CTF3 : Design of Driving Beam Combiner Ring

In CTF3 the beam compression of the driving beam structure between the main linac and the decelerating section is obtained with a delay loop and a combiner ring which increase the pulse current by a factor 10. The design of the combiner ring is presented. Tunable isochronicity condition, corrected up to second order, should assure preservation of the correlation in the longitudinal phase space during the compression. Path-length tuning devices are included in the combiner ring layout to compensate for orbit variations.