  For the successful generation of ion-beam-driven high energy density matter
and heavy ion fusion energy, intense ion beams must be transported and focused
onto a target with small spot size. One of the successful approaches to achieve
this goal is to accelerate and transport intense ion charge bunches in an
accelerator and then focus the charge bunches ballistically in a section of the
accelerator that contains a neutralizing background plasma. This requires the
ability to control space-charge effects during un-neutralized (non-neutral)
beam transport in the accelerator and transport sections, and the ability to
effectively neutralize the space charge and current by propagating the beam
through background plasma. As the beam intensity and energy are increased in
future heavy ion fusion (HIF) drivers and Fast Ignition (FI) approaches, it is
expected that nonlinear processes and collective effects will become much more
pronounced than in previous experiments. Making use of 3D electromagnetic
particle-in-cell simulation (PIC) codes (BEST, WARP-X, and LTP-PIC, etc.), the
theory and modelling studies will be validated by comparing with experimental
data on the 100kV Princeton Advanced Test Stand, and future experiments at the
FAIR facility. The theoretical predictions that are developed will be scaled to
the beam and plasma parameters relevant to heavy ion fusion drivers and Fast
Ignition scenarios. Therefore, the theoretical results will also contribute
significantly toward the long-term goal of fusion energy production by
ion-beam-driven inertial confinement fusion.
