Review of light-ion driver development for inertial fusion energy

The concept of a light ion beam driver for Inertial Fusion Energy (IFE) is based on multi-terawatt, multi-megavolt pulsed power generators, two-stage ion acceleration and charge neutralised transport. In this paper we discuss the present status for each of these components and identify the main issu es for research. Only modest extrapolations from presently available techno logies seem necessary for the high voltage pulse generator. The greatest ch allenge of this approach is the accelerator, which will consist of two stag es, the injector and the post-accelerator. Large progress has been made in understanding the physical phenomena occurring in the injector gap. This pr ogress has become possible by new sophisticated diagnostics that allowed de tailed temporally and spatially resolved measurements of field and particle densities in the acceleration gap and by relativistic fully electromagneti c PIG-simulation tools, that stimulated analytic models. The conclusions dr awn from these studies, namely limiting the ion current density to small en hancements to reduce the beam divergence need still to be verified experime ntally. Systematic experimental research on post-acceleration at high power and voltage must aim at a complete understanding of instabilities coupling from the injector to the post-accelerator and at limiting voltages and bar riers for the extraction of unwanted ions from plasmas at the injection sid e. Ultimately the light ion approach requires rep-rateable large area ion s ources with ion masses greater than 1 and particle energies around 30 MeV. Although different cleaning protocols were able to reduce the amount of par asitic ions in the Li beam from a LiF field emission source the achievement s are still insufficient. A field of common interest between light and heav y ion beam driven fusion is beam transport from the accelerator to the targ et. Supposedly the most favourable concept for both approaches is self-pinc hed transport. Experimental evidence for self-pinched transport has recentl y been achieved in an experiment at NRL. Further experiments are needed to determine the dynamics and magnitude of net current formation, the efficien cy of transport and the effect of bunching. (C) 2001 Elsevier Science B.V. All rights reserved.