Speaker
Description
H$^-$ cyclotrons, such are TRIUMF 500 MeV machine, are essentially characterized by their large phase acceptance. Since beam extraction relies on charge exchange (H$^-$ to H$^+$) no turn separation is required. Bunches typically occupy several tens of degrees of rf phase, and consequently acquire, during the acceleration process, a large energy spread. This large energy spread leads neighboring bunches to overlap, making the charge distribution withing the cyclotron resemble a quasi-continuous ``slice'' of charge.
The dynamics of this charge distribution, in the presence of space charge forces, is the subject of this study. After a brief historical overview of the topic, we will consider the problem of numerically calculating the steady state of the charge distribution. We show how this problem can be solve with modest computational resources by making the assumption that the shape of a given bunch evolves slowly compared to the revolution period. We present simulation results, with application to the case of TRIUMF 500 MeV cyclotron. We also present benchmark test results against both experimental data and simulations using the computer code OPAL-CYC.
