Einzel lens chopper and behavior of the chopped beam in the KEK digital accelerator

The KEK digital accelerator (KEK-DA), which is a small-scale rapid-cycle induction synchrotron (IS), has commenced operation. A permanent magnet x -band electron cyclotron resonance ion source serves as the KEK-DA ion source and delivers various ions. A new Einzel lens beam chopper has been developed to provide the necessary pulse width of a few microseconds. The chopper is implemented by applying a rectangular pulse voltage generated by a solid-state Marx generator to the middle electrode of the Einzel lens. Momentum modulation at the bunch head and tail resulting from chopping in longitudinal direction has been observed. This intrinsic property of the chopped pulse has been clearly observed in a long drift (a free run in the circular ring) in KEK-DA.