Theoretical Study of High-Current Beams in Storage Rings

In storage rings with high current of heavy ions, as considered for drivers in inertial fusion, control of the resistive microwave instability and bunch compression against strong space charge have been identified as key questions. It is shown here that onset of the longitudinal microwave instability can be suppressed or at least delayed by Landau damping, if some fraction of the total beam intensity is used to form a stabilizing tail of the distribution function. The linearized theory dispersion relation is analyzed and computer simulation examples are given to demonstrate the nonlinear features. As an alternative method the stabilizing effect of finite bunch length is investigated numerically and a stability criterion is proposed on the basis of a broad-band resonator model centered at the cut-off frequency. Finally, it is shown by means of computer simulation that 30-fold bunch compression in a storage ring is possible practically without losses using only two RF harmonics.