Emittance variations in current-amplifying ion induction linacs

Since 1985 the Heavy Ion Fusion Accelerator Research program at the Lawrence Berkeley Laboratory has been studying current amplification and emittance variations in MBE-4, a four-cesium-beam induction linac. This experiment models much of the accelerator physics of the electrostatically focused section of a fusion driver. One of the initial concerns was possible interactions between the beams as they were accelerated or transported through the accelerator. With the exception of a weak interaction in the injector where the beams are at low energy and see each other for some distance, no such effect was observed. At low energy the beams interact primarily through their radial space-charge electric fields. These are easily controlled by radial shorting planes along the accelerator which are present for other reasons.<>