Plasma neutralization of an intense ion beam pulse is of interest for many applications, including plasma lenses, heavy ion fusion, high energy physics, etc. Comprehensive analytical, numerical, and experimental studies are underway to investigate the complex interaction of a fast ion beam with a background plasma. The positively charged ion beam attracts plasma electrons, and as a result the plasma electrons have a tendency to neutralize the beam charge and current. A suite of particle-in-cell codes has been developed to study the propagation of an ion beam pulse through the background plasma. For quasi-steady-state propagation of the ion beam pulse, an analytical theory has been developed using the assumption of long charge bunches and conservation of generalized vorticity. The analytical results agree well with the results of the numerical simulations. The visualization of the data obtained in the numerical simulations shows complex collective phenomena during beam entry into and ex it from the plasma.

The U.S. Heavy Ion Fusion Virtual National Laboratory is proposing as its next experiment the Integrated Beam Experiment (IBX). All experiments in the U.S. Heavy Ion Fusion (HIF) program up to this time have been of modest scale and have studied the physics of selected parts of a heavy ion driver. The mission of the IBX, a proof-of-principle experiment, is to demonstrate in one integrated experiment the transport from source to focus of a single heavy ion beam with driver-relevant parameters--i.e., the production, acceleration, compression, neutralization, and final focus of such a beam. Present preconceptual designs for the IBX envision a 5-10 MeV induction linac accelerating one K{sup +} beam. At injection (1.7 MeV) the beam current is approximately 500 mA, with pulse length of 300 ns. Design flexibility allows for several different acceleration and compression schedules, including the possibility of longitudinal (unneutralized) drift compression by a factor of up to ten in pulse length after acceleration, and neutralized drift compression. Physics requirements for the IBX, and preliminary physics and engineering design work are discussed in this paper.