Free-electron-laser oscillator with a linear taper
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We present experiments and simulations showing the behavior of a free-electron laser !FEL" with both positive and negative linear tapers along the wiggler. We show the power desynchronism curve widths, efficiency, exhaust electron energy spread, and wavelength dependence as a function of taper for 3- and 6-#m optical wavelengths and for resonators with 10% and 2% loss/pass. Simulations of the experiments, using a multimode analysis, are seen to be in general agreement with the experimental results, carried out at the IR Demo FEL at Thomas Jefferson National Accelerator Facility. We find that short-pulse effects are more effective than tapers in producing high efficiency with low exhaust energy spread, and the expected performance enhancement of FEL tapering is not achieved.
The article of record as published may be found at http://dx.doi.org/10.1103/PhysRevE.66.056502