mode - CERN Accelerator School

“Practical” standing wave
structures
From disc-loaded structure to a real cavity (Linac4 PIMS, Pi-Mode Structure)
1. To increase acceleration efficiency (=shunt impedance ZT2 !) we need to
concentrate electric field on axis (Z) (Z) and to shorten the gap (T) (T) →
introduction of “noses” on the openings.
2. The smaller opening would not allow the wave to propagate →
introduction of “coupling p g slots” between cells.
3. The RF wave has to be coupled into the cavity from one point, usually in
the center.
14