Longitudinal instability in HIF beams

The longitudinal instability which is certain to occur in the heavy ion fusion (HIF) beams in an induction linac (linear accelerator) and is currently considered to be a major question as to the feasibility of the induction linac as an option in accelerator design is discussed. The instability in question is a close relative of the well-known microwave instability in circular accelerators but with distinctive features in this unfamiliar parameter range. That it should occur in a linear accelerator is due to the fact the ions are non-relativistic all the way (10 GeV at mass 200 to 50 MeV/nucleon to beta =0.3) and regenerative bunching can occur at an unpleasant rate in a kiloampere beam subjected to the impedance of the accelerating modules themselves. The author presents the results of analytic and computational work on module impedances, growth rates and feedback (forward) systems.<>