AbstractIn many respects, high-energy accelerators are well suited to inertial fusion power production. Accelerators have long life, good reliability, and high pulse repetition rates. They can also have high efficiency. Nevertheless, existing accelerators have not been designed to be fusion drivers and they have not established that they can produce sufficiently intense beams to drive ICF targets. Establishing that properly designed accelerators can produce the required beams, while retaining the other desirable features of existing accelerators, is the principal scientific goal of the heavy ion fusion program. Until recently, we planned to establish the physics of intense ion beams by building a scaled driver known as ILSE. Because of declining support for fusion research in the US it is not now possible to construct ILSE. Other proposed fusion projects have also been cancelled. Because ILSE will not be built, we have restructured the US heavy ion fusion program. The restructured program is based on a large number of small experiments coupled with an expanded effort in numerical simulation. Experiments on ion sources, injection, matching, beam combining, recirculation, and focusing are underway. The goal of the simulation program is to perform accurate end-to-end simulations of the entire accelerator. The experiments and simulations will establish much of the science of high intensity beams. Reducing cost and increasing accelerator efficiency are also important goals of this scientific research. In addition we are developing key technologies that will reduce cost and increase efficiency. Before the program is in a position to build a full-scale fusion driver, it will be necessary to perform accelerator experiments that are larger than the experiments that are currently in progress. We plan to build a new accelerator to do these experiments. This new accelerator will also be designed to perform experiments on those aspects of target physics that are unique to ions.