The Resistive Longitudinal Instability Threshold in Finite Charged Beams

Heavy ion beams are considered as possible drivers in an inertial confinement fusion scheme (1). The high required intensities introduce space - charge effects. It has been shown analytically that a finite cold beam is longitudinally stable when a small resistive term is present (2,3). This is confirmed by our simulations (4) which show that for resistivities causing less than one e-folding of a perturbation over the bunch length, the beam is stable (unlike coasting beam), probably due to end reflections. However, for resistivities causing more than three e-foldings, the beam is unstable (emittance deteriorated exponentially). We discuss the implication of this instability threshold for a few cases: (a) a full-scale driver model; (b) a multiple-beam driver; (c) single beam transport experiment-SBTE (LBL); (d) slow e-beam experiment (Maryland).