focusing

Paper	Title	Other Keywords	Page
MOAAU04	First Lasing at SCSS	emittance, undulator, radiation, gun	16
	T. Shintake RIKEN Spring-8 Harima, Hyogo
	On 20 June, the SCSS prototype accelerator firstly generated pulses at VUV 49 nm FEL radiation, using ultra-low emittance beam provided by a newly developed single-crystal CeB6 thermionic cathode. SCSS prototype accelerator has been recently constructed in 2004-2005 at SPring-8 site in Japan, and comissioned recently. Its major purpose is to test hardware components developed at RIKEN/SPring-8 in SCSS R&D required to realize X-ray FEL at 1 Angstrom wavelength. One of the most challenging ideas in SCSS is to use CeB6 single crystal cathode to generate ultra-low emittance beam. We start from a lower beam current of 1 A from 500 kV e-gun, then we compress the bunch length more than a few 100 times to generate a few 100 A beam without deteliorating the emittance in the injector. Careful design was made on rf-cavities and magnetic lenses to perform velocity bunching in the injector system, which has been installed in the prototype accelerator. After four C-band accelerators, beam energy reaches 250 MeV. On 15 June, evening 4 pm, we firstly closed the upstream undulator, after one hour tuning, we observed narrow spectrum peaked at 49 nm in the intense VUV radiation, which was totally different from the natural undulator radiation (spontanenous mode). We performed careful measurements on various aspects, and announced "the first lasing" on 20 June.
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MOPPH046	Seeding the FEL of the SCSS Prototype Accelerator with Harmonics of a Ti:Sa Laser Produced in Gas.	laser, undulator, radiation, simulation	138
	G. Lambert, M. Bougeard, W. Boutu, B. Carré, D. Garzella, M. Labat CEA, Gif-sur-Yvette O. V. Chubar, M.-E. Couprie SOLEIL, Gif-sur-Yvette T. Hara, H. Kitamura, T. Shintake RIKEN Spring-8 Harima, Hyogo
	A particular seeded configuration will be tested in 2006 on the SCSS test facility (SPring-8 Compact Sase Source, Japan). This facility is based on a thermionic cathode electron gun (1 nC), a C-band LINAC (5712 MHz, 35 MV/m) and two in-vacuum undulators (15 mm of period). The maximum electron beam energy is 250 MeV and the SASE emission from visible to 60 nm can be obtained. The external source, obtained by the High order Harmonic Generation (HHG) process, can be tuned from the 3th (260 nm) to the 13th harmonic (60 nm) of a Ti: Sa laser generated in a gas cell. The experiment contains a first chamber, dedicated to harmonic generation and a second one for harmonic beam diagnostics and adaptation of the harmonic waist in the modulator. The tests have been performed in Saclay (15 mJ, 10 Hz, 50 fs). An energy of 2e-6J with a high stability for the 3th harmonic and a good transversal shape with an optimized energy level and a high stability for the 13th harmonic have been obtained at the modulator center place. The performances using PERSEO, GENESIS and SRW will be updated. The chambers will be installed on the SCSS test facility in the beginning of July for seeding tests during summer.
MOPPH047	Seeding SPARC Facility with Harmonic Generation in Gases: Preliminary Tests of the Harmonic Generation in Gas Chamber	laser, undulator, electron, photon	142
	O. Tcherbakoff, M. Bougeard, P. Breger, B. Carré, D. Garzella, M. Labat, G. Lambert, H. Merdji, P. Monchicourt, P. Salieres CEA, Gif-sur-Yvette M.-E. Couprie SOLEIL, Gif-sur-Yvette A. Doria, L. Giannessi ENEA C. R. Frascati, Frascati (Roma)
	A coherent short wavelength source can be realised with a Free Electron Laser by using High Gain Harmonic Generation configuration. The injection of an external light source in the first part of an undulator results in a coherent light emission in its second part. The SPARC FEL (Frascati, Italy), delivering an electron beam at 200 MeV passing through an undulator of 6 sections, can be configured to test such schemes. We propose to use High order Harmonic Generation (HHG) in gases process as the seed. HHG produces a coherent XUV source by focusing an intense laser pulse into a gas medium. This beam, composed of odd harmonics of the fundamental laser, is then shaped using a telescope of two spherical mirrors, allowing the focusing at a given position, in the SPARC undulator. Appropriate tuning of the undulator gaps will amplify the 3rd and 5th harmonics seeded, and non-linear harmonics of those wavelengths, allowing the perspective of producing VUV coherent radiation. The chambers for harmonic generation and shaping have been realised and tested at the CEA (Saclay, France). We present these tests as well as simulations of the expected performances of the SPARC FEL with this seed.
TUPPH022	Development of a Compact Cherenkov Free-Electron Laser in Terahertz Spectral Range	electron, cathode, radiation, laser	364
	M. R. Asakawa, N. Miyabe Kansai University, Osaka M. Kusaba, K. Nakao, Y. Tsunawaki OSU, Daito, Osaka
	A Cherenkov free-electron laser (CFEL) generating terahertz radiation is now being developed under the joint research of Osaka Sangyo university and Kansai university. The main feature of this CFEL is its compactness. Electron beamlets emitted by a Spindt cathode are accelerated up to 60 keV in a D. C. electron gun and then are injected into 100μm-gaps between stacked plates of silicon, which acts as radiator. The radiation frequency will be ranged from 0.8 to 2 THz according to the acceleration voltage. In order to suppress diverging of the beamlet with a high current density about 1kA/cm2, the electron gun and the radiator section are immersed in a longitudinal magnetic field produced by a super-conducting (SC) coil. The total length of the CFEL section, i.e., the distance between the cathode and beam dumper, is 4 cm and the diameter of this section is less than 2 cm. Such compact laser module is placed in the bore of SC coil. In spite of the large size of the cryostat and the power supply of the SC coil, the total footprint is about 1×1 m2.
TUPPH040	Emittance Compensation of Superconducting Gun and Linac System for Beams with Large Chromatic Variance	emittance, linac, gun, chromatic-effects	419
	B. Buckley Cornell University, Ithaca, New York D. Kayran, V. Litvinenko BNL, Upton, Long Island, New York
	Among the methods of emittance compensation for a superconducting rf gun and linac system include utilizing a solenoid and drift space after the gun to achieve a specific beam envelope with zero beam divergence before entrance into the linac. Studies on this method have assumed minimal energy spread in the beam. However, in cases where chromatic effects cannot be ignored this one solenoid emittance compensation technique is inadequate. Proposed is a new method of emittance compensation utilizing two solenoids in order to minimize emittance in beams with large energy spread. We present a theoretical basis for the new technique along with a computer optimized configuration. The results are compared with previous methods of emittance compensation.
THPPH006	Photocathode Laser for the Superconducting Photo Injector at the Forschungszentrum Rossendorf	laser, gun, emittance, radiation	564
	I. Will, G. Klemz MBI, Berlin F. Staufenbiel, J. Teichert FZR, Dresden
	We report on the design of the photocathode laser for a superconducting RF gun under development at the Forschungszentrum Rossendorf. The laser consists of a short-pulse oscillator, a pulse-picking Pockels cell, a linear amplifier chain and a frequency conversion stage. It generates pulses of about 5 ps duration with 13 MHz repetition rate and 1 W average power at 263 nm wavelength. Both the oscillator and the amplifiers are pumped by fiber-coupled semiconductor diodes. Nd:YLF is used as the gain medium of this laser. It introduces only small distortions on the optical wavefront of the laser beam and supports pulses of a few picoseconds duration. The beamline which transfers the laser beam to the photocathode of the RF gun has a large impact on the final beam profile. One can optimize the emittance of the electron beam by illuminating the cathode with a nearly flat-top beam profile. This is achieved by a pair of aspheric lenses and appropriate imaging optics in the beamline. Simulation of the beamline and its effect on the laser profile at the photocathode of the RF gun are also presented.
THPPH040	Study on Focusing Property of New Type Wiggler and SASE-FEL Experiment at the ISIR, Osaka University	wiggler, electron, radiation, permanent-magnet	672
	S. Kashiwagi, G. Isoyama, R. Kato ISIR, Osaka H. Sasaki, K. Tsuchiya, S. Yamamoto KEK, Ibaraki
	We have developed a new type of wiggler based on the edge-focusing wiggler for free electron laser (FEL) in the infrared region at the Institute of Scientific and Industrial Research (ISIR), Osaka University. The strong focusing (SF) scheme is adopted for the new wiggler in order to keep the beam size small along the wiggler. The period length of the wiggler is 60 mm, the number of periods is 32, and the total length is 1.938 m, including end magnet blocks for the orbit compensation. The wiggler consists of four FODO cells for double focusing. Focusing elements and defocusing elements are incorporate with single wiggler periods with edge angles of +5 and -5 degrees, respectively, and they are separated by three normal wiggler periods. The focusing properties of the SF wiggler for FEL and SASE are studied using a high-intensity electron beam at ISIR L-band linear accelerator. Optics parameters of electron beam are changed at the entrance of the SF wiggler, and the profiles of the electron beam are measured using screen monitors at several points along the wiggler. We will present the result of the beam experiments using the focusing wiggler in this conference.
THPPH058	Beam Spreading and Emittance Oscillation of an Intense Magnetized Beam in Free Space	emittance, space-charge, electron, booster	721
	C.-X. Wang, K.-J. Kim ANL, Argonne, Illinois
	Intense beams with large angular momentum have important applications in electron cooling and in producing flat beams suitable for ultrafast x-ray generation, Smith-Purcell radiators, and possibly for a future linear collider. To gain basic understanding of the influence of beam angular momentum in an otherwise space-charge-dominated beam, the behavior of such a beam in free space will be examined here, in particular, beam spreading due to space-charge force, as well as emittance oscillation. Drift space is an important part of a split photoinjector and plays a significant role in emitance compensation of a high-brightness photoinjector.
FRAAU03	Wave-Front Observations at FLASH	diagnostics, alignment, optics, laser	794
	M. Kuhlmann, E. Plönjes, K. I. Tiedtke, S. Toleikis DESY, Hamburg P. Mercere SOLEIL, Gif-sur-Yvette P. Zeitoun LOA, Palaiseau
	During the first user operation of the Free-Electron Laser in Hamburg (FLASH) wavefront measurements have been recorded in the vacuum-ultraviolet region using a Hartmann sensor (by Imagine Optic). The Hartmann principle is based on a pinhole array, which divides the incoming beam into a large number of sub-rays monitored in intensity and position of individual spots. The identification of the local slope of the incident wavefront makes the aberrations from a perfect spherical wavefront visible. Ray tracing in upstream direction accesses the beam focal point in size and position. The intense and coherent vacuum-ultraviolet FEL beam leads to unique requirements for the wavefront sensor setup. We report an optimized setup to observe the metrology of flat and curved mirrors at FLASH beamlines. The effects of solid and gaseous filters are selectively described in the wavelength regime of 10nm to 32nm. The use of wavefront measurements to provide reliable machine parameter is discussed. The wavefront sensor proved to be a valuable tool to observe the FEL beam quality and the performance of optical elements, filters and diagnostic tools.
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FRAAU04	A New Generation of X-Ray Optics Based on Pyrolytic Graphite	photon, optics, vacuum, alignment	798
	H. Legall, H. Stiel MBI, Berlin A. Antonov, I. Grigorieva Optigraph GmbH, Berlin V. Arkadiev IAP, Berlin A. Bjeoumikhov IfG, Berlin A. Erko BESSY GmbH, Berlin
	Highly Oriented Pyrolytic Graphite (HOPG) is a mosaic crystal, which consists of a large number of small nearly perfect crystallites. The unique structure of HOPG crystals enables them to be highly efficient in an energy range between 2 keV up to several 10 keV. The mosaicity of the crystal is responsible for the dramatic increase of integral reflectivity in comparison to perfect crystals. Furthermore thin HOPG crystal films can be easily bent and exhibit a very high thermal conductivity making them interesting for application in experiments with high average power x-ray sources. For application in x-ray spectroscopy the achievable spectral resolution of the crystal optics is in particular of interest. Recently performed measurements with very low foil thickness have revealed a spectral resolution of E/DeltaE=2900 in 004-reflection (H. Legall et al., Opt. Expr. 14 (2006)). This is by far the highest spectral resolution reported for HOPG crystals. The integral reflectivity of these films is still comparable to that of ideal Ge crystals. In the present work we will present new results concerning the energy resolution, integral reflectivity and application of thin bent Graphite films.
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