  The superconducting (SC) High Intensity and Energy (HIE) ISOLDE linac will
replace most of the existing accelerating infrastructure of the Radioactive ion
beam EXperiment (REX) at CERN, however, the 101.28 MHz RFQ and 5 MV IH cavity
will remain in the role of injector for the upgrade, boosting the beam up to an
energy of 1.2 MeV/u. We present the results of a beam dynamics investigation of
the injector focused most critically on matching the longitudinal beam
parameters from the RFQ to the SC machine, which is complicated largely by the
IH cavity employing a Combined Zero Degree (KONUS) beam dynamics design. The
longitudinal beam parameters at the RFQ are reconstructed from measurement
using the three gradient method and combined with beam dynamics measurements
and simulations of the IH structure to design the matching section for the SC
linac.
