  The interaction of short relativistic charged particle bunches with
waveguides and other accelerator system components is a critical issue for the
development of X-ray FELs (free electron lasers) and linear collider projects.
Wakefield Cherenkov losses of short bunches have been studied previously for
resistive wall, disk-loaded, corrugated and dielectric loaded waveguides. It
was noted in various publications [1] that if the slowdown layer is thin, the
Cherenkov loss factor of a short bunch does not depend on the guiding system
material and is a constant for any given transverse cross section dimensions of
the waveguides. In this paper, we consider a new approach to the analysis of
loss factors for relativistic short bunches and formulate a general integral
relation that allows calculation of the loss factor for a short relativistic
bunch passing an arbitrary waveguide system. The loss factors calculated by
this new method for various types of waveguides with arbitrary thickness
slowdown layers, including infinite media, are shown to be equivalent to those
obtained by a conventional approach.
