FEL 2006 - List of Keywords (coupling)

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

coupling

Paper	Title	Other Keywords	Page
MOPPH016	Mode Couplings in a Raman Free-Electron-Laser with Ion-Channel Guiding	electron, wiggler, space-charge, plasma	75
	B. Maraghechi, B. Maraghechi IPM, Tehran T. Mohsenpour AUT, Tehran
	The free-electron laser (FEL) theory in the collective or Raman regime relies on the unstable coupling between the radiation and the negative-energy space-charge wave. Due to the high density and low energy of electron beam a focusing mechanism like an axial magnetic field is usually required to guide the beam. We have shown in our previous study that, in addition to the above coupling that constitutes the regular FEL resonance, there are other unstable coupled-mode structures in the group II orbits. In the present analysis we are studying the mode-couplings when the electron beam is guided by an ion-channel. Using fluid model, a general dispersion relation of a FEL with a one-dimensional helical wiggler and an ion-channel guiding is derived. A numerical analysis of the general dispersion relation will be used to study interactions among all possible waves. In group II orbits, with relatively large wiggler induced velocities, new couplings between the negative and positive-energy space-charge waves as well as between the right and left circularly polarized electromagnetic waves are expected to be found. These instabilities are distinct from the usual FEL resonance.

MOPPH025	Free Electron Laser as Paradigmatic Example of Systems with Long-Range Interactions	electron, laser, free-electron-laser, bunching	87
	D. Fanelli, A. Antoniazzi, S. Ruffo Università di Firenze, Florence J. Barre' Université de Nice Sophia-Antipolis, Nice T. Dauxois ENS LYON, Lyon G. De Ninno ELETTRA, Basovizza, Trieste
	Long range interactions are such that the two-body interaction potential decreases at large distance with a power which is smaller or equal to the space dimension. Examples include gravitational forces, unshielded Coulombic interaction. In presence of long-range interactions, physics is very peculiar and a wide range of striking phenomena appears. In particular energy is non additive, hence the system under scrutiny cannot be divided into independent macroscopic parts, as it is usually the case for short-range interactions. These unexpected features are systematically detected, independently of the specific nature of the long-range interactions involved. FEL are one of the most interesting examples of systems with long-range interactions, where the interplay between collective (wave) and individual (particles) degrees of freedom is well known to be central and, in this respect, provides a unique experimental ground to investigate such universal pecularities. In this presentation I will review the main characteristics of such systems and dicuss the statistical theory of the Vlasov equation, a wide general approach that enables to analytically investigate the laser saturated regime.

MOPPH026	Overview of Perseo, a System for Simulating FEL Dynamics in Mathcad	simulation, undulator, electron, resonance	91
	L. Giannessi ENEA C. R. Frascati, Frascati (Roma)
	The computing performances of today's personal computers are sufficient for executing interactively one dimensional FEL simulations. Mathcad is a versatile tool for implementing math expressions, plotting data and analysing results with the main prerogative of the simplicity of the user-interface. This suggested to develope a set of functions devoted to the simulation of FEL dynamics that can be accessed from the Mathcad environment. The result is Perseo, a flexible tool that can be simply programmed to set up FEL simulations in a wide variety of practical configurations. Perseo allows the time dependent simulation of SASE and seeded FEL configurations, oscillator configurations and exhotic configurations like master oscillator power amplifier or multiple stages cascaded FELs. The model include higher order harmonics and startup from shot-noise. Perseo is freely available at http://www.perseo.enea.it

MOPPH052	Study of a Deflecting Dispersive Chicane for BESSY Soft X-Ray FEL	radiation, electron, dipole, simulation	158
	A. Meseck, G. Wuestefeld BESSY GmbH, Berlin
	High power, short pulse lengths and full coherence are the main parameters of the second generation free electron lasers like BESSY soft X-ray FEL. To provide radiation with these properties, cascades of HGHG stages are planned. In these stages an energy modulation is imprinted on the electron beam by seeding radiation. A dispersive section converts this energy modulation to a spatial modulation which is optimized for a particular harmonic. The following radiator is tuned to this harmonic and generates radiation with high power. The separation of the electron beam and seeding radiation after the modulation is desirable, as not only the quality of the radiator improves but also the seeding radiation itself can be used for diagnostics. A simple bending magnet leads to the separation but it causes a coupling of the longitudinal and transverse motion and could spoil the longitudinal modulation. Based on an exact linear model, a dispersive chicane is designed for one stage of the BESSY FEL which bends the electron beam without the coupling effects. The linear model will be presented and used to design a chicane. Simulations of the spatial modulation will also be discussed.

MOCAU04	Focal Point Laser-Field as Optical Seeder	laser, electron, cathode, radiation	242
	T. Shintake RIKEN Spring-8 Harima, Hyogo
	Focusing optical laser into its wavlength size, and crossing the electron beam through the focal point, interaction of electron with laser field becomes non zero, as a result, creates velocity modulation. In contrast with modulation scheme using undulator, this method does not require energy resonance condition to the electron beam, thus works all energy, even with energy chirp. Using it in front of the bunch compressor, with energy chirp, the wavelength can be compressed by large factor with bunch length compression.
	Slides
	Talk

TUPPH018	New Resonator for the Israeli FEL	radiation, wiggler, electron, controls	349
	A. Faingersh, J. Dadoun, Kh. Garb, A. Gover, Y. Socol University of Tel-Aviv, Faculty of Engineering, Tel-Aviv G. G. Denisov, M. Y. Shmelyov IAP/RAS, Nizhny Novgorod M. Einat, B. Kapilevich, B. Litvak, Y. Pinhasi, A. Yahalom CJS, Ariel
	The Israeli FEL resonator was re-designed in order to reduce the overall round-trip losses and achieve control on the radiation output-coupling. In its new configuration, the resonator consists of overmoded corrugated rectangular waveguide and two radiation mode splitters, separating the high-energy e-beam from the laser radiation. The electron input splitter is based on Talbot effect in an overmoded rectangular waveguide. The radiation out-coupling is done in the output splitter. It is based on novel design and it combines Talbot effect between two parallel plates with free space propagation, and focusing by two curved cylindrical mirrors in a confocal imaging scheme. The waveguide and the splitters were tested experimentally, showing improved performance in comparison with the former resonator. The measured unloaded Q-factor of the new version is increased by a factor of ~ 3, attaining up to Q=30,000. Accordingly, the round-trip losses are ~15%. Rotating grids control the radiation out-coupling allowing wide variation for maximization of the radiation output power and extraction efficiency. The design layout and the testing results are presented.

TUPPH033	A FEL Amplifier Based on Planar Bragg Waveguides	electron, undulator, resonance, lattice	393
	N. S. Ginzburg, K. E. Dorfman, A. Malkin, R. M. Rozental IAP/RAS, Nizhny Novgorod
	A planar periodic Bragg structure can be used for wave guiding in the direction transverse to the lattice vector. Open Bragg waveguide can provide high selectivity over the transverse coordinate when its size essentially exceeds wavelength. We study several new schemes of FEL amplifiers based on these structures. In a transverse current amplifier scheme it is beneficial to use a grating with a step of corrugation, that results in the existence of a single low dissipative mode located near defect. The sheet electron beam moves across the waveguide to be resonant to one of partial waves forming the operating mode. Another way is a traditional traveling wave amplifier scheme where electron beam moves along waveguide axis. To increase effective size of operating mode is suggested a structure with regular longitudinal corrugation that couples two partial waves propagating at some angle to the axis to the wave propagating directly along the axis. This wave, which in moving reference frame is transformed into a cut off mode, is excited by the electrons. Analysis shows rather high gain and efficiency of the novel application schemes with simultaneous discrimination of parasitic modes. 1. N.S. Ginzburg, A. M.Malkin, N. Yu. Peskov et. al. Improving selectivity of free electron maser with 1D Bragg resonator using coupling of propagating and trapped waves, PR ST-AB 8,040705(2005)

THPPH007	First RF-Measurements at the 3.5-Cell SRF-Photo-Gun Cavity in Rossendorf	gun, cathode, electron, simulation	567
	A. Arnold, H. Buettig, D. Janssen, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, J. Teichert, R. Xiang FZR, Dresden T. Kamps, D. Lipka, F. Marhauser BESSY GmbH, Berlin G. Klemz DESY Zeuthen, Zeuthen W.-D. Lehmann IfE, Dresden A. Matheisen, B. van der Horst DESY, Hamburg J. Stephan IKST, Drsden V. Volkov BINP SB RAS, Novosibirsk I. Will MBI, Berlin
	At the Forschungszentrum Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF-Photo-Gun) is nearly finished. One of the main attention was focussed at the treatment of the cavity. Their RF properties were measured at room temperature. The warm tuning was carried out considering pre-stressing and tuning range of both tuners (half cell and full cells). The adjusted field profiles and pass band frequencies of the four fundamental modes met the requirements. An external Q study of the main coupler yielded to an optimal antenna length and showed very good agreement between simulation and measurement. Furthermore the characteristics of the choke filter and both HOM filters were simulated, measured and tuned at the pi-mode frequency. The preparation (etching and rinsing) and the cold test were successfully done at DESY. The poster presents the setup for the measurements as well as a comparison of the simulated and measured results. Submitted as poster to the 2006 FEL conference

THPPH025	Design of the Cavity BPM for FERMI@ELETTRA	dipole, simulation, undulator, electron	613
	P. Craievich, D. Castronovo, M. Ferianis ELETTRA, Basovizza, Trieste M. Poggi INFN/LNL, Legnaro, Padova
	The Beam Position Monitors (BPM) are fundamental diagnostics for a seeded FEL, like FERMI@ELETTRA, as they allow to measure the electron beam trajectory non destructively and on a shot-by shot basis. A cavity BPM provides sub-micrometer resolution relying on excitation of the TM110 dipoles modes by beam when it passes through the cavity off axis. Therefore for the seeded FEL FERMI, we adopted a set of cavity BPMs to be located upstream the modulating undulator to correct the electron beam trajectory to the micrometer level. In this paper we first discuss the requirements for this cavity BPM including that for beam based alignment. The scaling from an X-band design to the final C-band design is presented. The resolution to stay below one micrometer has been cross-checked both analytically and numerically, The losses of the common mode TM010 have been checked for too, leading to the final dimensions preserving the losses of the X-band cavity BPM.

THPPH054	Linac Coherent Light Source Undulator RF BPM System	dipole, undulator, linac, vacuum	706
	R. M. Lill, L. H. Morrison, G. J. Waldschmidt, D. R. Walters ANL, Argonne, Illinois R. Johnson, Z. Li, S. Smith, T. Straumann SLAC, Menlo Park, California
	The LCLS will be the world's first x-ray free electron laser when it becomes operational in 2009. LCLS is currently in the construction phase. The beam position monitor (BPM) system planned for the LCLS undulator will incorporate a high resolution X-band cavity BPM system described in this paper. The X-band cavity BPM system will provide high-resolution measurements of the electron beam trajectory on a pulse-to-pulse basis and over many shots. The X-band cavity BPM size, simple fabrication and high resolution make it an ideal choice for the LCLS beam position detection. We will discuss the system specifications, design, and prototype test results.