Longitudinal beam dynamics for heavy ion fusion

The longitudinal wall impedance instability is of potential importance for a heavy ion fusion (HIF) driver because complete stabilization of this mode via momentum spread is impractical due to the requirement of focusing the beam onto the inertial confinement fusion target. This instability is being studied with the WARPrz particle-in-cell code. The impedance of the induction linac modules is modeled as a wall impedance corresponding to a continuum of resistors and capacitors in parallel. We discuss simulations of the this instability, including reflection of perturbations off the beam end, the effect of finite temperature on the growth rate, and errors in intermittently-applied axial confining fields as a seed for this instability. We also present very long simulations in which we study the approach to equilibrium.<
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