A precise 3D beam dynamics model of the PSI Injector II

We have developed a precise beam dynamics model of the PSI Injector II, a high intensity separate-sector isochronous cyclotron operating at 2.2 mA current. A particle distribution with an intensity of 9.5 mA (DC) is injected into the central region and shaped by a sophisticated collimator system. This defines the initial condition for the subsequent formation of a round stationary bunch. The intensity limits are estimated based on the developed models, additionally supported by fitted scaling laws and measurements. In this research we consider two configurations: production and upgraded (adding two new cavities). The model is based on the OPAL (Object Oriented Parallel Accelerator Library) simulation code, a tool for charged-particle optics calculations in large accelerator structures and beam lines, including 3D space charge.

Even though Injector II has been successfully operating for years, we do not know if the current production configuration is the best possible. Since we would like to extract as much current as possible with minimal losses, detailed simulations are needed to estimate those limits. This gives us possibility to look into the operation after the upgrade.

This is the first attempt to model Injector II using powerful computing, allowing multi-particle space charge simulations. We have been able to perform more detailed analysis of the bunch parameters and halo development than any previous study. Also optimisation techniques enable better matching of the simulation set-up with Injector II parameters and measurements.

We have found that the production configuration current scales to the power of four with the beam size, setting the limit to approximately 3 mA. Further analysis of the upgraded configuration suggests that intensities up to 5 mA could be produced with an adjusted collimation scheme.