  A three-cell 1.3 GHz, Normal Conducting (NC) buncher is designed for a
possible future upgrade of the European XFEL to operate in a continuous-wave
(CW) / long pulse (LP) mode. The RF geometry of the buncher is optimized for
high shunt impedance, large mode separation as well as multipacting free in the
operation range. The bunchersupport cavity voltage of 400 kV with an RF power
dissipation of 14 kW. A tapered waveguide-based RF power coupler is designed to
feed the RF power to the buncher. The RF power coupler port is optimized for
field asymmetry compensation. The thermal load due to RF power dissipation is
analyzed using Multiphysics simulations in CST and a simplified cooling scheme
is designed.
