| Paper | Title | Other Keywords | Page |
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| TUPEA041 | Drift Calibration Techniques for Future FELs | cavity, injection, electron, laser | 1419 |
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Future FELs (Free-Electron-Lasers) requires a precise detection of the cavity field in the injector section with a resolution of much less than 0.01 deg in phase and 0.01% in amplitude for a cavity operation frequency at 1.3GHz. Long-term stable SASE (Self Amplified Spontaneous Emission) operation mainly suffers from injector accelerator components and the stability of the reference distribution. Especially thermal instabilities of the distributed cavity field detectors, probe pickup cables and their mechanical vibrations influence the energy stability dramatically on a scale of 0.1%, a scale which is 10 times worse than required. To eliminate the long-term amplitude and phase changes, we injected a reference signal prior to the arrival of the cavity field signal. This enabled pulse-to-pulse calibration which compensated for the drifts of the field detectors. We demonstrated a dramatic phase and amplitude stability improvement from the ps-range to the 0.008 deg (peak-to-peak) range in phase and 0.02% (peak-to-peak) in amplitude; this represents an improvement in drifts by a factor of about 100. The injected calibration was successfully employed during FLASH operation. |
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| TUPEC055 | Computation of Electromagnetic Modes in the Transverse Deflecting Cavity | cavity, emittance, simulation, laser | 1847 |
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The X-ray Free Electron Laser (SwissFEL) under development at the Paul Scherrer Institut (PSI) will employ a special type of a deflecting cavity, LOLA*, for beam diagnostics. Since this cavity's design breaks the symmetry, a complete 3-dimensional eigenmodal analysis is indispensable. The 3-dimensional eigenmodal solver femaxx employs the finite element method and has been developed in a collaboration between PSI and the Swiss Federal Institute of Technology Zurich (ETH). The femaxx code uses the graphical frontend program heronion for the application of boundary conditions, including symmetry, and generates a tetrahedral mesh. We use femaxx to analyze the existing LOLA cavity design**, compute electromagnetic eigenmodes with their corresponding eigenfrequencies, and associated performance figures. Since these are large computational problems femaxx has been optimized for distributed memory parallel compute clusters. For the further usage in the beam dynamics code OPAL we sample the eigenmodal fields on a 3-dimensional Cartesian grid. * A. Falone, et al: RF deflector for bunch length measurement at low energy at PSI. Proceedings of PAC2009. |
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| TUPD075 | Start-to-end Simulation of a Compact THz Smith-Purcell FEL | electron, simulation, radiation, emittance | 2093 |
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Terahertz (THz) radiation has generated much recent interest due to its ability to penetrate deep into many organic materials without the damage associated with ionizing radiations. The generation of copious amounts of narrow-band THz radiation using a Smith-Purcell FEL operating as a backward wave oscillator is being pursued by several groups. In this paper we present start-to-end simulations of a Smith-Purcell FEL operating in the superradiant regime. Our concept incorporates a double grating configuration to efficiently bunch the electron beam, followed by a single grating to produce Smith-Purcell radiation. We demonstrate the capabilities and performances of the device, including initial beam properties (emittance and energy spread), with the help of numerical simulations using the conformal finite-difference time-domain electromagnetic solver VORPAL. |
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| TUPE026 | Classical and Quantum Mechanical Analyses on Electromagnetic Wave Emissions in the Planar Cherenkov Free Electron Laser | electron, coupling, damping, laser | 2197 |
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In the Cherenkov free electron laser, the interacted electron with the electromagnetic (EM) wave can be represented as a point particle or as a spatially spreading electron wave in the classical or quantum mechanical framework, respectively. In our previous theoretical analysis for the optical region, the electron is described by a plane wave with finite spreading length. This electron wave model was successfully implied for the optical region whereas the spreading length of the electron wave is greater than the wavelength of the optical wave. In this work, when the EM wavelength is sufficiently greater than the spreading length of the electron wave, such as in the microwave region, the electron is assumed to be a spatially localized point particle. This classical analysis is performed using same parameters used in the quantum electron wave model, such as a coupling coefficient between the electron beam and the EM field and the electron relaxation time. Also, we present analytical expressions to describe the stimulated and spontaneous emissions. We show that the classical treatment is consistent with the quantum analysis applied in the optical regime. |
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| WEPEB068 | Feasibility Tests of the Beam Halo Monitoring System for Protecting Undulator Permanent Magnets against Radiation Damage at XFEL/SPring-8 | electron, undulator, radiation, permanent-magnet | 2851 |
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A beam halo region of an electron beam at a linear accelerator might hit the undulator magnets and degrade undulator permanent magnets. An interlock sensor is indispensable to protect the magnets against radiation damage. We have been developing an electron beam halo monitor using diamond detectors for an interlock sensor at the X-ray free electron laser facility at SPring-8 (XFEL/SPring-8). The diamond detectors are operated in photoconductive mode. Pulse-by-pulse measurements are adopted to suppress the background noise efficiently. The feasibility tests of this monitor have been performed at the SPring-8 compact SASE source (SCSS) test accelerator for XFEL/SPring-8, and the results will be summarized. |