| Paper | Title | Page |
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| TUPEC054 | Modeling Nanometer Structured Laser Induced Field Emission | 1844 |
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Laser induced field emission has become an enabling technology for building ultra-low emittance electron sources for particle accelerators, such as the x-ray free-electron laser (SwissFEL) under development at the Paul Scherrer Institut (PSI). One approach consists of a sharp pyramidal tip with lateral dimensions of a few nanometers, illuminated by a laser to increase the extracted electron current. Another approaches uses conventional cathodes. In both cases, there are structural details on the nanometer scale, that determine the interaction between the laser and the cathode and thus directly the quantum efficiency of the emitter. We use a 3-d full-wave finite element time domain electromagnetic approach* to understand the nano-optical interaction between structure and laser pulse. For example, the lightning rod effect of sharp tips enhances the electric field in the vicinity. Also, optical antenna concepts have been proposed to enhance the electric field at the field emitter's tip so that higher currents can be extracted. We use dispersive material models for the metals in the optical region of the electromagnetic spectrum. *Benedikt Oswald and Patrick Leidenberger, Journal of Computational and Theoretical Nanoscience, Vol 6(3), 2009, pp. 784-794. doi 10.1166/jctn.2009.1109 |
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| TUPEC055 | Computation of Electromagnetic Modes in the Transverse Deflecting Cavity | 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. |