki-City

A triode rf gun* is being developed, which is aimed at drastic reduction of electrons back-streaming and hitting the thermionic cathode. Thermionic rf guns in general show advantages over photocathode guns such as low cost, easy operation and high averaged current (high repetition rate), which are suitable for FELs for various uses. They however suffer from the electron back-bombardment resulting in limited macro-pulse duration of severalμseconds. In order to reduce the back-streaming electrons, the triode rf gun employs an rf cavity much shorter (e.g. ~2 mm) than the rf wavelength as the first cell with a thermionic cathode. The phase and amplitude of the rf field in the first short cell are then controlled independent from the successive cells. We have designed a triode rf gun and fabricated the additional short rf cavity which is to be installed in the S-band 4.5-cell rf gun used in the KU-FEL. The results from PIC simulations showed that the back-bombardment power is expected to reduce drastically by more than 80% without loss of beam brightness. Preliminary results from the cold testing and rf conditioning of the additional cavity will be also presented.

*K. Kanno et al., Japanese J. Applied Physics 41 (2002) 62-64, and
K. Masuda et al., Proc. of 27th Intnl. FEL Conf. 2005 (2006) 588.

• T. Tanikawa
  Sokendai - Okazaki, Okazaki, Aichi
• M. Adachi, M. Katoh, H. Zen
  UVSOR, Okazaki
• M. Hosaka, Y. Taira, N. Yamamoto
  Nagoya University, Nagoya

Light source technologies based on laser seeding are under development at the UVSOR-II electron storage ring. In the past experiments, we have succeeded in generating coherent THz radiation with various spectral properties and coherent DUV radiation with various polarizations. We carried out these experiments by utilizing a part of the existing free electron laser system and an SR beam-line opened for users. Last year, we started a new five year project, which contains construction of new undulators and beam lines dedicated to the source developments and also upgrade of the laser system. We have designed the seeding laser system and the undulators based on numerical simulations. A spectrometer for VUV has been constructed. A seeding light source based on HHG is under development. In this presentation, we report the results from the design studies and the preliminary experiments.

• S. Kashiwagi, K. Furuhashi, G. Isoyama, R. Kato, M. Morio, N. Sugimoto, Y. Terasawa
  ISIR, Osaka
• H. Hayano, H. Sugiyama, J. Urakawa, K. Watanabe
  KEK, Ibaraki
• D. Kubo, M. Kuriki, C. Shonaka
  HU/AdSM, Higashi-Hiroshima

We have begun the development of L-band photocathode RF gun for the 40 MeV L-band linac at ISIR, Osaka University to advance studies such as FEL and pulse radiolysis experiments in the future with the high-intensity and low emittance electron beam. Before it installs the RF gun into Osaka University, we plan to develop and commission the L-band RF electron gun for the Superconducting RF Test Facility (STF) at High Energy Accelerator Research Organization (KEK). While waiting for delivery of an RF cavity and an input coupler from the Fermi National Accelerator Laboratory, we have fabricated a test RF gun cavity and a coaxial input coupler made from Aluminium and investigated the rf properties of them. The resonant frequency and field balance of the real RF gun cavity have been adjusted using a tuning apparatus at KEK-STF. Some results of the development are reported, including the tuning of RF characteristics of the cavity, design of an input coupler and solenoid magnet for emittance compensation, and computer simulation for characteristics of the accelerated electron beam.

• R. Kato, K. Furuhashi, G. Isoyama, S. Kashiwagi, M. Morio, Y. Terasawa
  ISIR, Osaka

The performance of the free-electron laser based on self-amplified spontaneous emission strongly depends on time-sliced characteristics of the electron beam, such as longitudinal charge distribution, slice energy spread and transverse slice emittance. We have developed a longitudinal phase space measurement system consisted of a Cherenkov radiator, a bending magnet and a streak camera and reconstructed the longitudinal phase-space image of the high brightness electron beam accelerated by the L-band electron linac at ISIR, Osaka University [1]. Using a quadruple magnet instead of the bending magnet, this technique can be applied to measure the transverse slice emittance of the electron beam. A few slice emittance measurement techniques were already studied and turned into actual utilization; however our idea provides a simpler and more convenient technique. This paper describes a design conceptual of the slice emittance measurement system.

[1] R. Kato et al., “Study on Longitudinal Phase-space of High-brightness Electron Beams at ISIR, Osaka University”, Proceedings of EPAC’08, Genoa, Italy, June 23 - 27, 2008, pp.1161-1163.

• K. Sakaue
  RISE, Tokyo

We have been developing a pulsed-laser storage technique in a super-cavity for a compact x-ray sources. The pulsed-laser super-cavity enables to make high peak power and small waist laser at the collision point with the electron beam. Recently, using 357MHz mode-locked Nd:VAN laser pulses which stacked in a super-cavity scattered off a multi-bunch electron beam, we obtained a multi-pulse x-rays through the laser-Compton scattering. Detecting a x-ray pulse-by-pulse using high-speed detector makes it possible to measure the 3-dimensional beam size with bunch-by-bunch scanning the laserwire target position and pulse timing. This technique has a feasibility of measuring femto-second bunch length by stacking femto-second pulse in an optical cavity. Design study of femto-second laserwire monitor and the experimental demonstration using pico-second pulse storage and multi-bunch electron beam will be presented at the conference.

• J.P. Dai, M. Hou, G. Pei, J.R. Zhang
  IHEP Beijing, Beijing
• Q. Gu, M.H. Zhao, S.P. Zhong
  SINAP, Shanghai

Transverse RF deflectors are widely used for the measurements of ultra-short bunch length and other slice parameters. This paper presents the development of an S-band LOLA-type RF deflector and the bunch length measurement of the electron beam produced by the photocathode RF gun of Shanghai DUV-FEL facility. The deflector’s VSWR is 1.06, the whole attenuation 0.5dB, and the bandwidth 4.77MHz for VSWR less than 1.1. With laser pulse width of 8.5ps, beam energy of 4.2 MeV, bunch charge of 0.64 nC, the bunch lengths for different RF input power into the deflector were measured, and the averaged rms bunch length of 5.25 ps was obtained.

• W.H. Hwang, K.M. Ha, K.R. Kim, S.H. Kim, S.H. Kim, S.S. Park, Y.G. Son
  PAL, Pohang, Kyungbuk
• M. Yoon
  POSTECH, Pohang, Kyungbuk

Pohang Accelerator Laboratory, PAL, has been proposing a 0.1 nm SASE FEL. This machine will be designed with an S-band rf linear accelerator to produce a 10.053 GeV electron beam. The output power of klystron is 80 MW at the pulse width of 4 μs and the repetition rate of 30 Hz. The beam energy spread is 0.037%(rms), and rf phase stabiltity is 0.1 degrees(rms). The SASE FEL needs the modulator stability of 0.1%. We developed the modulator DeQing system to use the existing modulator systems that are “line type modulator system”. And we also are considering an inverter power supply to meet the required specification of the FEL machine. We are developing the phase amplitude detection system(PAD) and phase amplitude control(PAC) system to obtain the required rf stability. This paper describes the rf system for PAL XFEL(PxFEL).

• S.-H. Jeong, D.E. Kim, K.-H. Park
  PAL, Pohang, Kyungbuk
• B.-K. Kang
  POSTECH, Pohang, Kyungbuk

This paper presents the corrector magnet power supply for the PLS II. The required current for the magnet was ±30 A with the high stability of ~5ppm and It has high resolution about 1 ppm to accomplish a stable beam orbit correction. This power supply has been implemented by a digital signal processing technology. And it shows the high stability and other good output responses. Various experimental results such as stability, bandwidth and simulation are given in this paper.

• S. Thorin, N. Čutić, F. Lindau, S. Werin
  MAX-lab, Lund
• F. Curbis
  Uni HH, Hamburg

Existing thermionic RF-gun (tungsten-BaO) at the MAX-lab linac injector has been adapted for photocathode operation (with 10 ps laser pulses at 263 nm). Important parameters of this gun for free electron laser experiments, like emittance and charge, were measured giving 5.5 mmmrad and 200 pC. Here we report more detailed on that setup, including laser and electron optics.

• S. Werin, N. Čutić, F. Lindau, S. Thorin
  MAX-lab, Lund
• J. Bahrdt, K. Holldack
  BESSY GmbH, Berlin
• C. Erny
  Lund Laser Centre, Lund University, Lund

A facility for seeding and harmonic generation utilizing an optical klystron is under commissioning at MAX-lab. The facility utilizes the 400 MeV linac accelerator, improved operation of an RF-gun, an undulator system of two undulators and a magnetic chicane, combined laser system for gun and seeding. The goal is to seed the electron beam at 266 nm and generate the harmonics 2-5 (133-54 nm). Currently the system is under commissioning. We report on the operation of the sub-systems and the latest results on the commissioning towards achieving harmonic generation.

• R. Ganter, B. Beutner, S. Binder, H.-H. Braun, M. Broennimann, M. Dach, T. Garvey, C.H. Gough, C.P. Hauri, M. Heiniger, R. Ischebeck, S. Ivkovic, Y. Kim, E. Kirk, F. Le Pimpec, K.B. Li, R. Luescher, P. Ming, A. Oppelt, M. Paraliev, M. Pedrozzi, J.-Y. Raguin, L. Rivkin, T. Schietinger, T. Schilcher, B. Steffen, S. Tsujino, A.F. Wrulich
  PSI, Villigen

In the frame of the SwissFEL project, an electron gun based on diode acceleration followed by a two cell RF cavity is under test at PSI. The diode consists of a photocathode / anode assembly and is driven with a voltage pulse of 500 kV maximum in 200 ns FWHM . The metal photocathode is illuminated by a Nd:YLF laser operating at 262 nm wavelength with a pulselength of 10 to 35 ps (FWHM) producing electron bunches of up to 200 pC. The distance from cathode to anode can be varied from 0 to 30 millimeters with a typical cathode field of 50 MV/m during the commissioning phase. Electrons leave the diode through an anode aperture and enter a two cells RF Cavity (1.5 GHz), which accelerates the beam to a maximum energy of 5 MeV. Beam characteristic measurements are presented and compared with simulations.

• M. Pedrozzi, Y. Kim
  PSI, Villigen

The X-ray FEL project at PSI involves the development of an injector complex that enables operation of a SASE FEL at 0.1 nm with permanent-magnet undulator and minimum beam energy. In order to extensively study the generation, transport and time compression of high brightness beams and to support the component developments necessary for the XFEL project, PSI is presently constructing a 250 MeV injector test facility. In the low energy region enough space has been reserved to accommodate complex electron source configurations while at high energy a 16 m diagnostic line will be used for projected and slice parameter characterization. The first installed electron source will be a 2.5 cell S-band RF-Photo injector, previously developed at CERN within the CTF program, which should provide a projected emittance below 0.4 mm mrad at 200 pC. Four S-band travelling wave cavities will boost the energy up to 270 MeV and a fourth harmonic X-band cavity will be used to linearize the longitudinal phasespace distribution in front of the magnetic compression chicane. In this paper we describe the overall accelerator facility with its main components and we discuss the expected beam performances.

• B. Ketenoğlu, M. Tural, O. Yavas
  Ankara University, Faculty of Engineering, Tandogan, Ankara
• P. Arikan
  Gazi University, Faculty of Arts and Sciences, Teknikokullar, Ankara
• S.O. Ozkorucuklu
  SDU, Isparta
• O. Sahin, I. Tapan
  UU, Bursa

A SASE FEL facility was first proposed in Feasibility Report of the TAC (Turkish Accelerator Center) project in 2000. Conceptual Design Report (CDR) of the project was completed in 2005. Technical Design Report (TDR)studies of TAC were started in 2006 in frame of an inter universities project with support of State Planning Organization (SPO) of Turkey. Main goal of the SASE FEL proposal is to cover VUV and soft X-rays region of the spectrum besides IR-FEL, Bremsstrahlung and Synchrotron Radiation proposals of TAC. Up to now, optimization studies based on a special RF linac or an Energy Recovery Linac (ERL) for the SASE FEL facility were completed. Today, ERLs provide a powerful broad range of applications like: electron cooling devices, high average brightness, high power FELs, short-pulse radiation sources and high luminosity colliders. In this study, main parameters for two linac options and SASE FEL are given.

*On behalf of the TAC SASE FEL working group

• J.W. McKenzie, B.L. Militsyn
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire

Future FEL-based light sources require high brightness electron beams delivered in short bunches at high repetition rates. The design of a photoinjector able to operate at a repetition rate of 1 MHz and above is presented. Beam dynamic simulations are presented for bunch charges ranging from 100 pC up to 1 nC, optimised for low slice emittance and high peak current. This injector is a suitable candidate for the UK’s New Light Source project.

• S.L. Smith, C.D. Beard, R.K. Buckley, S.R. Buckley, P.A. Corlett, D.J. Dunning, P. Goudket, S.F. Hill, F. Jackson, S.P. Jamison, J.K. Jones, L.B. Jones, P.A. McIntosh, J.W. McKenzie, K.J. Middleman, B.L. Militsyn, A.J. Moss, B.D. Muratori, J.F. Orrett, P.J. Phillips, Y.M. Saveliev, D.J. Scott, B.J.A. Shepherd, N. Thompson, A.E. Wheelhouse, P.H. Williams
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• K. Harada
  KEK, Ibaraki
• D.J. Holder, P. Weightman
  The University of Liverpool, Liverpool
• M. Surman
  STFC/DL/SRD, Daresbury, Warrington, Cheshire

ALICE (Accelerators and Lasers In Combined Experiments), a 35 MeV energy recovery linac based light source, is being commissioned and developed as an experimental R&D facility for a wide range of projects that could employ synchronized ultra-short (<1ps) electron bunches and light pulses. A suit of light sources includes an IR FEL, Compton backscattering (CBS) X-ray source, high power THz source and a multi-TW femtosecond laser. The full energy recovery and coherently enhanced, due to shortness of the electron bunches, THz radiation have been already demonstrated on ALICE. Completion of the first phase of the CBS x-ray source experiment and first lasing of the IR FEL by the end of 2009. Status of ALICE experimental facility and latest results on FEL, THz, and CBS development are reported in this paper.

• P.H. Williams, D. Angal-Kalinin, S.L. Smith
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• R. Bartolini, I.P.S. Martin
  JAI, Oxford
• P.H. Williams
  Cockcroft Institute, Warrington, Cheshire

We describe a design for a two-pass recirculating 1.3 GHz superconducting linac as a driver for the suite of free-electron lasers proposed in the UK New Light Source project. The machine will deliver longitudinally compressed electron bunches with repetition rates of 1 kHz with an initial upgrade path to increase this to 1 MHz. A modular philosophy is employed to separate beam injection and extraction from a three stage compression scheme. Results show that the necessary high peak currents can be achieved whilst preserving beam quality.

• J.H. Han, H.C. Huang, S.A. Pande
  Diamond, Oxfordshire

The proposed New Light Source for the UK has the baseline specification of an FEL photon energy ranging up to 1 keV and a repetition rate of 1 kHz. In order to fulfil this specification, an injector with a normal conducting L-band photocathode gun and a superconducting L-band cavity module has been designed. To allow the implementation of a second stage injector with even higher repetition rate, a merging system with a dog leg is being considered. The beam parameter optimisation for several operation modes has been carried out using the ASTRA code. Technical issues of the RF design and thermal behaviour of the gun are also discussed.

• J.H. Han, J. Rowland
  Diamond, Oxfordshire
• K. Flöttmann, S. Schreiber
  DESY, Hamburg

Linac based Free Electron Lasers require very high quality and stable electron beams both for the lasing process, and for use of the FEL beams in experiments. Various kinds of jitter in the injector may sensitively affect the FEL operation. In this paper, we study the jitter sources in the FEL injector and simulate how much they impact on the beam dynamics. Then, we discuss the required jitter tolerances to maintain good machine performance. Measurements have been carried out at the FLASH Free Electron Laser at DESY and beam dynamics simulations are applied to the UK's New Light Source facility.

• A.H. Lumpkin, A.S. Johnson, J. Ruan, J.K. Santucci, Y.-E. Sun, R. Thurman-Keup
  Fermilab, Batavia
• P. Piot
  Northern Illinois University, DeKalb, Illinois

The A0 photoinjector (A0PI) facility at Fermilab has an ongoing proof-of-principle experiment to demonstrate the exchange of the transverse horizontal and longitudinal emittances[1]. This experiment relies on measurements of the transverse emittances and longitudinal emittance upstream and downstream of an emittance-exchanger beamline. At several locations along the accelerator beamline, YAG:Ce powder scintillator screens are used to determine beam size, divergence, and energy spread when used in an electron beam spectrometer. The screens have ~5-micron grain size and are deposited on a metal substrate as provided by DESY[2]. We have recently performed direct comparisons of beam image and slit image sizes using both the OTR screens and the YAG:Ce screens. For micropulse charges of 250 pC and with beam energies of 15 MeV, we systematically observed larger beam image sizes with the YAG:Ce screens than with the OTR screens. We deduced a YAG:Ce screen spatial resolution limit of σ=140 to 180 microns. Results at both the beam profile stations at different drift lengths from the slits and in the electron spectrometer will be reported as well as the needed corrections to the emittances.

[1] T.W. Koeth et al., Proceedings of PAC09, Vancouver, Canada.
[2] The YAG:Ce samples were manufactured at DESY and the associated specifications were provided by Klaus Floettmann, DESY.

• A.H. Lumpkin
  Fermilab, Batavia
• Y.L. Li, S.J. Pasky, N. Sereno
  ANL, Argonne

The observations of the strong enhancements of the optical transition radiation (OTR) signal observed after bunch compression of photocathode beams in the Advanced Photon Source (APS) linac chicane and at the Linac Coherent Light Source (LCLS) continue to be of interest. Spectral-dependence measurements of the coherent OTR (COTR) were done at APS initially at the 375-MeV station using a series of band pass filters inserted before the CCD camera, but recent tests with an Oriel spectrometer with ICCD readout have extended those studies. In this case we used a microchannel plate image intensifier with a GaAs photocathode to explore the NIR regime out to 880 nm. We report for the first time an ~40% intensity modulation of ~20-nm period throughout the observed broadband COTR spectra for some localized spatial structures. This effect was observed at full electron beam compression as determined from the CTR monitor located after the chicane, and it persisted with two different grating dispersions and for different spectrometer offsets. In addition, the observation of a ring-like COTR image structure in x-y space for a mismatched beam at 355 MeV will be presented and discussed.

• R.B. Fiorito, M. Cornacchia, A.G. Shkvarunets, J.C.T. Thangaraj
  UMD, College Park, Maryland
• S. Di Mitri, M. Veronese
  ELETTRA, Basovizza
• H. Loos, J. Wu
  SLAC, Menlo Park, California

Recent observations of coherent optical transition radiation (COTR) at LCLS and other laboratories have been recognized as a signature of theμbunching instability, which affects the longitudinal phase space of the electron beam and ultimately the performance of the Free Electron Laser. In addition, the COTR emission limits the utility of OTR screens as beam profiling diagnostics. In an effort to understand and predict the extent of COTR emission and to help specify required instrumentation for new FELs, we have developed codes at UMD and SLAC-LCLS that use the output from the ELEGANT particle tracking code to predict the emission of COTR at specific wavelengths or within a band width. The COTR codes provides plots of the intensity patterns in the transverse plane, simulating a virtual OTR screen. Both incoherent and coherent intensities are produced thus providing an estimate of theμbunching gain at the observed wavelengths. Since the ELEGANT simulation of microbunching strongly depends on the number of particles, efforts have been carried out to speed up the COTR code analysis. The results of these codes applied to the LCLS and FERMI@elettra linac FELs are presented.

• R.A. Bosch, K.J. Kleman
  UW-Madison/SRC, Madison, Wisconsin
• J. Wu
  SLAC, Menlo Park, California

In high-current magnetic bunch compression, shot-noise-induced energy and current fluctuations at the chicane entrance may cause microbunching. For the case where the energy fluctuations are the primary cause of microbunching, we perform approximate simulations with fewer particles than the bunch population by using a reduced value of the space-charge impedance upstream of the chicane. This method is applied to bunch-compressor designs for the Wisconsin Free Electron Laser (WiFEL).

• E.J. Montgomery, D.W. Feldman, P.G. O'Shea, P.Z. Pan, N. Sennett, C. Stortstrom
  UMD, College Park, Maryland
• K. L. Jensen
  NRL, Washington, DC

High performance FELs demand photocathodes with high quantum efficiencies (QE), kHr life, kA/cm² peak and A/cm² average current, and ps response. In harsh accelerator vacuum conditions, having delicate cesium-based coatings, efficient photocathodes face shortened life. The UMD dispenser photocathode extends lifetime by resupplying cesium from a subsurface reservoir through a porous substrate [1], and recesiation can rejuvenate cesiated cathodes (Cs:Ag) after contamination [2]. These studies have validated theory that can presently treat both coated metals and semiconductors [3, 4]. Other alkali metals (Na, K) may also be deposited singly or together for better QE (e.g., Cs2KSb and other high QE multi-alkalis). Towards that end and to refine theory, we here report fabrication and testing of K:Ag and Na:Ag complementing the previously cited Cs:Ag work. Models of coating-dependent QE analyze the K and Na data on metal (e.g., silver) polycrystalline surfaces. The status of an effort to incorporate these models into PIC beam simulation codes such as MICHELLE [5] shall also be indicated.

[1] Moody et al, APL 90,114108(2007)
[2] Montgomery et al, AIP Proc. 1086, 599(2009)
[3] Jensen et al, JAP104, 044907(2008)
[4] Jensen et al, JAP102, 074902(2007)
[5] Jensen et al, JVSTB26(2), 831(2008)

• J.J. Welch, H.-D. Nuhn, J.A. Sevilla
  SLAC, Menlo Park, California

Undulator magnets for the LCLS need to be maintained at a very stable and accurate temperature in order to stay within the tolerance required for the FEL. At the LCLS the temperature of the undulator magnets is mainly determined by the temperature of the surrounding air. Furthermore, the climate control system which controls the temperature of the air must never accidentally go out of a safe operating range of ± 2.5 C or the magnets may lose calibration and have to be removed and remeasured. This was one motivation for the sighting the Unduator Hall underground in a tunnel where the thermal inertia of the surrounding earth provides stability. In this paper we describe the technical solution adapted by the LCLS for controlling the air temperature in the Undulator Hall and its initial performance. We also discuss thermal issues of heat balance and steady state and transient temperature behavior of the undulators system and the surrounding earth.

• J.D. Jarvis, H.L. Andrews, C.A. Brau, B.K. Choi, J.L. Davidson, W.P. Kang, C.L. Stewart, Y.M. Wong
  Vanderbilt University, Nashville, TN

We present new results in the measured electron energy spectrum from diamond field emitters. The energy spectrum from a clean diamond surface has been measured and is comparable in shape and width to that of metal emitters. The results suggest that the emitted spectrum is sensitive to the presence of adsorbed species on the emitter surface. Electrons significantly below the cathode’s Fermi level are emitted by resonant tunneling. Furthermore, these resonant surface states can increase the total emitted current by more than an order of magnitude while maintaining a narrow spectral width (~0.5 eV). Experiments are also being performed with individual multiwall carbon nanotubes (MWCNTs). We have observed beams emitted from individual residual gas molecules that approach the quantum-degenerate limit of electron-beam brightness. This limit has profound consequences for the behavior of an electron. Tightly bound designer adsorbates may greatly enhance the emission properties and improve performance in electron injector systems.

• J.D. Jarvis, H.L. Andrews, C.A. Brau, B.K. Choi, J.L. Davidson, W.P. Kang, Y.M. Wong
  Vanderbilt University, Nashville, TN

Diamond field-emitter arrays (DFEAs) possess several advantages over photocathodes: high brightness, ruggedness, no drive laser requirement, and minimal heating. A gated DFEA with micron-scale cathode-gate spacing has the added benefits of direct e-beam modulation and low operating voltages < 100 V. A second gate can be integrated, creating built-in focusing capability. We have developed two types of self-aligning gate fabrication methods. First, pyramidal molds are formed on a SOI (silicon on insulator) substrate then coated with CVD nanodiamond. The bulk layer of silicon is thinned, followed by oxide etching and opening the diamond tip isolating the gate electrode and insulating layer from the cathode. The second method uses additive physical evaporation depositions of insulating and gate electrode layers on top of the DFEAs. Chemical etching of the insulating layer separates and opens cathode tip due to ‘lift off’ type step coverage of the evaporation technique. A 2-mask fabrication process has been used to pattern the gate to optimize active gate area and increase yield. Fabrication techniques and electrical behavior of the gated DFEAs will be discussed.

• J.D. Jarvis, H.L. Andrews, C.A. Brau, B.K. Choi, J.L. Davidson, B.L. Ivanov, W.P. Kang, C.L. Stewart, Y.M. Wong
  Vanderbilt University, Nashville, TN

We present recent advances in the uniformity conditioning of diamond field-emitter arrays (DFEAs), and new results from emittance measurements of their emitted electron beams. DFEAs have shown considerable promise as potential cathodes for free-electron lasers. They have demonstrated their rugged nature by providing high per-tip currents, excellent temporal stability, and significant resistance to back-bombardment damage during poor vacuum, close-diode DC operation. Until now, the successful conditioning of high-density arrays has been precluded by thermal damage to the anode. We report successful uniformity conditioning of densely packed DFEAs using microsecond-pulsed high-current conditioning (HCC). A high degree of spatial uniformity was confirmed in low-current DC testing following these HCC procedures. The conditioned arrays will be used to refine previous measurements of the normalized transverse emittance of the emitted electron beams.

• F.E. Hannon, S.V. Benson, G.H. Biallas, D.B. Bullard, F.K. Ellingsworth, P. Evtushenko, C. Hernandez-Garcia, K. Jordan, M. Marchlik
  JLAB, Newport News, Virginia

A new 500kV DC photocathode electron gun is being developed at Jefferson Laboratory (JLab) with the aim of improving on the performance of the present FEL injector. The design benefits from the use of two inverted ceramic insulators to allow for a photocathode preparation chamber and load-lock system to be placed directly behind the gun. The electrostatic design emphasises the requirement to minimise the electric field gradients on the internal surfaces and incorporates shaped electrodes to provide some transverse focusing to the electron beam. Finally, provisions have been made to maintain ultra high vacuum conditions inside the gun chamber to prolong cathode lifetime during CW operation. This paper presents an overview of the electron gun and load-lock design.

• J.T. Donohue
  CENBG, Gradignan
• L. Courtois, J. Gardelle, P. Modin
  CESTA, Le Barp

A few years ago, a new theory for producing coherent Smith-Purcell (SP) radiation from an initially continuous electron beam was proposed. It was two-dimensional (2-D), and it has been supported by 2-D particle-in-code simulations. We report here the results of an experiment using an intense continuous flat beam that confirms the theory. A maximum voltage of 200 kV was supplied by a single-shot pulsed-power source. The beam was typically 10 cm wide and a few mm thick, with a peak current of 200 A. The laminar grating had twenty 2-cm periods, and radiation was observed at the predicted fundamental grating mode frequency near 4 GHz. The second and third harmonics were also observed at the angles predicted by the SP formula. Direct evidence for beam bunching was obtained using both a current monitor and a pick-up loop placed at the end of a groove. In general, good agreement between this experiment and theory is found.

• T. Kii, M. A. Bakr, K. Higashimura, R. Kinjo, K. Masuda, H. Ohgaki, T. Sonobe, S. Ueda, K. Yoshida
  Kyoto IAE, Kyoto
• H. Zen
  UVSOR, Okazaki

We proposed a table-top seeded THz FEL amplifier using a multi-bunch photocathode RF gun and injection-seeded terahertz parametric generator (IS-TPG) [1]. Although the first numerical study was carried out under simplified condition [2], a slippage effect, which has prominent effect to long wavelength FEL was not taken into account. In order to discuss feasibility and expected THz output power, start-to-end simulation of FEL was performed by simulation code Parmela [3] and 3D time-dependent FET simulation code GENESIS 1.3 [4]. The peak output power of about 10 kW at 185μm was expected from the design scheme.

[1] K. Kawase, et al., Applied Physic Letters 80(2002),p195
[2] T. Kii, et al., Proc. of FEL2008, in press.
[3] L.M. Young, et al., PARMELA, LA-UR-96-1835,(2001)
[4] S. Reiche, NIM A429(1999) p242.

• H. Hama, M. Yasuda
  Tohoku University, School of Scinece, Sendai

To evaluate fundamental characteristics of conventional FELs with oscillator configuration, we assume an electron pulse sufficiently longer than the FEL wavelength in general (long pulse approximation). In the process of microbunching, the optical pulse gains the power exponentially. Taking finite bunch length into account, head of the optical pulse does not grow than tail due to slippage. Consequently if there is no detuning for an optical cavity, the electrons are no longer able to be microbunched because of no power growth at head of the optical pulse, which is well known as lethargy effect. Meanwhile recent progress of the linac technology enables us to have high brilliant beam in 6-dimensional phase space, accordingly the electron bunch length reaches much shorter than the wavelength of THz radiation. We have studied THz FEL employing such pre-bunched beam by applying 1-D FEL equations*. Since bunching factor of the electrons is already close to unity, non-linear power amplification is expected to occur. Bunching factor is resulted from long pulse approximation basically, so that we have to discuss the pre-bunched FEL carefully. The paper will describe consideration on it.

*M. Yasuda et al., " DEVELOPMENT OF THz LIGHT SOURCE USING PRE-BUNCHED FEL", Proc. 30th Int. FEL Conf., Gyeongju, Korea (2008).

• D. Li, K. Imasaki
  ILT, Suita, Osaka
• M.R. Asakawa
  Kansai University, Osaka

The interest on the terahertz radiation sources keeps growing in recent years because this frequency provides widely applications in medical, industrial and material science The Cherenkov free-electron lasers have an advantage over the usual undulator free-electron lasers, and they can generate terahertz radiation with low energy electron beam. We plan to construct a compact terahertz Cherenkov free-electron laser with moderate (~10 mW) average power. To achieve this goal, a compact electron beam source is in developing, and a double-slab Cherenkov free-electron laser resonator is studied. To perform a preliminary lasing experiment, this resonator is designed to generate the millimeter wave. In this paper, we aim at the analysis of the gain for the double-slab Cherenkov device. The dispersion equation is derived and solved numerically, as well as the single-pass gain is worked out for the parameters of our experiment.

• R. Kuroda, M. Koike, K. Yamada
  AIST, Tsukuba, Ibaraki

A compact THz-FEL has been developed based on a laser photocathode rf gun system at AIST. The rf gun has been improved using a Cs2Te photocathode with a compact load-lock system. The multi-bunch electron generation has been performed with the rf gun and the multi-pulse UV laser system. The undulator has been designed to generate THz-FEL. The preliminary experiment of THz applications has been carried out using a coherent synchrotron radiation in the THz region with 40 MeV electron beam. In this conference, we will report a present status and results of the experiment.

• D. Wang, J. Chen, H.X. Deng, C. Feng, J. Yan
  SINAP, Shanghai

The Shanghai Deep UV FEL is a new FEL facility working at Deep UV wavelength. Based on a newly upgraded 160 MeV linac with a photo-injectors, the SDUV is capable of providing intense FEL beam at 262nm with 9 meters of undulators. Both SASE and HGHG modes are going to be tested. This paper shows the s3e simulation studies of typical working modes of the SDUV.

• D. Wang, J. Chen, H.X. Deng, Q. Gu, D.G. Li, M. Zhang, Z.T. Zhao
  SINAP, Shanghai

The Shanghai Deep UV(SDUV) FEL is expected to start its first experiments this summer. This paper will report the latest progress on beam commissioning and hopefully the early results of FEL experiments.

• H.-S. Kang, Y.-G. Jung, C. Kim, H.-G. Kim, K.R. Kim, W.W. Lee, B.R. Park, J. Park, Y.J. Park, Y.G. Son, H.S. Suh, I.H. Yu
  PAL, Pohang, Kyungbuk
• D.E. Kim, C.M. Yim
  POSTECH, Pohang, Kyungbuk

A femto-second THz radiation (fs-THz) facility is under commissioning at the Pohang Accelerator Laboratory (PAL), which uses a 60-MeV electron linac that consists of an S-band photocathode RF gun with 1.6 cell cavity, two S-band accelerating structures, and two chicane-type bunch compressors. The linac is designed to generate THz pulse with energy up to 10 μJ by transition radiation from a metal target hit by sub-picosecond electron beam. The linac takes advantage of the advanced technologies such as an inverter-type klystron modulator with stability below 100 ppm and a high precision synchronization timing system with a laser oscillator. The THz radiation energy measured with a Golay cell is 0.5 μJ/pulse from the electron beam with charge of 0.1 nC. We will present the properties of THz radiation as well as the electron beam parameters.

• N.Yu. Peskov, N.S. Ginzburg, S.V. Kuzikov, A. Sergeev
  IAP/RAS, Nizhny Novgorod
• A.K. Kaminsky, E.A. Perelstein, S.N. Sedykh
  JINR, Dubna, Moscow Region

The JINR-IAP FEM-oscillator was elaborated during the last few years based on 0.8 MeV / 200 A / 250 ns linac LIU-3000 (Dubna). This 30-GHz FEM generates currently 20 MW / 200 ns pulses with spectrum width of ~6 MHz and repetition rate of up to 1 Hz. The high efficiency and stability of the FEM was achieved by using reversed guide magnetic field regime and advanced type of Bragg resonator, i.e. resonator with a step of phase of corrugation. The parameters achieved allow the FEM to be used in several applications. Test facility to study the life time of the metals in strong RF-fields was constructed based on the FEM. This information would be beneficial, in particular, when designing high-gradient accelerating structures for future linear colliders. Degradation of the copper surface was studied at different temperature rise during each pulse (from 50° to 250° C) in consequence of up to ~100 000 pulses. Investigation of possibility to use JINR-IAP FEM in medical and biological applications was also started. The effect of the powerful 30-GHz pulses on the biological tissue including the cancer cells was studied. Project to advance JINR-IAP FEM into sub-mm wavelengths is developed.

• A.V. Savilov, I.V. Bandurkin, V.L. Bratman, N.Yu. Peskov
  IAP/RAS, Nizhny Novgorod
• A.K. Kaminsky, S.N. Sedykh
  JINR, Dubna, Moscow Region

Various schemes of THz electron masers operating in the regime of frequency multiplication are discussed. The use of this approach makes possible the realization of high-harmonic cyclotron masers operating at low (tens kV) accelerating voltages in long-pulse and CW regimes with the relatively low (1W-1kW) output power. Our first modeling experiment has demonstrated co-generation of second and fourth cyclotron harmonics in a simple microwave system. As for realization of pulsed high-power THz masers, it is attractive to use the regime of frequency multiplication in moderately-relativistic (hundreds kV) high-current FEMs and Smith-Purcell autooscillators. In our experiment based on a 0.8MeV/200A e-beam, a two-wave FEM was realized. In this experiment, the low-frequency (30GHz) wave was excited in the ubitron regime, and a feedback system partially reflected this wave back to the operating cavity. This backward low-frequency wave was scattered on the electrons into the forward high-frequency (360GHz) wave. The use of the regime of frequency multiplication provided the stimulated character of this process, and, therefore, a quite high power (~100kW) of the high-frequency wave.

• V.Yu. Zaslavsky, N.S. Ginzburg, A. Malkin, N.Yu. Peskov, A. Sergeev
  IAP/RAS, Nizhny Novgorod
• K.K. Kamada, Y. Soga
  Kanazawa University, Kanazawa

Periodical Bragg structures may be considered as an effective way of controlling the electromagnetic energy fluxes and provision of spatially coherent radiation in the free electron lasers with oversized interaction space. A new scheme of terahertz band FEL with hybrid Bragg resonator consisting of advanced input Bragg mirror and traditional output Bragg mirror is proposed. Advanced Bragg mirror exploits coupling between two counter-propagating waves and the quasi cutoff wave and provides mode selection over the transverse index. Main amplification of the synchronous wave by the electron beam takes place in the regular section of the resonator. Small reflections from the output traditional Bragg mirror are sufficient for the oscillator self-excitation. Results of simulation of nonlinear dynamics of the FEL with a hybrid Bragg resonator is presented and demonstrate its operability in the terahertz frequency band with high (megawatt level) radiation power. In difference with the existing terahertz band FELs [1-2], the above scheme would be driven by a long pulse (microsecond) electron beam from Induction linear accelerators or Electrostatic accelerators.

[1] V.P. Bolotin, et al., Nucl. Instr. & Meth. Phys. Res. A, 2005, v.543, p.81.
[2] Y.U. Jeong, et al., Nucl. Instr. & Meth. Phys. Res. A, 2004, v.528, p.88.

• V. Volkov, S.A. Krutikhin, G.Y. Kurkin, S.V. Miginsky, V.M. Petrov, M.A. Tiunov, N. Vinokurov
  BINP SB RAS, Novosibirsk

The projected electron RF gun of 10 MeV L-band injector for FEL employs a commercial thermionic cathode-grid assembly with 0.08 mm gap that conventionally used in metal-ceramic RF tubes. Three-dimensional (3D) computer simulations have been performed that use the mesh refinement capability of the both Microwave Studio (MWS) and 2D SAM codes to examine the whole region of the real cathode-grid assembly in static fields in order to illustrate the beam quality that can result from such a gridded structure. These simulations have been found to reproduce the beam current dependency on applied potentials that are observed experimentally. Based on it ASTRA RF beam simulations also predict a complicated time-dependent response to the waveform applied to the grid during the current turn-on, calculation of the dissipated power by electrons at the grid, and particle tracking downstream of the grid into RF gun cavity and further on. These simulations may be representative in other sources, such as BINP Microtron-Recuperator 180 MHz injector and other RF injectors for industrial and scientific applications.

• T. Denis, K.-J. Boller, P.J.M. van der Slot
  Mesa+, Enschede

The photonic free-electron laser (pFEL) aims to realize a compact TeraHertz source that emits Watt-level and tuneable radiation. For this purpose it uses a photonic structure, which coherently couples the Cerenkov radiation from a set of individual electron beams streaming through this structure. The resulting transverse coherence of the radiation allows a power scaling of the device by extending its cross-section and the number of electron beams. To study the fundamental physics of such devices, and to compare single beam with multi-beam performance, we first designed a single electron beam pFEL operating at a low frequency of around 22 GHz. Choosing such low operating frequency facilitates pumping of the pFEL by a single electron beam. This electron beam possesses a relatively high current of 2 A and its acceleration voltage is tuneable between 7 kV and 15 kV. It is guided by a solenoid through a metal photonic structure of 30 cm length. The general design of the single beam pFEL will be presented.

• R.T. Jongma, A.C.N. Engels, R.W. Lof, F.J.P. Wijnen, G.F.A.J. Wulterkens, V. Zhaunerchyk, P.A.W. van Dael, A.J.A. van Roij, A.P. van Vliet, W.J. van der Zande
  Radboud University, Nijmegen
• K. Dunkel, C. Piel
  RI Research Instruments GmbH, Bergisch Gladbach
• U. Lehnert, P. Michel, W. Seidel, R. Wünsch
  FZD, Dresden
• A.F.G. van der Meer
  FOM Rijnhuizen, Nieuwegein

The Radboud University in Nijmegen received funding to realize a narrow-band THz laser system and a 45 T hybrid magnet system. Based on results of predesign studies [1], all review committees agreed to continue the project and enter the realization phase. In this paper we present the technical solutions for realization of the main system components. We present the details of the RI Research Instruments GmbH (a former ACCEL Instruments GmbH activity) LINAC system. Operation of the full system (including the electron source) at 3 GHz is desirable and deemed feasible after first experimental studies. As the Nijmegen FEL will operate at wavelength up to 1.5 mm, the cavity will be fully waveguided, complicating the incorporation of an intra-cavity Fox-Smith interferometer required to induce coherence between micropulses and a Michelson interferometer as most ideal outcoupler. The optical distribution system comprises 150 m of vacuum tubing with 25 cm effective diameter (planar and refocusing) mirrors. A robust yet cost efficient realization taking boundary conditions on optical beam parameters at diagnostics station and user stations into account is foreseen.

[1] Design of the Nijmegen high-resolution THz-FEL, R.T. Jongma_, et al. Proc. FEL-08.

• V. Zhaunerchyk, R.T. Jongma, W.J. van der Zande
  Radboud University, Nijmegen

The THz region of the spectrum does not know versatile powerful light sources. FEL technology clearly is well suited for the generation of THz radiation. The Nijmegen THz-FEL oscillator is scheduled to be in operation early 2011 and will produce THz light in the 0.1 mm (3 THz)- 1.5 mm (0.2 THz) spectral range. Electron bunches will be generated by an RF LINAC at a rate of 3 GHz such that 150 optical pulses will propagate simultaneously through a 7.5 m long optical cavity. A relatively short length of the electron bunches and the high Q-factor of the RF LINAC will give rise to strong coherent spontaneous emission. Allμpulses will tend to be coherent. Our aim is to induce full inter-pulse coherence by means of an intra-cavity Fox-Smith interferometer. The present study is devoted to the investigation into competition between spontaneous and induced inter-pulse coherence which is foreseen to be relevant for the most ambitious aim of the Nijmegen FEL project: generation of single mode THz radiation with pulse lengths of 7 microseconds, based on a RF type electron accelerator.

• H.L. Andrews, C.A. Brau, J.D. Jarvis
  Vanderbilt University, Nashville, TN
• R. Durant, C.F. Guertin, T.H. Lowell, M.R. Mross, A. O'Donnell
  Vermont Photonics, Bellows Falls

We present further experimental observations of evanescent waves in a Smith-Purcell free-electron laser (FEL) with vertical conducting walls bounding the sides of the grating.  Evanescent waves are the basis of oscillator operation of the Smith-Purcell FEL. They have group veloctiy anti-parallel to the electron beam and for sufficiently high current, provide feedback to bunch the electron beam. A grating with side walls supports multiple transverse modes; we have observed emission from the two lowest such modes. The observed wavelengths and wavelength shift with changing operating voltage agree with theoretical predictions. Additionally, strong radiation from the upstream end of the grating confirms the negative group velocity.