CERN Accelerating science

Article
Title	The Effect of Liner Induced Phase Fluctuations on the Gain of a Cerenkov FEL
Author(s)	De la Fuente, Isabel ; Boller, K ; Van der Slot, Peter
Affiliation	(UTWENTE, Enschede)
Publication	2004
In:	26th International Free Electron Laser Conference and 11th FEL User Workshop 2004, Trieste, Italy, 29 Aug - 3 Sep 2004, pp.e-proc. MOPOS39
Subject category	Accelerators and Storage Rings
Abstract	It is well known that wiggler errors can degrade the gain of a FEL. A similar process takes places in a Cerenkov FEL where the phase velocity of the amplified EM wave is determined by parameters of the dielectric liner. Thus deviations in the inner radius (R<sub>d</sub>) of the liner will result in fluctuations of the phase velocity of the EM wave. E.g., for a quartz liner (&epsilon;<sub>r</sub>=4.4) with R<sub>d</sub> = 1.5 mm and outer radius of 4 mm, the derivative of the longitudinal wavenumber with respect to R<sub>d</sub> is about 10<sup>5</sup> m<sup>-2</sup> for a frequency of 50 GHz. Thus fluctuations in the R<sub>d</sub> induce phase fluctuations that may degrade the gain of a Cerenkov FEL. In contrast to the undulator FEL, where the relative phase fluctuations are a result from deviations in the electron trajectories, the phase fluctuations are a result of pertubations in the radiation field for a Cerenkov FEL. As an example of the influence of pertubations in the inner radius of the liner on the gain we will present results of an analysis for a 100 kV Cerenkov FEL operating at a frequency of 50 GHz.