Emittance dilution through coherent energy spread generation in bending systems

For a bunched beam, coherent energy spread generated within a bending system may couple to the transverse (bending) plane coordinates through the chromatic transfer functions of the particular beamline-even an achromatic beamline. The resulting transverse emittance dilution is dependent on the magnitude of the energy spread, its generation rate along the beamline, and the beamline´s chromatic transfer functions. The coherent energy spread may be due to resistive-wall wakefields or coherent synchrotron radiation. For specific beamlines, such as a periodic arc or wiggler, the longitudinal-to-transverse coupling is minimal and, in ideal cases, completely suppressed resulting in reduction or cancellation of all transverse emittance dilution effects. This is of particular interest for micro-bunch transport or compression systems such as exist in future FEL or linear collider projects