  The high-power RF coupler is the connecting part between the RF transmission
line and the RF cavity and provides the electromagnetic power to the cavity and
the particle beam. In addition to this RF function it also has to provide the
vacuum barrier for the beam vacuum. High-power couplers are one of the most
critical parts of the RF cavity system in an accelerator. A good RF and
mechanical design as well as a high quality fabrication are essential for
efficient and reliable operation of an accelerator.
