  The successful operation of a Two-Beam accelerator based on extended
relativistic klystrons hinges upon decreasing the cumulative dipole BBU growth
from an exponential to a more manageable linear growth rate. We describe the
theoretical scheme to achieve this, and a new experiment to test this concept.
The experiment utilizes a 1-MeV, 600-Amp, 200-ns electron beam and a short
beamline of periodically-spaced rf dipole-mode pillbox cavities and solenoid
magnets for transport. Descriptions of the beamline are presented, followed by
theoretical studies of the beam transport and dipole-mode growth.
