Developing the Chalk River Superconducting Cyclotron for operation in pi -mode

The Chalk River Superconducting Cyclotron operates in two RF modes. In the pi -mode, the voltages on the four dees move in opposition in adjacent dees, giving rise to high RF surface currents in the cavity wall under the magnetic hills, and to vertical asymmetries in the dee excitation. Studies on a half-scale RF model of the accelerating cavity have confirmed the current distribution and the magnitude of the vertical asymmetries. Cavity cooling provided in the initial design required augmentation for n-mode operation, but the magnet cryostat prevents access to the outside of the cavity. Additional cooling has been installed with cooling lines passing through high-RF-field regions to demountable cooling plates. Concurrently, instrumentation leads have been added to provide extra diagnostics of beam trajectories entering the extraction system.<>