  The maximum beam current can be accelerated in an Energy Recovery Linac (ERL)
can be severely limited by the transverse multi-pass beam breakup instability
(BBU), especially in future ERL light sources with multi-GeV high energy beam
energy and more than 100 mA average current. In this paper, the multi-pass BBU
of such a high energy ERL is studied based on the simulation on a 3-GeV ERL
light source proposed by KEK. It is expected to provide a reference to the
future high energy ERL projects by this work.
