MOC01
SLAC, Menlo Park, California, USA
A metallic pipe with corrugated walls supports propagation of a high-frequency mode that is in resonance with a relativistic beam propagating along the axis of the pipe. This mode can be excited by a beam whose length is a fraction of the wavelength. In this work, we discuss another option of excitation of the resonant mode'via the mechanism of the free electron laser instability. This mechanism works if the bunch length is much longer than the wavelength of the radiation, and hence does not require bunch compression. It provides an alternative to excitation by short bunches that can be realized with relatively low energy and low peak-current electron beams.
SLAC, Menlo Park, California, USA
Suppression of microbunching instability in modern FELs is an important issue that often limits the performance of the machine. A technique to suppress the instability with the help of a reversible electron beam heater was proposed by C. Behrens, Z. Huang, and D. Xiang [*]. It employs transverse deflecting cavities synchronized in a way that one of the cavities, located before a bunch compressor, generates a slice energy spread, while the other one removes it after the beam passes through the bunch compressor. Being an attractive approach, this concept unfortunately imposes extremely tight tolerances on the synchronization of the cavities. In this paper we demonstrate that a reversible heater equivalent to that of Behrens et al. can be designed using much simpler elements: bend magnets and quadrupoles in combination with the energy chirp of the beam.
* C. Behrens, Z. Huang, and D. Xiang, PRST-AB 15, 022802 (2012).