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| MOPPH001 | Quantum Electrodynamics Theory of a Multimode Undulator Oscillator | |
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| We have studied the operation of a free electron oscillator (FEO) in a multimode regime. Our device includes a long undulator, two mirrors and a space-uniform e-beam of a Gaussian energy spread. Using the Heisenberg picture and neglecting both the contributions of the electron intrinsic magnetic moment and the positron fields we have derived a set of temporal equations for the operators of the electron and electromagnetic fields. The set correctly describes both the evolution of the modes’ fields from a spontaneous noise and the process of amplification. We have neglected the nonlinear losses and studied a non steady-state lasing regime. Namely, applying a perturbation theory for the electron operators and a technique of slowly varying functions for the electromagnetic field operators we have calculated the operators of the electric fields. Using this result we have estimated the oscillator energy flux in the forward direction. It is shown that within the framework of the chosen model the total flux is a sum of fluxes of unlocked modes. We have estimated the oscillator line width, the number of activated modes and, as a result, the power of the FEO that operates in the exponential regime with unlocked modes. | ||
| MOPPH002 | Generation of Short Pulses by an Undulator Oscillator with an Electron Absorber Placed into Cavity | |
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| We have considered the operation of an e electron oscillator, which contains a long undulator, two mirrors, a space-uniform e-beam and an absorber which allows tuning the lifetime of the electrons within the cavity. Our study is based on the quantum electrodynamics approach. Using a Heisenberg picture we have derived two temporal deferential equations for the electromagnetic field operators. The equations describe the electron absorption by the absorber as well as a wide-band spontaneous noise produced by the electron, and the process of the amplification of the activated modes by the electron beam. To maintain a constant value of the system gain we have adopted that there is a pumping mechanism, which compensates the process of the electron absorption and supports the same density of the active medium. We have estimated the oscillator energy flux in the forward direction at a fixed point. It is shown that the device produces a chain of pulses. Since the contribution of losses is omitted the pulse amplitudes exponentially increase in time. The duration of the pulses may be short due to the large number of the locked modes. | ||
| MOPPH003 | VOLC: Volume Free Electron Laser Simulation Code | 14 |
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First lasing of Volume Free Electron Laser (VFEL) in mm wavelength range was obtained recently*. Мulti-wave volume distributed feedback where electromagnetic waves and electron beam spread angularly one to other in a spatially-periodic target is the VFEL distinctive feature**. Mathematical model and numerical methods for VFEL nonlinear stage simulation were proposed*** and implemented in computer code VOLC that means "VOLume Code". It was developed on the basis of multiple Fortran codes created in 1991-2006 years. VOLC allows to simulate different geometries of two- and three-wave VFEL in amplifier and oscillator regimes. Electron beam is modelled by averaging over initial phases of electrons. Dimensionality is 2D (one spatial coordinate and one phase space coordinate) plus time. All numerical results obtained using VOLC are in good agreement with analytical predictions of VFEL theory. Different roots to chaos in VFEL were investigated using VOLC. Some successful simulations of VFEL experimental setup at INP were carried out. A description of VOLC possibilities and representative numerical results are presented.
* V. G. Baryshevsky et al., NIMA483 (2002) 21. ** V. G. Baryshevsky, NIMA445 (2000) 281. *** K. Batrakov, S. Sytova, Computational Mathematics and Mathematical Physics 45 (2005) 666. |
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| MOPPH004 | Measurement and Analysis of CSR effects at FLASH | 18 |
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| The vacuum-ultra-violet Free Electron Laser in Hamburg (FLASH) is a linac driven SASE-FEL. High peak currents are produced using magnetic bunch compression chicanes. In these magnetic chicanes, the energy distribution along an electron bunch is changed by effects of Coherent Synchrotron Radiation (CSR). Energy changes in dispersive bunch compressor chicanes lead to transverse displacements along the bunch. These CSR induced displacements are studied using a transverse deflecting rf-structure. Recent experiments and simulations concerning the charge dependence of such transverse displacements are presented and analyzed. In these experiments an over-compression scheme is used which reduces the peak current downstream the bunch compressor chicanes. Therefore other self interactions like space charge forces which might complicate the measurements are suppressed. | ||
| MOPPH005 | Improvements of the Tracking Code Astra for the Simulation of Dark Current Losses in the FLASH Linac | 22 |
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| 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. | ||
| MOPPH006 | Longitudinal Wake Field for an Electron Beam Accelerated through a Ultra-High Field Gradient | 26 |
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| Electron accelerators with higher longitudinal field gradients can produce high-energy beams with compact, cheap setups. Laser-plasma acceleration appears to constitute the more promising breakthrough in this direction, delivering field gradients up to TV/m. Here we describe the impact of longitudinal wake fields on the electron beam, based on solution of Maxwell's equations for the longitudinal field. We consider an acceleration distance much smaller than the overtaking length (the length that electrons travel as a light signal from the tail of the bunch overtakes the head of the bunch), that is the case for laser-plasma devices. We give expressions for impedance and wake function that may be evaluated numerically. We show that the rate of energy loss in the bunch due to radiative interaction is equal to that of coherently radiated energy in the far-zone. A limiting expression is found for a large distance of the electron beam from the accelerator compared with the overtaking length. We derive analytical solutions for a Gaussian transverse and longitudinal bunch shape. We apply our analytical asymptote by studying the feasibility of a Table-Top FEL based on laser-plasma driver. Numerical estimations indicate that the effects of the time-dependent energy change induced by the longitudinal wake pose a serious threat to the operation of this device. (See DESY 06-222) | ||
| MOPPH007 | Theory of Nonlinear Harmonic Generation in Free-Electron Lasers with Helical Wigglers | 30 |
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| Coherent Harmonic Generation (CHG), and in particular Nonlinear Harmonic Generation (NHG), is of importance for both short wavelength Free-Electron Lasers (FELs), in relation with the achievement of shorter wavelengths with a fixed electron-beam energy, and high-average power FEL resonators, in relation with destructive effects of higher harmonics radiation on mirrors. In this paper we present a treatment of NHG from helical wigglers with particular emphasis on the second harmonic. Our study is based on an exact analytical solution of Maxwell's equations, derived with the help of a Green's function method. In particular, we demonstrate that nonlinear harmonic generation (NHG) from helical wigglers vanishes on axis. Our conclusion is in open contrast with results in literature, that include a kinematical mistake in the description of the electron motion. (See DESY 07-058) | ||
| MOPPH008 | Unaveraged Three-Dimensional Modelling of the FEL | |
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| A new three-dimensional model of the FEL is presented. A system of scaled, coupled Lorentz-Maxwell equations are derived in the paraxial limit. A minimal number of limiting assumptions are made and the equations are not averaged in the longitudinal direction of common radiation/electron beam propagation, allowing the effects of coherent spontaneous emission and non-localised electron propagation to be modelled. The equations are solved numerically using a parallel Fourier split-step method. | ||
| MOPPH009 | Undulator Radiation in a Waveguide | 34 |
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| 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) | ||
| MOPPH010 | Three-Dimensional Analysis of the Surface Mode Supported by a Reflection Grating | 38 |
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| In a Smith-Purcell Free-Electron Laser (SP-FEL), the electron beam interacts with the surface mode supported by a metallic reflection grating to produce coherent radiation. All the previous analyses of SP-FEL had considered the localization of the surface mode only in the direction perpendicular to the grating surface and assumed translational invariance along the direction of grooves of the grating. In this paper, we include the localization of the surface mode along the direction of grooves and study the three-dimensional structure of the surface mode in order to include diffraction effects in the analysis of SP-FELs. Full three-dimensional Maxwell-Lorentz equations are derived for the self-consistent nonlinear analysis of SP-FELs. | ||
| MOPPH011 | Comparison Between Kinetic and Fluid Description of Plasma-Loladed Free-Electron Laser | 42 |
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In the kinetic treatment of the plasma-loaded FEL in Ref.* single particle equation of motion, for both beam and plasma electrons in the radiation fields, are used. Therefore, interaction terms between the wiggler and the space-charge wave, in the transverse velocity of electrons, which are important elements in the fluid model, are neglected. A dispersion relation of a plasma-loaded FEL with kinetic theory is found in Ref.* that takes into account the velocity spread of both beam and plasma electrons. In the present analysis, a dispersion relation is obtained, by the fluid theory, with the interaction terms between the wiggler and the space-charge wave in the transverse velocity of electrons taken into account. Since these interaction terms are inherently missing in the kinetic theory the two dispersion relation are compared to find out about the importance of these terms. It was found that although the absence of these terms has considerable effects on the growth rate, the general kinetic dispersion relation may be used to study the temperature effects of a warm beam/plasma on the instability of a free-electron laser with a plasma background.
* S. Babaei and B. Maraghechi, "Kinetic description of plasma-loaded free-electron laser", Phys. Plasmas, to be published. |
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| MOPPH012 | Conservation Laws in Quasilinear Theory of Raman Free-Electron Laser | 46 |
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| A quasilinear theory of the free-electron laser, in Raman regime, is presented to establish that conservation laws on number, energy, and momentum are upheld. A high density electron beam is assumed so that the space-charge potential is no longer negligible. A sufficiently broad band spectrum of waves is assumed so that saturation will be due to the quasilinear spread of the beam electrons. Otherwise, for the single mode excitation, saturation will be due to the electron trapping in the space-charge potential. It is shown that the quasilinear slow variation of the background distribution function is in the form of the diffusion equation in momentum space. An expression for the time evolution of the spectral energy density is derived. Conservation laws to the quasilinear order (second order) are derived and are proved to be satisfied. Results of the present investigation may be used to study the quasilinear saturation of free-electron laser in the presence of the space-charge wave. | ||
| MOPPH013 | Raman Scattering of a Perturbed TM Mode in a Dielectric Loaded Plasma Waveguide | |
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| The stimulated Raman scattering of a perturbed TM mode in a dielectric loaded partially filled plasma waveguide is considered. The radiation is the result of the scattering of the pump electromagnetic wave, which is EH waveguide mode, off of a space-charge wave. In the analysis, a non linear wave equation for the three-wave interaction is used to investigate the coupling of the space-charge and the waveguide modes. Dispersion relations for electromagnetic modes are solved numerically to study the frequency characteristics of the interaction of the EH waveguide modes with the space-charge modes. Formulas for the spatial and temporal growth rates of the backscattered wave near the electron cyclotron frequency are derived and the effect of the dielectric liner on the growth rates is investigated. The numerical studies show that the presence of the dielectric liner has an effect on the phase matching condition and leads to a rather larger growth rates close to the electron cyclotron resonance. | ||
| MOPPH014 | Velocity Shot Noise, Space Charge Effects and Coherence Enhancement Schemes in SASE FEL | |
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| We employ a formulation of the linear transfer matrix of FEL to explore new operating schemes and limiting effects in the high gain regime of FEL. These include analysis of SASE seed radiation injection, pre-bunching schemes, study of the role of velocity shot noise and collective (space charge effects). We propose new schemes for enhancement of the temporal coherence of SASE radiation, and study them by employing the transfer matrix formulation. The numerical computations indicate that X-Ray pulses, spatially and temporally (Fourier transform limited) coherent, are attainable with available high gain FEL parameters. The theoretical model is based presently on single transverse mode excitation (optically guided). Extension to a multi transverse modes excitation model will be outlined. | ||
| MOPPH015 | Limit for Harmonic Conversion in a Single Cascade of Coherent Harmonic Generation | 50 |
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Harmonic generation is a reliable method for producing coherent high-brightness photon pulses from relativistic electron bunches. The standard process leading to Coherent Harmonic Generation (CHG) is initiated by a powerful seed laser. As a consequence, reaching short wavelengths generally requires a high order frequency conversion. For that reason some of the projects which are presently under development for coherent VUV and soft-Xray emission are based on a series of two or more consecutive "cascades". In these setups, the radiation produced into one CHG stage is used as a seed in a following CHG cascade. The required number of cascades is related to the maximum harmonic conversion which can be obtained in single stages. In this paper the mechanism underlying the CHG, i.e. the bunching creation into the modulator, is studied in detail and the physical limits for the single-stage CHG are investigated. The identification of the limiting parameters may allow the implementation of new methods for enhancing the conversion efficiency. One of these methods, which relies on a simple modification of the standard CHG scheme, has been recently proposed* and shown to be able to significantly improve the system performance. Results are confirmed by numerical simulations using the codes Ginger and Genesis. Expected impact on some of the existing projects for CHG is also presented.
* E. Allaria, G. De Ninno, Phys. Rev. Lett., to be published. |
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| MOPPH017 | 1D Linear Intensity Spiking Evolution in a Single Shot of a SASE FEL | 54 |
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| The analysis is based on the 1D Maxwell-Lorentz equations which are reduced to the usual averaged linear equation in the limit of vanishingly small radiation field A(z,t) and average length lm. It is shown that if this equation is solved with initial shot noise conditions in which the widths of the spikes and the average distance between successive spikes are both uniformly smaller than the cooperation length Lc, it may lead to large amplitude coherent signals. The intensity spiking RMS relative amplitude decreases from the 100% values it has at t=0, down to values of the order or less than 0.1% in time intervals from ten to twenty gain times. | ||
| MOPPH018 | Particle-in-cell Simulation of Two-stream Smith-Purcell Free-electron Laser | |
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| An approach to enhancement of terahertz (THz) Smith-Purcell (SP) radiation from an open rectangular grating driven by two electron beams is presented in this paper. The two electron beams with a velocity separation propagate over the grating. With the help of a two-dimensional particle-in-cell (PIC) simulation, some nonlinear processes from spontaneous emission to superradiant radiation are demonstrated. The optimum voltage ratio is obtained where the SP radiation power achieves the maximum. The simulation results show that the enhancements of radiation power, the shortened saturation time, and the decrease of critical current for spontaneous SPR to superradiant at a proper voltage ratio. The simulation results can correspond to the linear analyses. | ||
| MOPPH019 | Optimized Designs for CAEP IR Free-electron Laser | 58 |
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| The characteristics of CAEP IR free-electron laser are estimated and the optimized designs of the resonator parameters such as radius of output hole, the size of mirror, the resonator length is carried out using our 3D FEL oscillator code. Based on the appropriate parameters, the saturated power, output power, gain and construction of optical modes are calculated. | ||
| MOPPH020 | FEL with Orotron Type Feedback | 61 |
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| In microwave electronics orotron is widely used as a source of RF radiation in millimeter and submillimeter wavebands. In this device an electron beam is coupled to a mode of quasi-optical resonator by means of the periodical grating one of the resonator mirror. In our paper we discuss a relativistic modification of such a device. A novel FEL scheme is suggested in which the slow wave structure of orotron is replaced by shallow Bragg corrugation which provides the coupling of the transverse (with respect to direction of beam propagation) mode of a two-mirror cavity with longitudinally propagating wave. The latter can be excited by the electron beam wiggling in undulator field. Described scheme allows to combine selective properties of an orotron with relativistic frequency conversion of a free electron laser. The transverse mode provides the feedback in the system thus leading to self-excitation, while the propagating wave is responsible for energy extraction in the steady-state regime of operation. The discussed system was investigated both analytically and numerically using direct codes and averaged equations approach. | ||
| MOPPH021 | Karat Pic-Cod Simulation of Smith-Purcell Radiation from Gratings with Different Profiles | |
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| Particle-in-cell simulation of Smith-Purcell radiation from gratings with lamellar, triangle, "volume" and "flat" profile using PIC-code KARAT is carried out. The paper present some calculation results compared with experimental data obtained on the 6-Mev microtron. It is shown that the maximal SPR yield for different gratings are in agreement with experiment. | ||
| MOPPH022 | A Description of Guided FEL Radiation Using Dielectric Waveguide Eigenmodes | 65 |
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| An analysis of the radiation field of an FEL in terms of eigenmodes of a linear dielectric waveguide is presented. | ||
| MOPPH023 | Enhancing FEL Power with Phase Shifters | 69 |
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| Undulator taper is a well-known technique to increase the FEL efficiency past saturation by maintaining the resonant condition. In this paper, we demonstrate that shifting the electron bunch phase relative to the radiation is equivalent to tapering the undulator parameter. Using discrete phase changes derived from optimized undulator tapers for the LCLS x-ray FEL, we show that placing appropriate phase shifters between undulator sections can reproduce the power enhancement of these undulator tapers. The phase shifters are relatively easy to implement and operate, and hence can be used to aid or replace the undulator taper for optimizing the FEL performance. | ||
| MOPPH025 | Three-dimensional Theory of the Cerenkov Free-Electron Laser | 73 |
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| We present an analytical theory for the operation of a Cerenkov free-electron laser which includes diffraction of the optical mode in the direction transverse to the electron beam. Because the width of the optical mode depends on the gain, the usual cubic dispersion relation is replaced by a 5/2-power dispersion relation, however, only two of these roots are allowed. These two roots both have positive real parts, indicating that they are slow waves. For a narrow electron beam, the optical mode is much wider than the beam, thus reducing the gain by an order of magnitude from that predicted by the two dimensional theory. In the limit of a wide electron beam, the two dimensional theory is recovered. | ||
| MOPPH026 | Three-Dimensional Theory of the Smith-Purcell Free-Electron Laser | 77 |
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| We present an analytic theory for the operation of a Smith-Purcell free-electron laser (SPFEL) that includes transverse diffraction of the optical beam. For the case of an infinitely wide electron beam, this theory agrees with previous two-dimensional analyses. When the electron beam is narrow compared to the mode, the gain (amplifier regime) is substantially reduced by diffraction, while its dependence on the beam current is increased due to gain guiding. A 5/2-power dispersion relation replaces the conventional cubic dispersion relation. Additionally, the constituent waves of the laser mode are found to have different transverse decay rates. An estimate of the start current (oscillator regime) of the device is obtained by satisfying the appropriate boundary conditions on the beam axis. | ||
| MOPPH027 | Status of the KAERI THz FEL for the Application on Security Inspection | |
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| Terahertz (THz) technology has been considered as a new tool for security inspection due to its safe energy range to human irradiation, foot-print spectral characteristics for most chemicals and bio-materials, and relatively high spatial resolution for imaging. One of the main tasks in the THz inspection technology is to develop a high power and compact source to realize a real-time imaging. We have developed a compact terahertz (THz) free electron laser (FEL). The FEL operates in the wavelength range of 100–1200 micrometers, which corresponds to 0.3–3 THz. THz radiation from the FEL shows much higher power of 100 W when compared to the power level, < 100 mW, of the table-top sources by conventional lasers. The THz FEL beam shows a good performance in pulse-energy stability, polarization, spectrum and spatial distribution. We report the experimental studies of the transmission and reflection-type scanning imaging of baggage and a window dummy. The required power level of the THz sources is estimated for the practical applications of the inspection imaging. | ||
| MOPPH028 | On NMR probing of the kinetics of a free-electron laser-induced chemical exchange | 81 |
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Determination of the quantum yields of photochemical reactions (in particular, molecular photoisomerization reactions) is an efficient application of NMR spectroscopy*,**. We are proposed a combined approach for study the kinetics of photo-induced chemical exchange (PICE) reactions (see Scheme), which involves a free-electron laser (FEL) and NMR spectroscopy**. Scheme hv A↔B Continuous and pulse IR-irradiation of the chemical system in the presence of PICE can be achieved using FEL. Based on the analytical equations derived in the work we consider the time-dependent dynamics of variation of the instant NMR line shape for two-site chemical exchange. If one induce an abrupt increase in the rate constant of chemical exchange (for example, by quickly heating the system or PICE), then the NMR line shape will change with time, ultimately reaching another new steady state. Our calculations show that there are beats and oscillations (on the NMR line shape) damped with time. The information about the time-dependent instant line shapes provides possibility to predict the real kinetics of PICE. Prospective objects are molecular conformers and spin isomers. So, FEL can be used in the setup for PICE studies in combination with a NMR spectrometer.
* S. P. Babailov, E. M. Glebov, et al., Concepts in Magn. Reson., 2006, 8, 571. ** S. P. Babailov, Russ. Chem. Bull., Int. Ed., 2006, 10, 1631. |
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| MOPPH029 | Nondestructive Transfer of Complex Molecular Systems into Aerosol Phase by Means of Terahertz Irradiation of Free Electron Laser | |
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Original investigations of ablation of various substances under the action of submillimeter radiation of the free electron laser (FEL) developed and built at Budker Institute of Nuclear Physics were carried out at the Chemical and Biological user station of the Siberian Center for Photochemical Research. It was shown that ablation can be nondestructive. In order to determine the size distribution of aerosol products, we used the Diffusion Aerosol Spectrometer (DSA) developed at the ICKC SB RAS* and sampling for examination with electron microscope. The arrangement of experiments and equipment involved allowed us to determine the disperse composition of irradiation products within particle size range 3nm – 10mkm. At the present moment we have classified the aerosol products of ablation of the following substances: Crustal minerals, Fullerene-like complexes based on molybdenum; Polymers with different molecular masses, Biological macromolecules**. The most impressive results are obtained under ablation of biological macromolecules. In order to reveal whether the enzymatic activity of ablation products is conserved, we carried out a test for histochemical coloring of the collected aerosol of horse radish peroxidase. The test showed that this complicated enzyme remained active after ablation. We believe that this result is extremely important for biotechnology.
* A. N. Ankilov et al. Atmospheric Res., 2002, 62, 209-237.** A. K. Petrov et al. Nuclear Inst. and Methods in Physics Res., 2007, 575, 68-71. |
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| MOPPH030 | Terahertz Imaging and Radioscopy with 160x120 Microbolometer 90 fps Camera | 83 |
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| Uncooled micromolometer camera for IR and THz high-speed imaging has been developed. The 160x120 focal plane array consists of resistive vanadium oxide elements on a silicon nitride bridge. The element size is 48x48 micron at 51 micron array period. We describe device fabrication process and focal plane array operational characteristics. The camera was used as a recorder in quasi-optical systems with Novosibirsk terahertz free electron laser as a radiation source. Radioscopy of the objects, which are of interest for biology and security applications, has been demonstrated. The recording rate up to 90 frames per second has been obtained. | ||
| MOPPH031 | Spectroscopy and Spectrally Resolved Radioscopy of Biological Substances Using Terahertz Free Electron Laser Radiation | 86 |
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| High average power and monochromacity of terahertz Novosibirsk free electron laser are favorable for the development of time and space resolved spectroscopic and radioscopic techniques for study of highly absorbing substances, in particular, biological ones. To study highly absorbing objects we applied a homemade attenuated total reflection spectrometer, which enables operation in both conventional and imaging mode. By measuring the reflection coefficients for p- and s-polarized radiation, the real (n) and imaginary (k) parts of refractive index can be derived. Using a microbolometer matrix (see the paper by Esaev et al. at this conference), imaging radioscopy of the samples containing amino acids and DNA had been performed. The methods developed were applied also for examination of bones of intact and senescence-accelerated mice that, probably, would lead to study osteoporosis development. | ||
| MOPPH032 | Development of Metal Mesh Based Quasi-optical Selective Components and Their Application in High-power Experiments at Novosibirsk Terahertz FEL | 89 |
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| Successful realization of terahertz research programs at the Novosibirsk FEL-facility requires detailed development, designing and optimization of passive quasi-optical selective components, intended for polarization and frequency gating of powerful THz-beams of NovoFEL radiation. Along with desired selective characteristics such components should be capable of operating over a long period of time under high-power load conditions (a few hundred Watts of average incident radiation power) without noticeable degradation of their properties. It admits to employ in selective components only low absorbing and thermostable materials, such as high conductivity metals and special types of polymers. This report is devoted to development of metal mesh based selective structures, such as polarizing beamsplitters (attenuators) and different frequency filters, and their application in high-power THz-experiments. Possibilities and prospects of two main production technologies are discussed: 1) conventional photolithography destined for manufacturing thin metal structures deposited on low-absorbing thermostable polymer films; 2) LIGA-technique intended for producing thick substrate-free metal structures. | ||
| MOPPH033 | Diffraction Optical Elements and Optical Systems with a High Power Monochromatic Terahertz Source | 93 |
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| We have developed reflective diffraction optical elements (DOE) for focusing radiation of terahertz free electron lasers (FEL). Metal-dielectric Fresnel zone plates and metallic kinoform "lenses" were fabricated and tested using FEL radiation. A microbolometer camera (see the paper by Esaev et al. at this conference) sensitive to THz radiation had been applied for recording both terahertz beam caustic and terahertz images. Diffraction efficiency of a kinoform lens appears to be about unity. Quality of images obtained with the kinoform lens was studied. The lens was used as a key element for a Toepler optical system, which were used for studying condense matter non-uniformities and deformations. The experiments were performed at Novosibirsk and KAERI FELs. | ||
| MOPPH034 | Diagnostics of an Electron Beam using Coherent Cherenkov Radiation | 95 |
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| A comparison of coherent Cherenkov and transition radiations as a diagnostic tool for longitudinal distribution of an electron beam is studied in this paper. Two methods will be used for the 7th harmonic bunching experiment at Neptune linear accelerator facility at UCLA. Coherent Cherenkov radiation is produced in an aerogel with an index of refraction close to unity. | ||
| MOPPH036 | First Experiences with the FIR-FEL at ELBE | 97 |
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| We show the design and the parameters of operation of the long-wavelength (U100) FEL of ELBE. First lasing has been shown in August, 2006. Since then, the laser has undergone thorough commissioning and is available for user experiments since fall, 2006. Besides in-house users the IR beam is available to external users in the FELBE (FEL@ELBE) program witch is a part of the integrated activity on synchrotron and free electron laser science in the EU. At the beginning of 2007 lasing in the full designed wavelength range from 20μm to 200μm was demonstrated. The laser power typically reaches several W in CW operation but drops for very long wavelengths depending on the size of the used outcoupling hole. However, there exists a serious problem with small gaps in the providable wavelength spectrum. We attribute this behaviour to the transmission characteristics of the overmoded partial waveguide used from the undulator entrance to the first mirror. | ||
| MOPPH037 | Characterization of a New High-Q Talbot Effect Confocal Resonator for mm-Wave FEL | |
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| A new FEL resonator for mm- wave range was assembled and characterized before installation into the high voltage terminal of the Tandem electrostatic FEL accelerator. The measured unloaded Q-factor of the new resonator is Q=30,000. Accordingly, the round-trip losses are ~18% for the total length of the resonator about 1.5m The reflector of the new resonator utilizes in one transverse dimension the Talbot effect for imaging and splitting the radiation mode field for the purpose of the laser radiation. In the other transverse dimension optical imaging is realized by means of two confocal mirrors. A 3-wire grid assembly, remotely controlled, provides fine tuning of the laser frequency and control over the resonator out-coupling coefficient. The new resonator includes an integral e-beam profile diagnostics means installed on the safety shield. All e-beam diagnostics and tuning motors are remote controlled in a Lab View environment. | ||
| MOPPH038 | Experimental and 3D Simulation Studies of the Spectral Characteristics of Electrostatic Accelerator FEL with Space Charge Dominated Transport | |
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| One of the important properties of the FEL it is the ability to generate high power radiation within a wide frequency range. By varying the acceleration energy of the tandem electrostatic FEL in the range 1.3-1.44 MeV we tuned the FEL lasing radiation between 80GHz to 110GHz. The tuning range is limited by the resonator frequency dispersion one hand and the beam trajectories on the other hand. At low acceleration energies space charge effects make it difficult to keep the electron trajectories in the wiggler confined to the axis. Because of this and because of difficulty to keep optimal e-beam injection parameters into the wiggler, the oscillation threshold is reduced and the tuning range of the FEL is limited. The finite size of the e-beam inside the wiggler also has a reduction effect on the lasing frequency. The measured spectral tuning characteristics of the FEL matches well the results of FEL lasing 3-D simulation (with FEL3D). The electron trajectories and the beam transport were calculated with GPT simulations in the space charge dominated regime. | ||
| MOPPH039 | Sideband Instability in a Compact THz Free-Electron Laser at KAERI | |
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| Frequency offset of a Sideband instability has been observed in a compact waveguide-mode terahertz (THz) free-electron laser (FEL). The spectra of the FEL pulses were measured by a Fabry-Perot spectrometer having a resolution of 10(-4) of the central wavelength at a 2-3 THz range. The shift of the sideband was measured to be 0.5-1.2 micrometers depending on the FEL wavelength from 110 to 165 micrometers. An increase of the sideband shift for a longer wavelength can be explained by the change of the wave’s group velocity in a plane-parallel waveguide. Mode competition between the sidebands and primary wave was observed by changing the cavity length of the FEL. We could decrease the number of the modes and reduce the linewidth of the spectra by controlling the cavity detuning. We have discussed the complexity of the sideband instability depending on the FEL wavelengths and its gain characteristics. | ||
| MOPPH040 | A Study of Detection Schemes in Electro-Optic Sampling Technique | 101 |
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| Electro-Optic Sampling (EOS) is the ingenious tool for the measurement of the electron beam or Thz radiation. There are two traditional detection schemes: one is the crossed polarizer scheme and another is balanced detection one. A new detection scheme called Near Crossed Polarizer scheme in the EOS technique is developed to increase the Signal to Noise Ratio in the experiment. The new detection scheme is studied in detail and the 3D scanning result with electron beam in FLASH is compared with the detection scheme. The new detection scheme has an analytical problem which shows two solutions for the relative phase shift for specific measurement of the electron beam. That problem is also studied through the comparative study between simulation and the analyzed data from the TEO setup in FLASH. | ||
| MOPPH041 | Comparative Study of Electro-Optic Effect between Simulation and Measurement | 104 |
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| The short, intense, and low emittance electron beams are crucial to make high quality X-ray beam for X-ray free electron laser (XFEL). Electro-Optic Sampling (EOS) is a promising method to measure the electron bunch length non-destructively. A simulation study is done with the pulse propagation method, which utilizes Fourier transform to investigate the evolution of electromagnetic pulse inside the electro-optic (EO) crystal. The experimental result measured with spatial decoding method at Free electron LASer in Hamburg (FLASH) facility in Deutsches Elektronen-Synchrotron (DESY) is analyzed in terms of the relative phase shift between the horizontal and vertical component of the laser pulse. In this report, the experimental results expressed in terms of the "Relative Phase Shift Г" are compared with the simulation result. The simulation and the experimental result show similar values within reasonable error. The way to increase the signal level is also proposed. | ||
| MOPPH042 | Losses in Optical Resonator of Novosibirsk Terahertz Free Electron Laser: Theory and Experiment | 107 |
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Design of optical resonator of Novosibirsk terahertz free electron laser (NovoFEL)was made on base simple analitical theory discribed in paper*. Direct comparison of the theory and many experiments on NovoFEL is presented.
* Kubarev V. V. Babinet principle and diffraction losses in laser resonators. Quantum Electronics 30(9)824-826(2000). |
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| MOPPH043 | Control and Diagnostic System of Novosibirsk FEL Radiation | 111 |
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| The architecture the main capabilities of control and diagnostic system of the Novosibirsk FEL coherent radiation are described. The client-server model is used for software, controlling this system. The developed software is capable to work both in client and server mode. Also it can control various equipment – from FEL optical cavity mirrors to local equipment of users stations. The mode of control program operation and controlled equipment are determinates by external configuration files. Some results of the system operation are also presented. | ||
| MOPPH044 | Status of Novosibirsk ERL and FEL | |
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| The Novosibirsk terahertz free electron laser is based on the energy recovery linac (ERL) with room-temperature radiofrequency system. Some features of the ERL are discussed. The results of emittance measurements and electron optics tests are presented. The first stage of Novosibirsk high power free electron laser (FEL) was commissioned in 2003. Now the FEL provides electromagnetic radiation in the wavelength range 110 - 230 micron. The average power is 400 W. The minimum measured linewidth is 0.3%, which is close to the Fourier-transform limit. Four user stations are in operation. The second stage of the ERL, which has four orbits, is under construction. | ||
| MOPPH045 | Measurement of timing jitter based on HGHG FEL spectrum dynamics | |
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| We discuss impact of temporal shift between seed laser and electron beam on the HGHG FEL radiation spectrum. Following analysis of experimental data reveals basic properties of the time jitter in the accelerator-FEL driver at Source Development Lab (BNL). | ||
| MOPPH046 | Operation of Near-infrared FEL at Nihon University | 114 |
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| The near-infrared FEL at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University has been operated for a variety of scientific applications since 2003. The stability of the FEL power was improved appreciably by the advanced stability of the 125 MeV electron linac. Currently fundamental FEL wavelength ranges from 1 to 6 microns, which is restricted by the electron energy and the optical devices. The higher harmonics in the visible region is also available. The maximum macropulse output energy of 60 mJ/pulse has been obtained at a wavelength of 1725 nm. The short FEL resonator at LEBRA causes relatively high optical energy density on the surface of the resonator mirrors; present copper-based Ag mirrors in use at LEBRA are not durable enough for long term operation. As an alternative way of generating intense harmonics in the visible to near-UV region, second and third harmonic generation by means of non-linear optical devices has been tested for the FELs around 1.5 microns as input fundamental photons. | ||
| MOPPH047 | Influence of Terahertz Electromagnetic Radiation on Neurons In-vitro | |
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| Isolated neurons of mollusk in vitro at various stages of network neogenesis were studied earlier. The influence of submillimeter laser radiation (from 70 up to 418 mkm) it was investigated. 40-50 hours after laser irradiation (81.5 mkm) the formation of heterogeneities of the cell surface with the subsequent creation of arbitrarily directed process - like frames is observed in 12-15% of cells which were at the process shaping stage. In neurons which have formed processes, 15-20 hours after the exposition there is disturbance in the processes growth zones. The disturbance of formation of interneuron connections and thickening of processes terminations are observed. Similar alterations of cells are absent at smaller power density, exposition at other wavelengths, and in control neurons (without exposure). There is disturbance of cell adhesion to surface in 70-80% of neurons after irradiation at 418-mkm wavelength. Experiments on high power Novosibirsk teraherz free electron laser have shown influence of such radiation on functional characteristics alive neurons. The alterations observed can be the result of a modification of separate (possibly, individual) molecules of neuron regulation or structure-forming systems. | ||
| MOPPH048 | ARC-EN-CIEL Project Electron Beam Dynamics | 118 |
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| ARC-EN-CIEL project is based on the development of fourth generation light source of high brilliance and tunable in the UV-X domain. The project will evolved into three phases leading to different light performances: first and second phases are in single pass configuration with energy of 220 MeV and 1 GeV respectively, while third phase comports recirculation loops at 1 GeV and 2 GeV. For delivering a high brilliance light source with high peak power short pulses, the high charge electron beam should have subpicoseconde duration with low emittance and energy spread. In order to keep optimal slice characteristics for light production, phase space non linearities due to optics aberrations and collective effects should be minimized. In ERL configuration, a critical consequence of collective effects is the Beam Break Up instability, which forms a feedback loop between the beam and the cavities. This contribution aims at presenting the electron beam dynamics for the ARC-EN-CIEL project in single pass and ERL configuration, especially on the conditions for minimizing non linearities and Beam Break Up instability. | ||
| MOPPH050 | Status of the Undulator System of the Seeded HGHG-FEL Test Bench at MAX-lab | 122 |
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| Within the EUROFEL Design Study a seeded HGHG-FEL will be set up at the 400 MeV linac at MAX-lab. The undulators and the dispersive section have been installed. A glass fibre based power meter system for integrated dose measurements as well as a Cherenkov system for a fast detection of electron losses have been integrated. We report on the performance of all components. Simulations on the acceptable radiation doses inside the undulator magnets will be presented. In the first step of commissioning the THz radiation as produced by the bunched electron beam inside the dispersive section will be used for the optimization of the longitudinal and transverse overlap of the electron beam and the laser beam. | ||
| MOPPH051 | Nonlinear Harmonic Generation in the BESSY Soft X-Ray FEL | 126 |
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| Free Electron Lasers do not only radiate at the fundamental frequency, they may also radiate coherently at higher harmonics. This process is referred to as nonlinear harmonic generation or NHG. NHG is of high interest, because it extends the FEL output wavelength of FELs to several harmonics of the FEL resonant frequency. In cascaded High Gain Harmonic Generation (HGHG) FELs, harmonic radiation may be used to improve frequency-conversion and reduce the number of HGHG-stages. BESSY proposes to build a cascaded HGHG FEL with three FEL lines. They cover a wavelength range of 51 nm (Low-Energy FEL) to 1.2 nm (High-Energy FEL) and consist of up to four HGHG-stages. In this paper, we present studies of the BESSY High-Energy FEL harmonic content performed with the upgraded version of the simulation code Genesis 1.3. | ||
| MOPPH052 | Output Performance of the STARS HGHG Demonstrator at BESSY | 130 |
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| BESSY is planning to construct a free-electron laser facility (STARS) to demonstrate cascaded high-gain harmonic generation (HGHG) FELs. A 325MeV superconducting linear accelerator will drive two HGHG-stages, where the second stage is seeded by the radiation from the first stage. Such a cascading of the HGHG scheme, originally pioneered by L. H. Yu, allows a reduction of the STARS output wavelength down to the few 10nm range. This paper describes the expected performance of the facility, the achievable wavelength range, the harmonic content of the radiation, the potential of super-radiant pulses and first considerations about the stability of the source. | ||
| MOPPH054 | Small-Aperture Vacuum-Chamber Design for STARS | 134 |
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| 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. | ||
| MOPPH055 | Measurements of the Projected Normalized Transverse Emittance at PITZ | 138 |
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| The main objective of the Photo Injector Test facility at DESY in Zeuthen (PITZ) is the production of electron beams with minumum transverse emittance at 1 nC bunch charge. PITZ consists of a photo cathode RF gun, solenoids for the compensation of space charge induced emittance growth and a booster cavity. In order to study the emittance evolution along the beam line three Emittance Measurement SYstems (EMSY's) were installed downstream of the booster cavity. In a first operation periode in October 2006 the emittance was measured for moderate gun gradients of about 40 MV/m. A new gun cavity is presently installed at PITZ and conditioning up to a gradient of 60 MV/m is ongoing. In this work we present recent results from measurements of the normalized projected transverse emittance of the electron beam. The emittance is measured using the so called single slit technique. Data are presented for different gun and booster gradients, solenoid strengths and initial beam size at the cathode. | ||
| MOPPH057 | Development of mm-Wave TDR Technique for Direct Estimating of the Quality of the FEL’s Resonator Mirrors | |
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Radiated power of the Israeli FEL is greatly dependent on the quality of input/output mirrors of the quasi-optical resonator, where an interaction between electron beam and EM fields is taken placed. Since they are located in the close proximity to the electron beam transport area, the probability of their damaging is increased and regular diagnostics of mirror's quality is urgently required. However, such a diagnostic is time consuming due to the required vacuum-opening. The time domain reflectometry (TDR) method allows estimating the mirror’s quality by means of direct measurements of its power reflectance. We have developed the TDR's experimental set-up in 90-105 GHz permitting to perform such measurements. The key element of this setup is the pulse modulated pin-switch with a rise time of 1-2 ns. The forward and backward signals have been recorded independently using the two separated detectors and Tektronix digital scope. We have investigated the TDR's patterns of various damaged mirrors and conclude that the suggested technique can be recommended for remote diagnostics and estimating their quality without vacuum opening.
Israeli Ministry of Science |
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| MOPPH058 | Status of the SPARX Project | 142 |
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| The SPARX project consists in an Soft-X-ray-FEL facility jointly supported by MUR(Research Department of Italian Government), Regione Lazio, CNR, ENEA, INFN and the University of Roma Tor Vergata. It is the natural extension of the ongoing activities of the SPARC collaboration. The aim is the generation of electron beams characterized by ultra-high peak brightness at the energy of 1 and 2 GeV, for the first and the second phase respectively. The beam is expected to drive a single pass FEL experiment in the range of 13.5-6 nm and 6-1.5 nm, at 1 GeV and 2 GeV respectively, both in SASE and SEEDED FEL configurations. A hybrid scheme of RF and magnetic compression will be adopted, based on the expertise achieved at the SPARC. high brightness photoinjector presently under commissioning at Frascati INFN-LNF Laboratory. | ||
| MOPPH060 | The Drive Laser System for CFEL | 146 |
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| A reliable and compact drive system is one of the key components for the stable operation of FEL. We have developed a solid-state drive laser system to meet the requirements of the CFEL(CAEP FEL) research. The system consisted of a passive mode-locked oscillator with a timing stabilizer,a regenerative amplifier and a frequency conversion part. After the 4-th harmonics,the duration of 15 picoseconds Gaussian pulses with wavelength 266nm at a repetition rate 54.17MHz were obtained. These micropulses were contained within a macropulses envelope as long as 1 to 6μmicroseconds,which was emitted from the drive laser at a repetition rate at 3Hz,6Hz or 12Hz,one single micropulse energy as large as 4μmicroJoules was achieved. The design specifications, configuration and diode-pumped amplifier of the drive laser system are also described. | ||
| MOPPH061 | Design of the PAL Test FEL Machine | 149 |
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| In a road to the PAL-XFEL, the 1st stage will be to build a test machine, whose design parameters are presented here. It will be a 230 MeV machine that has the target wavelength of visible range. The design details and simulation results are shown in this paper. | ||
| MOPPH062 | Features of the PAL-XFEL Design | 152 |
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| The PAL-XFEL design has been revised since the previous conference. The 2nd bunch compressor has been moved to a higher energy to eliminate the space charge effect and the total linac energy has been increased from 3.7 GeV to 4.0 GeV. Details and reasons of these design revisions are explained in this paper. | ||
| MOPPH063 | Potentialities of ELMI Device for Submillimeter Generation by Stimulated Intercavity Scattering in Planar FEM | 156 |
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Paper describes main features of a project on two-stage generation of submillimeter radiation at the ELMI device. This novel variant of a two-stage scheme based on stimulated intercavity scattering was proposed earlier in the paper*. In accordance with the scheme, at the first stage a sheet electron beam drives a 2D Bragg free electron maser (FEM) of planar geometry to generate 4-mm pump wave. At the second stage this wave undergoes stimulated scattering at the supplementary electron beam to produce submillimeter radiation. A key feature of a proposed scheme is to use two sheet beams with a few kiloampers currents that transported in parallel channels, which are connected by a special waveguide* for synchronization of beam radiation in different channels**. Production of two sheet beams by one accelerator diode with two cathodes is also similar to the process of operation of the multibeam diode described in Ref.**. Two-stage scheme allows us to use high power 4-mm radiation produced in the first channel by the sheet beam moving in an undulator quasi-static magnetic field, as an EM-undulator for the secondary stage FEL operating in Terahertz wave range. In the paper we describe results of theoretical and experimental investigations of various aspects of the two-stage scheme and some testing experiments on units for realization of this scheme at the ELMI device.
* A. V.Arzhannikov et al. Proc. Int. Workshop, N. Novgorod, Vol.1,p.228-232,2006.** A. V.Arzhannikov et al. Digest Tech. Papers, PPPS-2001, Las Vegas, Nevada, Vol.1, p.561-564,2001. |
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| MOPPH064 | A Project of SC ERL at KAERI | 160 |
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| A project of an ERL at Korea Atomic Energy Research Institute is described. The ERL will be connected to the existing machine without any modification. It consists of two 180° bents and two straight sections: one is for an FEL, another for a Compton X-ray source. One can choose the regime controlling the lenses. The total ERL is isochronous to avoid any problem with longitudinal beam instability. It will be possible to control both Sx and Sy transormation matrix elements independently to suppress longitudinal beam instability and allow the increase of beam current. Sextuples will be installed in bents to suppress chromatic aberration. This design provides operation in FEL regime with high electron efficiency in the range of electron energies 12–22 MeV. | ||
| MOPPH068 | The NCAS-FEL: an FEL Oscillator with High Slippage | 163 |
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In normal operation of FEL oscillators with little or no slippage, the cavity length needs to be slightly smaller than the synchronous value due to the lethargy in the gain build-up. If the FEL experiences high slippage, i.e., when the slippage becomes comparable or even larger than the length of the electron pulse, a different cavity detuning may be required. We use the one dimensional Medusa1D code to study the NCAS-FEL* as an example of an FEL oscillator having high slippage. Medusa1d is basically equal to the fully three dimensional Medusa code** with the 3D effects stripped out. It includes multiple wiggler segments, electron beam transport elements, harmonics and a simple oscillator model. Medusa1D can also include 3D effects using the fitting formula of Xie***. The NCAS-FEL is a RF-linac based FEL dedicated for high resolution spectroscopic studies in the wavelength range from 100 micron to 1.5 mm. The design of the NCAS-FEL is currently under way, and we report here initial results of this design and focus on the effects of high slippage on cavity detuning and the development of coherence within the optical pulse.
* Proceedings of FEL 2006, Berlin, Germany (2006) p485 - 487 ** Phys. Rev. ST-AB 8, 110701 (2005)*** Nucl. Instrum. Methods Phys. Res., Sect. A 445, 59 (2000) |
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| MOPPH069 | 3D Modelling of the ERLP IR-FEL | 167 |
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| An Energy Recovery Linac Prototype (ERLP) facility is currently being commissioned at Daresbury Laboratory; it serves as a testbed for technologies to be used in the proposed 4th Generation Light Source (4GLS) facility. As part of the ERLP facility, an infra-red oscillator FEL is due to be commissioned early in 2008. In this paper we present full three dimensional, time-dependent modelling of the ERLP IR-FEL using Genesis 1.3 in combination with a paraxial optical propagation code (OPC). We also discuss how this work will be used to inform commissioning of the FEL. | ||
| MOPPH072 | The IR-Beam Transport System from the ELBE-FELs to the User Labs | 171 |
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| In the Forschungszentrum Dresden-Rossendorf, two free-electron lasers (FELs) have been put into operation. They produce laser light in the medium and the far infrared wavelength range (4-200 microns). The IR light is transported to several laboratories in the same building and to the adjacent building of the High Magnetic Field Laboratory (HLD) as well. The latter is up to 70m away from the FELs. Constructional peculiarities, the large wavelength range (a factor of 50 between the shortest and the longest wavelengths), the high average power in cw regime, and the beam property requirements of the users pose a challenge to the beam line design. The transport system includes vacuum pipes, plane and toroidal gold-covered copper mirrors, exit windows, and diagnostic elements. The designed transport system produces a beam waist at selected spots in each laboratory representing an image of the outcoupling hole. Spot size and position are independent of the wavelength. In the HLD the beam is fed into a circulare waveguide, guiding the radiation to the sample inside of a cryostat. To ensure the desired beam properties, the transport system has been analyzed by means of various ray and wave optical models. | ||
| MOPPH073 | Thermal and Non-thermal Laser Cutting Utilizing Advanced Industrial Lasers and ERL-FELs | 175 |
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| The JAEA and JLAB energy-recovery free-electron lasers (ERL-FEL) have successfully demonstrated capabilities of a few hundreds fs ultra-fast pulse lasing, 6-9% high conversion efficiency, one GW high peak power, a few kW average power, and wide tunability of infrared wavelength regions. Utilizing the high average and high peak power lasing and energy-recovery linac (ERL) technology, we could realize a more powerful and more efficient FEL than 20kW and 25%, respectively, for nuclear industry, pharmacy, medical, defense, shipbuilding, semiconductor industry, chemical industries, environmental sciences, space-debris cleaning, power beaming and so on very near future. We have performed their thermal and non-thermal cutting and machining experiments and characterized their resultant effects. In order to compare some characteristic differences of thermal and non-thermal laser cutting utilizing advanced industrial laser like fiber, and water-guided ones and the ERL-FELs, we have performed some cutting trials of them. In the presentation, we plan to discuss these differences and how to apply all the lasers to the above applications in the fields. | ||
| MOPPH074 | Preliminary Design of the Proposed IR-FEL in India | 179 |
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| We propose to build a infra-red free-electron laser facility in India. We present details of the preliminary design of the FEL. |