FEL 2007 - List of Keywords (vacuum)

A B C D E F G H I K L M O P Q R S T U V W

vacuum

Paper	Title	Other Keywords	Page
MOPPH005	Improvements of the Tracking Code Astra for the Simulation of Dark Current Losses in the FLASH Linac	simulation, gun, linac, space-charge	22
	S. M. Meykopff, L. Fröhlich DESY, Hamburg
	At the Free Electron Laser in Hamburg FLASH, the activation of components due to dark current emitted by the gun has become a serious problem. To improve the understanding of dark current transport in the linac, simulations with the Astra tracking code have been conducted. These studies require a big amount of computing time due to the high number of simulated macroparticles. Therefore, the parallelized version of Astra had to be enhanced by features like dynamic load balancing and an improved aperture model. The paper will provide an overview of the new features and discuss possible remedies of the dark current problem based on the simulation results.

MOPPH009	Undulator Radiation in a Waveguide	undulator, resonance, radiation, diagnostics	34
	E. Saldin, E. Schneidmiller, M. V. Yurkov, G. Geloni DESY, Hamburg
	We propose an analytical approach to characterize undulator radiation near resonance, when the presence of the vacuum-pipe considerably affects radiation properties. This is the case of the far-infrared undulator beamline at the Free-electron LASer (FEL) in Hamburg (FLASH), that is designed to deliver pulses in the TeraHertz (THz) range. This undulator can be used for pump-probe experiments where THz pulses are naturally synchronized to the VUV pulse from the FEL, as well as the development of novel electron-beam diagnostics techniques. Since the THz radiation diffraction-size exceeds the vacuum-chamber dimensions, characterization of infrared radiation must be performed accounting for the presence of a waveguide. We developed a theory of undulator radiation in a waveguide based on paraxial and resonance approximation. We solved the field equation with a tensor Green's function technique, and extracted figure of merits describing in a simple way the influence of the vacuum-pipe on the radiation pulse as a function of the problem parameters. Our theory, that makes consistent use of dimensionless analysis, allows treatment and physical understanding of many asymptotes of the parameter space, together with their region of applicability. (See DESY 07-031)

MOPPH054	Small-Aperture Vacuum-Chamber Design for STARS	electron, undulator, scattering, radiation	134
	J. Bahrdt, V. Duerr, M. Scheer, G. Wuestefeld, A. Meseck BESSY GmbH, Berlin
	To demonstrate and investigate the cascaded HGHG-scheme proposed for the BESSY Soft X-ray FEL, BESSY plans to build a test-facility called STARS consisting of two HGHG stages. The radiator in the second stage is planned as an APPLE III device which provides the highest field for a circular beam pipe. The minimum Gap of 7 mm translates into a 5 mm inner diameter of the vacuum chamber. An analysis of the impact of the wakefields and the expected vacuum profile is thus required. Results of this analysis an vacuum measurements are presented.

WEBAU03	Performance Tests of the Photon Monochromator for Self-seeding at FLASH	photon, undulator, electron, radiation	306
	H. K. Bechtold, J. Hartvig, H. Juul, V. Toft Aarhus University, Aarhus R. Follath, G. Reichardt, F. Senf, F. Siewert BESSY GmbH, Berlin U. Hahn, J. Viefhaus, R. Treusch DESY, Hamburg S. V. Hoffmann ISA, Aarhus Ch. Knoechel LBNL, Berkeley, California R. Reininger UW-Madison/SRC, Madison, Wisconsin
	A single pass FEL amplifier can produce extremely intense and fully coherent radiation at short wavelengths if it is seeded by a coherent light beam resonant with the magnetic structure and collinear with the electron beam. Since at the present time a single pass SASE FEL is the only source of sufficiently intense, tunable radiation in the soft X-ray region, it has been proposed to use such a source in combination with a narrow-band monochromator for seeding an FEL amplifier. By means of such a "Self-Seeding", the soft X-ray free electron laser FLASH at DESY will be modified so that it can provide coherent radiation in space and time in a wavelength range from about 60-6nm (~20-200eV). In this presentation, we will focus on the performance of the photon monochromator beamline which was setup and tested at the synchrotron radiation storage ring ASTRID in Aarhus, Denmark. The optical, mechanical and vacuum design will be described along with results on the resolving power of the monochromator which have been obtained scanning across rare gas resonance lines at various energies. Based on these results we will conclude that the monochromator is mechanically very stable and reproducible and behaves according to its specifications with resolving powers between 10000 and 20000, i.e. bandwidths of a few meV only. J. Feldhaus, E. L. Saldin, J. R. Schneider, E. A. Schneidmiller, and M. V. Yurkov, Opt. Commun. 140, 341 (1997)
	Slides

WEPPH017	UV Performances of Pulsed Laser Deposition Grown Mg Photocathodes	laser, cathode, gun, electron	366
	G. Gatti, F. Tazzioli, L. Cultrera INFN/LNF, Frascati (Roma) P. Miglietta, A. Perrone INFN-Lecce, Lecce C. Ristoscu INFLPR, Bucharest - Magurele
	We report a detailed description of the laser cleaning procedure and emission performance measurement on a Pulsed Laser Deposited Mg film. During the tests performed after the end of each cleaning operation we have evidenced an increase of Quantum Efficiency (QE) in time. Then the QE apparently stabilizes at a remarkably higher value. The study of this phenomenon is important because it determines both the working QE value and the lifetime of the cathode. Moreover, the stability of the QE has been revealed for a time scale of several days after each laser cleaning process, in our vacuum conditions.

WEPPH019	Determination of the Wakefield Budget for the FERMI FEL Undulator System	undulator, impedance, electron, coupling	374
	C. Bontoiu, P. Craievich, L. Rumiz ELETTRA, Basovizza, Trieste M. Castronovo Università degli Studi di Trieste, Trieste R. Vescovo, A. A.G. Lutman DEEI, Trieste
	The FERMI project aims to achieve very high-brightness photon beam pulses of minimum bandwidth. These goals can be marred by the presence of large wakefields generated along the length of the undulator small-gap vacuum chamber. Estimations of the induced energy-spread caused by the resistive wall and surface roughness wakefields along the length of the vacuum chamber of the FERMI FEL undulator are presented. The energy spread and losses induced by the resistive wall wakefield are determined for three possible transverse geometries of the vacuum chamber, namely circular, rectangular and elliptical cross-section, while the energy spread and losses induced by the surface roughness wakefields are obtained for the circular cross-section case. In this last case in-house surface profile measurements are used to provide realistic estimates.

WEPPH028	Development of a Compact Cherenkov Free-Electron Laser Operating Terahertz Wave Range	electron, radiation, cathode, free-electron-laser	406
	M. R. Asakawa, N. M. Miyabe Kansai University, Osaka A. Ikeda, M. Kusaba, Y. Tsunawaki OSU, Daito, Osaka
	We designed a compact Cherenkov Free-Electron Laser(CFEL) device capable of delivering mW-level output power at frequencies of up to THz from 10GHz to 1 THz. CFEL has the advantage of generating higher frequencies at lower electron beam energy. Due to lower electron beam CFEL device is compact. Our CFEL device consists of a waveguide partially filled with two lined parallel dielectric slabs through which a relativistic electron beam propagates. We call this structure "double-slab". In our device, the electron beam is generated using the Spindt cathode. We used a super conducting magnet to compress and guide the electron beam along the dielectric slabs. Assuming a dielectric slab thickness of 0.65mm,length of 11cm and electron beam energy 50keV ,the output power generated by the device was numerically calculated to be mW-level at 46GHz. Currently , we are conducting the POP experiment at millimeter wave range.

WEPPH029	Development of the Longitudinal Phase-Space Monitor for the L-band Electron Linac at ISIR, Osaka University	electron, photon, radiation, linac	409
	T. Igo, G. Isoyama, S. Kashiwagi, M. Morio, R. Kato ISIR, Osaka
	The correlation between longitudinal positions of electrons in a bunch and their energies has a critical effect on the temporal evolution of SASE, and various methods are being developed to measure the longitudinal phase-space profile. We are developing a system to measure the longitudinal phase-space distribution of electrons by a combination of a bending magnet, a profile monitor, and a streak camera at the Institute of Scientific and Industrial Research (ISIR), Osaka University. In the preliminary experiments using a profile monitor utilizing optical transition radiation (OTR), it was confirmed that the monitor had higher momentum resolution than the presently used momentum analyzer consisting of a slit and a current meter. However, we could not obtain the sufficient number of photons to obtain the phase-space image since, in addition to a low photon yield, the angular distribution of OTR emitted by the electron beam in the energy region of 10 – 20 MeV, with which THz-SASE and THz-FEL experiments are conducted at this laboratory, is too large to concentrate it efficiently on a streak camera. In order to increase the number of photons, we try to use silica aerogel as a radiator of the profile monitor by following the example of PITZ. We will present an outline of the phase-space monitor we are developing and its experimental results. R. Kato et al, FEL’06, Berlin, Germany, August 2006, THPPH041, p.676, http://www.jacow.org.** J. Roensch et al, FEL’06, Berlin, Germany, August 2006, THPPH019, p.597, http://www.jacow.org

WEPPH034	Fourier and Non-Fourier Models for Photoemission	laser, electron, cathode, lattice	428
	A. M. Mihalache, E. Mitru, M. Oane, C. Petit-Jean-Genaz INFLPR, Bucharest - Magurele
	This paper is a theoretical study on the photoemission properties of metallic photocathodes in the high intensity ultrashort laser pulse regime, using Fourier and non-Fourier models. First of all the Fourier-model was used. Next an analysis of the electron gas heating phenomenon and how this phenomenon leads to coupled heat equations (two temperature models). The authors also try to show that it is possible to use, in the second approximation, a non-Fourier model instead of two temperature models, using a single temperature hypothesis (the electron gas temperature equals with the lattice temperature). The distributions for thermal fields and photocurrents function of space, time, laser-intensity, incident angle and relaxation time are also represented.

WEPPH039	The Optical Replica Synthesizer in FLASH	laser, undulator, electron, simulation	438
	G. Angelova, V. G. Ziemann UU/ISV, Uppsala J. Boedewadt, S. Khan, A. Winter Uni HH, Hamburg A. Meseck BESSY GmbH, Berlin E. Saldin, H. Schlarb, B. Schmidt, E. Schneidmiller, M. V. Yurkov DESY, Hamburg P. M. Salen, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm
	During the shutdown in spring 2007 the optical replica synthesizer, a novel device to diagnose ultra-short electron bunches, is assembled in the FLASH accelerator. We report on the status of the construction work with emphasis on the two electro-magnetic undulators needed for micro-bunching and replica-pulse generation.

WEPPH046	A Superconducting RF Photo-Injector for Operation at the ELBE Linear Accelerator	gun, laser, cathode, electron	449
	A. Arnold, H. Buettig, D. Janssen, M. Justus, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, R. Xiang, J. Teichert FZD, Dresden T. Kamps BESSY GmbH, Berlin G. Klemz, I. Will MBI, Berlin W.-D. Lehmann IfE, Dresden A. Matheisen, B. van der Horst DESY, Hamburg J. Stephan IKST, Drsden V. Volkov BINP SB RAS, Novosibirsk P. vom Stein ACCEL, Bergisch Gladbach
	For the ELBE superconducting linear accelerator at Forschungszentrum Dresden-Rossendorf (FZD) a radiofrequency photoelectron injector with a superconducting cavity (SRF gun) is under development. The SRF gun combines the excellent beam quality which can be delivered by RF photoinjectors with the possibility of continuous wave operation. The superconducting niobium cavity of the injector consists of 3½ cells and contains a Cs2Te photocathode which is normal-conducting and cooled by liquid nitrogen. The RF frequency of the cavity is 1.3 GHz. The final electron energy will be about 9.5 MeV and the average electron current will be 1 mA. In the past years the SRF photo injector has been designed and fabricated. Several critical subsystems have been tested. For the cavity, the results of the RF measurements will be shown. An UV driver laser system has been developed which fulfils the different requirements (77 pC at 13 MHz, 1 nC at 500 kHz) for the future operation at ELBE. A photo cathode preparation system was developed and installed. The equipment is now in operation and the first series of Cs2Te photo cathodes have been produced.

WEPPH047	Electro-Optic Spectral Decoding for Single-Shot Characterisation of the Coherent Transition Radiation Time Structure at FLASH	laser, radiation, electron, background	453
	E.-A. Knabbe, B. Schmidt, P. Schmüser, B. Steffen, V. R. Arsov DESY, Hamburg
	Characterisation of the longitudinal profiles of ultrashort electron bunches is of primary importance for controlling the lasing process of SASE FEL. Non-destructive, single-shot techniques, are preferable. Presently the most promising ones are the Electro-Оptic (EO) laser diagnostics and the THz spectroscopy of coherent transition radiation (CTR). Whereas the former are applied directly in the electron beam line, the latter offer possibility to detect shorter temporal structures, but outside the tunnel. Therefore it is important to know the transfer function of the CTR beam line. We present a single-shot EO detection of temporal CTR profiles, generated from electron bunches, kicked to an off-axis screen at DESY's VUV-FEL (FLASH). The THz radiation is transported through a 20 m long line from the accelerator tunnel to an experimental station outside. The measurements are performed in air and in vacuum with 0.5 mm ZnTe and 0.175 mm GaP crystals in crossed-polarisers detection scheme. Pulses with less than 1 ps FWHM have been measured.

WEPPH052	In-situ Undulator Field Measurement with the SAFALI System	undulator, laser, feedback, electron	468
	H. Kitamura, T. Tanaka RIKEN Spring-8 Harima, Hyogo T. Seike JASRI/SPring-8, Hyogo-ken
	Although the in-vacuum undulators (IVUs) have many advantages over out-vacuum undulators, magnetic measurement after assembling vacuum components, i.e., final verification of magnetic performance, is not an easy task. In addition, remeasurement after installation in the accelerator beamline is not trivial. The situation is more severe for cryogenic permanent magnet undulators (CPMUs), an extension of IVUs. We have recently developed a magnetic measurement system to measure the field inside the vacuum chamber. With optical laser beams introduced into the vacuum chamber, the alignment of the Hall probe positions is dynamically carried out, which ensures a high stability and accuracy of the measurement. This system is called SAFALI for Self-Aligned Field Analyzer with Laser Instrumentation. The SAFALI system has been applied to field measurement of two different undulators. One is an IVU installed in Swiss Light Source in 2001 and had been operated for about 3 years. The other is a CPMU prototype to demonstrate the principle of CPMU. The purpose of the measurement of the former is to investigate the radiation damage during operation, while that of the latter is to check the performance variation according to the temperature change of magnets. In the conference, details of the SAFALI system are given together with the results of the field measurements.

WEPPH055	Experimental Investigation of Smith-Purcell Radiation From Gratings of Different Profile	target, radiation, electron, microtron	480
	V. A. Cha, D. V. Karlovets, Yu. A. Popov, A. Potylitsyn, L. G. Sukhikh, G. A. Naumenko TPU, Tomsk B. N. Kalinin, G. A. Saruev INPR, Tomsk
	Smith-Purcell radiation (SPR) is widely considered as the spontaneous mechanism for FEL. There are a few theoretical SPR models, which predict large difference between radiation intensity from relativistic electrons for grating with different profile. To choose the most effective grating we carried out the absolute coherent SPR intensity measurements on the 6.2 MeV electron beam. The coherent SPR spectra and angular distributions were investigated. Gratings with lamellar, triangular and so-called "flat" gratings were studied. It was shown the grating consisted of the conductive strips is more preferable target for SPR generation.

THBAU01	Research Highlights from FLASH	free-electron-laser, laser, electron, radiation	499
	J. Feldhaus, R. Treusch DESY, Hamburg
	The Free electron LASer in Hamburg (FLASH) has started regular user operation in summer 2005, providing XUV radiation pulses with pulse energies in the 10 - 100 μJ range and pulse durations of 10 - 50 fs. The science programme at FLASH covers a broad range of novel applications including fundamental studies on atoms, ions, molecules and clusters, creation and characterisation of warm dense matter, diffraction imaging of nanoparticles, spectroscopy of bulk solids and surfaces, investigation of surface reactions and spin dynamics, and the development of advanced photon diagnostics and experimental techniques. So far, 16 science projects have been pursued involving approximately 200 scientists from 11 countries. Some of the research highlights will be presented.
	Slides