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Efficiency and sideband observations of a Raman FEL oscillator with a tapered undulator

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3 Author(s)
F. G. Yee ; Dept. of Appl. Phys., Colombia Univ., New York, NY, USA ; T. C. Marshall ; S. P. Schlesigner

Power and spectral measurements are reported from the Columbia Raman free-electron laser (FEL) oscillator experiment. High-power radiation pulses (~12 MW, 100 ns) are generated at a wavelength of ~2.5 mm, using a 750-kV electron beam injected into a helical undulator. The undulator is made up of a 40-cm long constant-period (1.45 cm) section followed by an equal length of tapered undulator. The period is decreased by 7.6% in such a way that the on-axis field remains constant. It is reported that the taper allows an increase in total power efficiency from ~4 to ~12%. Most noteworthy is that the tapered undulator reduces the sideband radiation compared with a constant-period undulator FEL which is studied in the same configuration. The power was measured calorimetrically and compared with the results of a 1-D Raman code. The reduction of sideband power observed in the experiment was consistent with computational results obtained with a 2-D sideband code

Published in:

IEEE Transactions on Plasma Science  (Volume:16 ,  Issue: 2 )