Session: THPOS - 02 Sep 2004
FEL Oscillators, FEL Experiments, New Concepts and Ideas, Users Workshop

THPOS01 Low Emittance Gun Project based on Field Emission
Romain Ganter, Arno Candel, Micha Dehler, Jens Gobrecht, Chris Gough, Gerhard Ingold, Simon C. Leemann, Kevin Shing Bruce Li, Martin Paraliev, Marco Pedrozzi, Jean-Yves Raguin, Leonid Rivkin, Volker Schlott, Harald Sehr, Andreas Streun, Albin Wrulich, Sasa Zelenika (PSI, Villigen)

The design of an electron gun capable of producing beam emittance one order of magnitude lower than current technology would reduce considerably the cost and size of a free electron laser emitting at 0.1nm. Field emitter arrays (FEAs) including a gate and a focusing layer are an attractive technology for such high brightness sources. Electrons are extracted from micrometric tips thanks to voltage pulses between gate and tips. The focusing layer should then reduce the initial divergence of each emitted beamlets. This FEA will be inserted in a high gradient diode configuration coupled with a radiofrequency structure. In the diode part very high electric field pulses (several hundreds of MV/m) will limit the degradation of emittance due to space charge effect. This first acceleration will be obtained with high voltage pulses (typically a megavolt in a few hundred of nanoseconds) synchronized with the low voltage pulses applied to the FEA (typically one hundred of volts in one nanosecond at frequency below kilohertz). This diode part will then be followed by an RF accelerating structure in order to bring the electrons to relativistic energies.

THPOS02 Field Emitter Arrays for a Free Electron Laser Application
Kevin Shing Bruce Li, Micha Dehler, Romain Ganter, Jens Gobrecht, Jean-Yves Raguin, Leonid Rivkin, Albin Wrulich (PSI, Villigen)

The development of a new electron gun with the lowest possible emittance would help reducing the total length and cost of a free electron laser. Field emitter arrays (FEAs) are an attractive technology for electron sources of ultra high brightness. Indeed, several thousands of microscopic tips can be deposited on a 1 mm diameter area. Electrons are then extracted by applying voltage to a first grid layer close to the tip apexes, the so called gate layer, and focused by a second grid layer one micrometer above the tips. The typical aperture diameter of the gate and the focusing layer is in the range of one micrometer. One challenge for such cathodes is to produce peak currents in the ampere range since the usual applications of FEAs require less than milliampere. Encouraging peak current performances have been obtained by applying voltage pulses at low frequency between gate and tips. In this paper we report on different tip materials available on the market: diamond FEAs from Extreme Devices Inc., ZrC single tips from Applied Physics Technologies Inc. and Mo FEAs from SRI International.

THPOS03 Undulators for the BESSY Soft-X-Ray FEL
Johannes Bahrdt, Winfried Frentrup, Andreas Gaupp, Bettina Kuske, Atoosa Meseck, Michael Scheer (BESSY GmbH, Berlin)

BESSY plans a linac based high gain harmonic generation FEL user facility with three FEL lines [1]. The modulators and most of the radiators are planar pure permanent magnet undulators. The last radiator and the final amplifier produce radiation of linear polarization with arbitrary orientation as well as elliptically or helically polarized light. They will have a modified APPLE II design which provides higher fields compared to a conventional APPLE II [2]. Detailed calculations for this design will be presented. FEL 3D-calculations provide information about the radiation field distribution at the end of the undulator. A beamline designer needs the information about the effective source size at the waist and the location of the waist. The electric fields calculated by GENESIS have been propagated and the source characteristics have been derived for various FEL parameters. The FEL process requires tight gap tolerances within and between modules. We present a new gap measurement system with a gap positioning accuracy of 1.5 microns.

THPOS04 Characterization of Laser-Electron Interaction at the BESSY Femtoslicing Facility
Shaukat Khan, Karsten Holldack, Torsten Kachel, Rolf Mitzner, Torsten Quast, Friedmar Senf (BESSY GmbH, Berlin)

A "femtoslicing" facility to generate ultrashort x-ray pulses by laser-electron interaction [1] is being commissioned at the BESSY II storage ring. The energy modulation of electrons by femtosecond laser pulses of several mJ in an undulator is a good test case for FEL seeding schemes. The dependence of the interaction efficiency on various parameters is measured and compared to simulations and analytical results.

THPOS05 Exploring the Spatial Resolution of the Photothermal Beam Deflection Technique in the Infrared Region
Wolfgang Seidel, Harald Foerstendorf (FZR, Dresden), François Glotin, Jean Michel Ortega, Rui Prazeres (LURE, Orsay)

In photothermal beam deflection spectroscopy (PTBD) generating and detection of thermal waves occur generally in the sub-millimeter length scale. Therefore, PTBD provides spatial information about the surface of the sample and permits imaging and/or microspectrometry. Recent results of PTBD experiments are presented with a high spatial resolution which is near the diffraction limit of the infrared pump beam (CLIO-FEL). We investigated germanium substrates showing restricted O+-doped regions with an infrared absorption line at a wavelength around 11.6 microns. The spatial resolution was obtained by strongly focusing the probe beam (i.e. a HeNe laser) on a sufficiently small spot. The strong divergence makes it necessary to refocus the probe beam in front of the position detector. The influence of the focusing elements on spatial resolution and signal-to-noise ratio is discussed. In future studies we expect an enhanced spatial resolution due to an extreme focusing of the probe beam leading to a highly sensitive technique for detection of sorbed species on surfaces in the far infrared region.

THPOS06 Measurement and Calculation of the 'Electron Efficiency' on the ‘CLIO’ Free-Electron Laser
Rui Prazeres, François Glotin, Jean Michel Ortega (LURE, Orsay)

This paper describe recent measurements which have been performed with the CLIO FEL in the wavelength range 40 to 120µm. The FEL electron efficiency, η, is deduced from the electron energy loss. It gives an absolute measurement of the optical power produced by the electron beam, which is then compared to the extracted power of the FEL measured optically. The ratio is compared to numerical simulation taking into account the diffraction of the optical mode in the optical cavity and in the beam line.

THPOS08 Experiments on the Synchronization of an Ultrafast Cr:LiSAF Laser with the ELETTRA Storage Ring and FEL Pulses
Mario Ferianis, Miltcho B. Danailov, Giovanni De Ninno, Bruno Diviacco, Mauro Trovò (Elettra, Basovizza, Trieste), Marcello Coreno (CNR-IMIP, Basovizza (TS)), Gamal Elsayed Afifi (NILES, Cairo)

The techniques for synchronizing ultrafast lasers to external radio frequency reference sources are well established and characterized in the literature. However, data lack on the minimum light-to-light jitter which can be achieved in different synchrotron operation modes when an external laser is locked to the storage ring master clock. Here we present first results for the synchronization of an ultrafast Cr:LiSAF laser with electromagnetic radiation coming from the Elettra storage ring in four bunch and multi-bunch mode. In addition, data on the synchronization of the same laser with the Elettra FEL pulses, both in free running and Q-switching regime, are reported. In our experiments, laser-to-RF locking was continuously monitored using a built-in phase detection. The laser light to storage ring light locking was characterized by simultaneous acquisition of two/three pulse trains by a streak camera. In addition, pulse jitter was determined by processing of the signal of fast photodiodes monitoring the different light beams.

THPOS09 Electron-Beam Stabilization for the European Storage-Ring Free-Electron Laser at Elettra
Mauro Trovò, Daniele Bulfone, Miltcho B. Danailov, Giovanni De Ninno, Bruno Diviacco, Vincenzo Forchi`, Marco Lonza (Elettra, Basovizza, Trieste), Luca Giannessi (ENEA C.R. Frascati, Frascati - Roma)

The temporal structure of the storage-ring free-electron laser at Elettra shows high sensitivity to electron-beam instabilities. In fact, even small beam orbit oscillations (of the order of few microns) may perturb the FEL dynamics and periodically switch off the laser. In order to improve the FEL operation and performance, a longitudinal multi-bunch feedback and a local orbit feedback have been activated. This paper reports on the beneficial effect of these feedback systems. Plans for a future "slow" longitudinal feedback are also briefly described.

THPOS13 Proposal of Laser-Driven Acceleration with Bessel Beam
Dazhi Li, Kazo Imasaki (ILT, 2-6 Yamada-oka, Suita, Osaka)

A possible approach of realizing multi-stage laser-driven acceleration with Bessel beam is explored. With using a set of annular slits, Bessel beam is truncated and structured into several separate sections during its transportation, leading to the possibility of accelerating electrons stage by stage. Bessel beam is regarded as diffraction-free beam, allowing a very long acceleration distance in contrast to the Gaussian beam. In this paper, the transportation characteristics of the structured Bessel beam is analyzed based on scalar diffraction theory, as well as the acceleration mechanism is demonstrated numerically.

THPOS14 Laser Compton Scattering Gamma Ray Induced Photo-Trasmutation
Dazhi Li, Kazo Imasaki (ILT, 2-6 Yamada-oka, Suita, Osaka), S. Amano, S. Miyamoyo, T. Mochizuki (LASTI, Hyogo)

High brightness beams of gamma rays produced with laser Compton scattering have the potential to realize photo-transmutation through (γ,n) reaction, implying an efficient method to dispose long-lived fission products. Preliminary investigations have been carried out in understanding the feasibility of development of a transmutation facility to repose nuclear waste. A laser Compton scattering experimental setup based on a storage ring started to generate gamma-ray beams for studying the coupling of gamma photons and nuclear giant resonance. This paper demonstrates the dependency of nuclear transmutation efficiency on target dimensions and gamma ray features. 197Au sample was adopted in our experiment, and experimental results correspond to the theoretical estimations.

THPOS15 Tunability and Power Characteristics of the LEBRA Infrared FEL
Toshinari Tanaka, Ken Hayakawa, Yasushi Hayakawa, Akira Mori, Kyoko Nogami, Isamu Sato, Kazue Yokoyama (LEBRA, Funabashi), Ken-ichiro Ishiwata, Koichi Kanno, Keisuke Nakao, Takeshi Sakai (Graduate School of Science and Technology, Funabashi)

Application of the infrared (IR) Free-Electron Laser (FEL) was started in October 2003 at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University. The FEL system consisted of silver-coated copper mirrors has demonstrated wavelength tunability ranged from 940 to 6100 nm as a function of the electron energy and the undulator K-value. Wavelength dependence of the FEL output power has been measured in term of different electron beam currents, electron energies and the undulator K-values. Approximate 25 mJ/macropulse has been obtained in the range 2 to 3 microns, which corresponds to peak power of 2 MW, provided that the FEL pulse length is 0.4 ps as resulted from the measurement by an interferometric method. The power decrease observed in the longer wavelength range is due to a large diffraction loss in the FEL guiding optics and the vacuum ducts.

THPOS16 Amplification of Short-Pulse Radiation from the Electron Undergoing Half-Cyclotron Rotation
Makoto R. Asakawa, H. Marusaki (OU-iFEL, Hirakata, Osaka), Kazo Imasaki (ILT, 2-6 Yamada-oka, Suita, Osaka), Nobuhisa Ohigashi (Kansai University, Osaka), Yoshiaki Tsunawaki (Osaka Sangyo University, Osaka)

Electrons undergoing half-cyclotron rotation emitts a half-cycle electromagnetic wave. A novel light source based on such short-pulse radiation is under developing at Institute of Free Electron Laser Osaka university. In this presentation, the experiments to amplify the radiation in the optical resonator will be discussed.

THPOS17 Status of Institute of Free Electron Laser, Osaka university
Hiroshi Horiike, Makoto R. Asakawa, Kunio Awazu, Manabu Heya, H. Kondo, Y. Naito, Sachiko Suzuki, N. Tsubouchi (OU-iFEL, Hirakata, Osaka)

Research activities at iFEL Osaka, including development of FEL systems and application programs, will be reviewed.

THPOS18 Development of a Pump-Probe System using a Non-Coated ZnSe Beam Splitter Cube for an MIR-FEL
Manabu Heya, Kunio Awazu, Hiroshi Horiike, Katsonuri Ishii, Sachiko Suzuki (OU-iFEL, Hirakata, Osaka)

A pump-probe technique is essential for a proper understanding of laser interaction with tissue and material. Our pump-probe system divides the incident mid-infrared Free Electron Laser (MIR-FEL) into two beams with equal intensity, and crosses simultaneously the two incoming beams at the same position. One is for a pump beam, another is for a probe beam. Time-resolved absorption spectroscopy involving this technique gives us information on the vibrational dynamics of molecules. We have developed this system for an MIR-FEL using a non-coating ZnSe beam splitter cube. The beam splitter cube is composed of two ZnSe prisms in the shape like a trapezoid. The two pulses with equal intensity are generated due to Fresnel reflection and transmission at the boundary between two prisms, then are reflected due to total reflection at other side boundaries between each prism and air, and illuminate simultaneously the same spot. We have conducted a proof-of-concept of experiment of this system using an MIR-FEL. We showed that this system is applicable for a broad waveband (6-11 μm). Thus, we proved that this system without complicated optical alignment is useful for absorption spectroscopy.

THPOS19 Medical Application of Free Electron Laser Trasmittance using Hollow Optical Fiber
Sachiko Suzuki, Kunio Awazu, Katsonuri Ishii (OU-iFEL, Hirakata, Osaka)

Mid-infrared Free Electron Laser (FEL) is expected as new application for biomedical surgery. However, delivery of MIR-FEL into the body is difficult because the common glass optical fibers have strong absorption at MIR region. A good operational and flexible line for FEL is required at medical field. A Hollow optical fiber is developed for IR laser and high-power laser delivery. We evaluated the fiber for FEL transmission line. This fiber is coated with cyclic olefin polymer (COP) and silver thin film on the inside of glass capillary tube. It is 700 μm-bore and 1m in lengths. The fiber transmission loss of the measured wavelength region of 5.5 μm to 12 μm is less than 1dB/m when the fiber is straight and 1.2 dB/m when bent to radius of 20 cm. Additionally, the output beam profile and the pulse structure is not so different form incidence beam. In conclusion, the fiber is suitable for delivery of the FEL energy for applications in medical and laser surgery.

THPOS21 Recent Results of the JAERI Energy-Recovery Linac FEL
Ryoichi Hajima, Hokuto Iijima, Nobuhiro Kikuzawa, Eisuke John Minehara, Ryoji Nagai, Nobuyuki Nishimori, Tomohiro Nishitani, Masaru Sawamura (JAERI/FEL, Ibaraki-ken)

A research program towards a high-power FEL utilizing an energy-recovery linac is carried forward at Japan Atomic Energy Research Institute (JAERI). In this paper, we summarize recent results of the research activity at the JAERI ERL-FEL, which include the reinforcement of the injector, replacement of the RF control system and so on.

THPOS22 Misalingment Tolerance of a Hole-Coupling Optical Resonator for JAERI ERL-FEL
Ryoji Nagai, Ryoichi Hajima, Nobuhiro Kikuzawa, Eisuke John Minehara, Nobuyuki Nishimori, Masaru Sawamura (JAERI/FEL, Ibaraki-ken)

The misalignment tolerance of a hole-coupling optical resonator for the JAERI ERL-FEL is estimated with a wavelength of 22 μm by a Fox-Li procedure simulation code. The output power stability depends on the misalignment tolerance. It is found that the misalignment tolerance of the hole-coupling mirror is less than the non-coupling mirror and the offset of the non-coupling mirror is compensable tilting the mirror.

THPOS23 JAERI 200 kV Electron Gun with an NEA-GaAs Photocathode
Tomohiro Nishitani, Ryoichi Hajima, Nobuhiro Kikuzawa, Eisuke John Minehara, Ryoji Nagai, Nobuyuki Nishimori, Masaru Sawamura, T. Yamauchi (JAERI/FEL, Ibaraki-ken)

The GaAs photocathode with negative electron affinity surface (NEA-GaAs) has been expected to be low emittance (<0.5 πmm・mrad) electron beam source. In order to generate low emittance electron beam required from ERL-FEL, we have started the developmental program of a 200keV electron gun with the NEA-GaAs photocathode for the first time in JAERI. An NEA surface has the problem that lifetime is limited by gun vacuum condition and by ion back bombardment between anode- and cathode-electrode. In order to long an NEA surface lifetime, the JAERI 200keV electron gun system consists of a 200kV DC-gun chamber on extreme high vacuum condition and an NEA activation chamber with load-lock system.

THPOS25 Modification of Hydroxyapatite Crystal Using IR Laser
Saburoh Satoh, A. Danjyo, M. Goto, W. Guan, N. Hayashi, S. Ihara, C. Yamabe, Y. Yamaguchi (Saga University, Saga)

The first application of laser technology to dentistry was for the removal of caries. However, reports of laser application on improvement of dental surface were emerged, much attention has been focused on the laser’s potential to enhance enamel’s hardness and resistance to acid. Most of the previous reports concentrated on the photo issue interaction. Few research has pursued the photochemical phenomenon occurred during laser irradiation on biological tissues. In order to find a creative method to remineralize the dissociating enamel and exposed coronal of dentine, the authors developed a novel procedure during laser irradiation. Slice of sound molar and artificial HAp pellet were irradiated separately, with CO2 laser under different laser parameters. Tow series of samples covered with saturation calcium ion solution were irradiated separately. To investigate the crystal morphology, XRD pattern were surveyed. The comparison of each cases show that the chemical coating affected the ablation process evidently though distinct XRD results were observed. After CO2 laser irradiation, the (002) reflection was increased significantly that indicates the crystal growth in c-axis.

THPOS26 Vibrational Excitation of Ammonia Molecules by FEL-SUT
Yoshihiro Ogi, Koichi Tsukiyama (TUS-Kagurazaka, Shinjuku, Tokyo)

Free Electron Laser at Tokyo University of Science (FEL-SUT) was employed for exciting single vibrational modes of ammonia molecules. FEL is tuned to 10.5 μm, corresponding to the X1A1' (ν2 = 1) ← (ν2 = 0) transition of NH3. The population of the vibrationally excited states is probed by the (2 + 1) resonance enhanced multiphoton ionization (REMPI) technique via the B 1E" Rydberg state. Maximum excitation efficiency of ν2 = 1 ← ν2 = 0 transition was about 50 %, which was estimated by taking account of Franck-Condon factors and the rotational line strengths. Rotational analyses of the spectra revealed that vibrational ladder climbing up to ν2 = 2 in NH3 was realized for the first time. Experimental results on ν4 vibrational excitation of NH3 and ND3 will be also reported.

THPOS27 Optimization of the NIJI-IV FEL System for the Coherent Harmonic Generation in a Q-switched Regime
Hiroshi Ogawa, Norihiro Sei, Kawakatsu Yamada, Masato Yasumoto (AIST-PRI, Tsukuba, Ibaraki)

The Coherent Harmonic Generation (CHG) in the VUV region at the storage ring NIJI-IV has been numerically investigated. The harmonic radiation is produced in an FEL oscillator with a hole-coupled resonator including a 6.3-m optical klystron ETLOK-II. The evolution of light pulses through Q-switched FEL process is simulated using the code GENESIS1.3 and its extended code. The parameters of the NIJI-IV FEL system will be optimized for different electron-beam energy of 310-450MeV and optical cavity configurations.

THPOS28 Performance of the Optical Klystron ETLOK-III for Developing Infrared Storage Ring Free Electron Lasers
Norihiro Sei, Hiroshi Ogawa, Kawakatsu Yamada, Masato Yasumoto (AIST-PRI, Tsukuba, Ibaraki)

Oscillations of free electron lasers (FELs) with the compact storage ring NIJI-IV in a wade wavelength region of 1-12 micron are planned in the AIST. The optical klystron ETLOK-III for developing infrared FELs has been installed in a long straight section of the NIJI-IV. The ETLOK-III has two undulator sections of 7 periods of 20 cm and one 75 cm dispersive section. The maximum K value is about 10. Electron injection to the NIJI-IV with the ETLOK-III is now in progress. Fundamental and higher harmonics of spontaneous emission from the ETLOK-III will be observed in detail. The electron-beam qualities will be also evaluated by using the measurements of the spontaneous emission. In the presentation, we will report the experimental results and discuss the performance of the ETLOK-III.

THPOS29 Improved Performance of the NIJI-IV Compact VUV/IR FEL and its Application to the Surface Observation
Kawakatsu Yamada, Hiroshi Ogawa, Norihiro Sei, Kazutoshi yagi Watanabe, Masato Yasumoto (AIST-PRI, Tsukuba, Ibaraki)

At AIST, efforts to increase the FEL power as well as to shorten the lasing wavelength below 190 nm are being made, to use the NIJI-IV FEL as an intense light source for real-time surface observation using the photoelectron emission microscopy (PEEM). By irradiating a transition-metal surface with the 200-nm FEL, fine structure of one- micron scale was successfully observed with spatial and temporal resolutions of a few hundreds nm and 33 ms, respectively. In addition, a 3.6-m optical klystron for lasing in the infrared was recently installed into the north straight section of the NIJI-IV to extend the lasing wavelength range up to ~ 10 microns. One of our interests in the infrared-FEL application is to utilize it for a Raman spectroscopy which can examine adsorbed molecules and their bonding conditions on the metal surface. Establishment of a total surface analysis system using NIJI-IV compact VUV/IR FEL combined with characteristic surface analysis techniques is one of our goals in the near future. Improved performance of the NIJI-IV FEL obtained this year will be reported. Typical results of the PEEM measurement will be discussed.

THPOS30 Photo-Acoustic Spectroscopy with Infrared FEL
Masato Yasumoto, Hiroshi Ogawa, Norihiro Sei, Kawakatsu Yamada (AIST-PRI, Tsukuba, Ibaraki)

Photo-acoustic spectroscopy (PAS) is a sensitive technique for measuring small absorptions of samples. In an ordinary PAS a pulse laser is used as a light source for inducing photo-acoustic signals. In our novel PAS an infrared FEL is used as the light source. The infrared FEL is continuously tunable in the wavelength with a high repetition rate. Thus, the PAS with the infrared FEL can be applied in various samples compared with the ordinary PAS. We will show the feasibility of the novel PAS.

THPOS33 A mm-Wave, Table Top Cerenkov Free-Electron Laser
Isabel de la Fuente, Klaus Boller, Peter van der Slot (UTWENTE, Enschede)

We have designed and constructed a compact (0.5 x 1.5 m), 100 kV Cerenkov FEL operating at a frequency of 50 GHz. The electron beam is produced by a gridded thermionic electron gun with a beam current of 800 mA. Simulations shows that 800 mA is sufficient to produce an output power of ~ 1 kW peak at 50 GHz using a total cavity reflectivity of about 10 to 20 %. The average power approaches 1 kW when the electron pulse length is extended to CW. A depressed collector will be used to increase the overall efficiency of this device. Special attention has been given to the outcoupler that has to combine multiple functions. First it has to separate the radiation field from the electron beam. Second it has to be transparent for the electron beam and acts as a partial reflector for radiation. Finally it has to convert the generated TM01 mode in the interaction region into the fundamental TE01 mode of the standard rectangular output port. We will present the overall design and experimental set-up, first experimental results and discuss possible applications for this table-top Cerenkov FEL.

THPOS35 Reasearches of Thomson Scattering X-Ray Source at Tsinghua University
Wenhui Huang, Huaibi Chen, C. Cheng, Y. Cheng, Q. Du, Taibin Du, Y.Ch. Du, Y.Ch. Ge, X.Z. He, J.F. Hua, G. Huang, Y.Zh. Lin, Chuangxiang Tang, B. Xia, M.J. Xu, X.D. Yuan, Sh.X. Zheng (Tsinghua University, Beijing)

The bright and tunable short pulse X-ray sources are being widely used in various research fields including materials, chemistry, biology and solid physics. Thomson scattering source is one of the most promising approaches to short pulsed X-ray sources. Researches on Thomson scattering x-ray sources are being carried out in Tsinghua University. Some theoretical results and the preliminary experiment on the Thomson scattering between electron beams and laser pulses are described in this paper.

THPOS36 Preliminary Design of a Synchronized Narrow Bandwidth FEL for Taiwan Light Source
Wai Keung Lau, June Rong Chen, Tai Ching Fan, Feng Zone Hsiao, Kuo Tung Hsu, Ching-Shiang Hwang, Chin Cheng Kuo, Guo Huei Luo, Duan Jen Wang, Jau Ping Wang, Min Huey Wang (NSRRC, Hsinchu), Cheng Wei Chen, Huan Yang Chen (NTHU, Hsinchu)

Design study of a narrow line-width, high power IR-FEL facility has been carried out at NSRRC. This machine is designed to synchronize with the U9 undulator radiation of Taiwan Light Source and therefore provide new opportunity for chemical dynamics and condensed matter research. It has been proposed to use a super-conducting linac to provide a 60 MeV high quality electron beam to drive a 2.5-10 microns FEL oscillator with U5 undulator. Operating this linac in energy recovery mode will also be considered as an option to improve overall system effeciency and reduce heat loss and radiation dosage at the beam dump. Performance requirements and outcomes from this preliminary design study will be reported.

THPOS37 Status of 30 GHz Facility for Experimental Investigation of the Copper Cavity Lifetime (Clic Collider Project)
Alim Kaminsky, Artem Elzhov, Eugene Gorbachev, Vitaly Kosukhin, Elkuno Perelstein, Nikolay Pilyar, Tatiana Rukoyatkina, Sergey Sedykh, Anatoly Sergeev, Alexey Sidorov, Vladimir Tarasov (JINR, Dubna, Moscow Region), Naum Samuilovich Ginzburg, Sergey Kuzikov, Nikolay Peskov, Mikhail Petelin, Alexander Sergeevich Sergeev, Nikolay Zaitsev (IAP RAS, Nizhny Novgorod)

Facility for experimental investigation of a copper cavity lifetime under multiple action of 30 GHz power pulses is now created by the collaboration of CLIC team (CERN) [1], FEM groups of JINR (Dubna) and IAP RAS (Nizhny Novgorod). Design of the test cavity, estimation of the operating parameters of the FEM oscillator and the RF power transmission line was already reported at FEL’03 [2]. Last year was devoted to the achievement of the design parameters of all the elements of the facility. We have developed the equipment and the procedure of RF transmission line adjustment, improved the stability of the linac power supplies, created the new system of data acquisition. Start of the full-scale experiments is planned to the end of 2004.

THPOS38 The Coherent Synchrotron Radiation Influence on the Storage Ring Longitudinal Beam Dynamics
Evgueni G. Bessonov, Rouslan Mikhailovich Feshchenko (LPI, Moscow), Vasily Ivanovich Shvedunov (MSU, Moscow)

We investigate influence on the storage ring beam dynamics of the coherent Synchrotron Radiation (SR) self fields produced by an electron bunch. We show that the maximum energy gain in the RF cavity must far exceed the energy loss of electrons due to the coherent SR.

THPOS45 Isochronous Bend for a High Gain Ring FEL
Alexander Nikolaevich Matveenko, Oleg Alexandrovich Shevchenko, Nikolai Aleksandrovich Vinokurov (BINP, Novosibirsk)

The recently proposed ring free electron laser (FEL) consists of several undulators with isochronous bends between them. Isochronous bends are necessary to preserve the beam bunching between undulators. Such FEL configuration may be used as an independent soft X-ray source or as a master oscillator for an X-ray FEL (high gain harmonic generator or other type). The lattice of the compact 500-MeV 60 degree bend for a soft X-ray (50 nm) FEL is proposed. Fundamental restrictions due to quantum fluctuations of synchrotron radiation and technically achievable fields to construct isochronous bends of a shorter wavelength ring FEL are discussed.

THPOS46 Numerical Modeling of the Novosibirsk Terahertz FEL and Comparison with Experimental Results
Oleg Alexandrovich Shevchenko, Alexander Viktorovich Kuzmin, Nikolai Aleksandrovich Vinokurov (BINP, Novosibirsk)

Recently a new high-power terahertz FEL has been put in operation at the Siberian Center for Photochemical Research in Novosibirsk. The first lasing at the wavelength near 140 micrometer was achieved in April 2003. Since then some experimental data were obtained which required theoretical explanation. In this paper we use a simple 1-D model for numerical simulations of the FEL operation. The model is based on excitation of multiple longitudinal radiation modes by charged discs. We restrict our consideration to only the fundamental transverse mode. This approximation is valid in the case of long-wave FELs. We compare the results of numeric simulations with some analytical estimates and experimental data.

THPOS47 Start-To-End Simulations of the Energy Recovery Linac Prototype FEL
Christopher Gerth, Marion Bowler, Bruno Muratori, Hywel Owen, Neil R. Thompson (CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire), Bart Faatz (DESY, Hamburg), Brian W.J. McNeil (Strathclyde University, Glasgow)

Daresbury Laboratory is currently building an Energy Recovery Linac Prototype (ERLP) that serves as a testbed for the study of beam dynamics and accelerator technology important for the design and construction of the proposed 4th Generation Light Source (4GLS) project. Two major objectives for the ERLP are the operation of an oscillator infra-red FEL and demonstration of energy recovery from an electron bunch with an energy spread induced by the FEL. In this paper we present start-to-end simulations including the FEL of the ERLP. The beam dynamics in the high-brightness injector, which consists of a DC photocathode gun and a super-conducting booster, have been modelled using the particle tracking code ASTRA. After the main linac, in which the particles are accelerated to 35 MeV, particles have been tracked with the code ELEGANT. The 3D code GENESIS was used to model the FEL interaction with the electron beam. Different modes of operation and their impact on the design of the ERLP are discussed.

THPOS48 The Two-Beam Free Electron Laser Oscillator
Neil R. Thompson (CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire), Brian W.J. McNeil (Strathclyde University, Glasgow)

A one-dimensional model of a free-electron laser operating simultaneously with two electron beams of different energies [1] is extended to an oscillator configuration. The electron beam energies are chosen so that an harmonic of the lower energy beam is at the fundamental radiation wavelength of the higher energy beam. Potential benefits over a single-beam free-electron laser oscillator are discussed.

THPOS51 Harmonic Cascade FEL Designs for LUX, a Facilty for Ultrafast X-ray Science
Corlett John, William M. Fawley, Gregory Penn, Alexander A Zholents (LBNL/CBP, Berkeley, California), Weishi Wan (LBNL/ALS, Berkeley, California), Matthias Reinsch, Jonathan Wurtele (UC Berkeley, Berkeley)

LUX is a proposed facility for ultrafast X-ray science, based on an electron beam accelerated to ~3-GeV energy in a superconducting, recirculating linac.Included in the design are multiple FEL beamlines which use the harmonic cascade approach to produce coherent XUV & soft X-ray emission beginning with a strong input external laser seed at ~200 nm wavelength. Each cascade module generally operates in the low-gain regime and is composed of a radiator together with a modulator section, separated by a magnetic chicane. The chicane temporally delays the electron beam pulse in order that a "virgin" pulse region (with undegraded energy spread) be brought into synchronism with the radiation pulse. For each cascade, the output photon energy can be selected over a wide range by varying the seed laser wavelength and the field strength in the undulators. We present numerical simulation results, as well as those from analytical models, to examine predicted FEL performance. We also discuss lattice considerations pertinent to harmonic cascade FELs, as well as sensitivity studies and requirements on the electron beam.

THPOS53 Novel Method for Phase-Space Tomography of Rapidly Evolving E-beams
Kevin Chalut (Duke University, Durham, North Carolina), Vladimir N. Litvinenko (BNL, Upton, Long Island, New York), Igor V. Pinayev (BNL/NSLS, Upton, Long Island, New York)

Traditional tomographic methods based on Radon transformation require a full set projections covering full 180-degrees. This technique is applicable only to a stationary distribution of electrons, which do not evolve. In addition, this method can’t work with incomplete sub-set of data such as a few projections covering total angle of few degrees. We present novel method of tomography working with a limited number of non-degenerated linear projections. We present the description of the method, discuss its advantages as well as limitations. We compare the method with the Radon transformation. We present the application of this method to the study the dynamics of e-beam in longitudinal phase space using dual sweep streak-camera with psec resolution. This method allowed us to restore the evolution of e-beam during a giant pulse in a storage ring FEL when the distribution of the electrons changes completely during one synchrotron oscillation. We discuss another possible applications of this method in advanced FEL systems, where effects of space charge, nonlinearities or coherent synchrotron radiation impair traditional diagnostics methods.

THPOS54 Characterization of Storage Ring FEL operating in the Giant Pulse Mode
Igor V. Pinayev, Kevin Chalut (Duke University, Durham, North Carolina), Vladimir N. Litvinenko (BNL, Upton, Long Island, New York)

In this paper we present the experimental results on the storage ring free electron laser operating in the giant pulse mode with variable repetition rate. The experiments were conducted in the wide range of the electron beam energies from 270 MeV to 600 MeV with the giant pulses generated using a gain modulator. Dependence of the peak and average power, and the other properties and parameters of giant pulses on the pulse repetition rate are studied. In particular, it is found that the average lasing power in the giant pulse mode reaches levels of 70-90% of that in the CW power mode. Applications of such mode of operation are discussed.

THPOS56 VISA IB: Ultra-High Bandwidth, High Gain SASE FEL
Gerard Andonian, Ronald Barkley Agustsson, Alex Murokh, Claudio Pellegrini, Sven Reiche, James B Rosenzweig, Gil Travish (UCLA, Los Angeles, California), Marcus Babzien, Ilan Ben-Zvi, Jung Yun Huang, Vladimir N. Litvinenko, Vitaly Yakimenko (BNL, Upton, Long Island, New York), Ilario Boscolo, S. Cialdi, Alessandro Flacco (INFN Milano, Milano), Massimo Ferrario, Luigi Palumbo, C. Vicario (INFN/LNF, Frascati (Roma))

The results of a high energy-spread SASE FEL experiment, the intermediary experiment linking the VISA I and VISA II projects, are presented. A highly chirped beam (~1.7%) was transported without correction of longitudinal aberrations in the ATF dogleg, and injected into the VISA undulator. The output FEL radiation displayed an uncharacteristicly large bandwidth (~11%) with extremely stable lasing and measured energy of about 2 microJoules. Start-to-end simulations reproduce key features of the measured results and provide an insight into the mechanisms giving rise to such a high bandwidth. These analyses are described as they relate to important considerations for the VISA II experiment.

THPOS57 Acceleration of Electrons in a Diffraction Dominated IFEL
Pietro Musumeci, Chan Joshi, Claudio Pellegrini, J. Ralph, James B Rosenzweig, C. Sung, Sergei Tochitsky, Gil Travish (UCLA, Los Angeles, California), Sergey Tolmachev, Alexander Varfolomeev, Alexander Varfolomeev Jr., Timofey Yarovoi (RRC Kurchatov Institute, Moscow), Salime Boucher, Adnan Doyuran, Robert England, Rodney Yoder (UCLA/DPA, Los Angeles - California)

We report on the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected ina 50 cm long undulator strongly tapered both in period and field amplitude. A CO2 10 μ m laser with power >300 GW is used as the IFEL driver. The Rayleigh range of the laser (1.8cm) is shorter than the undulator length so that the interaction is diffraction dominated. Few per cent of the injected particles are trapped in stable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometers. Experimental results on the scaling of the accelerator characteristics versus input parameters like injection energy, laser focus position and laser power are discussed. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the first 25-30 cm of the undulator. An energy gradient of >70 MeV is inferred. In the second section of the undulator higher harmonic IFEL interaction is observed.

THPOS58 Free Electron Lasers in 2004
William B. Colson, Brett W. Williams (NPS, Monterey, CA)

Twenty-seven years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs operating in the infrared, visible, UV, and x-ray wavelength regimes are listed and discussed.

THPOS59 Stability of a Short Rayleigh Range Laser Resonator with Misaligned or Distorted Mirrors
Peter P. Crooker, Joseph Blau, William B. Colson (NPS, Monterey, CA)

Motivated by the prospect of constructing an FEL with short Rayleigh length in a high-vibration shipboard environment, we have studied the effect of mirror vibration and distortion on the behavior of the fundamental optical mode of a cold-cavity resonator. A tilt or transverse shift of a mirror causes the optical mode to rock sinusoidally about the original resonator axis. A longitudinal mirror shift or a change in the mirror’s radius of curvature causes the beam diameter at a mirror to dilate and contract with successive impacts. Results from both ray-tracing techniques and wavefront propagation simulations are in excellent agreement.

THPOS60 Gain and Coherent Radiation from a Smith-Purcell Free-Electron Laser
Charles A. Brau, Heather L. Andrews, Charles H. Boulware, Jonathan D. Jarvis (Vanderbilt/DPA, Nashville - Tennessee)

We have developed a new theory to describe the gain of a Smith-Purcell FEL. The theory shows that the electrons interact with an evanescent mode whose frequency lies slightly below the frequency range of Smith-Purcell radiation, and whose group velocity is negative. Computations indicate that very high gain should be observed even at very low current with suitable bright electron beams. An experiment is under construction to test these predictions.

THPOS62 Preliminary Measurements of the High-Gain FEL Radiation Properties along the Radiator
Timur Shaftan, Henrik Loos, Brian Sheehy, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

We present experimental results on evolution of properties of the DUV FEL output radiation along the radiator. Intercepting the electron beam at the different locations inside the undulator we recorded and analyzed transverse profiles, spectra and intensity of the FEL output. Shot-to-shot fluctuations of the FEL radiation may significantly affect the accuracy of measurement. In the paper we present and discuss a single-shot measurement technique, based on a special imaging system.

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.

THPOS66 Expected Properties of Radiation from VUV-FEL at DESY (Femtosecond Mode of Operation)
Evgeny L. Saldin, Evgeny A. Schneidmiller, Mikhail V. Yurkov (DESY, Hamburg)

For the next three years the nominal "long pulse" (200 fs) mode of FEL operation at VUV-FEL, based on a linearized bunch compression, is not available due to the lack of a key element - a 3rd harmonic RF cavity. Essentially nonlinear compression leads naturally to a formation of a short high-current leading peak (spike) in the density distribution that produces FEL radiation. Such a mode of operation was successfully tested at VUV-FEL, Phase I. In this paper we present optimized parameters of the beam formation system that allow us to get a current spike which is bright enough to get SASE saturation for the VUV-FEL, Phase 2 at shortest design wavelength down to 6 nm. The main feature of the considered mode of operation is the production of short (15-50 fs FWHM) radiation pulses with GW-level peak power that are attractive for many users. Main parameters of the SASE FEL radiation (temporal and spectral characteristics, intensity distributions, etc.) are presented, too.