Induction acceleration is one of two principal approaches for producing ion beam for heavy-ion inertial fusion. This approach was first suggested by the late Denis Keefe of Lawrence Berkeley Laboratory and is the main approach of the US heavy-ion-fusion program. Induction accelerators have the ability to handle high beam currents; therefore, accumulation rings or storage rings are not required. This paper reviews the target and accelerator considerations that are important for the design of induction accelerators for fusion. These considerations, including some important assumptions, have led to a standard induction accelerator concept; however, a careful examination of the assumptions and considerations shows that many of them are not truly fundamental. Through improvements in technology, changes in design, and alternate ways of focusing beams, it appears possible to circumvent or relax the constraints imposed by the standard orthodoxy. If it is possible, it will lead to induction accelerators that are more efficient and less costly than the standard concept.

The US study of high-energy multigap accelerators to produce large currents of heavy ions for inertial fusion is centered on the single-pass induction linac method. The large technology base associated with multigap accelerators for high-energy physics gives confidence that high efficiency, high repetition rate, and good availability can be achieved, and that the path from scientific demonstration to commercial realization can be a smooth one. In an induction linac driver, multiple (parallet to) ion beams are accelerated through a sequence of pulsed transformers. Crucial to the design is the manipulation of electric fields to amplify the beam current during acceleration. A proof-of-principle induction linac experiment (MBE-4) is underway and has begun the first demonstration of current amplification, control of the bunch ends, and the acceleration of multiple beams. A recently completed experiment, called the Single Beam Transport Experiment has shown that we can now count on more freedom to design an alternating-gradient quadrupole focusing channel to transport much higher ion-beam currents than formerly believed possible. A recent Heavy Ion Fusion System Assessment (HIFSA) has shown that a substantial cost saving results from use of multiply-charged ions, and that a remarkably broad range of options exist for viable power-plant designs. The driver cost at 3 to 4 MJ could be $200/joule or less, and the cost of electricity in the range of 50 to 55 mills/kWhr.

Heavy-ion induction accelerators are being developed as fusion drivers for ICF power production in the US Inertial Fusion Energy (IFE) program, in the Office of Fusion Energy of the US Department of Energy. In addition, they represent an attractive driver option for a high-yield microfusion facility for defense research. This paper describes recent progress in induction drivers for Heavy-Ion Fusion (HIF), and plans for future work. It presents research aimed at developing drivers having reduced cost and size, specifically advanced induction linacs and recirculating induction accelerators (recirculators). The goals and design of the Elise accelerator being built at Lawrence Berkeley Laboratory (LBL), as the first stage of the ILSE (Induction Linac Systems Experiments) program, are described. Elise will accelerate, for the first time, space-charge-dominated ion beams which are of full driver scale in line-charge density and diameter. Elise will be a platform on which the critical beam manipulations of the induction approach can be explored. An experimental program at Lawrence Livermore National Laboratory (LLNL) exploring the recirculator principle on a small scale is described in some detail; it is expected that these studies will result ultimately in an operational prototype recirculating induction accelerator. In addition, other elements of the US HIF program are described.

LBL and LLNL propose to build, at LBL, the Induction Linac Systems Experiments (ILSE), the next logical step towards the eventual goal of a heavy-ion induction accelerator powerful enough to implode or ''drive'' inertial-confinement fusion targets. ILSE, although much smaller than a driver, will be the first experiment at full driver scale in several important parameters. Most notable among these are line charge density and beam cross section. Many other accelerator components and beam manipulations needed for an inertial fusion energy (IFE) driver will be tested. The ILSE accelerator and research program will permit experimental study of those beam manipulations required of an induction linac inertial fusion driver which have not been tested sufficiently in previous experiments, and will provide a step toward driver technology.

Since 1993, US research toward a heavy ion inertial fusion driver has concentrated on the multiple-beam ion-induction linac. This type of accelerator is unique in its ability to continuously amplify both the beam current and energy during the acceleration process. In a conceptual driver, many beams are accelerated in parallel through common induction cores in a linac that is 5--10 km long to final energies near 10 GeV in less than 0.2 msec. Past experiments at LBL have investigated the transport of intense ion beams in alternating gradient focusing structures and the acceleration of multiple ion becomes with current amplification in an induction linac. At present our major project is the development of a pulsed, 2-MV injector that produces beams at full driver size and intensity. In addition, a major activity is the development of a physics and engineering design for a larger Induction Linac Systems Experiments (ILSE) to test in a scaled way almost all the manipulations needed in a full-scale driver. We hope to begin construction of this experiment near the beginning of 1995.

The idea of using nuclear fusion as a source of commercial electrical power has been pursued worldwide since the 1950s. Two approaches, using magnetic and inertial confinement of the reactants, are under study. This paper describes the difference between the two approaches, and discusses in more detail the heavy-ion-driven inertial fusion concept. A multibeam induction linear accelerator would be used to bring (almost equal to)100 heavy ion beams to a few GeV. The beams would then heat and compress a target of solid D-T. This approach is unique among fusion concepts in its ability to protect the reaction chamber wall from neutrons and debris.

An assessment of heavy-ion fusion has been completed. Energetic heavy ions, for example 10-GeV uranium, provided by an rf linac or an induction linac, are used as alternatives to laser light to drive inertial confinement fusion pellets. The assessment has covered accelerator technology, transport of heavy-ion beams, target interaction physics, civilian power issues, and military applications. It is concluded that particle accelerators promise to be efficient pellet drivers, but that there are formidable technical problems to be solved. It is recommended that a moderate level research program on heavy-ion fusion be pursued and that LASL should continue to work on critical issues in accelerator development, beam transport, reactor systems studies, and target physics over the next few years.