| Paper | Title | Page |
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| MOPB23 | Three-Dimensional Modes of a Lamellar Grating for Smith-Purcell Experiments | 83 |
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Several years ago Andrews and Brau * presented a two-dimensional (2-D) theory for the production of coherent Smith-Purcell radiation by an initially continuous beam. An essential component of their analysis was the dispersion relation for a lamellar grating (i.e., rectangular profile) relating frequency and axial wave number k. Both simulations and an experiment performed at CESTA ** using a wide beam have confirmed the validity of their approach. However, all gratings are three-dimensional objects, and one may ask what modifications of the theory might be necessary. We present here our solution to the problem, which assumes a progressive wave in the direction of the grooves, with wave number q. A surprisingly simple modification of the Andrews and Brau 2-D dispersion relation is found. We have extensively tested our theory, both with simulations using the 3-D PIC code "MAGIC", and with measurements of the properties of the surface wave on the CESTA grating made using a network analyzer. Extremely good agreement is found, both with and without sidewalls on the grating. * H. L. Andrews and C. A. Brau, Phys. Rev. ST Accel. Beams 7, 070701 (2004). |
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| TUPA07 | Dependence of Gain on Current in the Coherent Smith-Purcell Experiment at Cesta | 226 |
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At FEL 2009, we presented experimental results on coherent Smith-Purcell obtained at CESTA in the microwave frequency domain * . Those results strongly supported the two-dimensional theory proposed by Andrews and Brau some years ago ** , and were consistent with simulations performed with the PIC code "MAGIC". That experiment used a large current, 200 A, for a grating of width 10 cm. In a follow-up experiment, emittance slits were used to reduce the current to as low as 2 A, with a quite thin, flat, and wide beam. The gain as a function of current and also of vertical beam position was measured in detail. In particular, the start current for our set-up was found. In parallel, 2-D simulations of the experiment with "MAGIC" were extensively compared with the experimental results. Very good agreement between simulations and experiment is obtained. This lends confidence that simulations of a scaled-down version of our experiment will be a reliable guide for Terahertz frequency coherent Smith Purcell experiments. Such simulations suggest that radiation in the range 100-200GHz should be feasible. * J. T. Donohue, J. Gardelle, L. Courtois and P Modin, Proceeedings of FEL 2009. |