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 microbunch transport or compression systems such as exist in future FEL or linear collider projects. Contributed to the 1997 Partcle Accelerator Conference Vancouver, B.C., Canada, May 12-16, 1997 * Work supported by Department of Energy contract DE–AC03–76SF00515. EMITTANCE DILUTION THROUGH COHERENT ENERGY SPREAD GENERATION IN BENDING SYSTEMS P. Emma, SLAC, Stanford, California, USA* R. Brinkmann, DESY, 22603 Hamburg, GERMANY